Bridge widening is commonly required in congested bridges. During construction, one or two lanes on the old bridge remain open; the vehicle traffic generates vibrations affecting the early age concrete of the closure pour, which may induce a negative effect on the durability of the bridge, i.e., initial crack in the closure pour. To quantitatively evaluate the mechanical performance of closure pours under vibration load, this paper examined three construction schemes for closure pours in bridge-widening projects. An equivalent full-scale segment model was designed to test the three schemes, including vibration tests and static tests. In the vibration tests, the setting time, the development of deflection, strain, and cracking of the closure pour during the construction period were obtained. Adding I-shaped steel beams to restrain the movement of the old and new bridges significantly improved the performance of the closure slab. In the static test, the final load-carrying capacity, damage, and failure modes were investigated. The slabs poured with the restraining steel beams showed superior crack resistance performance. The peak load-carrying capacity of the closure pour was about 50 times the maximum expected load, demonstrating the satisfactory load-carrying capacity of the closure pour. (C) 2017 American Society of Civil Engineers.

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.

利用三折线半刚性节点模型,结合碗扣式脚手架竖向承载力足尺试验,对碗扣式脚手架的竖向失稳问题进行了有限元模拟、结果对比和性能分析.模拟中重点考虑碗扣节点的材料非线性和构件的初始几何非线性.结果表明,三折线半刚性节点模型精度可靠,适用于碗扣式脚手架的精细化数值模拟.此外,对影响碗扣式脚手架受力性能的因素进行了研究,包括底端边界条件、碗扣式半刚性节点初始刚度和伸长段长度.研究发现:以上因素对碗扣式脚手架受力性能有不同程度影响,中间立杆离地对承载力影响较大,承载力随碗扣节点初始刚度增大而增大并呈现三段式变化,承载力随伸长段长度增大而减小并呈现两段变化.

In this paper, a modified laminated finite-element model based on subcell of unit cell and CDM material model was developed in nonlinear explicit finite-element code to investigate the dynamic response of 2D triaxial braided composite under ballistic impact of projectile. Six subcells, which were considered as laminate with different stacking sequences using solid elements, were employed to represent one unit cell of triaxial braided composites, therefore, the fiber-laying direction of braiding architecture is reproduced. In the prediction of the subcell model, an approximate round conical deformation area forms in the target and the failure modes are mainly longitudinal and transverse cracking due to tension. Compared with the continuum model, the subcell model is capable of analyzing the energy absorption of fiber in each direction. Although the failure modes are similar for both methods, the subcell model is more effective in prediction of impact wave propagation than the continuum model because it describes the fiber arrangement of triaxial braided composites. The developed subcell model will be an effective tool for the design process of carbon/ epoxy composite fan casings. (C) 2016 American Society of Civil Engineers.

In the current paper, meso-scale model methods based on yarn architecture of triaxial braided composites were employed to investigate its dynamic response in LS-DYNA. Numerical simulations were conducted on single layer braided textile. The dynamic response and energy absorption mechanism of triaxial braided textile under impact was discussed. The influence of friction action and boundary conditions was also addressed. It is found that the main response of triaxial braided textile under projectile impact are the transverse wave propagation, yarn tension, yarn fracture and pull-out successively. In the initial stage of impact, the yarns are still in the crimped state and the interaction force between the projectile and textile is very low. After the yarns are straighten, the interaction force and yarn strain energy increase rapidly and reach its maximum value before the yarn fracture. Yarn strain energy, yarn kinetic energy and friction sliding energy are the main energy absorption modes. The yarn strain energy and kinetic energy increase first and decrease later, while the sliding energy increase significantly in the process of perforation. The boundary constraint has evident influence on the deformation, interaction force and energy absorption of braided textile. The boundary conditions change the proportional relations of yarn internal energy and yarn kinetic energy. It also influences the distributions of strain energy of yarns in each direction. The friction factor has great influence on the ballistic performance. When the friction factor is smaller, the yarns are apt to sliding away and give rise to the deduction of energy absorption.

In this paper, a simple and designable shock isolation system with ideal high-static-low-dynamic-stiffness (HSLDS) is proposed, which is intended for the horizontal plane shock isolation application. In this system, the isolated object is suspended by several bearing cables and constrained by a number of uniformly distributed pretensioned cables in the horizontal plane, where the low dynamic stiffness of the system is main controlled by the pretension of the planar cables, whilst the high static stiffness is determined by the axial stiffness of the planar cables and their geometric settings. To obtain the HSLDS characteristic of the system, a brief theoretical description of the relationship between the restoring force and displacement is derived. By obtaining the three-order Taylor expansion with sufficient accuracy of the restoring force, influence of planar cable parameters on the low dynamic and high static stiffness is thus given, therefore, the required HSLDS isolator can be easily designed by adjusting the planar cable length, pretension and tensile stiffness. Finally, the isotropy characteristic of the restoring force of the system with different numbers of planar cables is investigated. To evaluate the performance of the system, a rigid isolated object and flexible cables coupling simulation model considering the contacts of the system is established by using multibody dynamics approach. In this model, flexible cables are simulated by 3-node cable element based on the absolute nodal coordinate formulation; the contact between cable and isolated object is simulated based on Hertz contact theory. Finally, the time-domain shock excitation is converted from the design shock spectrum on the basis of BV043/85 criterion. The design procedure of this isolator and some useful guidelines for choosing cable parameters are presented. In addition, a summary about the performance of the isolators with different numbers of cables shocking in an arbitrary direction is given in the conclusion.

Fiber-reinforced plastic-wrapped concrete columns (FRP-C) have been extensively used in building structures and transportation infrastructures around the world during the past two decades. These members are actually subjected to a long-term sustained axial compression before they experience the designated ultimate loading. However, little attention has been given to the performance of FRP-C after sustained axial compression compared with that of its short-term instant performance. This study aims to establish a design-oriented numerical model for the long-term deformation of circular FRP-C after sustained load. A modified constitutive model of FRP-wrapped concrete is proposed for numerical analysis of FRP-C considering two dominant effects of sustained axially compressive loading. Numerical verifications against existing tests indicates that the ultimate strength will be slightly enhanced while the ultimate strain will be conspicuously reduced in most cases of normal strength FRP-C after a long-term sustained load.

Concrete-filled steel tubular (CFST) columns are widely used in infrastructure applications and thus usually are subject to long-term service loading. However, understanding the influence of sustained loading on the ultimate performance of these structural members is still lacking. The objective of this work is to develop a constitutive model to account for strength and ductility change of CFST columns under sustained loading, validated by experimental data reported in the literature.In this framework, a simplified analytical method equipped with a monolithic iterative scheme is developed to efficiently estimate the creep deformation of these composite columns at any designated target time. Based on the calculated creep status, an analytical stress-strain curve is proposed to characterize the post-creep mechanical behavior of steel-confined concrete. This stress-strain behavior incorporates the combined effects of enhanced compressive strength of plain concrete and reduced confining strength provided by steel tube, both of which are caused by sustained load. Finite element based numerical study together with the available test database are used to validate the mechanical analysis and to assess the performance of the proposed constitutive model. The predicted post-creep response is found to be in good agreement with the experimental results for CFST columns with circular and square cross-sections. Finally, an extensive parametric study based on a pushover analysis is conducted to examine the influence of individual critical design parameters on structural ultimate strength and ductility due to long-term service loading. (C) 2015 Published by Elsevier Ltd.

In case of tubular steel scaffold collapse under construction,a new displacement monito-ring system of tubular steel scaffold with cuplok joint is introduced to minimize casualties and property losses.The tubular steel scaffold of a 40 meters long box girder in Maanshan Yangtze River Bridge is taken as an example to propagate structural geometry nonlinear analysis and displacement calculation un-der design load through scaling and superimposing the lowest eighenmode onto the perfect geometry to create an initial imperfection for displacement graded threshold value.Laser transmitters which are placed in key positions of the tubular steel scaffold are used for trajectory tracking to obtain horizontal and verti-cal displacements by the reference coordinate system.System signals are transmitted through wireless net-work to PC terminal in control center.It is shown that the new displacement monitoring system of tubular steel scaffold with cuplok joint is practical and feasible with simple operation and controllable costance.

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.

The fiber element technology of OpenSees is mature, has powerful capacity of nonlinear analysis and can be therefore used for the refined analysis of bridge and structural engineering. However, as the sophisticated constitutive models for the FRP (fiber reinforced plastic) confined concrete are not available in the material library of the current OpenSees, the constitutive models for the concrete need to be developed for sake of the analysis of the FRP confined concrete piers/columns. By reviewing and analyzing part of the constitutive models for the FRP confined concrete, a modified Lam-Teng model is proposed and at the time the program is written, the modified model is built in the material library of the OpenSees and the expansion of the library is consequently successfully realized. The numerical simulation is implemented for the axial compression failure tests of 3 groups of the FRP confined concrete piers/columns, for the horizontal cyclic loading test of 1 group of the circular section FRP confined concrete piers/columns and the hysteretic behavior test of 1 group of the existing damaged piers retrofitted by the FRP and the calculation prediction of the simulation matches well the tests. The results of the work demonstrate that the proposed technical solution to the development of the constitutive models based on the OpenSees is feasible, the modified Lam-Teng model is capable of describing the mechanical behavior of the FRP confined concrete piers/columns and the calculation prediction is accurate and reliable.

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.

OpenSees is a well-recognized open source platform with high compatibility, and it has a well-developed fiber element method to cope with nonlinear structural analysis. Fiber reinforced polymer (FRP) confined concrete can effectively improve the seismic performance of concrete structures. However, sophisticated constitutive models for FRP confined concrete are not available in the current version of OpenSees. In this paper, after reviewing several typical FRP confined concrete constitutive models, a modified constitutive model for FRP confined concrete in circular sections was proposed based on Lam and Teng (2003)’s model with four main modifications including the determination of FRP rupture strain, ultimate condition, envelope shape, and hysteretic rules. To embed the proposed constitutive model into OpenSees is a practical solution for engineering simulation. Hence, the secondary development of OpenSees New UserMat was briefly demonstrated and a set of critical steps were depicted in a flow chart. Finally, with the numerical implementations of a series of FRP confined concrete members covering a wide range of load cases, FRP confinement types and geometric properties, the utility and accuracy of the proposed model compared with Lam and Teng (2003)’s model and new material secondary development in OpenSees were well validated.

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.

Based on embedded atom method (EAM), an embedded atom hyperelastic (EAH) constitutive model is developed. The proposed EAH constitutive model provides a multiscale formalism to determine mesoscale or macroscale material behavior by atomistic information. By combining the EAH with cohesive zone model (CZM), a multiscale embedded atom cohesive finite element model (EA-cohesive FEM) is developed for simulating failure of materials at mesoscale and macroscale, e.g. fracture and crack propagation etc. Based on EAH, the EA-cohesive FEM applies the Cauchy-Born rule to calculate mesoscale or macroscale material response for bulk elements. Within the cohesive zone, a generalized Cauchy-Born rule is applied to find the effective normal and tangential traction-separation cohesive laws of EAH material. Since the EAM is a realistic semi-empirical interatomic potential formalism, the EAH constitutive model and the EA-cohesive FEM are physically meaningful when it is compared with experimental data. The proposed EA-cohesive FEM is validated by comparing the simulation results with the results of large scale molecular dynamics simulation. Simulation result of dynamic crack propagation is presented to demonstrate the capacity of EA-cohesive FEM in capturing the dynamic fracture.

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.

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。

In general,Self-Centering Pier(SCP) consists of load bearing components,self-centering components,energy dissipaters and joints(e.g.tongue groove joint etc.).SCP has outstanding reparability and negligibly small post-earthquake residual deformation.Its mechanical characteristics,including bearing capacity,lateral stiffness and hysteretic behaviour are analyzed theoretically.The analytical expression of the lateral stiffness of SCP as a function of the flexural stiffness of load bearing components,the tensile stiffness of self-centering components and energy dissipater,the initial pretension and the physical dimension of pier is derived.The concept and formula of the intrinsic lateral stiffness of SCP are proposed to reveal the inherent property of SCP.The upper bound and lower bound of SCP lateral stiffness are the flexural stiffness of load bearing components and the intrinsic lateral stiffness of SCP respectively.The fan-bladed hysteretic behaviour of SCP is the result of superposing the hysteretic behaviour of energy dissipaters upon the self-centering components.Based on performance-based design principle,self-centering 3 steps(SC3S) design method in which post-earthquake residual deformation is considered,is proposed for engineering practice.