Response Of Reinforced Concrete Beams Research Articles

Flexure‐axial‐shear interaction of ductile beams with single‐crack plastic hinge behaviour

AbstractOne of the key damage observations in modern reinforced concrete (RC) frame buildings, damaged following the 2010/2011 Canterbury and 2016 Kaikoura earthquakes, was localised cracking at the beam‐column interface of capacity‐designed beams. The localised cracking in the beams was due to curtailed longitudinal bars at the beam‐column interface. Following these observations, without experimental data to justify desirable seismic performance, modern beams controlled by localised cracking were assumed to be potentially earthquake‐vulnerable. To address this, an experimental program was carried out on six RC beam specimens susceptible to single‐crack plastic hinge behaviour due to curtailed longitudinal bars. The experimental data show that RC beams with single‐crack plastic hinge behaviour can undergo significant inelastic drift demands without loss of lateral resistance. However, contrary to conventional beams with distributed cracking, the response of RC beams with single‐crack plastic hinge behaviour due to curtailed longitudinal bars is mainly dominated by hinge rotation (via bond‐slip) and shear sliding at the column face. The current paper studies the interdependence of axial elongation, bond‐slip and shear sliding deformation of RC beams with single‐crack plastic hinge behaviour under cyclic demands. A procedure for seismic assessment of RC beams with single‐crack plastic hinge behaviour due to curtailed longitudinal bars is proposed. The proposed formulations can be adopted to develop adequate numerical models for simulating the response of RC frames with beams susceptible to single‐crack plastic hinge behaviour due to curtailed longitudinal bars.

Analysis of static response of RC beams with NSM CFRP/GFRP rods

In this paper experimental results of investigation on reinforced concrete (RC) beams strengthened with the near surface method (NSM) are analyzed considering the response under bending tests on two beams. One of the RC beams was damaged by bending until the yield of reinforcement and successively strengthened with carbon fiber polymer (CFRP) rod, while the second beam was strengthened with glass-FRP rod. Both the beams have been subjected to bending tests until failure. Experimental diagrams and discussion on static response are presented in the paper. It also places a particular emphasis on the non-linear response of RC sections strengthened with CFRP and GFRP rods under bending moment beyond the first elastic behavior.

Cyclic Response of Steel Fiber Reinforced Concrete Slender Beams; an Experimental Study.

Reinforced concrete (RC) beams under cyclic loading usually suffer from reduced aggregate interlock and eventually weakened concrete compression zone due to severe cracking and the brittle nature of compressive failure. On the other hand, the addition of steel fibers can reduce and delay cracking and increase the flexural/shear capacity and the ductility of RC beams. The influence of steel fibers on the response of RC beams with conventional steel reinforcements subjected to reversal loading by a four-point bending scheme was experimentally investigated. Three slender beams, each 2.5 m long with a rectangular cross-section, were constructed and tested for the purposes of this investigation; two beams using steel fibrous reinforced concrete and one with plain reinforced concrete as the reference specimen. Hook-ended steel fibers, each with a length-to-diameter ratio equal to 44 and two different volumetric proportions (1% and 3%), were added to the steel fiber reinforced concrete (SFRC) beams. Accompanying, compression, and splitting tests were also carried out to evaluate the compressive and tensile splitting strength of the used fibrous concrete mixtures. Test results concerning the hysteretic response based on the energy dissipation capabilities (also in terms of equivalent viscous damping), the damage indices, the cracking performance, and the failure of the examined beams were presented and discussed. Test results indicated that the SFRC beam demonstrated improved overall hysteretic response, increased absorbed energy capacities, enhanced cracking patterns, and altered failure character from concrete crushing to a ductile flexural one compared to the RC beam. The non-fibrous reference specimen demonstrated shear diagonal cracking failing in a brittle manner, whereas the SFRC beam with 1% steel fibers failed after concrete spalling with satisfactory ductility. The SFRC beam with 3% steel fibers exhibited an improved cyclic response, achieving a pronounced flexural behavior with significant ductility due to the ability of the fibers to transfer the developed tensile stresses across crack surfaces, preventing inclined shear cracks or concrete spalling. A report of an experimental database consisting of 39 beam specimens tested under cyclic loading was also presented in order to establish the effectiveness of steel fibers, examine the fiber content efficiency and clarify their role on the hysteretic response and the failure mode of RC structural members.

Analytical Model for Torsional Response of RC Beams Strengthened With Ferrocement U-Wraps

Wrapping technology is one of the most effective ways of strengthening concrete elements. Several research articles have confirmed the effectiveness of fibre-reinforced polymers (FRP) as wrapping material for enhancing the strength of reinforced concrete (RC) elements. Wrapping three sides of RC members is a convenient method of strengthening the beams that support the slabs. Its cost effectiveness over FRP makes ferrocement a good substitute as a wrapping material for strengthening RC beams. Limited research is reported regarding the torsional strength of ferrocement U-wrapped RC beams subjected to pure torsional loads. In this paper, an analytical model to predict the torsional response of RC beams with ferrocement U-wraps is presented. This analytical model is based on Hsu’s softened membrane model. The analytical model is validated by conducting experimental tests. In this investigation, 12 RC beams wrapped with ferrocement on three sides are tested under pure torsional loading. The different categories of beams tested in this investigation are under-reinforced beams, partially over-reinforced beams (longitudinal and transverse) and completely over-reinforced beams. The variations of U wraps considered in this investigation are three, four and five layers of mesh reinforcement in the ferrocement. The test results indicate that the cracking torque does not depend on the number of mesh layers present in the ferrocement wrapping. Ferrocement wrapping is more effective in the post-cracking stage than in the pre-cracking stage. The increase in the number of mesh layers in the ferrocement increases the ultimate torsional strength of the wrapped beam irrespective of the categories mentioned. The proposed analytical model is capable of predicting the torsional response with reasonable accuracy.

Bending-shear response of self-consolidating and high-performance reinforced concrete beams

The shear strength and the fracture behavior of self-compacting reinforced concrete (RC) beams were investigated. Beams with and without shear reinforcement (stirrups) made with self-consolidating as well as normal vibrated concrete (both ordinary and high-performance) were tested in four-point bending considering four shear arm ratios (a – shear span/d – distance from extreme compression fiber to centroid of tension reinforcement=1.5, 2.5, 3.5, 4.5). The response of RC beams was assessed based on the results of crack patterns, load at first cracking, ultimate shear capacity, and failure modes. Comparisons with similar tests on normal vibrated concrete beams show that self-compacting concrete beams exhibit similar shear strength associated with a more brittle behavior. Finally, the code-based shear resistance predictions for RC beams are considered. While Eurocode 2 predictions exhibit, in terms of shear strength, a lower bound of the experimental results, the crack spacing is not accurately predicted by code specification.

Numerical Analysis on the Load-Carrying Capacity for the FRP Reinforced Four-Point Bending Concrete Beam

In this paper, different types of debonding failure modes are described. Study of concrete cracking behavior and interfacial debonding fracture in fiber reinforced polymer (FRP)-strengthened concrete beams are carried out. A finite element analysis is performed to investigate the different types of debonding propagation along FRP–concrete interface and crack distribution in concrete. The proposed FE, denoted as FRP–FB (force-based) beam, is used to predict the load-carrying capacity and the applied load-midspan deflection response of RC beams subjected to four-point bending loading. Numerical simulations and experimental measurements are compared based on numerous tests available in the literatures and published by different authors. The numerically simulated responses agree remarkably well with the corresponding experimental results. It demonstrates that the proposed two-dimensional frame finite element (FE) is able to accurately estimate the load-carrying capacity of reinforced concrete (RC) beams flexurally strengthened with externally bonded fibre reinforced polymer (FRP) strips and plates.

Numerical prediction of dynamic response of RC beams

In this study, an attempt has been made to develop a finite-element numerical procedure for the non-linear transient dynamic analysis of reinforced concrete (RC) beams. New material constitutive relationships have been employed depending on various experimental data. Eight-node serendipity degenerated plate elements have been used to represent the concrete beam elements. A layered approach was adopted to discretise the concrete and steel reinforcement through the thickness of the beam. Strain-hardening plasticity and elastic perfectly plastic models have been used to model the compressive behaviour of the concrete used in this study. Strain rate effect was included by assuming the dynamic yield function to be a function of the current strain rate in addition to being the total plastic strain. Geometrical non-linearity in the layered approach is considered in the mathematical model, which is based on the total Lagrangian approach taking into account Von Karman assumptions. A new model is used to consider the effect of tension stiffening in the cracked concrete. Steel reinforcement is considered as an elastic plastic material with linear strain hardening. Implicit Newmark with a corrector–predictor algorithm is employed for time integration of the equation of the motion. A computer program coded in MATLAB has been developed for the non-linear finite-element dynamic analysis of RC beams subjected to the dynamic loadings. Finally, various numerical examples validating the proposed formulation are given.

Nonlinear Analysis of Shear-Critical Reinforced Concrete Beams Using Fixed Angle Theory

This paper proposes a solution methodology for the application of the fixed-angle theory to predict the shear response of reinforced concrete (RC) beams subjected to the combined actions of shear and flexure. The proposed solution, based on the fixed-angle theory, takes into account the effect of flexural moment on the shear strength of RC beams and calculates the concrete constitutive relationships by transforming the concrete stresses and strains from the principal direction of concrete stresses to that of the applied stresses. To verify the effectiveness of the proposed solution method, seven shear-critical RC beams were tested and their corresponding experimental shear stress-strain relationships were compared with the predicted ones by using the proposed methodology. Furthermore, the shear strengths of 150 RC test beams, reported in the literature with various shear span-to-depth ratios, steel reinforcing ratios, and support conditions, were compared with the predicted shear strengths obtained by the proposed method and other existing truss models. The results presented in this paper show that the proposed formulation can predict the shear response of RC beams with reasonable accuracy.

Nonlinear analysis of reinforced concrete beams strengthened with polymer composites

Strengthening of existing old structures has traditionally been accomplished by using conventional materials and techniques, viz., externally bonded steel plates, steel or concrete jackets, etc. Alternatively, fibre reinforced polymer composite (FRPC) products started being used to overcome problems associated with conventional materials in the mid 1950s because of their favourable engineering properties. Effectiveness of FRPC materials has been demonstrated through extensive experimental research throughout the world in the last two decades. However there is a need to use refined analytical tools to simulate response of strengthened system. In this paper, an attempt has been made to develop a numerical model of strengthened reinforced concrete (RC) beams with FRPC laminates. Material models for RC beams strengthened with FRPC laminates are described and verified through a nonlinear finite element (FE) commercial code, with the help of available experimental data. Three dimensional (3D) FE analysis has been performed by assuming perfect bonding between concrete and FRPC laminate. A parametric study has also been performed to examine effects of various parameters like fibre type, stirrup`s spacing, etc. on the strengthening system. Through numerical simulation, it has been shown that it is possible to predict accurately the flexural response of RC beams strengthened with FRPC laminates by selecting an appropriate material constitutive model. Comparisons are made between the available experimental results in literature and FE analysis results obtained by the present investigators using load-deflection and load-strain plots as well as ultimate load of the strengthened beams. Furthermore, evaluation of crack patterns from FE analysis and experimental failure modes are discussed at the end.