How to obtain earthquake ground motions for engineering design

The earthquake ground motions that ultimately are selected for engineering design depend chiefly on the criticality of a site or structure and the engineering analyses that are to be performed. Several key steps are necessary in this selection process: They are (1) a reconnaissance to understand the hazards and obtain preliminary earthquake ground motions; (2) decisions on the application of deterministic or probabilistic methods; (3) selection of appropriate motions for requirements in design; (4) consideration of thresholds at which motions become significant for engineering; and (5) decisions on specifying appropriate earthquake ground motions for sizes of earthquakes, distances from sources, the structures, sites, and testing to be done. This paper presents five tables that show steps for evaluating these factors and for enabling the investigator to specify earthquake ground motions appropriate for engineering design.     

考虑散射效应沉积河谷空间相关多点地震动模拟

提出了一种考虑地震波散射效应的沉积河谷空间相关多点地震动模拟方法。基于弹性波传播理论,采用合理功率谱、相干函数和传递函数模型,借助原型谱表示法得到沉积河谷空间相关多点地震动,并验证了方法的可行性。其中,传递函数应用动力边界元法计算,可在很宽的频带内精细模拟沉积河谷中波型转换及聚焦效应。针对常见V型河谷开展了计算模拟,结果表明,河谷地形及松软沉积层对地震波传播具有显著影响,河谷地表地震动空间差异性十分显著,一维模型难以考虑地震波的散射及聚焦效应,从而会明显低估沉积内部部分区域的地震动峰值加速度。沉积河谷中大跨结构抗震设计宜采用考虑地震波散射效应的空间相关多点地震动输入。     

Shaking table tests on slope reinforced by anchored piles under random earthquake ground motions

Acta Geotechnica - Many studies have reported that the seismic responses of slopes and retaining structures are notably different under the effect of multiple seismic waves. Previous experimental...     

Geologic site conditions and site coefficients for estimating earthquake ground motions in the inland areas of Korea

Site characterization and site-specific ground response analyses were conducted at two representative inland areas in Korea. In situ tests included 25 boring investigations, 7 crosshole tests, 18 downhole tests and 41 SASW tests, and in the laboratory, resonant column tests were performed. The soil deposits in Korea, which were shallower and stiffer than those in the western US, were examined. The fundamental site periods were distributed in the narrow band ranging from 0.1 to 0.4 s. Most sites were designated as site classes C and D based on the mean shear wave velocity of the upper 30 m from the current Korean seismic design guide. Based on the ratio of the acceleration response spectra of ground surface to rock-outcrop, short-period (0.1–0.5 s) site coefficient, F_a ranged from 1.0 to 2.7, and mid-period (0.4–2.0 s) site coefficient, F_v ranged from 1.0 to 1.6, regardless of the input rock outcrop acceleration levels of 0.05 and 0.14 g. The site coefficients specified in the Korean seismic design guide, which is similar to NEHRP provisions and UBC, underestimate the ground motion in the short-period band and overestimate the ground motion in the mid-period band. These differences can be explained by the differences in the depth to bedrock and the soil stiffness profile between Korea and western US. Also, the site coefficients should be re-evaluated accounting for the local geologic conditions on the Korean peninsula.     

Geologic site conditions and site coefficients for estimating earthquake ground motions in the inland areas of Korea

Site characterization and site-specific ground response analyses were conducted at two representative inland areas in Korea. In situ tests included 25 boring investigations, 7 crosshole tests, 18 downhole tests and 41 SASW tests, and in the laboratory, resonant column tests were performed. The soil deposits in Korea, which were shallower and stiffer than those in the western US, were examined. The fundamental site periods were distributed in the narrow band ranging from 0.1 to 0.4 s. Most sites were designated as site classes C and D based on the mean shear wave velocity of the upper 30 m from the current Korean seismic design guide. Based on the ratio of the acceleration response spectra of ground surface to rock-outcrop, short-period (0.1–0.5 s) site coefficient, F_a ranged from 1.0 to 2.7, and mid-period (0.4–2.0 s) site coefficient, F_v ranged from 1.0 to 1.6, regardless of the input rock outcrop acceleration levels of 0.05 and 0.14 g. The site coefficients specified in the Korean seismic design guide, which is similar to NEHRP provisions and UBC, underestimate the ground motion in the short-period band and overestimate the ground motion in the mid-period band. These differences can be explained by the differences in the depth to bedrock and the soil stiffness profile between Korea and western US. Also, the site coefficients should be re-evaluated accounting for the local geologic conditions on the Korean peninsula.     

A novel insight into vertical ground motion modelling in earthquake engineering

Recent observations of failure and damage of buildings and structures under seismic action has led to an increasing interest for an in-depth analysis of the vertical component of site ground motion. In particular, when dealing with saturated soils, the current engineering practice does not usually go beyond the simplified $u$–$p$ formulation of the Biot's equations describing the coupled hydro-mechanical behaviour, thus neglecting some terms of fluid inertial forces, despite the presence of more refined formulations, for example, the $u$–$U$ formulation. Therefore, a theoretical and numerical validation of the $u$–$p$ formulation as compared with the $u$–$U$ formulation is proposed in this work, where the numerical simulations are compared with the analytical solution for the $u$–$p$ formulation, which is also derived and illustrated in this text. The comparison between the two formulations and the analytical solution is provided for different levels of permeability and dynamic actions, which are representative of a wide scenario of site ground properties and seismic hazard in the vertical direction. In particular, the soil response is analysed in terms of acceleration and pore pressure time history, frequency content, acceleration response spectrum, and amplification ratio of acceleration. This study extends the discussion of the limits of applicability of the $u$–$p$ formulation with respect to the rigorous solution of Biot's equations (obtained here with $u$–$U$ formulation) to the context of a complex dynamic regime provided by the vertical components of real earthquake records, and paves the way for further investigations.     

Critical slip surface and landslide volume of a soil slope under random earthquake ground motions

Finding the critical slip surface and estimating the landslide volume are of primary importance for slope seismic design. However, this may be difficult due to the uncertainty of ground motions. To address this problem, a new method for calculating uncertainties is recommended in this paper, especially for the critical slip surface and landslide volume under random earthquake ground motions. Firstly, a series of intensity–frequency nonstationary random earthquake ground motions were generated based on an improved orthogonal expansion method. A given number of potential slip surfaces were set in a soil slope. Subsequently, the factor of safety (FOS) of each slip surface for all ground motions was calculated and the minimum FOS curves were obtained. It was found that the critical slip surfaces and failure times are uncertain under different earthquakes. The Monte Carlo method was used to verify the accuracy of probability density evolution method (PDEM), and the results of the PDEM and the Monte Carlo method are consistent, meaning that the PEDM has higher computational efficiency. Moreover, the distributions of earthquake-triggered landslide volume and landslide depth were analyzed by considering equivalent extreme events. Both landslide volume and depth exhibit a normal distribution for a homogeneous soil slope. The framework of this study is meaningful for slope seismic design in engineering, for example, the location of critical slip surface can be used for slope reinforcement, and the distribution of sliding volume can be used for disaster assessment.     

Seismic performance evaluation of dam-reservoir-foundation systems to near-fault ground motions

Ground motion records obtained in recent major strong earthquakes have provided evidence that ground motions recorded near the near-fault regions differ in many cases from those observed further away from the seismic source. As the forward directivity and fling effect characteristics of the near-fault ground motions, they have the potential to cause more considerable damage to structures during an earthquake. Therefore, understanding the influence of near-fault ground motions on the performance of structures is critical to mitigate damage and perform effective response. This paper presents results of a study aimed at evaluating the effects of near-fault and far-fault ground motions on seismic performance of concrete gravity dams including dam-reservoir-foundation interaction. Koyna gravity dam is selected as a numerical application. Four different near-fault ground motion records with an apparent velocity pulse are used in the analyses. The earthquake ground motions recorded at the same site from other events that the epicenter far away from the site are employed as the far-fault ground motions. The seismic performance evaluation method based on the demand-capacity ratio, the cumulative overstress duration and the spatial extent of overstressed regions is presented. The concrete damaged plasticity model including the strain hardening or softening behavior is employed in nonlinear analyses. Nonlinear seismic damage analyses of the selected concrete dam subjected to both near-fault and far-fault ground motions are performed. The results obtained from the analyses show the effects of near-fault ground motions on seismic performance of concrete gravity dams and demonstrate the importance of considering the near-fault ground excitations.     

如何解决开展防震宣传担心引起谣传问题

解决开展防震宣传活动担心引起谣传问题 ,必须做到 :一、更新观念 ,与时俱进 ;二、端正认识 ,进一步理解自己的职能 ;三、把积极、大胆开展活动作为解决谣传问题的根本途径 ;四、注意工作方法 ,尽量避免群众“担心”。     

Robust attenuation relations for peak time-domain parameters of strong ground motions

This study presents new attenuation models for the estimation of peak ground acceleration (PGA), peak ground velocity (PGV), and peak ground displacement (PGD) using a hybrid method coupling genetic programming and simulated annealing, called GP/SA. The PGA, PGV, and PGD were formulated in terms of earthquake magnitude, earthquake source to site distance, average shear-wave velocity, and faulting mechanisms. A worldwide database of strong ground motions released by Pacific Earthquake Engineering Research Center (PEER) was employed to establish the models. A traditional genetic programming analysis was performed to benchmark the proposed models. For more validity verification, the GP/SA models were employed to predict the ground-motion parameters of the Iranian plateau earthquakes. Sensitivity and parametric analyses were carried out and discussed. The results show that the GP/SA attenuation models can offer precise and efficient solutions for the prediction of estimates of the peak time-domain characteristics of strong ground motions. The performance of the proposed models is better than or comparable with the attenuation relationships found in the literature.     

岩土工程中的设计地震动参数确定

与岩土工程相关的设计地震动参数的规定分散在各行业的工程设计规范之中,比较了主要技术规范中设计地震动参数规定之间的差别,讨论了在岩土工程的勘察与设计中确定地震动参数的方法和内容,分析和研究了确定设计地震动参数时不同规范之间需要协调的主要问题,指出了在目前岩土工程中的设计地震动参数确定方面的需要重点关注的参数选择的合理性,提出了具有地震工程专业基础（注册地震安评工程师）的注册土木工程师（岩土）确定具体设计地震动参数应更符合工程建设的实际需要的建议。     

An application of disjunctive kriging for earthquake ground motion estimation

For earthquake ground motion studies, the actual ground motion distribution should be reproduced as accurately as possible. For optimal estimation of ground motion, kriging has been shown to provide accurate estimates. Although kriging is accurate for this application, some estimates it provides are underestimates. This has dire consequences for subsequent design for earthquake resistance. Kriging does not provide enough information to allow an analysis of each estimate for underestimation. For such an application, disjunctive kriging is better applied. This advanced technique quantifies the probability that an estimate equals or exceeds particular levels of ground motion. Furthermore, disjunctive kriging can provide improved estimation accuracy when applied for local estimation of ground motion.     

场地地震安全性评价中确定设计地震动参数若干问题研究

本文研究确定设计地震动参数中涉及的若干问题,其中包括基岩水平加速度反应谱衰减关系的选择、震源深度对基岩水平加速度峰值及基岩反应谱曲线的影响、强度包络线函数及输入随机相位的选择、土体非线性特性参数和土层剪切波速值的选择、设计地震动反应谱的标定等问题。本文基于一个典型场地计算剖面,采用一维等效线性化模型并通过逐项变换某些研究参数的方法,研究了各种因素对设计地震动参数可能产生的影响及存在的误差和相应的规律。     

近断层速度脉冲地震动引起的边坡永久位移预测模型

基于小波分析方法,从NGA数据库的3 551条地震记录中选取189条速度脉冲地震动,地震动均转换成发生最强脉冲的方向。基于Newmark方法,分析了近断层速度脉冲地震动作用引起的边坡永久位移值。结果表明：近断层速度脉冲地震动对边坡产生特殊的破坏作用,表现在滑动位移值大、滑动体破坏力强等方面;边坡永久位移值与速度脉冲地震动的峰值速度具有高度相关性,位移值较大时尤为明显。建立了基于单变量形式的峰值速度及双变量形式的峰值速度、峰值加速度两种边坡永久位移预测模型,模型简单实用,与回归数据具有很好的相关性,前者更适用于预测对实际工程影响较大的永久位移值,且离散性较小。提出的预测模型为考虑近断层地震动速度脉冲特性影响的边坡永久位移值的概率地震灾害分析提供了基础。