Simple General Solution for Interfacial Stresses in Plated Beams

The flexural strength of a reinforced concrete, metallic or timber beam can be increased by bonding a thin plate, made of steel or fiber-reinforced polymer, to its tension face. A main failure mode of such plated beams involves debonding of the plate end from the beam and such plate-end debonding depends strongly on the interfacial stresses between the beam and the plate. Consequently, many analytical solutions have been developed for the interfacial stresses of specific plated beam problems, with almost all of them being for simply supported plated straight beams of constant section subjected to simple loadings. The existing analytical solutions are therefore neither general enough nor simple enough for direct exploitation in assessing the risk of plate-end debonding failure. This paper corrects this deficiency by presenting a simple, accurate yet general solution for interfacial stresses. The solution is applicable to plated beams of all geometric (e.g., curved beams), sectional (e.g., tapered beams), loading (e.g., a linearly varying distributed load), and boundary conditions (e.g., continuous beams). The accuracy of the solution is demonstrated through comparisons with finite element results. The paper also presents simple and accurate approximations for the peak values of interfacial shear and normal stresses at the plate end. In these approximate expressions, only the sectional forces and properties of the plate end section are involved, which greatly facilitates their direct exploitation in predicting debonding failure.     

Experimental Study of Interfacial Shear Stresses in FRP-Strengthened RC Beams

This paper presents the results of an experimental study on the distribution of shear stresses along the interface between concrete and the carbon fiber-reinforced polymer (FRP) in 29 plate-strengthened beams, where the primary test variables are: Clear cover, plate length, plate thickness (area), and compressive strength of concrete. FRP strain measurement was accomplished using either the photographic technique of digital image correlation or a series of electrical-resistance strain gages, both providing similar results. The distribution of shear stresses is found to be smoother than predicted by several analytical expressions available in the literature. Another substantial observation is the existence of a second region of peak stress, occurring near the center of the shear span in all of the beams with longer plate lengths, which the authors believe is associated with the singular application of shear corresponding to the point load, as well as the transition from elastic to plastic behavior occurring in the rebar. Because the overall nature of the stress distribution is sufficiently smooth, it is very reasonable to approximate it as a constant stress.     

Interfacial Behavior and Debonding Failures in FRP-Strengthened Concrete Slabs

It has been demonstrated, through laboratory investigations and various field projects, that the external bonding of fiber- reinforced polymer (FRP) laminates is an effective technique for the structural enhancement of reinforced concrete slabs. In such applications, failure is generally governed by debonding of the FRP laminate. Nevertheless, numerical simulations to date of FRP-strengthened slabs have usually been based on the assumption of full bond between the concrete and FRP. In this study, the interfacial behavior between the FRP laminates and the concrete substrate is accounted for by introducing appropriate bond-slip models for the interface in a nonlinear finite-element analysis of FRP-strengthened two-way slabs. The numerical model is capable of simulating slabs strengthened in shear or in flexure; it can be applied to arbitrary FRP configurations, and can also accommodate both passive as well as prestressed FRP strengthening schemes. Results are presented in terms of load-deflection relationships, ultimate load capacities, failure modes, and interfacial slip and stress distributions. When compared to test results reported in the literature, the analysis is shown to lead to excellent predictions in that, for the entire set of FRP-strengthened specimens considered, the average of the numerical-to-experimental load capacity ratios is 0.966, with a standard deviation of 0.066. Furthermore, in all cases when FRP debonding was observed experimentally, the analysis correctly predicted the mode of failure.     

Influence of Reinforcing Bars on Shrinkage Stresses in Concrete Slabs

It is well known that cracking in concrete slabs significantly influences their service life. Concrete shrinkage may be the principle reason for the initial crack formation in the slabs. This paper presents an attempt to provide an analytical tool for the prediction of stress distribution in reinforced concrete slabs after undergoing matrix shrinking restrained by the reinforcing bars. The model incorporates the material parameters of the reinforcing bar and the concrete matrix, and it enables prediction of the stress development in concrete with time.     

Improved Method for Determining Interfacial Stresses in Composites

The conventional finite element method shows its weakness in determining the stress distributions along fiber matrix interfaces. This is because the chosen element displacement functions do not explicitly and/or implicitly satisfy the equilibrium and compatibility conditions that prevail at the interfaces. A procedure has been proposed to modify the conventional finite element method so as to allow the elastic stresses along the fiber matrix interfaces of two‐ and three‐dimensional fiber‐reinforced composites to be determined with improved accuracy. The results obtained by this modified method for a two‐dimensional problem are compared with both a photoelastic and a traditional finite elelment solution. The comparison shows that the modified solution is in better agreement with the photoelastic test data than the traditional solution. The results obtained by the modified method for a three‐dimensional problem are compared with a traditional finite element solution and the modified method is found to be superior.     

Flexural and Interfacial Behavior of FRP-Strengthened Reinforced Concrete Beams

Although there is a large amount of experimental data available on the fiber-reinforced polymer (FRP) strengthening of concrete structures, a full understanding of the various debonding phenomena is somewhat lacking. As a contribution to fill this need, two-dimensional and three-dimensional (3D) nonlinear displacement-controlled finite-element (FE) models are developed to investigate the flexural and FRP/concrete interfacial responses of FRP-strengthened reinforced concrete beams. Interface elements are used to simulate the FRP/concrete interfacial behavior before and after cracking. The analysis is carried out using two different relations for the interface; namely, nonlinear and bilinear bond–slip laws. The results predicted using these two laws are compared to those based on the full-bond assumption. The FE models are capable of simulating the various failure modes, including debonding of the FRP, either at the plate end or at intermediate cracks. The 3D model is created to accommodate cases of FRP-strengthened reinforced concrete beams utilizing FRP anchorage systems. In addition, the models successfully represent the actual interfacial behavior at the vicinities of cracks including the stress/slip concentrations and fluctuations. Results are presented in terms of the ultimate load carrying capacities, failure modes and deformational characteristics. Special emphasis is placed on the FRP/concrete interfacial behavior and cracking of the concrete. The numerical results are compared to available experimental data for 25 specimens categorized in six series, and they show a very good agreement.     

Interfacial Convection and Mass Transport in Thin Liquid Layer

Investigations into the phenomenology of convection flows next to the interface between two liquids have been carried out in laboratory experiments using various liquids. Then convection flows have been observed in industrial tests during continuous casting. The results show that the motional velocity of volume elements next to the interface due to disturbances of interfacial tension (produced by mass and charge transfer) depends on liquid layer thickness and on liquid properties. A new dimensionless number is introduced to describe this manner of convective flow; it is also suitable for evaluation of experimental results. Furthermore, a dimensionless function is theoretically developed to describe the relation between convective flows near the interface in the slag layer and mass transport. Casting powders melt on the surface of the liquid metal forming a liquid slag layer. Samples taken during casting have revealed convective flows in the flux layer and mass exchange with the liquid metal. Coefficients of the developed dimensionless function have been determined empirically for Ti‐transport from the interface into the flux layer.     

Technological Investigation on the Continuous Casting of Mid－Width Thin Slabs

ＴｅｃｈｎｏｌｏｇｉｃａｌｉｎｖｅｓｔｉｇａｔｉｏｎｏｎｔｈｅＣｏｎｔｉｎｕｏｕｓＣａｓｔｉｎｇｏｆＭｉｄＷｉｄｔｈＴｈｉｎＳｌａｂｓＡＮＹｏｎｇ；ＺＨＡＭＧＢａｉＴｉｎｇ；ＺＨＡＮＧＨｕｉ；ＮＩＭａｎＳｅｎａｎｄＪＩＸｉｕＱｉｎＴｅｃｈｎｏｌｏｇｉ...     

厚钢板坯料生产制备方法的研究

本文介绍了厚板坯料的几种生产制备方法,对比了不同方法的特点,推荐了坯料生产制备方法。     

薄规格宽幅板生产实践

为提高薄规格宽幅板的生产能力,分析了设备、冷却系统、坯料加热等影响因素。通过提高轧机精度、改善轧辊冷却系统、优化坯料加热、提升生产组织和作业计划等措施,保障了薄规格宽幅板生产稳定性及准确性,满足了市场需求。     

薄板的平直度控制

薄板的平直度是铝板带材质量的主要指标,平直度的好坏直接影响着产品的质量,本文根据400/965×1450 mm四重不可逆式冷轧机的生产实践,分析了各种因素对板带平直度的影响,介绍了在生产实践中调整辊型的方法及对不良板形的纠正措施。     

大平板薄壁铸件的铸造工艺

针对壁薄、面积大、表面不加工的平板铸造易出现弯曲变形、表面质量不好等问题,采用平做立浇、组型串铸、中部敝开、砂型表面用钢板紧固的铸造工艺,能有效控制大平板薄壁铸件发生弯曲变形,并可以提高铸件表面质量。     

连铸板坯热装炉对钢板性能的影响及改善措施

比较分析了船体用结构钢CCS／B、低合金钢Q345B、压力容器用钢16MnR热装炉与冷装炉板坯轧制后钢板的拉伸性能、冲击性能、冷弯性能，提出了改善板坯热装对钢板不良影响的措施。     

薄规格花纹板试轧与工艺改进

通过对轧制薄规格（厚度≤2.3 mm）花纹板的研究,得到如下结论：优化温度制度、降低精轧末架负荷、调整末架上下辊的辊压、优化精轧工作辊辊型及层流冷却工艺是解决轧制不稳定、带钢出精轧末架轧机后易跑偏、严重边浪与中浪等问题的有效途径,解决了因花纹的纹高要求不能在平整机上平整,需经多次矫直、增加生产成本的问题。平整线拉矫比例从78%下降到5%以下,再未发生同卷钢需2次甚至3次的拉矫,板形质量达到同规格的平板水平。     

薄规格钢板淬火过程中的板形控制

在薄规格钢板的淬火过程中,板形变化是较难控制的方面之一。首先介绍了辊式淬火机的冷却过程及机理,再根据鲅鱼圈厚板部5500生产线的淬火实践生产,将该机理成功应用于淬火机设备的调整和校正,配以合理的淬火工艺参数,将薄规格HQ785T1钢板淬火后的板形不平度稳定在可控范围内,最后根据结果分析了影响板形变化的原因。     

On Edge Stresses Control in Strengthened RC Beams with FRP Strips: Adhesive Layer Profile Effect

A high-order analytical model for the analysis of reinforced concrete (RC) beams strengthened with fiber-reinforced plastic (FRP) strips bonded with adhesive layer of variable thickness is presented. The model is based on the closed-form high-order approach, and it provides the means for the analysis of beams retrofitted with generally curved FRP strips and adhesive layers of arbitrary profile. The analysis is comprehensive and includes the local and overall response of the structure. An emphasis is put on the stress concentration that occurs at the edge of the FRP strip and in many cases leads to brittle and sudden failure of the strengthened member. The field equations and the boundary and continuity conditions are derived using the variational principle of virtual work along with the kinematic relations of small deformations. The governing equations of the generally curved FRP strip include large curvatures and are introduced via coordinate transformation from its local curvilinear system into the global Cartesian one. The derived model is used for the investigation of various adhesive profiles and their influence on the shear and vertical normal stresses at the edges of the FRP strip. The results focus on the stress concentrations involved and reveal that proper design and application of the adhesive profile can significantly reduce the edge stresses, thus preventing the brittle mode of failure. The paper is concluded with a summary and recommendations for the analysis, design, and application of the strengthening process.     

超薄规格钢板淬火的板型控制研究

在超薄规格钢板的淬火过程中,根据淬火后钢板板型的总体变化规律,研究了其淬火板型的控制机理和控制技术。结果表明,对于超薄规格钢板,淬火机设备在安装或校准的过程中,不仅要确保喷嘴精度,即钢板上下面冷却速度相同,而且要保证下喷嘴喷射角度有一定的负偏差,即喷嘴的喷水交叉线和钢板的上下面中心线三线重合,才能实现钢板上下面同步相变。该板型控制机理成功应用于淬火机设备的调整和校正,配以合理的淬火工艺参数,超薄规格钢板淬火后的板型不平度稳定在可控范围内。     

板形锁定法在轧制宽薄中厚板中的应用

厚度控制系统特别是AGC系统对中厚板板形的开环控制有一定影响，特别是刚度偏小的轧机在轧制宽薄中厚板时容易出现边浪。为此提出一种针对轧制宽薄中厚板的板形控制策略——板形锁定法，即在轧制宽薄中厚板的最后一两个道次，AGC不投入，而改用APC控制，通过理论和实践证明，该策略对保证中厚板的板形有一定效果，而且对厚度精度的影响很小。     

Finite-Element Analysis of Lamb Wave Propagation in a Thin Aluminum Plate

Structural health monitoring (SHM) is an emerging technology that can be used to identify, locate, and quantify structural damages before failure. Among SHM techniques, Lamb waves are widely used since they can cover large areas from a single location. The development of various structural simulation programs has lead to increasing interest in whether SHM data obtained from the simulation can be verified by experimentation. The objective of this research is to determine the Lamb wave responses of SHM models using the finite-element software package ABAQUS CAE as a computational tool for an isotropic plate. These results are compared to experimental results and theoretical predictions under isothermal and thermal gradient conditions to assess the sensitivity of piezoelectric generated Lamb wave propagation. Simulations of isothermal tests are conducted over a temperature range of 0–190°F using 100 and 300?kHz as excitation frequencies. The changes in temperature-dependent material properties are used to measure the differences in the response signal’s waveform and propagation speed. An analysis of the simulated signal response data demonstrated that elevated temperatures delay the Lamb wave propagation, although the delays are found to be minimal at the temperatures tested.