• Structural Engineering and Mechanics
• /
• v.88 no.2
• /
• pp.169-178
• /
• 2023

Lightweight aggregate concrete (LWAC) has various advantages, but it has limitations in ensuring sufficient ductility as structural members such as reinforced concrete (RC) columns due to its low confinement effect of core concrete. In particular, the confinement effect significantly decreases as the axial load increases, but studies on evaluating the ductility of RC columns at high axial loads are very limited. Therefore, this study examined the effects of concrete unit weight on the seismic performance of RC columns subjected to constant axial loads applied with different values for each specimen. The column specimens were classified into all-lightweight aggregate concrete (ALWAC), sand-lightweight aggregate concrete (SLWAC), and normal-weight concrete (NWC). The amount of transverse reinforcement was specified for all the columns to satisfy twice the minimum amount specified in the ACI 318-19 provision. Test results showed that the normalized moment capacity of the columns decreased slightly with the concrete unit weight, whereas the moment capacity of LWAC columns could be conservatively estimated based on the procedure stipulated in ACI 318-19 using an equivalent rectangular stress block. Additionally, by applying the section lamina method, the axial load level corresponding to the balanced failure decreased with the concrete unit weight. The ductility of the columns also decreased with the concrete unit weight, indicating a higher level of decline under a higher axial load level. Thus, the LWAC columns required more transverse reinforcement than their counterpart NWC columns to achieve the same ductility level. Ultimately, in order to achieve high ductility in LWAC columns subjected to an axial load of 0.5, it is recommended to design the transverse reinforcement with twice the minimum amount specified in the ACI 318-19 provision.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
• /
• 2010.04a
• /
• pp.371-376
• /
• 2010

The strength of steel material in a concrete filled steel tube (CFT) is reduced in fire, but the filled interior concrete structurally ensures the fire resistance due to its high thermal capacity. More, the contractibility of CFT is excellent since it can be constructed without form work. This research analyzed the interior concrete strength and deformation characteristics, which are the influence factors of the fire resistance of CFT, in proportion to the axial load ratio. The fire resistance performance according to changes of the axial load ratio showed great fluctuation. As $280{\times}280{\times}6$ CFT columns with the concrete strengths of 24 MPa and 40 MPa and the axial load ratios of 0.9, 0.6, and 0.2 in accordance with KS F 2257-1 and 7 were heated with loading to examine the fire resistance performance, the 24 MPa concrete exhibited the fire resistance time as 27, 113, and 180 minutes for the axial load ratios, 0.9, 0.6, and 0.2 respectively. In case of 40 MPa concrete, the fire resistance time were turned out to be 19 and 28 minutes for the axial load ratios, 0.9 and 0.6 respectively. The results of 40 MPa concrete showed the much lower fire resistance performance when comparing with those of 24 MPa concrete. The fire resistance performance was not increased significantly when the axial load ratio was reduced. Therefore, the deceased fire resistance performance of high strength concrete is assumed to be caused by the internal pressure increase upon the heat application.

• Steel and Composite Structures
• /
• v.25 no.5
• /
• pp.603-615
• /
• 2017

This experimental research presents the seismic performance of steel reinforced high-strength concrete (SRHC) short columns. Eleven SRHC column specimens were tested under simulated earthquake loading conditions, including six short column specimens and five normal column specimens. The parameters studied included the axial load level, stirrup details and shear span ratio. The failure modes, critical region length, energy dissipation capacity and deformation capacity, stiffness and strength degradation and shear displacement of SRHC short columns were analyzed in detail. The effects of the parameters on seismic performance were discussed. The test results showed that SRHC short columns exhibited shear-flexure failure characteristics. The critical region length of SRHC short columns could be taken as the whole column height, regardless of axial load level. In comparison to SRHC normal columns, SRHC short columns had weaker energy dissipation capacity and deformation capacity, and experienced faster stiffness degradation and strength degradation. The decrease in energy dissipation and deformation capacity due to the decreasing shear span ratio was more serious when the axial load level was higher. However, SRHC short columns confined by multiple stirrups might possess good seismic behavior with enough deformation capacity (ultimate drift ratio ${\geq}2.5%$), even though a relative large axial load ratio (= 0.38) and relative small structural steel ratio (= 3.58%) were used, and were suitable to be used in tall buildings in earthquake regions.

• Journal of Korean Society of Steel Construction
• /
• v.25 no.1
• /
• pp.71-80
• /
• 2013

Fire-resistant (FR) test data for a square concrete-filled steel tube (CFT) columns consisting of high-strength steel (fy>650MPa) and high strength concrete (fck>100MPa) under axial loads are insufficient. The FR behavior of square high-strength CFT members was investigated experimentally for two specimens having ${\Box}-400{\times}400{\times}15{\times}3,000mm$ with two axial load cases (5,000kN and 2,500kN). The results show that the FR performance of the high-strength CFT was rapidly decreased at earlier time (much earlier at high axial load) than expected due to high strength concrete spalling and cracks. In addition, a fiber element analysis (FEA) model was proposed and used to simulate the fiber behaviour of the columns. For steel and concrete, the mechanical and thermal properties recommended in EN 1994-1-2 are adopted. Test results were compared to those of numerical analyses considering a combination of temperature and axial compression. The numerical model can reasonably predict the time-axial deformation relationship.

• Structural Engineering and Mechanics
• /
• v.18 no.4
• /
• pp.493-516
• /
• 2004

This paper addresses the behavior and strength of structural walls with a concrete compressive strength exceeding 69 MPa. This information also enhances the current database for improvement of design recommendations. The objectives of this investigation are to study the effect of axial-load ratio on seismic behavior of high-strength concrete flexural walls. An analysis has been carried out in order to assess the contribution of deformation components, i.e., flexural, diagonal shear, and sliding shear on total displacement. The results from the analysis are then utilized to evaluate the prevailing inelastic deformation mode in each of wall. Moment-curvature characteristics, ductility and damage index are quantified and discussed in relation with axial stress levels. Experimental results show that axial-load ratio have a significant effect on the flexural strength, failure mode, deformation characteristics and ductility of high-strength concrete structural walls.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 1996.04b
• /
• pp.86-93
• /
• 1996

The lubrication characteristics of high-speed ball bearings has been investigated empirically using 45mm bore split inner ring ball bearings employed in small industrial gas turbine engines with oil-jet lubrication method. For the close structural simulation, experiments carried out with bearing mounting supports of real engines, such as bearing housings and oil nozzle assemblies with squeeze film dampers. Thus the results of tests can be directly applied to the design and the development of gas turbine engines. Testing was done by varying operating speeds, axial load on bearings, and lubricant flowrates. During testing, the temperature of bearing at outer-ring face, the power consumption of the driving motor, and the rotating resistance of the bearing were measured. From this study, the representative factors for lubrication characteristics at high speed was found, and the most important one was not operating speed but axial load up to 1.95 million dmN speed and 303 kgf axial load. Furthermore, the detailed variation of the rotational resistance of the bearing could be visualized by measuring the change of the radial load under the bearing supports. The rotational resistance consists of the frictional resistance and the bearing-cavity oil resistance.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2001.11a
• /
• pp.41-46
• /
• 2001

The main objective of this study is to provide data on high strength concrete columns subjected to axial load and biaxial bending. For the design of biaxial bending, the approximate method (Bresler load contour method, PCA load contour method) is presented in ACI code. The present study investigate whether the methods are valid in high strength concrete and compare analysis results(by FEM method) with experimental results. Also, this study examines whether statics method and failure surface equation(by Hsu) are adequate.

• Land and Housing Review
• /
• v.7 no.1
• /
• pp.31-41
• /
• 2016

In this paper, we propose experimental results, which target the major variables that influence the structural performance of a wall, as well as the resulting seismic and hysteretic behavior. Results also provide the basis for the application of performance based design by identifying the nonlinear hysteretic behavior of the wall with boundary element details recently proposed in previous study by Chun et al(2011). From the experimental results, the crack and fracture patterns of a specimen, which adopt the proposed boundary element details, showed similar tendencies regardless of whether axial force or high performance steel bars is applied. Furthermore, results show that the maximum strength of the specimen can be predicted accurately based on the design equation proposed by the standard. In addition, with a higher axial force, there is a tendency that both the initial load and maximum strength increase as deformation capacity reduces, requiring consideration of the reduced deformation capacity due to a high axial force. For walls under such high axial forces, using high performance steel bars is a very effective manner of enhancing deformation capacity. Therefore, reinforcing the plastic hinge region with boundary elements using high performance steel bars is preferable.

• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 2000.10a
• /
• pp.356-363
• /
• 2000

The objectives of this study are to investigate seismic performance of spirally reinforced bridge columns and to provide test result for developing improved seismic design criteria. Quasi-static test was conducted for 12 columns of which variables were transverse reinforcement ratio and spacing, longitudinal reinforcement ratio, and axial load level. Sufficient seismic performance was observed from the test for the columns with greater confinement steel amount than the requirement of the Korean Bridge Design Specification. The columns with 0.84% of the confinement steel requirement provided adequate performance under less than 0.2 of axial load level, but showed lower ductility under 0.3 of axial load level. The current provision for the region of confinement steel distribution may be non-conservative under high axial load level, therefore a modified provision is proposed.

• Earthquakes and Structures
• /
• v.18 no.6
• /
• pp.677-689
• /
• 2020

A building structural system of moment resisting frame (MRF) with concrete filled steel tubular (CFST) columns and wide flange H beams, is one of the most conveniently constructed structural systems. However, there were few studies on evaluating seismic performance of full-scale CFST columns under high axial compression. In addition, some existing famous design codes propose various limits of width-to-thickness ratio (B/t) for steel tubes of the ductile CFST composite members. This study was intended to investigate the seismic behavior of CFST columns under high axial load compression. Four full-scale square CFST column specimens with a B/t of 42 were carried out that were subjected to horizontal cyclic-reversal loads combined with constantly light, medium and high axial loads and with a linearly varied axial load, respectively. Test results revealed that shear strength and deformation capacity of the columns significantly decreased when the axial compression exceeded 0.35 times the nominal compression strength of a CFST column, P₀. It was obvious that the higher the axial compression, the lower both the shear strength and deformation capacities were, and the earlier and faster the shear strength degradation occurred. It was found as well that higher axial compressions resulted in larger initial lateral stiffness and faster degradation of post-yield lateral stiffness. Meanwhile, the lower axial compressions led to better energy dissipation capacities with larger cumulative energy. Moreover, the study implied that under axial compressions greater than 0.35P₀, the CFST column specimens with B/t limits recommended by AISC 360 (2016), ACI 318 (2014), AIJ (2008) and EC4 (2004) codes do not provide ultimate interstory drift ratio of more than 3% radian, and only the limit in ACI 318 (2014) code satisfies this requirement when axial compression does not exceed 0.35P₀.