古代石塔地震安全性评价研究——以清净化城塔为例

本文采用反应谱分析法对西黄寺清净化城塔进行了地震安全性分析,找出其薄弱环节,得出对其结构抗震安全性评价有价值的结论。目前的反应谱分析多般基于线弹性应力应变模型,但结构一旦出现开裂,结构的应力应变关系将是非线形性的,若求解开裂结构的位移和应力,反应谱分析不再适用。但反应谱分析结果能够帮助分析人员找出结构的薄弱环节,判断结构在关键部位是否会出现裂缝以及其定性地判定裂缝开展的程度。从这个意义上讲,反应谱分析对结构的抗震分析具有重要的作用。     

Site Classification Using Horizontal-to-vertical Response Spectral Ratios and its Impact when Deriving Empirical Ground-motion Prediction Equations

We classify sites based on their predominant period computed using average horizontal-to-vertical (H/V) response spectral ratios and examine the impact of this classification scheme on empirical ground-motion models. One advantage of this classification is that deep geological profiles and high shear-wave velocities are mapped to the resonance frequency of the site. We apply this classification scheme to the database of Fukushima et al. [2003] Fukushima, Y., Berge-Thierry, C., Volant, P., Griot-Pommera, D. A. and Cotton, F. 2003. Attenuation relation for west Eurasia determined with recent near-fault records from California, Japan and Turkey. Journal of Earthquake Engineering, 7(3): 1–26.  [Google Scholar], for which stations were originally classified as simply rock or soil. The calculation of average H/V response spectral ratios permits the majority of sites in the database to be unambiguously classified. Soft soil conditions are clearly apparent using this technique. Ground-motion prediction equations are then computed using this alternative classification scheme. The aleatoric variability of these equations (measured by their standard deviations) is slightly lower than those derived using only soil and rock classes. However, perhaps more importantly, predicted response spectra are radically different to those predicted using the soil/rock classification. In addition, since the H/V response spectral ratios were used to classify stations the predicted spectra for different sites show clear separation. Thus, site classification using the predominant period appears to be partially mapped into the site coefficients of the ground-motion model.     

Seismic Fragility Curves for Un-Anchored On-Grade Steel Storage Tanks: Bayesian Approach

In this article, Bayesian approach is used for estimation of seismic fragility of un-anchored on‐grade steel storage tanks based on historical data and American Lifeline Alliance tanks database. The approach properly accounts for epistemic as well as aleatory uncertainties. The point and interval estimates of the fragility are formulated based on structural reliability method that implicitly or explicitly reflects the influence of epistemic uncertainty. The fragility curves developed herein are compared to corresponding relations currently available in the technical literature, the comparison suggest that actual tank performance is better than that predicted in the literature. Finally, application of fragilities in loss estimation methodology is investigated and showing a considerable scatter in the results corresponding to different fragilities.     

Modeling the Cyclic Flexural and Shear Response of the R. C. Hollow Box Columns of an Existing Viaduct

The cyclic response of R.C. hollow box columns, constructed as part of a typical single-column bent viaduct, built in the 1970’s in Central Europe, was studied both experimentally and analytically. Moderate displacement ductility capacity (between 3 and 4) was observed regardless of the column construction details, which are nowadays considered inappropriate for seismic regions. Standard analytical flexural models correlated with the experimental results quite well. Shear strength was estimated using the two methods included in the EC8 standards, as well as the method developed at the University of California, San Diego. Quite different results were obtained. The most accurate was the third method.     

Effect of Nonlinear Seismic Torsion on the Performance of Skewed Bridge Piers

This article presents an analytical investigation on the effect of seismic torsion on the performance of a skewed bridge. A nonlinear torsional hysteretic model developed by the authors is applied to idealize the torsional behavior of bridge piers. Deterioration of the torsional strength of piers due to combined flexure is considered and deterioration of flexural strength due to torsion is not taken into account. The effects of pounding between deck and abutments, cable restrainers, and damage of bearing supports are also included in analysis. It is found that the eccentric impact force due to lock of bearing movement results in extensive torsion in piers.     

Probabilistic Seismic Design of Pile Foundations in Non Liquefiable Soil by Response Spectrum Approach

The behavior of pile foundations in non liquefiable soil under seismic loading is considerably influenced by the variability in the soil and seismic design parameters. Hence, probabilistic models for the assessment of seismic pile design are necessary. Deformation of pile foundation in non liquefiable soil is dominated by inertial force from superstructure. The present study considers a pseudo-static approach based on code specified design response spectra. The response of the pile is determined by equivalent cantilever approach. The soil medium is modeled as a one-dimensional random field along the depth. The variability associated with undrained shear strength, design response spectrum ordinate, and superstructure mass is taken into consideration. Monte Carlo simulation technique is adopted to determine the probability of failure and reliability indices based on pile failure modes, namely exceedance of lateral displacement limit and moment capacity. A reliability-based design approach for the free head pile under seismic force is suggested that enables a rational choice of pile design parameters.     

Site Effects at Long Periods from Digital Strong Motion Records of the KiK-net,Japan

The high-quality digital records of the Japanese KiK-net were examined, with the aim of studying the influence of local site conditions on the displacement spectral ordinates at long periods. The attention was limited to those records for which the velocity profiles up to 100–200 m depth were known, and corresponding surface and borehole accelerograms were available. Based on the available records and with the support of 1D numerical simulations, different aspects that may have an influence on the amplification of long period spectral ordinates were studied, including the bedrock velocity profile, the site classification using V_s,30, and the earthquake magnitude.

Small amplification factors at long periods were found, ranging from 1 to 1.3, with median value from 1.05 to 1.1, for Eurocode 8 site classes B and C, respectively. Only for two records on soft soils (at the boundary between Eurocode 8 classes C and D), from small magnitude earthquakes, large amplification factors were obtained, up to about 4. A good correlation was found of the amplification levels with the response spectral ratio D(T₀)/D(10), where D(T₀) and D(10) are displacement spectral ordinates of the input signal at bedrock, at the fundamental period T₀ of the soil profile and at T = 10 s, respectively.     

One-Dimensional Ground Response as a Preliminary Tool For Dynamic Analyses in Geotechnical Earthquake Engineering

This article discusses how to calibrate some parameters of two-dimensional finite element models for numerical analyses in geotechnical earthquake engineering. The calibration was made through the simulation of the one-dimensional vertical propagation of S-waves in elastic layers, whose theoretical solutions are available in literature. The numerical results were compared with those obtained by frequency domain analyses. The influence of several sources of damping arising in the model, including that deriving from boundary conditions and numerical integration, was investigated. The proposed calibration procedure constitutes a useful preliminary step for performing advanced dynamic analyses of any geotechnical system.     

The Influence of Masonry Infill Walls in the Framework of the Performance-Based Design

In this article, a performance-based seismic design (PBD) methodology is proposed for the design of reinforced concrete buildings, taking into account the influence of infill walls. Two variants of the PBD framework are examined: The first is based on the non-linear static analysis procedure (NSP) while the second relies on the non-linear dynamic analysis procedure (NDP). Both design approaches are compared in the context of structural optimization with reference to the best possible design achieved for each case examined. Life-cycle cost analysis is considered a reliable tool for assessing the performance of structural systems and it is employed in this study for assessing the optimum designs obtained. The optimization part of the problem is performed with an Evolutionary Algorithm while three performance objectives are implemented in all formulations of the design procedures. The two most important findings can be summarized as follows: (i) if structural realization follows the design assumptions, then total expected life-cycle cost of the three type of structures, bare, fully infilled and open ground story, is almost the same and (ii) if an open ground story building is designed as bare or as fully infilled frame, real performance will be much worse than anticipated at the design stage.     

Neural Network-Based Damage Detection from Transfer Function Changes

This article puts forth the work on a neural network-based approach to determine the degree of damaged floors of the building considering changes in the transfer function. The transfer function is considered for that part of forced vibration in which system vibrates linearly after the structure has been damaged considering the building is instrumented during the earthquake. The results showed that accuracy of degree of damage detected increased with the increase in the number of combination of damages. The instrumentation of the first floor is expected to give best results for damage detection based on the transfer function-based approach.