@article{el-hacha_el-agroudy_rizkalla_2006, title={Bond characteristics of high-strength steel reinforcement}, volume={103}, DOI={10.14359/18227}, abstractNote={This paper summarizes an investigation undertaken to study the bond characteristics of high-strength steel reinforcement bars commercially known as microcomposite, multistructural, formable steel (MMFX). The objective of the investigation is to examine the applicability of the ACT 318-02 equation and a current proposed equation by Zuo and Darwin on bond behavior of steel reinforcement to the concrete member. The experimental program included two phases. The first phase of the experimental program consisted of testing four beam-end specimens reinforced with MMFX steel bars, whereas the second phase included testing eight beam-splice specimens reinforced with MMFX steel bars. The selected four factors considered in this study were bar size, level of confinement, bonded length, and bar cast position. The bond behavior of the MMFX steel bars was found to be similar to that of conventional Grade 420 MPa (60 ksi) steel up to the proportional limit of 550 MPa (80 ksi). The bond strength of the MMFX significantly changes as the tensile stresses developed in the bar exceed the proportional limit. The test results indicated that both the AC! 318-02 equation and the current proposed equation by Zuo and Darwin on bond are adequate and resulted in conservative prediction at low stress levels up to 550 MPa (80 ksi). At high stress levels, however, the prediction using both equations is unconservative due to the nonlinear behavior of the MMFX stress-strain relationship. Based on the limited number of specimens considered in this study, modification to both the AC1 318-02 equation and the Zuo and Darwin equation is proposed to predict the bond forces beyond the proportional limit for MMFX steel bars.}, number={6}, journal={ACI Structural Journal}, author={El-Hacha, R. and El-Agroudy, H. and Rizkalla, S. H.}, year={2006}, pages={771–782} }
 @article{el-hacha_rizkalla_2004, title={Near-surface-mounted fiber-reinforced polymer reinforcements for flexural strengthening of concrete structures}, volume={101}, DOI={10.14359/13394}, abstractNote={Use of fiber-reinforced polymer (FRP) materials to strengthen bridges has been adopted extensively in the last decade. FRP has been used in different configurations and techniques to use the material effectively and to ensure long service life of the selected system. One of these innovative strengthening techniques is near-surface mounting (NSM) that consists of placing FRP reinforcing bars or strips into grooves precut into the concrete cover in the tension region of the strengthened concrete member. This method is relatively simple and considerably enhances the bond of the mounted FRP reinforcements, thereby using the material more effectively. This paper presents test results of reinforced concrete (RC) T-beams strengthened in flexure with different strengthening systems using FRP reinforcing bars and strips as NSM reinforcement and externally bonded FRP strips. The FRP reinforcements used in this investigation include carbon FRP (CFRP) reinforcing bars and strips and glass FRP (GFRP) thermoplastic strips. Behavior and effectiveness of the materials used for the various strengthening systems are compared. The structural performance and modes of failure of the tested beams are presented and discussed. Test results indicated that using NSM FRP reinforcing bars and strips is practical, significantly improves the stiffness, and increases the flexural capacity of RC beams. The limitations of using NSM FRP reinforcing bars and strips are controlled by serviceability requirements in terms of overall deflections and crack widths rather than delamination, observed by many researchers, of externally bonded FRP reinforcement. Strengthening of RC beams using NSM FRP strips provided higher strength capacity than externally bonded FRP strips using the same material with the same axial stiffness.}, number={5}, journal={ACI Structural Journal}, author={El-Hacha, R. and Rizkalla, S. H.}, year={2004}, pages={717–726} }
 @article{el-hacha_wight_green_2003, title={Innovative system for prestressing fiber-reinforced polymer sheets}, volume={100}, number={3}, journal={ACI Structural Journal}, author={El-Hacha, R. and Wight, R. G. and Green, M. F.}, year={2003}, pages={305–313} }