Nonlinear Finite Element Analysis of Connections for Precast Elements

Abstract

Now a days, there is increasing trend towards construction of buildings using precast concrete. In precast concrete construction, all the components of structures are produced in controlled environment and transported to the site. At site, such individual components are connected appropriately. Connections are the most critical elements of any precast structure, as they are playing important role in transferring forces from one element to another element. In past, major collapse of precast structure took place because of connection failure. Therefore, it is very important to understand behaviour of connections in precast structures. Generally, experimental studies can be undertaken to investigate behaviour of any structural elements. But experimental studies are quite costly and time consuming. Many times, it is difficult to conduct experiments on full scale test specimen due to handling issues and availability of testing facilities. With advances in computational methods and availability of effective computational tools, numerical analysis can be used as an alternative to experimental studies. Finite Element (FE) analysis is an effective numerical tool as it is frequently used to overcome experimental limitations in understanding the performance of structures and structural components. In this study, behaviour of precast connections is studied under progressive collapse scenario by performing numerical analysis. Precast beam-column assembly is considered for study, which is having two span beam and three columns with removed middle column. Nonlinear Finite Element (FE) analysis is carried out on precast beam-column assemblies using ABAQUS software. FE models are developed for different types of wet and dry precast connections considered for the study. Concrete Damage Plasticity (CDP) model is used to represent nonlinear material properties. Concrete is modelled using 8-noded linear brick element (C3D8R) and steel reinforcement bars are modelled using 2-node linear truss element (T3D2). The numerical analysis results in terms of ultimate load carrying capacity, deflection profile of specimen at specified load values and failure modes are compared with that observed during available experimental studies. From the comparison of results of FE analysis and experimental studies, difference of 1.05% to 24.5% is observed in ultimate load carrying capacity. Close agreement of results of numerical analysis with that of experimental study indicates that, FE models are about to capture behaviour of precast beam column connections under column removal scenario. Stress contours and scalar stiffness degradation contours obtained from numerical analysis, closely matches with the failure pattern of specimen observed during experimental studies. To further understand the effect of various parameters on response of test specimens subjected to loading under column removal scenario, parametric study is carried out. Various parameters such as beam longitudinal reinforcement ratio, location of connection, size of test specimen and boundary conditions, effect of transverse members on precast beam column assembly etc. are considered for the study, to understand their effect on the behaviour of precast beam column assembly. From the results of parametric studies carried out using FE models developed in present study, it is reflected that, ultimate load carrying capacity of precast connections is enhanced by 14.5% to 16.5%, when connections are provided away from beam column junction, as connection region is subjected to smaller magnitude of internal forces. From the numerical analysis results, it is also evident that FE model is about to capture size effect of the specimen on its overall response. Ultimate load carrying capacity of full scale monolithic specimen obtained from FE analysis, is increased by 9.43 times as compared to reduced (1/3rd) scale specimen, which is closely matches with the scale factor of 9.68, obtained through dimensional analysis to calculate ultimate load carrying capacity of full scale prototype specimen. It is also observed that, full scale specimen is capable to undergo higher deflection as compared to reduced scale specimen. Results of numerical analysis also suggests that, boundary conditions considered at two end columns of beam column assembly plays important role in behaviour of specimen. An increase of 32% in ultimate load carrying capacity is observed for the specimen considered in this study, when horizontal restraint are provided at two locations along the height of column, as compared to providing lateral restraints at the end of column. Change in boundary conditions also permit higher deflection of specimen and higher amount of axial compressive forces and axial tensile forces are developed.