• Land and Housing Review
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• v.1 no.1
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• pp.43-50
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• 2010

In this study, the influences of steel dampers on the behavior of RC frames were investigated using the experimental approach to suggest the installation methods of steel dampers using K-barces. The performances of RC frames with dampers can be evaluated by superposition the load-displacement curves of RC frames and steel dampers with regard to the influences of K-braces. Three specimens are tested to investigate the cyclic behavior of RC frames with dampers. The performances of RC frames with dampers with respect to strength, rigidity, and hysteretic performance are examined. It was found that test results demonstrates the effect of seismic retrofit on RC frames with steel dampers(D-RCF-KBSF, D-RCF-KBSP) compared with RC frames(N-RCF). An approximate design curves may not be good agreement with those of the tests, it is conservative enough so that you can design of RC frames with steel damper with regard to the influences of K-braces.

• Advances in concrete construction
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• v.8 no.3
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• pp.173-185
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• 2019

This article presents a comparative study of the effect of steel layouts on the seismic behavior of transition steel-concrete composite connections, both experimental and analytical investigations of concrete filled steel tube-reinforced concrete (CFST-RC) and steel reinforecd concrete-reinforced concrete (SRC-RC) structures were conducted. The steel-concrete composite connections were subjected to combined constant axial load and lateral cyclic displacements. Tests were carried out on four full-scale connections extracted from a real project engineering with different levels of axial force. The effect of steel layouts on the mechanical behavior of the transition connections was evaluated by failure modes, hysteretic behavior, backbone curves, displacement ductility, energy dissipation capacity and stiffness degradation. Test results showed that different steel layouts led to significantly different failure modes. For CFST-RC transition specimens, the circular cracks of the concrete at the RC column base was followed by steel yielding at the bottom of the CFST column. While uncoordinated deformation could be observed between SRC and RC columns in SRC-RC transition specimens, the crushing and peeling damage of unconfined concrete at the SRC column base was more serious. The existences of I-shape steel and steel tube avoided the pinching phenomenon on the hysteresis curve, which was different from the hysteresis curve of the general reinforced concrete column. The hysteresis loops were spindle-shaped, indicating excellent seismic performance for these transition composite connections. The average values of equivalent viscous damping coefficients of the four specimens are 0.123, 0.186 and 0.304 corresponding to the yielding point, peak point and ultimate point, respectively. Those values demonstrate that the transition steel-concrete composite connections have great energy dissipating capacity. Based on the experimental research, a high-fidelity ABAQUS model was established to further study the influence of concrete strength, steel grade and longitudinal reinforcement ratio on the mechanical behavior of transition composite connections.

• Structural Engineering and Mechanics
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• v.81 no.6
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• pp.715-728
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• 2022

A new type of buckling-restrained braces (BRBs) with a longitudinally profiled steel plate working as the core (LPBRB) is proposed and experimentally investigated. Different from conventional BRBs with a constant thickness core, both stiffness and strength of the longitudinally profiled steel core along its longitudinal direction can change through itself variable thickness, thus the construction of LPBRB saves material and reduces the processing cost. Four full-scale component tests were conducted under quasi-static cyclic loading to evaluate the seismic performance of LPBRB. Three stiffening methods were used to improve the fatigue performance of LPBRBs, which were bolt-assembled T-shaped stiffening ribs, partly-welded stiffening ribs and stiffening segment without rib. The experimental results showed LPBRB specimens displayed stable hysteretic behavior and satisfactory seismic property. There was no instability or rupture until the axial ductility ratio achieved 11.0. Failure modes included the out-of-plane buckling of the stiffening part outside the restraining member and core plate fatigue fracture around the longitudinally profiled segment. The effect of the stiffening methods on the fatigue performance is discussed. The critical buckling load of longitudinally profiled segment is derived using Euler theory. The local bulging behavior of the outer steel tube is analyzed with an equivalent beam model. The design recommendations for LPBRB are presented finally.

• Earthquakes and Structures
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• v.23 no.5
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• pp.473-491
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• 2022

The research investigates experimentally the effect of confinement on structural behavior at the ends of beam-column in reinforced concrete (RC) frames. In the experimental study, five specimens consisting of 1/3-scaled RC frames having single-bay, representing the traditional deficiencies of existing buildings constructed without receiving proper engineering service is investigated. The RC frame specimens were produced to represent most of the existing buildings in Turkey that have damage potential. To decrease the probable damage to the existing buildings exposed to earthquakes, the carbon Textile Reinforced Mortar (TRM) strengthening technique (fully wrapping) was used on the ends of the RC frame elements to increase the energy dissipation and deformation capacity. The specimens were tested under reversed cyclic lateral loading with constant axial loads. They were constructed satisfying the weak column-strong beam condition and consisting of low-strength concrete, such as compressive strength of 15 MPa. The test results were compared and evaluated considering stiffness, strength, energy dissipation capacity, structural damping, ductility, and damage propagation in detail. Comprehensive investigations of these experimental results reveal that the strengthening of a brittle frame with fully-TRM wrapping with non-anchored was effective in increasing the stiffness, ductility, and energy dissipation capacities of RC bare frames. It was also observed that the frame-only-retrofitting with an infill wall is not enough to increase the ductility capacity. In this case, both the frame and infill wall must be retrofitted with TRM composite to increase the stiffness, lateral load carrying, ductility and energy dissipation capacities of RC frames. The presented strengthening method can be an alternative strengthening technique to enhance the seismic performance of existing or moderately damaged RC buildings.

• Journal of the Korean Geotechnical Society
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• v.23 no.3
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• pp.141-147
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• 2007

Various approaches have been developed for the dynamic response analysis of piles. In one of the approaches, the soil-pile interaction is approximated by using parallel nonlinear springs, namely the p-y curves. Currently available p-y curve recommendations are based on static and cyclic lateral load tests. Other researchers have attempted to extend the p-y curves by incorporating the effects of liquefaction on soil-pile interaction and derived scaling factors of p-y curves to account fur the liquefaction. However, opinions on the scaling factors vary. In this study, the sealing factors, which reflect the variation of the elastic moduli of surrounding soils, were established combining the relationship between excess pore pressures and the natural frequencies of a soil-pile system obtained from Ig shaking table tests and the relationship between the elastic moduli of surrounding soils and the natural frequencies of a soil-pile system obtained from numerical analyses. As a result, the scaling factors were presented in an exponential function.

• Structural Engineering and Mechanics
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• v.87 no.2
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• pp.137-149
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• 2023

In this study, to explore the working performance of the CFST split spherical node wind power tower, two groups of CFST split spherical joint plane towers with different web wall thicknesses and a set of space systems were analyzed. The tower was subjected to a low-cycle repeated load test, and the hysteresis and skeleton curves were analyzed. ABAQUS finite element simulation was used for verification and comparison, and on this basis parameter expansion analysis was carried out. The results show that the failure mode of the wind power tower was divided into weld tear damage between belly bar, high strength bolt thread damage and belly rod flexion damage. In addition, increasing the wall thickness of the web member could render the hysteresis curve fuller. Finally, the bearing capacity of the separated spherical node wind power tower was high, but its plastic deformation ability was poor. The ultimate bearing capacity and ductility coefficient of the simulated specimens are positively correlated with web diameter ratio and web column stiffness ratio. When the diameter ratio of the web member was greater than 0.13, or the stiffness ratio γ of the web member to the column was greater than 0.022, the increase of the ultimate bearing capacity and ductility coefficient decreased significantly. In order to maximize the overall mechanical performance of the tower and improve its economy, it was suggested that the diameter ratio of the ventral rod be 0.11-0.13, while the stiffness ratio γ should be 0.02-0.022.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.6
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• pp.201-210
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• 2023

This study is to evaluate the ductility strengthening effect of aramid fiber sheets on piloti-type structures. Two piloti-type structure specimens were prepared and tested under statical cyclic lateral loads. The ductility strengthening effect was validated from the analysis of lateral load-displacement relationship, displacement ductility ratio, work damage index and torsion behavior. Test results showed that the post-peak behavior of piloti-type structures with columns strengthened with aramid fiber sheets tended to be ductile resulting from preventing shear failure and minimizing torsion due to the effective lateral confinement of column concrete by aramid fiber sheet. Consequently, the displacement ductility ratio and work damage index of piloti-type structures with columns with strengthened with aramid fiber sheets were 4.63 and 42.81 times higher than those of non strengthened piloti-type structures.

• Earthquakes and Structures
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• v.26 no.1
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• pp.49-58
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• 2024

The purpose of this study was to develop a system capable of restoring the seismic performance of a precast concrete (PC) connection damaged by an earthquake. The developed PC connection consists of a top-and-seat angle, post-tensioning (PT) tendons, and U-shaped steel. The PC beam can be replaced by cutting the PT tendons in the event of damage. In addition, the seismic performance of the developed PC beam-column connection was evaluated experimentally. A PC beam-column connection specimen was fabricated, and a quasistatic cyclic loading test was conducted to a maximum drift ratio of 2.3%. Subsequently, the PC beam was replaced by a new PC beam, and the repaired PC connection was loaded to a maximum drift ratio of 5.1%. The structural performance of the repaired PC connection was then compared with that of the original PC connection. The difference in the load at the drift ratio of 2.3% between the original and the repaired PC specimens was only 0.2%. The residual drift ratio in the repaired PC specimen did not exceed 1.0% at the 2.0 % drift ratio cycles, which satisfies the life safety performance level specified in ACI 374.2R-13. When the developed PC connection system is used, structural performance can be restored by rapidly replacing the damaged elements.

• Journal of the Korea Concrete Institute
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• v.23 no.6
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• pp.711-722
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• 2011

Beam-column gravity or Intermediate Moment frames subjected to unexpected large displacements are vulnerable when no seismic details are provided, which is typical. Conversely, economic efficiency of those frames is decreased if unnecessary special detailing is applied as the beam and column size becomes quite large and steel congestion is caused by joint transverse reinforcement in beam-column connections. Moderate seismic design is used in Korea for beam-column connections of buildings with structural walls, which are to be destroyed when the unexpected large earthquake occurs. Nonetheless, performance of such beamcolumn connections may be substantially improved by the addition of steel fibers. This study was conducted to investigate the effect of steel fibers in reinforced concrete exterior beam-column connections and possibility for the replacement of some joint transverse reinforcement. Ten half-scale beam-column connections with non-seismic details were tested under cyclic loads with two cycles at each drift up to 19 cycles. Main test parameters used were the volume ratio of steel fibers (0%, 1%, 1.5%) and joint transverse reinforcement amount. The test results show that maximum capacity, energy dissipation capacity, shear strength and bond condition are improved with the application of steel fibers to substitute transverse reinforcement of beam-column connections. Furthermore, several shear strength equations for exterior connections were examined, including the proposed equation for steel fiber-reinforced concrete exterior connections with non-seismic details.

• The Journal of Advanced Prosthodontics
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• v.6 no.2
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• pp.126-132
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• 2014

PURPOSE. This study was conducted to evaluate the influence of the implant-abutment connection design and diameter on the screw joint stability. MATERIALS AND METHODS. Regular and wide-diameter implant systems with three different joint connection designs: an external butt joint, a one-stage internal cone, and a two-stage internal cone were divided into seven groups (n=5, in each group). The initial removal torque values of the abutment screw were measured with a digital torque gauge. The postload removal torque values were measured after 100,000 cycles of a 150 N and a 10 Hz cyclic load had been applied. Subsequently, the rates of the initial and postload removal torque losses were calculated to evaluate the effect of the joint connection design and diameter on the screw joint stability. Each group was compared using Kruskal-Wallis test and Mann-Whitney U test as post-hoc test (${\alpha}$=0.05). RESULTS. The postload removal torque value was high in the following order with regard to magnitude: two-stage internal cone, one-stage internal cone, and external butt joint systems. In the regular-diameter group, the external butt joint and one-stage internal cone systems showed lower postload removal torque loss rates than the two-stage internal cone system. In the wide-diameter group, the external butt joint system showed a lower loss rate than the one-stage internal cone and two-stage internal cone systems. In the two-stage internal cone system, the wide-diameter group showed a significantly lower loss rate than the regular-diameter group (P<.05). CONCLUSION. The results of this study showed that the external butt joint was more advantageous than the internal cone in terms of the postload removal torque loss. For the difference in the implant diameter, a wide diameter was more advantageous in terms of the torque loss rate.