International Concrete Abstracts Portal

Using fabric formwork, it is possible to cast architecturally interesting, optimised structures that use up to 40% less concrete than an equivalent strength prismatic section, thereby offering significant embodied energy savings. This paper reports on the latest techniques for the design, optimisation and shape prediction of fabric formed con-crete beams before new test results of an innovative anchorage method for both steel and fibre reinforced polymer longitudinal reinforcing bars are presented. Two 2m span beams were tested and the ‘helically confined splayed bar’ was shown to provide full anchorage in both cases. The two beams both exceeded their design capacity and showed remarkably similar behaviour at the serviceability limit state, with the steel reinforced section going on to display considerable ductility. Potential areas of future development are then highlighted, with the use of woven advanced composite fabrics as participating formwork for both beam and shell elements being of particular interest.

Existence of positive post-yield stiffness and mitigation of both residual deformation and damage level are critical indices in the performance of reinforced concrete (RC) bridge frame columns to assure the quick recovery of bridge original functions after a massive earthquake. In this study, because bond between longitudinal reinforcement and concrete is a key factor controlling the performance of RC structures, effects of bond parameters on the required post-earthquake recoverability of RC bridge columns reinforced with innovative composite rebars: steel fiber composite bars (SFCBs), are studied. Results of experimentally tested columns reinforced with different products of SFCBs are firstly presented. Afterward, a computer program is employed to investigate the effect of bond parameters on the recoverability indices (post-yield stiffness, residual deformations, and damage level) of columns reinforced with steel basalt-fiber composite bars (SBFCBs). The study showed that weaked bond between SFCBs and the surrounding concrete at plastic hinge zone would play an important role in the recoverability of structures reinforced with SBFCBs, where the achieved post-yield stiffness, residual deformations, and damage level could be controlled.

When RC is strengthened by using externally bonded reinforcement (EBR) it is not sufficient to perform checks just for the end anchorages. The bond forces must be transferred where the load is applied. These bond forces may be transferred by the elements in between flexural cracks which are mainly influenced by the bond behavior of the internal and external reinforcement. Therefore the models which were derived from end anchorage tests must be expanded to include other effects as well. The here considered laboratory tests had shown that aside from the bond friction a self-induced contact pres-sure on the strip occurs as a result from the element's curving under load. This article presents a model for bond force transfer which includes the increased bond strength resulting from the positive curvature of structural elements. By considering the curvature for the bond force transfer strengthened elements can be design in a more economic and safe way.

An analytical model is developed in this work to derive the bond-slip relationship at the reinforcement-substrate concrete interface (joint) for externally bonded FRP (EB-FRP). The model is generally applicable to both long joints (infinite bond length) and short joints. The bond-slip relationship for short joints with a limited bond length is a general model for EB-FRP joints. When the bond length approaches infinity, the model degenerates to a well-known existing analytical model. It is concluded from the modeling that the existing model for long joints is not applicable to short joints that have a bond length that is less than the effective bond length, or at locations in long joints that are closer than the effective bond length to the free end of the reinforcement. The bond-slip relationship is verified with test results.

The paper deals with the results of an experimental program aimed at the investigation of the bonding behavior of different types of FRP materials for strengthening: externally bonded carbon (EBR) plates, and bars or strips externally applied according to the Near Surface Mounted (NSM) technique. The overall experimental program consists of 18 bond tests on concrete specimens strengthened with EBR carbon plates and of 24 bond tests on concrete specimens strengthened with NSM systems (carbon, basalt and glass bars and carbon strips). The performances of each reinforcement system are presented, discussed and compared in terms of debonding load, load - slip relationship, and strain distribution; the failure mode of each system is also analyzed. The results of the experimental program allow a comparison of the effectiveness of the various EBR and NSM strengthening systems tested and evidence of some differences in the bond behavior.