Hussein M. Elsanadedy

Experimental and Numerical Study for the Shear Strengthening of Reinforced Concrete Beams Using Textile-Reinforced Mortar

In this paper, the effectiveness of textile-reinforced mortars (TRMs), as a means of increasing the shear resistance of reinforced concrete beams, is experimentally and numerically investigated. Textiles comprise of fabric meshes made of long woven, knitted or even unwoven fiber rovings in at least two (typically orthogonal) directions. Mortars—serving as binders—may (or may not) contain polymeric additives usually used to have improved strength properties. These TRMs may be considered as an alternative to fiber-reinforced polymers (FRP), providing solutions to many of the problems associated with application of the latter without compromising much of the performance of strengthened members. In the present study, a new type of textile (basalt-based textile) was used as strengthening material. Two different mortar types’ viz. cementitious and polymer-modified cementitious mortars were used as binding material for the textile sheets. The studied parameters also included the number of textile layers as well as the orientation of the textile material. The experimental program comprises of testing two control beams which were intentionally designed to be deficient in shear, in addition to testing eight beams which were externally upgraded by TRM sheets for enhancing their shear capacity. On the basis of the experimental response of reinforced concrete members strengthened in shear, it is concluded that textile-mortar composite provides substantial gain in shear resistance; this gain is higher as the number of layers increases. With higher number of layers, textile with 45° orientation along with polymer-modified cementitious mortar provides the highest shear strength enhancement. Nonlinear finite-element (FE) analysis was also carried out on the tested beams using LS-DYNA, which is transient nonlinear dynamic analysis software. The numerical analysis carried out involved case studies for TRM modeled, with and without mortar. Good agreement was achieved between the experimental and numerical results especially for the ultimate load carrying capacity for the case of FE models incorporating mortar. The study was extended numerically to include additional cases of TRM-strengthened specimens with more number of TRM layers as well as a case of FRP-strengthened specimen.

Textile-Reinforced Mortar versus FRP as Strengthening Material for Seismically Deficient RC Beam-Column Joints

In this paper, efficiency and effectiveness of textile-reinforced mortars (TRM) on upgrading the shear strength and ductility of a seismically deficient exterior beam-column joint has been studied. The results are then compared with that of carbon fiber-reinforced polymer (CFRP) and glass fiber-reinforced polymer (GFRP)-strengthened joint specimens. Five as-built joint specimens were constructed with nonoptimal design parameters (inadequate joint shear strength with no transverse reinforcement) representing an extreme case of preseismic code design construction practice of joints and encompassing the vast majority of existing beam-column connections. Out of these five as-built specimens, two specimens were used as baseline specimens (control specimens) and the other three were strengthened with TRM, CFRP, and GFRP sheets, respectively. All five subassemblages were subjected to quasi-static cyclic lateral load histories to provide the equivalent of severe earthquake damage. The response histories of control and strengthened specimens were then compared. The test results demonstrated that TRM can effectively improve both the shear strength and deformation capacity of seismically deficient beam-column joints to an extent that is comparable to the strength and ductility achieved by well-established CFRP, and GFRP-strengthening of joints.

Effect of blast loading on CFRP-Retrofitted RC columns - a numerical study

This study aims to investigate the effect of blast loads generated as a result of explosive charges on the existing exterior RC circular columns of a typical building in the city of Riyadh. A procedure has been developed for evaluating the dynamic characteristics of the circular column with and without retrofitting. A wide range of parametric studies have been performed as part of this investigation to examine the effects of stand-off distance, charge weight and the presence of CFRP retrofitting on the level of damage to the RC column. The nonlinear finite element analysis was carried out using LS-DYNA software with explicit time integration algorithms. Different charge weights of 100, 200, 500 and 1000 kg equivalent weight of TNT at stand-off distances of 1, 4 and 15 m were considered. Results described in this paper indicate that CFRP strengthening could be an effective solution to limit the damage caused by moderate explosions. The stand-off distance was found to play a very important role in mitigating the adverse effects of a blast. The results also indicate that the maximum lateral deflection experienced by the column decreased exponentially with the increase in the stand-off distance and also decreased for the columns strengthened with CFRP, compared with the unstrengthened columns.

Seismic Design Guidelines for Squat Composite- Jacketed Circular and Rectangular Reinforced Concrete Bridge Columns

Lack of shear reinforcement in older squat reinforced concrete (RC) bridge columns caused brittle shear failures during past earthquakes. This article reports on an object-oriented computer code, based on a moment-curvature analysis with inclusion of fiber-reinforced polymer-confined concrete models, that was developed to predict the seismic performance of reinforced concrete squat bridge columns. The study involved the seismic assessment of 65 as-built shear-deficient columns in addition to the performance prediction of ductile composite-jacketed columns. For the composite-jacketed columns, the developed software was calibrated through a parametric study of two displacement models and six different concrete confinement models. Subsequently, the authors devised a methodology for the seismic design of shear-deficient columns upgraded with composite-material jackets. The authors conclude that the UCSD shear strength model provides the best correlation with all experimental data.

Seismic design criteria for circular lap-spliced reinforced concrete bridge columns retrofitted with fiber-reinforced polymer jackets

This article reports on the development of an object-oriented computer code that can be used for predicting the behavior of circular lap-spliced bridge columns retrofitted with advanced composite-material (fiber-reinforced polymer) jackets. The authors begin by explaining the need for adequate retrofitting of circular bridge columns, particularly in earthquake-prone areas such as California. The numerical model used is based on a moment-curvature analysis of the column section with the inclusion of bond-slip mechanism and fiber-reinforced polymer-confined concrete models. The authors calibrated the software through a parametric study comparing the experimental and predicted results for different test data available in the literature. Accordingly, an optimum computational tool was developed to accurately predict the performance of all columns. The authors conclude that, in the proposed design approach, jacket thickness within the lap-splice zone will be the greater of: requirement for confinement of the compression concrete, anti-buckling constrain, and requirement for clamping on the lap-splice region.

Prediction of Intermediate Crack Debonding Strain of Externally Bonded FRP Laminates in RC Beams and One-Way Slabs

Interface crack propagation of FRP (fiber-reinforced polymer) strengthened reinforced concrete (RC) flexural member is often initiated from the toes of the intermediate cracks and propagates towards the supports. This type of FRP delamination is commonly termed intermediate crack (IC) debonding and is common for flexural members with high shear span-to-depth ratios. If the ultimate FRP strain at IC debonding failure is known, the moment capacity of the member can be obtained through a simple section analysis. This research deals with the prediction of ultimate FRP strain at IC debonding, using neural networks and regression models. Basic information on neural networks and the types of neural networks most suitable for the analysis of experimental results are given. A set of experimental data for FRP-strengthened RC beams and one-way slabs, covering a large range of parameters, for the training and testing of neural networks is used. The available test results were not only compared with current code provisions but with equations proposed by other researchers as well. The prediction models based on neural network are presented. A new design equation is also suggested.

Progressive Collapse Analysis of RC Buildings Against Internal Blast

This paper seeks to explore the vulnerability of a typical reinforced concrete (RC) building against progressive collapse as a consequence of internal blast. The emphasis has been on the local model analysis for which two approaches – one involving the use of CONWEP and another using fluid-structure interaction through Alternate Lagrangian Eulerian (ALE) element formulation - have been employed. The finite element model of the structure was created using LS-DYNA, which uses explicit time integration algorithms for solution. The results of the study are proposed to be used to control or prevent progressive collapse of the building. In order to validate the employed numerical models, blast test results of a RC column available in literature were validated using LS-DYNA modeling of the RC column. The deformation response of the column was compared which showed acceptable prediction.

Effect of Longitudinal Steel Ratio on Behavior of RC Beams Strengthened with FRP Composites: Experimental and FE Study

AbstractThis study experimentally and numerically investigates the effect of longitudinal steel ratio on the flexural performance of RC beams externally strengthened with fiber-reinforced polymer (FRP) composites. The experimental program consisted of testing 11 beams under four-point bending until failure. Each beam was duplicated to verify the repeatability of the results. Three beams were tested as control specimens; the remaining eight beams were externally strengthened in flexure with FRP composites. The primary experimentally studied parameters were longitudinal steel ratio and axial FRP stiffness. Three different steel ratios were examined. For the lowest steel ratio, four different FRP systems with six axial stiffness values were investigated. However, for the other two steel ratios, only one FRP system was studied. In addition to the experimental program, a numerical study utilizing nonlinear finite-element (FE) analysis was conducted. As a result of the numerical study, new FRP stiffness and rei...

Numerical Models for Composite-Jacketed Reinforced Concrete Bridge Columns

This paper describes findings from a comprehensive experimental and analytical study on seismic repair and retrofit of model scale bridge columns using advanced composite-material jackets. This study has two phases. In the first phase, fourteen half-scale circular and rectangular reinforced concrete columns were tested for shear and confinement enhancement in a fixed-fixed condition. Three columns were tested in the as-built condition, while ten columns were tested after being retrofitted with different composite-jacket systems. The last column was tested after being repaired with carbon-epoxy composite jacket. In addition to the experimental study, an object-oriented computer program, based on moment-curvature analysis, was written to predict the seismic behavior of all column data. For as-built columns, the program was used to evaluate different shear strength models. However, for repaired and retrofitted column samples, the program was calibrated through a parametric study on two displacement models and six different concrete confinement models. In the second phase of this study, thirteen half-scale circular and square column models with insufficient lap splice length were tested in flexure under lateral cyclic loading. Three column samples were tested in the as-built configuration, whereas ten column samples were tested after being retrofitted with different composite-jacket systems. Another object-oriented computer code was developed for predicting the behavior of the tested columns. The numerical model is based on a moment-curvature analysis of the column section with the inclusion of a bond-slip mechanism. Three different bond-slip models were utilized in the analysis. The developed software was calibrated through a parametric study comparing the experimental and predicted results.

Behavior and Design Aspects of FRP-Strengthened URM Walls under Out-of-Plane Loading

AbstractThe use of externally bonded fiber-reinforced polymer (FRP) composites for upgrading the out-of-plane flexural resistance of unreinforced masonry (URM) walls is experimentally and analytically investigated in this study. A total of six hollow concrete block walls were tested to failure using an airbag and a reaction frame to obtain a uniform load on the wall. The masonry walls were placed horizontally and tested as one-way slabs with span direction perpendicular to the bed joints. The first wall was left unstrengthened to be used as control specimen; the other five walls were strengthened using different schemes of externally attached glass-fiber-reinforced polymer (GFRP) sheets. The main parameters studied experimentally were FRP reinforcement ratio and stiffness. In addition to the experimental program, an analytical model was developed to predict the ultimate moment capacity of the URM walls. The procedure outlined in standard guidelines was also utilized to compute the flexural capacity of wal...