| The existing researches on the progressive collapse of reinforced concrete(RC) frame structures mainly focus on the beam-column substructures, which have ignored the influence of the slabs. Actually, the framed beams and the slabs act jointly as an integrated floor system to resist progressive collapse. The slabs have significant effects on the failure mechanism, the damage mode and the development of the resistance and deformation of the framed beams in the process of progressive collapse. Experimental tests and theoretical researches were conducted on the progressive collapse of beam-slab substructures under the removal scenario of an edge column in this study. The major contributions of the work presented in this thesis are listed as follows:(1) Five one-third scaled substructures were designed, including four beam-slab specimens and one beam specimen, and were statically loaded to study the collapse mechanism of the edge area of the RC frame structures.(2) The load-deformation relationship and the strain development at critical sections of the specimens were analyzed. Based on the analysis and the typical experimental phenomena, the local material damage mechanism and the overall collapse-resisting mechanisms at different deformation stages were studied. Under small deformation, the floor system mainly depended on the flexural capacity and the compressive arch action to provide the collapse resistance. The flexural capacity was provided by the framed beams and the connected floor slab within a certain width in two directions along and perpendicular to the edge beam. Due to the restraint boundary condition and the uneven deformation of the slab, the compressive arch action only developed in the edge beam and a part of slab close to the free edge. Under large deformation, the resistance was provided by the catenary tensile force of the reinforcement in the beam and the slab along the peripheral direction. The reinforcement which was closer to the edge beam had a larger contribution to the tensile force due to the uneven deflection of the slab.(3) By comparing the beam-slab specimens and the beam specimen, it was found that the slab significantly improved the progressive collapse resistance of the framed beams. Under beam mechanism, the peak load of the beam-slab specimens was approximately 2.5 times of that of the beam specimen while under catenary mechanism, it was approximately 2 times of the peak load of the beam specimen.(4) The effects of various design parameters, for instance, the slab thickness, the beam height, and the seismic design intensity, on the progressive collapse resistance were studied in detail. Results showed that the peak load under beam mechanism was mainly affected by the beam height and the reinforcement ratio, and it would be obviously improved when increasing the beam height. However, the peak load under catenary mechanism was mainly determined by the reinforcement area in the section and was little affected by the sectional dimension. Increasing the reinforcement area in the beam could significantly increase the peak load under catenary mechanism.(5) The theoretical method was proposed to calculate the peak load under catenary mechanism of the edge area beam-slab substructure. The calculation method was validated by the test results which confirmed its good accuracy. The tie force method in the existing design guidelines was verified by the test results and its disadvantages were found. An improved tie force method was proposed in this paper and was validated by the test results. It was confirmed to be on the safe side, reliable, and to ensure a certain reserved capacity, which was suitable for engineering design. |
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