摩擦摆支座剪力销装置剪断力试验研究

针对实际桥梁工程应用中常见的摩擦摆支座剪力销装置的剪断力进行试验研究。分析了摩擦摆支座水平承载力达到发挥其减隔震功能所需起始力时，支座摩擦力对剪力销剪断力的影响规律，研究结果表明，剪力销剪断时支座摩擦力占比较大且不可忽略。通过摩擦摆支座剪力销单体剪断试验、支座水平滞回性能试验及支座减隔震起始力试验，验证了摩擦摆支座发挥减隔震功能前的约束力主要是由支座摩擦力和剪力销剪断力组成，并分析了剪力销不同排列布置方式对其整体剪断力的影响规律。试验结果表明，进行剪力销设计时有必要考虑支座摩擦力的影响，且剪力销布置排数越少越有利于剪断。     

基底隔震储罐频率特征与减震机理分析研究

研究不同高径比橡胶基底隔震储罐的频率特征,探讨储罐隔震体系3种不同振动频率随支座隔震频率变化规律.分析在不同频谱特性地震波激励下,隔震体系各振型组分对地震响应(基底剪力、支座位移和晃动波高)的影响,以及响应峰值随支座隔震频率和阻尼比的变化特点.研究表明,基底剪力峰值与场地地震波频谱特性密切相关.支座隔震频率不能完全反映减震机理的实质,隔震振型频率是影响基底剪力的重要参数.在软弱场地上隔震储罐的减震效率低,有效隔震频率范围窄.晃动波高峰值是储罐自振特性和地震波频谱特性等多种因素导致的结果,隔震系统设计时需特别考虑晃动波高增大的影响.     

大型LRB基础隔震储罐支座参数优化配置研究

铅芯橡胶支座(LRB)参数的优化配置是大型LRB基础隔震储罐设计的关键问题。采用Bouc-Wen模型模拟LRB的非线性力学性能,结合Newmark增量法和龙格库塔积分法求解了隔震储罐非线性动力方程,得到了不同类型场地上大型LRB隔震储罐的地震响应特点和设计参数优化配置规律。研究结果表明:支座隔震频率是影响大型隔震储罐减震效果的主要参数。I类场地上最优隔震频率范围为0.5～5rad/s,II类、III类场地上最优隔震频率范围为2～5rad/s,IV类场地上最优隔震频率范围为1.5～3rad/s。支座屈服强度对储罐地震响应的影响取决于场地类型和隔震频率。在II和III类场地上存在最优屈服强度使得基底剪力最小,且最优屈服强度随隔震频率增大而增大。     

位于不同场地的隔震储罐在地震作用下响应对比分析

就橡胶垫隔震体系和摩擦摆隔震体系,研究分析大型立式储液罐在不同场地实际地震作用下的响应,同时将地震响应与非隔震储罐进行对比分析。分析结果表明:在柔软场地,摩擦摆隔震系统的减震效果要好于橡胶垫系统。摩擦摆支座控制隔震层位移的能力要好于橡胶垫支座。此外,进行了参数影响分析,来衡量储罐储液量、高径比和隔震系统的隔震周期对储罐主要响应的影响。储罐储液量较小时,摩擦摆支座的减震率要好于橡胶垫支座。隔震储罐高径比不宜取为0.8,此时脉冲位移和基底剪力的峰值响应都较大。隔震周期在2 s～3 s区间范围内时,可以取得最优减震效果。     

剪力键对隔震桥梁地震反应的影响

减、隔震支座中增设剪力键,能提高桥梁的综合性能。为精确分析隔震桥梁的地震反应,建立了设置剪力键的减、隔震支座滞回模型,提出了剪力键的数值模拟方法。以某连续梁桥为背景,建立了全桥有限元分析模型,通过3种情况下桥梁地震反应分析结果的对比研究,验证了剪力键模拟方法的有效性。变化剪力键的水平承载力大小,分析了剪力键对减、隔震桥梁地震反应的影响。结果表明,剪力键对隔震桥梁的墩底弯矩有较大影响,隔震桥梁的地震反应分析时需考虑剪力键的影响。     

2017年8月8日四川九寨沟MS7.0地震前甘肃南部地区视应力变化

利用甘肃省区域台网提供的地震波形资料,计算甘肃南部地区2010年1月～2017年8月M_L≥2.0地震的视应力,分析九寨沟地震前甘南地区视应力的时空演化特征,所得结果如下：①M_L2.6～3.1、M_L2.0～2.5震级段地震视应力的空间分布具有较好的一致性,九寨沟M_S7.0地震前,距震中较近的川甘交界地区的舟曲、文县等地呈现出较为集中的视应力高值异常;②M_L2.0～2.5、M_L2.6～3.1地震的视应力在大区域范围内随时间的变化趋势有一定差异,M_L2.6～3.1地震视应力变化更为明显,在较大区域范围内表现为震前显著升高,而M_L2.0～2.5地震视应力则在震前一两年内开始下降;③随着区域划分范围向震中靠近,M_L2.0～2.5、M_L2.6～3.1地震视应力的变化逐渐趋于一致,至震中附近时,2个震级段视应力均表现为“震前几年长时间升高—临震前几个月下降”的同步变化。     

FVD与FPB在大跨长联减隔震体系梁桥中的联合作用机理研究

为验证液体黏滞阻尼器(FVD)与摩擦摆支座(FPB)组合在大跨长联减隔震体系梁桥中的应用效果,以一联(50+8×100+50) m预应力混凝土连续梁桥为工程背景,建立全桥有限元模型,通过输入场地地震安评报告提供的50年超越概率为2%的三条人工模拟地震波,开展单独及组合使用液体黏滞阻尼器和摩擦摆支座的大跨长联梁桥减隔震研究,从能量耗散的角度揭示液体黏滞阻尼器与摩擦摆支座组合在大跨长联减隔震体系梁桥中的联合作用机理。结果表明,大跨长联梁桥仅使用黏滞阻尼器,其长周期特性激发黏滞阻尼器充分发挥耗能,但无法避免对固定墩的地震损伤;仅使用摩擦摆支座隔震在纵(横)向强震下会引起支座位移超限;摩擦摆支座与黏滞阻尼器组合的减震机理为摩擦摆支座提供墩梁间的弱连接,激发墩梁间的相对速度,促进黏滞阻尼器(速度型)充分发挥阻尼耗能作用。另外,组合减震方案中摩擦摆支座为辅助耗能装置,黏滞阻尼器为主要耗能装置,且主控梁体位移;相比仅使用摩擦摆支座隔震,由于黏滞阻尼器激发的阻尼力增强了墩梁间约束,这种组合减隔震可能使结构输入能量增加,从而导致地震反应加剧。     

大跨铁路钢桁连续梁桥减隔震方案比较研究

为研究适用于大跨铁路钢桁连续梁桥的减隔震方案及合理优化参数,以一座全长504 m的三跨铁路钢桁连续梁特大桥为工程背景,使用非线性结构分析软件SAP2000建立有限元模型,采用快速非线性分析方法分析对比摩擦摆、阻尼器、速度锁定器等减隔震方案在各种装置参数下的减震效率。研究表明:由于大跨铁路钢桁连续梁桥墩身自振导致的地震力较大,摩擦摆方案内力减震效率一般,同时墩底内力对滑动面半径变化并不敏感,在选取滑动半径时应更多地考虑行车平顺性和梁端位移值的限制。速度锁定器会极大地增加此类桥梁地震输入能量,不适用于此类桥型。阻尼器方案对活动墩内力减震效果明显,但不能有效降低固定墩内力。摩擦摆支座附加阻尼器组合减震方案能有效控制此类桥梁的内力和位移响应。研究结论可为大跨度钢桁连续梁桥减隔震设计提供参考。     

LRB支座选取及其对连续梁桥减隔震效果的影响

本文以桥梁上部结构自重等荷载引起的墩台处支座反力为考虑因素,通过选择合适的铅芯橡胶支座并进行了一系列的数值分析,使桥梁结构减隔震效果达到最佳。基于大型有限元软件Midas Civil建立某三跨连续梁桥,采用动力时程分析方法,初选了六组支座作为研究对象,以墩底内力、支座内力、支座滞回耗能特性、墩顶加速度、主梁观测点加速度等为主要考虑因素,对铅芯橡胶支座的减隔震效果进行了分析。结果表明,当选取桥台处LRB支座竖向承载力约为支座反力的1.12倍,桥墩处LRB支座竖向承载力约为支座反力的1.10倍,且所有LRB支座铅芯屈服力约为梁体自重的0.056倍时,减隔震效果最佳。     

大型滑移基础隔震储罐地震反应影响因素研究

采用Bouc-Wen微分连续性模型模拟滑移支座的力学性能,对大型滑移基础隔震储罐非线性地震反应进行了仿真分析,得到了不同类型场地上大型滑移隔震储罐的地震响应特点,总结出了支座摩擦系数、复位刚度以及地震强度等因素对地震反应的影响规律.研究结果表明:大型滑移隔震储罐不适合建立在Ⅰ类场地上,而在Ⅱ类场地上减震效果最好.在Ⅳ类场地上隔震储罐出现晃动波高放大现象,并且需要增大支座摩擦系数和设置复位装置来控制过大位移反应.增大滑移支座复位刚度可以显著降低支座的残留位移.大型滑移隔震储罐在高地震强度地区的减震效果更好.     

Characterization of rocking shallow foundations using centrifuge model tests

This paper presents new results of centrifuge model tests exploring the behavior of rocking shallow foundations embedded in dry sand, which provides a variety of factors of safety for vertical bearing. The results of slow (quasi‐static) cyclic tests of rocking shear walls and dynamic shaking tests of single‐column rocking bridge models are presented. The moment–rotation and settlement–rotation relationships of rocking footings are investigated. Concrete pads were placed in the ground soil to support some models with the objective of reducing the settlement induced by rocking. The behavior of rocking foundation was shown to be sensitive to the geometric factor of safety with respect to bearing failure, L_f/L_c, where L_f was the footing length, and the L_c was the critical soil‐footing contact length that would be required to support pure axial loading. Settlements were shown to be small if L_f/L_c was reasonably large. Placement of concrete pads under the edges of the footing was shown to be a promising approach to reduce settlements resulting from rocking, if settlements were deemed to be excessive and also had impacts on the energy dissipation and rocking moment capacity. A general discussion of the tradeoffs between energy dissipation and re‐centering of rocking foundations and other devices is included. Copyright © 2011 John Wiley & Sons, Ltd.     

地震作用下简支梁桥支座-挡块-桥墩相互作用研究

为了提高中小跨径简支梁桥的抗震能力,促进多级抗震设计思想的完善,以汶川地震中的寿江大桥为背景,构建了支座-挡块-桥墩相互作用分析模型,采用增量动力分析（IDA）方法,以挡块强度和墩高作为变化参数,研究了支座滑移、挡块限位和桥墩塑性三者之间抗震性能状态的耦合关系。研究表明:提高挡块强度可有效地控制支座的滑移,但会增大桥墩的曲率延性系数,且桥墩越矮,曲率延性系数增长越快;随着挡块强度的变化,支座滑移比的变化幅度明显大于桥墩曲率延性系数;随着墩高的增大,挡块的相对限位能力会提高;对于中小跨径简支梁桥而言,理想的抗震状态为:允许挡块破坏,使得支座出现小幅滑移,桥墩出现可修复的塑性损伤。因此,在挡块设计中,可优先考虑支座的限位效果,再综合考虑桥墩的地震响应,当桥墩为矮墩时,挡块的设计强度不可过大。     

A method of estimating the stress exponent in the flow law for rocks using fold shape

On the basis of experiment and theory, we expect rocks to deform in a linear fashion when diffusive processes control deformation, and nonlinearly in most other situations. The geometric characteristics of buckle folds in layered materials are dependent on rheological parameters, and in particular depend strongly on the stress exponent,n _L , of the stiff layers involved. Thus, information about the deformation rocks have undergone and their rheological state during deformation can be obtained by studying fold shapes and strain distributions. This is important because there is uncertainty in extrapolating laboratory-derived flow laws to the very slow natural strain rates and large strains found in nature.We have studied the development of buckle folds in linear and nonlinear materials using finite-element modeling, and interpolated the numerical results to construct plots relating several geometric parameters to variations in power-law exponent,n _L , and viscosity ratio,m, of layer to matrix. Such plots allow for a comparison of the results of numerical models with data for many natural and experimentally-produced folds, and there is consistency among the data for folds produced in physical models, using both linear and nonlinear materials and the numerical simulations. data for folds from the Appalachian Mountains, the Alps and elsewhere, however, suggest high values ofn _L in the flow laws for a number of rock types. The unexpectedly high estimates ofn _L suggest that other factors, such as strain softening or anisotropy, may influence fold shape, and thus complicate the estimation of the rheological properties of rocks.     

考虑上部结构影响的山区桥梁支座刚度设计方法研究

为了合理计算山区桥梁支座刚度,针对桥墩高度不相同的特点,考虑上部结构对桥墩顶部的转动约束作用,提出在横桥向可将墩顶视为自由约束,而在纵桥向将墩顶视为定向约束。分别按照地震作用下各墩底剪力和弯矩相等的原则,推导桥梁支座纵、横桥向的刚度设计公式,并给出各桥墩支座的设计方法。为验证方法的正确性,以墩底剪力相等的原则为例,利用OpenSees建立一座墩高不等的5跨连续梁桥模型,并依支座刚度取值不同分三种工况:工况一各桥墩支座刚度相同;工况二按墩顶自由计算各支座的纵、横桥向刚度;工况三按墩顶定向约束计算各支座的纵、横桥向刚度。分别对三种工况下的桥梁结构输入三条地震动记录进行时程分析,考察各桥墩的底部剪力。分析结果表明:工况一各桥墩纵、横桥向的底部剪力均不相同;工况二各桥墩横桥向的底部剪力相同而纵桥向的底部剪力不同;工况三各桥墩纵桥向的底部剪力相同而横桥向的底部剪力不同。上述结果表明在桥梁支座设计时,横桥向桥墩的抗推刚度应按墩顶自由计算,而纵桥向桥墩的抗推刚度应按墩顶为定向约束计算。     

Empirical predictors of annual bed load travel distance,and implications for salmonid habitat restoration and protection

Measurements of annual travel distance (L_b) of bed load sediment at 16 locations in Alaska, the intermountain USA, west coast USA and Scotland are strongly correlated with bankfull channel width (r² = 0·86, p < 0·001). Travel distance of particles is probably limited by trapping in bars, which have a longitudinal spacing proportional to channel width. Increased abundance of woody debris reduces bar spacing and may reduce L_b. Longer cumulative duration of bed load transporting flows in a year appears to increase L_b. Other predictors of annual travel distance such as stream power per unit length, drainage area and bankfull discharge were less well correlated with L_b (r² ranging from 0·27 to 0·51). Stream power per unit bed area, basal shear stress and slope were not significantly related to L_b (r² < 0·05). Most correlations were improved when regressions were limited to data from the west coast USA. Travel distance estimates can be used to help identify reaches that may take longer to recover from large, short‐term increases in sediment supply. Published in 2001 by John Wiley & Sons, Ltd.     

Lateral load pattern in pushover analysis

The seismic capacity curves of three types of buildings including frame, frame-shear wall and shear wall obtained by pushover analysis under different lateral load patterns are compared with those from nonlinear time history analysis. Based on the numerical results obtained a two-phase load pattern; an inverted triangle (first mode) load pattern until the base shear force reachesβ times its maximum value, V_max, followed by a (x/H)^α form, hereβ and α being some coefficients depending on the type of the structures considered, is proposed in the paper, which can provide excellent approximation of the seismic capacity curve for low-to-mid-rise shear type buildings. Furthermore, it is shown both the two-phase load pattern proposed and the invariant uniform pattern can be used for low-to-mid-rise shear-bending type and low-rise bending type of buildings. No suitable load patterns have been found for high-rise buildings.     

Research on seismic behavior and shear strength of SRHC frame columns

The seismic behavior of steel reinforced high strength and high performance concrete(SRHC)frame columns was investigated through pseudo-static experiments of 16 frame columns with various shear span ratios,axial compression ratios,concrete strengths,steel ratios and stirrup ratios.Three kinds of failure mechanisms are presented and the characteristics of experimental hysteretic curves and skeleton curves with different design parameters are discussed.The columns’ductility and energy dissipation were quantitatively evaluated based on seismic resistance.The research results indicate that SRHC frame columns can withstand extreme bearing capacity,but the abilities of ductility and energy dissipation are inferior because of SRHC’s natural brittleness.As a result,the axial load ratio should be restricted and some construction measures adopted,such as increasing the stirrup ratio.This research established effect factors on the bearing capacity of SPHC columns.Finally,an algorithm for obtaining ultimate bearing capacity using the flexural failure mode is established based on a modified planesection assumption.The authors also established equations to determine shearing baroclinic failure and shear bond failure based on the accumulation of the axial load force distribution ratio.The calculated results of shear bearing capacity for different failure modes were in good agreement with the experimental results.     

Coupling behavior of shear deformation and end rotation of elastomeric seismic isolation bearings

This paper presents a mechanical model for predicting the behavior of elastomeric seismic isolation bearings subject to combined end rotations and shear deformation. The mechanical model consists of a series of axial springs at the top, mid‐height and bottom of the bearing to vertically reproduce asymmetric bending moment distribution in the bearings. The model can take into account end rotations of the bearing, and the overall rotational stiffness includes the effect of the variation of vertical load on the bearing and the imposed shear deformation. Static bending tests under various combinations of vertical load and shear deformation were performed to identify the mechanical characteristics of bearings. The test results indicate that bearing rotational stiffness increases with increasing vertical load but decreases with increasing shear deformation. Simulation analyses were conducted to validate the new mechanical model. The results of analyses using the new model show very good agreement with experimental observations. A series of seismic response analyses were performed to demonstrate the dynamic behavior of top‐of‐column isolated structures, a configuration where the end rotations of isolation bearings are typically expected to be larger. The results suggest that the end rotations of elastomeric bearings used in practical top‐of‐column isolated structures do not reduce the stability limit of isolation system. Copyright © 2016 John Wiley & Sons, Ltd.     

模块化预制拼装铁路实心桥墩抗震性能数值分析

为适应施工期短的严/高寒地区和近海铁路桥梁工程发展,提高铁路桥梁工程的施工效率和工程质量.文中提出了一种用于铁路桥梁工程中的模块化预制拼装实心桥墩,该桥墩不仅可以纵向节段连接,还可以通过多个可互连的模块水平连接.基于ABAQUS程序,开展了铁路桥梁模块化预制拼装桥墩在单调、往复荷载作用下力学性能数值分析,对该桥墩的承载...     

Aeolian sediment flux decay: Non-linear behaviour on developing deflation lag surfaces

Wind tunnel simulations of the effect of non-erodible roughness elements on sediment transport show that the flux ratio q/q_s, shear velocity U*, and roughness density λ are co-dependent variables. Initially, the sediment flux is enhanced by kinetic energy retention in relatively elastic collisions that occur at the roughness element surfaces, but at the same time, the rising surface coverage of the immobile elements reduces the probability of grain ejection. A zone of strong shearing stress develops within 0·03 to 0·04 m of the rough bed because of a relative straightening of velocity profiles which are normally convex with saltation drag. This positive influence on fluid entrainment is opposed by declining shear stress partitioned to the sand bed. Similarly, because the free stream velocity U_f is fixed while U_* increases, velocity at height z and particle momentum gain from the airstream decline, leading eventually to lower numbers of particles ejected on average at each impact. When the ratio of the element basal area to frontal area σ is approximately equal to 3·5, secondary flow effects appear to become significant, so that the dimensionless aerodynamic roughness parameter Z₀/h and shear stress on the exposed sand bed T_s decrease. It is at this point that grain supply to the airstream and saltation drag appear to be significantly reduced, thereby intensifying the reduction in U_*. The zone of strong fluid shear near the bed dissipates.