Behavior of Precast Connections under Column Removal Scenario

Abstract

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 compo- nents are connected. This leads to faster construction, reduced formwork and scafolding, less requirement of skilled labors, massive production with reduced amount of construc- tion waste, better quality and better surface finishing as compared to normal reinforced concrete construction. Because of such advantages, the precast concrete construction 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. Progressive collapse as a structural engineering point of view started taking attention when partial collapse of 22 storey Ronan Point apartment building occurred in London on May 16, 1968. Progressive collapse is the result of a localized failure of one or two structural elements that lead to a steady progression of load transfer that exceeds the ca- pacity of other surrounding elements, thus initiating the progression that leads to a total or partial collapse of the structure.Progressive collapse of a structure can be prevented by providing continuity, ductility and redundancy to redistribute additional forces through an alternate load path. Precast construction now a days getting worldwide acceptance, so it is one of necessity to check effectiveness of precast connections under progressive collapse scenario. The main objective of this study is to investigate the effectiveness of different types of cast in place concretes, which may be used for wet precast connections. In this study, six storey reinforced concrete building is considered having 4 bays in longitudinal direction and 3 bays in transverse direction each having 4m c/c spacing. Beam column assembly forming T-shape, from the peripheral corner of the building is considered for the experimental work. Six precast wet connections having same connection mechanism but different types of cast in place concretes are considered. T-shaped frame is made by connecting precast beam and column. Point load is applied at the end of cantilever beam. De ection and strain is measured at considered locations. Comparison of crack patterns and failure be- haviour of each specimen is done with each-other. Results are compared with monolithic control specimen. Superior type of concrete from all six different types is found out from above mention comparison of results. This superior type of wet concrete found from above mentioned experimental comparison is further used in precast frames considered for progressive collapse study from the pe- riphery of same six storey reinforced concrete building. Progressive collapse resistance for beams are evaluated for removal of middle column from ground oor located on long side of plan as suggested by General Services Administration (GSA) guidelines. First oor level beams on either side of removed column are considered for study. For understanding the effect of sudden removal of column which leads to progressive collapse, total 4 frames are tested including one monolithic frame and three Precast frames. Design and detailing was done considering lateral load and seismic detailing. Test specimen is having two span beam with end column restrained and center removed column. For handling purpose, one third scaled models were casted and tested. From the results of exterior beam-column junction, it is observed that connection having micro-concrete with polypropylene fibres as cast-in-place concrete performed batter than monolithic specimen in terms of load carrying capacity and de ection aspects. It has 19.7% higher load carrying capacity than monolithic connection. It is also performed bat- ter in terms of failure pattern due to its crack arresting ability. In specimens considered under column removal scenario, both precast dry connection-1 and wet connection-1 have almost same load carrying capacity as that of monolithic connection. Dry connection-1 and wet connection-1 has 7.8% and 9.5% lower load carrying capacity than monolithic connection respectively.