Experimental Investigation of Progressive Collapse of Prestressed Concrete Frames after the Loss of Middle Column

Tao Yang,Wanqing Chen,Zhongqing Han

doi:10.1155/2020/8219712

Abstract

Accidental loads such as explosion and vehicle impact could lead to failure of one or several load-bearing members in the structures, which is likely to trigger disproportionate progressive collapse of overall structures. Prestressed concrete (PC) frame structures are usually at great risk of collapse once load-bearing members fail, because the members in PC frame structures are usually subjected to much more load than those in common reinforced concrete (RC) frame structures. To investigate the progressive collapse behaviors of PC frame structures, five one-fourth reduced scaled frame substructures were fabricated and collapse tests were conducted on them. Influence of span-to-depth ratios of frame beams and prestress action modes on the collapse performance of PC frame structures was discussed. Experimental results indicated that PC frame substructures with different prestress action modes, including bonded prestress and unbonded prestress, presented different collapse resistance capabilities and deformability. Tensile force increment of the unbonded prestressing strands almost linearly increased with the vertical displacement of the failed middle column. Catenary action is one of the most important mechanisms in resisting structural collapse. Prestressing strands and longitudinal reinforcing bars in the frame beams benefited the formation and maintaining of catenary action. The ultimate deformability of the PC frame structures was tightly connected with the fracture of prestressing strand. In addition, a calculation method of dynamic increase factors (DIFs) suitable for PC frame structures was developed, which can be used to revise the design collapse load when static collapse analysis is conducted by the alternative path method. The DIFs of the five substructures were discussed on the basis of the proposed method; it revealed that the DIFs corresponding to the first peak loads and the ultimate failure loads for the PC frame substructures were less than 1.49 and 1.83, respectively.

Highlights

Load-bearing members in frame structures might fail under accidental loads such as explosion, vehicle impact, and so on, which can trigger disproportional collapse of integral structures
Vertical displacement of the frame beams almost linearly increased with the load applied on column B, but the duration of this stage was relatively short. (2) e elastic-plastic stage: when the applied load kept rising, large deformation and plastic strain produced in the substructures, and the first peak load appeared. ereafter, the number of cracks on the beams increased markedly, some cracks at the beam ends propagated from the tensile zone to the compressive zone of the beams, and the load-bearing capacity of the residual substructures began to decrease
Collapse tests were carried out on five frame substructures, and the following conclusions based on the experiments are drawn: (1) In the scenario of a middle-column loss, cracks mainly distributed on the frame beam ends

Summary

Introduction

Load-bearing members in frame structures might fail under accidental loads such as explosion, vehicle impact, and so on, which can trigger disproportional collapse of integral structures. As reinforced concrete (RC) frame structures are widely used in industrial and civil buildings, many research works have been conducted to investigate their collapse mechanisms. Some researchers investigated the influence of slabs on structural collapse performance by tests or numerical analysis [4, 5], and it was found that slab could significantly improve the resistance capability against collapse after the failure of load-bearing columns. Qian et al [16] studied the collapse resistance of posttensioned concrete beam-column subassemblages with unbonded posttensioning strands and found that the effective prestress may significantly affect the ultimate deformability and load capacity of the PC frames. Is paper reports the experimental results of five reduced scaled beam-column frame substructures after a middle-column removal; the influence of spanto-depth ratios and prestress action modes on progressive collapse of PC frame structures was assessed. A calculation method of dynamic increase factor (DIF) of collapse load for PC frame structures was developed

Experimental Design

Experimental Observations

Experimental Results

Discussions

Conclusions