§27-594 Combination of Loads

Dead loads, live loads (including impact) and reduced live loads, where applicable, shall be considered as basic loads. Wind, earthquake, thermal forces, shrinkage, and unreduced live loads (where live load reduction is permitted by subchapter nine of this chapter) shall be considered as loads of infrequent occurrence. Members shall have adequate capacity to resist all applicable combinations of the loads listed in subchapter nine of this chapter, in accordance with the following:

(a) Where design is based on allowable working stresses, the loads as described in subchapter nine of this chapter shall be multiplied by the following factors and the design shall be based on the resulting load values:

(1) For combinations of basic loads, only, the factor shall be 1.0, except that for the design of temporary structures (defined as a structure which will be in place six months or less) the factor shall be 0.75.

(2) For any combination of one or more basic loads with any one load of infrequent occurrence, the factor shall be 0.75, except that for the design of temporary structures the factor shall be 0.67.

(3) For any combination of one or more basic loads with two or more loads of infrequent occurrence, the factor shall be 0.67.

Exception. The provisions of reference standards RS 10-8 and RS 10-9 relating to increases of allowable unit stresses for short-time loading shall apply.

(b) Where design is based on ultimate strength criteria (including plastic design of steel structures and proportioning of suspended structures), the loads, as described in subchapter nine of this chapter shall be multiplied by the factors indicated in subdivision (e) of section 27-639 of article eleven of this subchapter and in the applicable reference standards. The design shall be based on the resulting load values.

Exceptions. 1. Where combinations of load for which factors are given in the reference standard include the load of wind (or earthquake) the design additionally shall consider combinations of load wherein each other of the loads of frequent occurrence as listed in this paragraph are substituted for the load of wind.

2. The design also shall consider combinations of load wherein two most critical of the loads of infrequent occurrence are combined with the basic loads. For such combination, however, the factors indicated in the reference standards and in subdivision (e) of section 27-639 of article eleven of this subchapter for suspended structures, for the combination of basic loads plus one load of infrequent occurrence may be reduced fifteen per cent.