Bond beam

Abstract: This work experimentally examines the local bond aspect between steel bars and concrete confined with ordinary transverse steel. The test parameters included diameter of reinforcing bar, ratio of concrete cover to bar diameter, and area of transverse reinforcement. Results were compared with those of similar specimens for concrete confined either internally using steel fiber reinforcement or externally using fiber-reinforced polymer (FRP) sheets. Based on the comparisons, a unified expression for the local bond strength of confined concrete is derived, and a general model for the local bond stress-slip response is proposed and used to conduct an analytical evaluation of the effect of confinement on development/splice strength. Results predicted by the analysis were in good agreement with experimental results. For small development/splice lengths corresponding to local bond conditions, confining the concrete only slightly increases the local bond resistance but leads to considerable improvement in the ductility of bond failure. The corresponding ductility at the local level allows, for the practical range of development/splice lengths, more bar lugs to participate in resisting the applied bar force resulting in a more uniform bond stress distribution along the development/splice length and, consequently, a sizable increase in the average bond strength at bond failure as compared with plain unconfined concrete. The bond strength due to FRP confinement increases in proportion to the modulus of elasticity of the FRP material. For the same area of transverse reinforcement per unit length along the splice, taking into account the relative modulus of elasticity of the confining materials, external confinement of concrete using FRP sheets is more effective in increasing the development/splice strength than internal confinement with ordinary transverse steel. A general design expression is proposed to estimate the development/splice length of steel bars embedded in concrete confined with ordinary transverse steel, FRP, or steel-fiber reinforcement.

Abstract: Steel-to-concrete bond is a basic aspect of the behaviour of reinforced concrete structures both at serviceability and ultimate states. When bond rules were originally developed, experimental results were mainly obtained on normal-strength concrete and a minimum relative rib area (bond index) was required by building codes to ensure good bond properties. The arrival into the market of high-performance concrete and newer structural needs may require different bond indexes. In the present paper, the experimental results of pull-out tests on short anchorages are presented. Several pull-out tests on ribbed bars, embedded in cubes of normal- and high-strength concrete with a concrete cover of 4·5 times the bar diameter, were carried out in order to better understand the influence of the relative rib area and bar diameter on the local bond behaviour, as well as on the splitting crack width generated by the wedging action of ribs. A total of 96 tests were performed on machined bars of three different diameters (...

Abstract: This paper deals with the experimental characterization of the mechanical tensile and shear bond behavior of fiber-reinforced polymer (FRP) sheets externally glued on masonry prisms, in terms of load capacity and stress distribution along the bonded length. The brick masonry adopted tries to replicate ancient brick masonry, by using handmade low-strength solids bricks and low-strength lime-based mortar. Key parameters relative to the FRP-masonry interface response, particularly bonded length, FRP materials, anchor scheme adopted, and shape of masonry substrate, were studied. Finally, an analytical bond stress-slip formulation was developed, allowing deducing local bond stress-slip curves directly from the experiments.

Abstract: A new interface model to simulate the bond-slip behavior of reinforcing bars is presented. The model adopts a semiempirical law to predict the bond stress-versus-slip relations of bars, accounting for the bond deterioration caused by cyclic slip reversals, the tensile yielding of the bars, and the splitting of concrete. The wedging action of the ribs is represented by assuming that the normal stress of the interface is proportional to the bond stress. The model has been implemented in a finite-element analysis program and has been validated with laboratory experiments that include monotonic and cyclic bond-slip and anchorage tests of bars with different embedment lengths and a test on an RC column subjected to cyclic lateral loading. The model is easy to calibrate and computationally efficient, and it accurately predicts the bond-slip behavior of bars embedded in well-confined concrete. It also simulates bond failure attributable to the splitting of concrete in an approximate manner.