Truss Systems Copy

T R U S S S Y S T E M T R U S S S Y S T E M SS

WHAT IS A TRUSS?WHAT IS A TRUSS?• Trusses are Trusses are triangulated frameworkstriangulated frameworks used for used for large large spans and heavy loads for elementsspans and heavy loads for elements in buildings. in buildings.

• Trusses tend to be a Trusses tend to be a stronger, lighterstronger, lighter and and less less expensiveexpensive approach to roof framing. approach to roof framing.

•GEOMETRY:GEOMETRY: Trusses are Trusses are strong because they strong because they make use of the make use of the most most efficient geometric efficient geometric shapeshape we know of - we know of - the the triangle.triangle.

•Trusses are a series of Trusses are a series of triangles fastened triangles fastened together with gusset together with gusset plates. The plates. The outside outside members of a truss are members of a truss are called chords/principal called chords/principal membersmembers while the while the inner inner pieces are known as web pieces are known as web members.members.

•A truss is a A truss is a type of framework, usually comprising type of framework, usually comprising straight struts and ties,straight struts and ties, which is designed to be stiff, which is designed to be stiff, even if all the joints are considered to be pinned. This even if all the joints are considered to be pinned. This is is achieved by the inclusion of a sufficient number of achieved by the inclusion of a sufficient number of triangles. triangles. •Some or all of Some or all of the the joints may joints may be fixed rather be fixed rather than pinnedthan pinned, , but the main but the main contribution to contribution to the stiffness is the stiffness is provided by the provided by the triangulation.triangulation. Simple 2-dimensional trusses. Simple 2-dimensional trusses.

•The trusses are just simple The trusses are just simple schematics of how the members schematics of how the members should be arranged. The should be arranged. The ends of ends of the members all connect at a the members all connect at a common point (the joint)common point (the joint) to form to form triangles. triangles.

Examples of Examples of structures that are structures that are

NOT trusses.NOT trusses.

•The The ends of the ends of the members do not members do not

connectconnect at common at common points. The resulting points. The resulting structure does work, structure does work,

but the members but the members see a substantial see a substantial

amount of bending. amount of bending. This structure is This structure is called a frame. called a frame.

HISTORY:HISTORY: Trusses have been used for many Trusses have been used for many centuries; centuries;

•Andrea PalladioAndrea Palladio illustrates truss bridges in his illustrates truss bridges in his Books Books of Architecture of Architecture as early as 1570.as early as 1570. However, it is in the However, it is in the

nineteenth centurynineteenth century that that industrial expansion—in industrial expansion—in

particular the particular the need for need for long-span exhibition long-span exhibition

halls, railroad terminals, halls, railroad terminals, and bridges—togetherand bridges—together

with the development of with the development of engineering and engineering and

improvements in the improvements in the production production of cast and of cast and

wrought ironwrought iron, and , and later later steel,steel, provide the motive provide the motive

and means for most of and means for most of the advances in truss the advances in truss

design that are design that are exploited within early exploited within early

twentieth-century twentieth-century architecture.architecture.

Labrouste: Biblioteque Labrouste: Biblioteque

Nationale (1875)Nationale (1875) Wood Truss System Wood Truss System

(1920(1920))

Piano & Rogers: Piano & Rogers: Pompidou Center Pompidou Center

(1977) (1977)

Grimshaw: Grimshaw: Waterloo Waterloo

Terminal (1994)Terminal (1994)

•The open construction of The open construction of trusses is lighter , yet just as trusses is lighter , yet just as

strong as, strong as, a beam with a a beam with a solid web between upper and solid web between upper and

lower lines.lower lines.

BASIC PARTS:BASIC PARTS:

•The members of truss The members of truss are known as are known as tie-tie-beams, posts, rafters, beams, posts, rafters, and struts;and struts; the the distance over which distance over which the truss the truss extends is extends is called the spancalled the span. The . The upper and lower lines upper and lower lines or beams are or beams are connected by connected by web web members.members.

Various Truss Various Truss Types:Types:1.HOWE:1.HOWE: These trusses may be These trusses may be

simple span, multiple bearing, simple span, multiple bearing, or cantilevered. Where the or cantilevered. Where the truss height exceeds truss height exceeds approximately 3m (10'). Spans approximately 3m (10'). Spans up to 9m to 12m.up to 9m to 12m.

2.FINK: 2.FINK: spans up spans up to 6m to to 6m to 9m.9m.

3.Mono: 3.Mono: This shape This shape may be simple span, may be simple span,

multiple span, or multiple span, or cantilevered. Top cantilevered. Top chord bearing is chord bearing is

possible. possible. 4.Inverted:4.Inverted:The The inverted truss is used inverted truss is used to to provide a vaulted provide a vaulted ceilingceiling along a portion along a portion of the span. of the span.

5. Cut-off :5. Cut-off :This shape may be This shape may be used used where a triangular truss where a triangular truss

will not fit.will not fit. Usually stubbed Usually stubbed exterior or at change to vaulted exterior or at change to vaulted

ceiling in opposite direction. ceiling in opposite direction.

6.Dual slope: 6.Dual slope: This truss This truss provides an asymmetric roof provides an asymmetric roof slope. slope.

7.Ridge truss: 7.Ridge truss: The ridge truss The ridge truss provides a stepped roof provides a stepped roof

appearance. appearance.

9.Piggyback (Three piece):9.Piggyback (Three piece): The The piggyback truss is a piggyback truss is a

combination of a gable end combination of a gable end truss on top of a hip truss, truss on top of a hip truss,

which can be transported in which can be transported in two sections. It is used when a two sections. It is used when a

single triangular truss is too single triangular truss is too large to transport. large to transport.

8.Hip:8.Hip:This shape is used to This shape is used to create hip roofs and is also create hip roofs and is also referred to as a Step up Hip referred to as a Step up Hip Truss Truss

10. Cathedral10. Cathedral :The cathedral :The cathedral truss provides a vaulted truss provides a vaulted ceiling along one portion of ceiling along one portion of the span. the span.

11. Scissor :11. Scissor :The scissor truss The scissor truss is used to create a vaulted is used to create a vaulted

ceiling along the entire span. ceiling along the entire span. The slope of the bottom chord The slope of the bottom chord

is usually equal to 1/2 of the is usually equal to 1/2 of the slope of the top chord. slope of the top chord.

12. Half Scissor12. Half Scissor :The half :The half scissor truss provides a scissor truss provides a single-sloped vaulted ceiling. single-sloped vaulted ceiling.

13. Attic :13. Attic : The attic truss provides The attic truss provides useable area within the roof useable area within the roof

space. Bottom Chord in centre space. Bottom Chord in centre designed as a floor. designed as a floor.

14. Flat or Parallel Chord :14. Flat or Parallel Chord :The The flat truss is used in roofs or flat truss is used in roofs or floors. It may be designed as top floors. It may be designed as top or bottom chord bearing, or for or bottom chord bearing, or for simple or multiple spans. It may simple or multiple spans. It may also be cantilevered at one or also be cantilevered at one or both ends. both ends. 15. Sloping Flat :15. Sloping Flat :This shape is This shape is

used to create a vaulted ceiling. used to create a vaulted ceiling. It may be top or bottom chord It may be top or bottom chord

bearing. bearing.

•Steel roof Steel roof trusses are trusses are commonly commonly fabricated from fabricated from angle sectionsangle sections and plates. and plates. ((channelchannel and and T-T-sectionssections can can also be used)also be used)

PARTS IN DETAIL:PARTS IN DETAIL:

•The principal rafter and The principal rafter and the main tie beam are the main tie beam are made of made of two angle two angle sections placed side by sections placed side by side,side, whereas the struts whereas the struts and ties are made of and ties are made of single angle sections.single angle sections.

•The The members are members are joined joined together by together by gusset plates gusset plates either either through through rivets or rivets or welding. welding.

•Gusset plate should Gusset plate should not be not be less than 6mm,less than 6mm, though its though its thickness is designed on the thickness is designed on the basis of forces to be carried.basis of forces to be carried.

•When rivets are used, the When rivets are used, the minimum pitchminimum pitch (the center-to- (the center-to-center distance of adjacent center distance of adjacent rivets) should not be less rivets) should not be less than than 3 times the rivet 3 times the rivet diameter.diameter.

•Max pitch is limited to Max pitch is limited to 15cm15cm for compression for compression members (small spans) members (small spans) and and 20cm 20cm for tension for tension members (large spans).members (large spans).

•At the foot short At the foot short angles are placed on angles are placed on both sides of gusset,both sides of gusset, connected to bearing connected to bearing plate. plate.

TRUSS FOR 7-9m SPAN:TRUSS FOR 7-9m SPAN:• The The rafters are rafters are equally divided by 2 equally divided by 2 purlinspurlins on each side on each side and the main tie and the main tie also equally also equally divided.(3 parts)divided.(3 parts)•The The main tie main tie extends for the full extends for the full width of the basewidth of the base plate and secured plate and secured to it by a to it by a countersunk rivet.countersunk rivet.•A short cleat is A short cleat is provided at the provided at the opposite side of the opposite side of the gusset.gusset.

•Section at ‘J’ shows a strut Section at ‘J’ shows a strut on each side of the gusset.on each side of the gusset.

•Size of these struts is Size of these struts is that of small angles: that of small angles: 50.8mmX50.8mmX6.32m50.8mmX50.8mmX6.32mm.m.

•The gusset The gusset does not project does not project below the main tie.below the main tie.

• The purlins are fixed to the The purlins are fixed to the rafters by means of rafters by means of bolts.bolts.

DETAIL SHOWING CONNECTION DETAIL SHOWING CONNECTION AT BASE PLATEAT BASE PLATE

•The members are fixed at The members are fixed at near side of the gusset or near side of the gusset or far side to far side to obtain balance.obtain balance.

Advantages of steel trusses :Advantages of steel trusses :1)1) The The sections are readily availablesections are readily available in the required in the required

dimensions resulting in minimum wastage of dimensions resulting in minimum wastage of material.material.

2)2) Steel trusses are Steel trusses are light in weight.light in weight.

3)3) Steel trusses are Steel trusses are stronger and more rigidstronger and more rigid than than timber trusses.timber trusses.

4)4) Steel trusses can be Steel trusses can be used over any spanused over any span, while , while timber are suitable only up to 15m.timber are suitable only up to 15m.

5)5) Steel trusses are Steel trusses are fire proof.fire proof.

6)6) Steel trusses are Steel trusses are termite proof.termite proof.

7) large trusses can be assembled from small 7) large trusses can be assembled from small members pinned together, facilitating members pinned together, facilitating production, transportation, and erection; production, transportation, and erection;

8) because all internal stresses are axial, with no 8) because all internal stresses are axial, with no bending stresses present, the truss is an bending stresses present, the truss is an extremely efficient structural form; extremely efficient structural form;

9) because trusses are typically assembled from 9) because trusses are typically assembled from individual elements bolted, welded, or nailed individual elements bolted, welded, or nailed together, it is relatively together, it is relatively easy to customize the easy to customize the overall shape of the trussoverall shape of the truss in relation to external in relation to external loads and spans; and to adjust the cross-loads and spans; and to adjust the cross-sectional area of each member in relation to sectional area of each member in relation to anticipated internal stresses. anticipated internal stresses.

10) As long as loads are applied only at the joints 10) As long as loads are applied only at the joints of a truss, and the joints act like of a truss, and the joints act like ""hinges",", every every member of the truss is in pure member of the truss is in pure compression or or pure pure tension -- -- shear, bending , bending moments, and , and other more complex other more complex stresses are all practically are all practically zero. This makes zero. This makes trusses physically stronger trusses physically stronger than other ways of arranging material.than other ways of arranging material.

Ex.1:Qantas Domestic Terminal, Sydney

•The lightweight roof structure gives a dramatic The lightweight roof structure gives a dramatic presence on set down at the elevated road level presence on set down at the elevated road level providing a providing a clear, seamless envelope of curved clear, seamless envelope of curved steelwork and skylights.steelwork and skylights.

•The roof is a The roof is a curved multi-curved multi-planar lattice structureplanar lattice structure consisting of consisting of seven rows of seven rows of three dimensionally framed three dimensionally framed elliptical trusses spanning elliptical trusses spanning 66m. 66m. •The trusses are positioned at The trusses are positioned at 19.2m centres, and are 19.2m centres, and are elevated elevated 13m above the 13m above the Departures Hall floor.Departures Hall floor.

ROOF OF DEPARTURE ROOF OF DEPARTURE HALLHALL•They are supported They are supported

vertically and stabilised vertically and stabilised laterally by dual laterally by dual opposing opposing diagonal legsdiagonal legs on offset column bases.on offset column bases.• Auxiliary columns, Auxiliary columns, concealed within the concealed within the glazed walls, are glazed walls, are included to included to reduce reduce movements, control roof movements, control roof deflections.deflections.

SECTIONSECTION

•The top and bottom chords of the The top and bottom chords of the truss structure are truss structure are tubular steel tubular steel membersmembers measuring 219mm and measuring 219mm and 356mm in diameter, respectively. 356mm in diameter, respectively. •The The web members are tapered web members are tapered from 110mm to 220mm from top to from 110mm to 220mm from top to bottom.bottom. This creates more visually This creates more visually pleasing members and minimises pleasing members and minimises the usage of steel. the usage of steel.

Web Members Web Members

Elliptical TrussElliptical Truss

•Bays of the truss framing system are Bays of the truss framing system are reinforced by interlaying pre-stressed rod reinforced by interlaying pre-stressed rod bracings.bracings. These bracings prevent These bracings prevent overloading of the connections, stabilise overloading of the connections, stabilise uplift and dead load deflective forces.uplift and dead load deflective forces.

•Rows of underslung Rows of underslung purlins spanning between purlins spanning between elliptical trusses elliptical trusses support support the ceiling panels and roof the ceiling panels and roof sheets at their lower and sheets at their lower and upper chord levels,upper chord levels, respectively.respectively.

Detail of Inclined Detail of Inclined LegsLegs

Ex.2:Reliant Stadium, Houston•Stadium with an operable roof, Stadium with an operable roof, and at 4.25 acres, it is the largest and at 4.25 acres, it is the largest such roof in the United States.such roof in the United States.•The operable portion of the roof The operable portion of the roof consists of consists of two enormous but two enormous but elegant fabric-cladelegant fabric-clad panels that panels that ride along ride along two parallel two parallel supertrusses.supertrusses.

•Two massive Two massive supertrusses clear supertrusses clear span 620’ span 620’ between between concrete concrete supercolumns along supercolumns along either field sideline.either field sideline.•The bottom chord of The bottom chord of each supertruss is each supertruss is gently arched to gently arched to accommodate for sight accommodate for sight lines of the seating lines of the seating bowl,bowl, creating a truss creating a truss with minimum depth of with minimum depth of 50’ at mid-span and a 50’ at mid-span and a maximum depth of 72’ maximum depth of 72’ at the supercolumns. at the supercolumns.

•In order to find an In order to find an economical design for a economical design for a truss with the mid-span truss with the mid-span depth shallower than the depth shallower than the depth at the supports, the depth at the supports, the structuralstructuralengineer engineer tied the truss tied the truss rigidly to the supercolumn, rigidly to the supercolumn, thereby achieving a rigid thereby achieving a rigid frame action between the frame action between the truss and its supporting truss and its supporting columns.columns.

•The erection The erection towers have been towers have been removed from removed from beneath the west beneath the west supertruss. supertruss. The The lacing of the truss lacing of the truss chords and chords and verticalverticalweb membersweb members are are visible in this visible in this picture. picture.

The box truss The box truss can be seen can be seen framing into the framing into the left side of the left side of the concrete concrete supercolumn.supercolumn.

Bibliography:Bibliography:

•www.aise.org

• http://www.espioneer.com/ssss/imageoct2003-04.pdfhttp://www.espioneer.com/ssss/imageoct2003-04.pdf

• www.tritontruss.comwww.tritontruss.com

•http://www.brantacan.co.uk/trusstwo.htmhttp://www.brantacan.co.uk/trusstwo.htm

•http://www.answers.com/topic/http://www.answers.com/topic/

• http://www.maplevalleytruss.com/common_trusses.htmhttp://www.maplevalleytruss.com/common_trusses.htm

• www.ideaphotos.com/.../History-Of-Trusses.htmlwww.ideaphotos.com/.../History-Of-Trusses.html