Preliminary Study On Seismic Performance Of Reinforced Concrete Frame Structures With Haunch Braces

Reinforced concrete (RC) frame structures with haunch braces, a new type of building structures, possesses better mechanical behavior and its typical characteristics are as follows: 1) the setting of bracing changes mechanical patterns for ordinary RC frame structures, making intersections of frame beam and bracing as well as intersections of frame column and bracing the crucial sections for the end of beam and column, 2) the setting of bracing reduces the span of long-span frame beam resulting in evident decrease of bending moment and shear in frame beam end, middle span as well as the top of columns so as to improve mechanical behavior of joint regions and decrease frame beam section dimensions and reinforcing bars simultaneously. Although reinforced concrete frame structures with haunch braces have bright potential of development and application, the seismic research on frame structures with haunch braces has been seldomly seen.This dissertation carries out exploratory preliminary study in terms of several critical problems that RC frame structures with haunch braces urgently settle for application and spreading in the earthquake zones, and mainly develops the following works using numerical simulation analyses:(1) Optimization of the setting location for bracing. Bracing is the precondition of normal work in this new type of structures, however, different bracing locations significantly affect structural mechanical behavior under vertical loading. Hence, according to the best optimization principle of internal forces at the structural members'controlled section, comparing and analyzing the effect of location change for bracing on frame force distribution by using SAP2000 to establish corresponding trussing model of frame with braces, a famed structural design & analyses software, is performed to find out rational setting location ranges for bracing at length.(2) Analyses on seismic response of strong column factor for RC frame structures with haunch braces. By simulating test of sub-assemblages in RC frame structures employing nonlinear finite element method, the influencing factors of the structural real strong column factor, such as material nonlinear property, axial compression ratio, participation of slab, are analyzed. The failure probability of"strong-column, weak-beam"design for single joint of RC frame structures with haunch braces is analyzed using reliability theory. Monte Carlo Simulation is performed to evaluate the probability of seismic displacement demand exceeding displacement capacity for a certain storey and the entire building for column sidesway mechanism.(3) By comparsion with seismic response of RC frame structures with haunch braces under horizontal earthquake, the effect of vertical earthquake on structural seismic performance is analyzed. In addition, this chapter summarizes seismic response laws, distribution characteristics of internal forces as well as the plastic-hinge development trend for frame structures with haunch braces subjected to earthquake and so forth, important parameters concerning seismic performance for structures.By research on three aspects as listed above, some key conclusions are made as follows:①the location of bracing significantly affects force distribution for RC frame structures with haunch braces under vertical loading, practical engineering design is suitable for adopting the following two parameters to determine the setting location of bracing: the inner angleαof bracing and beam should vary from 30°to 50°and the distance L1 from intersection of bracing and beam to beam end should vary from L/10～L/6 (L defines as nominal calculation span of framed beam),②with respect to frame structures with haunch braces, the reasonable strong column factor, around 2.8, is to avoid"column hinge sidesway mechanism"occurring, however, the values of strong column factor specified by current building seismic code in the country are lacking,③vertical earthquake actions have a significant effect on the maximum bending moment for middle span of frame beam, the maximum axial compressive force for frame columns as well as the effect of controlling plastic-hinge mechanism of structures, and then proper considerations should be given when the design for practical engineering to guarantee the sufficient safety for structures.