§ 27-579 Distribution of horizontal loads.

The following provisions shall apply to superstructure framing only, and shall not apply to structures wherein horizontal loads are transmitted to the foundation by stay-cables, arches, non-rectangular frames, or by frames, trusses, or shear walls not oriented in vertical planes.

   (a)   Distribution of horizontal loads to vertical frames, trusses and shear walls. Horizontal loads on the superstructure shall be assumed to be distributed to vertical frames, trusses, and shear walls by floor and roof systems acting as horizontal diaphragms. The proportion of the total horizontal load to be resisted by any given vertical frame, truss, or shear wall shall be determined on the basis of relative rigidity, considering the eccentricity of the applied load with respect to the center of resistance of the frames, trusses, or shear walls. For vertical trusses, web deformations shall be considered in evaluating the rigidity.

   (b)   Distribution of horizontal loads within rigid frames of tier buildings.

      (1)   ASSUMPTIONS. The distribution of horizontal loads within rigid frames of tier buildings may be determined on the basis of a recognized method of elastic analysis or, subject to limitations in paragraph two of this subdivision, may be predicated on one or more of the following simplifying assumptions:

         a.   Points of inflection in beams or columns are at their midspan and midheight, respectively. The story shear is distributed to the columns in proportion to their stiffnesses.

         b.   The change in length of columns due to axial effects of the horizontal loads may be neglected.

         c.   Vertical column loads due to horizontal forces are taken by the exterior columns only, or are resisted by the columns in proportion to the column distances from the neutral axis of the bent.

      (2)   LIMITATIONS.

         a.   For buildings over three hundred feet in height, the change in length of the columns, due to the effects of the horizontal loads, shall be evaluated or the framing proportioned to produce regular movements of the successive joints at each floor so that warping of the floor system may be neglected.

         b.   Simplifying assumptions used in design shall be subject to approval by the commissioner for any of the following conditions or circumstances:

            1.   For buildings over three hundred feet in height or for buildings with a height-width ratio greater than five.

            2.   At two-story entrances or intermediate floors.

            3.   Where offsets in the building occur.

            4.   Where transfer columns occur.

            5.   In any similar circumstances of irregularities or discontinuities in the framing.

   (c)   Distribution of load in self-relieving construction. The framing of self-relieving construction may be proportioned on the assumption that connections are fully rigid in resisting moments due to lateral load and that any larger moments due to the gravity loads or due to a combination of gravity and lateral loads will be relieved by deformation of the connection material, provided that:

      (1)   The fasteners shall be capable of developing the full moment capacity of the connection at the allowable unit stress established in subchapter ten of this chapter.

      (2)   The connection shall be capable of resisting the moment due to lateral load, and the shear due to lateral load plus vertical load, all at the allowable unit stresses established in subchapter ten of this chapter.

      (3)   The framing and the building are within the limitations established in subparagraph b of paragraph two of subdivision (b) of this section.

      (4)   The connections shall be detailed to permit the required deformations without fracture, and their capacity to so function shall be verified by test or other means.

   (d)   Structural walls and partitions. Walls and partitions, if specifically designed to resist the applied forces, may be considered as contributing to the resistance or rigidity of the structure with regard to horizontal loads.

Subchapter 10: Structural Work

Article 1: Scope and General Requirements

§ 27-580 Scope.

The provisions of this subchapter, supplemented by the additional requirements of subchapter eleven of this chapter, shall establish minimum requirements for materials, designs, and construction to be used for all structural elements in buildings. In addition, within special flood hazard areas and below the regulatory flood datum, as described in article ten of subchapter four of this chapter, materials, designs and construction required for structural elements by reference standard RS 4-5 shall be applicable.