Ct Morley

Precracked Reinforced Concrete T-Beams Repaired in Shear with Prestressed Carbon Fiber-Reinforced Polymer Straps

The results of an experimental and numerical investigation involving unstrengthened reinforced concrete (RC) T-beams and precracked RC T-beams strengthened in shear with prestressed carbon fiber-reinforced polymer (CFRP) straps are presented and discussed. The results provide insights into the influence of load history and beam depth on the structural behavior of both unstrengthened and strengthened beams. The strengthened beams exhibited capacity enhancements of 21.6 to 46% compared to the equivalent unstrengthened beams, demonstrating the potential effectiveness of the prestressed CFRP strap system. Nonlinear finite element (FE) predictions, which incorporated the load history, reproduced the observed experimental behavior but either underestimated or overestimated the post-cracking stiffness of the beams and strap strain at higher load levels. These limitations were attributed to the concrete shear models used in the FE analyses.

Precracked Reinforced Concrete T-Beams Repaired in Shear with Bonded Carbon Fiber-Reinforced Polymer Sheets

This study investigates the structural behavior of precracked reinforced concrete (RC) T-beams strengthened in shear with externally bonded carbon fiber-reinforced polymer (CFRP) sheets. It reports on seven tests on unstrengthened and strengthened RC T-beams, identifying the influence of load history, beam depth, and percentage of longitudinal steel reinforcement on the structural behavior. The experimental results indicate that the contributions of the external CFRP sheets to the shear force capacity can be significant and depend on most of the investigated variables. This study also investigates the accuracy of the prediction of the fiber-reinforced polymer (FRP) contribution in ACI 440.2R-08, UK Concrete Society TR55, and fib Bulletin 14 design guidelines for shear strengthening. A comparison of predicted values with experimental results indicates that the guidelines can overestimate the shear contribution of the externally bonded FRP system.

Application of virtual ant algorithms in the optimization of CFRP shear strengthened precracked structures

Many engineering applications often involve the minimization of objective functions. The optimization becomes very difficult when the objective functions are either unknown or do not have an explicit form. This is certainly the case in the strengthening of existing precracked reinforced concrete structures using external carbon fibre reinforced polymer (CFRP) reinforcement. For a given concrete structure, the identification of the optimum strengthening system is very important and difficult, and depends on many parameters including the extent and distribution of existing cracks, loading capacity, materials and environment. The choice of these parameters essentially forms a coupled problem of finite element analysis and parameter optimization with the aim of increasing the serviceability of the structure concerned. In this paper, virtual ant algorithms combined with nonlinear FE analysis are used in the optimization of the strengthening parameters. Simulations show that the location and orientation of the CFRP reinforcement has a significant influence on the behaviour of the strengthened structure. The orientation of the reinforcement with a fixed location becomes optimal if the reinforcing material is placed perpendicular to the existing crack direction. The implication for strengthening will also be presented.

Phased Nonlinear Finite-Element Analysis of Precracked RC T-Beams Repaired in Shear with CFRP Sheets

AbstractPhased nonlinear finite-element (FE) analyses were carried out to predict the behavior of precracked reinforced concrete (RC) T-beams repaired in shear with externally bonded (EB) carbon fiber–reinforced polymer (CFRP) sheets and subjected to two loading patterns (LPs). Appropriate constitutive relationships were employed to model the behavior of concrete, internal steel reinforcement, EB CFRP reinforcement, and CFRP-to-concrete interface and consequently predict the structural behavior and capture the failure modes of the strengthened beams. Three constitutive models for the behavior of concrete in shear were evaluated, namely, a total strain rotating crack model and two fixed-angle crack models with either constant or variable shear retention factors. The majority of published FE studies have considered rectangular sections that were strengthened before testing. The key feature of the FE models presented in this paper is the use of the phased-analysis technique to model realistically the process...

A plasticity model for punching shear of laterally restrained slabs with compressive membrane action

Abstract A plastic theoretical model is presented for the punching shear failure of laterally restrained concrete slabs, in which a parabolic Mohr failure criterion for concrete is adopted. The proposed method allows for the effect of compressive membrane action and a membrane-modified flexural theory of elasto-plasticity is used to calculate the compressive membrane forces. The predictions by the proposed analysis show good agreement with a wide range of experimental test results.

Modified Push-Off Testing of an Inclined Shear Plane in Reinforced Concrete Strengthened with CFRP Fabric

AbstractThis study reports the findings of an experimental investigation into the behavior of an inclined shear plane in reinforced concrete, such as a diagonal crack in the web of a beam, strengthened with externally bonded carbon fiber–reinforced polymer (CFRP) fabric. A modified push-off test of novel geometry was developed for this study. This test generates a diagonal failure plane subject to combined shear and tension. Both unwrapped and wrapped tests were conducted, allowing the load sharing and load-displacement behavior of the reinforced concrete, and the reinforced concrete with externally bonded CFRP fabric, to be investigated. Fully wrapped and U-wrapped CFRP fabric configurations were tested. Results indicate that for the arrangement tested, concrete, steel, and CFRP contributions to resistance are not independent, and that effective anchorage lengths given in the United Kingdom and United States guidance for U-wrapped CFRP may not be adequate in some cases.

STRENGTH AND BEHAVIOR IN SHEAR OF CONCRETE BEAM-AND-SLAB BRIDGES

Shear tests on four concrete beam-and-slab bridge specimens are reported. Quantities of longitudinal steel and shear stirrups were varied in an attempt to determine the strength and behavior in shear. These tests show that significant enhancement in shear strength of the beams is provided by the surrounding concrete slab. In addition, critical shear collapse mechanisms are described. These failure patterns have been used as the basis for an upper-bound plasticity approach to the problem of shear assessment of concrete beam-and-slab bridges.

Data supporting - Strut-and-tie models for deteriorated reinforced concrete half joints, Desnerck, Lees & Morley

This is the data supporting the publication - Strut-and-tie models for deteriorated reinforced concrete half joints, Desnerck, Lees & Morley to be published in Engineering Structures

Research Data Supporting "Experimental investigation of reinforced concrete T-beams strengthened in shear with externally bonded CFRP sheets"

Force-displacement, shear stress-normalised displacement and CFRP strain gauge data are provided.

Impact of Material Deterioration on the Strength of Reinforced Concrete Half-Joint Structures

Summary During the 1960’s and 1970’s a number of reinforced concrete (RC) bridges were constructed with ‘half-joints’ introduced into bridge decks. A half-joint is a particular type of RC structure that was introduced into bridge decks as a means of simplifying the design and construction operations. However, a major disadvantage is that there are problems associated with leakage of water through the joint leading to concrete deterioration and corrosion of the reinforcement. When assessing the integrity of existing half-joint structures, determining the influence of material deterioration and/or repair works is a challenge as current code provisions or guidelines do not pro-vide guidance on how to take any associated strength losses into consideration. This paper focusses on the impact of changes in the material properties (such as compressive strength, yield strength of the reinforcement, reinforcement bar diameter, etc.) on the load bearing capacity of reinforced half-joint structures. The vulnerability of a typical half-joint design to these changes is analysed using finite element models. The results allow designers, assessors and decision makers to better quantify the impact of observed deterioration phenomena on the predicted strength of the studied half-joint.