Strengthening the hogging and sagging regions in continuous beams with fiber-reinforced cementitious matrix (FRCM): Experimental and analytical investigations

Abstract

This paper reports on the flexural performance of ten reinforced concrete (RC) continuous beams strengthened with fabric-reinforced cementitious matrix (FRCM) systems. The test parameters included the type of the strengthening system used, the location of the deficient section that required strengthening, and the number of the fabric layers used. Apart from two unstrengthened control beams, two beams were strengthened with two layers of Polyparaphenylene benzobisoxazole (PBO) FRCM. The other six beams were strengthened with four layers of PBO-FRCM, two carbon FRCM (C-FRCM), and one layer of carbon fiber-reinforced polymer sheet (CFRP), all having the same axial stiffness. The test results confirmed the excellent rotational capacity of the FRCM-strengthened beams and their ability to efficiently redistribute moments between their critical sections. The moment redistribution ratio ranged between 20 and 31% for beams strengthened with FRCM in their hogging regions (51 and 77% of that of the control beams) compared to 8 and 13% for those strengthened in their sagging regions (42 and 65% of that of the control beams). The FRP-strengthened hogging and sagging sections showed moment redistribution ratios that ranged between 15 and 2%, respectively (37 and 9% of that of the control beams). The FRCM-strengthened beams also showed a remarkable ductile response with an average ductility index of 90% of that of their control beams compared to 42% only for the FRP-strengthened ones. Analytically, the capacity of the FRCM-strengthened beams predicted using a strain model that was previously developed by the authors agreed well with the experimental capacity obtained during the tests with an experimental-to-predicted ratio of 0.99 ± 0.02.