LOADS
LRFD Load Combinations (CBC 1605.2.1 and IBC 1605.2.1)
1.4(D + F) (Eq. 16-1)
1.2(D + F + T) + 1.6(L + H) + 0.5(Lr or S or R) (Eq. 16-2)
1.2D + (f1L or 0.8W) + 1.6(Lr or S or R) (Eq. 16-3)
1.2D + f1L + 1.6W + 0.5(Lr or S or R) (Eq. 16-4)
1.2D + f1L + 1.0E + 0.2S (Eq. 16-5)
= (1.2 + 0.2SDS)D + rQE + f1L + 0.2S (ASCE 12.4.2.3)
0.9D +/- 1.6W + 1.6H (Eq. 16-6)
0.9D +/- 1.0E + 1.6H (Eq. 16-7)
= (0.9 – 0.2SDS)D +/- rQE + 1.6H (ASCE 12.4.2.3)Simplified (D, L, Lr, W and E only):
1.4D (Eq. 16-1)
1.2D + 1.6L + 0.5Lr (Eq. 16-2)1.2D + (f1L or 0.8W) + 1.6Lr (Eq. 16-3)
1.2D + f1L + 1.6W + 0.5Lr (Eq. 16-4)
1.2D + f1L + 1.0E (Eq. 16-5)
= (1.2 + 0.2SDS)D + rQE + f1L (ASCE 12.4.2.3)
0.9D +/- 1.6W (Eq. 16-6)
0.9D +/- 1.0E (Eq. 16-7)
= (0.9 – 0.2SDS)D +/- rQE (ASCE 12.4.2.3)in which,
Floors in public assembly
1 for L > 100 psf
- f1 = Parking Garage L
- E = Combined effect of horizontal + vertical earthquake induced forces
E = Eh +/- Ev = rQE +/- 0.2SDSD in which, (ASCE 12.4.2)
QE = Effect of horizontal seismic forces from base shear, V , or diaphragm force, Fp. (ASCE 12.4.2.1)
Orthogonal effect of 1.0 QE + 0.3 QE ^ shall be considered for:
- horizontal irregularity Type 5 in ASCE Table 12.3-1, i.e. Non-parallel Systems – Irregularity (vertical LFRS elements are not parallel or symmetric about the major orthogonal axes of the LFRS) (ASCE 12.5.3)
- any column or wall that forms part of two or more intersecting LFRS and is subject to axial load due to seismic forces acting along either principal plan axis >= 0.2 * (axial design strength of the column or wall) (ASCE 12.5.4)
r = 1.3 except:
SDC B or C.
Drift calcs and P-deta effects.
Design of Non-structural components.
r = 1 for Design of Non-building structures that are NOT similar to buildings.
Where over-strength factor W0 is used.
Diaphragm loads determination.
Structure with damping systems
IBC 12.3.4.2 Redundancy Factor, ρ, for Seismic Design Categories D through F. For structures assigned to Seismic Design Category D, E, or F, ρ shall equal 1.3 unless one of the following two conditions is met, whereby ρ is permitted to be taken as 1.0:
a. Each story resisting more than 35 percent of the base shear in the direction of interest shall comply with Table 12.3-3.
b. Structures that are regular in plan at all levels provided that the seismic force–resisting systems consist of at least two bays of seismic force–resisting perimeter framing on each side of the structure in each orthogonal direction at each story resisting more than 35 percent of the base shear. The number of bays for a shear wall shall be calculated as the length of shear wall divided by the story height or two times the length of shear wall divided by the story height for lightframed construction.
- W = Wind load. Directionality factor must be applied.
- F = Fluid load;
- T = Temperature, shrinkage, moisture change, creep, different settlement load;
- H = Lateral earth pressure, ground water pressure or bulk materials pressure load;
- Lr = Roof live load;
- S = Snow load;
- R = Rain load;
- W = Wind load;
- D = Dead Load.
Typical Values of Dead Loads:
Building Elements | DL | |
| 1 | Lightweight Floor Finish | 8 psf/in |
| 2 | Suspended Ceiling | 2 psf |
| 3 | Plaster Ceiling | 8 psf/in |
| 4 | Electrical and Mechanical Utilities | 2 psf |
| 5 | Moveable Partitions | 20 psf |
ASD Load Combinations (CBC 1605.3.1 and IBC 1605.3.1)
D + F (Eq. 16-8)
D + L + H + F + T (Eq. 16-9)D + (Lr or S or R) + H + F (Eq. 16-10)
D + 0.75(L + T) + 0.75(Lr or S or R) + H + F (Eq. 16-11)
D + (W or 0.7E) + H + F (Eq. 16-12)
0.6D +/- 0.7E + H (Eq. 16-15)
= (0.6 - 0.14SDS)D +/- 0.7rQE + H (ASCE 12.4.2.3)
Simplified (D, L, Lr, W and E Only):
D (Eq. 16-8)
D + L (Eq. 16-9)D + 0.75(L + Lr) (Eq. 16-11)
D + (W or 0.7E) (Eq. 16-12)
0.6D +/- 0.7E (Eq. 16-15)
= (0.6 - 0.14SDS)D +/- 0.7rQE (ASCE 12.4.2.3)
Foundation Overturning Reduction (ASCE 12.13.4)
(Used for setting foundation size, overturning check. NOT applicable to foundation concrete strength design!):1. For Foundations of Equivalent Lateral Force Procedure designed structures NOT of inverted pendulum or cantilevered column type:
D (Eq. 16-8)
D + L (Eq. 16-9)D + 0.75(L + Lr) (Eq. 16-11)
D + (W or 0.7( 0.75E)) (Eq. 16-12)
0.6D +/- 0.7(0.75E) (Eq. 16-15)
= (0.6 - 0.105SDS)D +/- 0.525rQE (ASCE 12.13.4)
2. For Foundations of Modal Response Spectrum designed structures:
D (Eq. 16-8)
D + L (Eq. 16-9)D + 0.75(L + Lr) (Eq. 16-11)
D + (W or 0.7( 0.9E)) (Eq. 16-12)
0.6D +/- 0.7(0.9E) (Eq. 16-15)
= (0.6 - 0.126SDS)D +/- 0.63rQE (ASCE 12.13.4)
Alternative ASD Combinations (CBC 1605.3.2 and IBC 1605.3.2)
D + L + 1.3W) (Eq. 16-17)
D + L + 1.3W + S/2 (Eq. 16-18)
D + L + S + 0.65W (Eq. 16-19)
D + L + S + E/1.4 (Eq. 16-20)
= (1.0 + 0.143SDS)D + 0.71rQE + L + S
0.9D +/- E/1.4 (Eq. 16-21)
= (0.9 - 0.143SDS)D +/- 0.71rQE
Simplified (D, L, Lr, W and E only):
D + L + 1.3W (Eq. 16-17)
(Eq. 16-18)
D + L + 0.65W (Eq. 16-19)
D + L + E/1.4 (Eq. 16-20)
= (1.0 + 0.143SDS)D + 0.71rQE + L
0.9D +/- E/1.4 (Eq. 16-21)
= (0.9 - 0.143SDS)D +/- 0.71rQE
Special Seismic Combinations (CBC 1605.4 and IBC 1605.4)
General:
1.2D + f1L + Em (Eq. 16-22)
0.9D +/- Em (Eq. 16-23)
LRFD Design:
(1.2 + 0.2SDS)D + W0QE + f1L + 0.2S (ASCE 12.4.3.2)
(0.9 - 0.2SDS)D +/- W0QE + 1.6H (ASCE 12.4.3.2)
ASD Design:
(1.0 + 0.14SDS)D + 0.7W0QE + H + F (ASCE 12.4.3.2)
(1.0 + 0.105SDS)D +0.525W0QE + 0.75L + 0.75(Lr or S or R) + H + F
(ASCE 12.4.3.2)
(0.6-0.14SDS)D +/- 0.7W0QE + H (ASCE 12.4.3.2)Simplified (D, L, Em only):
General:
1.2D + f1L + Em (Eq. 16-22)
0.9D +/- Em (Eq. 16-23)
LRFD Design:
(1.2 + 0.2SDS)D + W0QE + f1L (ASCE 12.4.3.2)
(0.9 - 0.2SDS)D +/- W0QE (ASCE 12.4.3.2)
ASD Design:
(1.0 + 0.14SDS)D + 0.7W0QE (ASCE 12.4.3.2)
(1.0 + 0.105SDS)D +0.525W0QE + 0.75L + 0.75(Lr or S or R)
(ASCE 12.4.3.2)
(0.6-0.14SDS)D +/- 0.7W0QE (ASCE 12.4.3.2)- Em = The maximum effect of horizontal and vertical forces
= W0QE +/- 0.2SDSD in which, (ASCE 12.4.3.1)
QE = Effect of horizontal seismic forces from base shear, V or diaphragm force Fp.
(ASCE 12.4.3.1)
Orthogonal effect of 1.0 QE + 0.3 QE ^ shall be considered for:
- horizontal irregularity Type 5 in ASCE Table 12.3-1, i.e. Non-parallel Systems – Irregularity (vertical LFRS elements are not parallel or symmetric about the major orthogonal axes of the LFRS) (ASCE 12.5.3)
- any column or wall that forms part of two or more intersecting LFRS and is subject to axial load due to seismic forces acting along either principal plan axis >= 0.2 * (axial design strength of the column or wall) (ASCE 12.5.4)
W0 = Overstrength Factor. See ASCE Table 12.2-1 (ASCE 12.4.3.1)
Floors in public assembly
1 for L > 100 psf
- f1 = Parking Garage L
Live Load Reduction (CBC 1607.9)
Live load shall NOT be reduced for the following:
Public Assembly Occupancies.
- Passenger Vehicle Garages, except live load for members supporting >= 2 floors is permitted to be reduced by 20% maximum but not less than the calculated per formula above.
- One-way Slab, except live load for members supporting >= 2 floors is permitted to be reduced by 20% maximum but not less than the calculated per formula above.
- L>100 psf, except live load for members supporting >= 2 floors is permitted to be reduced by 20% maximum but not less than the calculated per formula above.
- Partition Load of 15 psf for floors of office buildings can not be reduced, except when the total floor live load >80 psf. (CBC 1607.5)
Note:
1. KLL is for converting Tributary Area of AT into Influence Area. KLL*AT = Influence Area.
See the ASCE Figure C4 copied below for how KLL is derived.
2. For walls, the reduced live load can also be determined using the same procedure for columns. For example, shear walls around an opening at slab edge can be collectively considered as an edge column without a cantilever slab.
Note:
- Special Purpose Roofs: Roofs used for promenade, roof gardens, assembly or other special purposes shall be designed for a minimum live load as required in Table 1607.1. Such roof live loads are permitted to be reduced per 1607.9. (CBC 1607.11.2.2)
- Landscaped Roof shall be designed for a live load of 20 psf while the weight of the landscaping materials shall be considered as dead load. (CBC 1607.11.2.3)
- Awning and canopies shall be designed for a live load per Table 1607.1 plus snow and wind loads. (CBC 1607.11.2.4)
- Greenhouse shall be designed for a minimum roof live load of 12psf. (CBC 1607.11.2.1)
Dead Loads
Definition of Dead Load
DEAD LOADS: The weight of materials of construction incorporated into the building, including but not limited to walls, floors, roofs, ceilings, stairways, built-in partitions, finishes,
cladding and other similarly incorporated architectural and structural items, and the weight of fixed service equipment, such as cranes, plumbing stacks and risers, electrical feeders,
heating, ventilating and air-conditioning systems and fire sprinkler systems. (IBC 1602.1)
Typical Values of Dead Loads:
Building Elements DL 1 Lightweight Floor Finish 8 psf/in 2 Suspended Ceiling 2 psf 3 Plaster Ceiling 8 psf/in 4 Electrical and Mechanical Utilities 2 psf 5 Moveable Partitions 20 psf
| Building Elements | DL | |
| 1 | Lightweight Floor Finish | 8 psf/in |
| 2 | Suspended Ceiling | 2 psf |
| 3 | Plaster Ceiling | 8 psf/in |
| 4 | Electrical and Mechanical Utilities | 2 psf |
| 5 | Moveable Partitions | 20 psf |
Live Loads
Definition of Live Loads
LIVE LOADS: Those loads produced by the use and occupancy of the building or other structure and do not include construction or environmental loads such as wind load, snow load,
rain load, earthquake load, flood load or dead load. (IBC 1602.1).
Uniform Live Loads and Concentrated Live Loads Minimum Values
Partition Load = 15 psf
for office buildings and other buildings where partition locations are subject to change. Provisions for partition weight shall be made, whether or not partitions are
shown on the construction documents, unless the specified live load exceeds 80 psf .
Truck and Bus Garage Live Load Minimum Values
Minimum live loads for garages having trucks or buses shall be as specified in Table 1607.6 below, but shall not be less than 50 psf. (IBC 1607.6)
The concentrated load and uniform load shall be uniformly distributed over a 10-foot width on a line normal to the centerline of the lane placed within a 12-foot-wide lane. The loads shall be placed within their individual lanes so as to produce the maximum stress in each structural member. Single spans shall be designed for the uniform load in Table 1607.6 and one simultaneous concentrated load positioned to produce the maximum effect. Multiple spans shall be designed for the uniform load in Table 1607.6 on the spans and two simultaneous concentrated loads in two spans positioned to produce the maximum negative moment effect. (IBC 1607.6.1)
Horizontal Loads on Interior Walls and Partitions
Interior walls and partitions that exceed 6 feet in height, including their finish materials, shall have adequate strength to resist the loads to which they are subjected but not less than a horizontal load of 5 psf. (IBC 1607.13)
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