Effects of Near-Fault Pulses on Nonlinear Soil-Structure Systems

ABSTRACT

This paper is focused on effects of near-fault pulse characteristics on seismic performance of soil-structure systems considering foundation uplifting and soil yielding. To this end, an extensive parametric study is conducted. Mid-to-high-rise buildings of different aspect ratios (SR) resting on shallow mat foundations are investigated. Different vertical load-bearing safety factors (F_S) of foundation as well as different soil types (i.e. soft to very dense) are considered in this study. Finite element method is used for numerical modeling. The underlying soil is simply modeled with a set of nonlinear springs and dashpots beneath the foundation. Mathematical near-fault pulse models of fling step and forward directivity are used as input ground motions. The results show that reduction in structural drift demands due to nonlinear soil-structure interaction (SSI) is more considerable in the case of short-period pulses compared to long-period ones. In more precise words, significant reduction occurs when pulse-to-fixed-base period ratio falls within 0.7–1.5 in the case of directivity pulses and 0.5–1.4 in the case of fling pulses. It is also demonstrated that the beneficial effects of nonlinear SSI reduce when the number of stories increases.     

The Archaeology of Trading Systems,Part 1: Towards a New Trade Synthesis

After almost three centuries of investigations into the question of what it means to be human and the historical processes of becoming human, archaeologists have amassed a huge volume of data on prehistoric human interactions. One of the largest data sets available is on the global distribution and exchange of materials and commodities. What still remains insufficiently understood is the precise nature of these interactions and their role in shaping the diverse cultures that make up the human family as we know it. A plethora of theoretical models combined with a multitude of methodological approaches exist to explain one important aspect of human interaction—trade—and its role and place in shaping humanity. We argue that trade parallels political, religious, and social processes as one of the most significant factors to have affected our evolution. Here we review published literature on archaeological approaches to trade, including the primitivist-modernist and substantivist-formalist-Marxist debates. We also discuss economic, historical, and ethnographic research that directly addresses the role of traders and trade in both past and contemporary societies. In keeping with the complexities of interaction between trade and other aspects of human behavior, we suggest moving away from the either/or perspective or strong identification with any particular paradigm and suggest a return to the middle through a combinational approach to the study of trade in past societies.     

Beijing’s institutional-balancing strategies: rationales,implementation and efficacy

China has in recent years been actively engaged in multilateral diplomacy. From the Shanghai Cooperation Organisation and the Conference on Interaction and Confidence Building Measures in Asia to the Asian Infrastructure Investment Bank and the One Belt, One Road initiative, Beijing is pursuing strategies and promoting norms that are viewed as concerted efforts by China to challenge some of the key institutional arrangements of the existing international order. This article seeks to discuss these contentious issues and assess the rationales, approaches and implications of Chinese diplomacy in initiating and promoting what can be considered as institutional-balancing strategies. The author suggests that the rationales behind these Chinese strategies have as much to do with Beijing’s shifting priorities and the need to address them as with reflecting a degree of dissatisfaction with existing multilateral institutions. And there are more marked differences in Chinese motivations and modalities in security arenas than in economic areas. However, it would be overstating Beijing’s intentions and capabilities if these China-sponsored initiatives are viewed as direct challenges to the existing international and regional orders.     

Optimal Control of Structures under Earthquakes Including Soil-Structure Interaction

It is well known that the soil-structure interaction (SSI) changes the dynamic response of a structure supported on flexible soil. The analysis of optimally controlled SSI systems has certain difficulties due to the nature of the SSI and the optimal control problem. In this paper, a two-step iteration-based numerical algorithm is proposed to handle optimally controlled SSI systems under earthquakes. First, the optimal control forces are obtained by using a fixed-base system. Then, the optimal control forces are converted to the frequency domain by the Fourier transform technique to be used in the equations of the SSI system. The lateral displacement and the rocking of the foundation are obtained from the equations of the SSI system containing the optimal control forces in the frequency domain. The lateral displacement and rocking of the foundation are then converted to the time domain by the inverse Fourier transform technique, and the lateral accelerations and the rocking accelerations of the foundation are obtained by the forward finite difference method. During the second step, the optimal control forces are calculated again by using the lateral acceleration and the rocking acceleration of the foundation along with the earthquake ground motion. Using the method explained above, the optimal control forces obtained in the time domain are used in the equations of the soil-structure system from which the behavior of foundation and structure is obtained. In the final section of the paper, a numerical study is conducted for a controlled structure supported on flexible soil.     

Evaluation of 2D Seismic Site Response due to Hill-Cavity Interaction Using Boundary Element Technique

This paper deals with the evaluation of two-dimensional site-effects due to the seismic interaction between hills with various configurations and underground cavities. The time-domain boundary element method is used to evaluate the site-effects of hill-cavity interaction subjected to vertically propagating in-plane SV and P waves. The presence of an underground cavity and the hill topography are expected to induce significant effects on the surface ground motion. To further examine the contribution of the amplification ratio of the hill-cavity system, a fairly simple approach, which can compute the response spectra of the hill’s surface motion above a cavity based on the real input motions, is also used to input motions.     

Tuned Mass Damper Positioning Effects on the Seismic Response of a Soil-MDOF-Structure System

Tuned mass dampers (TMDs) are effective structural vibration control devices. However, very little research is available on the experimental investigation of TMDs and their performance in systems undergoing dynamic soil-structure interaction. Geotechnical centrifuge tests are conducted to investigate story positioning effects of single and multiple TMDs in a soil-MDOF-structure system. The criteria for optimal story positioning will be established, and it is shown that story positioning influences TMD performance more than the number of TMDs used. Non-optimal story positioning was found to have the potential of reducing damping efficiency, amplifying peak structural response, and inducing lengthier high-intensity motion.     

商会在官、民、洋三元互动中的角色和作用——以1905年中美工约交涉及抵制美货运动为例

在1905年中美工约交涉及抵制美货运动中,中国商会在官、民、洋三者之间扮演着重要角色。商会在民间推动、政府默许下先则与美国使领直接交涉,继则发动和领导了抵制美货运动,最终又在民众日益激进、政府劝导停止、美方威胁分化并作有限让步情况下结束抵制运动。这一运动的过程和结果,在一定程度上影响了之后商会在官、民、洋互动格局中的关系的变化。     

Rocking of Non-symmetric Rigid Blocks in Buildings Considering Effects Associated with Dynamic Soil-Structure Interaction

A dynamic model for the estimation of the rocking and/or overturning response of a free-standing non-symmetric rigid block considering rotational and horizontal excitation is proposed. The block is situated at different levels of a building with flexible base subjected to earthquakes. Base flexibility introduces the rotational component of the excitation due to dynamic soil-structure interaction (DSSI). The model is used to assess the influence of the dynamic soil-structure interaction on the behavior of the block. An illustrative example of the proposed model for non-symmetric rigid blocks in 5-, 10-, and 15-story buildings located in soft soils considering earthquakes from different seismic sources is presented. Results show that it is important to consider kinematic effects as well as inertial effects of DSSI in the dynamic response of contents. The influence of base flexibility depends on the change of spectral intensities associated to the increase of the building structural period and is larger for higher building levels.     

Liquefaction-Induced Lateral Load on Pile in a Medium Dr Sand Layer

One-g shake-table experiments are conducted to explore the response of single piles due to liquefaction-induced lateral soil flow. The piles are embedded in saturated Medium Relative Density (Dr) sand strata 1.7–5.0 m in thickness. Peak lateral pile displacements and bending moments are recorded and analyzed by uniform and triangular pressure distributions. On this basis, the observed levels of pile bending moment upon liquefaction suggest a hydrostatic lateral pressure approximately equal to that due to the total overburden stress. Using the experimental data, comparisons with current recommendations are made, and the Showa Bridge case history is briefly assessed.     

Finite Element Analysis of Dam-Foundation Coupled System Considering Cone-Type Local Non-Reflecting Boundary Condition

This article deals with the seismic analysis of the dam-foundation coupled system considering direct coupling approach using displacement based finite element method. A cone-type local non-reflecting boundary condition (NRBC) is adopted to model the semi-infinite soil domain. The reservoir effect adjacent to dam body has also been incorporated in the analysis. The results depict the superiority of the proposed NRBC in absorbing spurious wave reflections over the traditional viscous boundary conditions. The analysis results show that the dynamic response of the dam gets highly affected due to the consideration of the elastic foundation domain at its base.