Contribution of Steel Casing to Single Shaft Foundation Structural Resistance

Experimental Study on Composite Action in Reinforced Concrete–Filled Steel-Tube Shaft Foundations

“…This latter issue was investigated by testing specimens with a natural steel-to-concrete bond, and specimens with reduced interface friction created by applying bentonite slurry and grease on the interior surface of the steel tube. Also, one specimen in the testing program had an alternative transition zone detail at the connection between the reinforced concrete column and the RCFST shaft to investigate a shear-head concept developed by Bruneau et al (2018) to transfer the column forces to the composite shaft. Finally, another specimen used a shear transfer mechanism at the top of the RCFST shaft to achieve the desired composite action when insufficient interface friction is present between the steel and concrete.…”

“…A thick layer of grease coating was used on the interior of the steel tube of this specimen to reduce the friction. According to Bruneau et al (2018), in the case where adequate friction cannot develop at the concrete-to-steel tube interface, composite action can be achieved by providing shear transfer mechanisms over a certain length at the top of the RCFST shaft. Four shear rings with 1.27 Â 1.27-cm (0.5 Â 0.5-in.)…”

“…The noncomposite case refers to a state where the strain distributions in the steel casing and the reinforced concrete core are independent of each other when subjected to bending. In most cases, the flexural strength of the noncomposite RCFST is on the order of 10%-20% less than that of the composite case (Bruneau et al 2018). The strength difference between noncomposite and composite cases is attributed to the differences in the positions of the neutral axes.…”

“…The AASHTO Guide Specifications for LRFD Seismic Bridge Design (AASHTO SGS) (AASHTO 2014a) and the Canadian Highway Bridge Design Code (Canadian Standards Association 2006) have adopted a plastic stress method proposed by Bruneau and Marson (2004) and similar to the AISC 360 (AISC 2016) PSDM (note that the AASHTO provisions only deal with CFST without internal reinforcement). Small variations exist between the various applications of each method in different codes [described in more detail by Bruneau et al (2018)].…”

“…The composite strength of CFSTs with internal reinforcing (i.e., RCFSTs) under cyclic loading has recently been studied by researchers (e.g., Brown et al 2013;Moon et al 2013;Bruneau et al 2018). For composite RCFSTs, PSDM can be used to calculate the flexural strength by idealizing the internal steel reinforcing as a thin steel ring (Moon et al 2012).…”