共查询到20条相似文献,搜索用时 655 毫秒
1.
双层双曲线网壳结构冷却塔温度应力的研究 总被引:3,自引:0,他引:3
把双层双曲线网壳结构竖向应用于冷却塔的筒壁 ,在网壳的周围挂金属面板 ,筒壁放在底部环梁上 ,形成了上面为网壳结构 ,下面为钢筋混凝土结构的新型结构。考虑双层双曲线网壳结构冷却塔由于均匀温度场变化 ,导致筒壁内外的温差 ,产生温度应力。并且结合边界约束条件的影响来探讨该结构的温度应力。分析了冷却塔杆件在均匀温度场变化下 ,由于不能自由地热胀冷缩 ,而产生了温度应力 ,同时给出了分析方法。并且根据有限元理论 ,用VisualBasic编制了温度应力分析程序。针对具体的工程实例探讨温度应力在边界的法线方向 ,约束条件分别为固定、弹性、放松三种情况下杆件温度应力的变化规律 ,给出了一些对网壳结构冷却塔设计有参考价值的结论和建议 相似文献
2.
本论文针对目前大多数网壳结构都横向应用于屋盖结构以及冷却塔大多数采用钢筋混凝土结构的现状 ,把双层双曲线网壳结构竖向应用于冷却塔的筒壁 ,在网壳的周围挂金属面板。作者根据某工程的结构特点 ,对其结构进行了结构选型 ,并且在假定节点为铰接情况下 ,采用空间杆系有限元和数值分析方法 ,对该结构进行了受力分析。应用满力优化准则 ,对该网壳结构进行了截面优化 ,取得了良好的建筑和经济效果。本文的研究开辟了网壳结构应用与冷却塔建设的新途径 ,提出了新的研究课题。 相似文献
3.
A tension stiffening model is presented which enables the calculation of average tensile stresses in concrete, after yielding of reinforcement, in reinforced concrete elements subjected to uniaxial tension, shear or flexure. To determine the average tensile stress-strain relationship for concrete, a crack analysis approach is employed taking into account the bond mechanism between concrete and deformed reinforcing bars, and numerical analyses are conducted to determine the tensile behavior of reinforced concrete members including post-yield response. Analytical parametric studies are conducted to determine the influence of various parameters including concrete compressive strength and reinforcement yield strength, ultimate strength, hardening stress, and hardening strain. Analysis results obtained from the proposed model, when compared to experimental results for uniaxial members, indicate good agreement for structural behavior after yielding of reinforcement. The proposed model makes it possible to accurately calculate reinforcement stresses at crack locations and, thus, average strain conditions which result in rupture of reinforcement. This leads to more realistic predictions of the uniaxial, flexural, and shear ductility of reinforced concrete members. 相似文献
4.
5.
Herbert A. Mang Helmut Floegl Friedrich Trappel Herbert Walter 《Engineering Structures》1983,5(3):163-180
Wind loadings govern the design of most cooling towers. Until now, proof of suffiecient safety against buckling under wind load has been a major concern for the designers of such shells.In this paper it is demonstrated that a typical cooling tower made of reinforced concrete would not buckle—at least not in the classical sense of the word. Failure would rather be initiated by rapid propagation of cracks in tensile zones followed by temporary stiffening and, finally, by yielding of the reinforcement.The theoretical part of this paper is restricted to a presentation of the constitutive model, discussion of the equation for incremental-iterative ultimate-load analysis and of the condition for instability. The numerical part contains a detailed study of a built hyperbolic cooling tower.It is shown that: (a), buckling loads resulting from linear and geometrically nonlinear prebuckling analyses are considerably larger than the ultimate load; and (b), results based on a certain form of ‘equivalent axisymmetric pressure’ are on the unsafe side of corresponding results from the ‘actual’ wind load. It is also demonstrated that the ‘crack load’, representing a lower bound to the ultimate load, can be estimated by means of a linear-elastic nonaxisymmetric analysis of the cooling tower. 相似文献
6.
The concept of directional nonlocality is defined to describe the inherent characteristics of concrete tensile cracks affecting the compressive behavior as well as the tensile behavior of concrete. In the cracked concrete, the crack damage in one direction is influenced by damages from other directions. In the present study, a material model was developed to describe the directional nonlocal effect by tension cracks in concrete planar members. For nonlinear numerical analysis of concrete, the proposed directionality parameter was employed in the plasticity model with multiple failure criteria, and an identical tension crack parameter was used for both the tensile behavior and compressive behavior of the concrete. In the proposed plasticity model, tensile and compressive micro failure surfaces defined in the prescribed multiple fixed orientations were used to describe the directional nonlocality in the micro-structure of concrete, and the overall failure surface of the concrete was calculated by averaging the multi-oriented micro-surfaces. The proposed plasticity model was used for nonlinear finite element analysis of reinforced concrete shear panels, and the analysis results were compared with test results. 相似文献
7.
8.
扰动应力场模型(DSFM)由于考虑了裂缝间的剪切滑移效应,融合了转动裂缝模型和固定裂缝模型的思想,可以更真实地模拟钢筋混凝土构件的受剪性能。通过大型通用有限元软件ABAQUS的二次开发接口,开发了基于DSFM模型思想的用户子程序UMAT,重点介绍将剪切滑移应变从总应变中分离出来的算法,并给出能够适应UMAT开发要求的编程方法和流程。利用所开发的UMAT子程序和ABAQUS内置的塑性损伤(CDP)模型对多伦多大学完成的多块钢筋混凝土平板试验进行分析。结果表明,所开发的子程序能够准确反应不同配筋形式的钢筋混凝土单元在不同受力状态下的响应,而ABAQUS内置的CDP模型由于无法反应钢筋混凝土单元斜裂缝出现后的剪应力强化效应,不能用于钢筋混凝土的受剪性能分析。 相似文献
9.
This paper investigates the effect of differential support settlement on shear strength and behavior of continuous reinforced concrete (RC) deep beams. A total of twenty three-dimensional nonlinear finite element models were developed taking into account various constitutive laws for concrete material in compression (crushing) and tension (cracking), steel plasticity (i.e., yielding and strain hardening), bond-slip at the concrete and steel reinforcement interface as well as unique behavior of spring-like support elements. These models are first validated by comparing numerical predictions in terms of load-deflection response, crack propagation, reaction distribution, and failure mode against that of measured experimental data reported in literature. Once the developed models were successfully validated, a parametric study was designed and performed. This parametric study examined number of critical parameters such as ratio and spacing of the longitudinal and vertical reinforcement, compressive and tensile strength of concrete, as well as degree (stiffness) and location of support stiffness to induce varying levels of differential settlement. This study also aims at presenting a numerical approach using finite element simulation, supplemented with coherent assumptions, such that engineers, practitioners, and researchers can carry out simple, but yet effective and realistic analysis of RC structural members undergoing differential settlements due to variety of load actions. 相似文献
10.
以某发电厂双曲线自然通风冷却塔工程环形承台基础施工为例,介绍了大体积混凝土跳仓法施工的技术要点。同时给出了混凝土配合比、温度控制措施以及施工缝做法,解决了大体积底板因混凝土收缩应力及水泥水化热作用而出现的裂缝问题。 相似文献
11.
历史上超大型冷却塔风毁事件多次发生,国内外现行规范中缺乏超大型冷却塔风致倒塌机制与失效判别准则。以我国西北地区某在建高228 m的冷却塔为背景,建立分层壳单元模型,考虑塔筒的多尺度壁厚及配筋率变化,通过刚体测压风洞试验获取了冷却塔表面风荷载,结合增量动力分析法分析了典型风速下塔筒位移和内力响应,确定临界倒塌风速为83 m/s;基于节点失效前后von Mises应力变化规律提炼了冷却塔倒塌过程中3种内力重分布机制,结合塔筒喉部位移构建了结构变形失效准则。研究表明:采用分层壳单元模型可以有效模拟超大型冷却塔倒塌全过程,中心破坏区域扩散形成裂隙网,直至完全倒塌破坏;塔筒首个单元失效首先引发滑动面机制,随后以转动铰机制和滑移面机制为主进行内力重分布;当结构变形失效指标(喉部迎风面与背风面的相对水平位移与喉部直径之比)不小于1.5%时,超大型冷却塔失效倒塌。 相似文献
12.
历史上超大型冷却塔风毁事件多次发生,国内外现行规范中缺乏超大型冷却塔风致倒塌机制与失效判别准则。以我国西北地区某在建高228 m的冷却塔为背景,建立分层壳单元模型,考虑塔筒的多尺度壁厚及配筋率变化,通过刚体测压风洞试验获取了冷却塔表面风荷载,结合增量动力分析法分析了典型风速下塔筒位移和内力响应,确定临界倒塌风速为83 m/s;基于节点失效前后von Mises应力变化规律提炼了冷却塔倒塌过程中3种内力重分布机制,结合塔筒喉部位移构建了结构变形失效准则。研究表明:采用分层壳单元模型可以有效模拟超大型冷却塔倒塌全过程,中心破坏区域扩散形成裂隙网,直至完全倒塌破坏;塔筒首个单元失效首先引发滑动面机制,随后以转动铰机制和滑移面机制为主进行内力重分布;当结构变形失效指标(喉部迎风面与背风面的相对水平位移与喉部直径之比)不小于1.5%时,超大型冷却塔失效倒塌。 相似文献
13.
14.
Tension stiffening is most often included in models of reinforced concrete by modifying the constitutive laws of the tensile concrete. In reality, tension stiffening is caused by the bond stress that develops at the steel–concrete interface between the primary cracks. In this paper, a modified CEB–FIP bond model is incorporated into a non-linear finite element program to accurately model tension stiffening at the serviceability limit states. The bond–slip relationship at any point along the reinforcement bar is modified to account for the local damage of the surrounding concrete, as well as the level of steel stress. A non-local analysis is undertaken to adjust the constitutive law of the bond interface element at each load step. The proposed model is shown to accurately predict the crack spacing, stresses and deformation in axially loaded tension members at typical in-service load levels. 相似文献
15.
16.
《Engineering Structures》1986,8(2):87-92
The ultimate behaviour of a hyperbolic cooling tower is investigated using a nonlinear finite element computer program developed at North Carolina State University. It is shown that a significant redistribution of meridional stresses occurs after yielding of the reinforcement, thus, increasing the ultimate strength beyond that predicted from the elastic analysis. The present study shows that the reduction in cracking strength does not change the ultimate load. The results of this and other7,8 studies are compared. None of the three sets of analyses agree directly with the other's results. Clearly, a more thorough study is needed in the future. It is possible that the other two studies show either a lack of significant meridional stress redistribution,7 or too much dependence on concrete tensile strength8 because they either do not allow change in crack direction,7 or have an incomplete model for crack change. 8 Out of nine, only two results give ultimate strength less than that predicted by the elastic analysis. It can be argued that both results are unrealistically low. Therefore, it is concluded that the present practice of using elastic stresses is at least safe. Other tentative conclusions are also discussed. 相似文献
17.
18.
为准确快速确定混凝土热力学参数中难以确定的绝热温升、导热系数、表面放热系数及反应速度,以云南普立大桥散索鞍支墩基础大体积混凝土施工实测温度为基础,采用遗传算法进行混凝土热力学参数的反演分析,并根据反演参数建立三维有限元模型预测后续混凝土施工中的温度场,然后通过混凝土内部实测温度及应力验证预测结果。最后依据预测结果,在混凝土浇筑早期采用表面降温,内部布设冷却水管的措施有效减小了内外温差并防止了裂缝产生。结果表明:混凝土内部温度达到峰值时表面拉应力最大值为1.5 MPa,出现表面裂缝的可能性较小;混凝土浇筑3 d后,抗裂指数都在1.5以上,一般不会产生裂缝;基于反演参数的温度场计算值与实测值吻合良好。 相似文献
19.
Shear Strength of Reinforced Concrete Members without Transverse Reinforcement A new theoretical model concerning the shear strength of reinforced concrete members without transverse reinforcement is presented, considering free‐bodies unilaterally bounded by a fictitious crack, inclined at π/4 to the tension chord and extending from the tension chord to the compression chord. It is assumed that the shear stress that can be transferred across a crack decreases linearly with the crack width and that the crack width at the level of the tension chord is proportional to the product of the tension chord strain at the crack and the chord distance. This results in a linear‐hyperbolic relationship between the shear strength and the (elastic) tension chord force at the crack, allowing to determine the governing crack location and other relevant quantities via equilibrium considerations. Due to potential strut or arch action for the transfer of loads applied in the vicinity of supports the crack location is somewhat restricted; it is assumed that the corresponding length is equal to twice the chord distance. 相似文献