An Experimental Investigation of Precast Connections under Column Removal Scenario

Abstract

Progressive collapse occurs, when a primary structural component fails like column in structure, resulting in the failure of adjoining structural elements, which in turn causes failure of large part of structure. Failure of large part of any structure will results into substantial loss of human lives and natural resources. Therefore, it is important to prevent progressive collapse which is also known as disproportionate collapse. Progressive collapse can be restricted by providing structural ductility, increasing redundancy and integrity within the structure providing alternate load paths for force distribution. Recently, 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 critical elements of any precast structure, because in past, major collapse of precast structure took place because of connection failure. In this study, behavior of different dry and wet precast connections are studied under column removal scenario which in turn represents progressive collapse scenario. A six storey reinforced concrete building is considered having 3 bays in transverse direction and 4 bays in longitudinal direction each having 4 m center to center span. Center column of perimeter frame from bottom storey is removed to simulate progressive collapse scenario. Six different type of precast connections which includes four wet connections and two dry connections are being designed and detailed at away from beam column junction and their behavior is evaluated by performing experiments. Typical specimen is having two span beam and three columns with removed middle column. The end columns of specimen are restrained vertically as well as in lateral direction by applying compressive loading at their ends and using a triangular frame attached with existing loading frame respectively. Load is applied at the top of removed middle column using hydraulic jack. Defection along the length of beam and central deflection at the location of removed middle column is measured with the help of LVDTs and dial gauges. Strain is measured at critical locations on concrete surfaces as well as on reinforcement bars embedded in concrete using electrical resistance strain gauges. Response of specimen is captured through Data Acquisition System (DAQ) in terms of load - displacement relationship, strain and failure pattern. From the experimental study it is observed that the precast wet connections are having higher load carrying capacity and moment resisting capacity as compared to precast dry connections except wet connection-3. However, load carrying capacity of precast connections are slightly lesser as compared to monolithic connection. Performance of precast connections can be enhanced by ensuring proper detailing at connection region. Failure pattern of precast connections is similar to that of monolithic connection, which advocates that forces are successfully transferred from one element to another element without any significant failure at connection region.