Analytical solutions for the time-dependent behaviour of composite beams with partial interaction

This paper presents a generic modelling for the time-dependent analysis of composite steel–concrete beams with partial shear interaction that occurs due to the deformation of the shear connection. The time effects considered in this modelling are those that arise from shrinkage and creep deformations of the concrete slab, and these effects are modelled using algebraic representations such as those of the age-adjusted effective modulus method (AEMM) and the mean stress method (MS), which are viscoelastic models for concrete deformation that can be stated algebraically. The generic model lends itself to closed form solutions for the analysis of composite beams subjected to a generic applied loading under a variety of end conditions. In this paper, the generic model is applied for the time-dependent analysis of composite beams that are simply supported and encastré, and to a propped cantilever, that are subjected to uniformly distributed loading and shrinkage deformations. Various representations of the structural behaviour of these beams are given in closed form which can also be used to benchmark available modelling techniques, i.e. finite element and finite difference formulations, which require a spatial discretisation to be specified as well as the time discretisation to perform a time analysis.     

钢－混凝土组合梁非线性有限元分析

提出了部分剪力连接钢-混凝土组合梁非线性有限元分析的简化模型，该模型同时考虑了钢、混凝土材料的非线性本构关系和剪力连接件的滑移非线性对组合梁刚度和强度的影响，推导了考虑滑移的剪力连接件单元刚度矩阵。利用该模型计算了连续组合梁的极限荷载、挠度、应力以及滑移，与已有的理论计算结果和实验结果吻合，证明本方法分析钢-混凝土组合梁非线性的可靠性和实用性。     

碳纤维布与钢板复合加固梁剥离破坏研究

通过12根碳纤维布与钢板复合加固钢筋混凝土梁的抗弯性能研究,结果表明复合加固方式能有效地改善被加固构件的受力性能,但常由于复合加固层的剥离可能导致加固效果的降低。复合加固层与被加固构件之间的剥离是由于薄弱截面在剪应力及正应力的集中作用下而产生的,文中对复合加固层与混凝土之间的粘结剪应力及剥离正应力的计算公式分别进行推导,并进一步对碳纤维布与钢板复合加固的剥离机理进行分析,为工程应用提供依据。     

A numerical model for static and free vibration analysis of elastic composite beams with end shear restraint

The end shear restraint, which is an un-classical type of end support, has a significant effect on the behavior of elastic composite beams. The principal aim of this paper is to present a numerical model for studying the effect of end shear restraint on static and free vibration behavior of elastic composite beams with various end conditions. The elastic composite beam, considered in this study, is composed of an upper concrete slab and a lower steel beam, connected at the interface by shear transmitting studs. This type of beam is widely used in constructions especially for highway bridges. The three types of end conditions considered in this study are simple, fixed and free supports. The numerical model is based on the combination of transfer matrix and analog beam methods. The field transfer matrices for the element of the elastic composite beam are derived. The present model is applied to the beam systems with and without end shear restraint and the static response and natural frequencies are calculated. the effect of shear stiffness between the upper slab and lower beam is also demonstrated.     

单钢板混凝土剪力墙抗爆性能研究

钢板混凝土剪力墙作为一种新型的抗侧力构件，具有良好的耗能能力和抗冲击性能，已逐渐应用于建筑工程结构的抗震和防护结构的抗爆设计。设计了3个试件，分别为普通钢筋混凝土板、单侧钢板混凝土板和夹心钢板混凝土板，开展了钢板混凝土剪力墙的接触爆炸试验，并通过非线性程序LS-DYNA建立了3个钢板混凝土剪力墙试件的数值模型，对比分析了不同试件在接触爆炸作用下的动态响应、破坏模式和抗爆性能。试验和数值分析结果表明:接触爆炸作用下，试验设计的3种试件呈现3种破坏模式；普通钢筋混凝土板中部发生混凝土贯穿破坏，钢筋发生较大弯曲变形；单侧钢板混凝土板由于栓钉拔出发生钢板和混凝土分离，丧失整体性和继续承载能力；夹心钢板混凝土板发生上层混凝土压碎，夹心钢板、上层和下层混凝土板连接性能较强，整体性较好，具有继续承载的能力，且夹心钢板混凝土板跨中挠度和混凝土碎块飞溅距离较小。单侧钢板混凝土板和夹心钢板混凝土板配置钢筋网可以显著增强混凝土层和钢板的连接性能，有效减小上下层混凝土的碎裂和剥落，增强其整体性和抗爆性能。     

钢-混凝土组合梁收缩徐变效应的随机分析

钢-混凝土组合梁是由混凝土板和钢梁通过剪力键连接而成的组合结构。由于混凝土的收缩徐变,将引起结构内力和应力重分布。混凝土收缩徐变具有离散性大的特点,进而导致结构长期响应表现出随机性。本文综合考虑徐变模型、收缩模型、混凝土抗压强度、混凝土弹性模量、环境湿度、钢材弹性模量、荷载以及剪力键刚度的随机性对钢-混凝土组合梁结构响应的影响。利用拉丁超立方抽样技术和基于响应面方法的蒙特卡洛抽样,研究了钢-混凝土组合梁挠度和应力时变效应的概率问题。     

复合材料层合加肋板中的瞬态波传播

研究复合材料加肋层合板结构受冲击载荷作用下的瞬态波传播.加肋层合板模型被处理成层合板的弯曲运动与层合梁的扭转与弯曲运动的耦合连续模型.通过Laplace变换,并采用回传射线矩阵法(MRRM),基于一阶剪切变形层合板理论,确定复合材料加肋层合板结构中传播的各条射线群.采用FFT变换,计算各种冲击载荷作用下加肋层合板结构的短时瞬态响应,并分析讨论脉冲类型对加肋层合板结构短时瞬态响应的影响.     

化爆作用下钢筋混凝土板柱节点冲切破坏的试验研究及分析

在TNT集团装药爆炸作用下 ,进行了四边简支钢筋混凝土板柱节点冲切破坏的试验研究 ,在土中自由场波传播理论的基础上 ,用介质结构相互作用理论和双剪强度理论对板柱节点冲切破坏机构进行了分析 ,分析结果与试验数据符合较好。     

??????????????????????Ч????????о?

提出了一种采用有限元法计算钢管混凝土受剪时等效剪切模量的方法,并对该方法 的正确性进行了验证;在分析了各种因素对等效剪切模量影响的基础上,给出了圆形和方形 钢管混凝土受剪时等效剪切模量的简化计算公式;与其他得到钢管混凝土剪切模量的方法进 行比较,分析了结果不同的原因,表明对钢管混凝土采用有限元计算研究其等效剪切模量的 方法更为合理.     

Process of debonding in RC beams shear-strengthened with FRP U-strips or side strips

Reinforced concrete (RC) beams may be strengthened for shear using externally bonded fiber reinforced polymer (FRP) composites in the form of side bonding, U-jacketing or complete wrapping. The shear failure of almost all RC beams shear-strengthened with side bonded FRP and the majority of those strengthened with FRP U-jackets, is due to debonding of the FRP. The bond behavior between the externally-bonded FRP reinforcement (referred to as FRP strips for simplicity) and the concrete substrate therefore plays a crucial role in the failure process of these beams. Despite extensive research in the past decade, there is still a lack of understanding of how debonding of FRP strips in such a beam propagates and how the debonding process affects its shear behavior. This paper presents an analytical study on the progressive debonding of FRP strips in such strengthened beams. The complete debonding process is modeled and the contribution of the FRP strips to the shear capacity of the beam is quantified. The validity of the analytical solution is verified by comparing its predictions with numerical results from a finite element analysis. This analytical treatment represents a significant step forward in understanding how interaction between FRP strips, steel stirrups and concrete affects the shear resistance of RC beams shear-strengthened with FRP strips.     

Debonding analysis of FRP–concrete interface between two balanced adjacent flexural cracks in plated beams

A cohesive interface modeling approach to debonding analysis of adhesively bonded interface between two balanced adjacent flexural cracks in conventional material (e.g., concrete or wood) beams strengthened with externally bonded FRP plates is presented. Both the strengthened beam and strengthening FRP are modeled as two linearly elastic Euler–Bernoulli beams bonded together through a thin adhesive layer. A bi-linear cohesive model, which is commonly used in the literature, is adopted to characterize the stress-deformation relationship of the FRP–concrete interface. Completely different from the single-lap or double-shear pull models in which only the axial pull force is considered, the present model takes the couple moment and transverse shear forces in both the substrates into account to study the second type of intermediate crack-induced debonding (IC debonding) along the interface. The whole debonding process of the FRP–concrete interface is discussed in detail, and closed-form solutions of bond slip, interface shear stress, and axial force of FRP in different stages are obtained. A rotational spring model is introduced at locations of the two adjacent flexural cracks to model the local flexibility of the cracked concrete beam, with which the relationship between the local bond slip and externally applied load is established and the real bond failure process of the FRP-plated concrete beam with the increasing of the externally applied load is revealed. Parametric studies are further conducted to investigate the effect of the thickness of adhesive layer on the bond behavior of FRP–concrete interface. The present closed-form solution and analysis on the local bond slip versus applied load relationship for the second type of IC debonding along the interface shed light on the bond failure process of structures externally strengthened with FRP composite plates and can be used effectively and efficiently to predict ductility and ultimate load of FRP-strengthened structures.     

钢框架-混凝土剪力墙混合结构连续化计算方法

提出了钢框架-混凝土剪力墙混合结构体系的一种连续化的计算方法，该方法考虑了这种结构中钢框架部分节点柔性连接，推导了考虑节点柔性连接时，钢框架-混凝土剪力墙混合结构中钢框架部分的层抗侧刚度．     

模拟酸雨腐蚀下预应力混凝土梁的抗弯性能研究

为了探讨酸雨腐蚀环境对预应力混凝土梁抗弯性能的影响,制作了8根预应力混凝土梁,从混凝土强度等级、预应力度和钢绞线腐蚀率等方面,进行8根预应力混凝土梁的三分点静载试验。试验结果及分析表明,混凝土强度对屈服后试验梁的抗弯性能影响较大,对弹性阶段的刚度影响较小;随着预应力度的增加,试验梁的开裂荷载逐渐增大,进入裂缝阶段后,刚度下降速度逐渐加快;钢绞线腐蚀率越大,试验梁的极限抗弯承载力越低;腐蚀率在一定范围内（>3.22%）,随着腐蚀率的增大,预应力混凝土梁试件的开裂弯矩、屈服弯矩和极限弯矩明显降低。根据试验结果,提出了模拟酸雨环境下预应力混凝土梁试件抗弯承载力的计算方法,同时采用ANSYS软件对预应力混凝土梁进行非线性有限元分析,将试验梁的计算值和模拟值与试验值进行比较,均吻合较好。     

复合砂浆钢绞线网加固RC梁受弯性能计算研究

分析了复合砂浆钢绞线网加固钢筋混凝土梁的受弯性能, 不同材料加固梁的受弯性能可采用同一公式进行计算, 研究表明加固梁受弯性能受本体梁的初始受力状态和是否采用三面U型加固影响较大. 采用正截面极限平衡法, 推导出复合砂浆钢绞线网加固钢筋混凝土梁极限抗弯承载力计算公式; 在混凝土结构设计规范公式基础上, 提出加固梁裂缝宽度和裂缝间距计算公式, 加固梁公式计算值与试验值吻合较好.     

Structural vibration of flexural beams with thick unconstrained layer damping

In this paper, the dynamic behaviour of free layer damping beams with thick viscoelastic layer is analysed. A homogenised model for the flexural stiffness is formulated employing Reddy and Bickford’s quadratic shear in each layer, in contrast to the classical model of Oberst and Frankenfeld for thin beams, which does not take into account shear deformations. The results provided by these two models in free and forced vibration are compared by means of finite element procedures with those of a 2D model, which considers extensional and shear stress, and longitudinal, transverse and rotational inertias.The viscoelastic material is characterised by a fractional derivative model, which takes into consideration the variation of the complex modulus with frequency. To avoid the frequency dependence of the stiffness matrices, the extraction of the eigenvalues and eigenvectors is completed by a new iterative method developed by the authors. The frequency response to a harmonic force is deduced by the superposition of modal contribution functions.From these numerical applications it can be concluded that the model for thick beams provides sufficient accuracy for practical applications, able to reproduce the mechanical behaviour of free layer damping beams with thick viscoelastic layer, reducing the storage needs and computational time with respect to a 2D model.     

Debonding of FRP-plated reinforced concrete beam,a bond-slip analysis. I. Theoretical formulation

External bonding of FRP plates or sheets has emerged as a popular method for strengthening reinforced concrete. Debonding along the FRP–concrete interface can lead to premature failure of the structure. In this study, a bond-slip model is established to study the interface debonding induced by a flexural crack in a FRP-plated concrete beam. The reinforced concrete beam and FRP plate are modeled as two linearly elastic Euler–Bernoulli beams bonded together through a thin layer of FRP–concrete interface. The interface layer is essentially modeled as a large fracture processing zone of which the stress–deformation relationship is described by a nonlinear bond-slip model. Three different bond-slip models (bi-linear, triangular and linear-damaging) are used. By dividing the debonding process into several stages, governing equations of interfacial shear and normal stresses are obtained. Closed-form solutions are then obtained for the interfacial shear and normal stresses and the deflection of the beam in each stage of debonding. In such a way, the proposed model unifies the whole debonding process, including elastic deformation, debonding initiation and growth, into one model. With such a superior feature, the proposed model provides an efficient and effective analytical tool to study FRP–concrete interface debonding.     

计及剪切影响的RC梁的非线性分析

为提高钢筋混凝土RC梁的计算效率和精度,提出了一种基于梁截面弯矩-曲率关系的宏观有限元方法,可用于各种跨高比RC梁的材料非线性分析。首先假定了混凝土和钢筋的非线性应力-应变关系,然后引入经过修正的Rodriguez截面模型,根据边界顶点把截面划分成若干梯形单元,利用quasi-Newton法求解由两个变量耦合而成的截面非线性平衡方程,由此建立RC截面的弯矩-曲率关系。在此基础上利用Timoshenko梁弯曲理论建立考虑横向剪切变形影响的RC梁的有限元分析模型。通过对试验梁的分析对比验证了所提出的分析方法的适用性。     

Continuum-based stability of anisotropic and auxetic beams

The critical buckling loads of pinned-pinned and cantilever beams are computed using the equations of three-dimensional elasticity rather than typical beam theories. These loads are influenced both by the nature of the assumed displacement field over the beam cross-section and by the inclusion of the terms from the full constitutive tensor. Of special interest are beams that are either anisotropic or auxetic. For anisotropic beams, an increased ratio of longitudinal to shear modulus for cantilevered beams increases the generation of shear buckling rather than flexural buckling. For isotropic auxetic beams, the values of Poisson ratio that define the limit between buckling loads that approach the classical buckling load from above or below are discussed.     

碳纤维布加固钢筋混凝土梁受力性能的试验研究

通过对8根矩形截面钢筋混凝土梁的静力加载试验,研究了抗弯和抗剪两种加固方式对钢筋混凝土梁的破坏形态和力学性能的影响,对比分析了碳纤维加固率、试验梁的状态、混凝土强度对加固效果的影响。结果表明：经碳纤维抗弯哥口抗剪加固后加圉梁相应的力学性能指标值明显提高;混凝土裂缝扩展得到了有效延缓,加固效果明显;抗弯加固后可显著提高混凝土梁的承载力和延性,但提高程度并不与加固率成正比;预裂粱抗弯加固后承载力和延性得到提高,但与其相同加固参数的梁相比,其承载力和延性有所降低;抗剪加固时混凝土强度越高,加固后混凝土梁的承载力和变形能力提高幅度越大,其中混凝土梁的变形能力受混凝土强度的影响较大。最后,对加固梁的极限承载力进行了理论分析与计算,建立了实用的理论计算公式,计算结果与试验结果吻合较好。     

ESPI技术对外贴纤维混凝土加固承载的实验研究

采用电子散斑干涉技术,对外贴碳纤维加固混凝土梁的外贴材料位移的分布特征,进行了全场实时测量,通过实验获得的散斑干涉条纹图可以得到外贴材料与混凝土梁的粘结传力长度随粘结长度及初始载荷之间的关系;了解用于加固的碳纤维材料的应变分布特点和产生梁侧剥离破坏时的碳纤维表面位移(应变)的演化过程。实验还说明了电子散斑干涉技术不仅可用于位移的测量,而且也可用于结构安全监测和破坏预报。文中给出了对C20D、C25A和C60C侧贴碳纤维板加固在不同载荷作用直到构件破坏前的位移测试及对试件C60C轴线上的剪应力分析结果。