Failure behaviors of reinforced concrete beams subjected to high impact loading

To attain a better understanding of the failure behavior of reinforced concrete (RC) beams under impact load, series of high speed impact experiments were performed using an instrumented drop-weight impact machine. The test program was successful in providing a substantial volume of test data including impact loads, mid-span deflections, crack profiles and strains. These data was analyzed, focusing on the impact load characteristics and the impact behaviors of RC beams. Various characteristic values and their relationships were investigated such as the drop height, the static flexural load-carrying capacity, the input impact energy and the beam response values. Two empirical formulas were proposed to estimate the maximum and residual deflection of the beam based on the static flexural load-carrying capacity and the input impact energy. The applicability of the proposed equations was confirmed by comparison with the experimental results obtained by other researchers.     

基于荷载时程分析法的钢筋混凝土与钢板混凝土墙冲击响应对比分析

为对比核电站核岛厂房钢筋混凝土结构(RC)与钢板混凝土结构(SC)外墙的抗冲击性能,基于荷载时程分析法,用显示非线性动力分析软件ANSYS/LS-DYNA仿真分析1/7.5比例飞机模型撞击RC、SC墙的冲击实验。将RC、SC墙破坏模式、混凝土碎片残余速度及背部钢板变形等计算结果与飞射物-靶体相互作用分析法计算结果及实验结果以及同厚度不同结构类别墙的计算结果进行对比。结果表明,基于荷载时程分析法计算结果有一定保守性,与实验结果吻合较好,且SC墙抗冲击性能优于RC墙,尤其背部钢板能有效约束混凝土撞击方向的运动及限制混凝土碎片飞溅。用于抗飞机撞击的SC结构墙体厚度可适当减薄。     

Nonlinear finite element analysis of reinforced concrete beams strengthened by fiber-reinforced plastics

Numerical analyses are performed using the ABAQUS finite element program to predict the ultimate loading capacity of rectangular reinforced concrete beams strengthened by fiber-reinforced plastics applied at the bottom or on both sides of these beams. Nonlinear material behavior, as it relates to steel reinforcing bars, plain concrete, and fiber-reinforced plastics is simulated using appropriate constitutive models. The influences of fiber orientation, beam length and reinforcement ratios on the ultimate strength of the beams are investigated. It has been shown that the use of fiber-reinforced plastics can significantly increase the stiffnesses as well as the ultimate strengths of reinforced concrete beams. In addition, with the same fiber-reinforced plastics layer numbers, the ultimate strengths of beams strengthened by fiber-reinforced plastics at the bottom of the beams are much higher than those strengthened by fiber-reinforced plastics on both sides of the beams.     

Reliability analysis of reinforced concrete grids with nonlinear material behavior

Reinforced concrete grids are usually used to support large floor slabs. These grids are characterized by a great number of critical cross-sections, where the overall failure is usually sudden. However, nonlinear behavior of concrete leads to the redistribution of internal forces and accurate reliability assessment becomes mandatory. This paper presents a reliability study on reinforced concrete (RC) grids based on coupling Monte Carlo simulations with the response surface techniques. This approach allows us to analyze real RC grids with large number of failure components. The response surface is used to evaluate the structural safety by using first order reliability methods. The application to simple grids shows the interest of the proposed method and the role of moment redistribution in the reliability assessment.     

Modelling the response of reinforced concrete panels under blast loading

A finite element model is developed for the simulation of the structural response of steel-reinforced concrete panels to blast loading using LS-DYNA. The effect of element size on the dynamic material model of concrete is investigated and strain-rate effects on concrete in tension and compression are accounted for separately in the model. The model is validated by comparing the computed results with experimental data from the literature. In addition, a parametric study is carried out to investigate the effects of charge weight, standoff distance, panel thickness and reinforcement ratio on the blast resistance of reinforced concrete panels.     

Modelling crack propagation in reinforced concrete using a hybrid finite element–scaled boundary finite element method

A previously developed hybrid finite element–scaled boundary finite element method (FEM–SBFEM) is extended to model multiple cohesive crack propagation in reinforced concrete. This hybrid method can efficiently extract accurate stress intensity factors from the semi-analytical solutions of SBFEM and is also flexible in remeshing multiple cracks. Crack propagation in the concrete bulk is modelled by automatically inserted cohesive interface elements with nonlinear softening laws. The concrete–reinforcement interaction is also modelled by cohesive interface elements. The bond shear stress–slip relation of CEB-FIP Model Code 90 and an empirical confining stress–crack opening relation are used to characterise slip and split failure at the concrete–reinforcement interface, respectively. Three RC beams were simulated. The numerical results agreed well with both experimental and numerical results available in the literature. Parametric studies demonstrated the importance of modelling both slip and split failure mechanisms at the concrete–reinforcement interface.     

Numerical simulation of reinforced concrete structures under impact loading

This study presents the performance of a combined finite‐discrete element method for prediction of the structural response of reinforced concrete beams under impact loading. A combination of finite and discrete element methods enables the modelling of the concrete and the reinforcement before the concrete cracking, as well as a discontinuous nature of the concrete caused by fracture and fragmentation under high impact loading. Discretization of the concrete with triangular finite elements is coupled with one‐dimensional reinforcing bars embedded inside the concrete finite elements. The cracking in the concrete activates the joint elements used to simulate the non‐linear behavior of both concrete and reinforcement. Numerical analysis based on experimental test data has been carried out to simulate the main features of the reinforced concrete beams impacted by free‐falling drop‐weights. A high level of accuracy was demonstrated in various comparisons between the experimental tests and the analysis results, including peak displacement, crack pattern, damage level and failure modes of reinforced concrete beams.     

Thermo-mechanical loading of GFRP reinforced thin concrete panels

The experimental investigation is focused on the thermo-mechanical behaviour of thin concrete panels reinforced with GFRP rebars. The considered thin panels (thickness of 4 cm) were exposed to increasing temperature and bending loading. These concrete elements are typical for low bearing function concrete layers in façade claddings. The influence of two aspects was studied: the concrete cover and the external surface of rebars. The heating condition was such that the temperature of the internal GFRP rebars reached about the transition temperature of the resins. This allowed to verify the variation of the deformability and the load carrying capacity of the panels with post-heating bending tests. As main outcome, the imposed temperature did not generate evident degradation of the GFRP reinforcement and of its adhesion to the concrete, while a reduction of the initial global stiffness was measured.     

A general 3D approach for the analysis of multi-axial fracture behavior of reinforced concrete elements

The behavior of cracked reinforced concrete structural components is here analyzed through a three-dimensional model, which includes all the interface phenomena generated along cracks, such as aggregate bridging and interlock, tension stiffening and dowel action, as well as the non-linear response of concrete in compression and in tension. The model is able to effectively describe the progressive development of multi-axial cracking, by considering the crack re-orientation and the change of the crack spacing as loading increases. The proposed formulation, which is expressed in terms of secant stiffness matrix, is obtained by taking into account the flexibility contributions of cracks and of the concrete between adjacent cracks, in both the singly and the multi-cracked stage. Finally, this model is implemented into a finite element code and is validated through comparisons with significant experimental data available in the literature.     

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.     

Reliability of reinforced concrete structures under fatigue

This paper focuses on time-variant reliability assessment of deteriorating reinforced concrete structures under fatigue conditions. A strategy combining two time scales, namely the micro-scale of instantaneous structural dynamics (or statics) and the macro-scale of structural lifetime, is proposed. Non-linear response of reinforced concrete structures is simulated by means of the finite element method with adequate material model. A phenomenological fatigue damage model of reinforced concrete is developed and calibrated against experimental results available in the literature. Reliability estimates are obtained within the response surface method using the importance/adaptive sampling techniques and the time-integrated approach. The proposed assessment strategy is illustrated by an example of a concrete arch under fatigue loading. The obtained results show a general inapplicability of local and linear fatigue models to system level of structures.     

Failure analysis of natural gas buried X65 steel pipeline under deflection load using finite element method

A 3D parametric finite element model of the pipeline and soil is established using finite element method to perform the failure analysis of natural gas buried X65 steel pipeline under deflection load. The pipeline is assumed to be loaded in a parabolic deflection displacement along the axial direction. Based on the true stress–strain constitutive relationship of X65 steel, the elastic–plastic finite element analysis employs the arc-length algorithm and non-linear stabilization algorithm respectively to simulate the strain softening properties of pipeline after plastic collapse. Besides, effects of the soil types and model sizes on the maximum deflection displacement of pipeline are investigated. The proposed finite element method serves as a base available for the safety design and evaluation as well as engineering acceptance criterion for the failure of pipeline due to deflection.     

Dynamic response and behavior of reinforced concrete slabs under impact loading

Reinforced concrete slabs are among the most common structural elements. In spite of the large number of slabs designed and built, the effect of their details on their behavior under impact loads are not always appreciated or properly taken into account. This experimental study was aimed at understanding the dynamic behavior of structural concrete slabs under impact loading to improve the state of the art of protective design. This study investigated the effects of different types of slab reinforcements and the applied impact loads on the dynamic response and behavior of reinforced concrete slabs.     

Synthesis of punching failure in reinforced concrete

A synthesis of punching failure in reinforced concrete is given here. First, some recent experimental results are presented allowing one to show the difference between flexural and punching failure. Second, the punching failure mechanism is discussed based on results obtained with numerical simulations demonstrating among others the influence of the concrete tensile strength. Then, using these results, an analytical model is derived for punching load prediction. The model allows a unified treatment of slabs with various types of reinforcement. Finally, the prediction's capabilities are discussed using extended databases as well as special experimental results.     

冲击载荷下玄武岩纤维增强混凝土的动态本构关系

为了研究玄武岩纤维增强混凝土的动态本构关系,利用Ф100mm分离式霍普金森压杆装置,对玄武岩纤维增强混凝土进行冲击压缩试验,得到了动态应力-应变曲线,对试验数据进行了分析,根据试验结果,通过叠加应变率强化效应和损伤软化效应,对混凝土静态Ottosen非线性弹性本构模型进行修正,建立了玄武岩纤维增强混凝土损伤型的动态本构模型,确定参数并将理论模型计算结果与试验结果进行了对比。研究表明,玄武岩纤维增强混凝土的动态性能存在明显的应变率强化效应,动态强度增长因子和峰值应变与应变率对数之间存在近似函数关系;建立模型的方法可行,理论模型计算结果与试验结果吻合较好,建立的本构模型可用来描述玄武岩纤维混凝土的动态力学行为,并能为玄武岩纤维增强混凝土的进一步研究和工程应用提供参考依据。     

低速冲击激励下嵌入黏弹性阻尼芯层的纤维金属混杂层合板动态响应预测模型

钢筋混凝土(RC)结构在遭受火灾作用时,常会由于楼层坍塌而继发冲击作用,对楼板产生高温与冲击的耦合作用。该文同时考虑高温热力耦合效应和冲击荷载作用下的应变率效应,开展了高温下RC板抗冲击性能研究。通过分别将RC板抗火和抗冲击的试验结果与模拟结果进行对比,验证了该文所建立模型的正确性。分析获得了RC板在不同受火时间和不同能量冲击荷载作用下的动力响应,讨论了板厚和配筋率对高温下RC板抗冲击性能的影响。结果表明：火灾高温作用将显著影响RC板的抗冲击性能。随着受火时间的增加,RC板的冲切破坏损伤更加严重,RC板的跨中峰值位移也更大。板厚的增加能明显改善RC板的高温下的抗冲击性能,而配筋率的增加对RC板在高温下的抗冲击性能的影响有限。     

Cost optimization of reinforced concrete cantilever retaining walls under seismic loading using a biogeography-based optimization algorithm with Levy flights

In this article, a new version of a biogeography-based optimization algorithm with Levy flight distribution (LFBBO) is introduced and used for the optimum design of reinforced concrete cantilever retaining walls under seismic loading. The cost of the wall is taken as an objective function, which is minimized under the constraints implemented by the American Concrete Institute (ACI 318-05) design code and geometric limitations. The influence of peak ground acceleration (PGA) on optimal cost is also investigated. The solution of the problem is attained by the LFBBO algorithm, which is developed by adding Levy flight distribution to the mutation part of the biogeography-based optimization (BBO) algorithm. Five design examples, of which two are used in literature studies, are optimized in the study. The results are compared to test the performance of the LFBBO and BBO algorithms, to determine the influence of the seismic load and PGA on the optimal cost of the wall.     

连续侧向冲击作用下钢筋混凝土管动力响应试验研究

为了揭示钢筋混凝土管在连续侧向冲击荷载作用下的破坏机理,完成了6个钢筋混凝土管的横向冲击测试,考虑了不同落锤高度、冲击次数以及简支、固支两种约束形式对钢筋混凝土管侧向冲击动力响应的影响。提出了冲击力和跨中变形的预测公式并采用试验数据进行了拟合,得到了不同冲击速度、冲击次数对管道冲击力峰值和跨中位移的变化规律。采用吸能系数来量化评价管道承受侧向撞击时的吸能能力。结果表明,固支约束管道变形破坏显著好于简支约束试件,承受多次侧向撞击后,吸能系数增大,抗冲击变形能力明显下降。     

Efficient technique for constitutive analysis of reinforced concrete flexural members

One of the most difficult issues in the theory of reinforced concrete (RC) is an adequate modelling of deformation behaviour, cracking and, particularly, post-cracking behaviour, as one of the major sources of non-linearity. Applying the concept of average cracking and average strains, deformation behaviour of RC can be modelled by stress–strain tension–stiffening relationships. The authors proposed an innovative inverse technique for constitutive modelling of flexural RC elements. The technique is based on the smeared crack approach and layer model of RC section. The inverse technique aims at deriving tension–stiffening constitutive models from experimental moment–curvature diagrams. The present analysis takes into account the shrinkage effect that is often neglected in other studies. Based on the inverse technique, free-of-shrinkage tension–stiffening relationships are derived using test data of shrunk RC beams. Examples of the application for the analysis of the experimental data obtained by the authors are presented to illustrate the calculation efficiency of the proposed technique.     

冲击荷载作用下EPS混凝土动态性能研究

配置聚苯乙烯(Expanded Polystyrene,EPS)颗粒体积掺量分别为10%,20%,30%,40%,50%的EPS混凝土,采用Φ100 mm分离式霍普金森压杆(SHPB)试验装置,以动态抗压强度和临界应变为指标,研究EPS混凝土在冲击荷载作用下的动态性能,探索EPS颗粒对混凝土动态性能的改善机理。结果表明:由于应变率效应,相同体积掺量的EPS混凝土动态抗压强度与临界应变随应变率的增加而提高,具有显著的应变率相关性;以临界应变为变形性能指标,由于EPS颗粒的微结构效应,在EPS颗粒体积掺量0～40%范围内,其变形性能随EPS体积掺量的增加而提高,当EPS颗粒体积掺量达到50%时,其变形能力有所降低。EPS颗粒体积掺量为40%时对混凝土变形性能的改善效果最佳。