建筑能耗分析用逐时降雨模型(2):月降水量随机模拟

在计算与分析广州地区33年实测月降水量序列统计参数的基础上,将月降水量序列进行对数变换,采用一阶AR(P)模型建立了月降水量随机模拟模型。通过与实测结果的比较检验了该模型的适用性。     

降雨条件下的基坑边坡渗流场模拟

在对多孔介质中的饱和-非饱和渗流数学模型简要分析的基础上,对影响渗流有限元计算分析结果的一些参数选取方法进行讨论,如非饱和土的水土特征曲线、水力传导系数及毛细水头等。利用相关程序对降雨条件下的基坑边坡内部渗流场进行模拟,分析地下水位线、坡体饱和度、压力水头及坡体内不同位置处的渗流速度随降雨时间的变化规律。模拟结果与实际情况比较吻合,可为基坑边坡稳定性的分析提供参考依据。     

Elastic local post-buckling of elliptical tubes

The elastic local post-buckling behaviour of elliptical tubes under compression is analysed in this paper. A brief outline of the local, distortional and global buckling behaviour of EHS tubes is firstly provided, where it is shown that local buckling modes govern the stability of short to intermediate length tubes while distortional modes control the stability of intermediate length to moderately long tubes and global buckling dominates the behaviour of longer tubes. Following this, an in-depth numerical study employing shell finite element modelling, of the elastic local post-buckling behaviour of compressed elliptical hollow section (EHS) tubes is presented. It is concluded that EHS tubes with a low to moderate aspect ratio can support loads up to their limit loads but are imperfection sensitive (shell-type behaviour), while EHS tubes with a moderate to high aspect ratio can carry loads higher than their limit loads (plate-type behaviour) and are imperfection insensitive. The slope of the ascending post-buckling path increases with the EHS aspect ratio and can reach values up to 40% of the slope of the linear primary path. The bound imperfection amplitude concept, separating the imperfection amplitude ranges where the EHS tube is sensitive and insensitive, is proposed. It is also found that, for increasing EHS aspect ratio, the compressive stresses grow and accumulate near the zones of minimum radius of curvature while the zones of maximum radius of curvature possess an approximately uniform and relatively low compressive stress level. Therefore, it is expected that an approach based on the effective width concept widely used for the evaluation of the strength of flat plates may be adapted to the design of EHS tubes with moderate to high aspect ratios.     

植被增加边坡降雨入渗对边坡稳定性影响研究

植被根系提高土壤渗透性和抗侵蚀性,植被盖度越大径流起始时间越长,植被提高边坡的入渗率和减少土壤流失相互促进,共同作用的结果是保持水土,所以植被增加边坡降雨入渗的作用是十分显著的.大多数植物的根系分布在浅层,根际区土壤储水能力强,由于植被对根际区下层土壤的渗透性影响不大,而且认为植被对降雨入渗对根际区土壤水分的影响明显,而对边坡根际区下层土壤水分影响不明显,植被增加边坡降雨入渗不影响边坡深层稳定性.     

城市化效应对上海短历时设计暴雨强度的影响

了解城市化对短历时设计暴雨强度的影响，对改善市政基础设施的设计、管理有重要意义。利用上海徐汇区40年完整的降雨资料和市郊站点25年的短历时降雨年最大值资料，分别推求了上海市中心城区和市郊区县的暴雨强度公式。通过同一时期中心城区和区县设计雨量的对比，结合气候和地理因素的影响分析，揭示了上海中心城区与市郊短历时设计暴雨强度的差异及其与重现期的关系。在国内目前的设计重现期下，城市化效应对上海城区排水系统的设计标准并无实质性影响；重现期〉1a，则中心城区的设计雨量反而小于郊县，其暴雨强度公式应用于多数区县排水系统的设计不甚安全；南汇区的短历时设计暴雨强度明显大于中心城区，其排水系统设计宜考虑采用当地的暴雨强度公式。     

考虑降雨影响的非饱和土基坑边坡突变失稳分析

降雨入渗往往是非饱和土基坑边坡失稳的主要诱发因素之一,同时边坡失稳又具有突发性。基于突变理论提出了考虑降雨入渗影响的非饱和土基坑边坡稳定性分析方法。根据分析边坡稳定性的塑性极限方法的上限理论建立了边坡失稳尖点突变模型,并得出边坡突发式滑坡的特征关系式,用突变理论对非饱和土边坡稳定进行了初步研究。研究表明,基坑边坡失稳是一种突发性的破坏,外界环境的变化(如降雨入渗导致土体抗剪强度的降低)是基坑边坡发生突发性破坏的决定性因素。     

奥斯卡·尼迈耶——拉戈阿住宅与卡诺阿斯住宅

本文旨在分析巴西建筑师奥斯卡·尼迈耶在1942年与1953年所建造的两幢自宅,归纳在其空间构成、结构以及体验上的异同,重点在于分析这两幢住宅与各自所处的环境关系。文章结论系于尼迈耶如何将柯布西耶的设计理念与巴西的环境相结合。在第一幢住宅中,他严格地遵守柯布所设定的原则,而其后则在卡诺阿斯住宅的自由形体中作出种种发展与修改。在第二幢住宅中,建筑与自然紧密联系,并可以在可视性与可达性上通过空间句法分析证明。同时也可认为拉戈阿住宅功能被明确区分为室内与室外两个独立部分,而卡诺阿斯住宅则作为一个完整的整体体系。全部的研究基于柯布西耶理念背景以及巴西自由形式运动。     

耐火钢柱的抗火性能参数分析与抗火临界温度估计

本文利用ANSYS有限元分析软件所建立的火灾升温条件下耐火钢柱的非线性有限元分析模型，进行了大量的参数分析，研究各种参数的变化对耐火钢柱抗火临界温度的影响，进而提出耐火钢柱抗火临界温度的简便估计方法。最后通过算例介绍了本文方法的使用。并验证了方法的可靠性。     

Effects of temperature on the shear strength of saturated sand

The effect of temperature on the shearing response of saturated, dense sand was investigated using a series of temperature-controlled, isotropically-consolidated, hollow cylinder triaxial compression tests, where specimens were heated in drained conditions followed by shearing in undrained conditions. As expected, the deviatoric stress at the peak state (i.e., the undrained shear strength) was observed to increase with increasing initial mean effective stress. However, it was observed to decrease linearly with increasing temperature. The effects of temperature on the deviatoric stress at the peak state were attributed to a linear increase in the magnitude of negative shear-induced pore water pressure at the peak state with temperature. The relationship between the undrained shear strength and the pore water pressure with changes in temperature was represented well by linear equations. When the shear strength was interpreted in terms of the critical state, no obvious changes in the critical state line in the $p^{\prime }-q$ plane were observed, and the critical state friction angle was unaffected by temperature. During drained heating, the dense sand specimens were observed to expand volumetrically, causing the normal consolidation line in the $e-{\left(p^{\prime }/p_{\text{a}}\right)}^{0.5}$ plane to shift upward with increasing temperature without a change in the slope. The negative pore water pressure during undrained shearing caused the state paths of the dense sand specimens to move to the right. As the magnitude of negative pore water pressure increased with increasing temperature, no obvious effects on the critical state line in the $e-{\left(p^{\prime }/p_{\text{a}}\right)}^{0.5}$ plane were observed.     

Lateral bracing of I-girder with corrugated webs under uniform bending

Lateral-torsional buckling may occur in an unrestrained beam where its compression flange is free to displace laterally and rotate. This paper presents the results of the theoretical and finite element analyses of the lateral-torsional buckling of I-girders with corrugated webs and lateral bracing, under uniform bending. It is well known that an elastic lateral brace restricts partially the lateral buckling of slender beams and increases the elastic buckling moment. However, a full study of the effect of lateral braces on lateral-torsional buckling has not been made especially for I-girder with corrugated webs. This paper develops a three-dimensional finite element model using ANSYS [User’s manual, version 10.0] for the lateral-torsional buckling analysis of I-girder with corrugated webs and uses it to investigate the effects of elastic lateral bracing stiffness on the critical moment of simply supported I-girders with corrugated webs under pure bending. It was found that for plastic and inelastic I-girder with corrugated webs, the effect of bracing initially is increased to some extent as the lateral unbraced length increases and then decreased until the beam behaves as an elastic beam. In other words, the effect of bracing depends not only on the stiffness of the restraint but also on the modified slenderness of the I-girder. Also, the results show that Winter’s simplified method to determine full brace requirements cannot be applied to I-girders with corrugated webs. Therefore, a general equation is proposed to determine the value of optimum stiffness (K_opt) in terms of the I-girder’s slenderness.