pile cap reinforcement formworkwhat is a pile cap? A pile cap is
a thick concrete mat that rests on piles and is usually part of the
foundation of a building especially a multi-storey building. It
helps to distribute the load from the pillars or piers to the
piles.Typical dimensions: 5m wide x 800mm thickConcrete used: Grade
40/20Nominal concrete cover to re-bars: 75mm blinding layer for
undersideMinimum cover to re-bars for precast concrete covers on
topside: 30mmThickness of all precast concrete covers: 125mmThe
pile caps were casted by employing a pump truck with hydraulic boom
placer to pump fresh concrete from truckmixer down to cap formwork
at Pok Fu Lam Road level.Nominal concrete cover to re-bars: 50mm,
with a 75mm blinding layer below the underside as wellConcreting
operation for the pile caps was launched simultaneously using two
different methods: one by crane-and-skip bucket and the other by
hydraulic excavator, in order to achieve faster placing
rates.Formwork is the term used for the temporary timber, plywood,
metal or other material used to contain, support and form wet
concrete until it has gained sufficient strength to be
self-supporting. Falsework is the term used to describe the
temporary system or systems of support for formwork.
reference:http://www.ask.com/question/what-is-a-pile-caphttp://civcal.media.hku.hk/queenmary/structures/trough/pile_cap/default.htmhttp://civcal.media.hku.hk/queenmary/structures/bridge/cap/default.htm
manufactured steel trusses
lift slabsLift slab constructionis a method of constructing
concrete buildings by casting the floor or roof slab on top of the
previous slab and then raising (jacking) the slab up withhydraulic
jacks, so being cheaper and faster as not requiring boxing and
supports for casting in situ.Johnstone Hall, a dormitory atClemson
University,Clemson,South Carolinawas erected using this method in
1954. Several of the blocks have now been demolished, and campus
legend says that that two other similar structures built elsewhere
collapsed before completion.[citation needed]The method was
involved in theL'Ambiance Plazacollapse inBridgeport,
Connecticutduring construction in 1987, and resulted in a major
nationwide federal investigation into this construction technique
in the United States, and a temporary moratorium of its use in
Connecticut.[1]A patent was issued toTom Slickfor this construction
method, called the "Youtz-Slick" method, in 1955.
what is lift slab construction?Ba s i c a l l y, the method
entails casting floor and ro o f slabs on or at ground level and
jacking them up into position. The traditional lift slab
construction sequence isi l l u s t rated in Fi g u re 1. Flat
plate floors are commonly used because they are so well suited to
stack-casting, req u i ring form w o rk at only the edges of the
slab and at floor openings.Special lifting collars or shearheads
are provided inthe slabs at the columns. Bond breaking compounds
areapplied between slabs to separate them. After the slabsh a ve
cured long enough to reach a pre s c ribed stre n g t h ,p owe rful
hyd raulic jacks mounted on top of the columnslift the slabs into
their re s p e c t i ve positions. A consoleconnected to each hyd
raulic jack synchro n i zes the number of turns of the check nuts
to assure that the concre t eslab is being raised the same amount
at all points.Lift slab can be used for heights up to about 16
stori e s. Economical column spacing ranges from 22 to 32feet.
Columns may be pipe, tubes or wide flange sections; concrete
columns may be used in 3- to 4-storybuildings not re q u i ring
splices.The big advantage of erecting concrete buildings using lift
slab construction is elimination of most formw o rk, an especially
important factor in areas where laborcosts are high. Co n c rete
floor construction at groundlevel is convenient and requires no
shore s, scaffolds orc ra n e s. Slabs can be cast and protected
easily duri n gcold weather without expensive heating and enclosure
sre q u i red for ord i n a ry construction. Another advantage
isreduced handling and hoisting of materials and suppliesthat can
simply be placed on top of the slabs and liftedwith them.Because
lift slab uses concre t e, the technique offersgood fire resistance
and good acoustic ra t i n g s. Mass designed into walls, floors
and roofs helps to reduce theNew developments inlift slab
construction
Figure 1. The lift slab technique reduces costs for multistory
buildings by eliminating most formwork. A typical liftingsequence
is illustrated above.
Figure 2. Recent changes in lift slab construction include
supporting the hydraulic jack off the column by a welded plate. The
old approach used jacks mounted on top of the columns. Columns can
now be up to 6 stories tall without field splices.
Figure 3. A lift slab system used extensively in Latin America
involves casting concrete bearing walls flat in the stack along
with the floor slabs. The wall panels are hinged to the floor with
plastic rope, allowing them to unfold automatically as the stack is
raised into position.
reference:http://en.wikipedia.org/wiki/Lift_slab_constructionhttp://www.concreteconstruction.net/images/New%20Developments%20in%20Lift%20Slab%20Construction_tcm45-343687.pdfhttp://books.google.com.ph/books?id=bC7KMKKyPbEC&pg=PT8&lpg=PT8&dq=lift+slabs&source=bl&ots=an3slS0iwW&sig=XLSV03v5xqNPkTAlsVh02Em2pXs&hl=en&sa=X&ei=C2rhUdyDCsWxrAeJm4HoDw&ved=0CFQQ6AEwCA
(jep daytoi kut han ku maala nga mayat daytoi kompleto . . .google
books gamin isu nga haan maala. . .)
steel space deck roofWhat is Steel Deck ? There are a wide
variety of steel deck products on the market today, basically
divided into two categories: roof deck and composite floor deck.
Steel deck is a structural panel element that acts as the surface
of a floor or roof. The deck is roll formed from structural quality
sheet steel and is engineered to span over joist or purlins.
Variations in the thickness, shape and depth of the deck can be
utilized to meet a variety of loading conditions and spans. The
deck can also be fastened to the supporting structure to enable it
act as a diaphragm and provide lateral bracing for the
structure.Advantages of Steel DeckVersatility: Steel deck products
are available from CSSBI Fabricator member companies in a range of
depths (38 to 76 mm, (1-1/2 to 3 in.)) and different rib spacing.
Roof deck can also be supplied as acoustical deck with perforations
in the web elements to attenuate sound. Steel deck products are
available in a variety of thickness to meet most structural
requirements. This extensive choice of options makes steel deck
applicable to a wide range of projects and structural designs.
High Strength to Weight Ratio: The strength of steel is used
with maximum efficiency in the design and fabrication of steel
deck, resulting in products with a high strength-to-weight ratio.
Consequently, delivery, erection and structural framing costs can
be lower than other systems.
Aesthetics: Although steel deck is primarily a structural
component, it is visually attractive when left exposed to the
interior of the building. With the properly specified prefinished
coating, steel deck is easy to maintain, durable and aesthetically
pleasing.
All-Weather Construction: Steel deck can be erected inmost
weather conditions, eliminating the costly delaysthat can occur
with other types of roof systems.
Required Fire Resistance Ratings: ULC and UL fire resistance
ratings are available for many standard roof and floor assemblies
incorporating steel deck.
Uniform Quality: Through engineering and continuously refined
production techniques, CSSBI fabricators produce deck that conforms
to explicit industry standards.
Proven Durability: Steel deck has a successful servicehistory of
over 60 years, which is indicative of theproducts durability.
Economy and Value: Value is determined by combininginitial
costs, life-cycle costs, and overall performance. Steel deck
assemblies are the best value in roof and floor designs. They
combine low cost with top performance
SECTION 05 31 23 - STEEL ROOF DECKING PART 1 - GENERAL 1.1
SUMMARY A. Furnish all materials and labor necessary to complete
metal decking installation per the Contract Documents. Edit list of
related sections for project requirements. Section numbers and
titles are those recommended in CSI MasterFormat; revise numbers
and titles to reflect actual sections in Project Manual. B. Related
Requirements: 1. Section 03 52 16: Lightweight Insulating Concrete.
2. Section 05 10 00: Structural Metal Framing. 3. Section 05 20 00:
Metal Joist. 4. Section 07 22 16: Roof Board Insulation. 5. Section
07 60 00: Flashing and Sheet Metal. 6. Section 09 91 00: Painting
1.2 REFERENCE STANDARDS FOR QUALITY ASSURANCE A. Codes/Standards
The work and materials of this section shall comply with: 1. ASCE
7: Minimum Design Loads for Building and Other Structures. 2.
Section properties shall be derived in accordance with AISI "North
American Specification for the Design of Cold-Formed Steel
Structural Members", latest edition. 3. Metal Decking is to be
attached to the structural frame in conformance with AWS D1.1
"Structural Welding Code Steel" and D1.3 "Structural Welding Code
Sheet Steel." 4. ICC Research Report No. ESR-1414. 5. IAPMO
Research Report No. IAPMO ES-0161 Insert the appropriate L.A. City
Research Report No. when applicable; 23783, 23784, 23803. 6. ASTM
A653, "Standard Specification for Steel Sheet, Zinc-Coated
(Galvanized) or Zinc-Iron Alloy-Coated (Galvannealed) by the
Hot-Dip Process". 7. Steel Deck Institute (SDI) Metal roof deck
profiles shall be in conformance with ANSI/SDI standard RD1.0
"Standard for Steel Roof Deck". 8. Factory Mutual (FM) Metal roof
deck profiles shall be in conformance with FM where applicable. ASC
Steel Deck, A Division of ASC Profiles, Inc. STEEL ROOF DECK PANELS
Guide Specification 05 31 23 - 2 1.3 SUBMITTALS A. Product Data for
each type of decking specified, including dimensions of individual
components, profiles, and finishes. B. Shop drawings: Prior to
fabrication, prepare shop drawings for work under this section and
submit to Architect. Shop drawings are to include deck layout, deck
type and gauge, framing and support of openings, dimensions and
sections, details of accessories and type and location of welds.
Manufacturers product literature and relevant approvals are to be
submitted with the shop drawings. 1.4 PRODUCT DELIVERY, STORAGE AND
HANDLING A. Metal Deck: Transport, store and erect metal deck and
accessories in a manner that will prevent corrosion, deformation or
other damage. Store deck clear of the ground with one end elevated
to promote drainage; protect metal deck from water and the elements
with a water resistant material. Include the following when
Acustadek is specified: B. Acustadek Sound Absorption Batts: Store
batts in an enclosed area, protected from the elements. PART 2 -
PRODUCTS 2.1 MATERIAL AND FINISHESA. Metal roof deck to be ASC
Steel Deck [select appropriate profile(s) and gauge(s)]. 1. B-36
[22], [20], [18], [16] gauge;1 1/2 inches deep by 36 inches wide.
2. N-32 [22], [20], [18], [16] gauge; 3 inches deep by 32 inches
wide. 3. N-24 [22], [20], [18], [16] gauge; 3 inches deep by 24
inches wide. 4. 2W-36 [22], [20], [18], [16] gauge; 2 inches deep x
36 inches wide. 5. 3W-36 [22], [20], [18], [16] gauge; 3 inches
deep by 36 inches wide. 6. BF-36 [20/20], [20/18], [20/16],
[18/20], [18/18], [18/16], [16/16] gauge; 1 1/2 inches deep by 36
inches wide. 7. NF-24 [20/20], [20/18], [20/16], [18/20], [18/18],
[18/16], [16/16] gauge; 3 inches deep by 24 inches wide. Deck units
are to be fabricated from sheet steel conforming to ASTM A653 SS
Grade 40 with a galvanized coating. 2W-36 and 3W-36 are available
in 24 wide panels; when specified, the designations are 2W-24 and
3W-24. When specifying CP-32, use the following, for CP-32 18
gauge; replace ASTM A653 SS Grade 80 with ASTM A653 Grade 33. 7.
CP-32 [26], [24], [22], [20], [18] gauge; 1 3/8 inches deep by 32
inches wide. Deck units are to be fabricated from sheet steel
conforming to ASTM A653 SS Grade 80, with a G-40 galvanized
coating. When specifying Deep Deck and Deep Cellular, using the
following: 1. Deep Deck [20], [18], [16], [14] gauge; 4 1/2, 6, or
7 1/2 inches deep by 12 inches wide. 2. Deep Deck Cellular [20/20],
[20/18], [20/16], [18/20], [18/18], [18/16], [16/16]gauge; 4 1/2,
6, or 7 1/2 inches deep by 24 inches wide. Deck units are to be
fabricated from sheet steel confirming to ASTM A653, Fy = 33ksi
with a galvanized coating. When specifying acoustical deck use the
following: ASC Steel Deck, A Division of ASC Profiles, Inc. STEEL
ROOF DECK PANELS Guide Specification 05 31 23 - 3 A. Metal roof
deck to be ASC Steel Deck [select appropriate profile(s) and
gauge(s).]1. B-36 Acustadek [22], [20], [18], [16] gauge, 1 1/2
inches deep by 36inches wide. 2. N-32 Acustadek [22], [20], [18],
[16] gauge, 3inches deep by 32 inches wide. 3. N-24 Acustadek [22],
[20], [18], [16] gauge, 3 inches deep by 24 inches wide. 4. BF-36
Acustadek [20/20], [20/18], [20/16], [18/20], [18/18], [18/16],
[16/16] gauge; 1 1/2 inches deep by 36 inches wide. 5. NF-24
Acustadek [20/20], [20/18], [20/16], [18/20], [18/18], [18/16],
[16/16] gauge; 3 inches deep by 24 inches wide. 6. Deep Deck
Acustadek [20], [18], [16], [14] gauge; 4 1/2, 6, or 7 1/2 inches
deep by 12 inches wide. 7. Deep Deck Cellular Acustadek [20/20],
[20/18], [20/16], [18/20], [18/18], [18/16], [16/16] gauge; 4 1/2,
6, or 7 1/2 inches deep by 24 inches wide. 8. 2WF-36 Acustadek
[20/20], [20/18], [20/16], [18/20], [18/18], [18/16], [16/16]
gauge; 2 inches deep by 36 inches wide. 9. 3WF-36 Acustadek
[20/20], [20/18], [20/16], [18/20], [18/18], [18/16], [16/16]
gauge; 3 inches deep by 36 inches wide. B. Acustadek perforations
are 1/8 or 5/32 diameter holes on staggered centers. The noise
reduction Coefficient is to be [select from chart on pages 23 and
24]. The NRC values were developed in accordance with ANSI C423, as
performed by Riverbank Laboratory. ASC Steel Deck panels, in their
standard sheet steel, contain approximately 24.3 percent
postconsumer recycled content and 9.4 percent pre-consumer recycled
content, for a total 29 percent recycled content as calculated for
this LEED credit. Higher percentages are available if specified. B.
[Or C. for acoustical deck] Sustainability Characteristics: 1.
Recycled Content: [29] [50] [75] percent post-consumer recycled
content [, calculated according to LEED Credit MR4]. 2. Shipping
Distance: Provide panels manufactured at the following factory: If
locally manufactured materials are a project requirement, select
factory closer to Project site. a. Fontana, California 92335 b.
West Sacramento, California 95691 If the project is subject to
Federal Buy American provisions, which requires that panels be
manufactured in the USA and that 50 percent of the cost of the
panels be of U.S.A. origin, use the following: C. [Or D. for
acoustical deck] Manufacturing Characteristics: Provide panels
complying with provisions of Buy American Act 41 U.S. C 10a 10d. If
the project is subject to Buy America Act (STAA) or American
Recovery & Reinvestment Act (ARRA) 2009 (which requires that
steel used in the manufacturing process be poured and melted in the
USA, use the following: C. [Or D. for acoustical deck]
Manufacturing Characteristics: Provide panels complying with
provisions of the Buy America Act (STAA) or the American Recovery
& Reinvestment Act (ARRA) 2009. 2.2 FABRICATION A. Metal Deck
Manufacture deck units to lengths as indicated on shop drawings.
Panel end conditions are to be butted or end-lapped, 2 minimum.
Sidelaps are to be male/female interlocking type allowing
connection with DeltaGrip tool. Sidelaps are to be nestable or
interlocking when using screw-type fasteners. When specifying CP-32
delete the last two sentences and insert: Sidelaps are to be
overlapping type. B. Accessories Fabricate steel deck accessories
(not including cell closures) from the same gauge and materials as
adjacent steel
deck.reference:http://www.cssbi.ca/Eng/_pdf/CSSBI-S15-01.pdfhttp://www.ascsd.com/files/Roof%20Deck%20Guide%20Specs.pdf
space framesInarchitectureandstructural engineering, aspace
frameorspace structureis atruss-like, lightweight rigid structure
constructed from interlockingstrutsin ageometricpattern. Space
frames can be used to span large areas with few interior supports.
Like thetruss, a space frame is strong because of the inherent
rigidity of the triangle; flexingloads(bendingmoments) are
transmitted astensionandcompressionloads along the length of each
strut.
If a force is applied to the blue node, and the red bar is not
present, the behaviour of the structure depends completely on the
bending rigidity of the blue node. If the red bar is present, and
the bending rigidity of the blue node is negligible compared to the
contributing rigidity of the red bar, the system can be calculated
using a rigidity matrix, neglecting angular factors.
Simplified space frame roof with the half-octahedron highlighted
in blue
The roof of this industrial building is supported by a space
frame structure.
Advantages of Space Frames1. One of the most important
advantages of a space structure is its lightweight. This is mainly
due tothe fact that material is distributed spatially in such a way
that the load transfer mechanism isprimarily axial tension or
compression. Consequently, all material in any given element
isutilized to its full extent. Furthermore, most space frames are
now constructed with steel oraluminum, which decreases considerably
their self-weight. This is especially important in the caseof
long-span roofs, which led to a number of notable examples of
applications.2. The units of space frames are usually mass produced
in the factory so that they can take fulladvantage of the
industrialized system of construction. Space frames can be built
from simpleprefabricated units, which are often of standard size
and shape. Such units can be easilytransported and rapidly
assembled on site by semi-skilled labor. Consequently, space frames
canbe built at a lower cost.SecondarybeamBeamBeamArch(a)
(b)PurlinFIGURE 24.2 Roof framing for a Circular Dome.24-4 Handbook
of Structural EngineeringCopyright 2005 by CRC Press3. A space
frame is usually sufciently stiff in spite of its lightness. This
is due to itsthree-dimensional character and to the full
participation of its constituent elements. Engineersappreciate the
inherent rigidity and great stiffness of space frames and their
exceptional ability toresist unsymmetrical or heavy concentrated
load. Possessing greater rigidity, the space framesallow also
greater exibility in layout and positioning of columns.4. Space
frames possess a versatility of shape and form and can utilize a
standard module to generatevarious at space grids, latticed shell,
or even free-form shapes. Architects appreciate the visualbeauty
and the impressive simplicity of lines in space frames. A trend is
very noticeable in whichthe structural members are left exposed as
a part of the architectural expression. Desire foropenness for both
visual impact as well as the ability to accommodate variable space
requirementsalways calls for space frames as the most favorable
solution.
Preliminary Planning GuidelinesIn the preliminary stage of
planning a space frame to cover a specic building, a number of
factorsshould be studied and evaluated before proceeding to
structural analysis and design. These include notonly structural
adequacy and functional requirements but also the esthetic effect
desired.1. In its initial phase, structural design consists of
choosing the general form of the building and thetype of space
frame appropriate to this form. Since a space frame is assembled of
straight, linearelements connected at nodes, the geometrical
arrangement of the elements surface shape,number of layers, grid
pattern, etc.needs to be studied carefully in the light of various
pertinentrequirements.2. The geometry of the space frame is an
important factor to be planned, which will inuence boththe bearing
capacity and the weight of the structure. Themodulesize is
developed from the overallbuilding dimensions, while the depth of
the grid (in the case of double-layer), the size of cladding,and
the position of the supports will also have a pronounced effect
upon it. For curved surface, thegeometry is also related to the
curvature, or more specically to the rise of the span. A
compromisebetween these various aspects usually has to be made to
achieve a satisfactory solution.3. In a space frame, connecting
joints play an important role, both functional and esthetic,
whichderives from their rationality during construction and after
completion. Since joints have adecisive effect on the strength and
stiffness of the structure and compose around 20 to 30% of thetotal
weight, joint design is critical to space frame economy and safety.
These are quite a fewproprietary systems that are used for space
frame structures. They should be selected on the basisof quality,
cost, and erection efciency. In addition, custom-designed space
frames have beendeveloped, especially for long-span roofs.
Regardless of the type of space frame, the essence of anysystem is
the jointing system.4. At the preliminary stage of design, the
choosing of the type of space frames has to be closely relatedwith
the constructional technology. The space frames do not have such a
sequential order oferection for planar structures and require
special consideration on the method of construction.Usually, a
complete falsework has to be provided so that the structure can be
assembled in the highposition. Alternatively, the structure can be
assembled on the ground, and a certain technique canbe adopted to
lift the whole structure, or its major part, to the nal
position.reference:http://en.wikipedia.org/wiki/Space_framehttp://img20.imageshack.us/img20/5880/ch24spaceframestructure.pdf
cold roll-formed sections welded togetherCold-formed steel
(CFS)is the common term for products made by rolling or pressing
thin gauges of sheet steel into goods. Cold-formed steel goods are
created by the working of sheet steel using stamping, rolling, or
presses to deform the sheet into a usable product. Cold worked
steel products are commonly used in all areas of manufacturing of
durable goods like appliances or automobiles but the phrase cold
form steel is most prevalently used to described construction
materials. The use of cold-formed steel construction materials has
become more and more popular since its initial introduction of
codified standards in 1946. In the construction industry both
structural and non-structural elements are created from thin gauges
of sheet steel. These building materials encompass columns, beams,
joists, studs, floor decking, built-up sections and other
components. Cold-formed steel construction materials differ from
other steel construction materials known as hot-rolled steel
(seestructural steel). The manufacturing of cold-formed steel
products occurs at room temperature using rolling or pressing. The
strength of elements used for design is usually governed by
buckling. The construction practices are more similar to timber
framing using screws to assemble stud frames.
Cold-formed steel buildingCold-formed steel members have been
used in buildings, bridges, storage racks,grain bins, car bodies,
railway coaches, highway products, transmission towers,
transmission poles,drainagefacilities, various types of equipment
and others.[1]These types of sections are cold-formed from steel
sheet, strip, plate, or flat bar inroll formingmachines, by press
brake (machine press) or bending operations. The material
thicknesses for such thin-walled steel members usually range from
0.0147 in. (0.373mm) to about in. (6.35mm). Steel plates and bars
as thick as 1 in. (25.4mm) can also be cold-formed successfully
into structural shapes (AISI, 2007b). History of cold-formed
steelThe use of cold-formed steel members in building construction
began in the 1850s in both the United States and Great Britain. In
the 1920s and 1930s, acceptance of cold-formed steel as a
construction material was still limited because there was no
adequate design standard and limited information on material use in
building codes. One of the first documented uses of cold-formed
steel as a building material is the Virginia Baptist Hospital[1],
constructed around 1925 in Lynchburg, Virginia. The walls were load
bearing masonry, but the floor system was framed with double
back-to-back cold-formed steel lipped channels. According to Chuck
Greene, P.E of Nolen Frisa Associates[2], the joists were adequate
to carry the initial loads and spans, based on current analysis
techniques. Greene engineered a recent renovation to the structure
and said that for the most part, the joists are still performing
well. A site observation during this renovation confirmed that
"these joists from the 'roaring twenties' are still supporting
loads, over 80 years later!" In the 1940s, Lustron Homes built and
sold almost 2500 steel-framed homes, with the framing, finishes,
cabinets and furniture made from cold-formed steel.
History of AISI design standards[edit]Design standards for
hot-rolled steel (seestructural steel) were adopted in 1930s, but
were not applicable to coldformed sections because of their
relatively thin steel walls which were susceptible to buckling.
Cold-formed steel members maintain a constant thickness around
their cross-section, whereas hot-rolled shapes typically exhibit
tapering or fillets. Cold-formed steel allowed for shapes which
differed greatly from the classical hot-rolled shapes. The material
was easily workable; it could be deformed into many possible
shapes. Even a small change in the geometry created significant
changes in the strength characteristics of the section. It was
necessary to establish some minimum requirements and laws to
control the buckling and strength characteristics. Also it was
observed that the thin walls underwent local buckling under small
loads in some sections and that these elements were then capable of
carrying higher loads even after local buckling of the members.In
the United States, the first edition of the Specification for the
Design of Light Gage Steel Structural Members was published by
theAmerican Iron and Steel Institute(AISI) in 1946 (AISI,
1946).[3]The firstAllowable Stress Design(ASD) Specification was
based on the research work sponsored by AISI atCornell
Universityunder the direction of late Professor George
Winter[3]since 1939.[4]As a result of this work, George Winter is
now considered the grandfather of cold-formed steel design. The ASD
Specification was subsequently revised in 1956, 1960, 1962, 1968,
1980, and 1986 to reflect the technical developments and the
results of continued research at Cornell and other universities (Yu
et al., 1996).[5]In 1991, AISI published the first edition of
theLoad and Resistance Factor DesignSpecification developed
atUniversity of Missouriof Rolla andWashington Universityunder the
directions of Wei-Wen Yu[4]and Theodore V. Galambos (AISI,
1991).[6]Both ASD and LRFD Specifications were combined into a
single specification in 1996 (AISI, 1996).[7]In 2001, the first
edition of the North American Specification for the Design of
Cold-Formed Steel Structural Members was developed by a joint
effort of the AISI Committee on Specifications, theCanadian
Standards Association(CSA) Technical Committee on Cold-Formed Steel
Structural Members, and Camara Nacional de la Industria del Hierro
y del Acero (CANACERO) in Mexico (AISI, 2001).[8]It included the
ASD and LRFD methods for the United States and Mexico together with
the Limit States Design (LSD) method for Canada. This North
American Specification has been accredited by the American National
Standard Institute (ANSI) as an ANSI Standard to supersede the 1996
AISI Specification and the 1994 CSA Standard. Following the
successful use of the 2001 edition of the North American
Specification for six years, it was revised and expanded in
2007.[9]This updated specification includes new and revised design
provisions with the additions of the Direct Strength Method in
Appendix 1 and the Second-Order Analysis of structural systems in
Appendix 2.In addition to the AISI specifications, theAmerican Iron
and Steel Institutehas also published commentaries on various
editions of the specifications, design manuals, framing design
standards, various design guides, and design aids for using
cold-formed steel. For details, see AISI[5]website.Common section
profiles and applications[edit]In building construction there are
basically two types of structural steel: hot-rolled steel shapes
and cold-formed steel shapes. The hot rolled steel shapes are
formed at elevated temperatures while the cold-formed steel shapes
are formed at room temperature. Cold-formed steel structural
members are shapes commonly manufactured from steel plate, sheet
metal or strip material. The manufacturing process involves forming
the material by eitherpress-brakingorcold roll formingto achieve
the desired shape.When steel is formed by press-braking or cold
rolled forming, there is a change in the mechanical properties of
the material by virtue of the cold working of the metal. When a
steel section is cold-formed from flat sheet or strip the yield
strength, and to a lesser extent the ultimate strength, are
increased as a result of this cold working, particularly in the
bends of the section.Some of the main properties of cold formed
steel are as follows:[10] Lightness in weight High strength and
stiffness Ease of prefabrication and mass production Fast and easy
erection and installation Substantial elimination of delays due to
weather More accurate detailing Non shrinking and non creeping at
ambient temperatures No formwork needed Termite-proof and rot proof
Uniform quality Economy in transportation and handling Non
combustibility Recyclable material Panels and decks can provide
enclosed cells for conduits.
A broad classification of the cold-formed shapes used in the
construction industry can be made as individual structural framing
members or panels and decks.Some of the popular applications and
the preferred sections are: Roof and wall systems (industrial,
commercial, and agricultural buildings) Steel racks for supporting
storage pallets Structural members for plane and space trusses
Frameless Stressed skin structures: Corrugated sheets or sheeting
profiles with stiffened edges are used for small structures up to a
30ft clear span with no interior frameworkCFS Decking
CFS purlins
CFS X-braced wall system
CFS stud/girt wall connectionThe AISI Specification allows the
use of steel to the following ASTM specifications in the table
below:[11]Steel DesignationASTM DesignationProductYield Strength Fy
(ksi)Tensile Strength Fu (ksi)Fu / FyMinimum Elongation (%) in
2-in. Gage Length
Carbon structural steelA363658-801.6123
A3650701.421
High-strength low-alloy Structural steelA24246671.4621
Low and intermediate tensile strength carbon steel
platesA283
A2445-601.8830
B2750-651.8528
C3055-751.8325
D3360-801.8223
Cold-formed welded and seamless carbon steel structural tubing
in rounds and shapesA500Round Tubing
A33451.3625
B42581.3823
C46621.3521
D36581.6123
Shape Tubing
A39451.1525
B46581.2623
C50621.2421
D36581.6123
High-strength carbonmanganese steelA529 Gr. 424260-851.4322
A529 Gr. 505070-1001.4021
Hot-rolled carbon steel sheets and strips of structural
qualityA570
Gr. 3030491.6321
Gr. 3333521.5818
Gr. 3636531.4717
Gr. 4040551.3815
Gr. 4545601.3313
Gr. 5050651.3011
High-strength low-alloy columbium vanadium steels of structural
qualityA572
Gr. 4242601.4324
Gr. 5050651.3021
Gr. 6060751.2518
Gr. 6565801.2317
High-strength low-alloy structural steel with 50 ksi minimum
yield pointA58850701.4021
Hot-rolled and cold-rolled high-strength low-alloy steel sheet
and strip with improved corrosion resistanceA606Hot-rolled as
rolled cut length50701.4022
Hot-rolled as rolled coils45651.4422
Hot-rolled annealed45651.4422
Cold-rolled45651.4422
Hot-rolled and cold-rolled high-strength low-alloy columbium
and/or vanadium steel sheet and stripA607 Class I
Gr.4545601.33Hot rolled (23)Cold rolled (22)
Gr.5050651.30Hot rolled (20)Cold rolled (20)
Gr.5555701.27Hot rolled (18)Cold rolled (18)
Gr.6060751.25Hot rolled (16)Cold rolled (16)
Gr.6565801.23Hot rolled (14)Cold rolled (15)
Gr.7070851.21Hot rolled (12)Cold rolled (14)
A607 Class II
Gr.4545551.22Hot rolled (23)Cold rolled (22)
Gr.5050601.20Hot rolled (20)Cold rolled (20)
Gr.5555651.18Hot rolled (18)Cold rolled (18)
Gr.6060701.17Hot rolled (16)Cold rolled (16)
Gr.6565751.15Hot rolled (14)Cold rolled (15)
Gr.7070801.14Hot rolled (12)Cold rolled (14)
Cold-rolled carbon structural steel sheetA611
A25421.6826
B30451.5024
C33481.4522
D40521.3020
Zinc-coated or zinc-iron alloy-coated steel sheetA653 SS
Gr. 3333451.3620
Gr. 3737521.4118
Gr. 4040551.3816
50 Class 150651.3012
50 Class 350701.4012
HSLAS Type A
5050601.2020
6060701.1716
7070801.1412
8080901.1310
HSLAS Type B
5050601.2022
6060701.1718
7070801.1414
8080901.1312
Hot-rolled and cold-rolled high-strength low-alloy steel sheets
and strip with improved formabilityA715
Gr. 5050601.2022
Gr. 6060701.1718
Gr. 7070801.1414
Gr. 8080901.1312
55% aluminum-zinc alloy-coated steel sheet by the hot-dip
processA792
Gr. 3333451.3620
Gr. 3737521.4118
Gr. 4040551.3816
Gr. 50A50651.3012
Cold-formed welded and seamless high-strength, low-alloy
structural tubing with improved atmospheric corrosion
resistanceA84750701.4019
Zinc-5% aluminum alloy-coated steel sheet by the hot-dip
processA875 SS
Gr. 3333451.3620
Gr. 3737521.4118
Gr. 4040551.3816
50 Class 150651.3012
50 Class 350701.4012
HSLAS Type A
5050601.2020
6060701.1716
7070801.1412
8080901.1310
HSLAS Type B
5050601.2022
6060701.1718
7070801.1414
8080901.1312
Typical stressstrain properties[edit]A main property of steel,
which is used to describe its behavior, is the stressstrain graph.
The stressstrain graphs of cold-formed steel sheet mainly fall into
two categories. They are sharp yielding and gradual yielding type
illustrated below in Fig.1 and Fig.2, respectively.
These two stressstrain curves are typical for cold-formed steel
sheet during tension test. The second graph is the representation
of the steel sheet that has undergone the cold-reducing (hard
rolling) during manufacturing process, therefore it does not
exhibit a yield point with a yield plateau. The initial slope of
the curve may be lowered as a result of the prework. Unlike Fig.2,
the stressstrain relationship in Fig.1 represents the behavior of
annealed steel sheet. For this type of steel, the yield point is
defined by the level at which the stressstrain curve becomes
horizontal.Cold forming has the effect of increasing the yield
strength of steel, the increase being the consequence of cold
working well into the strain-hardening range. This increase is in
the zones where the material is deformed by bending or working. The
yield stress can be assumed to have been increased by 15% or more
for design purposes. The yield stress value of cold-formed steel is
usually between 33ksi and 80ksi. The measured values ofModulus of
Elasticitybased on the standard methods usually range from29,000 to
30,000 ksi (200 to 207 GPa). A value of 29,500 ksi (203 GPa) is
recommended by AISI in its specification for design purposes. The
ultimate tensile strength of steel sheets in the sections has
little direct relationship to the design of those members. The
load-carrying capacities of cold-formed steel flexural and
compression members are usually limited by yield point or buckling
stresses that are less than the yield point of steel, particularly
for those compression elements having relatively large flat-width
ratios and for compression members having relatively large
slenderness ratios. The exceptions are bolted and welded
connections, the strength of which depends not only on the yield
point but also on the ultimate tensile strength of the material.
Studies indicate that the effects of cold work on formed steel
members depend largely upon the spread between the tensile and the
yield strength of the virgin material.Ductility
criteria[edit]Ductilityis defined as an extent to which a material
can sustain plastic deformation without rupture. It is not only
required in the forming process but is also needed for plastic
redistribution of stress in members and connections, where stress
concentration would occur. The ductility criteria and performance
of low-ductility steels for cold-formed members and connections
have been studied byDhalla,Winter, andErreraatCornell University.
It was found that the ductility measurement in a standard tension
test includes local ductility and uniform ductility. Local
ductility is designated as the localized elongation at the eventual
fracture zone. Uniform ductility is the ability of a
tensioncouponto undergo sizeable plastic deformations along its
entire length prior to necking. This study also revealed that for
the different ductility steels investigated, the elongation in
2-in. (50.8-mm) gage length did not correlate satisfactorily with
either the local or the uniform ductility of the material. In order
to be able to redistribute the stresses in the plastic range to
avoid premature brittle fracture and to achieve full net-section
strength in a tension member with stress concentrations, it is
suggested that: The minimum local elongation in a - 12 in.
(12.7-mm) gauge length of a standard tension coupon including the
neck be at least 20%. The minimum uniform elongation in a 3-in.
(76.2-mm) gauge length minus the elongation in a 1-in. (25.4-mm)
gage length containing neck and fracture be at least 3%. The
tensile-strength-to-yield-point ratio Fu /Fy be at least
1.05.Weldability[edit]Weldability refers to the capacity of steel
to be welded into a satisfactory, crack free, sound joint under
fabrication conditions without difficulty.[1]Weldingis possible in
cold-formed steel elements, but it shall follow the standards given
in AISIS100-2007, Section E.1.When thickness less than or equal to
3/16 (4.76mm):The various possible welds in cold formed steel
sections, where the thickness of the thinnest element in the
connection is 3/16 or less are as follows Groove Welds in Butt
joints Arc Spot Welds Arc Seam Welds Fillet Welds Flare Groove
Welds2.When thickness greater than or equal to 3/16 (4.76mm):Welded
connections in which thickness of the thinnest connected arc is
greater than 3/16 (4.76mm) shall be in accordance
withANSI/AISC-360. The weld positions are covered as perAISI
S100-2007(Table E2a)[9]Minimum material thickness recommended for
welding connections[edit]ApplicationShoporField
fabricationElectrodemethodSuggested minimum CFS thickness
CFS toStructural steelField-fabricationStick-welding54 mils to
68 mils
CFS toStructural steelShop-fabricationStick-welding54 mils to 68
mils
CFS to CFSField-fabricationStick-welding54 mils to 68 mils
CFS to CFSField-fabricationWire-fed MIG (Metal Inert Gas)
welding43 mils to 54 mils
CFS to CFSShop-fabricationWire-fed MIG (Metal Inert Gas)
welding33 mils
[12]Application in buildings[edit]Cold-formed steel
framing[edit]Cold-formed steel framing (CFSF) refers specifically
to members in light-frame building construction that are made
entirely of sheet steel, formed to various shapes at ambient
temperatures. The most common shape for CFSF members is a lipped
channel, although Z, C, tubular, hat and other shapes and
variations have been used. The building elements that are most
often framed with cold-formed steel are floors, roofs, and walls,
although other building elements and both structural and decorative
assemblies may be steel framed.Although cold-formed steel is used
for several products in building construction, framing products are
different in that they are typically used for wall studs, floor
joists, rafters, and truss members. Examples of cold-formed steel
that would not be considered framing includes metal roofing, roof
and floor deck, composite deck, metal siding, and purlins and girts
on metal buildings.Framing members are typically spaced at 16 or
24inches on center, with spacing variations lower and higher
depending upon the loads and coverings. Wall members are typically
vertical lipped channel stud members, which fit into unlipped
channel track sections at the top and bottom. Similar
configurations are used for both floor joist and rafter assemblies,
but in a horizontal application for floors, and a horizontal or
sloped application for roof framing. Additional elements of the
framing system include fasteners and connectors, braces and
bracing, clips and connectors.In North America, member types have
been divided into five major categories, and product nomenclature
is based on those categories. S members are lipped channels, most
often used for wall studs, floor joists, and ceiling or roof
rafters. T members are unlipped channels, which are used for top
and bottom plates (tracks) in walls, and rim joists in floor
systems. Tracks also form the heads and sills of windows, and
typically cap the top and bottom of boxed- or back-to-back headers.
U members are unlipped channels that have a smaller depth than
tracks, but are used to brace members, as well as for ceiling
support systems. F members are furring or hat channels, typically
used horizontally on walls or ceilings. L members are angles, which
in some cases can be used for headers across openings, to
distribute loads to the adjacent jamb studs.In high-rise commercial
and multi-family residential construction, CFSF is typically used
for interior partitions and support of exterior walls and cladding.
In many mid-rise and low-rise applications, the entire structural
system can be framed with CFSF.Connectors and fasteners in
framing[edit]Connectors are used in cold-formed steel construction
to attach members (i.e.studs,joists) to each other or to the
primary structure for the purpose of load transfer and support.
Since an assembly is only as strong as its weakest component, it is
important to engineer each connection so that it meets specified
performance requirements. There are two main connection types,Fixed
and Movement-Allowing(Slip). Fixed connections of framing members
do not allow movement of the connected parts. They can be found in
axial-load bearing walls, curtain walls, trusses, roofs, and
floors. Movement-Allowing connections are designed to allow
deflection of the primary structure in the vertical direction due
to live load, or in the horizontal direction due to wind or seismic
loads, or both vertical and horizontal directions. One application
for a vertical movement-allowing connection is to isolate non-axial
load bearing walls (drywall) from the vertical live load of the
structure and to prevent damage to finishes. If the structure is in
an active seismic zone, vertical and horizontal movement-allowing
connections may be used to accommodate both the vertical deflection
and horizontal drift of the structure.Connectors may be fastened to
cold-formed steel members and primary structure using welds, bolts,
or self-drilling screws. These fastening methods are recognized in
the American Iron and Steel Institute (AISI) 2007 North American
Specification for the Design of Cold-Formed Steel Structural
Members, Chapter E. Other fastening methods, such as clinching,
power actuated fasteners (PAF), mechanical anchors, adhesive
anchors and structural glue, are used based on manufacturer's
performance-based tests.Hot-rolled versus cold-rolled steel and the
influence of annealing[edit]Hot rolledCold rolled
Material propertiesYielding strengthThe material is not
deformed; there is no initial strain in the material, hence
yielding starts at actual yield value as the original material.The
yield value is increased by 15%30% due to prework (initial
deformation).
Modulus of elasticity29,000 ksi29,500 ksi
Unit weightUnit weight is comparatively huge.It is much
smaller.
DuctilityMore ductile in nature.Less ductile.
DesignMost of the time, we consider only the global buckling of
the member.Local buckling, Distortional Buckling, Global Buckling
have to be considered.
Main usesLoad bearing structures, usually heavy load bearing
structures and where ductility is more important ( Example Seismic
prone areas)Application in many variety of loading cases. This
includes building frames, automobile, aircraft, home appliances,
etc. Use limited in cases where high ductility requirements.
Flexibility of shapesStandard shapes are followed. High value of
unit weight limits the flexibility of manufacturing wide variety of
shapes.Any desired shape can be molded out of the sheets. The light
weight enhances its variety of usage.
EconomyHigh Unit weight increases the overall cost material,
lifting, transporting, etc. It is difficult to work with (e.g.
connection).Low unit weight reduces the cost comparatively. Ease of
construction (e.g. connection).
Research possibilitiesIn the advanced stages at present.More
possibilities as the concept is relatively new and material finds
wide variety of applications.
Annealing, also described in the earlier section, is part of the
manufacturing process of cold-formed steel sheet. It is aheat
treatmenttechnique that alters the microstructure of the
cold-reducing steel to recover
itsductility.reference:http://en.wikipedia.org/wiki/Cold-formed_steel
welded built-up columnsBuilt-up columns are used in steel
construction when the column buckling lengths are large and the
compression forces are relatively low. This guide covers two types
of built-up columns: Built-up columns with lacing Built-up columns
with battens. This document includes an overview of common details
for such members. It describes the design method according to EN
1993-1-1[1] for the determination of the internal forces and the
buckling resistance of each member (chords, diagonals, etc) of
built-up columns made of hot rolled profiles. It should be noted
that due to the shear deformation, battened built-up columns are
more flexible than solid columns with the same inertia; this must
be taken into account in the design. In order to derive the axial
resistance of a steel built-up column, the following must be
addressed: Analysis of the built-up column to determine the
internal forces by taking into account an equivalent initial
imperfection and the second order effects Verification of the
chords and bracing members (diagonals and battens) Verification of
the connections. A fully worked example of a built-up column with
an N-shape arrangement of lacings is given in Appendix A, which
illustrates the design principles.
TYPES OF BUILT-UP MEMBERS AND THEIR APPLICATION 2.1 General In
general, built-up columns are used in industrial buildings, either
as posts for cladding when their buckling length is very long, or
as columns supporting a crane girder. When used as a post for
cladding with pinned ends, the column is designed to support the
horizontal forces, mainly due to wind. Hence the bending moment in
such a built-up column is predominant compared to the compression
force.
A typical built-up column that supports a crane girder is shown
in Figure 2.2.They usually have a fixed base and a pinned end at
the top, and are designed toresist: The compression forces that
result either from the frame or from the cranerail The horizontal
forces that result from the effects of the crane applied on
theinternal chord and the wind loads applied to the external one.In
this case, the compression forces are predominant compared to the
bendingmoment.
The built-up columns are composed of two parallel chords
interconnected bylacings or battens see Figure 2.1. In general, the
truss system concentratesmaterial at the structurally most
efficient locations for force transfer.In an industrial building
and for a given height, built up columns theoreticallyhave the
least steel weight of any steel framing system.Any hot rolled
section can be used for the chords and the web members ofbuilt-up
columns. However, channels or I-sections are most commonly used
aschords. Their combination with angles presents a convenient
technical solutionfor built-up columns with lacing or battens. Flat
bars are also used in built-upcolumn as battens.This guide covers
two types of built-up columns with pinned ends that areassumed to
be laterally supported: Laced columns Battened columns.
The difference between these two types of built-up columns comes
from themode of connection of the web members (lacings and battens)
to the chords.The first type contains diagonals (and possibly
struts) designed with pinnedends. The second type involves battens
with fixed ends to the chords andfunctioning as a rectangular
panel.The inertia of the built-up column increases with the
distance between thechord axes. The increase in stiffness is
counterbalanced by the weight and costincrease of the connection
between members.Built-up columns provide relatively light
structures with a large inertia. Indeed,the position of the chords,
far from the centroid of the built-up section, is verybeneficial in
producing a great inertia. These members are generally intendedfor
tall structures for which the horizontal displacements are limited
to lowvalues (e.g. columns supporting crane girders).The axial
resistance of built-up columns is largely affected by the
sheardeformations. The initial bow imperfection is significantly
amplified becauseof the shear strains.It is possible to study the
behaviour of built-up columns using a simple elasticmodel.
Laced built-up columns2.2.1 GeneralThere is a large number of
laced column configurations that may beconsidered. However, the
N-shape and the V-shape arrangements of lacings arecommonly
used.
Figure 2.4 Built-up column with lacings in an industrial
building
The selection of either channels or I-sections for chord members
providesdifferent advantages. I-sections are more structurally
efficient and therefore arepotentially shallower than channels. For
built-up columns with a largecompressive axial force (for example,
columns supporting cranes), I orH sections will be more appropriate
than channels. Channels may be adequatein order to provide two flat
sides.Tee sections cut from European Column sections are also used
for the chordmembers. The web of the Tee sections should be
sufficiently deep to permiteasy welding of the bracing members.The
angle web members of the laced column allow use of gusset-less
weldedconnections, which minimises fabrication costs. Other member
types requireeither gussets or more complex welding.The centroidal
axes of the compression and tension web members are notnecessarily
required to meet at the same point on the chord axes. In fact,
lacedcolumns with an eccentricity at the joints can be as efficient
as those withouteccentricity. The chord-web joint can be separated
without an increase in steelweight. Although eccentric joints
require that local moments be designed for,there are several
advantages in doing so. Eccentric joints provide additionalspace
for welding, hence reducing fabrication complexity. In addition,
thereduced length of the compression chord provides enhanced
buckling andbending resistance which partly compensates for the
additional momentsgenerated by the joint eccentricity. For single
angles, it is recommended thatjoint eccentricity is minimised.
2.2.2 Various lacing geometriesThe N-shape arrangement of
lacings, as shown in Figure 2.5(a), can beconsidered as the most
efficient truss configuration, for typical frames inindustrial
buildings. The web of the N-shape arrangement comprises
diagonalsand posts that meet at the same point on the chord
axes.This arrangement reduces the length of the compression chords
and diagonals.It is usually used in frames with a significant
uniform compressive force.The V-shape arrangement of lacings
increases the length of the compressionchords and diagonals and
provides a reduction of buckling resistance of themembers. This
arrangement is used in frames with a low compressive force.The
X-shape configurations are not generally used in buildings because
of thecost and the complexity of fabrication.
\2.2.3 Construction detailsSingle lacing systems on opposite
faces of the built-up member with twoparallel laced planes should
be corresponding systems as shown inFigure 2.6(a) (EN 1993-1-1
6.4.2.2(1)).When the single lacing systems on opposite faces of a
built-up member withtwo parallel laced planes are mutually opposed
in direction, as shown inFigure 2.6(b), the resulting torsional
effects in the member should be taken intoaccount. The chords must
be designed for the additional eccentricity caused bythe transverse
bending effect, which can have a significant influence on themember
size.Tie panels should be provided at the ends of lacing systems,
at points where thelacing is interrupted and at joints with other
members.
2.3 Battened built-up columnsBattened built-up columns are not
appropriate for frames in industrialbuildings. They are sometimes
used as isolated frame members in specificconditions, where the
horizontal forces are not significant.Channels or I-sections are
mostly used as chords and flat bars are used asbattens. The battens
must have fixed ends on the chords.Battened built-up columns are
composed of two parallel planes of battenswhich are connected to
the flanges of the chords. The position of the battensshould be the
same for both planes. Battens should be provided at each end ofthe
built-up member.Battens should also be provided at intermediate
points where loads are applied,and at points of lateral
restraint.
reference:http://www.arcelormittal.com/sections/fileadmin/redaction/4-Library/4-SBE/EN/SSB06_Detailed_design_of_built-up_columns.pdf
hallow precast floor beamsAhollow core slab, also known as
avoided slaborhollow core plank, is aprecastslab ofprestressed
concretetypically used in the construction offloorsin
multi-storyapartment buildings. The slab has been especially
popular in countries where the emphasis of home construction has
been on precast concrete, including Northern Europe andsocialist
countriesofEastern Europe. Precast concrete popularity is linked
with low-seismic zones and more economical constructions because of
fast building assembly, lower self weight (less material),
etc.Theprecast concreteslab has tubular voids extending the full
length of the slab, typically with a diameter equal to the 2/3-3/4
of the slab. This makes the slab much lighter than a massive floor
slabs of equal thickness or strength. Reduced weight is important
because of transportation cost and less cost of material
(concrete). The slabs are typically 120cm wide with standard
thicknesses between 15cm and 50cm. The precast
concreteI-beamsbetween the holes contain the steel wire rope that
provide bending resistance to bending moment from loads.Slabs in
prestressed concrete are usually produced in lengths of about 120
meters. The process involvesextrudingwet concrete along with the
prestressed steel wire rope from a movingmold. The continuous slab
is then cut by big diamond circular saw according to the lengths
(and width) required on blueprint. Factory production provides the
obvious advantages of reduced time, labor and training. Another
fabrication system produces hollow-core floorslabs in Reinforced
Concrete (not prestressed). These are made on carousel production
lines, directly to exact length, and as a stock product. Although
the length is limited to about 7-8 metre, this type is much more
cost effective (needs less people, and is faster). Especially in
Belgium, this method is widely used in private housing.To meet
modern standards (both hollow-core and massive slab)
ofsoundproofingthe floor needs to be covered with a softfloor
coveringthat is able to dampen the sound of footsteps. An
alternative is to use a thin "floating" slab of concrete insulated
from the voided slabs.
Diagram of a concrete slab of hollow core constructionHollowcore
benefitsClear, unpropped spansFast and simple to erectProvides an
immediate working platformCan be used in all types of structure
Masonry, steel and concreteExcellent sound and fire
resistanceEasier installation of servicesHoles and notches
preformed during manufactureQuality service guaranteedAvailable
nationwide either supply only or supply and fixFactory manufacture
to consistent quality standards Complies with all relevant
standards and manufactured in accordance with BS EN ISO 9001 and BS
EN ISO140001
referencehttp://en.wikipedia.org/wiki/Hollow-core_slabhttp://www.heidelbergcement.com/NR/rdonlyres/DECAC297-B027-4E60-A7C0-7BCF29AEDC19/0/Flooring_Hollowcore.pdfprecast
prestressed concrete floor units
steel ring spacer
floor reinforcement cage
precast concrete wall frame
stud framesFraming, in construction known aslight-frame
construction, is a building technique based around vertical
structural members, usually calledstuds, which provide a stable
frame to which interior and exteriorwallcoverings are attached, and
covered by aroofmade of horizontal ceilingjoistsand
slopingrafters(or pre-fabricated rooftrusses).Modern light-frame
structures usually gain strength from rigid panels (plywoodand
other plywood-like composites such asoriented strand board(OSB)
used to form all or part of wall sections) but until
recentlycarpentersemployed various forms of diagonal bracing
(calledwind braces) to stabilize walls. Diagonal bracing remains a
vital interior part of many roof systems, and in-wall wind braces
are required by building codes in many municipalities or by
individualstate lawsin the United States.Light frame construction
using standardizeddimensional lumberhas become the dominant
construction method inNorth AmericaandAustraliabecause of
itseconomy. Use of minimal structural materials allows builders to
enclose a large area with minimal cost, while achieving a wide
variety of architectural styles. The ubiquitousplatform framingand
the olderballoon framingare the two different light frame
construction systems used in North America.
A wooden-frame house under construction in this example of
platform framing the location of the upper floor is readily
discerned by the wide joists between the floors, and the upper
structure rests on this platform.Walls[edit]Wall framing in house
construction includes the vertical and horizontal members of
exterior walls and interior partitions, both ofbearing wallsand
non-bearing walls. Thesestickmembers, referred to asstuds,wall
platesandlintels(headers), serve as a nailing base for all covering
material and support the upper floor platforms, which provide the
lateral strength along a wall. The platforms may be the boxed
structure of aceilingand roof, or the ceiling andfloorjoistsof the
story above.[1]The technique is variously referred to colloquially
in the building trades asstick and frame,stick and platform,
orstick and boxas the sticks (studs) give the structure its
vertical support, and the box shaped floor sections with joists
contained within length-longpost and lintels(more commonly
calledheaders), supports the weight of whatever is above, including
the next wall up and the roof above the top story. The platform
also provides the lateral support against wind and holds the stick
walls true and square. Any lower platform supports the weight of
the platforms and walls above the level of its component headers
and joists.Framinglumbershould be grade-stamped, and have a
moisture content not exceeding 19%.[2]There are three historically
common methods of framing a house. Post and beam, which is now used
predominately in barn construction. Balloon framing using a
technique suspending floors from the walls was common until the
late 1940s, but since that time,platform framinghas become the
predominant form of house construction.[3] Platform framing often
forms wall sections horizontally on the sub-floor prior to
erection, easing positioning of studs and increasing accuracy while
cutting the necessary manpower. The top and bottom plates are
end-nailed to each stud with two nails at least 3.25in (83mm) in
length (16dor16 pennynails). Studs are at least doubled (creating
posts) at openings, the jack stud being cut to receive the
lintels(headers) that are placed and end-nailed through the outer
studs.[3]Wall sheathing, usually a plywood or other laminate, is
usually applied to the framing prior to erection, thus eliminating
the need toscaffold, and again increasing speed and cutting
manpower needs and expenses. Some types of exterior sheathing, such
as asphalt-impregnatedfibreboard,plywood,oriented strand
boardandwaferboard, will provide adequate bracing to resist lateral
loads and keep the wall square. (Construction codes in most
jurisdictions require a stiff plywood sheathing.) Others, such as
rigid glass-fibre, asphalt-coated
fibreboard,polystyreneorpolyurethaneboard, will not.[1]In this
latter case, the wall should be reinforced with a diagonal wood or
metal bracing inset into the studs.[4]In jurisdictions subject to
strong wind storms (hurricane countries,tornado alleys) local codes
or state law will generally require both the diagonalwind bracesand
the stiff exterior sheathing regardless of the type and kind of
outer weather resistant coverings.Corners[edit]A multiple-stud post
made up of at least three studs, or the equivalent, is generally
used at exterior corners and intersections to secure a good tie
between adjoining walls and to provide nailing support for the
interior finish and exterior sheathing.Cornersand intersections,
however, must be framed with at least two studs.[5]Nailing support
for the edges of the ceiling is required at the junction of the
wall and ceiling where partitions run parallel to the ceiling
joists. This material is commonly referred to as 'dead wood'[6]or
backing.Exterior wall studs[edit]Wall framing in
houseconstructionincludes the vertical and horizontal members of
exterior walls and interior partitions. These members, referred to
asstuds, wall plates and lintels, serve as a nailing base for all
covering material and support the upper floors, ceiling and
roof.[1]Exterior wall studs are the vertical members to which the
wall sheathing andcladdingare attached.[7]They are supported on a
bottom plate or foundation sill and in turn support the top plate.
Studs usually consist of 1.5in 3.5in (38mm 89mm) or 1.5in 5.5in
(38mm 140mm) lumber and are commonly spaced at 16in (410mm) on
centre. This spacing may be changed to 12in (300mm) or 24in (610mm)
on centre depending on theloadand the limitations imposed by the
type and thickness of the wall covering used. Wider 1.5in 5.5in
(38mm 140mm) studs may be used to provide space for moreinsulation.
Insulation beyond that which can be accommodated within a 3.5in
(89mm) stud space can also be provided by other means, such as
rigid or semi-rigid insulation or batts between 1.5in 1.5in (38mm
38mm) horizontalfurring strips, or rigid or semi-rigid insulation
sheathing to the outside of the studs. The studs are attached to
horizontal top and bottom wall plates of 1.5in (38mm) lumber that
are the same width as the studs.[2]Interior
partitions[edit]Interior partitions supportingfloor, ceiling or
roof loads are called loadbearing walls; others are called
non-loadbearing or simply partitions. Interior loadbearing walls
are framed in the same way as exterior walls. Studs are usually
1.5in 3.5in (38mm 89mm) lumber spaced at 16in (410mm) on centre.
This spacing may be changed to 12in (300mm) or 24in (610mm)
depending on the loads supported and the type and thickness of the
wall finish used.[5]Partitions can be built with 1.5in 2.5in (38mm
64mm) or 1.5in 3.5in (38mm 89mm) studs spaced at 16 or 24in (400 or
600mm) on center depending on the type and thickness of the wall
finish used. Where a partition does not contain a swinging door,
1.5in 3.5in (38mm 89mm) studs at 16in (410mm) on centre are
sometimes used with the wide face of the studparallelto the wall.
This is usually done only for partitions enclosing clothes closets
or cupboards to save space. Since there is no vertical load to be
supported by partitions, single studs may be used at door openings.
The top of the opening may be bridged with a single piece of 1.5in
(38mm) lumber the same width as the studs. These members provide a
nailing support for wall finish, door frames andtrim.[5]Lintels
(headers)[edit]Lintels (or, headers) are the horizontal members
placed over window, door and other openings to carry loads to the
adjoining studs.[1]Lintels are usually constructed of two pieces of
2in (nominal) (38mm) lumber separated with spacers to the width of
the studs and nailed together to form a single unit. The preferable
spacer material is rigid insulation.[7]The depth of a lintel is
determined by the width of the opening and vertical loads
supported.Wall sections[edit]The complete wall sections are then
raised and put in place, temporary braces added and the bottom
plates nailed through the subfloor to the floor framing members.
The braces should have their larger dimension on the vertical and
should permit adjustment of the vertical position of the
wall.[4]Once the assembled sections are plumbed, they are nailed
together at the corners and intersections. A strip ofpolyethyleneis
often placed between the interior walls and the exterior wall, and
above the first top plate of interior walls before the second top
plate is applied to attain continuity of theair barrierwhen
polyethylene is serving this function.[4]A second top plate, with
joints offset at least one stud space away from the joints in the
plate beneath, is then added. This second top plate usually laps
the first plate at the corners and partition intersections and,
when nailed in place, provides an additional tie to the framed
walls. Where the second top plate does not lap the plate
immediately underneath at corner and partition intersections, these
may be tied with 0.036in (0.91mm) galvanized steel plates at least
3in (76mm) wide and 6in (150mm) long, nailed with at least three
2.5in (64mm) nails to each wall.[4]Balloon framing[edit]
Balloon framing is a method ofwoodconstruction also known as
"Chicago construction" in the 19th century[8] used primarily
inScandinavia,Canadaand theUnited States(up until the mid-1950s).
It utilizes long continuous framing members (studs) that run from
thesill plateto the top plate, with intermediate floor structures
let into and nailed to them.[9][10]Here the heights of window
sills, headers and next floor height would be marked out on the
studs with astorey pole. Once popular when long lumber was
plentiful, balloon framing has been largely replaced byplatform
framing.It is not certain who introduced balloon framing in the
United States. However, the first building using balloon framing
was probably a warehouse constructed in 1832 inChicago,Illinois,
byGeorge Washington Snow.[11]The following year, Augustine Taylor
(17961891) constructed St. Mary's Catholic Church inChicagousing
the balloon framing method.In the 1830s,HoosierSolon Robinson
published articles about a revolutionary new framing system, called
balloon framing by later builders. Robinsons system called for
standard 2x4 lumber, nailed together to form a sturdy, light
skeleton. Builders were reluctant to adopt the new technology,
however, by the 1880s, some form of 2x4 framing was
standard.[12]Alternatively, the balloon frame has been shown to
have been introduced in Missouri as much as fifty years
earlier.[13]The name comes from a French Missouri type of
construction,maison enboulin,[13]boulinbeing a French term for a
horizontal scaffolding support. Historians have also fabricated the
following story:[14]As Taylor was constructing his first such
building, St. Mary's Church, in 1833, skilled carpenters looked on
at the comparatively thin framing members, all held together with
nails, and declared this method of construction to be no more
substantial than a balloon. It would surely blow over in the next
wind! Though the criticism proved baseless, the name
stuck.[15]Although lumber was plentiful in 19th-century America,
skilled labor was not. The advent of cheap machine-made nails,
along with water-powered sawmills in the early 19th century made
balloon framing highly attractive, because it did not require
highly-skilled carpenters, as did thedovetail joints,mortises and
tenonsrequired bypost-and-beam construction. For the first time,
any farmer could build his own buildings without a time-consuming
learning curve.[16]It has been said that balloon framing populated
the western United States and the western provinces of Canada.
Without it, western boomtowns certainly could not have blossomed
overnight.[17]It is also a fair certainty that, by radically
reducing construction costs, balloon framing improved the shelter
options of poorer North Americans.[citation needed]For example,
many 19th-centuryNew Englandworking neighborhoods consist of
balloon-constructed three-story apartment buildings referred to
astriple deckers.
A very unusual example of balloon framing: The Jim Kaney Round
Barn, Adeline, Illinois, U.S.A.The main difference between platform
and balloon framing is at the floor lines. The balloon
wallstudsextend from the sill of the first story all the way to
thetop plateorend rafterof the second story. The platform-framed
wall, on the other hand, is independent for each floor.[18]Balloon
framing has several disadvantages as a construction method:1. The
creation of a path for fire to readily travel from floor to floor.
This is mitigated with the use of firestops at each floor level.2.
The lack of a working platform for work on upper floors. Whereas
workers can readily reach the top of the walls being erected with
platform framing, balloon construction requires scaffolding to
reach the tops of the walls (which are often two or three stories
above the working platform).3. The requirement for long framing
members.4. In certain larger buildings, a noticeable down-slope of
floors towards central walls, caused by the differential shrinkage
of the wood-framing members at the perimeter versus central walls.
Larger balloon-framed buildings will have central bearing walls
which are actually platform framed and thus will have horizontal
sill and top plates at each floor level, plus the intervening floor
joists, at these central walls. Wood will shrink much more across
its grain than along the grain. Therefore, the cumulative shrinkage
in the center of such a building is considerably more than the
shrinkage at the perimeter where there are many fewer horizontal
members. This problem, unlike the first three, takes time to
develop and become noticeable.5. Present-day balloon framing
buildings often have higher heating costs, due to the lack of
insulation separating a room from its exterior walls. However, this
can be remedied through the addition of insulation, as with any
other framed building.Since steel is generally more fire-resistant
than wood, and steel framing members can be made to arbitrary
lengths, balloon framing is growing in popularity again in light
gauge steel stud construction. Balloon framing provides a more
direct load path down to the foundation. Additionally, balloon
framing allows more flexibility fortradesmenin that it is
significantly easier to pull wire, piping and ducting without
having to bore through or work around framing members.[citation
needed]Platform framing[edit]In Canada and the United States, the
most common method of light-frame construction forhousesand
smallapartment buildingsas well as other small commercial buildings
isplatform framing. In builder parlance, platform framing might
also nowadays be called (only partly correctly) 'stick framing'or
'stick construction'as each element is built up stick by stick,
which was also true in the other stick framing method, in the
obsolete and labor intensive, but previously fashionable, balloon
framing method, wherein the outside walls were erected, headers
hung, then floor joists were inserted into a box made of walls.In
contrast, in platform framing a floor box and joists making up the
platform is built and placed on a supporting under structure (Sill
plates, headers, or beams) where it sits flat and gets fastened
down against wind lifting with galvanized metal tie straps. Once
the boxed floor platform is squared, leveled and fastened
thensubfloor,walls,ceilings, androofare built onto and above that
initial platform, which can be repeated floor by floor, 'without
the slow downs and dangers of fastening and leveling rough-sawn
joists of a new floor together to the walls from ladders extending
one or even twostoriesup.Generally, the flooring ('platform') is
constructed then the walls built on top of that layer, then another
atop that, and so forth making for quick efficient labor saving
construction methodologies and those have quickened further as
technologies such asjoist hangershave been developed to speed and
enhance the technology. The methods and techniques have become so
common and pervasive that evenSkyscrapersuse a modified form of
platform framing techniques and indeed the same tools and
technologies once construction builds the initial
structuralskeleton. Once the platform floor is laid down, the
builder's crew can with chalk line, rule and pencil directly
transfer an outline of the exterior and interior walls, their
openings and relative locations with ease and precision from the
plans or builders blue prints.As the survey group lays down the
notations and chalk lines, a carpenter crew can follow behind and
lay down 2x4 'bottom plates' and tack them to the floor box. The
topmost wall plates are cut only to the outside dimensions of the
walls. Butting two other two by fours against these cut to size and
fastened bottom plate allows the crew to rule across all three with
square and lay out studs, cripple studs, and openings for that
particular wall. The two loose studs are then quickly flipped on
edge after openings are cut in, and studs added on the marks with
quick reliable end nailing through the respective top and bottom
plates. A few minutes later the whole wall section can be levered
up and aligned in place and braced for later application of the top
plates and adjoining walls.The method provides builders options and
flexibility such as when and where there is a floor-level opening
(doorway) the next wall section can be aligned and fastened in
place separately with the top plate added then used then a lintel
and cripple studding added, or the entire wall could have been cut
and joined at the top all along and lifted up as one entity. In the
end, the outside walls are plumbed and fastened together with
'ell-configured reinforced corners' that provide nailing wood in
the interior angles and strength to the building forming in effect
wide posts at each corner and fastened lastly by overlapped top
plates which stagger their joints from the ones capping each plate
by which the studs are end nailed together. Each wall from top to
bottom ends up with a doubled plate, studs, and a doubled plate,
where structurally the doubled plates spread the weight of the roof
and loading across the studs of the wall, ultimately to the
foundation.Overall, the framed structure sits (most commonly) atop
aconcretefoundationonpressure treated wood 'sill', or 'beam'.When
on concrete, thesill plateisanchored, usually with (embedded) 'J'
bolts into the concrete substrate of the foundation wall. Generally
these plates must be pressure treated to keep from rotting from
condensing moisture. By various standards the bottom of thesill
plateis located a minimum 6 inches (150mm) above thefinished
grade(the surrounding ground) per standard builders practices, and
frequently more dependent upon building codes of the relevant
jurisdiction's local building codes. In North America, building
codes may differ not only state to state, but town to town, the
tighter specification applying at all times. This distance,
together with roofing overhangs, and othersystemfactors, is most
often selected both to prevent the sill-plate from rotting (due to
the invasion of splashed water) as well as providing a termite
barrier. The latter is particularly (more or less) important than
anti-rotting considerations depending upon the geographical
location.Alternatively, the room, room extension, deck or even a
house can be built aboveconcrete columnsU.S. builders callpierssome
others callpilasters, another of many term misuses common to
building trade parlance. In such cases, the pier (column) is
usually required to rest on bed rock or extend well below the zone
of average freezing soil depth (the same as a foundation) locally,
and frequently is required to also have flared out or mushroomed
bottom of greater surface than that the pier top (These are called
'big foots' in the building trade and building suppliers carry PVC
molds to conserve concrete which allow a builder to satisfy area
requirements and the building codes). Rigid pressure treated
'beams' (usually doubled or tripled up wider types of 2x boards)
are attached to the piers using galvanized metal brackets and serve
the same function as sills in foundation supported framing.The
floors, walls and roof of a framed structure are created by
assembling (using nails) consistently sized framing elements
ofdimensional lumber(e.g. 24s) at regular spacings (typically
divisions of 4 and 8 feet, or such as 12, 16, 19.2, or 24 inches on
center). The empty space formed between elements is called a stud
bay in the wall and a joist bay in the floor or ceiling. The
floors, walls and roof are typically made torsionally stable with
the installation of a plywood or composite wood skin referred to as
sheathing[citation needed]. Sheathing has very specific
requirements (such as thickness and spacing of nailing). These
measures allow a known amount of shear force to be resisted by the
elements. Spacing the framing members properly usually allows them
to align with the edges of standard sheathing. In the past,tongue
and grooveplanks installed diagonally were used as sheathing.
Occasionally, wooden orgalvanized steelbracesare used instead of
sheathing. There are alsoengineered woodpanels made for shear and
bracing.[citation needed]The floor, or the platform in this framing
type's name, is made up of joists (usually 2x6, 28, 210 or 212
depending on the span, on edge thus the wider joist supporting
weight for a greater distance) that sit on supporting foundation
walls, beams, columns or girders within and at right angle to
doubled outside members also on edge (the band), forming a box. The
outer perimeter is nearly the same (3inch vs. 3.5inches) width as
the support sill. The joists will generally be installed across the
shortest distance of any floor span rectangle. The outer layer of
the band will overlap the inner layer with staggered end joints
creating a stronger box. If joist hangers are not used, the
installation of the outer board in the band is delayed to allow
through-nailing directly into the ends of the joists.The floor
joists are spaced at 12in, 16in, and 24in on center, depending upon
the live load needs of the design the closer the spacing and the
wider the floor joist dimension, the less the floor will flex. It
is then usually covered with a 3/4-inch tongue-and-groove plywood
subfloor. In the century past, 1x planks set at 45-degrees to the
joists were used for the first subfloor layer, and a second layer
of 1x planks set at 90-degrees to the floor cladding topped that as
the second subfloor layer. In that same era, all flooring choices
were a very short menu of choices between finished wood types or
ceramic tiles versus today's extensive multipage menu of
manufactured flooring types.Where the design calls for a framed
floor, the resulting platform is where the framer will construct
and stand that floor's walls (interior and exterior load bearing
walls and space-dividing, non-load bearing partitions). Additional
framed floors and their walls may then be erected to a general
maximum of four in wood framed construction. There will be no
framed floor in the case of a single-level structure with a
concrete floor known as aslab on grade.[citation
needed]Stairsbetween floors are framed by installing three
90-steppedstringersattached to wall structures and then placing the
horizontaltreadsand verticalrisers(usually about 14 of each for an
8-ft. ceiling) upon the planes formed by the stringers.A framed
roof is an assembly of rafters and wall-ties supported by the top
story's walls. Prefabricated and site-builttrussedrafters are also
used along with the more common stick framing method.Trussesare
engineered to redistribute tension away from wall-tie members and
the ceiling members. The roof members are covered
withsheathingorstrappingto form the roof deck for the finish
roofing material.[citation needed]Floor joists can be engineered
lumber (trussed,I-joist, etc.), conserving resources with increased
rigidity and value. They are semi-custom manufactured to allow
access for runs of plumbing, HVAC, etc. andsome 'common-needs'
formsare pre-manufactured as semi-mass-produced standard products
made on a per order basis, like roofing trusses. Such products have
a post-order lead time from several weeks to several months.Double
framing is a style of framing used in some areas to reduce heat
loss and air infiltration. Two walls are built around the perimeter
of the building with a small gap in between. The inner wall carries
the structural load of the building and is constructed as described
above. The exterior wall is not load bearing and can be constructed
using lighter materials. Insulation is installed in the entire
space between the outside edge of the exterior wall and the inside
edge of the interior wall. The size of the gap depends upon how
much insulation is desired. The vapor barrier is installed on the
outside of the inner wall, rather than between the studs and
drywall of a standard framed structure. This increases its
effectiveness as it is not perforated by electrical and plumbing
connections.Materials[edit]Light-frame materials are most often
wood or rectangularsteeltubes or C-channels. Wood pieces are
typically connected withnailsorscrews; steel pieces are connected
with nuts and bolts. Preferred species for linear structural
members are softwoods such asspruce,pineandfir. Light frame
material dimensions range from 38mm by 89mm (1.5in by 3.5in; i.e.,
atwo-by-four) to 5cm by 30cm (two-by-twelve inches) at the
cross-section, and lengths ranging from 2.5m (8.2ft) for walls to
7m (23ft) or more for joists and rafters. Recently, architects have
begun experimenting with pre-cut modular aluminum framing to reduce
on-site construction costs.[citation needed]Wall panels built of
studs are interrupted by sections that provide rough openings
fordoorsandwindows. Openings are typically spanned by a header or
lintel that bears the weight of structure above the opening.
Headers are usually built to rest ontrimmers, also called jacks.
Areas around windows are defined by a sill beneath the window, and
cripples, which are shorter studs that span the area from the
bottom plate to the sill and sometimes from the top of the window
to a header, or from a header to a top plate. Diagonal bracings
made of wood or steel provide shear (horizontal strength) as do
panels of sheeting nailed to studs, sills and headers.[citation
needed]
Light-gauge metal stud framingWall sections usually include a
bottom plate which is secured to the structure of a floor, and one,
or more often two top plates that tie walls together and provide a
bearing for structures above the wall. Wood or steel floor frames
usually include arim joistaround the perimeter of a system of floor
joists, and often include bridging material near the center of a
span to prevent lateral buckling of the spanning members. In
two-story construction, openings are left in the floor system for a
stairwell, in which stair risers and treads are most often attached
to squared faces cut into sloping stair stringers.[citation
needed]Interior wall coverings in light-frame construction
typically includewallboard,lath and plasteror decorativewood
paneling.[citation needed]Exterior finishes for walls and ceilings
often include plywood orcompositesheathing,brickorstoneveneers, and
variousstuccofinishes. Cavities between studs, usually placed
4060cm (1624in) apart, are usually filled withinsulationmaterials,
such asfiberglassbatting, orcellulosefilling sometimes made
ofrecyclednewsprinttreated withboronadditives forfireprevention
andvermincontrol.[citation needed]Innatural building,straw
bales,cobandadobemay be used for both exterior and interior
walls.The part of a structural building that goes diagonally across
a wall is called a T-bar. It stops the walls from collapsing in
gusty winds.[citation needed]Roofs[edit]Main article:RoofRoofsare
usually built to provide a sloping surface intended to shed rain or
snow, with slopes ranging from 1cm of rise per 15cm (less than an
inch per linear foot) of rafter length, to steep slopes of more
than 2cm per cm (two feet per foot) of rafter length. A light-frame
structure built mostly inside sloping walls comprising a roof is
called anA-frame.Roofs are most often[citation needed]covered
withshinglesmade of asphalt, fiberglass and small gravel coating,
but a wide range of materials are used. Moltentaris often used to
waterproof flatter roofs, but newer materials include rubber and
synthetic materials.Steelpanels are popular roof coverings in some
areas, preferred for their durability.Slateortileroofs offer more
historic coverings for light-frame roofs.Light-frame methods allow
easy construction of unique roof designs. Hip roofs, which slope
toward walls on all sides and are joined at hip rafters that span
from corners to a ridge. Valleys are formed when two sloping roof
sections drain toward each other.Dormersare small areas in which
vertical walls interrupt a roof line, and which are topped off by
slopes at usuallyright anglesto a main roof section.Gablesare
formed when a length-wise section of sloping roof ends to form a
triangular wall section.Clerestoriesare formed by an interruption
along the slope of a roof where a short vertical wall connects it
to another roof section. Flat roofs, which usually include at least
a nominal slope to shed water, are often surrounded by parapet
walls with openings (calledscuppers) to allow water to drain out.
Slopingcricketsare built into roofs to direct water away from areas
of poor drainage, such as behind a chimney at the bottom of a
sloping section.Structure[edit]Light-frame buildings are often
erected onmonolithicconcrete-slab foundations that serve both as a
floor and as a support for the structure. Other light-frame
buildings are built over a crawlspace or abasement, with wood or
steel joists used to span between foundation walls, usually
constructed of poured concrete orconcrete blocks.Engineered
components are commonly used to form floor, ceiling and roof
structures in place of solid wood.I-joists(closed-web trusses) are
often made from laminated woods, most often chippedpoplarwood, in
panels as thin as 1cm (0.4in), glued between horizontally laminated
members of less than 4cm by 4cm (two-by-twos), to span distances of
as much as 9m (30ft). Open web trussed joists and rafters are often
formed of 4cm by 9cm (two-by-four) wood members to provide support
for floors, roofing systems and ceiling
finishes.reference:https://en.wikipedia.org/wiki/Framing_(construction)