双向地震作用下面向群体建筑的地震脆弱性评估方法研究OA

Seismic fragility assessment is a fundamental tool for quantifying the probabilistic distribution of building damage under earthquake excitation and plays an important role in urban seismic risk mitigation and re-silience assessment.With rapid urbanization,modern cities are characterized by dense building clusters com-posed of structures with diverse structural systems,construction periods,and seismic design levels.However,most existing simulation-based fragility assessment methods are primarily developed for individual buildings and are often limited to unidirectional ground motion input.Such simplifications restrict their applicability to regional-scale building portfolios and may underestimate structural vulnerability when bidirectional seismic ef-fects and directional coupling become significant.To address these limitations,a seismic fragility assessment framework is proposed in this study for building portfolios subjected to bidirectional earthquake ground motions.The framework aims to balance physical realism,computational efficiency,and practical applicability,enabling large-scale fragility analysis under limited structural information.A multi-degree-of-freedom(MDOF)bidirec-tional shear-building model is developed based on the bidirectional Bouc-Wen-Baber-Noori(BWBN)hys-teretic formulation.Compared with conventional piecewise-linear unidirectional macro-hysteretic models,the proposed model provides a smooth and unified representation of nonlinear restoring forces and captures key non-linear behaviors observed under strong earthquakes,including strength degradation,stiffness degradation,pinch-ing effects,and bidirectional coupling of restoring forces.By introducing coupling terms between orthogonal hor-izontal directions,the model naturally accounts for interaction effects induced by bidirectional ground motion input.To facilitate large-scale implementation,a hierarchical parameter calibration strategy is introduced.Model parameters are divided into two categories according to their physical significance.The first category includes pa-rameters governing fundamental dynamic characteristics,such as floor mass and initial lateral stiffness,which are determined from readily available building attributes(e.g.,structural type,building height,and construction pe-riod)and calibrated to match target dynamic properties such as the fundamental natural period.The second cate-gory consists of dimensionless hysteretic parameters controlling nonlinear degradation,pinching behavior,and en-ergy dissipation capacity.A building classification scheme considering structural type,number of stories,and seismic design level is proposed to enable rapid parameter assignment and consistent model generation for build-ing portfolios.The proposed methodology is demonstrated through seismic fragility analyses of three representa-tive buildings in Shanghai,including reinforced concrete,steel,and masonry structures constructed in different periods.Ten pairs of bidirectional earthquake ground motions are selected and scaled to a uniform peak ground acceleration.Nonlinear time-history analyses are conducted using the Newmark-β method,with the maximum interstory drift ratio adopted as the damage index,and fragility curves are derived for multiple damage states.The results reveal clear directional differences in damage demand under bidirectional excitation.In several cases,the critical damage state in one direction is governed by a different ground motion component than in the orthogo-nal direction,highlighting the importance of directional effects.Comparisons with unidirectional input scenarios show that neglecting bidirectional ground motion may significantly underestimate seismic fragility,particularly for structures with limited hysteretic energy dissipation capacity.Overall,the proposed bidirectional MDOF shear-building framework provides an efficient and scalable tool for regional seismic fragility assessment of build-ing portfolios.By integrating bidirectional hysteretic modeling with a practical parameter calibration strategy,the method improves both computational efficiency and result interpretability,offering a promising approach for urban-scale seismic risk analysis,loss estimation,and emergency management applications.