Load transfer mechanism of an unwelded, unbolted, grouted connection for prefabricated square tubular columns under axial loads

Abstract

This study develops a novel unwelded, unbolted, ultrahigh-performance fibre-reinforced concrete (UHPFRC) grouted connection for prefabricated square tubular composite columns. Herein, eight full-scale columns with UHPFRC grouted connections are tested to investigate their ultimate tensile and compressive resistance. The test results show that the novel connections exhibit good resistance and structural stiffness. The primary failure modes are punching shear of the end plate, welding fracture at the inner tube, tube yielding and local buckling of the steel tube. The test specimens are simulated using finite element analysis in ABAQUS. The experimental and simulated results are in good agreement, indicating that the FE simulations can capture the observed failure modes and ultimate resistance. Thereafter, existing analytical design formulas are evaluated to assess their suitability to predict the compressive and tensile resistance of prefabricated tubes with/without the novel grouted connections. A good agreement between the formula predictions and the test results are observed.These analytical formulas have the potential to be used in the design of the novel unwelded, unbolted, UHPFRC grouted connections for prefabricated steel, reinforced concrete and steel-concrete composite columns.

Axial-Load Resistance of a Novel UHPFRC Grouted SHS Tube-Sleeve Connection: Experimental, Numerical, and Theoretical Approaches

“…Three types of UHPFRC with 0%, 1% and 2% steel fiber in volume are prepared for the tests. Table 2 shows the mix proportions of the UHPFRC that consists of type II 52.5 R Portland cement, ultrafine silica fumes (SF), fine sands (grain size less than 4 mm), ground granulated blast furnace slags (GGBFS), polycarboxylate superplasticizer, shrinkage-reducing admixtures and steel fibers (12 mm in length and 0.6mm in diameter) [19]. With added steel fibers, the compressive strength of UHPFRC-1% and UHPFRC-2% tends to increase.…”

“…According to the material test results, the 28-day cylinder compressive strength and tensile strength of UHPC, UHPFRC (1%) and UHPFRC (2%) are used to calibrate the FE model. Sui et al [19] and Zhang et al [43] have discussed the compressive and tensile constitutive relationship for UHPFRC and UHPC, respectively, and proposed the nondimensional stresses-inelastic strain curves and nondimensional damage variables-inelastic strain curves, which are directly used in the current study. The yield surface and flow potential parameters, including the dilation angle, second stress invariant ratio (K), ratio of biaxial to uniaxial compressive strength (fb0/fc0), eccentricity and viscosity factor are specified as 45°, 0.667, 1.07, 0.1 and 0.0001, respectively.…”

“…To overcome these issues, a shear key-grouted column connection of square hollow section (SHS) was developed, which connects the upper and lower columns by filling the gap in the overlapped zone of the connection with grout [19]. The idea of the SHS column connection originates from the CHS column connection.…”

“…However, these equations cannot be directly applied to SHS column connections, as the confinement effect on the grout is quite different. Sui et al [19] investigated the load transfer mechanisms of a grouted prefabricated SHS column connection under axial compression and tension.…”

“…To address the important issues raised above, the current study designs a novel UHPFRC grouted SHS tube sleeve connection, which is an improvement of the sleeve connection reported by Sui et al [19]. As the space for grouting between the outer and the inner tube is limited, using UHPFRC with higher strength, higher ductility and better workability is more desirable than using normal concrete with coarse aggregates.…”