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Chapter 5 Loads

5.1 Scope

5.1.1

This chapter shall apply to selection of load factors and combinations used in design, except as permitted in Chapter 27.

5.2 General

5.2.1

Loads shall include self-weight; applied loads; and effects of prestressing, earthquakes, restraint of volume change, and differential settlement.

5.2.2

Loads and Seismic Design Categories (SDCs) shall be in accordance with the general building code, or determined by the authority having jurisdiction.

5.2.3

Live load reductions shall be permitted in accordance with the general building code or, in the absence of a general building code, in accordance with ASCE/SEI 7.

5.3 Load Factors and Combinations

5.3.1

Required strength U shall be at least equal to the effects of factored loads in Table 5.3.1, with exceptions and additions in 5.3.3 through 5.3.12.
Table 5.3.1—Load combinations
Load combination Equation Primary load
U = 1.4D (5.3.1a) D
U = 1.2D + 1.6L + 0.5(Lr or S or R) (5.3.1b) L
U = 1.2D + 1.6(Lr or S or R) + (1.0L or 0.5W) (5.3.1c) Lr or S or R
U = 1.2D + 1.0W + 1.0L + 0.5(Lr or S or R) (5.3.1d) W
U = 1.2D + 1.0E + 1.0L + 0.2S (5.3.1e) E
U = 0.9D + 1.0W (5.3.1f) W
U = 0.9D + 1.0E (5.3.1g) E

5.3.2

The effect of one or more loads not acting simultaneously shall be investigated.

5.3.3

The load factor on live load L in Eq. (5.3.1c), (5.3.1d), and (5.3.1e) shall be permitted to be reduced to 0.5 except for (a), (b), or (c):
(a) Garages
(b) Areas occupied as places of public assembly
(c) Areas where L is greater than 100 lb/ft2

5.3.4

If applicable, L shall include (a) through (f):
(a) Concentrated live loads
(b) Vehicular loads
(c) Crane loads
(d) Loads on hand rails, guardrails, and vehicular barrier systems
(e) Impact effects
(f) Vibration effects

5.3.5

If wind load W is based on service-level loads, 1.6W shall be used in place of 1.0W in Eq. (5.3.1d) and (5.3.1f), and 0.8W shall be used in place of 0.5W in Eq. (5.3.1c).

5.3.6

The structural effects of forces due to restraint of volume change and differential settlement T shall be considered in combination with other loads if the effects of T can adversely affect structural safety or performance. The load factor for T shall be established considering the uncertainty associated with the likely magnitude of T, the probability that the maximum effect of T will occur simultaneously with other applied loads, and the potential adverse consequences if the effect of T is greater than assumed. The load factor on T shall not have a value less than 1.0.

5.3.7

If fluid load F is present, it shall be included in the load combination equations of 5.3.1 in accordance with (a), (b), (c) or (d):
(a) If F acts alone or adds to the effects of D, it shall be included with a load factor of 1.4 in Eq. (5.3.1a).
(b) If F adds to the primary load, it shall be included with a load factor of 1.2 in Eq. (5.3.1b) through (5.3.1e).
(c) If the effect of F is permanent and counteracts the primary load, it shall be included with a load factor of 0.9 in Eq. (5.3.1g).
(d) If the effect of F is not permanent but, when present, counteracts the primary load, F shall not be included in Eq. (5.3.1a) through (5.3.1g).

5.3.8

If lateral earth pressure H is present, it shall be included in the load combination equations of 5.3.1 in accordance with (a), (b), or (c):
(a) If H acts alone or adds to the primary load effect, it shall be included with a load factor of 1.6.
(b) If the effect of H is permanent and counteracts the primary load effect, it shall be included with a load factor of 0.9.
(c) If the effect of H is not permanent but, when present, counteracts the primary load effect, H shall not be included.

5.3.9

If a structure is in a flood zone, the flood loads and the appropriate load factors and combinations of ASCE/SEI 7 shall be used.

5.3.10

If a structure is subjected to forces from atmospheric ice loads, the ice loads and the appropriate load factors and combinations of ASCE/SEI 7 shall be used.

5.3.11

Required strength U shall include internal load effects due to reactions induced by prestressing with a load factor of 1.0.

5.3.12

For post-tensioned anchorage zone design, a load factor of 1.2 shall be applied to the maximum prestressing reinforcement jacking force.