Nonlinear analysis of masonry structures using fiber-section line elements

For seismic analysis of unreinforced masonry (URM) buildings characterized by a box-like behavior, a widely accepted model is based on the equivalent frame idealization of walls. The equivalent frame model uses 1D elements to represent the vertical piers and horizontal spandrels which are connected by rigid nodes. The mechanical characterization of the elements is one of the crucial aspects to predict reasonably the building seismic behavior. Through the comparison with pseudo-static and dynamic experimental tests performed on two-story full-scale buildings, this paper validates the frame modeling in the OpenSees framework, which includes a fiber-section force-based beam element for the axial-flexural behavior, coupled with a cyclic shear-deformation phenomenological law.     

爆炸当量估算的初步研究

爆炸当量是评估爆炸能量的重要参数,快速估算爆炸当量对于有效开展应急救援工作至关重要。收集攀枝花铁矿爆破、宁夏煤矿爆破、河南汝阳钼矿爆破等矿山爆破资料,得到爆破的地方性震级M_L与爆炸当量Y之间的经验关系,并据此估算2019年7月19日河南省三门峡市气化厂爆炸事故的爆炸当量为16 t左右。     

Calibration and validation of a general infiltration model

A general infiltration model proposed by Singh and Yu (1990) was calibrated and validated using a split sampling approach for 191 sets of infiltration data observed in the states of Minnesota and Georgia in the USA. Of the five model parameters, f_c (the final infiltration rate), S_o (the available storage space) and exponent ‘n’ were found to be more predictable than the other two parameters: m (exponent) and a (proportionality factor). A critical examination of the general model revealed that it is related to the Soil Conservation Service (1956) curve number (SCS‐CN) method and its parameter S_o is equivalent to the potential maximum retention of the SCS‐CN method and is, in turn, found to be a function of soil sorptivity and hydraulic conductivity. The general model was found to describe infiltration rate with time varying curve number. Copyright © 1999 John Wiley & Sons, Ltd.     

Changes in overland flow and infiltration after a rangeland fire in a Mediterranean scrubland

Changes in overland flow and infiltration after a wildfire (summer 1989) in a typical Mediterranean scrubland were measured during the winters of 1990, 1991, 1992 and 1995 by means of simulated rainfall. Infiltration increases gradually from 1990 (sixth months after the forest fire) to 1995 (five and a half years after the forest fire). Overland flow decreases from 45% of rainfall after the forest fire to less than 6% five and a half years later. The reduction in overland flow was greatest in the first two years after the fire because of the quick recovery of vegetation. The steady-state infiltration capacity increased every year after the fire. Runoff and infiltration changes are mainly determined by the gradual recovery of vegetation. © 1998 John Wiley & Sons, Ltd.     

水平成层场地动剪应变与震动速度关系解析

以SHAKE2000为代表的频域等效线性化是目前主流的土层地震动计算方法。由于该方法在软土场地计算结果严重不合理,其改进方法成为目前研究热点,主要采用频率相关法,但一直没有取得实效。对频率相关法中土体动剪应变和震动速度成恒定比例关系的基本假定进行研究,从波动方程推导出了均匀全空间单向行波、单一均匀半无限场地、成层场地等3种典型场地中土体剪应变与震动速度关系的精确解答,通过数值试验研究了这一假定的合理性与偏差程度。结果表明：动剪应变和震动速度成恒定比例关系这一假定只有在无边界均匀介质单向行波情形下才成立,对于实际成层土场地,动剪应变与震动速度关系强烈依赖于波的频率和观察点的位置,如果在土层地震反应分析中忽略反射波而采用单向行波恒定比例假定将会使计算结果产生显著偏差;动剪应变与震动速度成恒定比例关系的假定导致的偏差达4个量级,即使对于单一均匀半无限空间模型偏差也十分显著;对实际土层地震动的求解,该假定在理论上定性错误,定量上偏差不可接受,必须放弃而另寻其他途径。     

没水倾斜板式防波堤消波性能分析

提出了一种将波浪中倾斜板问题等效化简为波浪中水平板单元组的方法,该方法建立在使用分离变量法求解水工结构边值问题的基础上,并使用伽辽金法精确求解连续边界条件,确定考虑衰减波态的速度势函数,从而求解没水倾斜板结构的消波性能。等效化简法计算精度于边界元法相当,且计算单元数量少、开销低。基于二维线性势波理论,对没水倾斜板式防波堤消波性能分析显示,没水板的倾斜角度、没水深度与板长是结构消波性能的控制因素:没水倾斜板防波堤的消波性能优于没水水平板防波堤的消波性能,随着没水板结构的倾斜角度增大,没水倾斜板结构的波浪透射系数显著减小,且长板优于短板,浅板优于深板;与前人的水槽实验对比显示,相对没水深度与波陡影响结构的消波性能,且波陡造成的波浪破碎贡献了显著的波能消耗。该结论对板式防波堤的结构配置、优化设计有重要意义。     

地基半空间等效集总体系的比拟法与实测分析

先略述莱斯默比拟法的形成;再由半空间理论等效为质弹体系,得出辐射阻尼比、刚度及参振土质量,并论述两体系的结合;最后经实测、分析和使用,考虑土体非匀质性折减阻尼比以作修正,使其更为实用。这有助于消除在我国长期认为阻尼比大而不安全、不便使用的疑虑,以便推动半空间理论在我国的实用化。     

Nonlinear response estimates of RC frames using linear analysis of SDOF systems

An approximate‐simple method for nonlinear response estimates of reinforced concrete frames subjected to near‐field and far‐field records is presented in this paper. The approximate method is based on equivalent single‐degree‐of‐freedom and linear multi‐degree‐of‐freedom models. In this procedure, the nonlinear maximum roof displacement is estimated using an effective period factor and elastic response spectrum with an equivalent damping. The effective period factor was proposed for far‐field and near‐field ground motion records. For regions of high seismicity, the maximum roof displacement can be estimated by applying an effective period factor of 2.3 and 2.1 for near‐field and far‐field records, respectively, and 9% damped displacement response spectrum. For regions of moderate seismicity, a lower effective period factor of 1.9 and 1.8, for near‐field and far‐field records, respectively, can be applied to estimate the maximum roof displacement. A relationship between linear and nonlinear response of multi‐degree‐of‐freedom systems was also proposed to obtain estimates of the maximum inter‐story drift of nonlinear responding reinforced concrete frames. In addition, the effects of number of ground motion records used in the analyses on the scatters of results were investigated. The required number of ground motions to produce a reliable response was proposed. Copyright © 2013 John Wiley & Sons, Ltd.     

Seismic shear distribution among interconnected cantilever walls of different lengths

Mid‐rise to high‐rise buildings in seismic areas are often braced by slender reinforced concrete (RC) walls, which are interconnected by RC floor diaphragms. In design, it is typically assumed that the lateral forces are distributed in proportion to the wall's elastic stiffness. Pushover analyses of systems comprising walls of different lengths have, however, shown that large compatibility forces can develop between them, which should be considered in design, but the analyses have also shown that the magnitude of the computed forces is very sensitive to the modelling assumptions. Using the results of a complex shell element model as benchmark, different simple hand‐calculation methods and inelastic beam element models are assessed and improved to yield reliable estimates of the base shear distribution among the individual walls comprising the interconnected wall system. Copyright © 2014 John Wiley & Sons, Ltd.     

基于各向异性梯度的裂缝密度反演

裂缝密度是评价裂缝性储层的重要参数. 本文提出一种利用各向异性梯度计算裂缝密度的新方法,即运用裂缝介质等效理论将高陡倾角裂缝介质等效为横向各向同性介质,得到裂缝介质AVO响应特征,从而得到裂缝介质的各向异性梯度,之后由该梯度与裂缝密度的关系得到裂缝介质的裂缝密度. 实际处理中可以根据地震数据直接求取裂缝介质的各向异性梯度,最后求取裂缝介质的裂缝密度. 模型试算表明, 该方法能得到裂缝介质准确的裂缝密度. 反演结果与初始模型基本一致验证了该方法的正确性; 另外地震记录添加一定的信噪比后也能反演得到准确的裂缝密度,证明了该方法的稳定性.