Softening Coefficient of Reinforced Concrete Elements Subjected to Three-Dimensional Loads

Reinforced concrete structures are prone to fail under the effect of complex threedimensional loading conditions. Accurate constitutive models for concrete under the effect of triaxial stresses are therefore necessary in order to predict the proper response. Strong interaction between in-plane and out of plane shear loads has been observed in experimental tests of concrete structures. This paper presents the derivation of concrete constitutive laws under the effect of triaxial stresses, in particular the softening coefficient, using the results of large-scale tests on representative concrete panels. The experimental program of 7 full-scale panel specimens is briefly described, and the results are then used to derive analytical expressions for the softening coefficient under the effect of bi-directional shear. Finally, existing membrane shear theories are modified to take into consideration the effect of applied out-of-plane shear. The response of the tested panels proved to be accurately predicted using the new theory

Behavior of Reinforced Concrete Membrane Elements Subjected to Bidirectional Shear Loads

The shear design and behavior of a typical membrane reinforced concrete (RC) element has been extensively studied in the past several decades. Such design requires knowledge of the constitutive behavior of RC elements subjected to a shear stress acting along its plane (in-plane shear). These constitutive models were accurately derived from experimental test data on representative RC panel elements. The true behavior of many large, complex structures, however, involves interaction between the in-plane and out-of-plane shear stresses acting on the RC element. To investigate this interaction, large-scale tests on representative concrete panels need to be conducted. The University of Houston is equipped with a unique universal panel testing machine that was used for this purpose. The panel tester enhanced the understanding of the in-plane shear behavior of RC elements. Recently, 10 additional hydraulic jacks were mounted in the out-of-plane direction of the universal panel tester to facilitate testing of concrete elements subjected to bidirectional and tridirectional shear stresses. The experimental program included designing, fabricating, instrumenting, and testing full-scale RC elements. The elements were subjected to different combinations of in-plane and out-of-plane shear loads. A strong interaction between in-plane shear strength and out-of-plane shear stresses was observed

Influence of Fiber-Reinforced Polymer Sheets on the Constitutive Relationships of Reinforced Concrete Elements

Fiber-reinforced polymer (FRP) started to find its way as an economical alternative material in civil engineering in the early 1970s. The behavior and failure modes for FRP composite structures were studied through extensive experimental and analytical investigations. Although research related to the flexural behavior of FRP-strengthened elements has reached a mature phase, studies related to FRP shear strengthening are less advanced. In all proposed models to predict shear capacity, the constitutive behaviors of concrete and FRP are described independently. The true behavior, however, should account for the high level of interaction between the two materials. Constitutive relations for FRP-strengthened reinforced concrete (RC) elements should provide a better understanding of the shear behavior of the composite structure. To generate these relations, large-scale tests of a series of FRP-strengthened RC panel elements subjected to pure shear were conducted. This paper presents the results of the test program and the calibration of the parameters of the constitutive model. These constitutive laws could easily be implemented in finite-element models to predict the behavior of externally bonded FRP-strengthened beams. The focus in this work is on elements failing because of concrete crushing and not because of FRP debonding. The newly developed model provides a good level of accuracy when compared with experimental results

Baseline formation for damage diagnosis in one dimensional-beam problems

A brief account of the theories behind modal analysis, dimensional analysis, the stereolithography process and the strain energy damage detection method is presented. An integrated system of those techniques is formulated to diagnose damage in beam-like structures. Damage diagnoses include detecting the defect and then localizing it. In the absence of a baseline for the pre-damaged structures, an attempt is made to create one, analytically, using dimensional analysis and physically using stereolithography. First, a preliminary diagnosis check is performed using shift in natural frequency. In this process, the expected natural frequencies obtained using dimensional analysis are compared to those obtained experimentally. The existence of frequency shift is statistically verified. Secondly, using stereolithography synthesized baselines and strain energy method damage is localized by observing the area of strain energy increase

Characterization Of The Orthotropic Elastic Constants Of A Micronic Woven Wire Mesh Via Digital Image Correlation

Woven structures are steadily emerging as excellent reinforcing components in dual-phase composite materials subjected to multiaxial loads, thermal shock, and aggressive reactants in the environment. Metallic woven wire mesh materials in particular display good ductility and relatively high specific strength and specific resilience. While use of this class of materials is rapidly expanding, a significant gap in property characterization remains. This research classifies the homogenized, orthotropic material properties of a representative twill dutch woven wire mesh through the use of in-plane uniaxial tensile experiments incorporating a Digital Image Correlation (DIC) strain measurement technique. Values for elastic modulus and Poisson\u27s ratio are calculated from the experimental data, and shear modulus values are identified by means of constitutive modeling. This approach establishes a reproducible method for characterizing the in-plane elastic response of micronic metallic woven materials via macro-scale uniaxial tensile tests, and shows that a homogenous orthotropic constitutive model may be employed to describe the macro-scale elasticity of this class of materials with reasonable accuracy. © 2013 Society for Experimental Mechanics

Characterization of the Orthotropic Elastic Constants of a Micronic Woven Wire Mesh via Digital Image Correlation

Woven structures are steadily emerging as excellent reinforcing components in dual-phase composite materials subjected to multiaxial loads, thermal shock, and aggressive reactants in the environment. Metallic woven wire mesh materials in particular display good ductility and relatively high specific strength and specific resilience. While use of this class of materials is rapidly expanding, a significant gap in property characterization remains. This research classifies the homogenized, orthotropic material properties of a representative twill dutch woven wire mesh through the use of in-plane uniaxial tensile experiments incorporating a Digital Image Correlation (DIC) strain measurement technique. Values for elastic modulus and Poisson\u27s ratio are calculated from the experimental data, and shear modulus values are identified by means of constitutive modeling. This approach establishes a reproducible method for characterizing the in-plane elastic response of micronic metallic woven materials via macro-scale uniaxial tensile tests, and shows that a homogenous orthotropic constitutive model may be employed to describe the macro-scale elasticity of this class of materials with reasonable accuracy. © 2013 Society for Experimental Mechanics