• Steel and Composite Structures
• /
• v.26 no.6
• /
• pp.719-731
• /
• 2018

Concrete filled steel tubular (CFST) laced columns have been widely used in high rise buildings in China. Compared to solid-web columns, this type of columns has a larger cross-section with less weight. In this paper, four concrete filled steel tubular laced columns consisting of 4 main steel-concrete tubes were tested under cyclic loading. Hysteresis and failure mechanisms were studied based on the results from the lateral cyclic loading tests. The influence of each design parameter on restoring forces was investigated, including axial compression ratio, slenderness ratio, and the size of lacing tubes. The test results show that all specimens fail in compression-bending-shear and/or compression-bending mode. Overall, the hysteresis curves appear in a full bow shape, indicating that the laced columns have a good seismic performance. The bearing capacity of the columns decreases with the increasing slenderness ratio, while increases with an increasing axial compression ratio. For the columns with a smaller axial compression ratio (< 0.3), their ductility is increased. Furthermore, with the increasing slenderness ratio, the yield displacement increases, the bending failure characteristic is more obvious, and the hysteretic loops become stouter. The results obtained from the numerical analyses were compared with the experimental results. It was found that the numerical analysis results agree well with the experimental results.

• Journal of Korea Foundry Society
• /
• v.36 no.1
• /
• pp.1-9
• /
• 2016

Improvement of the mechanical properties of a commercial aluminium casting alloy, A356, was achieved through an optimised combination of alloying elements, modification, and heat treatment. 0.7 wt.% Cu and an additional 0.2 wt.% Mg were added to an Al-7Si-0.35Mg alloy for strengthening at both room and elevated temperatures, whilst a subsequent decrease in the ductility was compensated for by the modification of eutectic Si by Sr addition at a level of up to 110 ppm. It was found that the dissolution of Cu-rich or Mg-rich phases could be maximised by solid-solutionising an alloy with 40 ppm Sr at $530^{\circ}C$, increasing the tensile and yield strengths to 350 MPa and 297 MPa, respectively, with a reasonably high strain of 5% after peak-aging at $210^{\circ}C$. Further addition of Sr up to 110 ppm is, however, more likely to interfere with the dissolution of the Cu-rich or Mg-rich phases during solid solution treatment, resulting in a slight decrease in both tensile and yield strengths at room temperature. Besides the Cu addition, such undissolved phases, on the other hand, may contribute to elevated temperature strength at $200^{\circ}C$.

• Journal of Korean Society of Steel Construction
• /
• v.19 no.1
• /
• pp.43-52
• /
• 2007

There is a growing range of applications for concrete-filled steel tube (CFT) member because of its superior performance. But a CFT member may be uneconomical or has weight problems because it is fully filled with concrete. In this study, a new type of member, called internally confined hollow (ICH) CFT member, was developed to solve the high cost and weight problems of the CFT member. To determine stress-strain model of the concrete in an ICH CFT column, possible failure modes of an ICH CFT column were suggested and confining pressure was derived from equilibriums for each failure mode. From the derived equations, a computer program was coded and parametric studies were performed for some examples. Analytical results showed that internally confined concrete has enhanced strength and ductility compared with those of unconfined or biaxially confined concrete.

• Journal of the Korean Society for Precision Engineering
• /
• v.29 no.6
• /
• pp.680-685
• /
• 2012

Ceramic femoral heads are now widely used in Total Hip Replacement (THR). Due to their high biocompatibility and low ductility, ceramic femoral heads are considered to be suitable for young and active patients. However, as in testing the mechanical stability of the femoral head, the conventional proof test (standard ISO 7206-10) has its limit of showing axisymmetric stress distribution on the contact surface, while non-uniformed stress distribution is expected after THR. Since non-uniformed stress distribution can result in the increased probability of ceramic femoral head fracture, it is considerable to evaluate the stress distribution in vivo-like conditions. Therefore, this study simulated the ceramic femoral heads under in vivo-like conditions using finite element method. The maximum stress decreased when increasing the size of the femoral head and stress distribution was concentrated on superior contact surface of the taper region.

• Earthquakes and Structures
• /
• v.19 no.4
• /
• pp.273-286
• /
• 2020

The pile group foundation is widely used for gravity pier of high-speed railway bridges in China. If a moderate or strong earthquake occurs, the pile-surrounding soil will exhibit obvious nonlinearity and significant pile group effect. In this study, an improved pushover analysis model for the pile group foundation with consideration of pile group effect is presented and validated by the quasi-static test. The improved model uses simplified springs to simulate the soil lateral resistance, side friction and tip resistance. PM (axial load-bending moment) plastic hinge model is introduced to simulate the impact of the axial force changing of pile group on their elastic-plastic characteristics. The pile group effect is considered in stress-stain relations of the lateral soil resistance with a reduction factor. The influence factors on nonlinear characteristics and plastic hinge distribution of the pile group foundation are discussed, including the pier height, longitudinal reinforcement ratio and stirrup ratio of the pile, and soil mechanical parameters. Furthermore, the displacement ductility factor, resistance increase factor and yielding stiffness ratio are provided to evaluate the seismic performance of soil-pile system. A case study for the pile group foundation of a railway simply supported beam bridge with a 32 m-span is conducted by numerical analysis. It is shown that the ultimate lateral force of pile group is not determined by the yielding force of the single one in these piles. Therefore, the pile group effect is essential for the seismic performance evaluation of the railway bridge with pile group foundation.

• Journal of the Korea Concrete Institute
• /
• v.24 no.3
• /
• pp.323-331
• /
• 2012

This paper presents a new strengthening method on concrete column against seismic loads for structural performance tests. An X-bracing using high performance carbon fiber threads called the "Carbon fiber anchor X-bracing system" is used to connect RC frames internally. The carbon fiber sheet is wrapped around the column to fix the top and bottom of the column after Super anchor was installed by drilling hole on the column. The structural performance was evaluated experimentally and analytically. Two types of columns specimens were made; flexure fracture scaled model and shear fracture scaled model. For the performance evaluation, cyclic loading tests were conducted on moment and shear resisting columns with and without X bracing. Test results confirmed that the bracing system installed on RC columns enhanced the strength capacity and provided adequate ductility.

• Journal of Ocean Engineering and Technology
• /
• v.30 no.6
• /
• pp.520-525
• /
• 2016

In this study, a mixture of polypropylene fibers and glass fibers were used to weave polypropylene/glass fiber-reinforced composite panels with characteristics such as highly elongated short fibers, high ductility, anti-fouling, and hydrophobicity as a result of a directional property. Mechanical and environmental tests were carried out with specimens fabricated with this composite panel, and its applicability to shipbuilding and ocean leisure industries was evaluated through a comparison with existing glass fiber-reinforced composite materials. The results of this experiment verified the excellence of the polypropylene/glass-mixed woven fiber-reinforced composite material compared to the existing glass fiber-reinforced composite material. However, the forming process needs to be changed to improve the weak interfacial bonding, and the properties of the composite material itself could be improved through mixed weaving with other fibers after development. Maximizing of the advantages of the polypropylene fibers and overcoming their shortcomings will improve their applicability to the shipbuilding, ocean leisure, and other industries, and increase the value of polypropylene fibers in the composite material market.

• Structural Engineering and Mechanics
• /
• v.19 no.6
• /
• pp.653-677
• /
• 2005

Concrete filled steel tubular columns (CFT) are widely used in civil engineering works, especially in large scale of works because of high strength, deformation, toughness and so on. On the other hand, as a kind of strengthening measure for seriously damaged reinforced concrete piers of viaduct in Hansin-Awaji earthquake of Japan in 1995, reinforced concrete piers were wrapped with steel plate. Then, a new kind of structure appeared, that is, reinforced concrete filled steel tubular column (RCFT). In this paper, compression test and bending-shearing test on RCFT are carried out. The main parameters of experiments are (1) strength of concrete, (2) steel tube with or without rib, (3) width-thickness ratio and (4) arrangement of reinforcing bars. According to the experimental results, the effect of parameters on mechanical characteristics of RCFT is analyzed clearly. At the same time, strength evaluation formula for RCFT column is proposed and tested by experimental results and existed recommendations (AIJ 1997). The strength calculated by the proposal formula is in good agreement with test result. As a result, the proposed evaluation formula can evaluate the strength of RCFT column properly.

• Magazine of the Korea Concrete Institute
• /
• v.7 no.5
• /
• pp.133-144
• /
• 1995

This study investigated to the properties of structural behaviors through a series of experiment with the key parameter, such as diameter-to-thickness(D/t) ratio, selenderness ratio of steel t~ube and strength of concrete under loading condition simple confined concrete by steel tube as a fundmental study on adaptability with structural members in high-rise building. The obtained results are sumnarised as follow. (1) The fracture mode of confined concrete was presented digonal tension fracture in the direction of $45^{\circ}$ with compression failure at the end of specimen in stub column, but the fracture mode of long column was assumed an aspect of bending fracture transversely. (2) The deformation capacity and ductility effect was increased by confine steel tube for concrete. (3) 'The emprical formula to predict the ultimate capacity of confined concrete by steel tube and concrete filled steel tube column using restraint of concrete considered D / t ratio, selenderness ratio of steel tube anti strength of' concrete were proposed.

• Journal of the Korea Concrete Institute
• /
• v.13 no.4
• /
• pp.321-328
• /
• 2001

This paper presents the tensile behavior of stud connections installed between reinforced concrete and steel members. Eight specimens are tested to verify the factors influencing the tensile behavior of the connection. Major variables considered in the test are the reinforcement ratios of concrete member and connection details. Test results indicate that the reinforcing bars near stud bolts contribute to the increase of the tensile strength of the member as well as to the reduction of brittle failure. It is shown that C-type or U-type connection has relatively high ductility. From the evaluation on the tensile strength of test results including those of peformed by previous researchers, it was shown CCD (Concrete Capacity Design) method overestimated the strength. In this paper, the reduction factor of 0.75 ø instead of ø is suggested for design purpose of the stud connection.