Research On Impact Behavior Of Reinforced Concrete Frames In Progressive Collapse Under Severe Ground Motions

The principle of "standing upright in severe earthquake" in current seismic design demands is to require the structure under severe earthquake can maintain the overall stability and guarantee the safety of personnel in the building. In the concrete design practice, this principle is achieved by checking the plastic deformation of the weak layer. However, such design practice is so rough that it covers the complex mechanical behavior of the actual structural components under strong earthquakes. Moreover the practical critical collapsed state of the elements of the structure is not clearly defined. The key to establish a design methodology to resist progressive collapse, which is more scientific and reasonable, is to describe the mechanical behavior of the whole process of structure exactly, especially those core and difficult problems, such as contact-impact analysis.In this paper, the whole process of progressive collapse due to partial collapse and impact is studied based on progressive collapse analysis and structural impact analysis. The impact mechanism is also established by the means of theoretical analysis and conceptual modeling. It provides theoretical support for impact simulation and post-processing of OpenSees.Firstly, the failure and internal forces redistribution analysis and progressive collapse analysis of reinforced concrete frame under severe ground motions are carried out. The process of load redistribution, the P-Delta effect and the shock effect of superstructure to substructure are analyzed emphatically.Secondly, a Hertz-damp model is choosed to establish the impact mechanics model of the beam-to-beam impact, which includes:describing the initial motion states of failed components; describing the motion locus of failed components; establishing beam-to-beam impact mechanics model; describing the force and motion states of active and passive impact components; describing the motion states of the main structure. Thirdly, the impact mechanics models of floor-to-floor impact because of column hinges, floor-to-floor impact because of vertical dropping floor and partial collapse impact are established, and the contact force is given by Hertz-damp model too.Once the equations of motion of active impact body and passive impact body are established, their displacement can be expressed by Duhamel-integration, and the impact response, including the time curves of compression, the time curves of impact force and the relationship curves between Hertz-damp impact force and displacement, can be obtained through numerical methods by MATLAB with Hertz-damp impact force.