CREEP, SHRINKAGE AND TEMPERATURE EFFECTS IN MULTI-STOREYED CONCRETE BUILDINGS

Abstract

Effects of creep, shrinkage and temperature are to cause cracking, excessive deflection, spalling and even partial collapse of reinforced concrete structures because strains due to these effects may amount several times in comparison to the strains on application of load. When designing high rise reinforced concrete buildings, length chnages of the vertical members caused by time-dependent (creep, shrinkage and temperature) effects must be considered because with increasing height of buildings, the importance of time dependent shortening of columns (and shear walls) becomes more critical due to the cumulative nature of such shortening. No rational method is available to consider creep, shrinkage and temperature effects in analysis and design of multi-storeyed concrete buildings. To take creep, shrinkage, temperature and some other unforeseen factors into account code (IS:456-1978) has specified a partial safety factor of 1.5 on (D.L + L.L) and of 1.2 on (D.l. + L.L + W.L). So there is a need of more rational design methods to consider creep, shrinkage and temperature effects in multi-storeyed concrete buildings. In the present study, methods have been presented to find effects of creep, shrinkage and temperature in multi-storeyed concrete buildings. 'Aging Coefficient Approach' has been used for the creep and shrinkage analysis of flexural elements of reinforced concrete. This approach is not directly applicable to the columns of high rise buildings. Fintel and Khan have presented a procedure to predict the inelastic (creep and shrinkage) shortening of columns in multi-storeyed concrete buildings as a function of the incremental loading sequence, the volume-to-surface ratio, and the effect of percentage of reinforcement. A method has also been, presented to convert temperature effects in terms of equivalent joint loads in a computer program of frame analysis. Two examples (one of a 6 storied building and other of a 10 storied building) have been presented to illustrate the detail procedure to incorporate the creep, shrinkage and temperature effects in the design of multi-storeyed buildings. Some conclusions have also been drawn to indicate the extent of these effects in multi-storeyed buildings which may be usefull in the design of such buildings.