Probabilistic Approach to Deflection Controlled Reinforced Concrete Slab Design


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Title: Probabilistic Approach to Deflection Controlled Reinforced Concrete Slab Design

Author(s): C. S. Putcha

Publication: Special Publication

Volume: 86


Appears on pages(s): 377-394

Keywords: concrete slabs; creep properties; deflection; loads robability theory; safety factor; reinforced concrete; reinforcing steels; structural analysis; structural design.

Date: 8/1/1985

Economical design of large span slabs which are required to support partitions can be controlled by deflections and other serviceability considerations rather than strength. This design is further complicated by considerations of variations in strength of concrete, placement of steel, etc. even for constant dead and live loads (short term, long term). Even in the deterministic case when the-parameters of long term live load, short term live load, fc, w,fy, maximum deflection limitations (due to loading, creep and shrinkage) are known, the solution for finding effective thickness and depth is found by trial and error amenable for iterative computerized approaches. This problem is especially severe when the partitions are installed while the slab is still shored. A probabilistic approach with variation in concrete strengths for given coefficient of variation to deflection controlled one way R. C. slab is developed with numerical examples and degenerate case of the-deterministic specified strength f'c. Comparison is made between the probabilistic design for long term deflection control and the professional practice oriented usual design procedure for numerical cases. This could be applied to both structural lightweight and normal weight concrete. Extension to the more generalized case of variability of loads, variability of methods of assessing creep and shrinkage deflections, etc. are also explored.