Effect of Concrete Creep Behavior on the Shortening of Vertical Structural Elements in High-rise Buildings: Analytical and Numerical approaches
Vertical structural elements are commonly subjected to the time-dependent behavior effects caused by creep. The creep causes shortening in these elements. Researches have been made to provide a better understanding of the effect of creep on structural elements. In its simplest definition, concrete creep is the deformation of structure under sustained load. Significant amount of creep takes place instantaneously with loading and carries on for the long-term dimensions. Creep is classified into basic creep that occurs under conditions where moisture losses or gains are prevented and drying creep that is an additional creep in a loaded specimen exposed to a drying environment and allowed to dry. The deformation due to creep occurs in the direction of the load being applied. Yet, this deformation doesn’t necessarily cause concrete failure or break apart. With the increase in the height of buildings, the importance of creep shortening becomes more critical. In high-rise buildings, the axial shortening in columns is inevitable, so it can’t be ignored. The shortening is differential between vertical structural members due to the difference in axial stiffness and load distribution areas on these elements. However, most engineers don’t consider the effect of creep in their analyses of high-rise buildings since such calculations are not straight forward and depends on several parameters. If not considered in analyses, structural safety will be compromised. Conventional structural analysis assumes that all structural loads are instantaneously applied to the entire completed structure. Most buildings are constructed by one story or several floor units at a time, or even if it is the same story, the construction sequence and loading sequence may be different depending on the construction plan. Therefore, the actual structural behavior can be significantly different from the conventional analytical behavior based on the above assumption. The objective of this study is to highlight the effect of concrete creep behavior on the shortening of vertical elements specifically in high rise buildings. Different methods are available to predict the creep including ACI 209R-92, Bazant Baweja B3, CEB MC90-99, GL2000 models. In this study, we will be considering the ACI 209R-92 model. Based on experimental data, a method will be developed to compute the elastic shortening due to creep taking into consideration the stress and modulus of elasticity depending on the time and height of high-rise buildings.
Sandy Jamal Eddine Chaaban
Dr. Yehia Temsah, Dr. Oussama Baalbaki