土木工程毕业设计外文翻译.doc

宁波工程学院毕业设计（论文）外文原文I：A fundamental explanation of the behaviour ofreinforced concrete beams in flexure basedon the properties of concrete under multiaxial stressM. D. KotsovosDepartment of Civil Engineering, Imperial College of Science and Technology, London (U. K.)The paper questions the validity of the generally accepted view that for a reinforced concretestructure to exhibit ductile behaviour under increasing load it is necessary for the stressstrain relationships of concrete to have a gradually descending post-ultimate branch.Experimental data are presented for reinforced concrete beams in bending which indicate the presence of longitudinal compressive strains on the compressive face in excess of 0.0035. It is shown that these strains, which are essential for ductile behaviour, are caused by acomplex multiaxial compressive state of stress below ultimate strength rather than postultimate material characteristics. The presence of a complex stress system provides a fundamental explanation for beam behaviour which does not affect existing design procedures.1. INTRODUCTIONThe plane sections theory not, only is generally considered to describe realistically the deformation response of reinforced and prestressed concrete beams under flexure and axial load, but is also formulated so that it provides a design tool noted for both its effectiveness and simplicity 1. The theory describes analytically the relationship between load-carrying capacity and geometric characteristics of a beam by considering the equilibrium conditions at critical cross-sections. Compatibility of deformation is satisfied by the plane cross-sections remain plane assumption and the longitudinal concrete and steel stresses are evaluated by the material stress-strain characteristics. Transverse stresses and strains are ignored for the purposes of simplicity. The stress-strain characteristics of concrete in compression are considered to be adequately described by the deformational response of concrete specimens such as prisms or cylinders under uniaxial compression and the stress distribution in the compression zone of a cross-section at the ultimate limit state, as proposed by current codes of practice such as CP 110 1, exhibits a shape similar to that shown in figure 1. The figure indicates that the longitudinal stress increases with thedistance from the neutral axis up to a maximum value and then remains constant. Such a shape of stress distribution has been arrived at on the basis of both safety considerations and the widely held view that the stress-strain relationship of concrete in compression consists of both an ascending and a gradually descending portion (seefig. 2). The portion beyond ultimate defines the post-ultimate stress capacity of the material which, Typical stress-strain relationship for concrete in compression. as indicated in figure 1, is generally considered to make a major contribution to the maximum load-carrying capacity of the beam.However, a recent analytical investigation of the behaviour of concrete under concentrations of load has indicated that the post-ultimate strength deformational response of concrete under compressive states of stress has no apparent effect on the overall behaviour of the structural forms investigated ( 2, 3). If such behaviour is typical for any structure, then the large compressivestrains (in excess of 0.0035) measured on the top surface of a reinforced concrete beam at its ultimate limit state (see fig. 1), cannot be attributed to post-ultimate uniaxial stress-strain characteristics. Furthermore, since the compressive strain at the ultimate strength level of any concrete under uniaxial compression is of the order of 0.002 (see fig. 2), it would appear that a realistic prediction of the beam response under load cannot be based solely on the ascending portion of the uniaxial stress-strain relationship of concrete.In view of the above, the work described in the following appraises the widely held view that a uniaxial stress-strain relationship consisting of an ascending and a gradually descending portion is essential for the realistic description of the behaviour of a reinforced concrete beam in flexure. Results obtained from beams subjected to flexure under two-point loading indicate that the large strains exhibited by concrete in the compression zone of the beams are due to a triaxial state of stress rather than the uniaxial post-ultimate stress-strain characteristics of concrete. It is shown that the assumption that the material itself suffers a completeand immediate loss of load-carrying capacity when ultimate strength is exceeded is compatible with the observed ductile structural behaviour as indicated by load-deflexion or moment-rotation relationships.2. EXPERIMENTAL DETAILS2.1. SpecimensThree rectangular reinforced concrete beams of 915 mm span and 102 mm height x 51 mm width cross-section were subjected to two-point load with shear spans of 305 mm (see fig. 3). The tension reinforcement consisted of two 6 mm diameter bars with a yield load of 11.8 kN. The bars were bent back at the ends of the beams so as to provide compression reinforcement along the whole length of the shear spans.Compression and tension reinforcement along each shear span were linked by seven 3.2 mm diameter stirrups. Neither compression reinforcement nor stirrups were provided in the central portion of the beams. Due to the above reinforcement arrangement all beams failed in flexure rather than shear, although the shear span to effective depthratio was 3.The beams, together with control specimens, were cured under damp hessian at 20 for seven days and then stored in the laboratory atmosphere (20and 40% R.H.) for about 2 months, until tested. Full details of the concrete mix used are given in table I.2.2. TestingLoad was applied through a hydraulic ram and spreader beam in increments of approximately 0.5 kN. At each increment the load was maintained constant for approximately 2 minutes in order to measure the load and the deformation response of the specimens. Load was measured by using a load cell and deformation response by using both 20 mm long electrical resistance strain gauges and displacement transducers. The strain gauges were placed on the top and side surfaces of thebeams in the longitudnal and the transverse directions as shown in figure 4. The figure also indicates the position of the linear voltage displacement transducers (LVDTs) which were used to measure deflexion at mid-span and at the loaded cross-sections.The measurements were recorded by an automatic computer-based data-logger (Solatron) capable of measuring strains and displacements to a sensitivity of 2 microstrain and 0.002 ram, respectively. 3. EXPERIMENTAL RESULTSThe main results obtained from the experiments together with information essential for a better understanding of beam behaviour are shown in figures 5 to 14. Figure 5 shows the uniaxial compression stressstrain relationships of the concrete used in the investigation, whereas figures 6 and 7 show the relationships between longitudinal and transverse strains, measured on the top surface of the beams (a) at the cross-sections where the flexure cracks which eventually cause failure are situated (critical sections) and (b)at cross-sections within the shear span, respectively.Figures 6 and 7 also include the longitudinal straintransverse strain relationship corresponding to the stress-strain relationships of figure 5. Figure 8 shows the typical change in shape of the transverse deformation profile of the top surface of the beams with load increasing to failure and figure 9 provides a schematic representation of the radial forces and stresses developing with increasing load due to the deflected shape of the beams. Typical load-deflexion relationships of the beams are shown in figure 10, whereas figure 11 depicts the variation on critical sections of the average vertical strains measured on the side surfaces of the beams with the transverse strains measured on the top surface. Figure 12 indicates the strength and deformation response of a typical concrete under various states of triaxial stress and figure 13 presents the typical crack pattern of the beams at the moment of collapse. Finally, figure 14 shows the shape of the longitudinal stress distribution on the compressive zone of a critical section at failure predicted on the basis of the concepts discussed in the following section.中文翻译I：在多向应力作用下从混凝土的特性看受弯钢筋混凝土梁变化的一个基本试验M. D. Kotsovos 伦敦皇家科学与技术学院土木工程系本文所探讨的问题是通常认为在荷载递增下钢筋混凝土结构呈现弹性状态，这必须是因为混凝土的应力-应变关系有一个逐渐递减的临界部分的真实性。试验数据显示受弯钢筋混凝土梁会在受压面的纵向压应变超出0.0035。这表明这些应变是钢筋混凝土结构的本质，它是由于一个比极限强度小的复杂多向的应力状态而不是塑性材料的特性引起的。一个复杂应力系统的存在为梁的状态提供了一个基本试验，而不是想象的一个现有设计过程。1.引言“剖面”理论不仅是通常认为能很真实地描述钢筋混凝土梁和预应力混凝土梁在弯矩和轴向荷载下的变形，而且能确切地阐述，所以它提供了一个设计工具，因为它的有效和简单而闻名1。假设在临界横截面伤是均衡的，这个理论分析地描述了一个梁的承载能力和几何特性之间的关系。变形协调必须满足“水平横截面荏苒水平”的假定和纵向混凝土和钢筋的应力是通过材料的应力-应变的特性来估算的。为了简化计算，忽略横向的应力和应变。受压混凝土的应力-应变特性认为能够被混凝土试块的变形充分地描述，例如在极限的有限状态下，棱柱体或圆柱体在横截面的受压区受单轴压力和应力，就像现行规范所建议的CP1101，显示出一个与图1相似的形状。图1表明纵向应力随着与中和轴的距离增加而增加至最大值，然后保持不变。这个分布图已经达到安全性和受压混凝土的应力-应变关系的广泛观点，由上升和逐渐下降的两部分组成(如图2所示)。超出极限的部分，材料的塑性应力能力如图1所示，被认为对梁的最大承载能力有较大的作用。 图1.临界面破坏建议CP为110的应力和应变分布 图2.受压混凝土结构的标准应力-应变关系然而，最近关于在集中力作用下的混凝土的变化的一个分析性调查表明，在压应力作用下混凝土的极限强度变形没有对所有被调查的结果形式的变化产生明显的影响(2,3)。如果这个变化对任何结果都是典型的，那么在钢筋混凝土梁的顶面被测的很大的压应变(超出量0.0035)在它的极限有限状态下(如图1)，不能对极限单轴应力-应变特性产生作用。因此，因为压应变在单轴压力下的任何混凝土的极限强度等级下为=0.002(如图2所示)，在混凝土的单轴应力-应变关系下降部分，将出现一个在荷载作用下梁变化的现在可行的预测。根据以上的观点，本文的描述都在以下的评价中，广泛的支持观