Concrete-filled Tubular Joints Research Articles

Formulae for hot-spot stress concentration factors of concrete-filled CHS T-joints based on experiments and FE analysis

Fatigue of welded concrete-filled tubular joints is a new subject to be investigated, compared with fatigue of welded tubular joints without concrete which has been studied well. Fatigue cracking is usually located at the hot spot stress of a welded concrete-filled tubular joint. A method of calculating its hot spot stress is essential for fatigue strength assessment. Hot spot stress concentration factors (SCF) of welded concrete-filled circular hollow section (called as CFCHS) T-joints respectively under axial force and in-plane bending are investigated experimentally and numerically in this paper. SCF testing was carried out on ten CFCHS T-joints with different non-dimensional geometric parameters β (ratio of brace to chord diameter), 2γ (ratio of chord diameter to thickness) and τ (ratio of brace to chord thickness). The experimental findings shows in most cases, a remarkable decrease in SCFs of CFCHS T-joints, compared with circular hollow section T-joints without concrete. Finite element (FE) modelling with 3D quadratic hexahedral solid element was developed and verified by the experimental data. It is found that the conversion relationship SCF= 1.2 SNCF (strain concentration factor) can be adopted for CFCHS T-joints. Using the reliable FE modelling, parametric study was conducted to know the effect of non-dimensional parameters on SCFs of CFCHS T-joints. Based on multiple regression analysis, a series of formulae are recommended for calculating SCFs in the chord and brace of CFCHS T-joints subjected to the axial force and in-plane bending in the brace and in the chord respectively, which are validated by both the experimental data and FE modelling.

Double-composite rectangular truss bridge and its joint analysis

This paper describes a novel composite tubular truss bridge with concrete slab and concrete-filled rectangular chords. With concrete slab plus truss system and joints reinforced with concrete and Perfobond Leiste rib, double composite truss bridge proved to be a fairly suitable solution in negative moment area. Perfobond Leiste shear connector (PBL) is widely implemented in the composite structure for its outstanding fatigue resistance. In this pilot bridge, Perfobond Leister ribs (PBR) were installed in the truss girder's joints, which played double roles as shear connector and stiffener. An erection method and overall bridge structural analysis were then presented. Typical joints in the pilot bridge were selected to analyze the effect of PBR. Investigation of the effect of PBR in concrete-filled tubular joints was elaborated. Comparison has revealed that concrete-filled tubular joints with PBR have much higher constraint capability than joints without PBR. For rectangular tubular truss, the punching shear force of the concrete filled joint with PBR is approximately 43% larger than that of the joint without PBR. Fatigue performance of the joint installed with PBR was improved, which was found through analysis of the stress concentration factor of joint. The PBR installed in the joints mitigated the stress concentration factor in the chord face. Therefore, the advantages of this new type of bridge are demonstrated, including the convenience of construction using rectangular truss, innovative concept of structural design and better global and local performances.

Fatigue and residual strength of concrete-filled tubular X-joints with full capacity welds

This paper presents the experimental findings on the fatigue performance and residual strength of the circular hollow section X-joints with a concrete-filled chord. The welding profile along the brace-to-chord intersection employs a recently proposed set of welding details, namely the full capacity tubular joint welds. The experimental investigation focuses on: 1) the stress concentration comparison corresponding to different stages of the specimen preparation, 2) the fatigue crack initiation life and propagation life; and 3) the comparison of the measured fatigue life with respect to the design S-N curves. The experimental measurement reveals that the fatigue crack propagation life contributes to a significant portion of the total fatigue life for both the hollow section tubular joints and the concrete-filled tubular joints. The total fatigue life of the test specimens complies with the life estimation based on the existing design S-N curves, originally developed for tubular joints fabricated using the complete joint penetration welds. The residual strength of the fatigue-cracked tubular joints follows approximately a linear relationship with respect to the percentage of the crack area along the brace-to-chord intersection.

Design of Concrete-Filled Stainless Steel Tubular Connections

A numerical study was performed on concrete-filled stainless steel tubular T- and X-joints using finite element analysis. The specimens were fabricated from square and rectangular hollow sections (SHS and RHS) with concrete-filled in the chord members. The geometric and material nonlinearities of stainless steel tubes as well as the concrete infill were carefully incorporated in the finite element models. The nominal compressive concrete strengths were ranged from 30 to 110 MPa. The numerical results showed good agreement with the experimental results for the concrete-filled stainless steel SHS and RHS tubular T- and X-joints. Therefore, an extensive parametric study was performed using the verified finite element models to investigate the strength and behaviour of concrete-filled stainless steel tubular connections. The joint strengths obtained from the parametric study and tests were compared with the current design strengths calculated using the CIDECT design rules for concrete-filled carbon steel tubular joints, which is the only existing design guideline for concrete-filled tubular joints. It should be noted that the current CIDECT design rules ignore the contribution of the steel tubes in the calculation of the joint strengths. In this study, design formulae of concrete-filled stainless steel tubular T- and X-joints are proposed. The proposed design formulae include the contribution of the stainless steel tubes. A reliability analysis was performed to assess the reliability of the current and proposed design rules. It is shown that the design strengths calculated using the proposed equations are generally accurate and reliable.

Tests of concrete-filled stainless steel tubular T-joints

This paper describes a test program on a wide range of concrete-filled cold-formed stainless steel tubular T-joints fabricated from square hollow section (SHS) and rectangular hollow section (RHS) brace and chord members. A total of 27 tests was performed. The chord member of the test specimen was filled with concrete along its full length. Both high strength stainless steel (duplex and high strength austenitic) and normal strength stainless steel (AISI 304) specimens filled with nominal concrete cylinder strength of 30 MPa were tested. The axial compression force was applied to the top end of the brace member, which was welded to the center of the chord member. Local buckling failure of brace member was the main failure mode observed during the tests. Hence, the axial compression force was then applied by means of a steel bearing plate to avoid failure of brace member. The failure modes of chord face failure and chord side wall failure as well as crushing of the concrete infill were observed. All the tests were performed by supporting the chord member of the specimen along its entire length to apply the pure concentrated force without any bending moment. The test results were also compared with design rules for carbon steel tubular structures, which is the only existing design guideline for concrete-filled tubular joints. It is shown that the design strengths predicted by the current design rules are quite conservative for the test specimens. It is also recommended that the contribution of stainless steel tubes should be included in the design rules since it has significant effects on the ultimate bearing capacity of concrete-filled stainless steel tubular T-joints.