Self-centering concrete bridge piers (SCCP),which have been used to retrofit bridge piers to give better seismic response,effectively reduce residual displacements during severe earthquakes.This study gives a simplified theoretical model for self-centering concrete bridge piers including a stiffness deterioration analysis and lateral force-displacement analysis.The stiffness deterioration analysis introduces 3 damage factors for 7u,γc and 7,.These damage factors illustrate the damage caused by increasing lateral displacements.The theoretical model has been validated against existing experimental data with good agreement.

A summary and review of 16 commonly used algorithms for structure modal parameter identification under the ambient excitation is presented in this paper. After the classification of identification algorithms into time domain and frequency domain, the time domain algorithms are divided into the one-stage methods and two-stage methods ulteriorly based on the process of the algorithms. On the basis of the classification, the applicable condition and basic process of the identification algorithms are described, among which the principle and realizing process of several important algorithms are discussed in detail. The modal validation methods in the structure modal parameter identification are presented basically at the end of this paper.

An atomistic potential based (AP-based) cohesive modeling methodology is briefly presented. For this purpose, pair potentials and and multi-body potential such as EAM are considered and their softening characteristics are shown. Based on the AP-based hyperela- sicity with softening mechanism, the cohesive law in terms of cohesive traction and separation displacement is obtained. The presented method is feasible and a few remarks are given.

The original concept of self-centering system was first proposed under the PRESSS research project in 1991 in UC San Diego. The particularly promising and effective structural solution was initially defined as hybrid system in literature and then self-centering system recently. In the ductile connection of self-centering system, inelastic demand is accommodated through the opening and closing (control rocking) of a pre-existing gap at the critical interface, with no consequent damage such as the plastic hinges in traditional structural elements. This paper provides an overview of the recent advances of self-centering system, especially for bridge piers, to summarize several analytical models and experimental tests that were widely recognized. Besides, a brief introduction of the study conducted by Tsinghua University is presented, including a stiffness degrading analytical model and a series of experimental tests.

预应力SSWM-M是由高强不锈钢绞线网和砂浆组合而成的层状或者壳状预应力结构,适用于结构补强加固.为了降低施工难度和改善预应力施加状况,本文提出一种新型张拉锚固系统一嵌固锚体系,并将该技术应用于广州黄阁桥的实际加固工程中,以研究预应力SSWM-M技术的加固效果和验证嵌固锚体系的适用性.通过对比加固前后的荷载试验结果,发现:在相同荷载条件下,黄阁桥加固后挠度减小幅度大,证明预应力SSWM-M加固技术可提高原结构的刚度,减小挠度.同时依据现场施工条件,对室内构件的预应力损失计算公式进行了参数修正,并结合有限元分析验证了修正公式的有效性.

Based on the average curvature modal and gapped smoothing method,a new algorithm to detect the local damage of a simply supported beam under the excitation of moving loads is proposed.Without need for the dynamic response data before a structure was damaged,this algorithm has good noise immunity,and could be used in the situation of multiple moving loads.Firstly,by calculating the dynamic response of a simply supported beam under the excitation of a mass-spring-dashpot vehicle system using Newmark-β time domain integral algorithm,the ascendancy of a basic mode in the response is confirmed,and this explains the meaning to average the curve modal.Thereafter,an FEM model including a moving mass-spring-dashpot vehicle system on a simply supported beam is built to conduct a numerical simulation.Here a triangle fitting function is constructed to fit the average curvature modal.The numerical simulation shows that the algorithm is effective in the situation of multiply damage location,multiply moving loads,and noise environment.This algorithm provides a new research thought for the damage detection of bridges opened in normal traffic.

The pre-stressed stainless steel wire mesh - mortar as a pre-stressed laminate or shell structure that is composed by high strength stainless steel wire mesh and mortar is suitable for structural strengthening and rehabilitation.To reduce the practical difficulty and provide a uniform and effective pre-stress,a jogged anchor is proposed for anchoring large diameter stainless steel wire mesh.In order to verify the applicability of the new construction technology,a further reforcement test is conducted on a griger bridge - Huangge Bridge,which was strengthened with large diameter pre-stressed stainless steel wire mesh - mortar.Through the contrast of load test,it was found that:in the same load condition,the reinforced Huangge Bridge restored the flexural capacity and stiffness.The prestress loss formula was modified by the construction conditions, which is suitable for engineering application.

The dynamic responses,as the input data of modal parameters identification,would affect the identification results whichever the identification method could be used.As one of the modal parameters identification with multi-input and multi-output in a time domain,the extended eigensystem realization algorithm(EERA) could be directly applied for an arbitrary random forced vibration system with the advantage of high accuracy,stable and so on.The paper identifies the modal parameters of two kinds of models,2-NDof spring-damping-mass system for numerical model and 6-story frame structure for experimental model,via EERA with the 3 different sets of input responses of acceleration,velocity and displacement.The conclusions show that EERA could apply to any dynamic response without any code change,and acceleration response should be used when higher modes need to be identified.

The pre-stressed stainless steel wire mesh (SSWM) –mortar (M) is a pre-stressed laminate structure for structural strengthening and rehabilitation. Pre-stressing the stainless steel wire mesh is the key technology for engineering practice. A jogged anchor is proposed for anchoring large diameter SSWM conveniently. The flexural performances of 5 damaged RC beams strengthened by pre-stressed SSWM-M and one referential RC beam were tested. The experimental results indicates that the large diameter pre-stressed SSWM-M has a better performance in controlling the crack growth, restoring the flexural capacity and stiffness than the small diameter pre-stressed SSWM-M.

约束混凝土本构模型的下降段影响着钢管混凝土的力学性能预测,结合6组方钢管混凝土短柱轴压破坏试验结果,提出一种软化特征可控的双参指数型约束混凝土本构.双参指数型本构考虑了方钢管宽厚比、混凝土强度、钢管截面含钢率等因素的影响,能够很好地模拟在不同约束条件下混凝土的软化行为.基于双参指数型本构,对6组方钢管混凝土试验结果进行了轴压破坏的受力全过程模拟,计算结果和试验结果吻合良好.

We use the distributed cohesive element method to simulate the dynamic fracture in structural specimen and arbitrary crack path is predicted. The focus in on convergence of the cohesive crack path as an approximation of the real crack as the spatial characteristic mesh size h approaches zero. We propose the structured mesh is satisfactory in capturing the real crack shape as we refine the mesh because the crack Hausdorff distance converges. However, the length of cohesive crack path does not converge as the mesh is refined. There is a finite length deviation between predicted cohesive crack path and physically real crack path on structured mesh.

This paper presents a self-centring bridge pier system connected by unbonded post-tensioned tendons and mild steel which can minimize the post-earthquake residual deformation and displays stable energy dissipate capacity.The basic mechanical concept of a self-centring system is explained.Referring to the quasi-static test,a simplified mechanical model and a finite element model is herein illustrated,considering flexural deformation,unbonded length of mild steel and strain penetration due to strain differences between the bar and concrete within the connection member.To solve the stress of concrete,two alternative methods,the equivalent rectangular stress map method and plane-section assumption method,are also critically discussed for better understanding of the principle of a self-centring system.Moreover,to provide a guide for structure design,the author indicates the intrinsic characteristic of the stiffness of a self-centring bridge pier which could result in vibration isolation.

The structural normal modes were computed from the identified complex modes in this paper firstly,and then based on Berman-Baruch Method(BB) which is one of the optimal matrix methods for structural model updating,the Improved Berman-Baruch Method(IBB) was proposed and derived.A reasonable optimal project function was defined and one constraint of BB that the normalized modes with mass matrix are required was released.The updated model via IBB was more physically meaningful,and it keeps the characters of band and sparse of system matrices.Two cases were taken as examples to show the validity and availability of IBB to update the non-proportional damping structure.One was the simulated experiment with a 6-DOF mass-spring-damping system to show the little discrepancy between exact and updated models;the other one was the practical experiment with a 6-DOF frame structure in the laboratory to demonstrate that the acceleration history agrees well between the experimental data and the simulated data generated from the updated model.

Wireless smart sensor networks (WSSN) have many advances compared with traditional structural health monitoring (SHM) such as wireless process, real-time calculation and low cost. However power consumption is considered as one of the most limitations in this field. The unique features offered by decentralized data aggregation (DDA) technique with the potential to overcome power consumption enable implementation of the dense array of WSSN on large structures. This paper presents a system identification of a simply supported plate based on the random decrement technique (RDT) and natural excitation technique (NExT) in combination with eigensystem realization algorithm (ERA) using Illinois Structural Health Monitoring Project (ISHMP) Services Toolsuite. Finally the system parameters including natural frequency and mode shapes are in accordance with numerical simulation showing efficacy and feasibility of decentralized NExT/ERA and RDT/ERA system identification.

A self-centring bridge pier is a combination of elastic recovery devices and internal or external energy dissipaters. During the cyclic loading test, it is proved that the self-centring system can minimize the residual drift of the pier whereas holding sufficient energy dissipate capacity as well as bearing capacity. It is worth noting that a simplified analytical model is proposed based on the experimental response regarding flexural deformation, unbounded length of mild steels and strain penetration. Comparison between the analytical model and test results has indicated that a reasonable envelope of the cyclic behavior of the system can be achieved by the model presented.

为了更好地控制结构震后残余变形,增强桥梁结构自复位性能,最大限度地强化震后继续服役的能力和增加再修复的可能,该文基于性能设计的理念,给出一种新型自复位桥梁墩柱节点体系的基本概念,并选取该体系的典型模型进行截面弹性承载力、滞回特性、设计控制参数等力学性能进行初步的推导和分析。研究结果初步表明,该自复位桥梁墩柱节点结构受力明确,构造合理巧妙,由于嵌合式接头限制了体系最小势能位置,能够帮助结构复位,震后残余变形小,震后弹性承载力不下降,能够满足对结构性能的更高要求。

Based on the hinged single-pole model, the paper derives the analytical solution of stability capacity of DSSB （Double-pole Steel-tubular Scaffolding with Bowl-Buckle） considering global effects of vertical tubes, horizontal tubes and bowl-buckle body between two adjacent fasteners. As for the DSSB discussed in the paper, the fasteners have long vertical distance, and the vertical tubes are extended to many stories with no vertical diagonal rods installed. The stability capacity of DSSB obtained by the presented method considering global effects, is much higher than that computed according to hinged single-pole theory, and is more consistent with the finite element results and experimental results. The method could be applied for the design of DSSB.

Recent advanced sensor technology has enabled wireless smart sensor network (WSSN) for structural health monitoring (SHM). Because of many attractive features such as wireless communication, battery powered, on board computation, and low cost, the WSSN makes the dense array of sensors feasible for engineering practice. In this study, a method for fatigue life monitoring using wireless smart sensor networks is explored by implementing Rainflow cycle counting algorithm in the sensor network, which extracts the loading features including the number of each load cycles, amplitude and mean of strain. Instead of sending back raw strain data to basestation, only the onboard processed histogram of the strain data is transmitted, which tremendously reduces the amount of data and the associated energy consumption in the wireless smart sensor networks. In addition, the feasibility of the method is experimentally verified through lab-scale tests.

In order to minimize post-earthquake residual structural deformation,to enhance seismic self-centering ability of bridge structures and to promote the continuous service condition with limited repair or even without retrofit,a series of new concepts of self-centering bridge pier joints has been presented.Based on a typical self-centering bridge pier joint structure,some mechanical factors including the flexural strength,hysteretic characteristics,working characters and control parameters have been derived and analyzed.The proposed joint that constrains the minimum potential position of the system,can help the structure reset.The paper shows that the unambiguous mechanical system of self-centering bridge pier joint has little post-earthquake residual deformation,prevents the elastic strength from weakening and holds the flexibility for construction,which can better satisfy more rigorous seismic requirements for next generation bridge system.