Study On Torsional Response Analysis And Torsion Resistance Design Method Of Building Structures Under Earthquake Action

Torsional response of aseismic structures, especially irregular layout structures, will aggravate structural damage during earthquakes. It is important to take some practical and reasonable design measures to control its effects. Recently, considerable research has been done in this topic, some specific requirements and control measures about torsional design of structures have been proposed, and some corresponding achievements have been presented in seismic codes in many countries which specify requirements and corresponding measures. However, these researches are majorly limited to one-storey simplified-elastic models or elastic-plastic story-shearing-beam models, and a systematic study on the laws of elastic-plastic torsional response of multistory structures is urgently required since the story-shearing-beam models can not reveal the true feature of structural response; a considerable difference exists in the seismic codes of various countries, which implies that we have not got a common review on this issue; the torsion control indices specified in Chinese seismic code has arisen some difficulties and arguments in engineering design, the reasonableness and effectiveness of these indices are to be investigated further; the ideas and practices about torsion analysis and design in present codes are mainly based on several elastic control indices and lack of systematicness. Aiming at the problems mentioned above, the paper firstly studies the laws of torsion response in single- and multi-story frame or frame-shear wall structures based on the fine elastic-plastic dynamic analysis using fiber model, then investigates the effectiveness of the torsion control indices and its effectiveness in controlling elastic-plastic torsional response. Finally, some recommendations for structural torsion analysis and design are suggested.The main research contents finished in this thesis and main conclusions are summarizes as follows:①Methods for structural torsion control and design in seismic codes of various countries are compared and reviewed.②Laws of elastic and elastic-plastic torsion response in single- and multi-story structures are complemented and improved.Elastic torsional response rules for one-storey or multi-storey structures are studied based on simplified dynamic analysis model, the effects of bi-directional seismic action on one-way or two-way eccentric structures are investigated and the relationship between torsional control indices are discussed; based on finite element analysis, the laws of elastic torsional response for multistory structures with uniform eccentricity, nonuniform mass eccentricity and nonuniform stiffness eccentricity are also studied.Based on fine fiber model, the rules of elastic-plastic torsion response for single- and multi-story frame structures and high-rise frame-shear wall structures are analyzed. It is concluded that the elastic-plastic torsion response of eccentric structures are mainly influenced by capacity design measures, eccentric ratio, intensity of ground motion, and strength eccentricity. Capacity design measures such as"strong-column-weak-beam"for frame structures and the bending and shear capability strengthening for frame-shear wall structures specified in current codes, are not always able to achieve the desired effects during strong earthquakes. When column hinges are predominant, rules of torsion response for mass- and stiffness-eccentricity structures are quite different. The optimal strength eccentricity is also purposely proposed to control the elastic-plastic torsion effect, since strength eccentricity has considerable influence on elastic-plastic torsion response.③Reasonableness and effectiveness of elastic torsion control indices are studies. By using elastic-plastic time history analysis based on fine fiber model, effectiveness of elastic torsion control indices to control the elastic-plastic torsion response of frame structures, which are designed according to current seismic code with various torsional period ratios and displacement ratios, are surveyed. It is shown that torsional period ratio may arise some unreasonable phenomena in the structure design and it cannot control the elastic-plastic torsion response in an effective manner, though it is a key step in concept design in the sense of strengthening the torsional stiffness of structures. Also, considering the relative provisions specified in the seismic codes of other countries, it is suggested that the limitation value of coupled torsional period ratio is to be cancelled or relaxed. As for torsional displacement ratio, it is a universal control index which must be controlled in design. Torsional displacement ratio is suggested to be calculated according to the displacement at the midpoint of plane view of structure. When the translation of structure is relatively small, the limitation value of torsional displacement ratio can be properly relaxed according to the seismic fortification intensity and measures, since torsional displacement ratio is a relative quantity which cannot quantitively indicate the real value of torsional angle under various translation of structures.④Various torsion analysis methods are surveyed.The effects of accidental eccentricity, bi-directional input, and infill wall on structural torsional response are investigated. Besides those required in current seismic code, above effects should be considered when it is computationally and conditionally allowed. Applicability of the static nonlinear analysis method, equivalent static method and amplifying factor of fringe frames is analyzed.⑤Torsional strengthening measures are suggested.Applicability of measures such as the strengthening of fringe frames, adjustment of the strength centre, control of axial force ratio, and torsion capacity check of member is explored, and some recommendations are provided.