2020年1月19日新疆伽师MS6.4地震烈度分布及房屋震害特征

以2020年1月19日伽师M S6.4地震现场烈度调查结果为基础,综合余震分布、发震构造及仪器烈度值等研究成果,确定了本次地震的烈度分布。此次地震极震区烈度为Ⅷ度(8度),Ⅵ度(6度)区及以上总面积为7599 km 2。分析各个烈度区内不同结构房屋的震害,结果表明,震害较重房屋主要是由于这些房屋年久失修,施工质量不高,缺乏必要的抗震措施等自身原因造成的,其中没有抗震措施的砖木结构房屋是震害主体。随着新疆地区农村房屋的抗震性能提高,在以后的地震烈度调查中,需要现场调查人员依据不同结构房屋的破坏等级及平均震害指数等参数综合判定调查点的烈度值,在没有明显震害的低烈度区,仪器烈度值将会成为烈度图绘制的重要依据。     

九寨沟7.0级地震甲蕃古城震害特征研究

在九寨沟7.0级地震现场震害调查的基础上,研究甲蕃古城及其周边出现的崩塌和滑坡、玻璃固定窗的破损和局部倒塌、片石砌体结构房屋倒塌、房屋开裂破坏等典型震害特征,分析了鞭梢效应等,探讨了改善房屋建筑抗震性能的构造措施和Ⅷ度区的烈度评定方法及依据等,以期为房屋建筑的抗震设防、减轻震害损失以及烈度评定等提供参考。     

考虑抗倒能力的砌体结构震害预测

以往对砌体结构的抗震鉴定或震害预测方法没有考虑构造柱、圈梁等抗震措施对增强砌体结构抗倒能力的影响,使得在高烈度下的鉴定或震害预测结果多为倒塌,这与震害实际不符合。实际在高烈度区,有一些砌体结构并没有倒塌。本文按照杨玉成等[1]提出的用抗倒增强系数修正楼层综合抗震能力指数方法,将抗倒增强系数的取值推广到不同工况;提出地震烈度为Ⅹ度时烈度影响系数为4.0;推演了杨玉成等提出的用综合抗震能力指数表示的震害预测判别标准。按此法进行了24栋建筑的分析,震害预测结果显示考虑抗倒能力的方法适用于高烈度下的砌体结构震害预测,简单易用,符合震害实际。     

地震作用下二级悬臂式挡土墙土压力计算的探讨

二级悬臂式挡墙由2个单级悬臂式挡墙呈上下砌垛方式组成。该结构不仅具有单级挡墙型式简单、占地少、对地基承载力要求不高、经济指标好和施工方便等一系列的特点,而且弥补了单级挡墙限制高度的缺点,同时具有重力式挡墙的一些优点,在工程中逐步得到了应用。以库伦土压力理论为基础结合物部-冈部法分别计算了峰值加速度为0.2g、0.3g和0.4g时,二级悬臂式挡墙在分级墙背理论和整体墙背理论下,上墙和下墙的地震主动土压力,并与同高度的单级悬臂式挡墙地震土压力进行了比较。结果表明:二级悬臂式挡墙受力更优,是1种较优的抗震支挡结构,分析结果可为二级悬臂式挡土墙的抗震设计提供参考。     

2017年8月9日精河6.6级地震烈度分布与房屋震害特征分析

通过对2017年8月9日精河6.6级地震灾区内共计355个调查点的实地调查,确定了此次地震的烈度分布。灾区最高烈度为Ⅷ度（8度）,灾区面积15623km²,灾区总人口487696人,其中,受灾人口133695人,地震共造成36人受伤;对各烈度区内不同结构类型房屋的震害现象进行了整理,分析了不同结构类型房屋的抗震能力与震害原因,结果显示,土木结构房屋倒塌及屋檐塌落是导致人员受伤的主要原因;砖木结构房屋缺乏抗震设施,破坏形式多样;砖混结构房屋在高烈度区破坏较重;框架结构房屋主体完好但填充墙普遍出现破坏。安居富民房屋抗震性能良好。     

基于概率和位移的框支剪力墙结构抗震性能评估方法

本文严格按照中国规范设计出典型的带转换层部分框支剪力墙钢筋混凝土结构,通过弹塑性分析程序IDARC2D对该结构进行多个地震动作用下的大震弹塑性时程分析,得到结构及各个构件的反应量的统计特征,再参照美国基于性能抗震设计规范ASCE-41-06的结构与构件变形限值作为性能指标,计算出结构和各个构件的可靠度和可靠指标,作为评价结构抗震性能的标准,总结归纳出基于概率和位移的抗震设计方法的思路.最后运用该方法,对7、8度烈度区的框支剪力墙结构进行可靠性分析,通过对比分析,研究考虑内力增强措施、层间位移角控制条件、竖向构件轴压比限制条件、层刚比控制准则和竖向构件最小配筋率等因素对不同抗震烈度区的框支剪力墙结构的可靠性的影响,从而评价中国规范抗震措施和构造措施的有效性.     

少筋混凝土重力式桥墩抗震研究现状

我国铁路桥梁普遍采用少筋混凝土重力式桥墩（配筋率<0.5%）,现有普通钢筋混凝土结构的延性抗震理论不适用于该类型桥墩。为了促进我国铁路重力式桥墩抗震理论的发展,详细论述了我国少筋混凝土重力式桥墩的研究现状和存在问题。首先,对少筋混凝土重力式桥墩的破坏特征及破坏机理进行了总结;其次,分析了各参数对少筋混凝土重力式桥墩抗震性能的影响;再次,对目前少筋混凝土重力式桥墩的抗震设计方法进行了汇总与分析;最后,对少筋混凝土重力式桥墩的数值分析模型进行了归纳与分析。通过对现有研究的汇总发现:目前对少筋混凝土重力式桥墩的试验研究主要以拟静力方法为主,还缺少振动台试验研究其动力状态下的破坏机理及抗震性能;少筋混凝土重力式桥墩的破坏机理及其与各影响因素之间的定量关系还不明确;已提出的少筋混凝土重力式桥墩的抗震设计方法存在塑性铰区计算不合理等问题,还需要进一步的完善。为少筋混凝土重力式桥墩抗震研究提供了方向。     

昆明市区地震震害的不均匀分布特点及其重复性

本文以澜沧耿马地震时昆明震害调查资料为基础,结合地震史料,研究了昆明市区震害的不均匀分布,烈度有两度的差别。相对高烈度区与历史强震破坏的重震害点大部分重合。据此分析了震害重复特点及其与地质构造和沉积盖层的关系。本文可用于研究昆明市区及邻区强震对市区可能造成震害的大致分布,为震害预测、防震抗震和城市规划提供一些依据。     

规则钢筋混凝土异形柱框架结构的抗震性能研究

本文按现行规范及技术规程设计了设防烈度为8度的一个规则的钢筋混凝土异形柱框架,并进行了单向水平地震作用下的空间三维非线性地震反应分析,考查了异形柱框架结构在设防和罕遇地震水准下的整体抗震性能,对结构能否达到抗震设防目标进行了初步评价。结果表明,8度区按规范设计的结构在设防烈度及罕遇烈度地震作用下基本能够达到预期的抗震设防目标。     

汶川8.0级地震甘肃陇南地区建筑震害调查

总结了2008年汶川8.0级地震在甘肃陇南地区造成的农村房屋和城镇房屋的典型震害及其原因。考察发现,由于农村房屋一般未经抗震设防设计,在本次地震中即使在低烈度地区仍然震害严重;而城镇房屋震害较轻,一般均表现出良好的抗震性能,严重破坏的大多是一些施工质量差,缺乏良好的抗震概念设计以及改建时未考虑抗震设计的建筑。建筑震害调查的几个地区设防烈度均为Ⅷ度,实际烈度为Ⅵ～Ⅸ度,因此这些地区的房屋震害情况刚好能反映这些地区房屋抵抗小震、中震及大震的能力。结果表明,严格按照抗震规范设计、并保证施工质量的建筑基本都能达到三水准设防目标。最后本文对灾后重建和抗震设防提出了建议。     

地震作用下重力式挡土墙土压力特性数值模拟研究

重力式挡土墙在地震作用下的土压力特性一直是挡土墙设计的重要内容。本文通过数值模拟,在挡土墙墙背轴线上设置一系列监测点,得到地震过程中监测点的加速度、土压力强度时程曲线;然后根据时程曲线分析墙后土压力强度分布特征、根据土压力强度分布求出总土压力、根据总土压力求出其对墙趾的力矩;最后分别将土压力强度分布、总土压力、总土压力对墙趾的力矩与现有的研究方法及规范对比。结果表明:地震作用下墙背各点加速度峰值在同时刻发生,但土压力峰值不在同时刻发生;现有的一些研究方法未考虑土压力强度峰值时程变化,其结果比实际偏大;在低地震烈度条件下,规范计算的总土压力及倾覆力矩偏于保守,而在高烈度条件下则偏于危险。     

岩石场地重力式挡土墙地震土压力振动台实验研究

结合汶川震区调查资料,利用大型振动台模型试验,分析了碎石土填料的岩石场地重力式挡土墙的地震土压力及其分布规律,并以此对我国现行铁路、公路抗震规范做合理性讨论和细化。研究发现,地震作用下,挡土墙的动土压力沿墙高呈单峰曲线状分布,且60%～80%集中作用于挡墙中部;随着地震峰值加速度的增加,地震土压力分布逐渐偏离现行振震设计规范所认为的三角形线性状,而呈现非线性状;合力作用点高于1/3墙高,0.4g地震加速度作用下,接近0.4倍墙高,对岩石场地下粗粒径墙背填料的地震土压力作用点高度,建议取0.35倍墙高。对比计算表明,现行规范能基本满足工程抗震设计需要,但建议对柔性挡土墙的抗震设计作出必要规定。     

Seismic lateral movement prediction for gravity retaining walls on granular soils

At present, methods based on allowable displacements are frequently used in the seismic design of earth retaining structures. However, these procedures ignore both the foundation soil deformability and the seismic amplification of the soil placed behind the retaining wall. Thus, they are not able to predict neither a rotational failure mechanism nor seismic induced lateral displacements with an acceptable degree of accuracy for the most general case. In this paper, a series of 2D finite-element analyses were carried out to study the seismic behavior of gravity retaining walls on normally consolidated granular soils. Chilean strong-motion records were applied at the bedrock level. An advanced non-linear constitutive model was used to represent both the backfill and foundation soil behavior. This elastoplastic model takes into account both the stress dependency of soil stiffness and coupling between shear and volumetric strains. In unloading–reloading cycles, the non-linear shear-modulus reduction with shear strain amplitude is considered. Interface elements were used to model soil–structure interaction. Routine-design charts were derived from the numerical analyses to predict the lateral movements at the base and top of gravity retaining walls located at sites with similar seismic characteristics to the Chilean subduction zone. Thus, wall seismic rotation can also be obtained. The developed charts consider wall dimensions, granular soil properties, bedrock depth, and seismic input motion characteristics. As shown, the proposed charts match well with available experimental data.     

Displacement – based parametric study on the seismic response of gravity earth-retaining walls

The essence of performance-based design of gravity earth-retaining structures lies in the estimation of the residual (i.e. permanent) displacements after a seismic event. The accomplishment of this task however can be very complicated due to two interacting phenomena: the coupled sliding and tilting rigid body motion of the wall on an inelastic base and the formation of failure surfaces in the soil backfill. In this study a large number of fully non-linear, time-history analyses of gravity retaining walls (GRW) were performed using advanced numerical modelling. Different types of soil parameters and varying wall geometry within a practical range were investigated. The influence of different ground motion parameters was discussed and the results were compared with some of the most common limit equilibrium Newmark׳s sliding block procedures, including the recommendations by Eurocode 8, Part 5 [20]. Lastly, some recommendations for fast preliminary assessment of the seismic permanent displacements of GRW were provided.     

重力式挡土墙地基抗震承载力探讨

高烈度地震区重力式挡土墙由于地基承载力不足导致墙身失稳是一种较常见震害类型。基于拟静力法原理,利用极限分析上限定理对地震作用下挡土墙地基极限承载力进行求解,通过典型算例分析了极限承载力随地震动峰值加速度的变化关系与机理,讨论了地基土强度参数对其变化趋势的影响,提出了同时考虑设防烈度和地基土性的挡土墙地基抗震容许承载力修正方法及相应修正系数取值建议。结果表明:设防烈度在9度及以内时,随着地震动峰值加速度增加,挡土墙地基极限承载力近似呈线性下降,下降速率与地基土黏聚力呈负相关性,而受内摩擦角的影响不显著;地震作用加剧挡土墙基底荷载倾斜与偏心导致地基破坏区缩减是造成极限承载力下降的主要原因;设防烈度大于7度时,挡土墙地基抗震容许承载力较天然工况下有所降低,8度和9度设防烈度对应的修正系数约为0.9和0.7。     

Seismic soil pressure for building walls: An updated approach

The Mononobe–Okabe (M–O) method developed in the 1920s in Japan continues to be widely used despite many criticisms and its limitations. The method was developed for gravity walls retaining cohesionless backfill materials. In design applications, however, the M–O method, or any of its derivatives, is commonly used for below ground building walls. In this regard, the M–O method is one of the most abused methods in the geotechnical practice. Recognizing the limitation of the M–O method, a simplified method was recently developed to predict lateral seismic soil pressure for building walls. The method is focused on the building walls rather than retaining walls and specifically considers the dynamic soil properties and frequency content of the design motion in its formulation.     

Predicting seismic permanent displacement of soil walls under surcharge based on limit analysis approach

Seismic permanent displacement of the soil walls plays an important role in design of these structures. Due to the increase in growth of urban areas and the limitations in use of flat grounds, many structures are built near slopes and retaining walls. During earthquakes, these structures can apply an additional surcharge on the wall. The intensity and location of the surcharge is of considerable importance on the seismic displacements of the soil wall. In this study, by using the limit analysis and upper bound theorem, seismic permanent displacement of the soil wall under surcharge has been analyzed. Thus, a formulation is presented for calculating the yield acceleration and seismic displacement for different surcharge conditions. The effect of seismic acceleration, surcharge intensity, its location and soil properties is investigated. A parameter called the “displacement coefficient” is proposed, and is a potential modification for Newmark’s sliding-block method.     

Earthquake-induced displacements of gravity retaining walls and anchor-reinforced slopes

This paper examines in terms of seismic performance, the effectiveness of anchor reinforcement against gravity retaining walls used to stabilize a dry homogenous fill slope in earthquake-prone environment. Both analyzed stabilizing measures have the same design yield acceleration estimated from a limit equilibrium approach. The earthquake-induced displacements are calculated using a sliding block formulation of the equation of motion. Sliding failure along the base of the gravity retaining wall and rotational failure of the soil active wedge behind the wall, as well as rotational failure of the slide mass of the anchor-reinforced slope were considered in the present formulation. For the specific characteristics of the analyzed fill slope and input horizontal ground motion, the slope reinforced with anchors appears to experience vertical and horizontal seismic displacements at slope crest smaller by 12% and respectively, 32% than the vertical and horizontal earthquake-induced deformations estimated at the top of the active wedge behind the gravity retaining wall.     

桥梁结构抗震挡块的研究现状与展望

综述了桥梁抗震挡块的几类典型结构形式,对常见挡块的实际震害形式、破坏机理以及力学分析模型的研究现状进行了分析,归纳总结了不同规范中桥梁抗震挡块的设计方法。对当前挡块抗震研究和设计中存在的问题进行了分析和讨论,并提出了一种新型的预应力装配式超高性能混凝土(UHPC)挡块形式。研究结果表明:传统整体式混凝土挡块的主要破坏模式为斜剪和平剪破坏,既有试验中已对两种模式的破坏机理进行了较深入的研究;相比传统整体式混凝土挡块,滑移型混凝土挡块和弹塑性钢挡块在抗震设计中更具可控性,值得进一步在国内推广和应用;美国规范按挡块类型分别给出了不同的设计策略,并对挡块的承载力计算方法和配筋形式进行了说明,值得我国桥梁抗震设计规范借鉴;提出的装配式UHPC挡块具有传力简单明确、自复位和震后修复更换方便等特点,可作为我国中小跨径桥梁结构抗震挡块设计及加固的一种有益补充,值得进一步展开深入的研究。     

Seismic response of retaining walls with cohesive backfill: Centrifuge model studies

Observations from recent earthquakes show that retaining structures with non-liquefiable backfills perform extremely well; in fact, damage or failures related to seismic earth pressures are rare. The seismic response of a 6-m-high braced basement and a 6-m free-standing cantilever wall retaining a compacted low plasticity clay was studied in a series of centrifuge tests. The models were built at a 1/36 scale and instrumented with accelerometers, strain gages and pressure sensors to monitor their response. The experimental data show that the seismic earth pressure on walls increases linearly with the free-field PGA and that the earth pressures increase approximately linearly with depth, where the resultant acts near 0.33 H above the footing as opposed to 0.5–0.6 H, which is suggested by most current design methods. The current data suggest that traditional limit equilibrium methods yield overly conservative earth pressures in areas with ground accelerations up to 0.4g.