Use of horizontal web bars for upgrading reinforced concrete beams in shear

Abstract: The existing recommendations in Eurocode 2 and the British Codes of Practice BS8110 and BS5400 for the shear design of reinforced concrete beams are essentially based on research conducted on normal strength concrete (NSC) specimens with cube strengths of up to 50 MPa. Fairly recently, some limited tests on High Strength Concrete (HSC) beams, as reported elsewhere, appeared to suggest that, in certain cases, the shear strength of HSC members made with limestone aggregate may turn out to be less ( or equal) to the characteristic shear resistances of nominally identical NSC beams. The present paper reports the salient features of test data for five beams (four HSC specimens made with limestone plus one NSC beam made with river gravel as coarse aggregate) with the experimental results demonstrating this, perhaps, initially puzzling observation. In addition, test results for another set of six similar reinforced concrete beams (three HSC plus three NSC, which included 10 mm limestone and 20mm river gravel, respectively), will be used to demonstrate that, once upgraded with Horizontal Web Bars (HWB), the shear resistance of the HSC beams is highly dependent on the additional dowel action generated by such HWB positioned on the two sides of the beam, in the vicinity of the neutral axis. A new design rule is, therefore, reported for upgrading of HSC beams in shear, using such Near Surface Mounted (NSM) HWB. Finally, it is perhaps worth mentioning that for durable and effective upgrading, such Near Surface Mounted HWB is to be encased with epoxy resin filling the grooves made on either side of the beam within the cover of stirrups close to the neutral axis, with intumescent paint used to cover the repaired area of the beam for fire protection.

Author(s): Jubin Motamed & Mohammed Raoof

Date Published: 01 June 2025

Depositing User: Basiratu Kolawole

Keywords: Reinforced Concrete, Beams, Shear, Upgrading, Dowel Action, Horizontal Web Bars & Bridges

Page(s): 1-14

Subject(s): Civil Engineering & structural engineering

Type of publication: Journal Article