碳纤维布加固已损伤高强钢筋混凝土梁抗弯性能试验研究

进行了5根碳纤维布加固高强钢筋混凝土梁抗弯性能的试验,其中3根为预裂梁,2根为对比梁,分析了不同损伤程度对加固效果的影响.试验结果表明,在一定范围内,损伤程度对加固梁的极限荷载影响不大,对梁的抗弯刚度影响较多.     

Finite element modeling of concrete beams prestressed with external tendons

In this study, a numerical model based on the finite element method incorporating an arc-length solution algorithm for materially and geometrically nonlinear analysis of concrete beams prestressed with external tendons is established. The second-order effects are taken into account. The effects of external tendons are expressed by equivalent nodal loads of the beam element and therefore analysis of externally prestressed concrete beams can be conducted with the ordinary bonded concrete beams. The section tangent stiffness matrix is derived by the layered approach, and then the nonlinear beam flexural theory is utilized to determine the element tangent stiffness matrix. An updated normal plane arc-length solution algorithm is used to trace the nonlinear response of the beams from zero loads up to ultimate loads. This algorithm can deal well with the changes of response during loading, so that the possible limit points on the load–deflection response prior to the ultimate limit state can be easily passed. Results predicted by the analysis are in good agreement with the experimental data.     

Seismic fragility relationships of reinforced concrete high‐rise buildings

A complete methodology is presented for the seismic fragility assessment of reinforced concrete high‐rise buildings. The key steps of the methodology are illustrated through an example of the fragility assessment of an existing 54‐story building with a dual core wall system. The set of rigorously derived probabilistic fragilities are the first published for high‐rise reinforced concrete buildings. The inelastic nonlinear dynamic analyses for the fragility assessments are made using a simplified lumped‐parameter model that was derived from highly detailed FE models using genetic algorithms. New definitions for performance limit states were based on the results of detailed pushover analyses of a distributed inelastic nonlinear finite element model that includes shear–flexure–axial interaction effects. To develop the fragility relationships, 1800 dynamic response history analyses were conducted. This study considered uncertainty in structural material values as well as in seismic demand. Thirty strong motion records were selected for use in the analyses that would produce an appropriate range in structural response characteristics due to variation in magnitude, distance and site condition. The overall approach is generic and can be applied to developing computationally efficient and probabilistically‐based seismic fragility relationships for reinforced concrete high‐rise buildings of different configurations. Copyright © 2007 John Wiley & Sons, Ltd.     

Zur Tragfähigkeit von Ankerplatten in bewehrtem Beton

Load‐carrying capacity of anchor plates in reinforced concrete. For the load transmission into concrete constructions frequently anchor plates with welded studs are used. At the Institute of Structural Design two test series at reinforced concrete specimens were accomplished, which show that reinforcement decisively influences the load‐carrying capacity and the actually calculated design loads tend to underestimate the real resistance. On the basis of 27test results and supplementary FE analyses a first mechanical model based on the component method is presented, describing the load‐carrying capacity of anchor plates with welded studs in reinforced concrete elements.     

FRP增强钢筋混凝土受弯梁中纤维板长度优化研究

采用有限元分析和试验研究的方法 ,探讨纤维薄板长度对FRP增强钢筋混凝土梁抗弯强度的影响 ,试图找到在满足增强梁抗弯强度前提下的最佳纤维板粘贴长度 ,为该类构件的优化设计奠定理论基础。有限元分析结果表明 ,纤维板粘贴长度不同 ,增强钢筋混凝土梁的应力分布、能量分布及极限承载力等均有较大变化。通过探讨钢筋和纤维板在承载过程中的能量变化 ,推算出纤维板最佳粘贴长度的下限为L/S =0 6 9;通过对试验梁刚度的探讨 ,又求得纤维板最佳粘贴长度的上限为L/S =0 83。上述分析结果在相同条件下进行的 5组 15根增强梁的三点弯曲试验中得到了初步验证。     

Nonlinear 3D finite element simulation of reinforced concrete flat plates retrofitted with externally bonded CFRP strips

In this study, a comprehensive 3D non-linear finite element modelling procedure is presented for the simulation of reinforced concrete flat plates, retrofitted with externally bonded carbon fibre-reinforced polymer (CFRP) strips and subjected to punching shear loads. The presented modelling procedure may be used to conduct parametric numerical analyses on the response of reinforced concrete elements similar to considered in this study. The modelling procedure is applied on: (i) a solid, un-retrofitted flat plate and (ii) eight flat plates with openings and retrofitted with externally bonded CFRP strips. In the procedure, debonding of CFRP strips from concrete surfaces is accounted for by defining appropriate bilinear shear stress–slip and normal stress–gap relationships. In the model, the corner lift-offs observed at the corners of the flat plates are also considered by defining appropriate restrains and frictional support conditions. Results obtained from the proposed modelling procedure are verified using experimental data available in the literature. From the verification, accuracy of the proposed modelling procedure is confirmed in terms of structural responses such as load displacement relationships and crack propagations of the test specimens.     

钢筋混凝土矩形板在线性分布荷载下的极限强度计算

按极限平衡法计算四边支承钢筋混凝土矩形板在均布荷载作用下的破坏简图,推导了钢筋混凝土矩形板在线性分布荷载作用下的极限强度近似计算公式。它和均布荷载的计算公式相同,仅将荷载集度以线性分布荷数的平均集度代替。与“精确”公式的计算结果相比较,误差在工程计算所允许的范围以内。     

Analytical compressive stress–strain model for concrete confined with high‐strength multiple‐tied‐spiral transverse reinforcement

The behavior of reinforced concrete members subjected to seismic loads is mainly based on the ultimate strength of concrete and its ductility. Based on this, an additional configuration of transverse reinforcement using high‐strength multiple‐tied‐spiral was proposed to improve the strength and ductility of concrete. In this paper, an experimental study of a number of axial loading tests on reinforced concrete columns confined with high‐strength multiple‐tied‐spiral transverse reinforcement is described. The effects of spacing of circular spiral and rectangular hoop, the confined area of circular spiral and concrete strength on axial behavior of confined concrete were investigated. The formulas of confined compressive strength and corresponding axial strain, factor to control the slope of descending branch, and stress in high‐strength circular spiral at confined strength are proposed based on the test results. A stress–strain model is also proposed that is found to give reasonably good prediction of the experimental behavior of reinforced concrete (RC) columns confined by high‐strength multiple‐tied‐spiral transverse reinforcement.     

Modeling of Tension Stiffening Behavior in FRP‐Strengthened RC Members Based on Rigid Body Spring Networks

Abstract: Allowing for the tension stiffening effects resulting from the bond between steel reinforcement and surrounding concrete leads to effective deformation analysis of reinforced concrete (RC) members when using a nonlinear finite element analysis modeled on the smeared crack concept. Nowadays, externally bonded fiber reinforced polymer (FRP) composites are widely used for strengthening existing RC structures. However, it remains unclear to what extent the tension stiffening of postcracking concrete is quantitatively influenced by the addition of FRP composites, as a result of the bond between the FRP and the concrete substrate. This article presents a discrete model, which is based on rigid body spring networks (RBSN), for investigating the tension stiffening behavior of concrete in FRP‐strengthened RC tensile members. A two‐parameter fracture energy‐based model was deployed to represent the bond‐slip behavior of the FRP‐to‐concrete interface. The reliability of the RBSN model was verified through comparisons with previous test results. Further parametric analysis indicates that the tension stiffening of concrete is hardly influenced by the addition of FRP composites before the yield of steel reinforcement has occurred although concrete crack patterns and crack widths may be influenced by the bond‐slip behavior of the FRP‐to‐concrete interface.     

浅析钢筋混凝土轴心受压构件加固方案

根据材料的强度理论对钢筋混凝土轴心受压构件承载力不足的分析表明:外包裹钢筋混凝土加固层具有反约束作用,其作用可作为三向应力分析并计算出包裹层的受力箍钢筋用量,从而达到加固的目的。     

预应力加强型钢拱梁及其改进结构的性能研究

加强型钢拱梁是根据结构在承受竖向荷载时的内力及变形图,在钢拱梁平面内增加适当的撑杆和加强型索,以改善其受力性能、提高刚度和承载力的新型结构体系.通过有限元软件AN SY S分析了加强型钢拱梁在不同竖向荷载作用下以及不同初始加强型时应力和位移的变化规律,并依据钢拱梁在全跨和半跨荷载作用下的受力特征对加强型钢拱梁进行了改进和有限元分析.结果表明能较大地提高结构的刚度和承载力,而改进后的加强型钢拱梁对于抵抗半跨荷载的刚度和承载力又有明显的改善.     

粘贴玻璃纤维条带加固RC双向板的承载力计算

本文对粘贴玻璃纤维条带加固钢筋混凝土板在跨中局部荷载作用下的受力性能进行了试验研究和理论分析,用线形模式、圆扇形模式和弯冲模式分别计算了粘贴玻璃纤维条带加固RC双向板的极限承载能力,并建立了粘贴玻璃纤维加固RC双向板极限承载能力的计算公式。     

Design concepts of an aircraft wing: composite and morphing airfoil with auxetic structures

This paper is categorized into two parts. (1) A frame work to design the aircraft wing structure and (2) analysis of a morphing airfoil with auxetic structure. The developed design frame work in the first part is used to arrive at the sizes of the various components of an aircraft wing structure. The strength based design is adopted, where the design loads are extracted from the aerodynamic loads. The aerodynamic loads acting on a wing structure are converted to equivalent distributed loads, which are further converted point loads to arrive at the shear forces, bending and twisting moments along the wing span. Based on the estimated shear forces, bending and twisting moments, the strength based design is employed to estimate the sizes of various sections of a composite wing structure. A three dimensional numerical model of the composite wing structure has been developed and analyzed for the extreme load conditions. Glass fiber reinforced plastic material is used in the numerical analysis. The estimated natural frequencies are observed to be in the acceptable limits. Furthermore, the discussed design principles in the first part are extended to the design of a morphing airfoil with auxetic structure. The advantages of the morphing airfoil with auxetic structure are (i) larger displacement with limited straining of the components and (ii) unique deformation characteristics, which produce a theoretical in-plane Poisson’s ratio of–1. Aluminum Alloy AL6061-T651 is considered in the design of all the structural elements. The compliance characteristics of the airfoil are investigated through a numerical model. The numerical results are observed to be in close agreement with the experimental results in the literature.     

Modellbildung zur Simulation von Stahlfaserbeton unter hochdynamischer Belastung

Modelling of Steel Fibre Reinforced Concrete under High Dynamic Loadings For structural protection against extraordinary loads it is important to find construction materials that offer properties that are especially applicable to the problem. One of these materials is steel fibre reinforced concrete. However, for high dynamic loads like from impact or detonation steel fibre reinforced concrete is not yet investigated sufficiently. This article describes a new empirical material model for the simulation of steel fibre reinforced concrete under high dynamic loadings. This material model also includes a damage model which describes the degradation of stiffness and strength in consequence of plastic (compaction and shear) strain. The model is implemented in a hydrocode and validated by a multitude of contact detonation tests. From these results it could be shown that the numerical simulations carried out with the new steel fibre reinforced concrete model are capable to complement or to reduce the expensive and time‐consuming experiments, respectively.     

半挖半填工况加筋土挡墙失稳机制试验研究与上限法分析

 设计并制作半挖半填工况的绿色加筋格宾模型挡墙,通过在挡墙顶部施加分级均布荷载,测试挡墙在各级荷载作用下的变形、土压力和筋材拉应变,并进行数值模拟,探讨挡墙承载力的发展规律和失稳模式;基于塑性极限分析的上限法,建立半挖半填工况加筋土挡墙的极限承载力,安全系数和极限高度的计算方法。研究表明：在墙顶分级均布荷载作用下,半挖半填工况加筋土挡墙承载力的发展过程可分为初始压密、正常发展、屈服和破坏失稳4个阶段;挡墙墙顶竖向沉降呈三角形分布,挡墙沿填挖交界面发生滑移失稳;挡墙面墙变形、土压力和筋材拉应变分布规律受挡墙的失稳模式影响;所推导的半挖半填工况加筋土挡墙稳定性分析方法考虑台阶面筋材的作用,具有较高的精度。     

Mechanical behaviours and engineering application of steel truss reinforced concrete transfer beam in tall buildings

A new type of steel reinforced concrete (SRC) transfer beam, the steel truss reinforced concrete (STRC) transfer beam, is developed and applied to a 100 m tall building in Guangzhou City to solve the difficulty of two built subways being buried under the building. Experimental studies on mechanical behaviours of STRC composite transfer beams were carried out, and the structural characteristics and economic characters of the transfer beam were introduced. Experimental investigations verify that the STRC transfer beam is of high limit bearing capacity, large rigidity and good ductility. Compared with normal reinforced concrete transfer beam, the limit bearing capacity of the STRC transfer beam can be enhanced 30–40%, and the rigidity can be improved 30–50%. In the STRC transfer beam, the strut‐and‐tie force transference mode is followed, the loads are mainly transferred by compressive diagonal SRC struts from the loading point and abutments, SRC struts and horizontal ties form a self‐balance system. The cost of material, fireproof and construction can be saved; more space for commercial function and convenient construction can be achieved by adopting STRC transfer beams. Copyright © 2010 John Wiley & Sons, Ltd.     

体外预应力加固低强度混凝土梁的裂缝计算分析

体外预应力加固法由于其特有的优点,得到了越来越多的应用,通过对5根低强度钢筋混凝土梁的预应力加固技术的试验研究、分析与整理的基础上,提出了低强度混凝土梁采用体外预应力方法加同的裂缝变形计算的理论和方法,为该方面进一步发展提供了一些参考。     

方底钢筋混凝土球扁壳基于双剪屈服准则的极限分析

利用双剪屈服准则建立了用机动法计算钢筋混凝土球扁壳的塑性屈服线理论,给出塑性屈服线求极限荷载的方法,使其更加合理。建立了矩形底的钢筋混凝土扁壳的屈服条件,并用无矩和有矩理论求解出方形底周边铰支的球扁壳的极限载荷。     

Vereinfachte,wirklichkeitsnahe Ermittlung der Durchbiegung von Stahlbetonträgern unter Kriechbeanspruchung

Simplified, realistical Estimation of Deflection of reinforced concrete Beams under service Loads A calculation method, which is based on the assumption of affinity of moment and curvature, for simplified estimation of deflections of reinforced concrete beams under service loads is presented. The influence of creep deformations is considered realistically and enables computational close‐to‐practice calculation of deflections with minimum expense.     

Ermittlung von Stabilisierungslasten im Holzbau

Calculation of lateral stability loads for timber constructions. Stability loads for lateral bracings are usually calculated by using a simplified method according to the standard for timber constructions. In this article two methods for an accurate calculation of stability loads for lateral bracings will be presented. The first possibility is based on the energy method and can be used for single‐span beams with continuous lateral support. Equations to determine the lateral loads for single‐span beams with constant normal forces or constant bending moments can be determined by using the energy method. Another possibility of verification is the computation of lateral stability loads using the 2^nd order flexural torsion theory for a three‐dimensional loaded beam with discrete lateral supports with any support and load cases by employing the transfer matrix method. The results of both methods will be compared in several examples.