独立式石箍窑洞加固模型振动台试验研究

应用配筋砂浆带等加固技术对一缩尺比例为1/4的独立式石箍窑洞震损模型进行加固,并对其进行模拟地震振动台试验,以研究独立式石箍窑洞加固模型的动力响应与抗震性能。通过白噪声扫频得到该模型各阶段的自振频率和阻尼比等动力特性,并研究了模型结构的破坏特征、动力响应及其滞回耗能。试验研究结果表明:随着输入地震动峰值加速度的增加,模型结构的自振频率和刚度下降,阻尼比增大,加速度放大系数呈下降趋势;在水平X向(面阔方向)地震作用下,窑脸侧拱顶的加速度响应大于背墙侧拱顶,中孔拱顶的加速度响应大于边孔拱顶的,中拱拱脚的相对位移值始终大于边拱拱脚,甚至大于边拱拱顶;在峰值加速度为1.00g的地震激励后,窑顶、拱顶和拱脚的X向最大侧移角分别达到了1/29、1/229和1/201。模型虽局部破坏明显,但仍未出现整体倒塌趋势,表明本文提出的方法对独立式石箍窑洞的加固效果显著。

Seismic damage of mountain tunnels during the 5.12 Wenchuan earthquake

A number of mountain tunnels suffered significant damage to various extent during the 2008 Wenchuan earthquake in China.Damage ranging from small to heavy cracking was observed both at the portal and inside the tunnels,while some sections close to the faults completely collapsed.A summary of qualitative data collected from reports and papers is presented regarding the behavior of the 55 mountain tunnels near the epicenter during the earthquake.Based on the seismic investigation and data collection of mountain tunnels,the tunnel damage is classified into six most common damage models involving cracking,spalling,shear failure,dislocation,pavement uplift and collapse.Detailed study and discussion are then carried out on the damage models.In order to examine the influencing factors of the damage magnitude of the mountain tunnels,the correlations between epicentral distance,earthquake intensity,overburden depth,geological condition and damage levels are analyzed.The relationships between earthquake parameters and different damagemodels are developed and discussed.Also,suggestions are provided to improve the seismic resistance of mountain tunnels.

Dynamic failure mode and energy-based identification method for a counter-bedding rock slope with weak intercalated layers

The dynamic failure mode and energybased identification method for a counter-bedding rock slope with weak intercalated layers are discussed in this paper using large scale shaking table test and the Hilbert-Huang Transform(HHT) marginal spectrum.The results show that variations in the peak values of marginal spectra can clearly indicate the process of dynamic damage development inside the model slope.The identification results of marginal spectra closely coincide with the monitoring results of slope face displacement in the test.When subjected to the earthquake excitation with 0.1 g and 0.2 g amplitudes,no seismic damage is observed in the model slope,while the peak values of marginal spectra increase linearly with increasing slope height.In the case of 0.3 g seismic excitation,dynamic damage occurs near the slope crest and some rock blocks fall off the slope crest.When the seismic excitation reaches 0.4 g,the dynamic damage inside the model slope extends to the part with relative height of 0.295-0.6,and minor horizontal cracks occur in the middle part of the model slope.When the seismic excitation reaches 0.6 g,the damage further extends to the slope toe,and the damage inside the model slope extends to the part with relative height below 0.295,and the upper part(near the relative height of 0.8) slides outwards.Longitudinal fissures appear in the slope face,which connect with horizontal cracks,the weak intercalated layers at middle slope height are extruded out and the slope crest breaks up.The marginal spectrum identification results demonstrate that the dynamic damage near the slope face is minor as compared with that inside the model slope.The dynamic failure mode of counter-bedding rock slope with weak intercalated layers is extrusion and sliding at the middle rock strata.The research results of this paper are meaningful for the further understanding of the dynamic failure mode of counter-bedding rock slope with weak intercalated layers.

Study on the Uncertainty of Earthquake Damage Prediction Based on Damage Indices for RC Structures

Seismic damage indices of structure are widely used to quantificationally analyze structural damage levels under earthquake action. In this paper, a five-storey building model and a seventeen-storey building model are established. According to seven typical indices and different earthquake-inputs, a structural damage prediction is performed, with the results showing serious uncertainty of structural damage prediction due to different indices. Understanding of this phenomenon aids the comprehension and application of the results of earthquake damage prediction.

Safety evaluation of Dagangshan arch dam resisting strong earthquakes with a rate-dependency anisotropic damage model

This paper presents a model to simulate the safe behavior of Dagangshan arch dam with a rate-dependency anisotropic damage model. This model considers the damage of asymmetry and anisotropy under cyclic loading of tension and compression, and it is used in the compiled finite element code. The material parameters used in the model can be identified from uniaxial static and dynamic experiments. Thereafter, it is used for analyzing damage and failure patterns of the dam subjected to water pressure and strong earthquakes. The numerical results show that it is necessary to consider both asymmetry between tension and compression and anisotropy of damage. Severe damage regions of the dam reveal brittle and risky positions clearly. Meanwhile damage patterns show the failure trend and safety behaviors of the dam. These results match well with that of the experiments carried out in DUT. The proposed model may be used to predict the damage patterns and potential failure modes of concrete structures like the dam. And the aseismic performance of the dam can be figured out.

Damage-induced material softening and its effect on seismic performance of steel structures

A numerical approach for simulating the seismic performance of steel truss structures, considering damage-induced material softening, is developed based on a ductile damage constitutive model by applying the backward Euler explicit algorithm. It is implemented in ABAQUS through a user-defined material subroutine, by which damage evolution could be incorporated into the analysis of seismic performance of steel structures. The case study taken up here is the investigation of a steel connection with a reduced beam section(RBS) and a steel frame with such connections. The material softening effect during the failure process is particularly investigated. The results show that material softening in the vulnerable zone has a significant effect on the distribution of stress and strain fields, as well as on the carrying capacity of the steel connection with RBS. Further, material softening is found to have almost negligible effect on the seismic performance of the steel frame in the early stages of the loading process, but has a large effect when the steel frame is about to fail. These findings offer a practical reference for the assessment of seismic structural failure, and help in understanding the damage mechanism of steel structures under seismic loading.