Abstract
Six concrete beam-column frame sub-assemblages reinforced with basalt fiber-reinforced polymer (BFRP) bars in the frame beams were designed to investigate the collapse resistance after a middle column removal. Effect of parameters, including span to depth ratio of frame beams, prestressing, as well as material types of stirrups in the beams, on the collapse resistance of the sub-assemblages, was investigated. Experimental results showed that the initial stiffness of the frame beams was apparently lower due to low elastic modulus of BFRP bars. The collapse resistance of the sub-assemblages presented wave-like increasing tendency with the vertical displacement of the failed middle column, and it mainly attributed to the cracking or crushing of concrete and rupture of BFRP bars in the frame beams. Top longitudinal BFRP bars at the beam ends near to the side column (BESCs) and bottom longitudinal BFRP bars at the beam ends near to the middle column (BEMCs) kept tensile during the loading process, which played an important role in resisting structural collapse. Adjacent structural members such as frame beams and columns could provide horizontal reaction forces to constrain the free deformation of the residual sub-assemblages after the middle column failed, and it was beneficial to mitigate the structural collapse risk. The vertical deformation of the frame beams was nearly linear and proportional to the vertical displacement of the failed middle column. Finally, the dynamic increase factor (DIF) of collapse load was discussed using energy conservation method, and a calculation method of DIF for prestressed concrete frame structures was developed. It was suggested that the DIF values for the non-prestressed frame structures reinforced with BFRP bars in the beams should be taken as 2.0, while those for the prestressed sub-assemblages can be taken between 1.44 and 2.0.
Highlights
Reinforced concrete (RC) frame structures are widely used in building engineering, unexpected failure of one or several columns due to explosion or vehicle impact is most likely to lead to the disproportionate collapse of frames, which might cause catastrophic consequences
The stiffness of the sub-assemblages reinforced with basalt fiber-reinforced polymer (BFRP) bars in the beams was obviously lower because of the low elastic modulus of BFRP bars
A series of cracks appeared on the frame beams, which mainly concentrated at the beam ends
Summary
Reinforced concrete (RC) frame structures are widely used in building engineering, unexpected failure of one or several columns due to explosion or vehicle impact is most likely to lead to the disproportionate collapse of frames, which might cause catastrophic consequences. Yu et al [2] experimentally investigated the progressive collapse resistance of RC beam-column sub-assemblages under a middle column removal scenario, Appl. Experimentally investigated the effects of adding different types of fibers to the concrete mixes on the flexural behavior of concrete beams reinforced longitudinally with BFRP bars, it showed that introducing basalt fibers to the concrete increased curvature ductility of the beams and improved the flexural capacities. Abed et al [19] investigated the shear performance of deep concrete beams reinforced with BFRP bars without web reinforcement, and the influence of parameters including the effective depth and the longitudinal reinforcement ratio on the shear capacity of the beams was studied.
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