Role of Reinforcement Detailing on Progressive Collapse Resistance of R.C. Beam

Abstract

Progressive collapse denotes a failure of a major portion of a structure that has been initiated by failure of a relatively small portion of the structure or failure of vertical load carrying element i.e. column. Failure of major portion will results in to substantial loss of human lives and natural resources. Therefore it is very important to prevent this type of disproportionate collapse which is also known as progressive collapse. Progressive collapse of a structure can be prevented by providing sufficient continuity, ductility and redundancy to redistribute additional forces through an alternate load path. In present study, role of reinforcement detailing on progressive collapse resistance is investigated for G+5 Reinforced Concrete (RC) building through experiment. The RC building considered for study is symmetric in nature having 4 bays in x-direction and 3 bays in z-direction each having 4 meter center to center. Progressive collapse resistanc for beams are evaluated for removal of middle column from ground floor located on long side of plan as suggested by General Services Administration (GSA) guidelines. Beam at first floor level on both the side of removed column is considered for the study. Total six specimens are tested to study the effect of reinforcement detailing on progressive collapse resistance. Specimens are designed by considering gravity loading, seismic loading with non-ductile detailing and seismic loading with ductile detailing. The values of Response Reduction factor (R) is considered as 3 and 5 during seismic design with non-ductile detailing and ductile detailing respectively. Each specimen contains two beam spans and one central removed column. End columns having half floor depth above and below floor level, while central column is of 300 mm height above and below beam. It represents the column removed scenario due to any accidental loading. Two different scale are considered i.e. 3/8th and 1/3rd scale, to prepare the specimens and to understand the effect of scaling on test results. To simulate exact condition as in prototype building, two end columns are fixed while on central column load is applied. To keep end column under compression, two triangle frame are fabricated which will not allow lateral movement of end columns and will also restrain column vertically. Testing is carried out by applying load at middle column using hydraulic jack. Displacements along both the spans are measured with dial gauge and strain are measured with mechanical strain gauges. Load displacement relationship, strain at critical location and crack pattern are observed during testing. Comparison of strain versus displacement and load versus displacement is carried out. From the results it is observed that ductile detailing of beam improves progressive collapse resistance of the beam.