• Steel and Composite Structures
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• v.39 no.2
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• pp.189-200
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• 2021

The compressive strength of circular concrete filled steel tubular (C-CFST) stubs strengthened with carbon fiber reinforced polymer (CFRP) is studied theoretically. According to previous experimental results, the failure process and mechanism of circular CFRP-concrete filled steel tubular (C-CFRP-CFST) stubs is analyzed, and the loading process is divided into 3 stages, i.e., elastic stage, elasto-plastic stage and failure stage. Based on continuum mechanics, the theoretical model of C-CFRP-CFST stubs under axial compression is established based on the assumptions that steel tube and concrete are both in three-dimensional stress state and CFRP is in uniaxial tensile stress state. Equations for calculating the yield strength and the ultimate strength of C-CFRP-CFST stubs are deduced. Theoretical predictions from the presented equations are compared with existing experimental results. There are a total of 49 tested specimens, including 15 ones for comparison of yield strength and 44 ones for comparison of ultimate strength. It is found that the predicted results of most specimens are within an error limit of 10%. Finally, simplified equations for calculating both yield strength and ultimate strength of C-CFRP-CFST stubs are proposed.

• Steel and Composite Structures
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• v.48 no.1
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• pp.89-102
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• 2023

This study investigates the eccentric performance of concrete-filled steel tubular (CFST) stub columns strengthened with steel tube and sandwiched concrete (STSC) jackets. It was revealed that the STSC jacketing method effectively weakened the cracking of concrete in CFST columns on the convex side and the crash on the concave side. Substantial increases in the eccentric bearing capacities were demonstrated after strengthening. A numerical study was further conducted. The decrease in diameter-to-thickness ratio and increase in strength of outer tube contributed to increase in peak load of all components, whereas the increase in sandwiched concrete strength resulted in load increase on itself and had negligible effects on other components. The parametric study showed the effect of inner concrete strength on columns' bearing capacity was magnified after strengthening, whereas that of inner tube thickness was reduced. Within the parameters investigated, high-strength concrete and high-strength steel can be applied without the concern of early abrupt failure of inner low-strength concrete or steel tube.

• Advances in concrete construction
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• v.10 no.6
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• pp.559-571
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• 2020

This study aimed to inspect the axial compression mechanical performance of basalt-fiber-reinforced recycled - concrete (BFRRC)-filled square steel tubular stub column. The replacement ratio of recycled coarse aggregate (RCA) and the basalt fiber (BF) dosage were used as variation parameters, and the axial compression performance tests of 15 BFRRC-filled square steel tubular stub column specimens were conducted. The failure mode and the load-displacement/strain curve of the specimen were measured. The working process of the BFRRC-filled square steel tubular stub column was divided into three stages, namely, elastic-elastoplasticity, sudden drawdown, and plasticity. The influence of the design parameters on the peak bearing capacity, energy dissipation performance, and other axial compression performance indexes was discussed. A mathematical model of segmental stiffness degradation was proposed on the basis of the degradation law of combined secant-stiffness under axial compression. The full-process curve equation of axial compressive stress-strain was proposed by introducing the influencing factors, including the RCA replacement ratio and the BF dosage, and the calculated curve agreed well with the test-measured curve.

• Steel and Composite Structures
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• v.23 no.1
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• pp.115-130
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• 2017

A new type of moment-resisting bolted connection was developed for use in composite steel- concrete construction to connect composite open section steel beams to concrete filled steel square tubular columns. The connection was made possible using anchored blind bolts along with two through bolts. It was designed to act compositely with the in-situ reinforced concrete slab to achieve an enhanced stiffness and strength. The developed connection was incorporated in the design of a medium rise (five storey) commercial building which was located in low to medium seismicity regions. The lateral load resisting system for the design building consisted of moment resisting frames in two directions. A major full scale test on a sub-assembly of a perimeter moment-resisting frame of the model building was conducted to study the system behaviour incorporating the proposed connection. The behaviour of the proposed connection and its interaction with the floor slab under cyclic loading representing the earthquake events with return periods of 500 years and 2500 years was investigated. The proposed connection was categorized as semi rigid for unbraced frames based on the classification method presented in Eurocode 3. Furthermore, the proposed connection, composite with the floor slab, successfully provided adequate lateral load resistance for the model building.

• Steel and Composite Structures
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• v.13 no.5
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• pp.451-471
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• 2012

Concrete filled steel tube (CFST) structures have been used widely in high-rise buildings and bridges due to the efficiency of structurally favourable interaction between the steel tube and the concrete core. In the current design codes only one loading condition in the column members is considered, i.e., the load is applied on the steel tube and concrete core at the same time. However, in engineering practice the tube structures may be subjected to various loading conditions such as loading on the concrete core only, preloading on the steel tube skeleton before filling of concrete core, and so on. In this research, a series of comparative experiments were carried out to study the structural performance of concrete filled circular steel tube columns subject to four concentric loading schemes. Then, a generalized prediction method is developed to evaluate the ultimate load capacity of CFST columns subject to various loading conditions. It is shown that the predictions by the proposed method agree well with test results.

• Steel and Composite Structures
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• v.47 no.6
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• pp.781-794
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• 2023

In order to directly apply seawater and sea sand in construction without desalination, a type of square concrete-filled steel tube (CFST) encased with prefabricated seawater sea-sand concrete filled Polyvinyl Chloride (PVC)/Glass Fiber Reinforced Polymer (GFRP) tube column was proposed. Twenty short columns were tested under uniaxial loads, and the test parameters included inner tube types, seawater sea-sand concrete replacement ratios, concrete strength, the wrapping area of Carbon Fiber Reinforced Polymer (CFRP) strips and the thickness of GFRP tube. The effects of the parameters on failure modes, loading capacity, ductility and strain responses were discussed. All the tested specimens failed with serious buckling of the steel tubes and fracture of the inner tubes. The specimens had good residual bearing capacity corresponding to 64% to 88.9% of the peak capacity. The inner GFRP tubes and PVC tubes wrapped by CFRP strips provided stronger confinement to the core concrete, and were good choices for the proposed columns. Moreover, an analytical model for the composite column with different inner tube types was proposed.

• Proceedings of the Korea Concrete Institute Conference
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• 1996.04a
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• pp.382-387
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• 1996

Three concrete filled steel tubular columns with six inner diaphrams are constructed and tested under field conditions. The size and shape of three columns are exactly same. The cross section is $40\times40cm$, and the height is 9m. Each column is constructed with normal concrete, CFST concrete, and high flowing concrete, respectively. Concrete is pumped into bottom parts of steel tubular columns from a concrete pump on the ground. Test data indicate that the slump flow of the concrete place in the top of the column is lower than that of the concrete before pumping by about 10~20cm. Slump flow loss of high flowing concrete caused by pumping is high compared to the other concretes. Concrete pump pressure of high flowing concrete is somewhat higher than that of CFST concrete.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.3
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• pp.140-148
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• 2016

This study examined the durability of face-slab concrete in Concrete-Faced Rock-filled Dams(CFRDs). The durability of face-slab concrete can be improved by optimizing the amount of fly ash in the cement mixture. Durability tests including plastic shrinkage, permeability, abrasion resistance, and repeated freezing and thawing were done on face-slab concrete specimens with different amounts of fly ash and blended PVA(Poly Vinyl Alcohol) fibre. When the effect of the fly ash content on concrete durability was evaluated, the results showed that a 15% fly ash content and 0.1% blended PVA fiber yielded the optimum durability level for concrete-faced rock-filled dams.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.11a
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• pp.183-188
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• 1999

Due to many advantages of advanced composite materials, research on the application of composites to the construction industry is initiated. In this paper, fabrication methods efficient for infrastructures and application examples of each method are discussed. It also presents the structural characteristics of concrete filled glass fiber reinforced composite tubular member. Experimental results shows that strength and ductility of composite compression member is considerably increased due to concrete confinement action of composite surface.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.427-430
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• 2005

The study for seismic characteristics of square concrete-filled steel tubular (CFT) columns is analytically conducted. For predicting the strength and ductility of CFT columns, fiber analysis technique is used. The analytical results show reasonable agreement with experiment results. The influence of the steel tube on the lateral response of CFT columns is studied for the evaluation of seismic performance.