Bond behaviour of deformed bars in self-compacting lightweight concrete subjected to lateral pressure

Abstract

The purpose of this paper is to present an experimental investigation into the bond behaviour between deformed bars and self-compacting lightweight concrete (SCLC) under lateral pressure. SCLC pull-out specimens made with two types of lightweight aggregate were tested under two orthogonal lateral pressures p1 and p2, perpendicular and parallel to the transverse rib of deformed bars respectively. It was found that, under uniaxial lateral pressure, the ultimate bond stress increases with an increase of p2 but is independent of p1. Under biaxial lateral pressures, the ultimate bond stress increases monotonically with an increase in p1 and/or p2. The slip at the ultimate bond stress is an increasing function of lateral pressure for specimens failing by splitting, but basically remains constant for specimens failing by pull-out. The ratio of residual to ultimate bond stress is mainly related to the ratio of cover depth to bar diameter. It was also found that the lightweight aggregate type has little influence on the bond behaviour of deformed bars. Based on the experimental results, empirical formulae for the ultimate bond stress, the slip at the ultimate bond stress and the ratio of residual to ultimate bond stress are formulated. Finally, a bond stress–slip model is proposed and verified with experimental results.

Bond Performance of Deformed Rebar in Steel Fiber Reinforced Lightweight-Aggregate Concrete Affected by Multi-Factors

“…Another reason may be owing to the changes of concrete cover from 5.75, 4.19 to 3.25 times the rebar diameter, which led to the increasing trend of the splitting failure of SFRLAC and decreased the lateral restraint to the bond surface. Similar regulations of bond strength of LAC reduced with the increasing rebar diameter are reported in previous studies [16][17][18][19][20]. As the proof, two of three specimens with 20mm rebar failed in splitting of SFRLAC in this test.…”

“…As the deformed rebar is popular used for the main reinforcement, the bond performance of deformed rebar in this new SFRLAC should also be reasonably evaluated. In this respect, the studies on bond properties of LAC dealt with expanded shale provide good references [15][16][17][18][19][20][21][22], and the enhancement of steel fibres on the bond of SFRLAC presents a bright prospect [23][24][25][26][27].…”

“…Lachemi et al [17] reported that under the conditions of equivalent workability and compressive strength, the bond properties of LAC with coarse expanded shale was significantly enhanced compared to the LAC with coarse lightweight slag aggregate. Wu et al [18] reported that the LAC with coarse expanded shale exhibited higher bond strength compared to the LAC with sintered pulverized fuel ash aggregate when equal water-binder ratio was used for both mixes. Meanwhile, the bond strength between deformed rebar and LAC with coarse expanded shale increases with the increasing tensile and/or compressive strength of LAC [19][20][21][22], and is higher than that of ordinary concrete in the same strength grade due to the lower water-binder ratio of LAC [19,20].…”

“…For the rebars with 5d and 8d bond length, the much more number of ribs gave the oppotunity of the redistribution of bond stress along bond length with the transfer of slip from loading-end to free-end [17][18][19][20]26], which let the SFRLAC work successively into effective states. In this condition, the bond reliability was higher because the ribs seceded bearing action one by one with the increasing slip, the obvious reduction of bond stress gave the forebode to aviod related damages.…”

Discussion: Bond behaviour of deformed bars in self-compacting lightweight concrete subjected to lateral pressure

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The paper by Wu et al (2013) presents interesting experimental results, empirical formulae and a model to characterise the bond behaviour of deformed bars in self-compacting lightweight concrete subjected to uniaxial and biaxial lateral pressures with different pressure ratios. The authors should be complimented for producing this detailed paper, which was of interest for the discusser, who would like to offer some comments for the authors' consideration and response, mainly about test parameters, normalised ultimate bond stress (UBS), slip at UBS and the ratio between residual and ultimate bond stress.

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