Diaphragm modeling and analysis requirements of the general building code shall govern where applicable. Otherwise, diaphragm modeling and analysis shall be in accordance with 126.96.36.199 through 188.8.131.52.
Calculation of diaphragm in-plane design moments, shears, and axial forces shall be consistent with requirements of equilibrium and with design boundary conditions. It shall be permitted to calculate design moments, shears, and axial forces in accordance with one of (a) through (e):
(a) A rigid diaphragm model if the diaphragm can be idealized as rigid
(b) A flexible diaphragm model if the diaphragm can be idealized as flexible
(c) A bounding analysis in which the design values are the envelope of values obtained by assuming upper bound and lower bound in-plane stiffnesses for the diaphragm in two or more separate analyses
(d) A finite element model considering diaphragm flexibility
(a) For a diaphragm idealized as a beam whose depth is equal to the full diaphragm depth, with moment resisted by boundary reinforcement concentrated at the diaphragm edges, design strengths shall be in accordance with 12.5.2 through 12.5.4.
(b) For a diaphragm or a diaphragm segment modeled as a strut-and-tie system, design strengths shall be in accordance with 23.3.
(c) For a diaphragm idealized with a finite-element model, design strengths shall be in accordance with Chapter 22. Nonuniform shear distributions shall be considered in design for shear. Collectors in such designs shall be provided to transfer diaphragm shears to the vertical elements of the lateral-force-resisting system.
(d) For a diaphragm designed by alternative methods, such methods shall satisfy the requirements of equilibrium and shall provide design strengths at least equal to required strengths for all elements in the load path.
If nonprestressed, bonded prestressing reinforcement is designed to resist collector forces, diaphragm shear, or tension due to in-plane moment, the value of steel stress used to calculate resistance shall not exceed the lesser of the specified yield strength and 60,000 psi.
Nonprestressed reinforcement and mechanical connectors resisting tension due to moment shall be located within h/4 of the tension edge of the diaphragm, where h is diaphragm depth measured in the plane of the diaphragm at that location. Where diaphragm depth changes along the span, it shall be permitted to develop reinforcement into adjacent diaphragm segments that are not within the h/4 limit.
For a diaphragm that is entirely cast-in-place, Vn shall be calculated by Eq. (184.108.40.206).
where Acv is the gross area of concrete bounded by diaphragm web thickness and depth, reduced by void areas if present; the value of used to calculate Vn shall not exceed 100 psi; and ρt is distributed reinforcement oriented parallel to the in-plane shear.
For diaphragms that are cast-in-place concrete topping slabs on precast elements, (a) and (b) shall be satisfied:
(a) Vn shall be calculated in accordance with Eq. (220.127.116.11), and cross-sectional dimensions shall be selected to satisfy Eq. (18.104.22.168). Acv shall be calculated using the thickness of the topping slab for noncomposite topping slab diaphragms and the combined thickness of cast-in-place and precast elements for composite topping slab diaphragms. For composite topping slab diaphragms, the value of f'c in Eq. (22.214.171.124) and (126.96.36.199) shall not exceed the lesser of f'c for the precast members and f'c for the topping slab.
(b) Vn shall not exceed the value calculated in accordance with the shear-friction provisions of 22.9 considering the thickness of the topping slab above joints between precast elements in noncomposite and composite topping slab diaphragms and the reinforcement crossing the joints between the precast members.
For diaphragms that are interconnected precast elements without a concrete topping, and for diaphragms that are precast elements with end strips formed by either a cast-in-place concrete topping slab or edge beams, it shall be permitted to design for shear in accordance with (a), (b), or both.
Collectors shall extend from the vertical elements of the lateral-force-resisting system across all or part of the diaphragm depth as required to transfer shear from the diaphragm to the vertical element. It shall be permitted to discontinue a collector along lengths of vertical elements of the lateral-force-resisting system where transfer of design collector forces is not required.
Except for slabs-on-ground, diaphragms that are part of floor or roof construction shall satisfy reinforcement limits for one-way slabs in accordance with 7.6 or two-way slabs in accordance with 8.6, as applicable.
Reinforcement designed to resist diaphragm in-plane forces shall be in addition to reinforcement designed to resist other load effects, except reinforcement designed to resist shrinkage and temperature effects shall be permitted to also resist diaphragm in-plane forces
Except for slabs-on-ground, diaphragms that are part of floor or roof construction shall satisfy reinforcement detailing of one-way slabs in accordance with 7.7 or two-way slabs in accordance with 8.7, as applicable.