Abstract:Many museum pieces are of cultural heritage and worthy of protection for their historical and artistic values.Because such relics are usually free-standing,they are easily damaged during earthquakes.For example,the 2008 Wenchuan earthquake in China led to substantial losses of property such that at least 216 museums were affected,and more than 3169 cultural relics were damaged.Slide motion is a typical seismic response mode of museum cultural relics;large slide sizes may cause relics to drop from their display stands and incur damage.Thus,it is important to study slide response of free-standing cultural relics under earthquake conditions and adopt aseismic measures for protection.In previous works,theoretical analyses were mainly used to study the slide responses of free-standing relics.Experimental studies were insufficient,and boundary conditions of showcases were seldom considered.To determine protection measures for movable cultural relics,slide responses of free-standing cultural museum relics under earthquake conditions are studied by considering various showcase boundary conditions.1：1 scale models were created on the basis of actual of a museum showcase sizes.A glass cultural relic was placed in the showcase by free-standing mode.The static friction coefficient between the relic bottom and its base was determined to be μ = 0.15 and the barycenter height values of the showcase and relic were calculated as 556 mm and 65 mm,respectively.To study seismic responses of the relic,acceleration sensors were set on the showcase bottom and relic top.In addition,a video admeasuring apparatus was used to capture displacement response values of the relic.Shaking table tests were conducted that considered two boundary conditions of the showcase bottom including fixed and free-standing status.Frequency distributions of the showcase under both boundary conditions were obtained by white noise excitation.Three different types of earthquake waves including those of El-Centro in 1940 and Taft and Artificial of Ⅱ site classification were applied to the models in east-west direction with intensities of PGA = 0.1g,0.2 g,0.4 g,and 0.7 g;time duration of 30 s;and time space of 0.02 s.Aseismic parameters such as displacement,acceleration,and dynamic magnification coefficients for both relic and showcase under the various boundary conditions were compared.Results show that under both showcase boundary conditions,relic sliding was minimal under small-intensity earthquake conditions,while the sliding was obvious under those of high intensity.For the duration of the tests,the relic slid under both showcase boundary conditions,and the showcase slid only under free-standing showcase boundary conditions.When earthquake intensity increased to certain degree,slide motion of the relic under fixed showcase boundary condition increased to a more significant degree than that under free-standing showcase boundary conditions.Regardless of showcase status,the prominent frequency factors were far greater than those of the input earthquake waves;thus,the showcase was not damaged significantly.The slide response for the relic under the free-standing showcase boundary condition was more significant under low-intensity earthquakes than that under fixed conditions and was significantly less when earthquake intensity increased,obviously due to friction between the showcase and shaking table.Thus,free-standing museum showcases are helpful for mitigating the slide response of cultural relic contained in them,provided that the distance between each showcase is sufficient to guarantee sliding motion during strong earthquakes.
