[Univ of Cambridge] [Dept of Engineering]

The Strength of Reinforced Concrete Slabs and the Implications of Limited Ductility

S.R. Denton



The accurate strength assessment of reinforced concrete structures is a fundamental requirement for their cost effective and safe management. Furthermore, it can provide significant environmental benefits through extending their life.  Reinforced concrete slabs are key elements of many structures, and in particular many bridges.  Because of their high degree of redundancy, their accurate strength assessment can present significant challenges.

Yield-line analysis has proved to be an effective approach for the strength assessment of existing concrete slab structures. Issues remain however concerning the application of this upper-bound plastic method, in particular in understanding the implications of limited ductility.

A systematic procedure is presented which enables conventional yield-line mechanisms to be converted into “wide” yield-line mechanisms, in which yield-lines are represented by regions of uniform curvature.  These “wide” yield-line mechanisms are used to investigate the significance of the reduction in the flexural capacity of slab elements when they are subjected to anti-clastic bending, compared with uni-axial bending.

The compatibility requirements for yield-line mechanisms are examined, and a simple and systematic procedure for checking their compatibility is presented.  An analogy between compatibility requirements in yield-line mechanisms and states of self-stress in pin-jointed trusses is demonstrated.

The implications of limited ductility on the strength of reinforced concrete slabs are explored both experimentally and theoretically.  An approach for analysing strain-softening structures, based upon the Galerkin method, is presented which offers the particular benefit that the results converge to those of an upper-bound plastic analysis for ductile structures.  The method therefore appears well suited to examining the implications of limited ductility and the results of its application to the analysis of one-way spanning reinforced concrete slabs with eccentric loading are compared with a series of experiments, with reasonable agreement achieved.  A detailed description of the experiments and results is presented.

An increment solution procedure for non-linear problems, that has been used in the analysis, is presented.  Details of a general numerical routine for reinforced concrete slab elements, to determine the moment-field corresponding to a specified curvature-field are also presented, together with the calibration of this routine against test results.

[Cambridge University | CUED | Structures Group | Geotechnical Group]

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