Subsoil Interventions Effect on Structural Seismic Response. Part II: Parametric Investigation

In the present article the effect of subsoil interventions on the response of soil-structure systems under strong earthquake shaking is studied. Several idealized configurations of commonly applied as well as innovative intervention techniques are examined, referring to increased or reduced stiffness of the initial subsoil conditions of the subsoil-foundation-structure system. Numerical analysis utilizing validated simulation procedures covers a large spectrum of structures and soil conditions. A parametric investigation of several key factors is also conducted. A comparative evaluation of the results in time and frequency domain is aiming in generalizing the conclusions to several earthquake and soil-structure combinations. Obtained results reveal a rather detrimental effect of the stiffness-increasing methods, whereas techniques related to modification of oscillation dynamic properties with flexible subsoil intervention schemes, present promising alternatives for an efficient mitigation of structural response to strong earthquakes.     

Definition of Seismic Input for Out-of-Plane Response of Masonry Walls: I. Parametric Study

Response of masonry walls to out-of-plane excitation is a complex, yet inadequately addressed theme in seismic analysis. The seismic input expected on an out-of-plane wall (or a generic “secondary system”) in a masonry building is the ground excitation filtered by the in-plane response of the walls and the floor diaphragm response. More generally, the dynamic response of the primary structure, which can be nonlinear, contributes to the filtering phenomenon. The current article delves into the details and results of several nonlinear dynamic time-history analyses executed within a parametric framework. The study addresses masonry structures with rigid diaphragm response to lateral loads. The scope of the parametric study is to demonstrate the influence of inelastic structural response on the seismic response of secondary systems and eventually develop an expression to estimate the seismic input on secondary systems that explicitly accounts for the level of inelasticity in the primary structure in terms of the displacement ductility demand. The proposed formulation is discussed in the companion article.     

Effect of Nonlinearity of Frame Buildings on Peak Horizontal Floor Acceleration

Using representative numerical models of eight code-designed steel moment-resisting frame buildings and several ground motions, time-history analyses are performed and a critical evaluation of Peak Horizontal Floor Acceleration (PHFA) demands is conducted. The frames are modeled alternatively as linear and nonlinear systems to isolate the effect of building nonlinearity on PHFA. In most cases, PHFA is reduced when nonlinear behavior of a building is considered; however, in some cases, significant amplification of PHFA is observed. Results from the numerical study provide insight into the trend of modal response modification factors presented taking ground motion spectral shape into account.     

Seismic Response of Base-Isolated Benchmark Building with Variable Sliding Isolators

The seismic response of base-isolated benchmark building with variable sliding isolators like variable friction pendulum system (VFPS), variable frequency pendulum isolator (VFPI), and variable curvature friction pendulum system (VCFPS), along with conventional friction pendulum system (FPS), was studied under the seven earthquakes. The earthquakes are applied bi-directionally in the horizontal plane ignoring vertical ground motion component. The shear type base-isolated benchmark building is modeled as three-dimensional linear elastic structure having three degrees of freedom at each floor level. Time domain dynamic analysis of the benchmark building was carried out with the help of constant average acceleration Newmark-Beta method and nonlinear isolation forces was taken care by fourth-order Runge-Kutta method. The base-isolated benchmark building is investigated for uniform isolation and hybrid isolation in combination with laminated rubber bearings through the performance criteria and time history response of important structural response parameters like floor accelerations, base displacement, etc. It is observed that variable sliding isolators performed better than conventional FPS due to their varying characteristic properties which enable them to alter the isolator forces depending upon their isolator displacements thus improves the performance of the structure. The VFPS efficiently controls large isolator displacements and VFPI and VCFPS improve super structural response on the cost of isolator displacement. It is also observed that the hybrid isolation is relatively better in comparison to the uniform isolation for the benchmark building.     

Experimental Study on Seismic Performance of Mechanical/Electrical Equipment with Vibration Isolation Systems

A prototype diesel generator equipped with a vibration isolation system consisting of restrained isolators (denoted as I/system) is quasi-statically and dynamically tested. Sequentially, the seismic simulation tests are conducted to further investigate the effectiveness of additional snubbers incorporated into the vibration isolation system (denoted as I/R system). Comparing the test results to the static design demands specified in ASCE 7-10, the recommended component amplification factor could represent the horizontal acceleration amplification phenomenon of the generator equipped with I/R system; however, the seismic force demands for static design of I/R system might not be appropriate and conservative enough.     

Unusual Overshooting in Steady-state Response for Structure-dependent Integration Methods

It is numerically illustrated that an unusual overshooting phenomenon might occur in the solution of a forced vibration response if a structure-dependent integration method is applied to conduct the analysis, such as Chang explicit method [2002] and CR explicit method [2008]. This overshooting may occur in the steady-state response of a high frequency mode and it becomes significant as the natural frequency of the mode increases. This unusual overshooting behavior can be successfully detected by using a local truncation error derived from a forced vibration response rather than a free vibration response. A missing loading term in the difference equation for displacement increment is responsible for this unusual overshoot. It is analytically and numerically verified that the unusual overshooting behavior will automatically disappear after introducing the missing loading term into the difference equation for displacement increment.     

Analytical Seismic Assessment of a Tall Long-Span Curved Reinforced-Concrete Bridge. Part I: Numerical Modeling and Input Excitation

The seismic response of bridges is affected by a number of modeling considerations, such as pier embedment, buried pile caps, seat-type abutments, pounding, bond slip and architecturally flared part of piers, and loading considerations, such as non-uniform ground excitations and orientation of ground motion components, which are not readily addressed by design codes. This article addresses a methodology for the nonlinear static and dynamic analysis of a tall, long-span, curved, reinforced-concrete bridge, the Mogollon Rim Viaduct. Various modeling scenarios are considered for the bridge components, soil-structure interaction system, and materials, i.e., concrete and reinforcing steel, covering all its geotechnical and structural aspects based on recent advances in bridge engineering. Various analysis methodologies (nonlinear static pushover, time history response to uniform and spatially variable seismic excitations, and incremental dynamic analyses) are performed. For the dynamic analyses, a suite of nine earthquake accelerograms are selected and their characteristics are investigated using seismic intensity parameters. A recently developed approach for the generation of non-uniform seismic excitations, i.e., spatially variable simulations conditioned on the recorded time series, is used. Methods for the evaluation of structural performance are discussed and their limitations addressed. The numerical results of the seismic assessment of the Mogollon Rim Viaduct are presented in the companion article (Part II). The sensitivity of the bridge response to the adopted modeling, loading and analyzing strategies, as well as the correlation between structural damage and seismic intensity parameters are examined in detail.     

基于SD法的公园景观综合感知研究——以福州市为例

本文以福州市主要的几个城市公园为研究样本,运用SD法,将声、味环境因素纳入公园景观的感知研究中,就声、味环境因素对评价者公园景观视觉感知的影响进行定量分析,揭示影响规律;并结合因子分析法,进行主要影响因子提取,为人性化的公园景观研究与设计提供参考。结果表明：声、味环境对评价者公园景观的视觉感知产生了明显的影响,且负面因素产生的影响比正面因素更为显著;声、味环境因素对于不同的公园景观视觉效果评价要素和因子的影响有所不同,心理要素和整体要素受影响程度最为显著,其次为环境要素;声、味环境因素影响下的公园景观视觉效果由形式因子、协调因子、空间因子、生态因子、污染因子、特色因子、认同因子和安全因子等8个评价轴构成。     

EDXRF探针分析古瓷产地的尝试

由于古汝瓷原料产地的信息能为汝瓷科技鉴定工作提供可靠的借鉴,本工作采用EDXRF探针技术测试了若干汝瓷和钧瓷等样品中的常量元素及微量元素。再利用多元统计中的因子分析处理成分数据,对各样品的因子得分用因子轮廓图和聚类分析图来表示。结果表明,新安钧瓷、古汝瓷和现代仿汝瓷能较好地加以区分,金钧和元钧能从釉的微量元素上加以区分,严和店窑青瓷也能和其他样品区分开。这说明上述两种数据处理方法相结合能较好地反映出样品中所隐含的产地信息,从而为汝瓷科技鉴定和其他古陶瓷的产地分析提供了参考。     

Long-Period Ground Motion Simulation and its Impact on Seismic Response of High-Rise Buildings

This paper first critically reviews a seismological model and then a three-segment curve model (in log-log space) to model the Q-f relationship is proposed to overcome the potential biased estimation in the long-period range by the “coda wave” method. The optimal curve-fitting process is performed to determine the Q-f relationship for the Hong Kong region. The calibrated seismological factors are incorporated with the stochastic simulation procedure to generate synthetic ground motions, which are validated through comparison with seismic records. The impact of long-period ground motions on the seismic response of high-rise buildings is finally manifested through a numerical study.