• Computers and Concrete
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• v.10 no.3
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• pp.277-294
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• 2012

The aim of the study is to determine the modal parameters of a prototype damaged arch dam by operational modal analysis (OMA) method for some damage scenarios. For this purpose, a prototype arch dam-reservoir-foundation model is constructed under laboratory conditions. Ambient vibration tests on the arch dam model are performed to identify the modal parameters such as natural frequency, mode shape and damping ratio. The tests are conducted for four test-case scenarios: an undamaged dam with empty reservoir, two different damaged dams with empty reservoirs, and a damaged dam with full reservoir. Loading simulating random impact effects is applied on the dam to crack. Cracks and fractures occurred at the middle of the upper part of the dams and distributed through the abutments. Sensitivity accelerometers are placed on the dams' crests to collect signals for measurements. Operational modal analysis software processes the signals collected from the ambient vibration tests, and enhanced frequency domain decomposition and stochastic subspace identification techniques are used to estimate modal parameters of the dams. The modal parameters are obtained to establish a basis for comparison of the results of two techniques for each damage case. Results show that approximately 35-40% difference exists between the natural frequencies obtained from Case 1 and Case 4. The natural frequencies of the dam considerably decrease with increasing cracks. However, observation shows that the filled reservoir slightly affected modal parameters of the dam after severe cracking. The mode shapes obtained are symmetrical and anti-symmetrical. Apparently, mode shapes in Case 1 represent the probable responses of arch dams more accurately. Also, damping ratio show an increase when cracking increases.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10b
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• pp.851-856
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• 2000

When subjected to the strong earthquake ground motion, upper-wall lower-frame structures have high possibility of the weak-story failure in the lower frame part. Sufficient strength, energy dissipation capacity and ductility should be provided at the joint between the deep beam and the lower column. In this study, a typical structure was selected for a prototype and four 1:2.5 scaled models, representing the subassemblage including the exterior column and the deep beam, were constructed. The transverse reinforcement was designed according to ACI procedure¹ and the procedure proposed by Sheikh². The inelastic behavior of the subassemblages subjected to the cyclic lateral displacement were evaluated through investigation of the ultimate strength, ductility, load-deformation characteristics. From the test of 4 specimens, it is concluded that the specimens designed according to Sheikh's procedure revealed higher ductility than that by ACI procedure.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.1118-1125
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• 2005

In this study, seismic safety of CFRD(Concrete-Face Rockfill Dam) type "D" dam in operation is evaluated from the results of 1-g shaking table test using similitude laws. Model dam is made by similitude law considering the grain size of prototype dam component. After the model dam is impounded to the normal water level(N.W.L), it is excited by artificial earthquake wave corresponding to standard design respond spectrum of the "D" dam site. Displacement response behavior of the dam is examined through the measurement of vertical and horizontal displacement of dam crest. Also, amplification characteristics of acceleration with dam height is examined through the measurement of acceleration with dam height. Finally, the purpose of this study is to evaluate seismic safety of "D" dam in operation. From the results of acceleration measurement, it was found that acceleration of dam crest was amplified about 1.52 times compared to the acceleration of dam bottom and amplification phenomenon is outstanding at three quarters of dam height from the bottom of dam. From the analysis of displacement behavior, it was estimated that vertical displacement of prototype dam is 6.8cm (0.1% of dam height) and horizontal displacement 12.3cm(0.2% of dam height). These percentages is much lower than 1% of dam height(general stability criteria). Therefore, it was concluded that seismic stability of "D" dam against an estimated earthquake is guaranteed.

• Nuclear Engineering and Technology
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• v.53 no.9
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• pp.3085-3099
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• 2021

Investigations of large commercial aircraft impact effect on nuclear power plant (NPP) buildings have been drawing extensive attentions, particularly after the 9/11 event, and this paper aims to numerically assess the damage and vibrations of NPP buildings subjected to aircrafts crash. In Part I of present paper, two shots of reduce-scaled model test of aircraft impact on NPP were conducted based on the large rocket sled loading test platform. In the present part, the numerical simulations of both scaled and prototype aircraft impact on NPP buildings are further performed by adopting the commercial program LS-DYNA. Firstly, the refined finite element (FE) models of both scaled aircraft and NPP models in Part I are established, and the model impact test is numerically simulated. The validities of the adopted numerical algorithm, constitutive model and the corresponding parameters are verified based on the experimental NPP model damages and accelerations. Then, the refined simulations of prototype A380 aircraft impact on a hypothetical NPP building are further carried out. It indicates that the NPP building can totally withstand the impact of A380 at a velocity of 150 m/s, while the accompanied intensive vibrations may still lead to different levels of damage on the nuclear related equipment. Referring to the guideline NEI07-13, a maximum acceleration contour is plotted and the shock damage propagation distances under aircraft impact are assessed, which indicates that the nuclear equipment located within 11.5 m from the impact point may endure malfunction. Finally, by respectively considering the rigid and deformable impacts mainly induced by aircraft engine and fuselage, an improved Riera function is proposed to predict the impact force of aircraft A380.

• Computers and Concrete
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• v.9 no.4
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• pp.245-255
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• 2012

The damping effect of a Concrete-filled Rectangular Steel Tube (CRST) frame structure is studied in this paper. Viscous dampers are employed to insure the function of the building especially subjected to earthquakes, for some of the main vertical elements of the building are not continuous. The shaking table test of a 1:15 scale model was conducted under different earthquake excitations to recognize the seismic behavior of this building. And the vibration damping effect was also investigated by the shaking table test and the simulation analysis. The nonlinear time-history analysis of the shaking table test model was carried out by the finite element analysis program CANNY. The simulation model was constructed in accordance with the tested one and was analyzed under the same loading condition and the simulation effect was then validated by the tested results. Further more, the simulation analysis of the prototype structure was carried out by the same procedure. Both the simulated and tested results indicate that there are no obvious weak stories on the damping equipped structure, and the dampers can provide the probability of an irregular CRST frame structure to meet the requirements of the design code on energy dissipation and deformation limitation.

• Journal of the Korea institute for structural maintenance and inspection
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• v.3 no.3
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• pp.253-260
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• 1999

Main objective of this study is to examine the hysteretic behaviors and to evaluate the capacity of precast concrete (PC) large panel structures simulated from the prototype of 15-story building, Two 1/2 scaled precast concrete wall specimens and one monolithic reinforced concrete specimen were designed and tested under the cyclic loading conditions. The main parameter of test specimens in PC large panel structure is the type of details for vertical continuity of vertical steel in horizontal joint. Also the behaviors of PC large panel structures are compared with that of monolithic reinforcement concrete wall structure. From the results, the stiffness and energy dissipation ratio of the precast concrete specimens are shown little bit lower than those of monolithic reinforced concrete specimen. In the PC large panel structures, the specimen connected vertically by welding (strong connection) showed higher strength than that of the specimen connected vertically by joint box. However the failure pattern of the former showed more brittle than that of the latter due to the diagonal compressive failure of wall panels.

• Structural Engineering and Mechanics
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• v.81 no.3
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• pp.317-333
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• 2022

Visco-Plastic Damper (VPD) as a passive energy dissipation device with dual behavior has been recently numerically studied. It consists of two bent steel plates and segments with a viscoelastic solid material in between, combining and improving characteristics of both displacement-dependent and velocity-dependent devices. In order to trust the performance of VPD, for the 1st time this paper experimentally investigates prototype damper behavior under a wide range of frequency and amplitude of dynamic loading. A high-axial damping rubber is innovatively proposed as the viscoelastic layer designed to withstand large axial strains and dissipate energy accordingly. Test results confirmed all assumptions about VPD. The behavior of VPD subjected to low levels of excitation is elastic while with increasing levels of excitation, a significant source of energy dissipation is provided through the yielding of the steel elements in addition to the viscoelastic energy dissipation. The results showed energy dissipation of 99.35 kN.m under a dynamic displacement with 14.095 mm amplitude and 0.333 Hz frequency. Lateral displacement at the middle of the device was created with an amplification factor obtained ranging from 2.108 to 3.242 in the rubber block. Therefore, the energy dissipation of viscoelastic material of VPD was calculated 18.6 times that of the ordinary viscoelastic damper.

• Geomechanics and Engineering
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• v.10 no.4
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• pp.405-422
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• 2016

The paper deals with the results of the laboratory cyclic plate load tests performed on the reinforced soft clay beds. The performances of the clay bed reinforced with geocells and geocells with additional basal geogrid cases are compared with the performance of the unreinforced clay beds. From the cyclic plate load test results, the coefficient of elastic uniform compression ($C_u$) was calculated for the different cases. The $C_u$ value was found to increase in the presence of geocell reinforcement. The maximum increase in the $C_u$ value was observed in the case of the clay bed reinforced with the combination of geocell and geogrid. In addition, 3 times increase in the strain modulus, 10 times increase in the bearing capacity, 8 times increase in the stiffness and 90% reduction in the settlement was observed in the presence of the geocell and geogrid. Based on the laboratory test results, a hypothetical case of a prototype foundation subjected to cyclic load was analyzed. The results revealed that the natural frequency of the foundation-soil system increases by 4 times and the amplitude of the vibration reduces by 92% in the presence of the geocells and the geogrids.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.178-188
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• 2007

In this paper, a half-scaled substructure test was performed to evaluate the buckling and structural safety of an existing transmission tower subjected to wind load. A loading scheme was devised to reproduce the dead and wind loads of a prototype transmission tower, which uses a triangular jig that is mounted on the reduced model to which the similarity law of a half length was applied. As a result of the preliminary numerical analysis carried out to evaluate the stability of a specimen for the design load, it was confirmed that the calculated axial forces of tower leg members were distributed to $80{\sim}90%$ of an admissible buckling load. When the substructured transmission tower was loaded by 270% of its maximum admissible buckling load, it was failed due to the local buckling that is occurred in joints with weak constraints for out-of-plane behavior of leg members. By inspection of load-displacement curves, displacements and strains of members, it is considered that this local buckling was due to additional eccentric force by unbalanced deformation because the time that is reached to yielding stress due to the bending moment is different at each point of a same section.

• Steel and Composite Structures
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• v.34 no.5
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• pp.715-732
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• 2020

High-strength steel composite Y-eccentrically braced frame (Y-HSS-EBF) is a novel structural system. In this study, the spatial substructure hybrid simulation test (SHST) method is used to further study the seismic performance of Y-HSS-EBF. Firstly, based on the cyclic loading tests of two single-story single-span Y-HSS-EBF planar specimens, a finite element model in OpenSees was verified to provide a reference for the numerical substructure analysis model for the later SHST. Then, the SHST was carried out on the OpenFresco test platform. A three-story spatial Y-HSS-EBF model was taken as the prototype, the top story was taken as the experimental substructure, and the remaining two stories were taken as the numerical substructure to be simulated in OpenSees. According to the test results, the validity of the SHST was verified, and the main seismic performance indexes of the SHST model were analyzed. The results show that, the SHST based on the OpenFresco platform has good stability and accuracy, and the results of the SHST agree well with the global numerical model of the structure. Under strong seismic action, the plastic deformation of Y-HSS-EBF mainly occurs in the shear link, and the beam, beam-columns and braces can basically remain in the elastic state, which is conducive to post-earthquake repair.