钢筋混凝土带暗柱等肢T形柱轴压比限值调整系数的研究

若干研究已表明设置暗柱能有效提高T形柱的延性,但迄今为止带暗柱T形柱轴压比限值的研究尚为空白,这影响了带暗柱T形柱的工程应用。文中采用非线性全过程数值计算方法,计算了不同肢长、不同抗震等级下带暗柱与不带暗柱钢筋混凝土等肢T形柱在不同纵向受力钢筋配筋率和不同体积配箍率时的截面曲率延性比;根据《混凝土异形柱结构技术规程》(JGJ149-2006)给出的各抗震等级下对异形柱截面曲率延性比的要求,确定了带暗柱与不带暗柱的等肢T形柱的轴压比限值,进而求出两者同一肢长下轴压比限值的比值;最后通过回归分析得到了带暗柱等肢T形柱轴压比限值的调整系数公式。利用此公式并根据《规程》JGJ149-2006中规定的不带暗柱T形柱的轴压比限值即可求出带暗柱等肢T形柱的轴压比限值。     

带暗柱钢筋砼等肢L形柱轴压比限值调整系数研究

至今,带暗柱的等肢L形柱轴压比限值调整系数尚未得到充分研究,因而限制了其在工程中的应用.为此,针对等肢L形柱,采用非线性全过程数值分析方法,通过C++编制程序,并使用相关实验数据对程序进行了验证;在不同抗震等级、肢高纵筋配筋率及体积配箍率下,计算了带暗柱与不带暗柱钢筋混凝土等肢L形柱的截面曲率延性比,并根据《混凝土异形柱结构技术规程》给出的不同抗震等级下异形柱截面曲率延性比的要求,确定了各抗震等级下带暗柱与不带暗柱的等肢L形柱的轴压比限值及其比值;最后通过拟合分析法及调整系数法确定了带暗柱等肢L形柱轴压比限值的调整系数.     

保护层厚度对钢筋混凝土等肢异形柱延性性能的影响

采用非线性全过程数值计算方法,计算并分析了不同保护层厚度的L形、T形和十字形钢筋混凝土等肢异形柱在多种工况下的截面曲率延性值,发现了保护层厚度对混凝土等肢异形柱的截面曲率延性有重要的影响,进而提出了不同保护层厚度的混凝土等肢异形柱在各抗震等级下的轴压比限值的调整及其保护层厚度的控制标准的建议.     

钢筋混凝土不等肢异形柱轴压比限值的研究

采用非线性全过程数值仿真算法确定不等肢T型、L型、十字型柱截面曲率延性比。再根据异形柱框架结构受地震作用时应具有的柱截面曲率延性水准确定不等肢T形、L形、十字形柱轴压比限值,为不等肢异形柱设计提供了必须的依据。     

较小剪跨比带暗柱十字形柱抗震性能试验研究

提出了带暗柱十字形柱,进行了４根较小剪跨比的十字形柱抗震性能试验,分析了轴压比对承载力,刚度,延性的影响,以及设暗柱对提高十字形柱抗震能力的作用,最后进行了理论计算,计算值与实测值符合较好。     

型钢混凝土异形柱的轴压比限值研究

利用有限元数值积分法编写了型钢混凝土(SSC)异形柱轴压比限值的计算机程序,利用该程序可以计算任意荷载角、任意配钢形式的SSC异形柱的轴压比限值.对不同配钢形式、不同配钢率、不同截面尺寸、不同混凝土强度等级、不同荷载角作用下的SSC异形柱的轴压比限值进行深入分析.得出了以下主要结论:荷载角、配钢形式、截面尺寸对轴压比限值有明显影响;合理配钢的SSC异形柱的轴压比限值比钢筋混凝土(RC)异形柱有所提高;箍筋约束混凝土作用对轴压比限值有明显提高.     

带交叉筋十字形短柱抗震性能试验研究

在提出带暗柱异形柱基础上，进一步提出带交叉筋异形柱这一设计方法，通过3根十字形短柱抗震性能的试验研究，分析比较了普通十字形柱，带暗柱十字形柱和带交叉筋十字形柱的性能，试验表明加配交叉钢筋可明显提高十字形短柱的抗震性能。     

钢骨混凝土异形柱正截面承载力及延性计算分析

用条带法对不同轴压比下钢骨混凝土异形柱正截面的承载力和延性进行了计算分析，绘制了相应的M-φ曲线。同时计算分析了在轴压力相同的情况下，随着含钢骨率的变化，钢骨混凝土异形柱承载力和延性的变化情况。文中的结论可供抗震设计参考。     

钢桁架(ST)约束混凝土组合柱抗震性能研究

目前,组合柱在建筑结构中进行了广泛应用和研究,研究表明:截面形式对组合柱的抗震性能有很大影响。首先,对钢桁架(ST)约束混凝土组合柱进行了试验研究。并在此基础上,利用有限元软件ABAQUS建立了数值分析模型;其次,基于数值分析模型,分析了组合柱中各部件的应力应变状态,分别考察了轴压比、缀板排列方式、体积配箍率、角钢肢宽与肢厚等因素对柱抗震性能的影响;最后,给出了组合柱在不同抗震等级下轴压比限值的建议值,可为后续组合柱的研究提供参考。研究表明:随着轴压比的增大,组合柱的延性变差,承载力先增大后减小;合理的缀板排列方式可有效抑制角钢的局部屈曲;随着体积配箍率的增大,组合柱的承载力有一定提升,延性提高较为显著;随着角钢肢宽和肢厚的增加,组合柱的承载力和延性均有显著提升。     

钢筋混凝土带暗柱十字形柱抗震性能试验研究

提出了带暗柱的十字形柱;进行了４根剪跨入λ＝３．８３３的十字形柱的抗震性能试验,分析了轴压比对其抗震性能的影响;论述了暗柱的设置对提高十字形柱抗震能力的作用。最后,将理论计算结果与实测结果进行了比较,二者符合得很好。     

带暗柱Z形短柱抗震性能试验研究

提出了带暗的Z形短柱。通过3根Z形短柱抗震性能的试验研究,分析比较了Z形柱在两个工程轴受力方向的承载力、刚度、延性、滞回曲线和破坏特征,分析了暗柱对提高Z形短柱抗震能力的作用。试验表明加设暗柱后可明显提高Z形截面短柱的抗震性能。     

设置芯柱-构造柱混凝土砌块墙体抗震剪切承载力计算

本文收集了国内大量的混凝土小型空心砌块墙片试验资料,通过研究芯柱一构造柱混凝土小型空心砌块组合砌体受力特征及影响抗震剪切承载力的主要因素,结合理论计算分析,提出了抗震剪切承载力的通用计算公式。该公式既适用于芯柱-构造柱混凝土小砌块墙体,又适用于只设置芯柱或构造柱砌块墙体结构。通过试验值与计算值的比较,证明本文所提出通用公式的准确性。     

Seismic response analysis of multidrum classical columns

This paper presents a numerical investigation on the seismic response of multidrum classical columns. The motivation for this study originates from the need to understand: (a) the level of ground shaking that classical multidrum columns can survive, and (b) the possible advantages or disadvantages of retrofitting multidrum columns with metallic shear links that replace the wooden poles that were installed in ancient times. The numerical study presented in this paper is conducted with the commercially available software Working Model 2D?, which can capture with fidelity the sliding, rocking, and slide‐rocking response of rigid‐body assemblies. This paper validates the software Working Model by comparing selected computed responses with scarce analytical solutions and the results from in‐house numerical codes initially developed at the University of California, Berkeley, to study the seismic response of electrical transformers and heavy laboratory equipment. The study reveals that relative sliding between drums happens even when the g‐value of the ground acceleration is less than the coefficient of friction, µ, of the sliding interfaces and concludes that: (a) typical multidrum classical columns can survive the ground shaking from strong ground motions recorded near the causative faults of earthquakes with magnitudes M_w=6.0–7.4; (b) in most cases multidrum classical columns free to dislocate at the drum interfaces exhibit more controlled seismic response than the monolithic columns with same size and slenderness; (c) the shear strength of the wooden poles has a marginal effect on the sliding response of the drums; and (d) stiff metallic shear links in‐between column drums may have an undesirable role on the seismic stability of classical columns and should be avoided. Copyright © 2005 John Wiley & Sons, Ltd.     

Modeling unstable alcohol flooding of DNAPL-contaminated columns

Alcohol flooding, consisting of injection of a mixture of alcohol and water, is one source removal technology for dense non-aqueous phase liquids (DNAPLs) currently under investigation. An existing compositional multiphase flow simulator (UTCHEM) was adapted to accurately represent the equilibrium phase behavior of ternary and quaternary alcohol/DNAPL systems. Simulator predictions were compared to laboratory column experiments and the results are presented here. It was found that several experiments involved unstable displacements of the NAPL bank by the alcohol flood or of the alcohol flood by the following water flood. Unstable displacement led to additional mixing compared to ideal displacement. This mixing was approximated by a large dispersion in one-dimensional simulations and or by including permeability heterogeneities on a very small scale in three-dimensional simulations. Three-dimensional simulations provided the best match. Simulations of unstable displacements require either high-resolution grids, or need to consider the mixing of fluids in a different manner to capture the resulting effects on NAPL recovery.     

Dynamic instability of frames having thin-walled columns

Dynamic instability of single storey frames having thin-walled columns has been investigated. The lateral loads sustained by the frame are dynamic in character, while the axial loads are deemed to be quasi-statically applied. The analytical model employed by the authors has the capability of modelling the combined action of the two ‘companion’ local modes whose amplitudes are variable along the length of the column and any type of end conditions of the members. For given levels of axial loads sustained by the columns, the magnitudes of lateral loads causing instability can be significantly smaller than those corresponding to static buckling, provided the dynamic load is of sufficient duration. There exists, however, a threshold value of axial force carried by the columns, below which there is no elastic instability—static or dynamic. For columns with overall critical loads several times greater than the local critical load, there is no danger of elastic instability, but the deflections under dynamic lateral loads of less than 1 per cent of the axial load may reach such huge values that there is a serious danger of localized plastic collapse. It is also shown that moment frames having thin-walled columns such as those fabricated out of cold formed steel are extremely vulnerable to moderate seismic excitations.     

Bounds on earthquake response of elastic columns

The dynamics of an elastic column subjected to vertical as well as horizontal ground acceleration during an earthquake strong motion is considered. The Liapunov method of stability analysis is employed and several bounds on the maximum lateral displacement and bending stress are obtained and discussed.     

Taylor columns in horizontally sheared flow

Abstract

Solutions of the steady, inviscid, non-linear equations for the conservation of potential vorticity are presented for linearly sheared geostrophic flow over a right circular cylinder. The indeterminancy introduced by the presence of closed streamline regions is removed by requiring that the steady flow retains above topography a given fraction of that fluid initially present there, assuming the flow to have been started from rest. Those solutions which retain the largest fraction in uniform and negatively sheared streams satisfy the Ingersoll (1969) criterion (that, in the limit of vanishingly small viscosity, closed streamline regions are stagnant) and so are unaffected by Ekman pumping. These flows are set up on the advection time scale. In positively sheared flows the maximum retention solutions do not satisfy the Ingersoll criterion and thus would be slowly spun down on the far longer viscous spin-up time.

For arbitrary isolated topography, both the partial retention and Ingersoll problems are reduced to a one-dimensional non-linear integral equation and the solution of the Ingersoll problem obtained in the limit of strong positive shear. The stagnant region is symmetric about the zero velocity line and extends to infinity in the streamwise direction. Its cross-stream width is proportional to the rotation rate and fractional height occupied by the obstacle and inversely proportional to the strength of the shear, decreasing inversely as the square of distance upstream and downstream.     

The fluid dynamics and thermodynamics of eruption columns

A new model for Plinian eruption columns is derived from first principles and investigated numerically. The dynamics particular to the momentum-driven basal gas-thrust region and the upper buoyancy-driven convective region are treated separately. The thermal interactions in the column are modelled by the steady-flow-energy equation. The main results of the present paper are that: (1) the basal gas-thrust region model predicts a very rapid initial expansion of the material on leaving the vent; (2) the gas-thrust region height decreases with initial temperature, inital gas content of the erupted material and initial velocity, but increases with vent radius; (3) the total column height increases with initial temperature, initial velocity and vent radius, but decreases with initial gas content; (4) column collapse occurs for initial velocities of the order of 100 m/s; the precise value increases as the initial gas content in the erupted material decreases; (5) for large vent radii or low initial gas content of the erupted material, the velocity in the column can increase with height once in the buoyancy-driven region instead of decaying to zero monotonically; (6) the interaction of the potential energy with the enthalpy is found to be the dominant thermal interaction in the upper part of the column. Previous models of eruption columns involve inconsistencies and simplifications; these are shown to lead to significant differences in the results in comparison to the present model.     

The dimensions and dynamics of volcanic eruption columns

Eruption columns can be divided into three regimes of physical behaviour. The basal gas thrust region is characterized by large velocities and decelerations and is dominated by momentum. This region is typically a few hundred metres in height and passes upwards into a much higher convective region where buoyancy is dominant. The top of the convective region is defined by the level of neutral density (heightH _B ) where the column has a bulk density equal to the surrounding atmosphere. Above this level the column continues to ascend to a heightH _T due to its momentum. The column spreads horizontally and radially outwards between heightH _T andH _B to form an umbrella cloud. Numerical calculations are presented on the shape of eruption columns and on the relationships between the heightH _B and the mass discharge rate of magma, magma temperature and atmospheric temperature gradients. Spreading rate of the column margins increases with height principally due to the decrease in the atmospheric pressure. The relationship between column height and mass discharge rate shows good agreement with observations. The temperature inversion above the tropopause is found to only have a small influence on column height and, eruptions with large discharge rates can inject material to substantially greater heights than the inversion level. Approximate calculations on the variation of convective velocities with height are consistent with field data and indicate that columns typically ascend at velocities from a few tens to over 200 m/s. In very large columns (greater than 30 km) the calculated convective velocities approach the speed of sound in air, suggesting that compressibility effects may become important in giant columns. Radial velocities in the umbrella region where the column is forced laterally into the atmosphere can be substantial and exceed 55 m/s in the case of the May 18th Mount St. Helens eruption. Calculations on motions in this region imply that it plays a major role in the transport of coarse pyroclastic fragments.