Khaled Soudki

Long-Term Performance of Corrosion-Damaged Reinforced Concrete Beams

Research is needed to clarify the interaction between the degree of corrosion, the corrosion crack width, and the load carrying capacity in the presence of a sustained load in reinforced concrete (RC) beams having well-anchored steel reinforcement. This article reports on a study that investigated the combined effect of corrosion and sustained loads on the structural performance of nine RC beams (each measuring 152 x 254 x 3200 mm). One beam was tested as a virgin while eight beams were exposed to accelerated corrosion for up to 310 days using an impressed current technique. Four beams were corroded under a sustained load that corresponded to approximately 60% of the yield load of the virgin beam. The four remaining beams were kept unloaded during the corrosion exposure. Test results showed that the presence of a sustained load and associated flexural cracks during corrosion exposure significantly reduced the time to corrosion cracking and slightly increased the corrosion crack width. The presence of flexural cracks during corrosion exposure initially increased the steel mass loss rate and, consequently, the reduction in the beam strength. As time progressed, no correlation between the reduction in the beam strength and the presence of flexural cracks was observed.

Comparison of Two Evolutionary Algorithms for Optimization of Bridge Deck Repairs

Most bridge management systems have been developed to support either network- or project-level decisions. Network-level decisions include the selection of bridges for repair while repair strategies are considered project-level decisions. This article introduces an integrated model for bridge deck repairs with detailed life cycle costs of both network-level and project-level decisions. Two evolutionary-based optimization techniques that are capable of handling large-size problems, namely genetic algorithms and shuffled frog leaping, are then applied on the model to optimize maintenance and repair decisions. Ten trial runs with different numbers of bridges were used to compare the results of both techniques. The results indicate that both techniques can be equally suitable, and that the key issue is determining the set of parameters that optimize performance. The best optimization strategy for this type of problem appears to be a year-by-year strategy coupled with the use of a preprocessing function to allocate repair funds first to critical bridges.

Stress-Strain Model for Fiber-Reinforced Polymer Jacketed Concrete Columns

Fiber-reinforced polymer (FRP) jackets are often used to confine and reinforce concrete columns. This article reports on a study of the stress-strain behavior of FRP-confined concrete columns that focused on rectangular column sections. The authors developed a new design-oriented model of the stress-strain response of FRP confined columns. Their test variables included the volumetric ratio of the FRP jackets, the aspect ratio of the column section, and the area of longitudinal and lateral steel reinforcement. Results showed that jacketing rectangular column sections with FRP sheets increases their axial strength and ductility. FRP jackets can be used to prevent premature failure of the concrete cover and buckling of the steel bars, leading to substantially improved performance. The authors include a discussion of the main parameters that control the stress and strain characteristics of FRP-confined rectangular column sections. They propose a general design model of the stress-strain response of FRP-confined concrete. The authors conclude that the results predicted by this model showed very good agreement with other test data of FRP-confined circular and rectangular columns reported in the literature.

Analytical Model to Predict Nonlinear Flexural Behavior of Corroded Reinforced Concrete Beams

No suitable analysis is presently available to predict the flexural behavior of corroded reinforced concrete (RC) beams. This article presents a new analytical model that predicts the nonlinear flexural behavior of both corroded and newly constructed reinforced concrete beams. The authors first review previous studies in this field, noting deficiencies that required a new model. They then explain how in the proposed model, the deflection of a reinforced concrete beam is calculated from the elongation of the steel reinforcement between flexural cracks rather than from the curvatures of beam sections. This model accounts for the reduction in the steel area and the change in bond strength at the steel-to-concrete interface caused by corrosion. The effect of a loading-unloading cycle on the flexural behavior is also taken into account. The authors also propose a new bond stress-slip model that accounts for the change in bond strength due to corrosion. A comparison of the model’s predictions with experimental results showed that the model accurately predicts the load-deflection curves of both corroded and newly constructed beams.

Front and Side View Image Correlation Measurements on FRP to Concrete Pull-Off Bond Tests

Understanding the transfer of force by bond between externally bonded fiber-reinforced polymer (FRP) reinforcement and concrete is an important step in formulating good models for predicting debonding failures observed in externally bonded reinforcement strengthened systems. In this paper, a 3D optical displacement measurement system was used to capture the full-field displacements from the front and side view in pull-off bond specimens. The experiments were carried using six specimens with carbon FRP (CFRP) strips having different axial stiffnesses but a constant bond length to the concrete substrate. Using the optical measurements, it was possible to obtain the in-plane displacement or slip and the out-of-plane displacement or separation between the CFRP strip and the concrete. It was demonstrated, that the usual assumption of pure shear stresses in such pull-off tests is not true and that the bond behavior is a two-dimensional problem involving shear and peeling stresses. The bond behavior in CFRP stri...

Fatigue Flexural Behavior of Corroded Reinforced Concrete Beams Repaired with CFRP Sheets

This study investigated the flexural behavior of corroded steel reinforced concrete beams repaired with carbon-fiber-reinforced polymer (CFRP) sheets under repeated loading. Thirty beams ( 152×254×2,000 mm ) were constructed and tested. Fatigue flexural failure occurred in 29 of these beams. The study showed that pitting of the steel reinforcement due to corrosion occurred only after about a 7% actual mass loss which coincided with a decrease in the fatigue performance of the beam. The controlling factor for the fatigue strength of the beams is the fatigue strength of the steel bars. Repairing with CFRP sheets increased the fatigue capacity of the beams with corroded steel reinforcement beyond that of the control unrepaired beams with uncorroded steel reinforcement. Beams repaired with CFRP at a medium corrosion level and then further corroded to a high corrosion level before testing had a comparable fatigue performance to those that were repaired and tested after corroding directly to a high corrosion level.

FRCM Strengthening of Shear-Critical RC Beams

AbstractThis paper presents the results of an experimental study conducted to investigate the effectiveness of different types of fabric-reinforced cementitious matrix (FRCM) composite systems to strengthen shear critical reinforced concrete (RC) beams. Seven shear-critical RC beams were tested. The test variables included the strengthening material (glass FRCM or carbon FRCM) and the strengthening scheme (side bonded or u-wrapped). The test results revealed that FRCM strengthening is effective in enhancing the load-carrying capacity of shear-critical RC beams. The increase in load-carrying capacity of the FRCM-strengthened beams ranged between 19 and 105%. Both strengthening schemes (side bonded and u-wrapped) exhibited similar behavior, suggesting that the excellent bond of the FRCM to concrete may not require u-wrapped applications for anchorage. The experimental results were also compared with theoretical predictions according to fiber-reinforced polymer (FRP) design guidelines in North America with s...

NEW SHEAR STRENGTHENING TECHNIQUE FOR CONCRETE SLAB-COLUMN CONNECTIONS

This paper presents an experimental program that involved tests on full-scale RC slab-column edge connections. The aim of this work was to examine a new method for strengthening existing RC slabs for punching shear. The new strengthening technique consists of shear bolts externally installed in holes drilled through the slab thickness. Different configurations of the shear bolts around the column were tested. Four slabs were strengthened and 2 slabs, used as control specimens, did not contain any shear reinforcement. Two of the tested slabs (1 strengthened and 1 control) contained openings in the area of the column. Slab dimensions were 1540 x 1020 x 120 mm with square columns. The openings, where present, were square and directly adjacent to the inner face of the column. The slabs were tested to failure under monotonic vertical shear forces and unbalanced moments. The presence of shear bolts substantially increased the punching capacity and ductility of the connections.

Evaluation of Shear Design Equations of Concrete Beams with FRP Reinforcement

Several codes and design guidelines addressing fiber-reinforced polymer (FRP) bars as primary reinforcement for structural concrete have been recently published worldwide. This reflects the great progress in FRP research area that has been conducted by the research community over the past two decades. Most of these design provisions follow the traditional approach of Vc + Vs for shear design. Nevertheless, both equations of concrete contribution Vc and FRP stirrup contribution Vs to shear strength in these guidelines are different in the manner that they are calculated. In this paper, five methods for FRP shear design, currently used in design practice, were reviewed. These methods include the American Concrete Institute design guide, ACI 440.1R-06; the Canadian Standards Association, CAN/CSA-S806-02; the ISIS Canada design manual, ISIS-M03-07; the British Institution of Structural Engineers guidelines; and the design recommendations of the Japan Society of Civil Engineers. The five methods for shear desi...

Effect of Partial Unbonding on Prestressed Near-Surface-Mounted CFRP-Strengthened Concrete T-Beams

The flexural behavior of RC T-beams strengthened with prestressed near-surface-mounted (NSM) carbon fiber-reinforced-polymer (CFRP) reinforcement was investigated. The specific objective was to study the effect of partial unbonding of the CFRP reinforcement on the beam flexural behavior to increase the deformability. A total of eight RC T-beams were tested under four-point monotonic loading. The main variables were the level of prestressing force in the CFRP bars and the unbonded length at the midspan of the beam. The test results showed that all of the prestressed strengthened beams effectively improved the ultimate load-carrying capacity and the serviceability performance compared to the unstrengthened beam. The partially bonded prestressed beams exhibited an enhancement of the deformability compared to the fully bonded beams while minimizing the reduction of the load-carrying capacity. Partial unbonding was more effective to improve the deformability at higher levels of prestressing force. The general behavior of the partially bonded beams was reasonably well predicted by an analytical model developed previously by the writers.