火灾下型钢混凝土平面框架的破坏机理

该文利用梁单元建立了型钢混凝土平面框架耐火性能分析的有限元计算模型,有限元模型得到了构件试验结果的验证。利用建立的有限元模型,对局部火灾下型钢混凝土平面框架的破坏机理和破坏形态进行了分析。研究表明:火灾下型钢混凝土平面框架出现了三种典型的破坏形态,即内柱破坏导致的框架破坏、边柱破坏导致的框架破坏以及混合破坏形态;火灾分布位置及破坏时梁内轴力是影响框架破坏形式的关键因素。     

钢框架梁翼缘削弱型节点力学性能的试验研究

梁翼缘削弱的梁柱刚性连接是将塑性铰外移的一种典型节点形式。为研究这种连接形式在循环荷载作用下的滞回性能,共进行了6个模型的拟静力加载试验,其中5个模型用于研究梁翼缘的削弱深度、削弱长度、削弱起始位置对节点连接的破坏形态、极限荷载、最大塑性转角、延性性能的影响。作为比较,还进行了一个传统型梁柱全焊接刚性模型连接的试验。试验结果表明:梁翼缘削弱节点比传统梁柱刚性连接具有良好的塑性变形能力和耗能性能,试验中5个节点的塑性转角都大于0.04rad,延性系数大于4.0,达到了抗弯钢框架连接塑性转角不小于0.03rad,延性系数不小于4.0的要求。而普通梁柱全焊接刚性连接的塑性转角仅达到0.026rad,延性系数仅为2.4。5个试件的破坏主要以翼缘削弱处平面外刚度较弱而导致梁发生扭转失稳或梁下翼缘与柱连接的对接焊缝的脆性断裂为主。研究结果表明:将梁翼缘进行适当的削弱后形成的骨型节点可以增加梁柱节点的耗能性能,是一种较为理想的延性节点。     

Turbo-BLAST系统中基于容量的天线选择和功率分配算法

在不完全信道状态信息条件下,提出了一种适用于Turbo BLAST系统的天线选择和功率分配算法。所提算法以信道容量最大化为准则,从所有天线中选取一组天线子集用于发射,并对选择的天线子集进行注水功率分配,以充分利用Turbo BLAST系统的空间复用增益并提高信道容量。在接收端,采用Turbo原理对接收信号进行迭代检测以改善系统的误比特率性能。仿真结果表明采用所提算法不仅可以显著提高系统的信道容量, 而且误比特率性能也得到明显的改善。      

Logics for Classes of Boolean Monoids

This paper presents the algebraic and Kripke modelsoundness and completeness ofa logic over Boolean monoids. An additional axiom added to thelogic will cause the resulting monoid models to be representable as monoidsof relations. A star operator, interpreted as reflexive, transitiveclosure, is conservatively added to the logic. The star operator isa relative modal operator, i.e., one that is defined in terms ofanother modal operator. A further example, relative possibility,of this type of operator is given. A separate axiom,antilogism, added to the logic causes the Kripke models to support acollection of abstract topological uniformities which become concretewhen the Kripke models are dual to monoids of relations. The machineryfor the star operator is shownto be a recasting of Scott-Montague neighborhood models. An interpretationof the Kripke frames and properties thereof is presented in terms ofcertain CMOS transister networks and some circuit transformation equivalences.The worlds of the Kripke frame are wires and the Kripke relation is a specializedCMOS pass transistor network.     

Equilibria and steering laws for planar formations

This paper presents a Lie group setting for the problem of control of formations, as a natural outcome of the analysis of a planar two-vehicle formation control law. The vehicle trajectories are described using the planar Frenet–Serret equations of motion, which capture the evolution of both the vehicle position and orientation for unit-speed motion subject to curvature (steering) control. The set of all possible (relative) equilibria for arbitrary G-invariant curvature controls is described (where G=SE(2) is a symmetry group for the control law), and a global convergence result for the two-vehicle control law is proved. An n-vehicle generalization of the two-vehicle control law is also presented, and the corresponding (relative) equilibria for the n-vehicle problem are characterized. Work is on-going to discover stability and convergence results for the n-vehicle problem.     

The interaction of ultrasound with imperfect interfaces: Experimental studies of model structures

Model specimens are prepared, each of which may be viewed as two sections of similar material joined imperfectly at a planar interface. Measurements of the ultrasonic reflection from, mode conversion at, and/or transmission through these imperfect interfaces, are reported. The interface structures include distributions of pores, contacts, and inclusions. Included are both near-periodic and random cases. As the frequency is increased, the measured reflection coefficients generally show an initially linear increase from zero, followed by a maximum which may exhibit multiple peaks, and a subsequent decay. These results are interpreted in terms of a quasi-static model and an independent scattering model for ultrasonic interactions with imperfect interfaces.     

The effect of foundation flexibility on the interaction between shear walls and frames

A simple and rapid hand method based on the continuum approach for the static analysis of uniform structures consisting of interacting shear walls and frames with planar loading for fixed and flexible foundations is presented. Although this is an over-simplified and restricted method of analysis, it is very useful for preliminary design. The effect of foundation flexibility on the interaction of shear walls and frames is studied and results are compared to those of a fixed base. Results were compared satisfactorily with the conventional method (the discrete system). Design charts which further simplify the hand computation are included. These charts include the distribution of the bending moments in the walls and of the shear forces in the walls and frames along the height of the structure. The results are presented in terms of dimensionless parameters.     

Design of non-linear steel frames for stress and displacement constraints with semi-rigid connections via genetic optimization

A genetic-algorithm-based optimum design method is presented for non-linear steel frames with semi-rigid connections and column bases. The design algorithm obtains the minimum total cost, which comprises total member plus connection costs, by selecting suitable sections from a standard set of steel sections such as American Institute of Steel Construction (AISC) wide-flange (W) shapes. A genetic algorithm is employed as the optimization method, which utilizes reproduction, crossover and mutation operators. Displacement and stress constraints of AISC Allowable Stress Design (ASD) specification and size constraints for beams and columns are imposed on the frame. The algorithm requires a large number of non-linear analyses of frames. The analyses cover both the non-linear behavior of beam-to-column connection and P- effects of beam-column members. The Frye and Morris polynomial model is used for modeling semi-rigid connections. Two design examples with various types of connections are presented to demonstrate the application of the algorithm. The semi-rigid connection and column base modeling results in more economical solutions than rigid connection modeling, but increases the sway of frames.     

Cost function analysis in the structural optimization of steel frames

An objective function used in structural optimization should be formulated in such a way that the most economic solution can be found. However, the objective function is usually simplified to represent the weight, disregarding the fabrication and erection costs of the structure. The paper presents a very detailed objective function that considers the self-manufacturing costs of the whole structure. The cost function includes all essential fabrication and erection activities. It considers both manufacturing costs as well as material costs. It is formulated in an open manner, offering users the possibility to define their own parameters on the basis of a certain production line. The cost function is implemented into the optimization system for planar steel frames.     

Reliability analysis of frame structures with brittle components

A review is provided of the recent developments in the reliability analysis of ductile (elastic-plastic) systems and of the stable configuration approach of structural system reliability analysis. These are combined to obtain a methodology for evaluating the reliability of frames that have primarily ductile components but also a few brittle components. The methodology is applied to two frame structures.