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.     

混凝土材料动态力学性能的实验研究

本文利用改装的直锥变截面式φ７４ｍｍ大尺寸Ｈｏｐｋｉｎｓｏｎ压杆对混凝土材料试件（φ７２×３６）进行了冲击压缩实验。为了避免这种装置加载波波头部分对混凝土材料实验数据精度的影响,在实验过程中还采用了予留间隙法。实验结果表明,混凝土材料不仅具有敏感的应变率效应,还具有十分明显的损伤软化效应。     

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.     

Insight into the tension stiffening behavior of reinforced concrete tension members revealed by finite element modeling

Abstract

The disasters happened in recent past pointed out the need of design criteria, ensuring adequate safety levels against progressive collapse. The attention was focused on the behavior of composite beam-to-column joint components in the field of large displacements. This article presents the experimental and numerical study enabling the simulation of the RC elements under tension. This has helped in understanding the non-negligible contribution of concrete in tension stiffening response up to failure especially in the case of discontinuous geometry marked in composite structures. The finite element model proposed may be considered a mid-way between smeared and discrete crack modeling approaches.     

Evaluation of the stress-strain behavior of confined recycled aggregate concrete under monotonic dynamic loadings

Recycled aggregate concrete (RAC) has been attracting worldwide research interests due to its ecological and economic significance. However, RAC has so far mainly been limited to non-structural applications or structural members subjected to static loadings. In this study, the effects of strain rates, the confinement, and the RCA replacement ratio on the mechanical behaviors of confined recycled aggregate concrete (CRAC) are investigated through dynamic tests. The corresponding dynamic increase factor (DIF), confining increase factor (CIF) and replacement ratio influence factor (RIF) are formulated. A constitutive model for CRAC is then proposed through applying DIFs, CIFs, and RIFs to the characteristic parameters. Finally, the predicted stress-strain relationships of test samples using the proposed constitutive model are compared and evaluated with the experimental results. It is concluded that the proposed constitutive model can be applied to the further dynamic nonlinear analysis of RAC structures.     

应变率突增对混凝土动态拉伸破坏影响的细观模拟

实际工程中混凝土结构往往遭遇多次动态荷载作用或在承受一定初始损伤荷载基础上再承受不同应变率的动态荷载.建立了哑铃型混凝土三维细观数值模型,模拟不同名义应变率单独作用下混凝土材料的单轴动态拉伸破坏行为,又分别对混凝土单轴拉伸应力应变曲线上升段和软化段的应变率突增行为开展了细观模拟,初步分析了应变率突增行为对动态拉伸破坏强...     

CFRP加固钢筋混凝土T梁抗爆动力响应数值模拟

为了研究CFRP加固钢筋混凝土T梁的抗爆性能,采用ANSYS/LS-DYNA有限元软件,建立了钢筋混凝土T梁—CFRP材料—空气域—TNT炸药的全耦合模型,进行爆炸荷载下钢筋混凝土T梁的数值模拟,对钢筋混凝土T梁的动态力学性能进行了分析,分别研究了CFRP外贴形式、CFRP厚度对钢筋混凝土T梁的影响.结果表明:相比普通...     

不同温度环境中沥青混凝土动态抗压性能试验研究

为研究沥青混凝土在不同温度环境中的动态力学特性,该研究在-20～30 ℃和10-5～10-2 s-1条件下对其进行了动态抗压试验研究.试验结果表明:温度和应变速率对沥青混凝土的力学性能有显著影响,降低温度或增加应变速率导致抗压强度和弹性模量增加,峰值应变减小;当温度大于20 ℃或小于-10 ℃时,应变速率由10-5 s...     

Rate dependent behavior and modeling of concrete based on SHPB experiments

The dynamic behavior of concrete is studied experimentally by testing annular and solid concrete specimens using split Hopkinson pressure bar (SHPB). The dynamic increase factor (DIF) of annular samples is relatively lower than the DIF of solid samples. The dynamic behavior of concrete seems to be independent of the quasi-static strength of concrete. The mode of failure of concrete was a typical ductile failure at high strain-rates and brittle at low strain-rates. No significant influence of strain-rate on the initial elastic modulus of concrete was observed. An empirical equation is proposed for the estimation of DIF of concrete based on the experiments. A model is developed for the prediction of stress–strain curve of concrete under dynamic loading which shows good agreement with the experiments.     

Constitutive modeling of reinforced concrete and prestressed concrete structures strengthened by fiber-reinforced plastics

A batch of constitutive models for steel reinforcing bar, prestressing tendon, concrete and fiber-reinforced plastic are proposed for the nonlinear finite element analysis of reinforced concrete structures, prestressed concrete structures, reinforced concrete structures strengthened by fiber-reinforced plastics and prestressed concrete structures strengthened by fiber-reinforced plastics. These material models have been tested against series of experimental data and good agreements have been obtained, which justifies the validity and the usefulness of the proposed nonlinear constitutive models.     

Numerical study of dynamic crack growth by the finite element method

Recent developments in numerical techniques for dynamic transient stress analysis have ensured that realistic models can now be employed in crack propagation studies. In this paper transient dynamic finite element solutions are undertaken for both double cantilever beam (DCB) and pipeline problems with propagation of the crack being permitted. Standard parabolic isoparametric elements are employed for spatial discretization with an explicit (central difference) scheme being employed for time integration. Both critical stress and energy balance crack propagation criteria are considered.The pressurised pipeline problem is solved for as a fully three-dimensional solid. Firstly, a stationary crack is considered and both large deformations and plasticity effects are accounted for. The transient case of a dynamically propagating crack is then modelled, employing both a stress and energy criterion. Elastic large deformation behaviour is permitted for this case.

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Résumé Des développements récents dans les techniques numériques pour l'analyse des contraintes dynamiques transitoires ont permis d'utiliser à présent des modèles réalistes dans les études de propagation des fissures. Dans ce mémoire, on envisage des solutions par éléments finis pour les transitoires dynamiques dans les cas de la poutre double cantilever et de problèmes de pipelines où l'on autorise la propagation d'une fissure. On recourt aux éléments paramétriques paraboliques standards pour réaliser une division discrète de l'espace, et l'on utilise pour l'intégration dans le temps un schéma explicite à différence centrale. On considére à la fois les critères de contraintes critiques et d'équilibre d'énergie lors de la propagation de la fissure. Le problème du pipeline pressurisé est solutionné en considérant ce dernier comme un solide tridimensionnel. En premier lieu, on considère une fissure stationnaire et l'on tient compte des effets des grandes déformations et de la plasticité. On met ensuite en équation le cas transitoire d'une fissure en propagation dynamique, en utilisant un critère de contrainte et un critère d'énergie. Ce cas permit d'envisager le comportement sous des déformations élastiques importantes.

     

预应力连续箱梁桥的基准动力有限元模型研究z

介绍了作为预应力混凝土连续梁桥的通扬运河特大桥的环境激励振动试验,并利用基     

Effects of mix design parameters and rheological properties on dynamic stability of self-consolidating concrete

Stability is a crucial property for successful placement and performance of self-consolidating concrete (SCC). Dynamic stability refers to the segregation resistance of concrete during flow and is not thoroughly described in literature to date. In this research, a newly developed dynamic stability test, the Tilting-box test, was employed to evaluate the effect of different mix design parameters on the dynamic segregation of SCC. Paste volume, water-to-binder ratio (w/b), maximum size of aggregate (MSA), aggregate density, and aggregate grain-size distribution were shown to affect the dynamic stability of SCC, while the coarse aggregate shape did not have a significant influence. The slump flow and V-funnel flow time as well as the rheological parameters were found to be an efficient tool for controlling dynamic segregation. Higher yield stress or plastic viscosity reduced the risk of dynamic segregation. Recommended workability characteristics and rheological parameters of SCC to ensure adequate dynamic stability level were proposed.     

Energy absorption evaluation of reinforced concrete beams under various loading rates based on particle swarm optimization technique

This study proposes an energy absorption model for predicting the effect of loading rates, concrete compressive strength, shear span-to-depth ratio, and longitudinal and transverse reinforcement ratio of reinforced concrete (RC) beams using the particle swarm optimization (PSO) technique. This technique avoids the exhaustive traditional trial-and-error procedure for obtaining the coefficient of the proposed model. Fifty-six RC slender and deep beams are collected from the literature and used to build the proposed model. Three performance measures, namely, mean absolute error, mean absolute percentage error and root mean square error, are investigated in the proposed model to increase its accuracy. The design procedure and accuracy of the proposed model are illustrated and analysed via simulation tests in a MATLAB/Simulink environment. The results indicate the minimal effect of swarm size on the convergence of the PSO algorithm, as well as the ability of PSO to search for an optimum set of coefficients from within the solution space.     

Experimental study on dynamic damage evolution of concrete under multi-axial stresses

The effect of stress state on the dynamic compressive strength and the dynamic damage evolution process of concretes are investigated by use of a Spilt Hopkinson Pressure Bar (SHPB) and the ultrasonic technique. The columned concrete specimen is encircled by a steel sleeve. The multi-axial loading includes the axial and the radial loadings. The axial loading is supplied by the incidence bar, and the radial ones are produced by the steel sleeve. Analysis of the dynamic damage evolution of the samples is based on the measurement of the changes of ultrasonic wave velocities before and after the impact tests. The waveforms in the test bars, the stress strain curves, the confining pressure of the specimen, the dynamic compressive strength and other information about the samples are obtained during the SHPB experiments. The results of the tests show that the loading rate and stress states of the specimen apparently influence the damage evolution process in concretes. The dynamic damage evolutions are accelerated with the increase of the strain rate and are delayed significantly under the confined pressure.     

Failure analysis of reinforced concrete walls under impact loading using the finite element approach

In this paper, the punching resistance of a reinforced concrete (RC) wall under missile impact loading is evaluated using the finite element approach. The model is analyzed using LS-DYNA, a commercially available software program. The structural components of the RC wall, missile, and their contacts are fully modeled. Included in the analysis is material nonlinearity, which considers damage and failure. Damping effect is also taken into account. The analysis results are then verified with the test results. Parametric studies with a varying number of layers of longitudinal rebar and shear bar spacing are carried out to investigate the punching behavior of RC walls under missile impact. The distance travelled, scabbing area, and failure mode of various RC walls are examined, and efficient designs are recommended thereafter.     

Numerical study of the interfaces of 3D‐printed concrete using discrete element method

3D concrete printing is an additive manufacturing method which reduces the time and improves the efficiency of the construction process. Structural behavior of printed elements is strongly influenced by the properties of the material and the interface surfaces. The printing process creates interface surfaces between layers in the horizontal and vertical directions. The bond strength between layers is the most critical property of printed elements. In this paper, the structural behavior of printed elements is studied using the discrete element method. The material is modelled using discrete particles with bonding between them. A new discrete model of a multilayer geometry is presented to study the behavior of the interfaces of printed concrete. The layers are made up of randomly placed particles to simulate the heterogeneous nature of concrete. The numerical model is developed to simulate the flexural behavior of multilayer specimens. A four‐point flexural test is simulated considering the interface surfaces between layers. This numerical model provides relevant results to improve the behavior of this kind of structural elements. The aim of this work is to provide a discrete element model to predict the mechanical behavior of 3D concrete printed components.     

速度脉冲激励作用下混凝土框架柱抗剪性能研究

研究等效速度脉冲地震作用下混凝土框架柱最不利抗剪性能。以混凝土框架结构底层柱为分析对象,采用等效正弦速度脉冲激励作为地震动输入,通过非线性动力时程分析,研究竖直和水平向联合速度脉冲地震作用对框架柱抗剪性能的影响,分析速度脉冲地震作用与竖向和水平向加速度峰值比、峰值输入时差、剪跨比以及基本振动周期等对抗剪需求和抗剪承载力的交互影响规律。结果表明：脉冲速度强度增大,框架柱抗剪需求增大;竖向与水平向峰值比增大,柱抗剪承载力减小。加速度峰值输入时差对柱的最不利抗剪性能有重要影响;剪跨比越大,速度脉冲的影响越显著。基于分析结果的非线性回归,建立了考虑速度脉冲及其交互因素影响的最不利剪力作用效应修正系数     

近爆作用下钢筋混凝土板动态破坏的数值模拟研究

当爆炸在结构构件表面发生时,产生的冲击波将会对结构构件造成损伤和破坏,而准确预测潜在的爆炸对结构构件造成的损伤是进行重要建筑物和防护结构抗爆设计的基础。为研究近爆作用下钢筋混凝土板的抗爆性能,采用AUTODYN软件建立了混凝土和钢筋的三维分离式实体模型,数值模型考虑了应变率对钢筋和混凝土材料动力本构特性的影响以及炸药-空气-结构之间的流固耦合相互作用,分析了不同炸药量作用下钢筋混凝土板的损伤机理和破坏特征,合理展现了钢筋混凝土板从混凝土开裂、碎片形成、部分钢筋屈服断裂到板局部震塌的动态演变过程。随着炸药量的增大,钢筋混凝土板的破坏模式逐渐由整体弯曲破坏转变为局部的冲切破坏     

基于LabVIEW的纳米颗粒动态散射光模拟

采用实验室虚拟仪器工程平台LabVIEW实现了纳米颗粒动态光散射信号的计算机模拟。用G语言(图形语言)设计了信号模拟的框图程序,给出了5nm, 15 nm两种粒径颗粒的模拟动态散射光信号及自相关函数。对模拟信号的粒度分析表明,这两种模拟信号产生的测量偏差分别为0.4nm和-0.6nm。