CIVDES3L3

Design Loads

Dead Loads

o An engineered design approach involves calculating a demand due to loads, and comparing the demand with the capacity of the member or element under consideration.

o Gravity (dead) loads are a natural starting point

dead load is an ever-present load

It is necessary to determine the magnitude of the vertical loads before the design seismic loads can be estimated.

2 /45

Dead Loads

Weights of all materials permanently attached to the structure including the following:

o weight of the roof or wood floor system

o sheathing

o framing

o Insulation

o ceiling

o piping, automatic fire sprinkler, ducts

o fixed equipment

o etc. 3 /45

Table 204-2 Minimum Design Dead Loads (kPa) [use actual when available]

CEILINGS

Asphalt singles . . . . . . . . . . . . . . . . . . . . . . . . .0.10

Cement tile . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.77

Clay tile (for mortar add 0.48 kPa)

Book tile, 50 mm . . . . . . . . . . . . . . . . . . . . 0.52

Book tile, 75 mm . . . . . . . . . . . . . . . . . . . . . 0.96

Ladowici . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.48

Roman . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .0.57

Spanish . . . . . . . . . . . . . . . . . . . . . . . . . . . . .0.91

Composition

Three-ply ready roofing . . . . . . . . . . . . . . . .0.05

Four-ply felt and gravel . . . . . . . . . . . . . . . .0.26

Five-ply felt and gravel . . . . . . . . . . . . . . . . .0.29

Copper or tin . . . . . . . . . . . . . . . . . . . . . . . . . . .0.05

Corrugated asbestos-cement roofing . . . . . . .0.19

Deck, metal 20 gage . . . . . . . . . . . . . . . . . . . . .0.12

Deck, metal 18 gage . . . . . . . . . . . . . . . . . . . . .0.14

Fiberboard, 13 mm . . . . . . . . . . . . . . . . . . . . .0.04

Gypsum sheathing, 13 mm . . . . . . . . . . . . . . .0.10

COVERINGS, Roof and Wall

Acoustical Fiber Board . . . . . . . . . . . . . . . . . . 0.05

Gypsum Board (per mm thickness) . . . . . . . 0.008

Mechanical duct allowance . . . . . . . . . . . . . . 0.20

Plaster on tile or concrete . . . . . . . . . . . . . . . 0.24

Plaster on wood lath . . . . . . . . . . . . . . . . . . . . .0.38

Suspended steel channel system . . . . . . . . . . 0.10

Suspended metal lath and cement plaster . . 0.72

Suspended metal lath and gypsum plaster . . .0.48

Wood furring suspension system . . . . . . . . . . 0.12

Sample Dead Load Calculation

Roof Dead loads D in psf

Roofing (5ply with gravel) 6.5

Reroofing 2.5

- in. plywood (3 psf x .) 1.5

Framing (estimate 2 x 12 @ 16 o.c.) 2.9

Insulation 0.5

Suspended ceiling (acoustical tile) 1.0

Roof dead load D 14.9 ~ 15.0 psf

5 /45

Sample Dead Load Calculation

Floor Dead loads D in psf

Floor covering (lightweight concrete 1 at 100 pcf) 12.5

1-1/8 plywood (3 psf x 1-1/8 ) 3.4

Framing (4 x 12 @ 4 o.c.) 2.5

Ceiling supports (2 x 4 @ 24 o.c.) 0.6

Ceiling ( drywall, 5 psf x ) 2.5

Floor dead load D 21.5 ~ 22.0 psf

6 /45

Live Loads

o Lr roof live load, including any permitted live load reduction

o L live load, including any permitted live load reduction

o For the reduction of both Lr and L, the area contribution load to the member under design consideration is taken into account.

for roof live load (Lr), the tributary area is used

for floor live load (L), the influence area is used 7 /45

NSCP Live Loads

Table 205-1 Minimum Uniform and Concentrated Live Loads

Use or Occupancy Uniform Load2 Concentrated Load

Category Description KPa KN

13. Office

Call Centers and BPO 2.9 9.0

Lobbies and ground floor corridors 4.8 9.0

Offices 2.4 9.02

Building corridors above ground floor 3.8 9.0

14. Printing plants

Press rooms 7.2 11.02

Composing and linotype rooms 4.8 9.02

15. Residential8

Basic floor area 1.9 06

Exterior balconies 2.94 0

Decks 1.94 0

Storage 1.9 0

8 /45

NSCP Live Loads

Use or Occupancy Vertical Load (kPa)

Lateral Load (kPa)

Category Description

1. Construction, public access at site (live load)

Walkway 7.2 -

Canopy 7.2 -

2. Grandstands, reviewing, stands bleachers, and folding and telescoping seating (live load0

Seats and footboards 1.75 -

3. Stage accessories (live load)

Catwalks 1.9 -

Follow spot, projection and control rooms 2.4 -

4. Ceiling framing (live load)

Over stages 1.0 -

All uses except over stages 0.5 -

Table 205-2 Special Loads

9 /45

Tributary Area, AT

o Tributary area - the area assumed to load a given member

o generally measured from midway between members on one side of the member under consideration to midway between members on the other side.

o for members spaced a uniform distance apart, the tributary width is equivalent to the spacing between members

o since tributary areas for adjacent members do not overlap, all distributed loads are assumed to be supported by the nearest structural member

Note: tributary area approach should only be used when the loading is uniform

10 /45

Influence Area, KLLAT

o In contrast to the tributary approach, the influence area recognizes that the total load experience by a structural member maybe influenced by loads applied outside the tributary area of the member

NSCP 205.6 Alternate Floor Live Load Reduction

o The influence area is four times the tributary area for a column

o Two times the tributary area for a beam, equal to the panel area for a two-way slab

11 /45

Tributary Area

12 /45

Tributary Area Calculations

AT (ft2) KLLAT (ft

2)

Joist J1 2 x 12 = 24 2 x 24 = 48

Joist J2 2 x 14 = 28 2 x 28 = 56

Girder G1 (12/2 + 14/2)20 = 260 2 x 260 = 520

Girder G2 (12/2 + 14/2) 24 = 312 2 x 312 = 624

Interior col. C1 (12/2 + 14/2) (20/2 + 24/2) = 286 4 x 286 = 1144

Exterior col. C2 (20/2 + 24/2) 12/2)= 132 4 x 132 = 528

Corner col. C3 (14/2)(20/2) = 70 4 x 70 = 280

13 /45

Reduction of Floor Live Loads

[NSCP 205.6 ] Alternate Floor Live Load Reduction

The unit live loads maybe reduced in accordance with the equation shown on any member, including flat slabs, having an influence area of 40 m2 or more

Note: The reduced live load shall not be less than 50% of the unit live load for members receiving load from one level only, nor less that 40 percent of the unit live load for other members.

= 0.25 + 4.57 1

Ai = Influence area, m2

L = reduced design live load per square meter of area supported by the member

Lo = unreduced design live load per square meter of area supported by the member (Table 205-1)

14 /45

Seatwork

Determine the following:

(a) tributary and influence areas are for J1, J2, G1, G2, C1 and C2

(b) axial force required for the design of the interior column C1 due to a dead load of 0.2 kPa and a floor live load L = 1.9 kPa.

15 /45

Roof Live Loads

o The live load on a roof is usually applied for a relatively short period of time during the life of the structure

o This is normally of no concern in the design of structures other than wood

o However in wood structures, the length of time for which a load is applied does have an effect on the capacity (resistance) of the member.

o The standard roof live load for small tributary areas on flat roofs is 20 psf (1 kPa)

16 /45

Reduction of Roof Live Loads

AT = tributary area supported by structural member, ft2

F = the number of inches or rise per foot for a sloped roof

Lo = minimum uniform live load per ASCE 7-10 Table 4-1

= 012 12 20

2 = 1

1.2 0.050.6

4 4 < < 12

12

and

1 = 1

1.2 0.0010.6

200 2

200 < < 600 2

600 2

NSCP Roof Live Loads

ROOF SLOPE

Method 1 Method 2

Tributary Area (m2) Uniform Load (kPa)

Rate of Reduction,

r

Maximum Reduction R (percentage) 0 to 20 20 to 60 > 60

Uniform Load (kPa)

1. Flat or rise less than 4 units vertical in 12 units horizontal (33.3% slope). Arch and dome with rise less than one-eight of span.

1.00

0.75

0.60

1.00

0.08

40

2. Rise 4 units vertical to less than 12 units vertical in 12 units horizontal (33.3% to less than 100% slope). Arch and dome with rise one-eight of span to less than three-eights of span.

0.75

0.70

0.60

0.75

0.06

25

3. Rise 12 units vertical in 12 units horizontal (100% slope) and greater. Arch of dome with rise three-eights of span or greater.

0.60

0.60

0.60

0.60

No reduction permitted 4. Awnings except cloth covered. 0.25 0.25 0.25 0.25

5. Greenhouses, lath houses and agricultural building. 0.50 0.50 0.50 0.50

Table 205-3 Minimum Roof Live Loads

Example Problem

Determine the uniformly distributed roof loads (including dead load and roof live load) for the purlins and girders in the building shown.

Also determine the total load on column C1.

Assume that the roof is flat (except for a minimum slope of in/ft for drainage).

Roof dead load D = 8 psf.

19 /45

Combined Dead and Live on Sloping Roof

= 12 +

= + 21

Load on horizontal plane:

Load along roof slope:

Equivalent total roof loads (D + Lr):

Combined D + Lr on sloping roof

L2 Lr from NSCP

Horizontal Roof D along roof slope

20 /45

Example Problem

The building is a standard residential occupancy. The rafters are sloped at 6 in./ft, and the roof covering consists of cement asbestos shingles.

Determine the shear and moment for the rafters under dead plus live load if they are spaced 4 ft o.c.

Roof dead load D has been estimated as 14 psf along the roof surface.

18

Lr = 62 psf

D = 14 psf

18

6

12

Rafters @ 4 o.c. Ridge beam

q

Other Loads

o Soil Loads and Hydrostatic Pressure (H)

soil lateral loading most commonly occurs at retaining walls

where retaining walls are provided, it is possible to develop hydrostatic pressure

it is also possible to have upward hydrostatic pressures on adjacent floor slabs

pressure can also be due to storage of grain, aggregates, or other bulk solids that can exert lateral pressures

22 /45

Other Loads

o Loads due to Fluids (F)

not intended to address flood loads or hydrostatic pressure

when fluids are contained in non-building structures or nonstructural components, other standards might be applicable and can provide guidance in the design

o Rain Loads (R)

primarily applicable to low slope roofs that are surrounded by parapets

need not be considered for sloped roofs that cannot develop water buildup

23 /45

Other Loads

o Flood Loads (F)

Section 211 of the NSCP

applies to buildings and other structures located in areas prone to flooding as defined on a flood hazard map

o Snow Loads (not applicable)

o Self-straining Loads

loads arising from temperature change, moisture change, creep, movement due to differential settlement or combinations thereof

o Earthquake Loads

NSCP Section 208

will not be considered in this course 24 /45

Other Loads

o Wind Loads (NSCP Section 207)

Method 1 simplified procedure

can be used for the large majority of wood frame buildings

Method 2 analytical procedure

can be used for determining wind loads on structures of all sizes, configurations and exposure conditions

requires defining more variables than Method 1

Method 3 wind tunnel procedure

for complex buildings that might be anticipated to have unusual dynamic behavior

Limited to a small group of buildings for which the time and expense of a detailed study can be justified

25 /45

Method 1 Simplified Method

o Main wind-force-resisting system (MWFRS) - is a system providing wind resistance for the overall structure.

o In wood frame buildings, the MWFRS most commonly consists of

Shearwalls sheathed walls that resist in-plane loads

Roof and floor diaphragms sheath floor and roof assemblies that transmit in-plane loads to the shearwalls

26 /45

Method 1 conditions (NSCP 207.4.1.1)

conditions for the MWFRS to be designed using Method 1

o simple diaphragm building

Both windward and leeward loads are transmitted through the floor and roof diaphragms to the same MWFRS

o building is low rise

has a mean roof height h less than or equal to 18 m

mean roof height h does not exceed least horizontal dimension

27 /45



o building is enclosed

meets requirements for wind-borne debris protection, if applicable

o building is regular

has no unusual geometrical irregularity in spatial form

o building is not classified as a flexible building

has a fundamental frequency greater than 1 hertz (fundamental period less than 1 second)

28 /45



o building does not have response characteristics that create unusual loading (such as galloping or vortex shedding)

o not sited in a location where unusual wind load effects might occur

o building has an approximately symmetrical cross section in each direction

o has a flat roof or a gable or hip roof with slope less than or equal to 45 degrees (12 in 12 pitch)

29 /45



o has a flat roof or a gable or hip roof with slope less than or equal to 45 degree

o Building is exempted from the torsional load cases as indicated in Note 5 of Figure 207-10, or the torsional load cases defined in Note 5 do not control the design of any of the MWFRSs of the building

30 /45

NSCP 207.4.2.1

For the design of MWFRS the basic formula for calculating design wind pressure ps is :

For components and cladding, the basic formula for calculating design wind pressure pnet is

= 9

= 9

l = adjustment factor for building height and exposure from Figures 207-2A and 207-3

Iw = Importance factor

Kzt = topographic factor as defined in Section 207.5.7

ps9 = simplified design wind pressure for Exposure B at h = 9m and Iw = 1.0 from Figure 207-2 kPa

pnet9 = net design wind pressure for Exposure B at h = 9 m and Iw = 1.0 from Figure 207-3 kPa

31 /45

Adjustment Factor for Building Height and Exposure l

Mean roof height (m)

Exposure

B C D

4.5 1.00 1.21 1.47

6.0 1.00 1.29 1.55

7.5 1.00 1.35 1.61

9.0 1.00 1.40 1.66

11.0 1.05 1.45 1.70

12.0 1.09 1.49 1.74

13.7 1.12 1.53 1.78

15.2 1.16 1.56 1.81

16.8 1.19 1.59 1.84

18.0 1.22 1.62 1.87

32 /45

Design Wind Pressures on Walls and Roofs of Enclosed Buildings

Basic Wind Speed (kph)

Roof Angle

(o)

Load Case

Horizontal Pressures, kPa Vertical Pressures, kPa Overhangs

A B C D E F G H Eoh Goh

150

0 to 5 1 0.66 -0.34 0.44 -0.21 -0.79 -0.45 -0.55 -0.35 -1.11 -0.87

10 1 0.75 -0.31 0.50 -0.18 -0.79 -0.48 -0.55 -0.37 -1.11 -0.87

15 1 0.83 -0.28 0.55 -0.16 -0.79 -0.52 -0.55 -0.40 -1.11 -0.87

20 1 0.92 -0.24 0.61 -0.13 -0.79 -0.55 -0.55 -0.42 -1.11 -0.87

1 0.83 0.13 0.60 0.14 -0.37 -0.50 -0.27 -0.40 -0.69 -0.59

25 2 0.00 0.00 0.00 0.00 -0.14 -0.27 -0.04 -0.18 0.00 0.00

1 0.74 0.51 0.59 0.41 0.06 -0.45 0.02 -0.39 -0.26 -0.30

30 to 45 2 0.74 -0.08 0.59 0.41 0.29 -0.22 0.25 -0.16 -0.26 -0.30

33 /45



Roof Angle

(o)

Load Case



200

0 to 5 1 1.18 -0.62 0.79 -0.36 -1.42 -0.81 -0.99 -0.63 -2.00 -1.57

10 1 1.34 -0.56 0.89 -0.32 -1.42 -0.87 -0.99 -0.67 -2.00 -1.57

15 1 1.49 -0.49 0.99 -0.28 -1.42 -0.93 -0.99 -0.71 -2.00 -1.57

20 1 1.64 -0.43 1.10 -0.24 -1.42 -0.99 -0.99 -0.75 -2.00 -1.57

1 1.48 0.24 1.08 0.24 -0.66 -0.90 -0.48 -0.72 -1.23 -1.05

25 2 - - - - -0.25 -0.49 -0.07 -0.31 - -

1 1.34 0.91 1.06 0.73 0.11 -0.81 0.04 -0.69 -0.47 -0.54

30 to 45 2 1.34 0.91 1.06 0.73 0.51 -0.40 0.45 -0.29 -0.47 -0.54

34 /45



Roof Angle

(o)

Load Case



250

0 to 5 1 1.84 -0.95 1.22 -0.57 -2.21 -1.26 -1.54 -0.97 -3.09 -2.42

10 1 2.07 -0.86 1.38 -0.50 -2.21 -1.35 -1.54 -1.04 -3.09 -2.42

15 1 2.31 -0.77 1.54 -0.44 -2.21 -1.44 -1.54 -1.10 -3.09 -2.42

20 1 2.54 -0.67 1.70 -0.37 -2.21 -1.54 -1.54 -1.17 -3.09 -2.42

1 2.31 0.37 1.67 0.38 -1.03 -1.40 -0.74 -1.12 -1.91 -1.63

25 2 - - - - -0.39 -0.76 -0.11 -0.49 - -

1 2.07 1.41 1.65 1.13 0.16 -1.26 0.05 -1.08 -0.73 -0.83

30 to 45 2 2.07 1.41 1.65 1.13 0.79 -0.62 0.69 -0.44 -0.73 -0.83

35 /45

Notes

207.1.4.1. Main Wind-Force Resisting System

The wind load to be used in the design of the MWFRS for an enclosed or partially enclosed building or other structure shall not be less than 0.5 kPa multiplied by the area of the building or structure projected onto a vertical plane normal to the assumed wind direction.

207.4.2.1.1 Minimum pressures

The load effects of the design wind pressures from Section 207.4.2.1 shall not be less than the minimum load case from Section 207.1.4.1 assuming the pressures, ps, for zones A, B, C and D are all equal to +0.50 kPa, while assuming zones E, F, G and H all equal to 0 kPa.

36 /45

notes

o The dimension is a defined as

10% of least horizontal dimension

0.4hmean whichever is smaller.

However a may not be taken less than 0.9m (3) or less than 4% of least horizontal dimension.

37 /45

Referenced Wind Zone Map and Importance Factor

Table 207-3 Importance Factor, Iw (Wind Loads)

Occupancy Category2

Description Iw

I Essential 1.15

II Hazardous 1.15

III Special Occupancy 1.15

IV Standard Occupancy 1.00

V Miscellaneous 0.87

1see Table 103-1 for types of occupancy under each category

Figure 207-24 Referenced Wind Zone Map of the Philippines

Topographical Factor Kzt

207.5.7 Topographic Effects

o accounts for significantly higher wind speeds at sites located on the upper half of an exposed hill, ridge or escarpment

o Kzt = 1.0 except for very exposed sites

o NSCP provides a series of five (5) criteria, all of which must be met in order to require evaluation for a Kzt of other than 1.0

39 /45


207.5.7.2 Topographic Factor

o The wind speed-up effect shall be included in the calculation of design wind loads by using the factor Kzt

where K1, K2 and K3 are given in Figure 207-4.

o If site conditions and locations of structures do not meet all the conditions specified in Section 207.5.7.1 the Kzt = 1.0.

= 1 + 123 2

40 /45


41 /45

Example Problem Wind Forces for MWRFS

Determine the design wind pressures based on the simplified method for the primary Lateral Force Resisting System (LRFS).

This is a gable structure that uses a system of diaphragms and shear walls for resisting lateral forces.

The building is a standard occupancy enclosed structure located in Zone 2. Exposure C is to be used, Kzt is 1.0.

Wind forces for designing MWFRS are obtained based on ps9 from NSCP. End zone and interior zone locations to be considered for horizontal pressures on the vertical projection of the building surface

Wind pressure zones on vertical and horizontal projections of building surfaces for MWFRS; wind direction parallel to transverse walls (end walls).

Zone A (wall end zone)

Zone B (roof end zone)

Zone C (wall interior zone)

Zone D (roof interior zone) 42 /45

Example Problem Wind Forces for MWRFS

Wind pressure zones on vertical and horizontal projections of building surfaces for MWFRS; wind direction perpendicular to transverse walls (end walls).

Zone E (windward roof end zone)

Zone F (leeward roof end zone)

Zone G (windward roof interior zone)

Zone H (leeward roof interior zone)

Determine the design wind pressures based on the simplified method for the primary Lateral Force Resisting System (LRFS).

This is a gable structure that uses a system of diaphragms and shear walls for resisting lateral forces.

The building is a standard occupancy enclosed structure located in Zone 2. Exposure C is to be used, Kzt is 1.0.

Wind forces for designing MWFRS are obtained based on ps9 from NSCP. End zone and interior zone locations to be considered for horizontal pressures on the vertical projection of the building surface

Wind Forces for MWRFS o wind Speed = 200 kph (zone 2, p. 2-72)

o Exposure C (No overhangs)

o total height of building = 5.8 m

o eave height = 3.6 m

Windward Leeward

Wind

direction

3.6 m

2.2 m

Interior zone

End zone

12.8 m

-0.52 kPa

-0.29 kPa

2.00 kPa

1.34 kPa

-1.73 kPa

-1.21 kPa

-0.92 kPa

-1.21 kPa

a = 2.56 m

Wind pressures on vertical and horizontal projections of building surfaces; wind direction parallel to transverse walls (end walls).

Wind Forces for MWRFS

Wind

direction

3.6 m

Interior zone

End zone

12.8 m

1.34 kPa

2.00 kPa

-1.21 kPa

-1.73 kPa

a = 2.56 m

2.2 m

-0.92 kPa

-1.21 kPa

Wind pressure on vertical and horizontal projections of building surfaces; wind direction perpendicular to transverse walls (end walls).

o wind Speed = 200 kph (zone 2, p. 2-72)

o Exposure C (No overhangs)

o total height of building = 5.8 m

o eave height = 3.6 m

CIVDES3L3

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