In order to propose more effective safety control indexes for anti-rock and anti-overturning of cultural relics in freestanding collections with large aspect ratios, shake table tests were carried out on freestanding ceramic vases and the critical conditions for rocking of freestanding cultural relics were obtained. The refined finite element models of cuboid and cylindrical hollow vases were established and validated by experiments. The numerical analysis were carried out by using the validated finite element model, and the critical values of peak accelerations corresponding to the initial rocking and overturning of freestanding cultural relics were obtained. Based on the theoretical derivation of the energy balance equation and fitting with experimental data, the safety criterion of ‘double-level’ freestanding cultural relics was put forward, which takes peak ground acceleration and peak ground velocity as safety control index respectively. The results show that the conditions for starting rocking of freestanding cultural relics do not depend on the spectral characteristics of seismic waves or the shape of the relic bottom surface, but the conditions for overturning are related to them. The peak ground acceleration cannot be used as a necessary and sufficient condition to judge whether the freestanding system is overturned or not. Especially for high-frequency excitation, the safety index controlled by peak ground acceleration is often too conservative.Based on the verification of the example, the proposed criterion of peak ground velocity and peak ground acceleration is found to be applicable and reliable.

To assess the seismic overturning risk of the freestanding museum collection, the freestanding collection and showcase are regarded as double freestanding regular blocks, and the propagation process of seismic actions in the museum building-showcase-artifact system is analyzed by using the split modeling method. Through the finite element calculation, the rocking response of freestanding museum collections with different width-to-height ratios under the unidirectional seismic action is investigated, and the seismic overturning fragility analysis of freestanding museum collections is carried out based on incremental dynamic analysis. Further, two methods are proposed to assess the seismic overturning risk of freestanding collections, one is to convolve the seismic overturning fragility curve of freestanding collections with the site hazard curve to calculate the seismic overturning risk, and the other is to assess the seismic overturning risk of artifacts based on dynamic amplification analysis. The two methods are also used to conduct the risk assessment of a freestanding pot housed in a museum to further illustrate and compare the two assessment methods. The results show that when the size of the showcase is certain, the greater the possibility of overturning during the earthquakes, and the greater the seismic risk. The two assessment methods proposed in this paper can effectively assess the overturning risk of freestanding museum collections under earthquakes, among which the risk assessment method based on fragility analysis can accurately calculate the seismic risk value of collections, while the assessment method based on dynamic amplification analysis is more convenient and easier for museum staff to use.

In order to obtain more data about seismic failure of museum artifacts and provide suggestions for scientifically performing seismic protection of museum artifacts, the shake table tests of a system comprised of artifacts in showcases within a full-scale three-story one-bay frame structure model were conducted. The seismic response of the system and the failure modes of the artifacts were investigated. The three-story reinforced concrete frame structure model was represented as the museum structure. There were six showcases and 23 freestanding and restrained artifact specimens inside the structure. Six earthquake records were selected with the peak ground acceleration (PGA) values scaled from 0.1g to 0.62g in 15 loading cases. The acceleration time histories of floor and showcase platform, the sliding displacement time histories of the freestanding glass blocks and ceramic pen containers on different floors and in different showcases, the rocking angle time histories of freestanding vases with different shapes, and the motion modes of medium-sized vases tied by fishing lines and restrained large-sized vases on different floors were recorded. The conclusions are drawn that the amplification factor, which is the ratio of the peak floor acceleration (PFA) to the PGA, ranges from 0.92 to 2.15 at the second-floor level, and it ranges from 1.28 to 3.93 at the third-floor level. The amplification factor has the smallest value in the case when the longitudinal reinforcing steels in the columns begin yielding. The amplification factor which is the ratio of the peak showcase platform acceleration to the PFA ranges from 0.82 to 1.98. The peak sliding displacement of the glass block on the sand paper on the third floor is 103 mm at the PGA level of 0.62g, while it is only 17 mm for the ceramic pen container on the polymethyl methacrylate board. The freestanding vase of white gourd-shape on the platform of the shake table is static at PGA=0.4g while overturns at PGA=0.31g. Overturning of the vase does not necessarily occur with the increase of the PGA due to the roughness of the bottom of the vase. The vases remain static or overturn immediately after rocking occurs during most earthquakes. The fasteners with the same shape as the bottom of the vase are not effective for controlling the rocking response of the large-sized vase on the third floor under the extremely rare earthquake. Restriction objects combined with fishing lines can control the motion response of the medium-sized vase well.

To study the seismic fixation effect of the tie up method on the museum collections and carry out the optimization analysis, the three large-size typical earthquake-vulnerable cultural relic replicas with the same type and different large sizes (height of 390 mm, 490 mm and 620 mm, respectively) were selected. The shaking table tests of the seismic system of cultural relic replicas fixed by fishing lines were carried out to obtain the key shape parameters affecting their motion states as well as the interaction between cultural relic replicas and fishing lines. The seismic fixation effect of using independent fishing line tie up method to fix cultural relics with larger sizes was verified. The corresponding finite element analysis models were established. Then the ergodic parameter analyses of the seismic system of cultural relic replicas fixed by fishing lines were carried out to obtain the size parameter limits in the case of using independent common fishing lines which effectively fixed cultural relics under earthquake action and the minimum required cross-sectional areas of fishing lines for cultural relics with different sizes which were effectively fixed. The results show that through appropriately increasing the initial pretension stress, the number and the cross-sectional area of fishing lines, the seismic responses of cultural relics and the variation range of internal force of the fishing lines are effectively reduced and the size parameter limits in the case of using independent fishing lines to effectively fix cultural relics are increased. In the case of fixing cultural relics by the independent fishing line tie up method, the larger the ratio of center height to bottom diameter of the cultural relics, the more obvious overall rocking responses of cultural relics are observed. The larger the body size and mass and the bottom diameter, the more significant overall sliding responses of cultural relics are observed. Comprehensively studying the fixation effect and the interaction between cultural relics and fishing lines, it is recommended to select a fishing line with a reasonable cross-sectional area and a 20% breaking stress as the initial pretension stress. For cultural relics that are not suitable for the independent fishing line tie up method, a combined fixation measure of fishing lines and fasteners can be used to reduce the dynamic responses of cultural relics and the variation of internal force of the fishing line.

After hundreds of years of deterioration and damage caused by environmental factors, most brick and stone cultural relics have potential safety problems. There are many contradictions that are difficult to coordinate between the measures to improve the safety of structures commonly used in engineering provided by the current national codes and the principles for the protection of cultural relics. For new measures, there is a lack of analysis and evaluation methods for their effectiveness in improving safety and stability performance of historical buildings. Taking Phase 1 of Tsinghua Universitys old library as an example, the repair measures of additional internal steel frames and external cables are proposed. The newly added structures basically do not invade the building body, do not change the force transmission path of the original structure, and basically achieve the cultural relic protection principle of not changing the original state, minimum intervention, and reversible measures. The analysis results of bearing capacity in normal use limit state show that after performance improvement measures are taken, with the gradual deterioration of the original structural materials, the bearing capacity of the original structure is reduced, and the load will be gradually transferred to the new structure. A mechanical model of the discrete structure is established to adapt to the interface between cultural relics and building materials. Under the 8-degree rare earthquake effects, the maximum inter-story displacement ratio of each part of the main structure is less than 1/100. The new structure has greatly improved the seismic performance and achieved the goal of structural stability to prevent earthquake collapse.

Aiming at the structures composed of brick walls (columns) and wooden roof trusses commonly used in ancient masonry buildings, considering a cultural relics exhibition hall as an example, a discrete body analytical model that conforms to the characteristics of ancient building materials and the structural mechanism is established. Four different masonry construction methods are selected to study the damage initiation and failure mechanism of ancient masonry buildings. The static pushover analysis is carried out for the brick column-wooden roof truss structure with different aspect ratios and different friction coefficients, and the whole process load-displacement curve of ancient buildings under different working conditions is obtained. This research is focused on comparing the instability process of masonry ancient buildings from yield damage to critical failure and the corresponding performance points in the whole process performance curve. It is found that the peak vertical displacement ratio of the column is the critical instability point of the structure. The method for determining the corresponding performance points of the stability performance indicators is studied. The displacement ratio limits without obvious damage to the structure are 1/240-1/200, 1/290-1/250, 1/340-1/300, respectively when the height-to-width ratios of the brick column are 8, 10, and greater than 12. The limits of lateral displacement ratio in the static stable state of the structure are taken as 1/40, 1/70, 1/100, respectively.