Experiments and a reverse-curved compressive arch model for the progressive collapse resistance of reinforced concrete frames

Abstract

The compressive arch action (CAA) is a critical force-transfer mechanism to mitigate the vulnerability of progressive collapse for reinforced concrete frames. To deeply analyze the mechanical behavior of concrete beam-column sub-assemblages under a middle-column-removal scenario, the progressive collapse tests and numerical simulations were accomplished, in which the stress distribution and the force-flow characteristic under CAA were revealed. To accurately evaluate the peak capacity of CAA, a mechanical model of a reverse-curved compressive arch (RCCA) is put forward. The theoretical formulas are derived on the basis of the model, considering both the bending deformation and the axial deformation of the arch. The theoretical calculation results (including the peak capacities and the corresponding displacements) agree well with the experimental results of 20 specimens. Moreover, a parametric analysis on CAA peak capacity is investigated considering the following factors: the axial and rotational restraint stiffness of end supports, the initial connection gap of test setups, the depth-to-span ratio of beams, the concrete strength and the reinforcement ratio of beams. The research results demonstrate that the relative axial (rotational) restraint stiffness should not be less than 1 and the initial connection gap should be less than 1.0 mm to ensure sufficient boundary constraints. According to the parametric analysis results, a simplified formula for CAA peak capacity is established, in which multiple influence coefficients are proposed for the formula. The proposed formula is practical and simple to apply because no iteration or derivation is required, and good calculation accuracy is also verified by 20 specimens. Based on the formulas, the CAA capacities of different column-spacing concrete frames designed with various depth-to-span ratios of beams are compared with the necessary gravity loads. The research results show that the larger the depth-to-span ratio, the greater the bearing capacity margin.