Strengthening of Composite Castellated Beams Web with Corrugated CFRP Laminated Struts

Abstract

A total of ten composite castellated beams was tested under center point load to investigate the effect of adding a new strengthening technique of corrugated CFRP (carbon fiber reinforced polymer) struts in order to strength the steel webs against out-of-plane displacement. The tested beams were divided into control beam with 0% castellation ratio and three groups, these groups have different castellation ratios of (33.3, 43.3 and 54.3) % with respect to control beam. The used corrugated CFRP struts were made by casting two layers of CFRP laminates in opposite sides using polyester resin in order to provide a perfect knitting and shear lag prevention between these layers. The strengthening by the mentioned struts have been done on group two and three in vertical and inclined position to satisfy the objectives of the present study. All of tested beams have 1560 mm length and their slabs are casted with self-compacted concrete of 55 MPa compressive strength. The slabs have the same dimensions for all beams 400 mm and 60 mm for width and thickness, respectively. The control beam without any castellation ratio or any type of strengthening was loaded up to failure under 122.45 kN, this beam used to compare the difference in ultimate load, out-of-plane displacement, deflection, toughness, ductility and stiffness with reference group which has no strengthening. Second and third groups had been loaded up to failure to compare their results with reference group. The beams of reference group reduce the ultimate load by (13.4, 16.7 and 26.5)% for beams with castellation ratio of (33.3, 43.3 and 54.3)% respectively when beams with vertical strengthening provided reduction by (6, 11.8 and 24.86)%, beams with inclined strengthening showed (9.1, 15.8 and 15)% load reduction. Out-of-plane displacements ware studied for tested beams to examine the best type of strengthening by comparing the out-of-plane displacement results for beams that are strengthened with vertical and inclined struts with reference group beams and identify which type present the best results. The beams with inclined strengthening reduce the out-of-plane displacements by (50, 86.2 and 87)% and III beams with vertical strengthening provide reduction by (60, 77.6 and 74.2)% when compared with reference group beams respectively. Both of vertical and inclined strengthened beams reduce the mid-span deflections by (21, 15.5 and 16.3)% and (13.75, 6.11 and 13.93)% respectively when their results compared with reference beams deflection The tested beams provided different results for toughness. The beams which are strengthened with vertical struts reduce the toughness by (19, 15 and 13.83)% while the beams with inclined strengthening reduce the toughness by (11.8, 7.8 and 6.3)% compared with reference beams that have same castellation ratios of (33.3, 43.3 and 54.3)%, respectively.