Development of design and construction guidelines for axial shortening of columns

Abstract

Axial shortening of columns in reinforced concrete buildings is a phenomenon that was commenced from the day of commencement of concrete building construction. However, this seems to start creating problems only before two or three decades ago. The reason for this can be argued as the capability of older concrete buildings to withstand the effects caused by axial deformation of columns. This means the ability of bearing the effects of axial shortening of columns in modem concrete buildings is lower than that of former concrete buildings. Reasons for this can be suggested in a glance as the sudden reduction taken place in member dimensions, specially in columns, in newly constructed concrete buildings, due to the adoption of high strength concrete in them. Creep, shrinkage and elastic stresses were identified as the major factors that contributes axial shortening of reinforced concrete columns. Dimensions of member, properties of material from which the member is cast, included reinforcement percentage and the surrounding environment condition can be mentioned as the main factors that influence the amount of creep and shrinkage. Methods are available from past literature to estimate possible axial deformation of reinforced concrete columns, taking all above mentioned influencing factors into account. This report includes recommendations and guidelines, which can be directly used to specify approximate shortening values those are possible to occur in different buildings. Special consideration is given throughout the report, to the effect of relative humidity on axial shortening of columns