计算模型对框架结构梁柱内力影响研究

结构抗震设计的基本原则之一是保证"强柱弱梁",但汶川地震等大量实际震害表明这一抗震设计目标并未能很好地实现。针对此问题,已开展大量研究,探讨了楼板、填充墙以及梁、柱、板配筋等因素对形成"强梁弱柱"的影响。本文则从计算模型方面,即结构分析中广泛采用的模型、精细有限元模型和楼板与梁分别考虑的模型,对梁柱内力影响进行了对比研究。结果表明,计算模型对梁、柱弯矩比有较大影响,是形成"强梁弱柱"的重要影响因素。     

不同模型对足尺钢框架振动台试验模拟的影响

本文分别采用纤维单元模型和塑性铰单元模型对一个四层足尺钢框架振动台试验进行模拟分析,在三维空间非线性分析程序Perform-3D中进行动力非线性分析,比较分析结果,并与试验结果对比,以研究两种模型应用于钢框架整体结构非线性分析的计算精度。文中并讨论了纤维单元模型截面纤维的划分、塑性区长度的取值等问题。最后对采用组合梁的整体结构模型进行了动力非线性分析。结果表明,纤维模型的建模速度比塑性铰模型快,但塑性铰模型能模拟结构的倒塌时间。Perform-3D程序的纤维单元模型和塑性铰单元模型用于计算我国规范规定的7度和8度地震作用的多层钢框架结构,其结果是真实可靠的,而且计算结果偏于安全。     

高层框支剪力墙结构地震反应分析的超元法

西方嵩层框支剪力墙结构地震反应分析的超元法，即将每榀框支墙中的上部剪力墙和落地墙简化处理成等效柱，底部框架简化处理成等代柱，楼板视为深梁，将连续分布的质量离散化，建立二维空间结构的“串并联质点系”振动模型，采用超级单元进行结构的地震作用计算及内力分析，此法计算简便并适用于结构竖向变刚度和考虑楼板变形等情况。     

建筑结构中抗震分析模型的优化研究

大多数建筑结构由梁、柱、支撑、剪力墙、地基和楼板等主要结构组成。一般而言,楼板对建筑结构的抗震性能可以忽略不计,所以进行建筑结构分析的模型是无楼板的。因此,楼板被刚性隔板代替,以提高分析效率。本文提出的建筑结构抗震分析解析模型考虑了楼板抗弯刚度,该模型采用超级单元、刚性隔板和子结构技术来减少自由度。通过实例分析,验证了该模型在多层建筑结构抗震分析中的有效性和准确性。且此模型能够显著减少计算量,提高分析效率,振动周期和响应时间等分析结果的精度与精化模型的结果非常接近,说明该模型的提出是合理的。     

损伤梁单元及其在RC结构构件非线性分析中的应用

本文介绍了一种基于损伤力学、断裂力学以及集中塑性理论建立的简化损伤梁单元模型。采用此单元模型,分析了实验梁在单凋加载下的受力性能,并与材料模型和弹塑性单分量模型分析结果进行比较。算例表明简化损伤粱单元模型对于RC结构构件的非线性分析有良好的适应性,可以有效地模拟构件的开裂、屈服和失效全过程;得到直接从力学意义出发的反映结构损伤的损伤内变量,对结构的损伤评估有启发意义。     

钢框架震害预测中的结构计算问题

针对在计算模型中可以用梁单元来描述的钢框架结构，本文运用ＳＡＰ５有限元计算程序，进行了大量的计算分析。在此基础之上，总结了单元划分的特点、结构的变形特征及水平地震动作用下结构动力反应中的振型参与情况，并给出了相对计算误差作为检验。本文最后计算了一个有实测数据的高２２ｍ的复杂钢框架。这一工作为有效地完成钢框架震害预测中的结构计算分析，提供了一定的初步经验。     

传统框架及楼板局部设缝框架梁端剪力增大系数分析

梁端剪力增大系数是实现结构"强剪弱弯"的关键措施之一。分析了传统框架的梁端剪力增大系数,表明现浇楼板对框架梁端抗剪承载力的影响不可忽略,抗震规范给出的梁端剪力增大系数难以实现梁"强剪弱弯"的抗震要求,由此对框架梁侧楼板局部设缝,以消除楼板对框架梁端抗弯承载力的贡献。进而分析了该楼板局部设缝框架的梁端剪力增大系数,表明当框架底部实配钢筋αAs≤1.1βAs+0.1As时,即框架梁端底部实配钢筋面积不超过该处计算配筋面积的1.1倍与支座负弯矩配筋面积的0.1倍之和时,现行抗震规范给出的梁端剪力增大系数对于楼板局部设缝的框架可以实现"强剪弱弯"的要求,从而使梁弯曲破坏先于受剪破坏。     

OpenSEES的剪力墙宏观单元的研究

重点研究三维剪力墙单元MVLEM3D的数值模型及计算原理,并采用开源非线性有限元程序OpenSEES进行剪力墙低周往复试验的数值分析,探讨不同单元划分形式对结果的影响。通过二次开发编制了基于OpenSEES的剪力墙结构分析程序SWNA,对不同弹簧个数、不同竖向及水平划分方式,建立剪力墙宏观单元模型进行分析,对比试验结果表明该数值方法能够很好地从宏观上模拟剪力墙弹塑性行为:包括中和轴移动、剪切变形影响、局部塑性状态及破坏机制等。通过单元及弹簧的划分对比,可知该单元可通过比较少的自由度模拟剪力墙结构,节省大量计算时间。对于强非线性分析,增加水平划分可以考虑局部的破坏变形,使骨架曲线下降段明显。因此该单元适用于高层建筑结构的整体弹塑性分析及基于性能的抗震评定。     

带现浇楼板RC框架结构抗震性能的多因素影响分析

采用pushover和非线性动力时程分析方法,分析了多因素下带楼板框架和不带楼板框架的抗震性能,并研究了在双向地震作用下框架结构的性能及需求。建立两组模型并完成对比分析,结果表明:考虑楼板的框架结构在不同轴压比及柱端弯矩增大系数作用下抗震性能会降低;在单向地震作用下可实现结构的"强柱弱梁"屈服机制;斜向地震作用下带楼板的框架结构,在轴压比取值高于0.56或者柱端弯矩增大系数高于2.0时,才能形成"强柱弱梁"屈服机制;斜向地震作用下用空间带楼板框架模型考虑结构体系的空间抗震机制更加合适。     

大型渡槽有限条法动力建模研究

根据渡槽结构特点，采用有限条划分渡槽槽身，推导出渡槽槽身结构的单元刚度矩阵、相容质量矩阵的显式表达式；渡槽支架采用空间梁单元模拟；联接槽身和支架的盆式橡胶支座采用弹性元件单元模拟。编程程序具体计算了某大型渡槽的模态，并用ANSYS对大型渡槽进行模态分析，计算结果表明：该模型计算的渡槽结构的固有频率和ANSYS计算结果接近。模型可用于大型渡槽的动力分析。     

钢框架结构典型震害的计算机模拟研究

为模拟钢框架结构的典型震害,本文基于ANSYS软件建立了钢框架结构简化模型。该模型可以考虑楼板对钢框架结构整体性能的影响,并且进一步考虑了楼板与钢梁之间的滑移、节点域变形,以及梁柱节点焊缝的断裂等因素。应用本文建立的钢框架结构模型对北岭地震中Blue Cross大厦的震害进行了模拟,与实际震害对比的结果表明,该模型能够比较精确地模拟地震作用下钢框架结构的响应。钢框架结构模型对节点焊缝断裂的钢框架结构震害研究有着重要的意义。     

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。     

高温后足尺有粘结预应力混凝土梁板力学性能研究

针对足尺有粘结预应力混凝土梁板高温后的抗弯承栽力开展了非线性计算分析。结果表明,综合配筋指标、有效预应力对高温后极限弯矩与常温下极限弯矩比值M_u~A/M_u的影响不大,预应力度和预应力筋的保护层厚度对M_u~A/M_u影响显著。高宽比近似相同的有粘结预应力混凝土梁,当第一排钢筋的保护层厚度相同时,受火时间为3 h,高度为700 mm的梁高温后截面承栽力下降幅度最大约为30%,高度为4500 mm的梁高温后截面承栽力下降幅度不到10%,高温后大尺度梁的力学性能优于小尺度梁。给出了考虑预应力筋保护层厚度和预应力度影响的有粘结预应力混凝土板M_u~A/M_u的计算公式,以及综合考虑预应力筋、非预应力筋合力点到梁底距离和预应力筋梁侧保护层厚度影响的有粘结预应力混凝土梁M_u~A/M_u的计算公式。     

General models for episodic surface denudation and its measurement by cosmogenic nuclides

In order to use cosmogenic nuclides to infer erosion rates and exposure ages, it is necessary to apply a quantitative model for the accumulation of these nuclides in an eroding surface. The most straightforward model assumes that the surface continuously erodes at a constant rate. In many cases, however, the erosion is episodic: denudation is the result of the spalling off of slabs of rock in a series of discrete events. In a previous paper, we discussed two models for such episodic erosion; in one model slabs of rock spalled off periodically, while in the other slabs spalled off at stochastic time intervals. In both models we took the slabs to have a given, fixed width. In this paper we expand the previously treated models to allow for a statistical distribution of widths; this makes the models more realistic, and broadens our discussion of the fluctuations in the nuclide concentration that may be observed. We present general results for both models, results which allow for any distribution of widths. We then explore the stochastic model in more detail, applying a particular choice of width distribution. This allows us to address an interesting limiting case: when the widths are very small, the average nuclide concentration is accurately given by the standard continuous erosion model; yet, perhaps surprisingly, the fluctuations about this average can be quite significant.     

复杂框支剪力墙结构空间弹塑性分析

结合某复杂框支剪力墙高层商住楼的模拟地震振动台试验和三维弹性有限元分析结果,提出该结构进行弹塑性地震反应分析的计算假定和弹塑性分析计算单元,建立了空问分析模型,进行了弹塑性动力时程分析,计算结果与试验结果比较接近。提出的计算方法对类似结构的弹塑性分析有一定的参考价值。     

Three‐dimensional beam–truss model for reinforced concrete walls and slabs – part 2: modeling approach and validation for slabs and coupled walls

A three‐dimensional beam–truss model (BTM) for reinforced concrete (RC) walls that explicitly models flexure–shear interaction and accurately captures diagonal shear failures was presented in the first part of this two‐paper series. This paper extends the BTM to simulate RC slabs and coupled RC walls through slabs and beams. The inclination angle of the diagonal elements for coupled RC walls is determined, accounting for the geometry of the walls and the level of coupling. Two case studies validate the model: (1) a two‐bay slab–column specimen experimentally tested using cyclic static loading and (2) a five‐story coupled T‐wall–beam–slab specimen subjected to biaxial shake table excitation. The numerically computed lateral force–lateral displacement and strain contours are compared with the experimentally measured response and observed damage. The five‐story specimen is characterized by diagonal shear failure at the bottom story of the walls, which is captured by the BTM. The BTM of the five‐story specimen is used to study the effects of coupling on shear demand for lightly reinforced RC coupled walls. The effect of mesh refinement and bar fracture of non‐ductile transverse reinforcement is studied. Copyright © 2016 John Wiley & Sons, Ltd.     

装配式钢混组合结构加固时抗震性能模糊综合评估模型研究

参数化的装配式钢混组合结构建筑信息模型缺少结构信息描述,无法实现装配式钢混组合结构图档的修正和自主更新,对结构构件的损伤评估效果差,抗震加固性能差。据此提出用于装配式钢混组合结构抗震加固的建筑信息模型,模型框架包括建筑设计模型、结构设计模型、结构抗震加固设计和损伤评估;通过结构构件的实体定义、属性定义和关联性定义,全面描述柱、梁、板和墙等钢混组合结构构件的抗震加固性能信息;采用模糊加固评估方法获取精准的结构构建综合损伤指数,评估结构构件的加固等级,提高抗震加固性能。经实验证明,所设计模型得到的结构损伤指数与实际损伤指数的误差低于0.03,说明该模型分析装配式钢混组合结构抗震加固性能准确性较高。     

Α mass-reduction design concept for seismic hazard mitigation

A mass reduction concept for seismic hazard mitigation is investigated herein. The proposed method is implemented through floating slabs, ie, slabs that have been seismically isolated from the skeleton of the structure. The investigation is based on time history analyses of MDOF models under scaled strong-motion seismic records complying with an EC8 spectrum. The purpose of these slabs is twofold; for selected short isolation periods, they act as a mass-damping system for the overall response of the structure, employing significantly more mass than traditional TMDs, while for longer isolation periods they provide seismic protection on their contents while effectively reducing the seismic mass of the structure. In the latter case, it is found that the response of the skeleton can be evaluated accurately from a corresponding reduced-mass model. The proposed design method does not necessarily aim at replacing existing seismic design approaches; it rather provides design versatility in the hands of the practicing engineers.     

Natural vibrations of shear wall buildings on flexible supports

A shear wall building is considered as an assembly of plane and curvilinear shear walls tied together by floor slabs to act as a composite unit. Based on this conception and the continuous medium approach, the governing dynamic equations and boundary conditions are derived from energy principles, using Vlasov's theory of thin-walled beams. All primary and secondary inertia forces, as well as the influence of elastic foundation flexibility, have been taken into consideration. A numerical solution of the dynamic equations is achieved by employing the Ritz-Galerkin technique, yielding both natural frequencies and mode shapes. The technique is applicable to buildings containing coupled and non-coupled, open section shear walls oriented in plan in any arbitrary manner. The use of the method is illustrated by the example of a complex building with unsymmetric plan, and the analytical natural frequencies of two shear wall building models are compared with those obtained experimentally by other investigators.     

Effects of plate and slab viscosities on the geoid

The effects of plate rheology (strong plate interiors and weak plate margins) and stiff subducted lithosphere (slabs) on the geoid and plate motions, considered jointly, are examined with three-dimensional spherical models of mantle flow. Buoyancy forces are based on the internal distribution of subducted lithosphere estimated from the last 160 Ma of subduction history. While the ratio of the lower mantle/upper mantle viscosity has a strong effect on the long-wavelength geoid, as has been shown before, we find that plate rheology is also significant and that its inclusion yields a better geoid model while simultaneously reproducing basic features of observed plate motion. Slab viscosity can strongly affect the geoid, depending on whether a slab is coupled to the surface. In particular, deep, high-viscosity slabs beneath the northern Pacific that are disconnected from the surface as a result of subduction history produce significant long-wavelength geoid highs that differ from the observation. This suggests that slabs in the lower mantle may be not as stiff as predicted from a simple thermally activated rheology, if the slab model is accurate.