BEHAVIOUR OF REINFORCED HIGH-STRENGTH CONCRETE BEAMS WITH OPENINGS SUBJECTED TO STATIC AND REPEATED LOADINGS

Abstract

This paper presents the results of an experimental research on reinforced high strength concrete beams with web rectangular openings to determine their behaviour and ultimate strengths, and to compare these strengths with those predicted using the available equations. Test variables were length of openings, details of steel reinforcement around the openings, longitudinal main steel ratio, and type of loading (static-repeated). Test results showed that the ultimate load of beams with openings reduces by about 10 to 45% compared to similar solid beams. Provided that the same amount and scheme of reinforcement used, an increase in opening length, decreases both stiffness and strength of the beam. Diagonal bars at corners of openings results in spreading of cracking away from openings and reducing beam deflection, but it does not have significant influence on strength of the beam. The effects of transverse openings on overall response of reinforced concrete beams in shear becomes remarkable as main steel ratio (ρ) increases. Increasing shear reinforcement (stirrups) in the top and bottom chords of the openings increases slightly the cracking load; while increases significantly the ultimate load. Repeated load has no effect on either strength or mode of failure of the tested beams. The available equations do not produce satisfactory results for predicating the ultimate shear strength of highstrength concrete beams with openings.