Direct Design of Reinforced Concrete Slabs Using Non Elastic Stress Fields

[摘要] Ultimate strength design of reinforced concrete can be carried out using elastic stress field in conjuction with Wood-Armer yield criterion. This procedure is known as Direct Design Method and has shown to produce well designed slabs. The object of this work is to explore in particular the effect on serviceability limit and ductility demand of using non elastic stress fields. This is the main object of the present work. The work divides into two convenient parts: i-Determination of elasto-plastic stress fields as input to Wood-Armer equations. This is accomplished using a nonlinear finite element program based on Mindlin plate element and Von-Mises criterion. ii-Assessment of these designed slabs using a nonlinear finite element program based on 'Layer' approach. This analysis and assessment has been done for slabs with various boundary conditions and loading systems. The results show that use of nonlinear stress fields has the following advantages: -a) The distribution of the design moments (M*x,M*y) is more uniform. -b) The congestion of reinforcement is avoided by smoothing out the peaks. -c) The maximum design moment is reduced by an average of 26%. -d) The slabs designed by non elastic stress field behaved satisfactorily at the service load (0.625 x design load) in terms of deflection and steel strain. -e) The average load at first yield of steel for all the tested slabs was 0.86 times the design load. -f) The results indicate that the ductility demand is not much different for all the slabs designed using elastic or non elastic stress field. -g) The average ultimate load for all the analysed slabs was 1.07 times the design load. -h) The sensitivity of the results to the level of plasticity spread was insignificant. A second part of this work consists of developing a nonlinear finite element program for the analysis of reinforced concrete slabs based on Wood-Armer criterion. This program has the advantage that in terms of the time required for a full analysis to determine the ultimate load, it is much faster than any standard nonlinear finite element programs based on layer analysis.

[发布机构] University:University of Glasgow

[关键词] Civil engineering