Smart Lead Rubber Bearings Equipped with Ferrous Shape Memory Alloy Wires for Seismically Isolating Highway Bridges

Shape memory alloys (SMA) can substantially improve the damping capacity and re-centering capability of elastomeric isolators. The objective of this study is to assess the seismic performance of smart lead rubber bearings (LRBs) equipped with double cross ferrous SMA wires. Hysteretic shear response of SMA wire-based LRB is determined using finite element method. The seismic response of a multispan continuous steel girder bridge isolated by SMA-LRB is evaluated. Hybrid SMA-LRB bearing exhibits a significantly lower shear strain demand (up to 46% reduction) and a higher energy dissipation capacity (up to 31% increase) compared to the LRB.     

Sustainability of Highway Bridge Networks Under Seismic Hazard

In order to evaluate the seismic risk of transportation networks, it is necessary to develop a methodology that integrates the probabilities of occurrence of seismic events in a region, the vulnerability of the civil infrastructure, and the consequences of the seismic hazard to the society, environment, and economy. In this article, a framework for the time-variant seismic sustainability and risk assessment of highway bridge networks is presented. The sustainability of the network is quantified in terms of its social, environmental, and economic metrics. These include the expected downtime, expected energy waste and carbon dioxide emissions, and the expected loss. The methodology considers the probability of occurrence of a set of seismic scenarios that reflect the seismic activity of the region. The performance of network links is quantified based on individual bridge performance evaluated through fragility analyses. The sustainability and risk depend on the damage states of both the links and the bridges within the network following an earthquake scenario. The time-variation of the sustainability metrics and risk due to structural deterioration is identified. The approach is illustrated on a transportation network located in Alameda County, California.     

博弈论视角下的卢沟桥事变

本文主要运用博弈论模型对卢沟桥事变从一个"地方性"事件演变为中日两国之间的全面战争这一过程进行分析.本文认为,卢沟桥事变发生伊始,中日两国都不同程度地想避免卷入全面战争,但是由于双方在卢沟桥事变后所采取的对策使得他们陷入了"谁是懦夫"的困境中,最终导致了全面战争的爆发.     

A Stability-Based Target Displacement for Direct Displacement-Based Design of Bridge Piers

P-Δ effects can cause instability if they are not properly accounted for during the design of bridge piers and other structures. When a bridge pier is designed with the Direct Displacement-Based Design Method, P-Δ effects are evaluated at the end of the design process and compared to the flexural strength of the pier to find a stability index. If the stability index exceeds the specified value, the design must be repeated, iteratively reducing the target design displacement. This article presents a model that when used at the beginning of design (without knowledge of strength) allows the estimation of the maximum lateral displacement that a bridge pier can sustain without exceeding the specified value of the stability index, therefore eliminating the need for iteration. The examples that are presented prove that the model is accurate and very useful for design of extended pile bents.     

Impact Stiffness of the Contact-Element Models for the Pounding Analysis of Highway Bridges: Experimental Evaluation

For the requirement of pounding analysis of highway bridges, how to properly choose the impact stiffness has become a primary issue for an achieving accurate result. This article presents an evaluation test of the impact stiffness of four types of contact-element models based on the shaking table test results of a steel highway bridge model. The analytical results indicate that the theoretical impact parameters are significantly larger than the identified values because the assumptions for deriving those models cannot match the actual impact conditions. The possible reasons causing those differences are discussed at the end of this study.     

The Impact of Flood-Induced Scour on Seismic Fragility Characteristics of Bridges

Earthquake in the presence of flood-induced scour is a critical multihazard scenario for bridges located in seismically-active, flood-prone regions. The present article evaluates seismic performance of four example reinforced concrete bridges when they are pre-exposed to regional flood hazards. Nonlinear time history analyses of the example bridges are performed for a suite of ground motion time histories in the presence and absence of scour expected from different intensity flood events. Fragility analysis is performed to develop seismic fragility curves of the example bridges for various scour depths. Results show nonlinear increase in bridge seismic fragility with increase in scour depth.     

Performance-Based Seismic Assessment of Superelastic Shape Memory Alloy-Reinforced Bridge Piers Considering Residual Deformations

The application of superelastic Shape Memory Alloy (SMA) reinforcement in plastic hinge regions of bridge piers has been proven to reduce the residual displacement after a strong shaking owing to its unique shape recovery characteristics; however, the maximum deformation of the piers could increase due to the relatively lower modulus of elasticity of SMA bars and lower hysteretic energy dissipation capacity. In this context, this article applies a recently formulated probabilistic performance-based seismic assessment methodology that considers both the maximum and the residual deformation simultaneously to evaluate the performance of SMA reinforced bridge piers.     

Analytical Seismic Assessment of a Tall Long-Span Curved Reinforced-Concrete Bridge. Part II: Structural Response

The seismic assessment of special bridges, even under the hypothesis of full knowledge of site conditions, structural characteristics, and seismic activity at their location, is not an easy and straightforward task due to the complexities and uncertainties related to the finite-element modeling approaches, structural loading scenarios, and seismic analysis methodologies. In this article, a series of nonlinear static and dynamic finite-element analyses on the Mogollon Rim Viaduct are performed with consideration of both uniform and conditionally simulated non-uniform seismic motions. The failure modes of the bridge using different numerical modeling approaches are discussed, and the degree of sensitivity of its response to the different seismic assessment strategies is evaluated. The effect of the multi-component, multi-support and multi-directional excitations of ground motions on the design and response are studied, and the pros and cons of the commonly used structural analysis methodologies of bridges are also addressed. The numerical results of the present study provide a deeper insight into the nonlinear behavior of curved reinforced-concrete bridges, and suggest practice-oriented approaches for their seismic assessment.     

领略贵州古村落风韵

引言：最近,受清华大学陈志华、李秋香两教授的邀请,我参与《中华古村落》大系的编撰工作。每省一卷,我承担贵州卷。每卷收录20个古村落,每个村落3000字,20幅照片。另外,写一篇一万字的《分卷序》。在此基础上,我撰写了《领略贵州古村落风韵》一文,主要介绍贵州古村落的自然环境、历史流年、地域特点、民族特色、美丽外观、鲜明个性、丰富的内涵等等。     

Setting Moon and Rising Nationalism: Lugou Bridge as Monument and Memory

This paper examines Beijing’s Lugou Bridge (Marco Polo Bridge) in terms of monument and memory. With 800 years of history to its credit, this structure carries with it a select set of textual memories passed down from one dynasty to the next, and finally into the 20th century when its traditional associations of architectural and natural beauty were supplemented by its modern association with the beginning of the Anti‐Japanese War of Resistance (Second World War in China). With the opening of Sino‐Japanese diplomacy in the 1970s, the Chinese authorities began to accredit further significance to the bridge as a site of Chinese indignation over Japan’s perceived refusal to take responsibility for its wartime aggression. This point was driven home most forcefully through the construction of the Anti‐Japanese War Memorial Hall in 1985, and the continuing use of the site as a tool of diplomacy. Lugou Bridge, therefore, serves to demonstrate how political authority and cultural nationalism are constructed through the continuing appropriation of monumental artefacts and traditions.