反复荷载作用下矩形钢管混凝土树状节点的非线性分析

本文在确定了往复应力作用下钢管混凝土的钢材和核心混凝土的应力-应变关系的基础上,利用纤维杆元模型,有限元模型对钢管混凝土Y形柱和十字形钢梁连接的节点的荷载-位移滞回关系曲线及其骨架曲线进行了计算,并与试验结果进行了比较。结果表明：由纤维杆元模型与试验所得的低周反复荷载作用下的骨架曲线极为相似,但在峰值荷载后差异较大;由纤维杆元模型和有限元所得的在低周反复荷载作用下滞回曲线也与在反复荷载作用下试验所得的结果相一致。纤维杆元模型能准确地预测节点的弹塑性行为和整体抗震性能,可用于节点滞回性能的非线性参数分析研究。在此基础上研究了方钢管混凝土柱的轴压比,宽厚比及核心混凝土强度对节点受力性能的影响。     

Stiffened steel box columns. Part 2: Ductility evaluation

The purpose of this study is to evaluate the ultimate strength and ductility capacity of stiffened steel box columns failed by local and overall interaction instability under a constant compressive axial force and cyclic lateral loading. In a companion paper, a finite element formulation accounting for both geometrical and material non‐linearity was developed to obtain cyclic hysteretic behaviour of such columns. In this paper, the effect of loading patterns on the cyclic inelastic behaviour is first studied; then, a parametric study is carried out to investigate the effects of flange plate width–thickness ratio parameter, column slenderness ratio parameter, stiffener's equivalent slenderness ratio parameter, magnitude of axial load, and material type of stiffeners on the strength and ductility of the columns. Last but not least, empirical formulae of both the ultimate strength and ductility capacities are proposed for stiffened steel box columns, and the limit values of various parameters for the required ductility demand are also discussed. Copyright © 2000 John Wiley & Sons, Ltd.     

OWC wave energy devices with air flow control

A theoretical model is developed to simulate the energy conversion, from wave to turbine shaft, of an oscillating-water-column (OWC) plant equipped with a Wells air-turbine and with a valve (in series or in parallel with the turbine) for air-flow control. Numerical simulations show that the use of a control valve, by preventing or reducing the aerodynamic stall losses at the turbine rotor blades, may provide a way of substantially increasing the amount of energy produced by the plant, particularly at the higher incident wave power levels. From the hydrodynamic point of view, a by-pass valve or a throttle valve should be used depending on whether the wave energy absorbing system is over-damped or under-damped by the turbine.     

纤维增强混凝土异形柱框架抗震性能的试验研究

通过薄弱部位应用纤维增强的混凝土异形柱框架和同条件下无纤维异形柱框架的拟静力试验研究,对比了两榀框架的破坏特征、出铰顺序、承载能力和延性、滞回特性、耗能能力及刚度退化等抗震性能指标。研究表明：应用纤维增强的异形柱框架承载能力和整体刚度显著提高,薄弱部位破坏程度减轻,耗能能力有所增强,纤维可以改善异形柱框架薄弱部位的抗震性能,提高异形柱框架结构的整体抗震能力。     

纤维加固混凝土圆截面短柱抗震性能试验研究

通过对3根抗剪不足的混凝土圆截面短柱的拟静力试验,不仅验证了横向包裹的碳纤维布能提高短柱的抗剪承载力,改善混凝土的变形性能,从而提高短柱的抗震性能,同时验证了具有一定破损的短柱经碳纤维布强约束加固后,同样具有良好的抗震性能。文章最后对碳纤维布加固短柱的延性提高机理进行了分析。     

Evaluating equilibrium and non‐equilibrium transport of ammonium in a loam soil column

Release of nitrogen compounds into groundwater, particularly those compounds from excessive agricultural fertilization, is a major concern in an aquifer recharge. Among the nitrogen compounds, ammonium ( ) is a common one. In order to assess the risk of agricultural fertilizer contamination to an aquifer through infiltration, adsorption onto a loamy agricultural soil profile (0–0.60 m depth) was studied using a soil column experiment and modelling simulation. The soil used in the experiment was drawn from an agricultural field in Xinzhen, Fangshan district, Beijing, China, and reconstituted in laboratory soil columns. Column experiments were conducted using bromide (conservative tracer) and ‐bearing aqueous solutions. The ammonium concentrations in the soil water samples were measured, and their values were plotted as the breakthrough curves. The chemical's soil–water distribution coefficients (K_d) were calculated using breakthrough curves. Then the retardation factor (R) in saturated soil was calculated. For the ‐bearing aqueous solutions, the strongest adsorption occurred at the soil depth of 0.30–0.45 m. The convection–dispersion equation model and chemical non‐equilibrium model in Hydrus‐1D were used to simulate transport in the loamy soil. The two‐site chemical non‐equilibrium model in Hydrus‐1D was best to simulate transport through the soil column. Parameter sensitivity study was conducted to investigate the influences of solute transport by K_d, the fraction of exchange sites assuming to be in equilibrium with the solution phase (f), the longitudinal dispersivity (λ), and the first‐order rate coefficients (ω). The sensitivity analysis results indicate K_d is the most critical parameter.     

Proposed methodology for building-specific earthquake loss assessment including column residual axial shortening

This paper proposes methodological developments for quantifying the impact of residual axial shortening of first-story steel columns on earthquake loss estimations in steel moment-resisting frame (MRF) buildings. A new formulation is proposed that accounts for the likelihood of having to demolish a steel MRF building due to column residual axial deformations in addition to residual story-drift ratios. The formulation is informed by means of data from a comprehensive survey conducted worldwide to assess the likelihood of steel column repairability due to residual axial shortening. A practical method for quantifying column axial-shortening in parameterized system-level numerical simulations is presented. The proposed approach is illustrated by conducting economic seismic loss estimations in two case-study steel MRF buildings designed in urban California according to the current seismic design practice. It is found that when the ground-motion duration is appreciable, the examined steel MRFs are more prone to column axial-shortening than residual story-drifts at moderate to high seismic intensities. The results suggest that economic losses due to demolition may be underestimated if column residual axial-shortening is neglected from loss estimations. Limitations as well as directions for future research are discussed.     

配置630 MPa级高强钢筋的混凝土柱抗震损伤指数模型修正

为了验证各种Park-Ang损伤指数修正模型能否对630 MPa级超高强钢筋混凝土柱的地震损伤进行准确评估。在配置630 MPa级高强钢筋的混凝土柱拟静力试验现象和实测数据的基础上,首先利用6种模型分别计算了8根典型试件的损伤指数,并与试验实测损伤指数范围进行了对比,分析了6种模型的适用性;然后在试验实测数据的基础上,对计算结果存在较大偏差的4种模型进行了参数拟合和模型修正。研究结果表明:Kunnath模型、Chai模型、修正的傅剑平模型、修正的王东升模型和修正的付国模型均能准确模拟630 MPa级高强钢筋柱的损伤指数发展规律,而修正后的Kumar模型计算结果反而偏小,效果较差。     

采用非线性纤维梁单元法的钢管混凝土组合框架动力响应分析

钢管混凝土结构已经广泛应用于我国高层和超高层建筑中,为研究该类结构的抗震性能,分别采用分离模量法和统一模量法对某13层钢管混凝土框架结构进行抗震性能分析,研究不同地震波作用下组合框架的模态和多遇地震下的弹性动力时程,对比组合框架顶点位移反应、加速度反应、层间侧移及动力放大系数等。研究结果表明,分离模量法和统一模量法建模方法在分析钢管混凝土框架抗震动力特性上总体相差不大,但前者可以考虑材料弹塑性,从而对结构弹塑性进行分析,而后者在弹塑性阶段需要用全曲线表达式,尚需进一步的研究。     

装配式H型钢柱框架-复合墙结构抗震性能试验研究

提出了一种装配式H型钢柱框架-复合墙抗震结构。为研究结构的抗震性能,进行了1榀足尺装配式H型钢柱框架与1榀足尺装配式H型钢柱框架-复合墙试件的低周反复荷载试验。对比分析了各试件的强度、刚度、延性、滞回特性、耗能能力及破坏特征。研究表明:内嵌复合墙破坏时被分割成多条条型复合墙板,在弹塑性变形后期对框架的支撑作用较为稳定;内嵌复合墙使框架的极限承载力提高了68%,使框架的初始刚度提高了394%;H型钢柱框架-复合墙试件的滞回曲线饱满,未出现捏拢现象;条型复合墙板企口连接的水平条带存在往复咬合错动,对结构耗能能力的提升有明显贡献。