Performance of insulated FRP-strengthened concrete flexural members under fire conditions

This paper presents the results of fire resistance tests on carbon fiber-reinforced polymer (CFRP) strengthened concrete flexural members, i.e., T-beams and slabs. The strengthened members were protected with fire insulation and tested under the combined effects of thermal and structural loading. The variables considered in the tests include the applied load level, extent of strengthening, and thickness of the fire insulation applied to the beams and slabs. Furthermore, a previously developed numerical model was validated against the data generated from the fire tests; subsequently, it was utilized to undertake a case study. Results from fire tests and numerical studies indicate that owing to the protection provided by the fire insulation, the insulated CFRP-strengthened beams and slabs can withstand four and three hours of standard fire exposure, respectively, under service load conditions. The insulation layer impedes the temperature rise in the member; therefore, the CFRP–concrete composite action remains active for a longer duration and the steel reinforcement temperature remains below 400°C, which in turn enhances the capacity of the beams and slabs.     

高斯涡旋光束通过像散透镜后的相位奇异特性

光场相位奇异特性研究在奇点光学研究领域中具有非常重要的意义。本文运用广义惠更斯-菲涅尔衍射积分公式推导出高斯涡旋光束通过像散透镜后的光场分布表达式,并研究了它在几何焦平面上的相位奇异特性。结果表明,高斯涡旋光束通过像散透镜后在几何焦平面上存在相位奇点,相位奇点受到透镜的像散系数、光束束腰宽度和涡旋离轴量等参数的影响。在一定条件下,几何焦平面上出现直刃型位错线或光涡旋。当像散系数为0时,光涡旋出现在y轴上。当像散系数不为0,而涡旋离轴量为0时,会出现直刃型位错线或光涡旋,且各自的位置都非常稳定。当像散系数、涡旋离轴量或束腰宽度改变时,光涡旋会发生移动。这对光学元器件的设计和涡旋光束相位奇点的控制有一定的参考价值。     

《钢骨混凝土结构设计规程》讲座 第三讲 钢骨混凝土梁、柱构件受剪承载力计算

介绍了钢骨混凝土构件的受剪性能及其影响因素。着重指出了对开孔梁受剪承载力计算和柱受剪承载力计算中轴压力的分配中应注意的问题。     

千兆电子伏重离子加速器——兰州冷却储存环

能量达千兆电子伏的兰州重离子加速器冷却储存环HIRFL-CSR,是一个集加速、累积、电子冷却及内外靶实验于一体的多功能双冷却储存环同步加速器系统,由主环CSRm和实验环CSRe构成,并以兰州重离子回旋加速器系统HIRFL作注入器。CSR将重离子束的能量从兆电子伏提高到千兆电子伏,同时利用空心电子束冷却技术将束流的动量分散及发射度降低1~2个数量级,并提供多种类的高电荷态重离子束以及放射性次级束(RIBs),以开展更高精度的物理实验及更广范围的应用研究。兰州冷却储存环于2006年建成并投入运行,实现了剥离注入与多圈注入、空心电子束对重离子束的冷却与累积、变谐波宽能区同步加速、等时性环型谱仪、RIBs的产生与收集以及重离子束的快慢引出,并实现了高能重离子束的空心电子束冷却,使得重离子束的动量分散降低到10^-5量级,而发射度收缩到0.1πmm•mrad以下。同时,完成了短寿命近滴线核素的高分辨质量测量物理实验及高能重离子束深层治癌的临床应用实验。     

对无粘结部分预应力混凝土迭合梁变形计算方法的研究和探讨

本文给出了无粘结部分预应力迭合梁变形的试验研究成果，在此基础上，结合无粘结部分预应力混凝土梁及普通混凝土迭合梁已有成果，提出了二套变形计算公式，经与试验结果验验知，这些公式精度较高，可满足工程设计要求。     

轻骨料混凝土梁受剪承载力的计算及其可靠度分析

在试验的基础上提出了集中荷载作用下轻骨料混凝土梁受剪承载力计算公式的模型。应用《建筑结构设计统一标准》(GBJ68—84)提供的结构可靠度分析的一次二阶矩法,对公式模型进行了可靠度分析,并按照《建筑结构可靠度设计统一标准》(GB50068—2001)的要求,确定了公式中的待定参数ω的值。建议的公式和可靠度分析结果可为轻骨料混凝土梁受剪承载力的设计计算提供依据。     

不同荷载工况下双段变截面H型钢梁相关屈曲性能分析

采用ANSYS软件中的板壳元,考虑双重非线性,对梁端受等弯矩、不等同号弯矩、不等异号弯矩和梁上均布荷载和两端简支与固接情况下双段变截面H型钢梁进行了全过程分析,并同时考虑了纵向焊接残余应力、初始几何缺陷的影响。根据获得的构件荷载-位移曲线和不同荷载时刻的构件整体与局部变形形态,对比分析了不同荷载工况对双段变截面梁的承载力、整体刚度、相关屈曲、塑性扩展等性能的影响。研究结果表明,对于受弯矩作用的双段变截面H型钢薄壁梁,其腹板宽厚比可尽量取大值;剪力对梁的相关屈曲性能影响很大,对主要受剪力作用的梁,要防止发生腹板局部屈曲;固接约束极大改善构件性能。     

剪力墙下部地基梁的有限元分析

采用有限元分析程序ANSYS,对剪力墙下部地基梁的三种截面和配筋各异的情况,建立了包括剪力墙、桩和地基梁的整体模型。通过分析和比较,指出目前的有些设计思路使得该类地基梁的设计截面和配筋明显偏大。应该采用有限元非线性静力分析的手段进行该类地基梁的设计,以得到安全经济的结果。     

非预应力筋对无粘结预应力混凝土梁性能影响分析

为跟踪无粘结预应力混凝土梁的全过程响应,建立了一种基于法平面弧长算法的有限元模型。该算法能较好地处理梁加载过程的响应变化,可穿越梁破坏前可能出现的极值点问题。设计了7根含有不同非预应力筋配筋率的无粘结预应力混凝土梁,利用提出的数值模型对这些梁进行非线性全过程分析。分析结果表明,没有配置受拉区非预应力筋的无粘结预应力混凝土梁的弯曲性能非常不理想,在梁内配置少量的受拉区非预应力筋,能极大改善梁的性能;随着非预应力筋配筋率的提高,无粘结部分预应力混凝土梁的开裂刚度和极限承载能力有显著提高,而后弹性挠度以及无粘结预应力筋极限应力则明显降低。     

Geometrically nonlinear bending analysis of Metal-Ceramic composite beams under thermomechanical loading

A new method is developed to derive equilibrium equations of Metal-Ceramic beams based on first order shear deformation plate theory which is named first order shear deformation beam theory2(FSDBT2). Equilibrium equations obtained from conventional method (FSDBT1) is compared with FSDBT2 and the case of cylindrical bending of Metal-Ceramic composite plates for non-linear thermomechanical deformations and various loadings and boundary conditions. These equations are solved by using three different methods (analytical, perturbation technique and finite element solution). The through-thickness variation of the volume fraction of the ceramic phase in a Metal-Ceramic beam is assumed to be given by a power-law type function. The non-linear strain-displacement relations in the von-Kármán sense are used to study the effect of geometric non-linearity. Also, four other representative averaging estimation methods, the linear rule, Mori-Tanaka, Self-Consistent and Wakashima-Tsukamoto schemes, by comparing with the power-law type function are also investigated. Temperature distribution through the thickness of the beams in thermal loadings is obtained by solving the one-dimensional heat transfer equation. Finally it is concluded that for Metal-Ceramic composites, these two theories result in identical static responses. Also the displacement field and equilibrium equations in the case of cylindrical bending of Metal-Ceramic plates are the same as those supposed in FSDBT2.