Resumo

GERBER, J D  e  VAN ZIJL, G P A G. Alternative wall-to-slab connection systems in reinforced concrete structures. J. S. Afr. Inst. Civ. Eng. [online]. 2017, vol.59, n.3, pp.36-47. ISSN 2309-8775.  http://dx.doi.org/10.17159/2309-8775/2017/v59n3a5.

In many reinforced concrete structures the walls precede the construction of the connecting floors. A system is, therefore, required to connect the floors to the already cast walls. There are many different floor-to-wall connection systems available in South Africa, but their behaviour and capacity are not always fully understood, especially when the moment capacity of the joint is to be utilised. This study focuses on four systems: continuous starter-bars, pre-bent site-installed starter-bars, pre-assembled starter-bars and cast-in anchors with mechanical couplers. The design procedure for the continuous starter-bar system is well understood and documented in design codes, but not enough information is available on the design procedure for the other systems. Certain practical aspects of the installation process are also not fully understood. Cold-bending and straightening of the starter-bars are inevitable in both bend-out systems. Previous research shows that this cold-working of the reinforcement can reduce the yield stress and E-modulus of the steel. In order to investigate these findings, a series of tensile tests are conducted. The results indicate that a significant reduction can be expected in both the yield stress and modulus of elasticity of the steel. Low-cycle fatigue tests further suggest that cold-bent steel also has a reduced ductility. The tensile tests are followed by the construction and testing of the systems in full-scale wall-to-slab connections. The effect of the cold-bending on the starter-bars is clearly visible, as both the responses of the bend-out systems are less satisfying than the results from the continuous starter-bar system. The experimental phase is followed by numerical analysis of the connection systems. The finite element analyses show that the structural performance is significantly more sensitive to a reduction in the yield stress of the starter-bars, than to the use of a lower concrete grade. It is concluded that all the alternative connection systems can be implemented successfully in a moment-fixed wall-to-slab connection, but that the site-installed bend-out system is the preferred method. However, in order to ensure that the system performs on the same level as conventional systems, it is recommended that the design should be conducted with a set of modified steel properties to allow for the negative effect of the cold-working on the starter-bars.

Palavras-chave : wall-to-slab; floor-to-wall; connection system; reinforced concrete; moment capacity; joint; starter-bar.

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