Behavior of Precast Beam-Column Connection under Progressive Collapse Scenario

Abstract

Progressive collapse is defined as the collapse of entire or a large part of a structure caused by damage or failure of a relatively small part of it. Pro- gressive collapse of building structures is initiated when one or more vertical load carrying members are seriously damaged or collapsed during any of the abnormal events. Once a local failure takes place, the buildings gravity load transfers to neighboring members in the structure. If these members are not properly designed to resist and redistribute the additional load, that part of the structure fails. As a result, a substantial part of the structure may collapse, causing greater damage to the structure than the initial impact. Thus it is necessary to provide suficient redundancy, ductility and continu- ity, which helps the structure to find alternate paths for load distribution during undesired failure event and thus to reduce progressive collapse. Now a days, there is an 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. This leads to faster construction, reduced formwork and scafolding, less requirement of skilled labors, massive production with reduced amount of construction waste, bet- ter quality and better surface nishing as compared to normal reinforced concrete construction. Because of such advantages, the precast concrete con- struction is being adopted world-wide including India. In precast concrete construction, connections are the most critical elements of the structure, because in past, major collapse of precast building took place because of connection failure. The main objective of this study is to investigate the behaviour of dif- ferent types of precast beam-column connections under progressive collapse scenario. The experimental test comprised a total of four precast wet connec- tions, four precast dry connections and one monolithic specimen. Reduced 1=3rd scaled test specimen with different connection detailing are constructed by providing connection at beam-column junction, which is part of 6 storey building. Each specimen includes two span beams and three columns with removed middle column. Removed middle column represents column re- moval scenario, which in turn indicates progressive collapse situation. Load is applied at location of removed middle column with the help of hydraulic jack. De ection is measured at seven different location along the length of the beam, using dial gauges and linear variable displacement transducer (LVDT). Response is measured in terms of ultimate load carrying capacity and de ection measured along the span of the beams under the application of monotonic vertical load at the location of removed central column. From the study, it is observed that precast elements, connected just away from the beam-column junction, perform satisfactorily as compared to mono- lithic connections. Precast dry connections just away from the beam-column junction performs superior in terms of load carrying capacity and displace- ment as compared to precast dry connections at beam-column junction and can be used as replacement of cast-in-place monolithic construction.