Nonsmooth dynamics prediction of measured bridge response involving deck‐abutment pounding

Earthquake‐induced deck‐abutment contact alters the boundary conditions at the deck level and might activate a different mechanical system than the one assumed during the design of the bridge. Occasionally this discrepancy between the assumed and the actual seismic behavior has detrimental consequences, for example, pier damage, deck unseating, or even collapse. Recently, an insightful shake‐table testing of a scaled deck‐abutment bridge model 1 , showed unexpected in‐plane rotations even though the deck was straight. These contact‐induced rotations produced significant residual displacements and damage to the piers and the bents. The present paper utilizes that experimental data to examine the validity and the limitations of a proposed nonsmooth dynamic analysis framework. The results show that the proposed approach satisfactorily captures the planar rigid‐body dynamics of the deck which is characterized by deck‐abutment contact. The analysis brings forward the role of friction on the physical mechanism behind the rotation of the deck, and underlines the importance of considering the frictional contact forces during deck‐abutment interaction even for straight bridges, which typically are neglected. Finally, the paper investigates the sensitivity of the rotation with respect to macroscopic contact parameters (i.e., the coefficient of friction and the coefficient of restitution). Copyright © 2017 John Wiley & Sons, Ltd.     

Non‐linear seismic response of arch dams with contraction joint opening and joint reinforcements

A comprehensive study of non‐linear seismic response of arch dams with contraction joint opening and joint reinforcements has been conducted. A numerical model of contraction joint reinforcements is presented for optimization control of the joint opening. The objective of this control is to reduce the joint opening and expectantly to balance the sustained loads between the horizontal and the vertical components of the dam, thus avoiding an overstress in the cantilever while retaining the release of arch tensile stresses to some extent. Several parameter studies such as critical element size and required number of joints to be simulated for convergence are also performed. As an engineering application, a 292‐m high arch dam (the Xiaowan arch dam) and the Big Tujunga dam are analysed in detail. The results demonstrate that the joint opening and the corresponding load transfer from the arch to cantilever components of the dam during strong earthquakes are substantial. It is also evident that by providing sufficient strength and reinforcement flexibility, the joint opening can be controlled to some extent. However, the stress redistribution due to reinforcement control is not sufficient to avoid the overstress in the cantilever for the Xiaowan arch dam. Thus, alternative measures are discussed. Copyright © 2000 John Wiley & Sons, Ltd.     

高速铁路无砟轨道地基泥岩膨胀性分类分级研究

红层泥岩是一种典型侏罗系沉积岩,其含有微量黏土矿物,易遇水软化、失水崩解,具有一定膨胀性,是引起兰新高速铁路路基持续上拱变形的一个重要因素,故重新判定该种土体膨胀性对高速铁路无砟轨道设计和施工具有重要意义。为此,选取等效蒙脱石含量、阳离子交换量、自由膨胀率和液限为泥岩膨胀性判别指标,通过兰新高速铁路上拱地段大量钻孔实测资料,提出了泥岩膨胀等级分级标准,采用改进层次分析法、基尼系数法和直觉模糊理论确定了判别指标组合权重,基于逼近理想解排序法(TOPSIS法)建立了泥岩膨胀性直觉模糊综合评价模型。结果表明：直觉模糊综合评价模型将泥岩膨胀性进行了定量化,克服了同一试样不同指标属于不同等级判别缺陷;室内膨胀量试验验证了膨胀等级分级标准和直觉模糊综合评价模型对兰新高铁地基泥岩适用性和准确性。研究成果对地基红层泥岩高速铁路路基长期持续上拱变形风险评估和工程控制措施提供技术支撑。     

季冻土区临水内、外拱护墙结构冻胀特征分析及治理

为厘清季冻土区临水内、外拱护墙结构冻胀平位移冻害机理,测试隔离层防冻害装置的有效性,在20101110-20110531、20131110-20140531、20171110-20180531三个观测年内,以长春某湖泊临水内、外拱护墙结构为研究对象,选择内、外拱护墙结构和设隔离层防冻害装置的试验内拱护墙结构三者相对比,用钢尺量距法观测三者寒期的平位移状态。结果表明：内拱护墙结构出现倾斜、裂缝导致的内向冻胀平位移冻害,其内向平位移曲线随气温均呈"半驼峰型",对应观测年持续降温-持续低温-持续升温-正温时段,内向冻胀平位移呈减小-增大-减小-稳定残余的位移运动,诱因是平冻胀应力的生成-增长-减弱-消失作用;外拱护墙结构出现较小的外向冻胀平位移,外向冻胀平位移曲线均呈"波浪型",无冻害发生,冰凸拱平冻胀应力推动外拱护墙结构压缩冻土凹拱形成外向冻胀平位移,冻土凹拱限制了外向冻胀平位移发展;设隔离层防冻害装置的试验内拱护墙结构未发生平位移冻害,其内向冻胀平位移较自然冻胀的内拱护墙结构减小83.92%,较外拱护墙结构减小51.74%,表明隔离层防冻害装置防治冻胀平位移冻害有效。     

大跨度钢管混凝土拱桥抗震性能指标研究

高轴压比钢管混凝土墩柱的试验结果对钢管混凝土拱肋具有较大的借鉴意义。为明确大跨度钢管混凝土拱桥的抗震性能指标,研究了高轴比钢管混凝土构件的破坏过程及延性性能。以弯矩作为性能指标将高轴压比钢管混凝土构件的试验破坏过程分为轻微损伤、有限损伤与严重损伤3个阶段,结合钢管混凝土截面性能状态的数值分析,探讨了高轴压比钢管混凝土构件的破坏机理。结果表明:高轴压比钢管混凝土构件具有一定的可用延性;提出了以计算等效屈服弯矩作为抗震性能指标,适当利用延性和实现钢管混凝土拱桥的有限损伤抗震设计,并给出了与有限损伤相关的截面性能状态及参数。研究成果弥补了规范在此方面的不足,可供高烈度地震区大跨度钢管混凝土拱桥抗震设计时参考。     

Introduction to dynamics of stone arches

The dynamic analysis of stone arches, made up of rigid voussoir laid dray, can be performed in two phases. First of all the value of the horizontal acceleration necessary to turn the structure into a mechanism and the corresponding mechanism must be determined. Then the dynamic behaviour of such a mechanism under a given acceleration time history can be studied. The first step is a static matter. The second one requires the solution of the non-linear equation of motion of the one-degree-of-freedom system in which the arch is turned. In this paper an iteration procedure is proposed to find out the mechanism. Then the structural behaviour of the mechanism is analysed. Both free and forced vibrations are investigated and the study is limited to the first-half cycle of vibration. Damping is not considered and sliding between the blocks at the hinge sections is not allowed. © 1998 John Wiley & Sons, Ltd.     

基于压力拱理论的水下隧道合理覆岩厚度研究

建立了水下隧道流固耦合数值模型,通过正交试验优化计算方案,分析土岩复合地层和全断面岩层拱顶竖直方向上围岩压力拱的成拱规律,并据此提出以成拱临界板厚为判据求解水下隧道合理覆岩厚度的思路,建立水下隧道合理覆岩厚度回归模型,并通过BP神经网络模型对回归模型进行评价与校验,结合佛莞城际狮子洋隧道工程,进行了合理覆岩厚度回归模型的应用算例分析。研究表明：土岩复合地层上覆岩层岩性较好时,压力拱高度主要受覆岩厚度影响,上覆岩层岩性较差时,压力拱高度主要受上覆软土厚度影响;压力拱高度随覆岩厚度增加线性增加,达到成拱临界板厚时,逐渐减小随后趋于稳定,上覆岩层岩性越差,成拱临界板厚越大;全断面岩层压力拱高度随覆岩厚度的变化比土岩复合地层平稳。算例分析表明,以成拱临界板厚为判据建立的合理覆岩厚度模型能给出较优的覆岩厚度预测值,可为土岩复合地层水下盾构隧道的设计和施工提供参考。     

Full-scale experimental modal analysis of an arch dam: The first experience in Iran

Forced vibration field tests and finite-element studies were conducted on the Shahid Rajaee concrete arch dam in Northern Iran to determine the dynamic properties of the dam–reservoir–foundation system. The first forced vibration tests on the dam were performed with two different types of exciter units, with a limited maximum force, bolted on the dam crest for alternative in-phase and out-of-phase sequencing. Because of an insufficient number of recording sensors, two arrangements of sensors were used to cover sufficient points on the dam crest and one gallery during tests. Two kinds of vibration tests, on–off and frequency sweeping, were carried out on the dam. The primary natural frequencies of the coupled system for both symmetric and anti-symmetric vibration modes were approximated during on–off tests in two types of sequencing of exciters, in phase and out-of-phase, with a maximum frequency of 14 Hz. The principal forced vibration tests were performed at precise resonant frequencies based on the results of the on–off tests in which sweeping around the approximated frequencies at 0.1 Hz increments was performed. Baseline correction and suitable bandpass filtering were applied to the test records and then signal processing was carried out to compute the auto power, cross power and coherence spectra. Nine middle modes of vibration of the coupled system and corresponding damping ratios were estimated. The empirical results are compared against the results from calibrated finite-element modeling of the system using former ambient vibration tests, considering the dam–reservoir–foundation interaction effects. Good agreement is obtained between experimental and numerical results for eight middle modes of the dam–reservoir–foundation system.     

乌东德高拱坝极限抗震能力研究

乌东德水电站是金沙江下游河段上4个水电梯级的最上游梯级,大坝为265 m高的双曲拱坝。采用非线性有限元法,将拱坝坝体-坝基作为一个整体系统,在考虑坝体横缝影响及无限地基辐射阻尼影响基础上,模拟坝肩控制性滑块各滑裂面在地震作用下张开、滑移的非线性力学行为,研究设计与校核地震作用下大坝的抗震性能,探讨大坝-坝基整体系统在强震作用下的抗震潜力。研究结果表明：设计地震条件下,坝体仅在拱端应力集中区域拉应力超过抗拉强度,压应力则均满足强度要求,坝肩块体稳定,大坝-坝基体系的整体安全性可以保证;校核地震条件下,坝体应力值略有增加,能够满足不溃坝的设防要求;以大坝-坝基代表性的位移、变形量变化曲线的拐点作为评价极限抗震能力的标准,可知拱坝-坝基体系的抗震超载安全系数为2.7,相应的基岩水平向峰值加速度0.729g,拱坝-坝基体系抗剪参数强度储备安全系数为2.0,乌东德高拱坝具备较强的极限抗震能力。     

Nonlinear earthquake analysis of high arch dam–water–foundation rock systems

A nonlinear finite element model for earthquake response analysis of arch dam–water–foundation rock systems is proposed in this paper. The model includes dynamic dam–water and dam–foundation rock interactions, the opening of contraction joints, the radiation damping of semi‐unbounded foundation rock, the compressibility of impounded water, and the upstream energy propagating along the semi‐unbounded reservoir. Meanwhile, a new equivalent force scheme is suggested to achieve free‐field input in the model. The effects of the earthquake input mechanism, joint opening, water compressibility, and radiation damping on the earthquake response of the Ertan arch dam (240 m high) in China are investigated using the proposed model. The results show that these factors significantly affect the earthquake response of the Ertan arch dam. Such factors should therefore be considered in the earthquake response analysis and earthquake safety evaluation of high arch dams. Copyright © 2011 John Wiley & Sons, Ltd.