利用增量法分析门式刚架的抗灾害能力

利用荷载增量法分析了门式刚架在水平荷载作用下的受力状况,得到刚架在破坏时的极限荷载以及塑性铰出现的先后顺序和出现塑性铰时与之对应的荷载值,通过采取一定措施对节点域进行加强,采取在出现塑性铰的节点域加腋的方式来提高节点的承载力,经计算节点承载力大为提高,使结构具有更大的安全储备,从而使结构具有一定的抵抗超越荷载的抗灾害能力。     

Laboratory investigation of the behavior of a geosynthetic encased stone column in sand under cyclic loading

This paper presents the results of a laboratory investigation into the behavior of a geosynthetic encased stone column (GESC) installed in sand under cyclic loading using a reduced-scale model. A number of test variables were considered, such as the geosynthetic encasement stiffness and the cyclic loading characteristics, including loading frequency and amplitude. The results indicate among other things that the overall benefit of the encasement to the performance of the stone column is greater under cyclic loading than under static loading. It is shown that the degree of load transfer to the column becomes smaller when subjected to cyclic loading than under static loading, leading to a 25% decreased stress concentration ratio. The encasement is found to be more effective in improving the stone column performance when subjected to lower frequency and/or smaller amplitude loading. The lateral bulging zone of the GESC under cyclic loading tends to extend beyond the reported critical encasement length for an isolated static loading case, and therefore full encasement is recommended. Practical implications of the findings are discussed in detail.     

不同加载角下T形柱承载力与延性分析

采用Abaqus软件建立T形柱的三维非线性有限元模型,分析了T形柱在不同加载角下的承载力与延性,计算结果与试验值符合良好,分析表明:加载角为45°时,承载力是最大的;加载角为0°时,承载力是最小的;加载角为90°时,延性是最好的。     

先期振动对筑坝材料变形特性的影响

通过大型振动三轴试验研究了先期振动荷载对高土石坝筑坝材料抵抗地震变形能力的影响,研究结果表明:经受过先期动应力作用的土石料,再次经受动应力作用时,其抵抗变形的能力明显提高,这是由于在初始动应力作用下,土石料颗粒破碎及试样内部重定向排列大部分已经完成,再次经受动应力作用时,土石料颗粒破碎的程度将降低,试样内部重定向排列的难度将加大,从而使得其变形量减小,抵抗变形的能力提高。抵抗变形的能力提高的幅值与土石料本身的性质、再次经受的动应力与先期动应力的比值,即先期动应力和再次经受的动应力大小有关。根据试验结果建立了先期振动对粗粒料变形能力影响的一般表达式,该表达式表明:先期振动对粗粒料抵抗变形能力的影响仅与k值有关,k反映了粗粒料对先期振动作用的敏感度,表示粗粒料经先期动应力作用后,在再次经受动应力作用时,粗粒料内部重定向排列和颗粒破碎的难易度,k值越小,粗粒料对先期振动的敏感性越大,反之则越小,k值大小与粗粒料本身的矿物组成有关,而与其自身的岩性、颗粒形状、级配、密度等没有关系。     

挤扩支盘桩抵抗水平荷载作用的数值模拟分析

利用有限元软件Adina,在与普通混凝土灌注桩对比的基础上,分析了支盘桩抵抗水平荷载的特性,并通过改变支盘设盘位置,分析了支盘抵抗水平力所起的作用,以及支盘桩抵抗水平荷载的能力与支盘埋设深度的关系。     

燃机发电机运输工程桥式托架承载力试验

以某燃机发电机运输工程桥式托架设计为例,对其进行了承载力试验,并将试验数据进行了分析,结果表明：在最大试验荷载3 000 kN作用下,托架未出现极限承载力的特征,该桥式托架的承载力达到了设计要求。     

斜拉桥索塔锚固区模型试验的斜向加载方法

重点探讨了斜拉桥索塔锚固区模型试验的加载方法,指出斜向加载试验主要有外围张拉和中央顶推两种切实可行的斜向加载方案,并对两种斜向加载方法进行了对比分析,得出当试验节段为多个节段时,中央顶推方案更加合理的结论。     

施工阶段对超高层建筑的影响分析及应对措施

本文以广州超高层建筑混凝土结构施工过程中为研究对象,通过有限元Midas/gen进行了一次性施工加载和阶段加载分析。表明了竖向位移在一次性加载时为252 mm,阶段加载时为225 mm。并提出了严格控制施工找平和阶段施工补偿的方法。     

Experimental study of beam-column behaviour of steel single angles

Twenty-eight rolled steel single angle specimens were tested to investigate their response when required to carry axial compressive loading at various end eccentricities. Results suggested that when eccentrically loaded with respect to the major principal axis, there is a critical eccentricity below which any consequent reduction in the ultimate load is marginal. In contrast, as eccentricity of loading with respect to the minor principal axis is increased, reduction of the ultimate load is more pronounced and no similar critical eccentricity can be identified. Test results, when compared with the corresponding values as determined from the design equations suggested by Adluri and Madugula (1992), in AISC Specification 2000 and AISC Specification 2005, indicated that the former two methods give a conservative estimate of the ultimate compressive capacity of single angles. This conservatism is more pronounced for specimens subjected to eccentric loading with respect to the major principal axis than that resulting from eccentric loading with respect to the minor principal axis. Although intended for doubly symmetric sections, the third method provides improved capacity estimates of single angles.     

Strength degradation of sandstone and granodiorite under uniaxial cyclic loading

Change in mechanical properties of rocks under static loading has been widely studied and documented. However, the response of rocks to cyclic loads is still a much-debated topic. Fatigue is the phenomenon when rocks under cyclic loading fail at much lower strength as compared to those subjected to the monotonic loading conditions. A few selected cored granodiorite and sandstone specimens have been subjected to uniaxial cyclic compression tests to obtain the unconfined fatigue strength and life. This study seeks to examine the effects of cyclic loading conditions, loading amplitude and applied stress level on the fatigue life of sandstone, as a soft rock, and granodiorite, as a hard rock, under uniaxial compression test. One aim of this study is to determine which of the loading conditions has a stronger effect on rock fatigue response. The fatigue response of hard rocks and soft rocks is also compared. It is shown that the loading amplitude is the most important factor affecting the cyclic response of the tested rocks. The more the loading amplitude, the shorter the fatigue life, and the greater the strength degradation. The granodiorite specimens showed more strength degradation compared to the sandstone specimens when subjected to cyclic loading. It is shown that failure modes of specimens under cyclic loadings are different from those under static loadings. More local cracks were observed under cyclic loadings especially for granodiorite rock specimens.     

空间KK型钢管—板节点受力性能分析

针对特高压输电塔结构空间KK型钢管—板节点进行非线性有限元分析,考查了节点的破坏模式和极限承载力。重点分析了腹杆加载比例、几何参数和主管应力比等对空间KK型钢管—板节点极限承载力的影响。结果表明,腹杆加载比例为正时,节点极限承载力随其增大而显著降低;腹杆加载比例为负时,其对节点极限承载力的影响不大;主管应力比对节点极限承载力的影响随腹杆加载比例的变化而对节点的受力性能形成复合影响效应。在此基础上,通过对数值结果的回归分析,并综合考虑各种因素对节点极限承载力的影响,提出了该类节点的极限承载力计算公式。     

Q345十字插板X型钢管节点受压承载力特性研究

介绍了钢管塔结构的横担—主材连接方式,开展了Q345十字插板X型钢管节点受压承载力试验研究;研究了节点的承载力—变形特点、破坏模式,探讨了节点的承载力计算理论,试验研究表明支管受压时十字插板钢管节点发生受压局部屈曲破坏,节点承载力计算值与实验值比较表明日本钢管塔结构的十字插板节点承载力计算理论可以应用于节点的承载力计算,且具有良好的精度。     

坑外荷载对软土地区基坑开挖变形性状的影响

针对基坑开挖时坑外通常存在着建筑材料、车辆和其他荷载的情况,基于Biot三维固结理论开发了可以考虑流固耦合的三维基坑有限元程序,分别研究了坑外荷载大小、荷载施加时间和荷载施加区域对基坑支护结构水平位移、坑外地表沉降和坑底隆起变形的影响。结果表明:荷载大小对基坑支护结构的水平位移、地表沉降和坑底隆起变形影响较大;荷载施加时间和荷载施加区域则仅仅对支护结构水平位移和地表沉降影响较大,对坑底隆起变形影响较小;在对基坑进行工程设计时,应考虑坑边荷载的影响。     

循环加、卸载条件下岩石类材料变形特性的实验研究

从不同位移速率、不同载荷水平和不同岩石孔隙性(如坚硬致密的细粒砂岩和软弱多孔的混凝土加气砖等)3个角度对岩石类材料在循环加、卸载条件下所形成的封闭塑性滞回环的演化规律进行探讨。通过对其实验结果的分析发现:(1)岩石类材料在循环加、卸载条件下的卸载曲线与加载曲线不重合,确实将形成一封闭的塑性滞回环;(2)循环加、卸载条件下,加载曲线段的位移变化量在第1次循环期间变化较大,但从第2次循环开始,其位移变化量的变化并不明显,而卸载曲线段的位移变化量在整个循环加、卸载过程中的变化似乎都不明显;(3)一般而言,位移速率越大纵向载荷–纵向位移曲线的斜率就越大,载荷水平越高第1次循环中载荷卸载至零时所残余的位移量也越大;(4)从第2次循环开始,在每次循环加、卸载完成之后,加载曲线段的起点与卸载曲线段的终点几乎是重合的,即从第2次循环实验开始几乎不再产生新的残余位移量;(5)针对具有不同孔隙性的岩石,在不同位移速率和不同载荷水平时其循环加、卸载条件下的变形响应程度将有所不同。     

动静组合载荷作用下岩石失稳破坏的突变理论模型与试验研究

应用突变理论分析了受一维静载岩石系统的稳定性及变化规律,建立了一维静载岩石系统在动载作用下的非线性动力学模型,发现静载岩石系统自振频率变化规律,以及动载作用与一维静载岩石系统的响应存在非线性关系,当动载力幅和频率达到一定值时,会引起一维动静组合加载岩石系统振幅的突跳,从而引起岩样子系统的失稳破坏,在一维静载岩石系统动载作用演化过程中,动载信号强度的大小起着决定性作用。上述理论分析与一维动静组合载荷岩石系统的失稳破坏试验结果是吻合的。     

多级加载下附加应力沿深度变化的单层地基一维固结

在岩土工程中,当天然土层的强度较小时,加载速率过快可能会导致地基失稳。在这种情况下,可以采用多级加载的方式来逐步提高地基强度,使地基在施加下一级更大的荷载时已固结到一定程度。另外,在很多情况下,外部荷载在地基内引起的总附加应力总是随着深度发生变化,而并非保持不变,例如,当土层中地下水位发生变化时即是如此。详细给出了一个考虑多级加载下附加应力沿深度变化的单层地基一维固结的完全显式解析解。然后,选取外部荷载二级施加的特例来分析单层地基的固结性状。最后,通过比较不同的计算项数所得的计算结果来评估所得的级数解的收敛性,以利于工程人员采用本文解时能够获得足够的精度。     

箱梁拼宽时隔板构造对翼缘应力的影响及处理

分析了箱梁拼接时设置隔板前后,在恒载、活载、支座沉降以及荷载组合下拼接段翼缘应力变化情况,根据分析提出了拼接段翼缘的相关处理措施,以保证箱梁拼接段工程质量,更好地解决桥梁的拓宽问题。     

Rate-Dependent Response of Dense Sand in Cyclic Triaxial Tests

A number of cyclic triaxial tests were performed on Monterey No. 0/30 and Sacramento River Sand to investigate the effect that loading frequency has on the response of sands. The tests were performed on dense, air pluviated sand with loading frequencies of 0.1 and 1.5 Hz at varying confining pressures, cyclic shear stresses, and peak shear stresses. Under certain loading conditions, the frequency of loading did have a noticeable effect on the response of the sand; larger axial strains were measured in the samples that were subjected to the lower frequency of loading. This difference in response measured at the two loading frequencies occurred mainly in the first few cycles of loading, when the difference in the strain rates was the greatest. Conditions that resulted in larger axial strains, such higher stress levels and larger cyclic shear stresses, also resulted in a greater difference between the axial strains measured at the two loading frequencies.     

加载速率对湿态混凝土强度的影响

首先研究了混凝土在自由吸水条件下的饱和度演化规律,然后对5种湿度状态下的混凝土进行了5种抗压加载速率下的单轴压缩试验和5种劈裂抗拉加载速率下的劈裂抗拉试验,最后建立了不同饱和度混凝土的抗压强度、劈裂抗拉强度随加载速率变化的预测公式,并分解了自由水与加载速率的独立效应.结果表明:相同加载速率下混凝土试件的抗压强度与劈裂抗拉强度均随饱和度的增加而降低;相同饱和度下混凝土试件的抗压强度与劈裂抗拉强度均随加载速率的提高呈近似指数关系增长;相同饱和度下混凝土劈裂抗拉强度随加载速率的变化幅度较抗压强度更为显著.     

循环加载高应力对大理岩Kaiser效应影响的试验研究

声发射法(AE)广泛用于地应力测量。当单次加载Kaiser效应不明显时,可采用循环加载方式。通常各循环峰值加载应力大于岩石在地壳中所受最大应力?m,将大于?m的加载应力称为高应力。为研究高应力对岩石Kaiser效应的影响,对取自铜绿山矿的垂直钻孔岩芯进行循环加载试验,根据声发射特征曲线变化趋势及变形率分析法(DRA)地应力测量结果,对比水压致裂法所测地应力量值,确定不同加载阶段Kaiser效应点位置。研究结果表明:当循环加载峰值应力大于?m时,高应力将削弱与?m对应声发射事件的能量,使后续加载循环Kaiser效应不明显,同时会改变岩石之前记忆的应力值,使AE法地应力测量结果产生偏差;多次循环加载可导致岩石内部微结构面的破坏,其产生的大量声发射事件会混淆Kaiser效应点的辨识;因岩石差异性,高应力可能会取代岩石之前所受最大应力,成为岩石记忆的新应力。鉴于此,采用循环加载方式时,首次加载峰值应力A?应不超过?m,同时应使岩石跨过压密阶段进入线弹性阶段。铜绿山矿所取岩样循环加载试验结果表明,A?较合适的取值范围为岩石单轴抗压强度的6%~28%。此外,还给出声发射法和DRA法联合用于地应力测量的合理加载方式。