Study On Infill Wall Function And Strong Beam-Weak Column Damage For Frame Structures

'Strong column and weak beam' is one of fundamental design principlesfor earthquake-resistant structures. It is expected that seismic energy isdissipated by the damage of beams prior to columns, thus structures cannot gofar as to collapse in strong earthquake. However, investigations of earthquakedamage have shown that more RC structures are damaged in 'strong columnand weak beam' pattern, rather than 'strong beam and weak column' pattern.The formation of 'strong column and weak beam' pattern is influencedby many factors, mainly as follows: the contribution of floors, the influence ofinfill walls, the strong beams and overreinforced beams, etc. Moreover, infillwalls are usually treated as non-structural components in seismic design, notinvolved in the seismic analysis However, a large number of earthquakedamage of structures have reveals that the contribution of infill walls cannotbe ignored for seismic performance of structures.In this paper, the influences of infill walls and the mechanism of 'strongbeam and weak column' pattern are studied, and the main work and results areas follows:1. Infill walls play an important role in energy dissipation and theredistribution of internal force for frame structures. Many time historyresponses of infill wall frame and bare frame structures are analyzed underfrequent and rare earthquake excitation. In light of energy dissipationmechanism analysis, it shows that infill wall is the main non-elastic energydissipative component for the frame structure; And the interaction betweeninfill walls and frame structure results in the redistribution of the internalforce in frame structures, namely, the distributed moment and axial force ofthe column increased, which is responsible for the estimation deviation of theinternal of force columns in structure design.2. The deviation of the analysis model is one of the causes for the 'strongbeam and weak column' pattern. Combined with the fine finite element model,the sources of the deviation of the simplified finite element model, which iswidely used nowadays, are analyzed. Meanwhile, through the internal forcedistribution comparison between the two models under different loads, it isrevealed that the contribution of floor slab is fully considered in the simplifiedfinite element model, thus the bearing moment of the columns is underestimated, leading to the columns damage prior to beams in earthquakes.3. The girder-slab coupled shells model is proposed. To improve thesimplified finite element model, which underestimates the contribution of thefloor slab, and the girder-slab coupled shells model are proposed based on thegirder-slab coupled rigid arm model. By comparing the internal forcedistribution under different loads, it is demonstrated that the new model ismore accurate than the simplified finite element model; moreover, with thesame computational accuracy requirement, the new model is more efficientthan the girder-slab coupled rigid arm model.4. The floor slab can significantly improve the bearing negative momentof beam ends, and promote the 'strong column and weak beam'. Bysimplifying both beam and slab into T-shape beams with different effectiveflange width, with the static and dynamic analysis of the two T-shape beams,the influence of different effective width on the bearing moment of beam andyield mechanism is discussed, and the participating ratio of steel bars in slabis an important parameter. With energy dissipation mechanism analysis, itfurther indicate that columns have become the main energy dissipativecomponents due to the contribution of floor, therefore, the column usuallydamage more severely in earthquakes.