Strength Of Concrete Infill Research Articles

Experimental investigation on concrete filled glass fibre reinforced polymer tubular beams under flexural loading

Fibre reinforced polymer (FRP) has expanded its importance throughout the world as it provides an immense potential solution to the crisis related with the infrastructure. Concrete filled fibre reinforced polymer tubular members are used as an innovative alternative material for concrete filled steel tubular members. This paper focuses on an experimental study on the behaviour of concrete filled glass fibre reinforced polymer tubular beams under flexural loading. Two different strength of concrete (Type 1 & Type 2) were used to infill the FRP tubular beams. Two types of configurations of FRP (S-type and B-type) were used in the investigation. The tubular beams were performed for four-point loading system. The effect such as strength of concrete infill on FRP tubular beams and configurations of FRP were investigated. The experimental results indicated that the FRP tubular beams filled with Type 2 concrete enhanced the ultimate load than the FRP tubular beams filled with Type 1 concrete. The concrete filled in unidirectional cloth FRP tubular beams exhibit a better performance than the woven roving FRP tubular beams. FRP tubes filled with higher grade of concrete increased the maximum deflection by 22.09%. The concrete filled in S-type of FRP tubular beams failed by premature buckling, rupture of fibres and crushing in the webs wherein concrete filled in B-type of FRP tubular beams failed by brittle mode of failure.

Evaluation of structural performance between active and passive preloading systems in circular concrete-filled steel tubes (CFST)

Concrete-filled steel tubes (CFST) are increasingly used thanks to the improved structural performance, especially under compression. This is basically due to the confinement effect provided by the tube, which usually enhances ductility and strength of concrete infill. Several researchers have been focused these last decades on these sections under different assumptions, especially those issues which derive from the construction process; the fact of loading the tube before concreting in preliminary constructive stages leads to a preloading stress which implies a different response of the section than the expected. These issues must be considered in the design process and derive into undesired preloading effects on one of the two components derived from the process itself.Nevertheless, few studies treat the fact of preloading as a design method itself before being under service loads (active methods) to enhance the capacities of CFST sections. This paper analyses and compares 4 different methodologies (2 passive versus to 2 active preloading methods) by describing the potential benefits and consequences of them on the whole section; while sometimes a pre-stress ratio on one component may enhance the global mechanical response, sometimes it does not and becomes even harmful. The ratio of confinement effect over the core and especially when it becomes activated reveals the grade of real enhancement of the compressive response of the section in terms of ductility and strength.

Behaviour of steel-concrete-steel SHS X-joints under axial compression

This paper presents the experimental investigation and finite element analysis on double-skin square hollow section (SHS) X-joints under axial compression, which were strengthened with concrete filled in the chord between inner tube and outer tube. A total of 22 orthogonal SHS X-joints with different brace to chord width ratio (β), hollow ratio of chord (χ) and shapes of inner tube of chord were tested, in which two traditional SHS X-joints and two concrete-filled SHS X-joints were tested for comparison. The effects of brace to chord width ratio (β), inner tube to outer tube thickness ratio of chord (ω), hollow ratio of chord (χ), shape of inner tube of chord and strength of concrete infill on the structural behaviour of steel-concrete-steel SHS X-joints under axial compression were evaluated. It is shown from the comparison that the inner tube and concrete infill significantly enhanced the ultimate strengths of SHS X-joints under axial compression. Furthermore, the ultimate strength and initial stiffness of steel-concrete-steel SHS X-joints under axial compression are improved with the increase of inner tube to outer tube thickness ratio of chord (ω) and strength of concrete infill. On the other hand, the ultimate strength and initial stiffness benefit from the increase of the β ratio and decrease of the χ ratio. The design equations are proposed based on the test and numerical results for steel-concrete-steel SHS X-joints, which were verified to be more accurate.

Fatigue life of an anchored blind-bolt loaded in tension

This paper investigates and reports on the fatigue behaviour of a novel blind-bolt system termed the Extended Hollo-bolt (EHB). The new blind-bolt is a modified version of the standard Lindapter Hollo-bolt, and its application relates to the construction of bolted, moment-resisting connections between open profile beams and concrete-filled tubular columns. The fatigue behaviour of the system is studied on the basis of constant amplitude loading tests, with a total of 56 experiments being reported. The specimens were subjected to tensile loading for various stress ranges, with the repeated load being selected relative to the design yield stress of the blind-bolt's internal shank. The influence of testing frequency and strength of concrete infill is also examined. An analysis of the results indicates that an increase in the concrete strength can increase the fatigue life of the EHB system. Within the tested range, the failure mode of the EHB under repeated loading was found to be due to internal bolt shank fracture, a mode which is consistent with its monotonic behaviour and also comparable with standard bolt–nut–washer system behaviour. The experimental results (S–N data) were further compared with the Eurocode 3 Part 1-9 guidelines. The fatigue design strength of the anchored EHB blind-bolt is found to be adequately represented by the current specification detail Category 50 that is provided for standard bolting systems.

Theoretical study on concrete-filled steel tubes under static and variable repeated loadings

This paper presents an analytical study for modelling the behaviour of concrete-filled steel tubular (CFST) columns subjected to Static Loading (SL) and Variable Repeated Loading (VRL). The variables considered in this study are concrete strength and load eccentricity. Simple mathematical models are developed and used in the analysis. The analytical results show that the incremental collapse (IC) occurs in high load ranges in CFST columns under VRL and instability failure occurs under SL. The CFST columns with large end load eccentricity were found to fail at a low upper limit load level than that with small eccentricity of loading. The IC failure was found to be unaffected by the strength of concrete infill. The hollow steel tubular (HST) columns showed similar behaviour under SL and VRL protocols. The study showed that the theoretical analyses satisfactorily model the actual behaviour of the columns under SL and VRL protocols.