Rational Analysis and Designof Two-Way Concrete Slabs


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Title: Rational Analysis and Designof Two-Way Concrete Slabs

Author(s): C. P. Siess and N. M. Newmark

Publication: Journal Proceedings

Volume: 45

Issue: 12

Appears on pages(s): 273-315

Keywords: no keywords

Date: 12/1/1948

A new method for the design of two-way building slabs is proposed and its step by step development is described. A new moment distribution procedure is used to compute moments in a number of rectangular slabs continuous over rigid beams. Several variables are studied in the analyses and include: the ratio of sides, the effect of discontinuous edges, the torsional stiffness of the beam, various types of loading, and combinations of panels of various sizes and shapes. Certhin conclusions are stated regarding the types of loading to be considered and the values of beam torsional stiffness to be assumed in the development of the design procedure. Moments obtained in the foregoing analyses are modified to take into account the effect of additional variables. First, the slab moments are increased by various amounts as a result of the deflection of the beams. Next, separate coefficients for dead and live load are replaced by combined coefficients for a live load-dead load ratio of 3.0. Then follows a study to determine the effect of discontinuous edges and this variable is eliminated from the procedure. Finally all slab moments are reduced by 20 percent in recognition of the redistribution of moments at high load. Additional studies are then made of the distribution of moments across the width of the slab and of the moments to be used for the design of the beams to complete the development of the design procedure. A proposed design procedure is presented in specification form and is compared with other procedures of a similar nature and with the moment distribution procedure described in the appendix.