框架和排架爆破拆除的后坐(1)

研究了框架、排架和框剪结构爆破拆除定向倾倒时后坐的机理。当前、中排立柱拆除后,爆破切口层上部的建筑重心总是企图沿重力线以最短距离落地,从而迫使现浇钢筋混凝土框架在切口层的后立柱顶形成塑性铰而机构后坐;排架后柱顶的铰连接后移,形成立柱后倒;装配式框架重心低于后柱的粱端塑性铰,牵拉后柱前倾,其重力分量推着柱根后滑;框剪结构在被剪力墙加固抗弯抗压稳定的立柱支撑下,将迫使结构的重心只能绕柱根微圆弧式下落,结构单向倾倒,其重力分量推动柱根后滑。多跨现浇钢筋混凝土框架,若后两排柱不炸但柱根割筋并削弱,当切口爆破后,框架可能单向倾倒,其重力分量也将推动柱根后滑。以多体动力学方程及其近似解计算结构的后坐值和阻止后坐的抗力,提出了判别立柱后滑的条件,估计了立柱后倒或后滑值。动力学方程后坐值的近似解与数值解仅差5％,为工程所容许。实例计算后坐值和爆堆后沿宽与实测相近,证实了后坐和爆堆后沿计算的原则和方法是正确的,可以应用。     

建筑爆破拆除动力方程近似解研究(2)

研究了框架以及其上的罐体和排架,当单切口前、中排支柱爆破拆除后所形成的双体运动.可以将后排柱简化为一个自由度体,而切口以上的结构可视为另一自由度上体.建筑物倒塌的现场观测发现,上体质心总是企图接近其重力线下落,由此将动力学方程组的数值解归纳为近似解组,两者间的误差在10%之内,为工程应用所容许.由此可较为直观、方便地用近似解组计算现浇钢筋混凝土框架、装配式钢筋混凝土框架以及排架结构在单切口爆破拆除时的倒塌姿态.     

钢板剪力墙边缘构件的计算方法研究

基于钢框架-钢板剪力墙的理想破坏机制,根据梁、柱塑性铰位置,推导了钢板剪力墙边缘构件的计算公式,给出了钢板剪力墙、梁和柱之间的强度关系。设计了一榀单跨五层钢框架-钢板剪力墙全尺寸分析模型,采用大型通用非线性有限元软件ABAQUS 6.10对其进行了非线性数值分析。结果表明:顶梁能为单侧拉力场提供足够的抗弯承载力,防止顶梁跨中形成塑性铰;各层钢板剪力墙承担的侧向荷载基本相同。表明按上述计算公式确定的边缘构件能够为钢板剪力墙提供足够的锚固强度,有效控制受压柱的塑性铰位置,防止柱中部形成塑性铰,使钢框架-钢板剪力墙实现理想的破坏机制,即“弱板强框架,强柱弱梁”,达到双重抗震设防的目的。     

多折定落点控爆拆除钢筋混凝土高烟囱设计原理

以广州纸厂高100m钢筋混凝土烟囱顺利实施定倒向、定落点、多折叠爆破拆除为例,提出了用多体-离散体系统动力分析来描述烟囱在初始失稳后到着地堆积的过程。多体-离散体动力分析方程由变拓扑多体系统动力学方程和离散体动力学方程组成,即变拓扑多体系统动力学方程来描述烟囱在初始失稳后,倾倒旋转和运动解体阶段,n折烟囱段在空中的动力运动,正算则数值模拟各拓扑的运动姿态,逆算烟囱各体间的作用力,以判断烟囱各段间相继的解体,其拓扑切换包括烟囱切口延时爆破的时间切换点、切口闭合的位移切换点和烟囱解体的动力切换点。空中解体后,用离散体系统动力分析方程来描述非完全离散直至完全离散体(含单体和多体)在空中的相互分离、钢筋牵拉、碰撞和滑移等下落运动,数值模拟烟囱各段塌落堆积的过程。现场观测的烟囱连续多折倾倒和解体的姿态以及着地堆积的形态,与数值模拟接近,证明了用多体-离散体动力分析来描述烟囱的爆破倒塌是正确的。     

减少框架爆破拆除后坐的措施(2)

根据"框架和排架爆破拆除后坐(1)",列举了14项爆破拆除工程,证实了文中所述后坐机制正确,计算方法可用.由此研究了减少框架爆破拆除的后坐措施,即:现浇钢筋混凝土框架,可采用炸断后跨梁端原地坍塌以防后坐,全炸下层柱原地坍塌,逐跨断裂降低前中跨的重心,横向倾倒改纵向倾倒,中柱仅炸底层,下向切口结合后方结构抵抗后坐,适当降低切口高度和延长逐跨断裂起爆时差等措施,均可减小后坐;框剪结构保留横向纵向剪力墙,以维持抗弯抗压的支撑后立柱,迫使结构单向倾倒而防止机构后坐;多跨现浇框架也可保留后2排柱的下部支撑结构,以支撑上部结构而减少下坐和机构后坐.     

延性纤维混凝土剪力墙抗震性能试验研究

该文为改善高性能混凝土剪力墙的抗震性能,提出在剪力墙塑性铰区采用延性纤维混凝土(DFRC),设计了4片剪跨比为2.1的剪力墙试件,并进行了拟静力试验。通过改变DFRC区高度、轴压比和约束箍筋数量,研究其破坏机理、耗能能力及变形性能。结果表明:1) 塑性铰区采用DFRC的剪力墙试件弹性阶段变长,剪力墙屈服后承载力降低缓慢;2) DFRC可有效控制剪力墙塑性铰区的弯剪斜裂缝的宽度,防止塑性铰区发生剪切破坏;3) DFRC区高度增大,剪力墙的变形和耗能能力明显提高,DFRC区约束箍筋数量增加,试件变形和耗能能力提高;4) 塑性铰区采用DFRC的剪力墙试件,塑性铰区损伤程度明显降低,对减轻剪力墙的地震破坏程度具有重要作用。     

两层带开洞预制剪力墙抗震性能试验研究与数值模拟分析

为研究带窗洞的预制装配式混凝土剪力墙中窗下墙对结构抗震性能的影响,该文对两个带不同高度窗下墙的两层预制剪力墙试件进行了低周反复荷载试验。在此基础上,提出了带窗下墙预制剪力墙结构的精细有限元数值模拟方法,结合试验结果分析揭示了窗下墙对带开洞预制剪力墙抗震性能的影响。试验和数值模拟分析结果表明,两试件在初始受力阶段,窗下墙与下层连梁作为一根整体连梁共同工作,此后二者逐渐脱开,形成两根并列布置的双连梁;两试件的破坏形态均为墙肢根部和双连梁两端形成塑性铰,最终塑性铰区混凝土被压碎;窗下墙较高的试件W-2承载力和初始刚度均大于W-1,延性和耗能能力则小于W-1;预制剪力墙构件中的窗下墙可显著提高该类构件的刚度、承载力和耗能能力,对带窗下墙的预制剪力墙结构进行抗震设计时应对窗下墙予以考虑。     

高层框架剪力墙结构楼房的控制爆破拆除

针对高层框架剪力墙结构楼房具有高宽比较小的特点,充分考虑待拆楼房的结构特征和其周围环境的局限性,设计了提高炸高和前移转铰点的方法,按照设计方案精心施工,对该楼房成功实施了爆破拆除。最后,介绍了定向倾倒的成功经验,探讨了在复杂环境中高层框架剪力墙结构楼房定向爆破拆除的可行性。     

钢筋混凝土烟囱拆除爆破倾倒过程摄影分析

为了精确观测钢筋砼烟囱爆破倾倒过程中爆破切口形成、切口闭合、烟囱倾倒运动及破坏规律,采用佳能1DX高级单反数码相机和佳能7D数码相机,对准南方碱业股份有限公司100 m高钢筋砼烟囱的爆破切口,拍摄了数百张高清晰照片。根据相机抓拍的烟囱状态变化和相应时刻,通过计算详细定量地描绘了烟囱的倾倒破坏过程和运动规律,发现该工况下烟囱爆破从起爆到倾倒触地经历了7个阶段。     

利用烟囱下坐减少倒塌长度的爆破实例

通常单向倾倒爆破拆除建(构)筑物时,为了保证建(构)筑物倾倒方向的准确,应尽量避免拆除对象后坐。本文通过介绍在倾倒空间不足的环境条件下,设计了独特的爆破切口,采用了合理的爆破网路,采取的单爆破切口的非折叠方式,恰好是利用了烟囱的后坐,有效缩减烟囱的定向倒塌长度,成功爆破拆除了一座高为50m的砖质烟囱,达到安全爆破的目的。可为同类工程设计施工参考。     

移动下击暴流作用下高层建筑风荷载特性研究

为研究移动下击暴流作用下高层建筑的风荷载特性,采用可移动的冲击射流装置对高层建筑模型进行了测压试验,并通过计算流体力学方法进行数值模拟,分析了风暴移动过程中,风场中不同位置的高层建筑模型表面风压分布特性及风荷载作用机理。结果表明:风暴的移动会使风暴前缘风速加强,而使后缘风速减弱,从而使建筑表面的整体风压出现相应变化。当建筑位于风暴移动中心线上时,气流分离形成的漩涡主要出现在顶面迎风侧前沿及侧面迎风侧上角部区域,这些区域负压相对较大;建筑顶面在风暴经过时会产生较大正压。当建筑位于风暴移动中心线外时,高层建筑的来流风风向会随风暴的移动而不断发生变化;当建筑位于风暴前缘时,与来流风夹角较小的侧面会由于气流在钝体边缘的分离作用而出现较大的负压区域;当建筑位于风暴后缘时,建筑顶面角部区域会由于锥形涡的产生而出现较大负压。     

Transient and stationary response statistics of van der Pol oscillators subjected to broad band random excitation

The joint probability density function of the state space vector of a white noise excited van der Pol oscillator satisfies a Fokker-Planck-Kolmogorov (FPK) equation. The paper describes a numerical procedure for solving the transient FPK equation based on the path integral solution (PIS) technique. It is shown that by combining the PIS with a cubicB-spline interpolation method, numerical solution algorithms can be implemented giving solutions of the FPK equation that can be made accurate down to very low probability levels. The method is illustrated by application to two specific examples of a van der Pol oscillator.     

Drag on a sphere accelerating rectilinearly in an elastico-viscous fluid

The exact solution for the drag on a sphere moving in an arbitrary manner along a rectilinear path in an otherwise-still elastico-viscous fluid of infinite extent is presented. The Fourier transform technique is used to derive the solution. This technique is based on the fact that drag on an accelerating body can be obtained by integrating the drag on an oscillating body over all possible frequencies. The solution is also expressed in terms of infinite series which is suitable for numerical evaluation of the drag. The solution for the drag on a sphere suddenly brought to uniform motion is presented as an example of this study.     

A moving Kriging interpolation‐based meshless method for numerical simulation of Kirchhoff plate problems

This paper mainly proposes an alternative way for numerical implementation of thin plates bending based on a new improvement of meshless method, which is combined between the standard element‐free Galerkin method and one different shape functions building technique. The moving Kriging (MK) interpolation is applied instead of the traditional moving least‐square approximation in order to overcome Kronecker's delta property where the standard method does not satisfy. Obviously, the deflection of the thin plates is approximated via the MK interpolation. To illustrate this approach, numerical analysis is examined in both regular and irregular systems. Three examples with different geometric shapes of thin plates undergoing a simply supported boundary are performed. In addition, two important parameters of the present method are also analyzed. A good agreement can be found among the proposed, analytical and finite element methods. Copyright © 2008 John Wiley & Sons, Ltd.     

Influence of pre-collision occupant parameters on injury outcome in a frontal collision

Optimal performance of adaptive restraint systems in the vehicle requires an accurate assessment of occupant characteristics including physical properties and pre-collision response of the occupant. To provide a feasible framework for incorporating occupant characteristics into adaptive restraint schemes, this study evaluates the sensitivity of injury risk in frontal collisions to four occupant parameters: mass, stature, posture and bracing level. The numerical approach includes using commercial multi-body software to develop occupant models that span a range of occupant parameters representative of the real-world driver population. Coupled with a multi-body model of the vehicle interior and standard restraint system, risk of occupant injuries within specific body regions are predicted through numerical simulations in conjunction with established injury risk functions. The results show occupant posture to be the most significant parameter affecting the overall risk of injury in frontal collisions. The causal relationship as predicted using the numerical model has been compared to the traffic injury epidemiology findings, and the feasibility of an analytical methodology to provide real-time estimates of injury severity has been discussed. Preliminary estimates from the study indicate that the proposed methodology will provide a framework to optimize restraint performance and potentially reduce the risk of injuries up to 35% (based on parameter-specific optimization), using accurate information regarding the pre-collision occupant characteristics.     

Equivalent inclusion method-based simulation of particle sedimentation toward functionally graded material manufacturing

A novel numerical approach based on Eshelby’s equivalent inclusion method is presented to simulate the Stokes’ flow of many spherical particles moving in a viscous fluid at a small Reynolds number. Many particles fall toward the bottom of the fluid at different velocities and thus form a graded microstructure in terms of the material phase and the particle size. For each particle, an eigenstrain rate, which is given in a polynomial form, is introduced to represent the mismatch between the particle and the rest of the fluid. Rongved’s fundamental solution of a point force in a semi-infinite domain with a fixed boundary (Rongved in J. Appl. Mech. 22, 545–546, 1955) is used to calculate the velocity field caused by the body force and eigenstrain rate. Based on Eshelby’s stress equivalent condition, the eigenstrain rate of each particle can be solved and the sedimentation process of a many-particle system can be simulated as a quasi-equilibrium process. If only one or two particles are considered, the results agree with the finite element results very well. Using a suspension of aluminum and high-density polyethylene (HDPE) powders mixed in ethanol, the microstructural evolution is illustrated along with the sedimentation process, which produces a graded mix collected at the fixed boundary for functionally graded material manufacturing.     

通用下部钻具三维小挠度静力分析的数学模型及应用

随着钻井技术的进步,以控制井眼轨道为目的的下部钻具组合发展迅速。在原来的普通增斜、降斜和稳斜钻具的基础上,发展了多种类型的导向钻具、带偏心弯接头的防斜钻具、带柔性接头防斜钻具和两稳定器间变刚度的增斜钻具等多种新型下部钻具组合。为了更好地应用这些新钻具,建立了适用于对普通下部钻具、导向钻具、带偏心弯接头和柔性接头的下部钻具进行三维小挠度静力学分析的数学模型,包括(1)微分方程,(2)钻头、稳定器、弯角、变截面、切点和井壁的边界条件,(3)钻头的侧向力和钻头转角。用该理论编写了应用软件。作为软件的部分功能,对几套钻具进行了增斜率随井斜角变化的预测, 并进行了初步分析。     

Starting flow generated by the impulsive start of a floating wedge

The initial stage of the plane unsteady flow caused by the impulsive vertical motion of a wedge initially floating on an otherwise flat free surface is investigated with the help of a combination of numerical and asymptotic methods. The liquid is assumed ideal and incompressible and its flow potential. Compressible effects give a negligible contribution to the flow close to the entering body at the stage considered in the present paper. The vertical velocity of the body is constant after the impulsive start. The flow domain is divided into an outer region, where the first-order solution is given by the pressure-impulse theory, and inner regions close to the intersection points between the free surface and the moving body. The relative displacement of the body plays the role of a small parameter. The inner solution is matched with the outer one. The outer solution is given in quadratures but the inner solution, which is shown to be nonlinear and self-similar, can be found only numerically. With the aim of deriving the inner solution, the inner region is divided into three parts. In the far-field zone the solution is given in terms of its asymptotic behavior while, in the jet region, attached to the wedge, the flow is described by a second-order shallow-water approximation. In the intermediate region a boundary-element method is used, which is suitably coupled with the solutions in both the jet and the far-field regions through an iterative pseudo-time stepping procedure. The procedure is dependent on the deadrise angle of the wedge. If the angle is equal or smaller than π/4, eigensolutions appear in the far-field asymptotics and their amplitudes are recovered together with the solution. The approach is applied to different values of the wedge deadrise angle. The obtained results can be used to improve the prediction of the hydrodynamic loads acting on floating bodies, the velocity of which changes rapidly.     

爆破拆除框架跨间下塌倒塌的切口参数

研究了爆破拆除框架楼房跨间下塌倒塌的动力学条件,即倾倒动能大于克服跨间下塌所需的功,包括阻止翻倒的势能增量、梁柱夹角形变的功和克服翻滚阻力的功。由此推导出跨间下塌倾倒时,楼房爆破下坐后质心高宽比η与切口高宽比λ的关系。给出了不同跨数和弯矩相似准数Kt条件下楼房翻倒的λ～η关系图及公式,跨间下塌最终倒塌角(φh+αf)与λ～η的关系图。通过楼房跨间下塌倒塌的实例验证了λ～η关系的合理性。