Study the Behaviour of Precast Connections Under Column Removal Scenario : An Experimental Investigation

Abstract

Progressive collapse in a structure occurs when typical structural members are failed and the adjoining structural elements cannot resist the redistributed forces and fails subse- quently and leads to complete collapse of structure. Failure of the structure will cause large loss of human lives, natural resources and economy, therefore it is important to prevent progressive collapse which is also known as disproportionate collapse. Progressive collapse can be prevented by providing structural integrity, ductility and by increasing redundancy within the structure providing alternate load paths for force distribution. The concept of precast construction includes buildings, where majority of structural com- ponents are standardized and produced in controlled environment in a location away from the building, and then transported to the site for assembly. These components are manufactured by industrial methods based on mass production in order to build a large number of buildings in a short time at low cost. For any precast construction, connections between different components are critical, because in past major failure occurred due to failure of connection. Therefore it is important to study the behaviour of different types of connection between various elements. In this study, behaviour of different dry and wet precast connections are studied during progressive collapse scenario. A six storey Reinforced Concrete(RC) building is consid- ered having 4 bays in longitudinal direction and 3 bays in transverse direction each having 4 m center-to-center spacing. Centre column of perimeter frame from bottom storey is removed, to simulate progressive collapse scenario and behaviour of precast connection adjoining to removed column are studied. Eleven different types of precast connections including 5 dry connection and six wet connection constructed at beam - column junction and away from beam - coulmn junction are evaluated experimentally. 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 compres- sive loading at their ends and using a triangular frame respectively. Load is applied at the top of removed column using hydraulic jack. Defection along the length of beam and central de ection at the location of removed middle column is measured with the help of LVDTs & dial gauges. Strain is measured at critical location on concrete surfaces as well as in reinforcement bars embedded in concrete using electrical strain gauges. Response of specimen is measured in terms of load - displacement relationship, strain and failure pattern. From the experimental study it is observed that the precast wet connection has load carry- ing capacity in a range of 87-95% with respect to monolithic specimen. The displacement ductility of wet connection is in the range of 5.3-5.5 while the displacement ductility of monolithic specimen is 7 both give comparable result with monolithic specimen. The per- formance of dry connection is also similar to wet connection as load carrying capacity is in a range of 87-94 % and displacement ductility is 6.6. So the behaviour can be improved more by proper detailing at junction.