钢梁-钢筋混凝土柱梁柱中节点非线性有限元模拟

借助ANSYS有限元分析软件,对5个"梁贯通"式RCS梁柱中节点进行三维非线性有限元分析,并和试验结果相比较。分析中考虑材料非线性以及混凝土的开裂与压碎。对单元类型的选取、钢和混凝土材料模型的定义、整体有限元模型的建立、施加荷载、设置求解选项并求解等数值模拟技术进行了深入的研究。研究表明,通过合理设置参数,ANSYS有限元软件能够模拟RCS梁柱节点在静力荷载作用下的性能,并和试验结果吻合较好。     

Numerical simulation of reinforced concrete beams with different shear reinforcements under dynamic impact loads

The behavior of concrete/reinforced concrete structures is strongly influenced by the loading rate. Reinforced concrete structural members subjected to impact loads behave quite differently as compared to the same subjected to quasi-static loading. This difference is attributed to the strain-rate influence on strength, stiffness, and ductility as well as to the activation of inertia forces. These influences are clearly demonstrated in experiments. Moreover, for concrete structures, which exhibit damage and fracture phenomena, the failure mode and cracking pattern depend significantly on loading rate. In general, there is a tendency that with the increase of loading rate the failure mode changes from mode-I to mixed mode. Furthermore, theoretical and experimental investigations indicate that after the crack reaches critical speed of propagation there is crack branching. The present paper focuses on 3D finite-element study of reinforced concrete beams with different amount of shear reinforcement under impact. The experiments reported in literature are numerically simulated using the rate sensitive microplane model as constitutive law for concrete, while the strain-rate influence is captured by the activation energy theory. Inertia forces are implicitly accounted for through dynamic finite element analysis. However, the impact was modeled not by explicit modeling of two bodies but by incrementing the load point displacement till the maximum value and at the rate reported from the test. The results of the numerical study show that the numerical analysis using the procedure followed in this work can very well simulate the impact behavior of reinforced concrete beams. The static and dynamic reactions, crack patterns and failure modes as predicted in analysis are in close agreement with their experimentally observed counterparts. It was concluded that under impact loads, of the order as simulated in this work (blunt impact with velocity of around 1 m/s), the shear reinforcement does not get activated and therefore the dynamic reactions, unlike static reactions, are almost independent of the amount of shear reinforcement in the beams. However, the presence of shear reinforcement significantly affects the crack pattern and the cracks are well distributed in the presence of shear reinforcement, thus avoiding the formation of shear plugs.     

Explicit finite element modeling of static crack propagation in reinforced concrete

We propose a methodology to model complex fracture processes in reinforced concrete beams subjected to static loading. The discrete cohesive approach, accompanied by an insertion algorithm, is adopted and a modified dynamic relaxation method is chosen as an alternative solver. The concrete matrix and steel re-bars are modeled explicitly; the connection in between is represented by means of interface elements. Such elements allow for slip of re-bars and transmit forces to the matrix that may generate secondary cracking around the reinforcement. The methodology is validated against three-point bending tests on lightly reinforced concrete (LRC) beams.     

Nonlinear finite element modeling of concrete deep beams with openings strengthened with externally-bonded composites

This paper aims to develop 3D nonlinear finite element (FE) models for reinforced concrete (RC) deep beams containing web openings and strengthened in shear with carbon fiber reinforced polymer (CFRP) composite sheets. The web openings interrupted the natural load path either fully or partially. The FE models adopted realistic materials constitutive laws that account for the nonlinear behavior of materials. In the FE models, solid elements for concrete, multi-layer shell elements for CFRP and link elements for steel reinforcement were used to simulate the physical models. Special interface elements were implemented in the FE models to simulate the interfacial bond behavior between the concrete and CFRP composites. A comparison between the FE results and experimental data published in the literature demonstrated the validity of the computational models in capturing the structural response for both unstrengthened and CFRP-strengthened deep beams with openings. The developed FE models can serve as a numerical platform for performance prediction of RC deep beams with openings strengthened in shear with CFRP composites.     

Nonlinear behavior of shear deficient RC beams strengthened with near surface mounted glass fiber reinforcement under cyclic loading

The aim of this investigation is to evaluate experimentally and numerically the cyclic loading response of reinforced concrete (RC) beams strengthened in shear with Glass Fiber Reinforced Polymer (GFRP) rods using the near surface mounted (NSM) technique. The experimental results indicated that the use of GFRP rods as NSM strengthening systems can significantly enhance the overall capacity and ductility of shear deficient RC members when subjected to cyclic loading. In particular, the increase in the load-carrying capacity of the strengthened specimens over the unstrengthened control specimen was in the range of 49–66%. Furthermore, the increase in the displacement over the control specimen ranged between 112% and 172%. A 3D finite element (FE) model was also developed to simulate the response of the tested specimens. The developed FE model integrates multiple simulation techniques, nonlinear material properties and corresponding constitutive laws. The models incorporate concrete cracking, yielding of steel reinforcement, bond–slip behavior between NSM reinforcement and adhesive material and between steel reinforcement and adjacent concrete material, respectively. The load–deflection response envelopes and the load–deflection hysteresis loops of the experimentally tested beams and those simulated by the FE models were compared. Good matching was observed between the predicted and measured results at all stages of cyclic loading.     

CFRP板加固RC&PPC梁抗剪性能试验研究

通过10片普通钢筋混凝土(RC)梁及4片部分预应力混凝土(PPC)梁采用CFRP板抗剪加固的试验研究和非线性有限元分析,研究不同损伤程度、剪跨比、配箍率及预应力水平等因素对CFRP板加固RC&PPC梁抗剪性能的影响。结果表明:采用CFRP板对RC&PPC梁进行抗剪加固能够有效抑制斜裂缝的开展,提高加固梁斜截面抗剪承载能力,并改善梁的延性;RC梁损伤后加固,随着配箍率的增大以及剪跨比的减小,将提高加固RC梁的斜向开裂荷载、箍筋屈服荷载以及抗剪极限承载能力;随着预应力水平的提高,PPC加固梁的极限承载力增大,CFRP板抗剪加固效果比较显著;非线性有限元模型能够预测CFRP加固RC/PPC梁的抗剪性能,有限元计算结果与试验结果吻合良好;在进行CFRP板抗剪加固设计时,应对CFRP板的强度进行有效折减。     

型钢混凝土结构ANSYS数值模拟技术研究

采用ANSYS程序对6个型钢混凝土梁试件的受力性能进行非线性有限元数值分析,对型钢混凝土结构数值模拟中混凝土和钢材材料模型定义、有限元建模、钢筋单元生成及后处理等关键技术进行系统研究。着重对型钢混凝土粘结滑移性能的数值模拟技术进行了研究。采用由ANSYS程序单元库中非线性弹簧单元combination-39组成的三维连接单元模拟型钢混凝土在不同部位及不同方向上的界面相互作用,建议了非线性弹簧单元粘结力-滑移曲线与型钢混凝土粘结滑移本构关系的转换技术,并提出了生成非线性弹簧单元的实用方法。最终形成考虑粘结滑移的型钢混凝土数值模拟技术。型钢混凝土梁数值模拟结果与试验结果吻合较好,表明所建立型钢混凝土结构ANSYS数值模拟技术合理、可行,可适用于基于ANSYS程序的型钢混凝土结构有限元数值模拟和受力性能深入研究。     

Studies on ductility and evaluation of minimum flexural reinforcement in RC beams

Some experimental investigations on ductility and prediction of minimum flexural reinforcement in reinforced concrete (RC) beams are reported. The minimum flexural reinforcement was evaluated using optimum ductility in RC beams. Beams of size 100 mm, 200 mm and 400 mm were tested, which were designed with varying percentages of flexural reinforcement i.e. 0.15, 0.30, 0.60 and 1.0. The beams were tested under four-point loading to study the flexural behaviour under uniform bending moment. The experimentally obtained average compressive strength of concrete was 30 MPa. The influence of beam size (depth) on cracking and normalised ultimate flexural strength, ductility and overall average rotation has been studied. The cracking in RC beams is complex phenomenon in small size beams, while the cracking strength decreases as the depth increases beyond 200 mm. The flexural strength of RC beams, from the present study, appears to decrease as the depth increases. The ductility of RC beams increases as the percentage of flexural reinforcement increases. The ductility number has been derived from dimensional analysis using fracture mechanics principles. The ductility of RC beams decreases as the depth of beams increases. An optimum percentage of flexural reinforcement has been established using optimum ductility number, N_p, which is equal to 0.20. The minimum flexural reinforcement was found to decrease as the beam depth increases, and decreases as the yield strength of reinforcement increases.     

A calculation method of cracking moment for the high strength concrete beams under pure torsion

In this study, a method is given to calculate cracking moments of high strength reinforced concrete beams under the effect of pure torsion. To determine the method, both elastic and plastic theories were used. In this method, dimensions of beam cross-section were considered besides stirrup and longitudinal reinforcements. Two plain high strength concrete (without reinforcement) and eight high strength reinforced concrete beams which have two different cross-sections (150 × 250 mm and 150 × 300 mm) were produced to examine the validity of the proposed method. The predictions of the proposed approach for the calculation of the cracking moment of beams under pure torsion were compared with the experimental and the analytical results of previous studies. From these comparisons it is concluded that the predictions of the proposed equations for the cracking moment of plain and reinforced high strength concrete beams under pure torsion are closer to the experimental data compared to the analytical results of previous theories.     

火灾下型钢混凝土梁力学性能的研究

采用纤维模型法和有限元软件ABAQUS计算了火灾下型钢混凝土梁的变形以及耐火极限,初步了解了型钢混凝土梁的高温力学性能。在此基础上,利用纤维模型法分析了截面尺寸、截面含钢率、受拉钢筋配筋率、型钢屈服强度、钢筋屈服强度、混凝土强度、截面高宽比和钢筋的混凝土保护层厚度等参数对火灾下构件承载力的影响规律,最后提出了型钢混凝土梁耐火极限的实用计算公式。     

Numerical modelling of concrete beams reinforced with pre-stressed CFRP

In this paper, a numerical simulation is presented on the behaviour of concrete beams, reinforced with pre-stressed CFRP. The numerical results are compared to experimental results. Nonlinear material behaviour is considered, namely: the inelastic compressive concrete behaviour, the elasto-plastic behaviour of steel reinforced bars, the bond-slip relationship between the concrete and the internal steel reinforced bars, the mode-II fracture interface between the concrete and the pre-stressed CFRP and concrete cracking. Cracking in concrete is modelled according to a discrete crack approach: micro-cracking is assumed to localize at fictitious cracks with initial zero width. Two different approximations are adopted: (i) the fictitious cracks are embedded within the finite elements, giving rise to a discrete strong discontinuity formulation and (ii) main cracks, similar to the experimentally observed, are introduced, using interface elements, along the element boundaries, since the beginning of the analysis. A non-iterative sequentially-linear approach is adopted in order to avoid convergence problems. The aim of the present analysis is to try to better understand the failure mechanisms found in the experimental tests. Despite the complexity of the multiple nonlinear aspects of the behaviour of the structure, it is concluded that the numerical results are similar and are close to those observed experimentally.     

碳纤维布加固复合受力钢筋混凝土箱梁抗扭性能的非线性有限元分析

采用有限元方法对碳纤维布加固钢筋混凝土构件进行非线性分析,是对有限的试验研究的有效补充和进一步深入探讨。根据4根碳纤维布加固钢筋混凝土箱梁的试验研究结果,建立了合理的三维有限元模型,对碳纤维布加固钢筋混凝土箱梁在弯剪扭复合受力下的抗扭性能进行了非线性有限元分析。计算得到的扭矩-扭转角关系曲线、钢筋和碳纤维布的应变曲线以及界面粘接单元的恢复力曲线等与试验结果吻合较好,可以较好地模拟碳纤维布加固箱梁的受扭性能。进一步通过对7根数值梁的计算结果分析,提出碳纤维布加固钢筋混凝土箱梁在复合受力下的剪扭相关性符合直线方程。     

A 3D Computational Model of RC Beam Using Lower Order Elements with Enhanced Strain Approach in the Elastic Range

A procedure has been described to carry out three-dimensional elastic analysis of reinforced concrete beam employing finite element technique, which uses lower order elements. The proposed procedure utilizes 8-noded isometric solid /hexahedral elements HCiS18 with enhanced assumed strain (EAS) formulation, recently developed in the literature, to predict load-deformation and internal stresses produced in case of a simply supported RC beams in the elastic regime. It models the composite behaviour of concrete and reinforcements in rigid /perfect bond situation and their mutual interaction in bond-slip condition considering continuous interface elements at the material level. Although, bond-slip relation are very much non-linear in behaviour even at the beginning of the loading condition, predictions from the proposed model /procedure are found to be very close to the experimental observations as far as accuracy is concerned in the elastic range. The sole purpose of this paper is to demonstrate the general applicability and to explore the potentiality of using lower order solid elements in the 3D finite element analysis with an aim of developing a general analytical method for the study of reinforced concrete beam in the elastic range.     

Flexural response predictions of reinforced concrete beams strengthened with prestressed CFRP plates

Existing experimental studies showed that the reinforced concrete (RC) beams strengthened with prestressed carbon fiber-reinforced polymer (CFRP) plates had three possible flexural failure modes (including the compression failure, tension failure and debonding failure) according to the CFRP reinforcement ratio. Theoretical formulas based on the compatibility of strains and equilibrium of forces were presented to predict the nominal flexural strength of strengthened beams under the three failure modes, respectively, and a limitation on the tensile strain level developed in the prestressed CFRP plate was proposed as the debonding failure occurred. In addition, the calculation methods for cracking moment, crack width and deflection of strengthened beams were provided with taking into account the contribution of prestressed CFRP plates. Experimental studies on five RC beams strengthened with prestressed CFRP plates and a nonlinear finite element parametric analysis were carried out to verify the proposed theoretical formulas. The available test results conducted by other researchers were also compared with the predicted values.     

Fatigue crack propagation behavior of RC beams strengthened with CFRP under cyclic bending loads

A fatigue crack propagation equation of reinforced concrete (RC) beams strengthened with a new type carbon fiber reinforced polymer was proposed in this paper on the basis of experimental and numerical methods. Fatigue crack propagation tests were performed to obtain the crack propagation rate of the strengthened RC beams. Digital image correlation method was used to capture the fatigue crack pattern. Finite element model of RC beam strengthened with carbon fiber reinforced polymer was established to determinate J‐integral of a main crack considering material nonlinearities and degradation of material properties under cyclic loading. Paris law with a parameter of J‐integral was developed on the basis of the fatigue tests and finite element analysis. This law was preliminarily verified, which can be applied for prediction of fatigue lives of the strengthened RC beams.     

An applicability of dynamic response analysis of shear-failure type RC beams with lightweight aggregate concrete under falling-weight impact loading

In order to establish a simple and rational impact response analysis method for lightweight aggregate reinforced concrete (RC) beams, three-dimensional elasto-plastic finite element analysis was conducted for shear-failure type RC beams under falling-weight impact loading. The, tensile strength of concrete was assumed as 1/16th of the compressive one. An applicability of the proposed analysis method was confirmed by comparing with the experimental results of twelve beams. From this study, following results were obtained: (1) three response wave configurations: impact force; reaction force; and mid-span displacement, and crack patterns can be rationally predicted by using proposed analysis method; and (2) maximum response values of impact force, reaction force, and displacement can be estimated considering 20, 20, and 10% safety margin, respectively.     

Analysis of reinforced concrete plates subjected to impact employing the truss‐like discrete element method

The prediction of the response of reinforced concrete structures subjected to projectiles impact still presents open questions. These include the rate dependence of material properties, the interaction between concrete and steel reinforcement and the simulation of fracture and fragmentation. Because the appearance of discontinuities in the target structure is difficult to account using a continuum approach, the application of discrete models was developed as an appealing alternative. A version of the discrete model in which nodal masses are linked by an array of uniaxial elements, herein called discrete element method, is used in this study. This method was implemented in the system Abaqus to take advantage of its numerical and post‐processing capabilities. A reinforced concrete rectangular plate subjected to impact of a projectile is examined in detail. Comparisons between experimental and numerical results are shown with the aim of validating the proposed method.     

CFRP-PCPs复合筋嵌入加固钢筋混凝土梁裂缝试验及计算方法研究

通过5根嵌入不同张拉控制应力的碳纤维增强塑料预应力混凝土棱柱体(CFRP-PCPs)复合筋加固钢筋混凝土梁受弯试验,对比分析试验梁的裂缝分布与发展,得到最大裂缝宽度与平均裂缝宽度在静力荷载作用下的变化特性。结果表明: 嵌入CFRP-PCPs复合筋能有效的减少被加固钢筋混凝土梁的裂缝宽度和高度。在试验基础上,根据国家现行混凝土规范,对平均裂缝间距和最大裂缝宽度计算公式进行参数修正,建立了CFRP-PCPs复合筋嵌入加固钢筋混凝土梁最大裂缝宽度计算公式,计算值与试验值吻合较好。     

GFRP筋橡胶集料混凝土梁受弯性能

为提高纤维增强聚合物复合材料(FRP)筋混凝土梁抗裂性能,改善其脆性破坏特征,将玻璃纤维增强聚合物复合材料(GFRP)筋与橡胶集料混凝土共同应用于梁构件中。采用ABAQUS对GFRP筋橡胶集料混凝土梁的受弯性能进行有限元模拟及参数分析,探究了橡胶掺量、GFRP筋配筋率、混凝土强度等级及截面高度对梁受弯性能的影响。结果表明:增加混凝土中橡胶颗粒的掺量可提高梁的开裂荷载,当橡胶掺量为15%时,开裂荷载提高了29%;增加配筋率可提高梁的开裂荷载和承载力,当受拉筋直径由10 mm增加至18 mm时,橡胶掺量为10%的GFRP筋橡胶混凝土梁开裂荷载提高了约15%,承载力提高了约85%,但配筋率增加至一定数值后,其影响不再明显;提高橡胶混凝土强度等级,可提高梁的开裂荷载及承载力,当橡胶混凝土强度等级由C25提高至C40时,开裂荷载提了高约53.7%,承载力提高了约23%;为更好地满足正常使用极限状态,GFRP筋橡胶混凝土梁的截面高度宜适当增加。