Calculation and Analysis on Critical Moment of Thin-walled Beams under Unequal End Moment

In this paper, comparing the bending-twisting model with the tension-bending one, the critical moment of the thin-walled beams under unequal end moment is derived easily by the improved CDC (column deflection curve) method based on the increment interaction equations of beam-columns.A simplified formula is presented and the calculated results show a good agreement with the numerical ones.     

Critical Temperature of Axially Restrained Steel Columns withPartial Fire Retardant Coating Damage

In order to investigate the fire resistance of steel columns with partial fire retardant coating damage in fire, based on the differential equation of equilibrium on each portion of steel column, the deflection of steel column after the fire retardant coating damage was derived, with the pined ends and rigid ends of the columns at elevated temperatures. The critical temperature calculation method was proposed for partial fire protection damage and axial restrained steel columns by taking the edge yielding criteria. The deflection and axial displacement were verified by finite element method at elevated temperature. With a case study, the critical temperature and relationship of axial force and temperature were obtained for pined column with axial restraint. It was shown that the axial force of the steel column at elevated temperatures was increased and the critical temperature was decreased by the axial restraint. The longer the fire retardant coating damage was and the higher the axial restraint was, the lower the critical temperature was.     

柱失效方程中荷载相关特性对承载力抗震设计可靠度的影响

以竖向荷载和水平地震作用组合下的钢筋混凝土柱和钢柱为对象,研究了失效方程中荷载相关特性对柱承载力抗震可靠性的影响。根据现行《混凝土结构设计规范》和《钢结构设计规范》分析了不同柱弯矩轴力相关曲线的特性。结合多个框架结构实例,对比了柱失效方程中荷载相关曲线与规范考虑情形的异同。实例分析表明:水平地震和竖向荷载组合作用下,小偏压RC柱和工字型钢柱的荷载相关曲线与规范考虑的情形较为符合,均近似为负相关的直线;水平地震和竖向荷载组合作用下,大偏压RC柱的荷载相关曲线则与规范考虑的情形有较大出入,存在明显的正相关段部分。在此基础上,考虑失效方程复杂特性,依据已有的荷载和抗力变量概率模型,采用Monte Carlo法分析了水平地震和竖向荷载组合作用下柱的可靠性。结果表明:钢柱和小偏压RC柱的承载力抗震可靠度随轴压力荷载效应比值的变化幅度较小,与规范模式计算结果较接近;大偏压RC柱的承载力抗震可靠度随轴压力荷载效应比值的变化会有较大幅度波动,与规范模式计算结果差异较大;当轴压力荷载效应比值为负时,大偏压RC柱的承载力抗震可靠度会低于规范计算值较多,现行柱可靠性设计方法会偏于不安全。     

Analysis on Seismic Capacity for RC Specially Shaped Columns in Different Horizontal Direction

With fiber beam-column element based on flexibility method of finite element, the RC specially shaped columns of different axial compression ratio under cyclic loading have been simulated and the analysis results have been compared in aspects of strength, stiffness and ductility in order to provide some suggestions for seismic-resistant design of specially shaped columns. The strength, stiffness and ductility of L,T-shaped columns are apparently different in different horizontal direction, but those of t-shaped column are close.     

Plastic Limit Load of Simply-Supported Annular Plates Based on Mises Yield Condition

In this paper,on basis of Mises yield condition, the plastic limit load of annular plate with simply support under uniformly distributing load is evaluated. Because of the nonlinearity of the Mises yield condition, the weighted residual method is employed to gain the results. A simple formula for calculating the plastic limit load has been worked out. Compared with the results based on maximum moment condition,the numerical results in this paper are reasonable.     

A Comparative Study of Confined Concrete Models under Cyclic Loading

In this paper,four models are selected as the representatives and applied to nonlinear dynamic analysis program for space frames which is based on the beam-column elements using the finite element flexibility method and the fiber model.Park's test on combined axial and bending columns under cyclic loading are taken as the calibrations,comparisons to material and structural member level are drawn and the analytical results of various models are discussed.     

Analysis of Fiber Renforced Concrete Beam-Column Joints Model

Due to the large stirrup ratio and reinforcement congest in beam-column joints, the ordinary reinforced concrete beam-column joints take inconvenience to construction. Cracked fiber renforced concrete (FRC) has strong bridge ability and better tensile performance so that it can replace part or all of the stirrups. Based on previous researches on resistance mechanism of reinforced concrete joints, a new model using FRC materials in the core zone of beam-column joints is presented. It is a kind of model in which horizontal shear supported by the diagonal strut mechanism and softening truss mechanism with a certain percentage. The calculation results of the model is compared with the existing test results. It is a bit conservative to specimens with low axial load ratio. However, the results are in line with the specimens with high axial load ratio. Therefore, the results totally demonstrate the rationality of the proposed model in this paper. Meanwhile, according to the proposed model, the shear capacity of beam-column joints can be not only calculated, it also check whether FRC compressive strength in core zone of joints and horizontal stirrup ratio meets design requirements, which has a higher practicability.     

Overall Stability Design of Restrained H Section Steel Columns under Axial Load in Fire

The effects of the restraint stiffness ratio, the axial load ratio and the column slenderness on the buckling temperature and failure temperature of a restrained H section steel column under axial load in fire were studied with a calibrated finite element method (FEM) model. And the calculation methods of buckling temperature and failure temperature were proposed. The effect of the restraint stiffness ratio on the buckling temperature and failure temperatures could be expressed with an exponent curve while polynomial functions was appropriate for the effects of the axial load ratio and the column slenderness. The results of the proposed method were in good agreement with those by FEM method and on the safe side.     

Fire-resistance performance of high-strength-steel H shaped columns under the axial compression

In order to investigate the fire-resistance performance of high-strength-steel column,this paper deduces the critical stress of high-strength-steel columns under the axial compression at high temperature by introducing the mechanical properties of high-strength-steel at high temperature.Moreover,coefficients of overall stability and critical temperature for high-strength-steel column under the axial compression are obtained which can provide a reference for design.The comparison of overall stability coefficient and critical temperature between high-strength-steel and normal steel is made.The results show that the overall stability coefficient and critical temperature for normal steel is not applicable for high-strength-steel,and the overall stability coefficient for high-strength-steel is smaller than that for normal steel.The paper uses the finite element analysis to validate the overall stability coefficient,and good match was found between them.     

Axial Force in Restrained RC Columns during Heating and Cooling Phases

Using the computer program of SAFIR, the influences of some parameters (i.e., axial/rotational restraint ratio, sectional dimension, load ratio, load eccentricity ratio, reinforcement ratio, and heating time, etc.) were analyzed on axial forces in restrained concrete columns exposed to ISO834 standard fire with cooling phase, compared with those in the standard fire without cooling phase.Based on the simulation results of 2880 cases, a practical calculation method for axial force in column was proposed.It was shown that: (a) for axially and rotationally restrained columns in fire with or without cooling phase, the enhancement coefficient of axial force increased gradually first, and then reduced gently or kept constant, and finally decreased quickly.However, in the late stage, the enhancement coefficient corresponding to fire without cooling phase dropped more significant than that with cooling phase; and (b) the influences of the rotational restraint ratio, column length and thickness of concrete cover on the enhancement coefficient of axial force in axially and rotationally restrained columns were limited subjected to fire with cooling phase, while the peak value of the enhancement coefficient increased with the increase of the axial restraint ratio, load eccentricity ratio and reinforcement ratio or with the decrease of the load ratio and sectional dimension.     

Geometric Nonlinear Stiffness Matrix Based on Tension-Compression and Torsion-Warping Interpolation Function

The conception and calculation formula on torsion-warping stability function is brought forward and the torsion-warping tangent stiffness matrix of bi-axisymmetric open thin wall and lightweight beam-column element is derived for the first time, based on torsion-warping stability interpolation function. At the same time, the spatial geometric tangent stiffness matrixes for beam-column element of lightweight steel structure based on tension-compression and torsion warping stability interpolation function are presented as well.     

Axial Force Stiffness Interaction in Seismic Analysis of RC Double Column Bridges

Earthquake induced dynamic axial force in reinforced concrete (RC) bridge bent columns will not only change the yield strength of the columns but also change their stiffness, which is seldom considered by the common lumped plasticity line model. Based on the fiber element model results that taking into account the influence of dynamic axial force on strength and stiffness simultaneously, the axial force stiffness interaction effect on the seismic responses of RC double column bridges was analyzed. The results show that, axial force stiffness interaction has a large effect on the seismic responses of the double column bridge in the elastic range, and it does not alter the ultimate capacity of the columns. Since the stiffness of the columns under compression and tension dynamic axial forces offset each other, the global displacement of bridge bent with equal columns is relatively unaffected by the axial force stiffness interaction, however, the differences of the column member forces are manifest. For the short column controls the global stiffness, the axial force stiffness interaction has significant influences on both the global displacement and member force responses. The influences become larger as the irregularity of the bridge bent increases, so the interaction between axial force and member stiffness should be sufficiently considered in seismic analyses.     

钢结构仿古建筑双梁柱中节点的受力机理

为研究钢结构仿古建筑双梁柱中节点的抗震性能,对4个全焊双梁柱中节点进行了水平低周反复加载试验。通过观测试件在侧向力作用下的受力过程和破坏形态,分析双梁柱中节点的受力机理。根据梁截面形式的不同,将其分为箱型截面梁与工字型截面梁2类,依据仿古建筑独特的构造特点,将各试件节点核心区划分为上、中、下3个区域。通过量测各区域内的应变大小,分析该类结构节点核心区在侧向力作用下的受理机理及破坏模式,并建立双梁柱节点的斜压杆受力模型。试验结果表明：仿古建筑双梁柱节点的破坏形式主要为沿下核心区对角线的剪切破坏,并通过理论计算分析提出一种考虑轴压比与梁截面形式的双梁柱中节点抗剪承载力修正公式。     

Wind Vibration Analysis on the Large -span Curtain Wall

The large-span structure requires wind vibration analysis when computing the wind load;however,the formula in current code on wind vibration coefficient can hardly be applied in large-span structure,making its computation difficult and troublesome.This paper makes wind vibration analysis on the large-span curtain wall combined with certain engineering background in the methods of both time domain and frequency domain,and then the derived results are compared.The analytical results demonstrate identical distribution and contiguous numerical value of wind vibration coefficient concluded from the two varied methods;furthermore,even if the method in time domain is higher in computational complexity,more data on the response of structure under wind can be obtained,which provides reference for the theoretical analysis and engineering design.     

Yield Displacement Calculation Method of High-Strength Concrete Shear Wall

It is assumed that concrete compressive stress of the cross-section compression zone is linear distribution when the cross-section of high-strength concrete shear wall reaches yield situation. Based on the plane section assumption, the yield curvature formula of shear wall section is obtained by using moment - curvature analysis method. The parameters affecting yield curvature of high-strength concrete shear wall are studied by using the yield curvature formula. The results show that longitudinal reinforcement yield strain is the most vital factor of the yield curvature in addition to axial load ratio. When axial load ratio is larger, both wing walls of shear wall section have larger impact. The yield curvature formula is presented, considering the impact of axial load ratio, boundary reinforcement yield stress and both ends of wing walls of shear wall section based on the regression analysis of calculation results. On this basis, the vertex yield displacement formula of high-strength concrete shear wall is proposed, and the calculation results of formula correspond well to the vertex yield displacement experimental values of the 12 high-strength concrete cantilever wall. The formula is also suited for the vertex yield displacement of comment concrete shear wall.     

BENDING PROBLEM OF RECTANGULAR PLATES STIFENED ALONG ONE DIRECTION UNDER LOCAL LOADS

By using mixed triangle series,this paper discusses the calculation of rectangular stiffened plates with simply supported edge along direction of stiffeners under several local loads,such as uniform load on local rectangular area,concentrated force,concentrated moment of couple,line loads,line moments of equal and some equivalent concentrated forces acting on a line with equaldistance among them.All analytical solutions of both displacements and internal forces are derived.A numerical example to treat an engineering problem is given.     

The Seismic Shear Capacity of I-Shaped and T-Shaped Reinforced Concrete Structural Walls

There are numerous shear walls with flanges in the high-rise buildings in P.R.China.The shear strength formula for shear walls in Chinese design codes lacks experimental data,while test results in other nations lack aseismatic shear strength test results for shear walls with flanges under axial force.In this paper,we report low-cyclic reverse load test results of shear wall models with large dimensions,one shear wall having an I-shaped cross-section and two with a T-shaped cross-section.We discuss why the aseismatic shear walls of high-rise buildings with large height-to-length ratios have small shear span ratios.We assess the reliability of the shear strength formulary in the Chinese codes for design of shear wall using the international shear wall test results.     

Deformation Capacity of FRP Confined Reinforced Concrete Circular Columns under Simulated Seismic Loading

The accurate calculation of the deformation capacity of structures is very important to performance-based seismic design, which satisfies the explicit deformation demands. The method to evaluate drift capacity of fiber reinforced polymer (FRP) confined reinforced concrete circular columns under simulated seismic loading is focused. Firstly, the moment-curvature relationship of FRP confined sections of reinforced concrete (RC) circular columns is simulated by numerical analysis. It is found that the calculated ultimate curvature is significantly less than the test result, and the difference is controlled by the axial load ratio of the tested columns. According to the numerical and the test results, an equation is proposed to modify the calculated ultimate curvature. Based on this, the drift capacity can be predicted with the equivalent plastic hinge method. The calculated result agrees well with the test result when FRP amount is low, but it is significantly larger when FRP amount increases. Finally, the main parameters exerting influences on the drift capacity of the FRP-confined RC circular column are analyzed.     

Studies on dynamic contact characteristics of ball screws

Based on Hertz contact theory, a computational method of contact deformation in operating process of ball screws is established in terms of variable contact angles and the centrifugal force. Through the force balance equations, contact deformation in operating process is derived. Taking a ball screw as an example, the influence of its operating condition, contact angles and helix angle on contact characteristics is studied by numerical method. Analysis indicates that the contact deformation on the side of screw decreases and that of nut increases when the screw rotation speed increases and there exists a speed that the later is greater than the former. At the same time, the difference between contact angles increases. Variety of contact angles increase as the axial load decreases, which leads to higher influence on contact deformations. Contact deformations decrease as the contact angle and helix angle increase.