双向地震下博物馆滑移型文物的易损性评估

Fragility evaluation of sliding artifacts in the museum under bidirectional seismic excitation

为科学开展博物馆滑移型文物的防震预防性保护工作,亟需对其地震风险进行量化评估。为解决风险评估的核心问题,提出了双水平向地震作用下博物馆滑移型文物的易损性评估方法,主要步骤为:考虑结构及浮放界面摩擦行为的非线性,构建博物馆-展柜-文物系统三维非线性有限元模型;将双向谱加速度和文物滑移量的最大均方根值分别作为地震动强度指标和工程需求参数,开展增量动力分析;建立文物滑移的概率地震需求模型及易损性函数。开展了代表典型滑移型文物的浮放物体在双向地震激励下的振动台试验,并结合单向地震激励下的理论滑移运动方程,对模拟滑移的有限元模型的正确性进行了验证;对所采用的地震动强度指标的有效性和充分性进行了检验,分析了固定和浮放展柜、所处楼层、滑移限值、单向和双向地震作用、基础隔震等因素对某四层框架结构博物馆中滑移型文物易损性的影响。结果表明:对于隔震结构及滑移限值取较小值时的非隔震结构,文物的滑移易损性对所处楼层不敏感,而对于滑移限值取较大值时的非隔震结构,则随楼层的升高而增大;非隔震结构内部浮放展柜中文物的滑移易损性低于固定展柜的情况,而隔震结构内部浮放和固定展柜中文物的滑移易损性十分接近;双向地震作用下文物的滑移易损性大于单向地震作用。

In order to perform seismic protection for museum collections with potential sliding failure scientifically,seismic risk assessment is necessary.As a main concern in risk assessment,a fragility assessment method for sliding artifacts in the museum subjected to bidirectional seismic excitation was proposed.The main steps are as follows:considering the nonlinear behavior of the structure and the interface between the artifact and the base,a three-dimensional nonlinear finite element model of the museum-showcase-artifact system was developed.The maximum values of the square root of sum of squares of the acceleration response spectral values and sliding displacements in the two horizontal directions were used as the intensity measurement and engineering demand parameter,respectively.Incremental dynamic analysis was performed,and then the probabilistic seismic demand model and fragility function for sliding of artifacts were developed.Shake table tests for a freestanding object representing a typical sliding artifact subjected to bidirectional seismic excitation were performed.The accuracy of the finite element model for simulation of sliding artifacts was examined by comparison with the theoretical sliding motion equation in the case of unidirectional seismic excitation and the shake table tests in the case of bidirectional seismic excitation.The efficiency and sufficiency of the intensity measurement were checked.Effects of freestanding and restrained showcases,floor level,sliding limit,unidirectional and bidirectional seismic excitation,and base isolation on fragility of sliding artifacts in a four-story museum of frame structure were investigated.Results show that the sliding fragility of the artifact is not sensitive to which floor it locates in the case of base-isolated structure and also in the case of ordinary structure with small sliding limits.On the other hand,the sliding fragility of the artifact increases as the floor level goes higher.Moreover,the sliding fragility of the artifact in the freestanding showcase is lower than that in the restrained showcase within the ordinary structure,while the sliding fragility of the artifacts in the freestanding and restrained showcases within the base-isolated structure is similar.Furthermore,the sliding fragility of the artifact under bidirectional seismic excitation is higher than that under unidirectional seismic excitation.