• Smart Structures and Systems
• /
• v.16 no.4
• /
• pp.701-723
• /
• 2015

Friction isolators are one of the most important types of bearings used to mitigate damages of earthquakes. The adaptive behavior of these isolators allows them to achieve multiple levels of performances and predictable seismic behavior during different earthquake hazard levels. There are three main types of friction isolators. The first generation with one sliding surface is known as Friction Pendulum System (FPS) isolators. The double concave friction pendulum (DCFP) with two sliding surfaces is an advanced form of FPS, and the third one, with fully adaptive behavior, is named as triple concave friction pendulum (TCFP). The current study has been conducted to investigate and compare seismic responses of these three types of isolators. The structure is idealized as a two-dimensional single degree of freedom (SDOF) resting on isolators. The coupled differential equations of motion are derived and solved using state space formulation. Seismic responses of isolated structures using each one of these isolators are investigated under seven near fault earthquake motions. The peak values of bearing displacement and base shear are studied employing the variation of essential parameters such as superstructure period, effective isolation period and effective damping of isolator. The results demonstrate a more efficient seismic behavior of TCFP isolator comparing to the other types of isolators. This efficiency depends on the selected effective isolation period as well as effective isolation damping. The investigation shows that increasing the effective isolation period or decreasing the effective isolation damping improves the seismic behavior of TCFP compared to the other isolators. The maximum difference in seismic responses, the base shear and the bearing displacement, for the TCFP isolator are calculated 26.8 and 13.4 percent less than the DCFP and FPS in effective isolation damping equal to10%, respectively.

• The Journal of Engineering Geology
• /
• v.12 no.1
• /
• pp.75-88
• /
• 2002

When unsymmetrical surcharge is worked on polluted soft soils, large plastic shearing deformation such as settlements, lateral displacement, upheavals and shearing failure occured in the soils and they have often done considerable damages to the soils and structures. Accordingly, this study conducts laboratory pilots test to investigate the determination method of lateral flow pressure of polluted soft soils by comparing it to existing equations. The model test is performed that a model stock device is made and polluted soils are filled in a container which fires the soils. Then the displacement is observed as surcharge load is increased by regular intervals at untrained condition. The result shows that test the lateral flow pressure is adequately calculated by the equation (P=K$_{0}$YH) and the maximum value of lateral flow pressure Is found near 0.3H of layer thickness(H) and is higher to ground surface than synthesis pattern, Poulos distribution pattern and soft clay soils(CL, CH) which is not polluted.

• Tunnel and Underground Space
• /
• v.15 no.1 s.54
• /
• pp.71-79
• /
• 2005

The stability of the intersection area of two tunnels is analyzed by observational method. The depth from ground surface to the intersected area is shallow and the geology around the area consists of soil and/or weathered rock. The tunnel is supported by reinforced protective umbrella method with 12 m long 3-layer steel-pipes and the intersected area is additionally reinforced with 6 m long rockbolts. The measured displacements are converged and mechanical stability of the intersected area of two tunnels is confirmed; tunnel arch settles to 6-7 mm at the crown and the sidewalls converges to about 5 mm. So based on the displacement measurements, the supporting system for the tunnel intersection proves to be effective to not only reduce the deformation of tunnels but also maintain the stability of tunnels.

• Journal of Industrial Technology
• /
• v.24 no.A
• /
• pp.227-238
• /
• 2004

This paper is results of experimental and nunerical works on the behavior of the cut-and-cover tunnel. Centrifuge model tests were performed to simulate the behavior of the cut-and-cover tunnels having cross sections of national road and subway tunnels. Model experiments were carried out with changing the cut slope and the slope of filling ground surface. Displacements of tunnel lining resulted from artificially accelerated gravitational force up to 40g of covered material used in model tests, were measured during centrifuge model tests. In model tests, Jumunjin Standard Sand with the relative density of 80 % and the zinc plates were used for the covered material and the flexible tunnel lining, respectively. Basic soil property tests were performed to obtain it's the property of Jumumjin Standard Sand. Shear strength parameters of Jumunjin Standard Sand were obtained by performing the triaxial compression tests. Direct shear tests were also carried out to find the mechanical properties of the interface between the lining and the covered material. Numerical analysis with the commercially available program of FLAC were performed to compare with results of centrifuge model experiment In numerical modelling. Mohr-Coulomb elasto-plastic constitutive model was used to simulaye the behavoor of Jumunjin Standard Sand and the interface element between the lining and the covered material was implemented to simulate the interaction between them. Compared results between model tests and numerical estimation with respect to displacement of the lining showed in good agreements.

• The Journal of Engineering Geology
• /
• v.14 no.4 s.41
• /
• pp.429-442
• /
• 2004

Landslide of the Whanpyeong Mountain which was occurred at Busan Metropolitan City in 1999 belongs to the category of plane failure. Automatic monitoring system to measure horizontal displacement, pore pressure change and load change has operating from reconstruction stage for evaluating rock slope stability (August, 2000$\~$Feburuary, 2002). As a result of the analysis on the monitoring performance data, it is suggested that infiltrated rain water from pound surface discharges rapidly through cut-slope because pressure head of water decreases rapidly after rainfall while rise of pore pressure is proportional to the amount of rain water. As a result of data analyses for inclinometers and load cells, it seems that slope is stablized be cause ground deformation is rarely detected. The areas especially similar to the study site where landslide is induced by heavy rain fall, change of pore pressure is rapidly analyzed using automatic monitoring system. Therefore, it is considered that automatic monitoring system is very effect for slope stability analysis on important cut-slopes.

• Tunnel and Underground Space
• /
• v.25 no.6
• /
• pp.515-526
• /
• 2015

Predicting and measuring tunnel convergence is very crucial for estimating tunnel stability and economical construction of NATM tunnels. The method to estimate the tunnel convergence that occurs before and after construction is proposed based on literature reviews. The total displacement occurring related to tunnel construction is determined to be about 2.5 times that of measured displacements. The results of displacement measurements at two tunnels constructed with similar rock types are examined for the investigation of factors affecting the tunnel convergence. The average convergence of Gyungju A Tunnel is about 6.7 times bigger than that of Daejeon B Tunnel. The possible causes of the large convergence in Gyungju A Tunnel are suggested. In order to predict the convergence of tunnels, careful investigation of the geological structures in the ground surface and the influence of external conditions as well as careful face mapping of the tunnel face should be conducted.

• Journal of the Korean Geotechnical Society
• /
• v.27 no.11
• /
• pp.27-37
• /
• 2011

A series of centrifuge model tests to investigate the suction pile pullout loading capacity in sand have been performed. The main parameters that affect the pullout loading capacity of a suction pile include the mooring line inclination angle and the padeye position of the suction pile. With respect to the padeye position, the maximum pullout loading capacity is obtained when the padeye position is near 75% of the pile length from the top. The direction of the pile rotation changes when the padeye position reaches somewhere near 50~75% for all mooring line inclination angles. The translation displacement of suction pile to develop the time of maximum pullout loading capacity decreased as the mooring line inclination angle increased. In addition, the vertical displacements of the center of a suction piles for all cases appeared to develop toward the ground surface.

• Earthquakes and Structures
• /
• v.10 no.5
• /
• pp.1089-1109
• /
• 2016

Modified two-surface model (M2SM) is one of the steel elasto-plastic hysteretic constitutive models that consider both analysis accuracy and efficiency. However, when M2SM is used for complex strain history, sometimes the results are irrational due to the limitation of stress-strain path judgment. In this paper, the defect of M2SM was re-modified by improving the judgment of stress-strain paths. The accuracy and applicability of the improved method were verified on both material and structural level. Based on this improvement, the nonlinear time-history analysis was carried out for a deck-through steel arch bridge with a 200 m-long span under the ground motions of Chi-Chi earthquake and Niigata earthquake. In the analysis, we compared the results obtained by hysteretic constitutive models of improved two-surface model (I2SM) presented in this paper, M2SM and the bilinear kinematic hardening model (BKHM). Results show that, although the analysis precision of displacement response of different steel hysteretic models differs little from each other, the stress-strain responses of the structure are affected by steel hysteretic models apparently. The difference between the stress-strain responses obtained by I2SM and M2SM cannot be neglected. In significantly damaged areas, BKHM gives smaller stress result and obviously different strain response compared with I2SM and M2SM, and tends to overestimate the effect of hysteretic energy dissipation. Moreover, at some position with severe damage, BKHM may underestimate the size of seismic damaged areas. Different steel hysteretic models also have influences on structural damage evaluation results based on deformation behavior and low cycle fatigue, and may lead to completely different judgment of failure, especially in severely damaged areas.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.21 no.2
• /
• pp.24-33
• /
• 2017

Domestic urban railway underground station structures, which were built in the 1970s ad 1980s, had been constructed as Cut-and-Cover construction system without seismic design. Because the trends of earthquake occurrence is constantly increasing all over the world as well as the Korean Peninsula, massive human casualties and severe properties and structures damage might be occurred in an non-retrofitted underground station during an earthquake above a certain scale. Therefore, to evaluate the retrofit effect and soil-structure interaction of seismic retrofitted underground station, a centrifugal shaking table test with enhanced stiffness on its structural main member are carried out on 1/60 scaled model using the Kobe and Northridge earthquakes. The seismic retrofitted members, which are columns, side walls, and slabs, are evaluated to comparing with existing non-retrofitted centrifuge test results Also, to simulate the scaled ground using variation of shear velocity according to site conditions such as ground depth and density, resonant column test is performed. From the test results, the relative displacement behavior between ground and structures shows comparatively similar in ground, but is increased on ground surface. The seismic retrofit effects were measured using relative displacements and moment behavior of column and side walls rather than slabs. Additionally, earthquake wave can be used to main design factor due to large structural deformation on Kobe earthquake wave than Norhridge earthquake wave.

• Journal of the Korean Geotechnical Society
• /
• v.15 no.6
• /
• pp.71-86
• /
• 1999

The displacements of soil nailed wall and the nail tensile force for 11 soil nailing sites were investigated by using measurements obtained from inclinometer and strain gauge. The maximum horizontal displacement which occurred between 5% and 15% of the final excavation depth was found to be below 0.3% and 0.2% of excavation depth for well and poorly constructed sites. It was also found that the maximum horizontal displacements for 0.4%, 0.3% and 0.2% of excavation depth occurred when the ratios of nail length to final excavation depth were 0.5, 0.5~0.6 and 0.6~0.7. But the maximum horizontal displacement increased by 0.3% of excavation depth when the ratio was above 0.7. This was probably due to the shallow excavation depth and the deep soil stratum. The non-dimensional maximum tensile force of nail, K, from ground surface to $(0.6H_f)$ of the final excavation depth was less than 0.8 and decreased linearly between $(0.6H_f)$ and the final excavation depth. Also, the maximum tensile force was found to reach up to 60% of the ultimate tensile force at final excavation.