Mohamed A. ElGawady

Retrofitting of Rectangular Columns with Deficient Lap Splices

The cyclic behavior of eight 0.4-scale reinforced concrete column specimens is investigated. The columns incorporated deficient design details to simulate bridge columns built in Washington State prior to 1971. Two columns were tested as reference specimens, five were tested after retrofitting using carbon fiber-reinforced polymer CFRP, and one was tested after retrofitting using a conventional steel jacket. All the specimens were tested under constant gravity load and incrementally increasing lateral loading cycles. The specimens had rectangular cross sections with aspect ratios of 1.5 and 2.0. The parameters investigated included the amount of CFRP reinforcement, different retrofitting jacket configurations, and different retrofitting materials. For the as-built specimens, two modes of failure occurred, namely low cyclic fatigue of longitudinal reinforcement and lap splice failure. For the retrofitted specimens, no lap splice failure was observed. All the retrofitted specimens failed due to low cyclic fatigue failure of the longitudinal bars. The retrofitting measures improved the displacement ductility, energy dissipation, and equivalent viscous damping. In addition, increasing the amount of CFRP reinforcement improved the performance of the test specimens.

Effects of Tendon Spacing on In-Plane Behavior of Posttensioned Masonry Walls

AbstractIn-plane behavior of unbonded posttensioned clay brick masonry walls are investigated using detailed finite-element (FE) models. FE models of three walls having different aspect ratios of 1.50, 1.00, and 0.67 are developed. Effects of tendon spacing on in-plane behavior of these walls are investigated using different tendon spacings ranging from 0.61xa0m (2xa0ft) to 3.81xa0m (12.5xa0ft). In addition, the effects of having different horizontal reinforcement ratios of 0%, 0.1%, and 0.5% on the in-plane behavior of the walls were investigated. The stresses in the tendons are calculated using different approaches, and then the flexural strength of each wall is calculated and compared with those obtained from the numerical analysis. The simulation results show that for spacing between tendons up to 2xa0m (6.6xa0ft), ignoring the elongation in the tendon in calculating the flexural strength results in too conservative design. For these walls, it is more appropriate to use equations provided by the Masonry Standard ...

Strain Rate Effect on Properties of Rubberized Concrete Confined with Glass Fiber–Reinforced Polymers

AbstractRubberized concrete possesses viscous damping that is higher than that of conventional concrete, making it a promising candidate for construction in high seismic regions. Confining rubberized concrete with glass fiber–reinforced polymers (GFRP) may result in superior performance. This paper investigates the behavior of rubberized-concrete-filled fiber-reinforced polymer tubes (RCFFT) under different strain rates. The rubberized concrete had 0, 10, and 20% volume replacement of fine aggregate with shredded rubber. Each test specimen’s behavior was compared to that of conventional concrete-filled fiber-reinforced polymer tubes (CFFT). The GFRP tubes were fabricated using wet-layup with different numbers of GFRP layers. Three different strain rates (representing static, earthquake, and severe earthquakes) were used to test these specimens under cyclic axial loading. The RCFFT behaved in a manner that was similar to conventional CFFTs. The rubberized concrete’s confinement limited the reduction in the...

Strength and Seismic Performance Factors of Posttensioned Masonry Walls

AbstractIn this study, the behavior of posttensioned masonry walls is investigated using a database of 31 tested walls. The accuracy of the current Masonry Standards Joint Committee (MSJC) in evaluating the strength of posttensioned masonry walls is studied using the available test results. Moreover, using the experimental results, the seismic performance factors including ductility, response modification factor, and displacement amplification factor are determined for different types of walls including fully grouted, partially grouted, ungrouted walls, walls with confinement plates, walls with supplemental mild steel, and walls with an opening. As a result of this study, it was determined that the MSJC underestimates the strength of fully grouted unbonded posttensioned walls by about 20%. Using the strain compatibility method to determine the flexural capacity of bonded masonry walls resulted in reasonable predictions of strength. Moreover, an average response modification factor of 4.27 to 7.76 and disp...

Experimental Investigation of In-Plane Cyclic Response of Unbonded Posttensioned Masonry Walls

AbstractThis paper reports on an experimental study on four unbonded posttensioned masonry walls (PT-MWs). All walls had identical thickness, height, and length of 190, 2,000, and 1,400xa0mm, respectively, and were constructed using concrete masonry units (CMUs) and mortar type N, and were fully grouted. Different horizontal spacing values of 400, 600, and 1,200xa0mm were used between the posttensioning bars in the walls. Only Wall W4 had horizontal bonded reinforcement, located in the fourth and seventh courses. Two different levels of posttensioning force corresponding to an average posttensioning compressive axial stress on the masonry of 1.35 and 2.7xa0MPa were applied to the walls. Different initial posttension stresses in the bars ranging from 0.32 to 0.63 of the yield stress of each bar were applied to the walls. The walls were subjected to incrementally increasing in-plane lateral displacement cyclic load applied to the top of each wall. The experimental results including damage pattern, force displacem...

Behavior of Hollow-Core Steel-Concrete-Steel Columns Subjected to Torsion Loading

AbstractThe torsional behavior of hollow-core steel-concrete-steel (HC-SCS) columns is presented using finite-element (FE) and analytical approaches. The HC-SCS columns consist of a concrete shell sandwiched between two steel tubes. Software was used to develop a three-dimensional model of an HC-SCS column that was subjected to torsional loading. The FE results were validated against the experimental results collected from six HC-SCS columns tested under pure torsion. The average error from the FE analysis was 4.8%, compared with experimental results, when predicting the column’s torsion strength. The study revealed that the interaction between the steel tube’s stiffness and concrete shell’s thickness controls the behavior of the column. A parametric study was conducted to further analyze each parameter affecting the column’s torsion behavior. The parametric analysis concluded that the torsional behavior of the column mainly depends on the outer steel tube’s properties and the thickness of the concrete sh...

Seismic Performance of Innovative Hollow-Core FRP–Concrete–Steel Bridge Columns

Abstract This paper presents the seismic behavior of hollow-core fiber-reinforced polymer–concrete–steel (HC-FCS) columns. The typical HC-FCS column consists of a concrete wall sandwiched between an outer fiber-reinforced polymer (FRP) tube and an inner steel tube. The inner steel and outer FRP tubes provide continuous confinement for the concrete shell; hence, the concrete shell achieves significantly higher strain, strength, and ductility than unconfined concrete in conventional columns. Three large-scale HC-FCS columns were investigated in this study. Each column had an outer diameter of 610 mm (24 in.) and a height-to-diameter ratio of 4.0. The steel tube was embedded into a reinforced concrete footing with an embedded length of 1.6–1.8 times the steel tube diameter, whereas the FRP tube only confined the concrete wall thickness and truncated at the top of the footing level. In general, the columns exhibited high lateral drift, reaching to 11.6%, and failed gradually as a result of concrete crushing a...

Seismic-Resistant Bridge Columns with Ultrahigh-Performance Concrete Segments

AbstractThe flexural capacity of a well-designed RC column deteriorates under extreme ground motion as a result of crushing of the core concrete and buckling of the longitudinal bars in the plastic hinge regions. Thus, it is important to minimize damage at the plastic hinge region to develop high-performance bridge columns. A column that uses ultrahigh-performance concrete (UHPC) segments at the plastic hinge region is proposed to address this issue. Three reduced-scale columns were constructed and tested at the Tokyo Institute of Technology in Japan. Two of the columns with different plastic hinge details were investigated using bilateral cyclic loading. The first column had a reinforced concrete core encased in an UHPC jacket. The second column had an UHPC hollow-core plastic hinge combined with posttensioning. Both columns were designed to have approximately the same nominal strength. They were tested under orbital bilateral cyclic loading customized to impose flexural deformations and investigate the ...

Dynamic and Static Behavior of Hollow-Core FRP-Concrete-Steel and Reinforced Concrete Bridge Columns under Vehicle Collision

This paper presents the difference in behavior between hollow-core fiber reinforced polymer-concrete-steel (HC-FCS) columns and conventional reinforced concrete (RC) columns under vehicle collision in terms of dynamic and static forces. The HC-FCS column consisted of an outer FRP tube, an inner steel tube, and a concrete shell sandwiched between the two tubes. The steel tube was hollow inside and embedded into the concrete footing with a length of 1.5 times the tube diameter while the FRP tube stopped at the top of footing. The RC column had a solid cross-section. The study was conducted through extensive finite element impact analyses using LS-DYNA software. Nine parameters were studied including the concrete material model, unconfined concrete compressive strength, material strain rate, column height-to-diameter ratio, column diameter, column top boundary condition, axial load level, vehicle velocity, and vehicle mass. Generally, the HC-FCS columns had lower dynamic forces and higher static forces than the RC columns when changing the values of the different parameters. During vehicle collision with either the RC or the HC-FCS columns, the imposed dynamic forces and their equivalent static forces were affected mainly by the vehicle velocity and vehicle mass.

Behavior of Hollow-Core FRP-Concrete-Steel Columns under Static Cyclic Flexural Loading

AbstractThis paper presents the seismic behavior of hollow-core fiber-reinforced polymer (FRP)-concrete-steel (HC-FCS) columns comparable with the conventional RC column. The typical HC-FCS column ...