= 6.4 — Arrangement of live load

== 6.4.1 For the design of floors or roofs to resist gravity loads, it shall be permitted to assume that live load is applied only to the level under consideration.

== 6.4.2 For one-way slabs and beams, it shall be permitted to assume (a) and (b):
(a) Maximum positive Mu near midspan occurs with factored L on the span and on alternate spans
(b) Maximum negative Mu at a support occurs with factored L on adjacent spans only

== 6.4.3 For two-way slab systems, factored moments shall be calculated in accordance with 6.4.3.1, 6.4.3.2, or 6.4.3.3, and shall be at least the moments resulting from factored L applied simultaneously to all panels.

=== 6.4.3.1 If the arrangement of L is known, the slab system shall be analyzed for that arrangement.

=== 6.4.3.2 If L is variable and does not exceed 0.75D, or the nature of L is such that all panels will be loaded simultaneously, it shall be permitted to assume that maximum Mu at all sections occurs with factored L applied simultaneously to all panels.

= R6.4 — Arrangement of live load

== R6.4.2 The most demanding sets of design forces should be established by investigating the effects of live load placed in various critical patterns.
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PART 2: LOADS & ANALYSIS 73
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=== 6.4.3.3 For loading conditions other than those defined in 6.4.3.1 or 6.4.3.2, it shall be permitted to assume (a) and (b):
(a) Maximum positive Mu near midspan of panel occurs
with 75 percent of factored L on the panel and alternate
(b) Maximum negative Mu at a support occurs with 75
percent of factored L on adjacent panels only

=== R6.4.3.3 The use of only 75 percent of the full factored live load for maximum moment loading patterns is based on the fact that maximum negative and maximum positive live load moments cannot occur simultaneously and that redistribution of maximum moments is thus possible before failure occurs. This procedure, in effect, permits some local overstress under the full factored live load if it is distributed in the prescribed manner, but still ensures that the design strength of the slab system after redistribution of moment is not less than that required to resist the full factored dead and live loads on all panels.
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74 ACI 318-19: BUILDING CODE REQUIREMENTS FOR STRUCTURAL CONCRETE


[ Lanjut Ke 6.5—Simplified method of analysis for
nonprestressed continuous beams and one-way
slabs ... ]






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