• Earthquakes and Structures
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• v.6 no.1
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• pp.71-87
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• 2014

Interaction between closely-spaced buildings subject to earthquake induced strong ground motions, termed in the literature as "seismic pounding", occurs commonly during major seismic events in contemporary congested urban environments. Seismic pounding is not taken into account by current codes of practice and is rarely considered in practice at the design stage of new buildings constructed "in contact" with existing ones. Thus far, limited research work has been devoted to quantify the influence of slab-to-slab pounding on the inelastic seismic demands at critical locations of structural members in adjacent structures that are not aligned in series. In this respect, this paper considers a typical case study of a "new" reinforced concrete (R/C) EC8-compliant, torsionally sensitive, 7-story corner building constructed within a block, in bi-lateral contact with two existing R/C 5-story structures with same height floors. A non-linear local plasticity numerical model is developed and a series of non-linear time-history analyses is undertaken considering the corner building "in isolation" from the existing ones (no-pounding case), and in combination with the existing ones (pounding case). Numerical results are reported in terms of averages of ratios of peak inelastic rotation demands at all structural elements (beams, columns, shear walls) at each storey. It is shown that seismic pounding reduces on average the inelastic demands of the structural members at the lower floors of the 7-story building. However, the discrepancy in structural response of the entire block due to torsion-induced, bi-directionally seismic pounding is substantial as a result of the complex nonlinear dynamics of the coupled building block system.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.69-72
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• 2008

The so-called Pier-Shafts system which consists of the continuous column and shaft is often used to support the highway bridge structure because of advantages in easy construction and low cost. In the earthquake region, the Pier-Shafts system undergoes large displacements and represents a nonlinear behavior under the lateral seismic loading. The soil-pile interaction should be considered for more accurate analysis of the Pier-Shafts system. In this study, a transverse response of a reinforced concrete Pier-Shafts system inside multi-layered soil medium is predicted using a finite element program which adopts an elasto-plastic interface model for the interface behavior between the shaft and the soil. Then, seismic analysis is performed to evaluate the performance of Pier-Shafts system under strong ground motion and their results are verified with experimental data.

• Computational Structural Engineering
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• v.10 no.4
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• pp.281-290
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• 1997

Current seismic design code is based on the assumption that the designed structures would be behaved inelastically during a severe earthquake ground motion. For this reason, seismic design forces calculated by seismic codes are much lower than the forces generated by design earthquakes which makes structures responding elastically. Present procedures for calculating seismic design forces are based on the use of elastic spectra reduced by a strength reduction factors known as "response modificaion factor". Because these factors were determined empirically, it is difficult to know how much inelastic behaviors of the structures exhibit. In this study, lateral strength required to maintain target ductility ratio was first calculated from nonlinear dynamic analysis of the single degree of freedom system. At the following step, base shear foeces specified in seismic design code compare with above results. If the base shear force required to maintain target ductility ratio was higher than the code specified one, the lack of required strength should be filled by overstrength and/or redundancy. Therefore, overstrength of moment resisting frame structure will be estimated from the results of push-over analysis.

• Smart Structures and Systems
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• v.4 no.6
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• pp.727-740
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• 2008

A down hole vertical seismic array is a sequence of instruments installed at various depths in the earth to record the ground motion at multiple points during an earthquake. Numerous studies demonstrate the unique utility of vertical seismic arrays for studying in situ site response and soil behavior. Examples are given of analyses made at two sites to show the value of data from vertical seismic arrays. The sites examined are the Lotung, Taiwan SMART1 array and a new site installed at Jingliao, Taiwan. Details of the installation of the Jingliao array are given. ARX models are theoretically the correct process models for vertical wave propagation in the layered earth, and are used to linearly map deeper sensor input signals to shallower sensor output signals. An example of Event 16 at the Lotung array is given. This same data, when examined in detail with a Bayesian inference model, can also be explained by nonlinear filters yielding commonly accepted soil degradation curves. Results from applying an ARMAX model to data from the Jingliao vertical seismic array are presented. Estimates of inter-transducer soil increment resonant frequency, shear modulus, and damping ratio are presented. The shear modulus varied from 50 to 150 MPa, and damping ratio between 8% and 15%. A new hardware monitoring system - TerraScope - is an affordable 4-D down-hole seismic monitoring system based on independent, microprocessor-controlled sensor Pods. The Pods are nominally 50 mm in diameter, and about 120 mm long. An internal 16-bit micro-controller oversees all aspects of instrumentation, eight programmable gain amplifiers, and local signal storage.

• Smart Structures and Systems
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• v.23 no.5
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• pp.449-466
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• 2019

Cable-stayed bridges are attractive due to their beauty, reducing material consumption, less harm to the environment and so on, in comparison with other kinds of bridges. As a massive structure with long period and low damping (0.3 to 2%) under many dynamic loads, these bridges are susceptible to fatigue, serviceability disorder, damage or even collapse. Tuned Mass Damper (TMD) is a suitable controlling system to reduce the vibrations and prevent the threats in such bridges. In this paper, Multi Tuned Mass Damper (MTMD) system is added to the Ahvaz cable stayed Bridge in Iran, to reduce its seismic vibrations. First, the bridge is modeled in SAP2000 followed with result verification. Dead and live loads and the moving loads have been assigned to the bridge. Then the finite element model is developed in OpenSees, with the goal of running a nonlinear time-history analysis. Three far-field and three near-field earthquake records are imposed to the model after scaling to the PGA of 0.25 g, 0.4 g, 0.55 g and 0.7 g. Two MTMD systems, passive and active, with the number of TMDs from 1 to 8, are placed in specific points of the main span of bridge, adding a total mass ratio of 1 to 10% to the bridge. The parameters of the TMDs are optimized using Genetic Algorithm (GA). Also, the optimum force for active control is achieved by Fuzzy Logic Control (FLC). The results showed that the maximum displacement of the center of the bridge main span reduced 33% and 48% respectively by adding passive and active MTMD systems. The RMS of displacement reduced 37% and 47%, the velocity 36% and 42% and also the base shear in pylons, 27% and 47%, respectively by adding passive and active systems, in the best cases.

• Geomechanics and Engineering
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• v.27 no.5
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• pp.447-463
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• 2021

Caisson-type structures are widely used as quay walls in coastal areas. In Korea, for a long time, many caisson-type quay walls have been constructed with a low front water depth. These facilities can no longer meet the requirements of current development. This study developed a new technology for deepening existing caisson-type quay walls using grouting and rubble mound excavation to economically reuse them. With this technology, quay walls could be renovated by injecting grout into the rubble mound beneath the front toe of the caisson to secure its structure. Subsequently, a portion of the rubble mound was excavated to increase the front water depth. This paper reports the results of an investigation of the seismic behavior of a renovated quay wall in comparison to that of an existing quay wall using centrifuge tests and numerical simulations. Two centrifuge model tests at a scale of 1/120 were conducted on the quay walls before and after renovation. During the experiments, the displacements, accelerations, and earth pressures were measured under five consecutive earthquake input motions with increasing magnitudes. In addition, systematic numerical analyses of the centrifuge model tests were also conducted with the PLAXIS 2D finite element (FE) program using a nonlinear elastoplastic constitutive model. The displacements of the caisson, response accelerations, deformed shape of the quay wall, and earth pressures were investigated in detail based on a comparison of the numerical and experimental results. The results demonstrated that the motion of the caisson changed after renovation, and its displacement decreased significantly. The comparison between the FE models and centrifuge test results showed good agreement. This indicated that renovation was technically feasible, and it could be considered to study further by testbed before applying in practice.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.2A
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• pp.131-143
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• 2009

Under transverse earthquake shaking, arching action of bridge structures develops along the deck between the abutments thus providing the so-called deck resistance. The magnitude of the arching action for bridge structures is dependent on the number of spans, connection condition between deck and abutment or piers, and stiffness ratio between superstructure and substructure. In order to investigate the arching action effects for inelastic seismic responses of PSC Box bridges, seismic responses evaluated by pushover analysis, capacity spectrum analysis and nonlinear time-history analysis are compared for 18 example bridge structures with two types of span numbers (short bridge, SB and long bridge, LB), three types of pier height arrangement (regular, semi-regular and irregular) and three types of connection condition between superstructure and substructure (Type A, B, C). The arching action effects (reducing inelastic displacement and increasing resistance capacity) for short bridge (SB) is more significant than those for long bridge (LB). Semi-regular and irregular bridge structures have more significant arching action than regular bridges.

• Journal of the Earthquake Engineering Society of Korea
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• v.2 no.4
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• pp.73-86
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• 1998

The purpose of this paper is to evaluate the shear stiffness, hysteretic behavior, and ultimate behavior of HDRB(High Damping Rubber Bearing), which will be included in the seismic isolation design guideline as requirements. To do this, two 1/8 scaled HDRB are designed, fabricated, and tested to show the mechanical characteristics. The shear stiffness obtained from the proposed equation of the shear stiffness shows a good agreement with those of the experiments. For analysis of the hysteretic behavior of HDRB using the modified rate model, the parameter equations are obtained from the experiments. Using the obtained parameter equations for the modified rate model, the seismic response analyses are carried out for 1-D system. The results of analysis well follow the hysteretic behavior of HDRB obtained from the experiments. To evaluate the ultimate behavior of HDRB used in this paper, the analyses are carried out using the modified macro model, which can consider the large shear deflection. The critical shear strain(CSS) is defined to express the maximum allowable shear strain and vertical load. From the analyses, the CSS, showing the instability, decreases significantly as increased the vertical loads. The CSS is not appeared for the design vertical load in the used HDRB. In analysis using about 5 times of design vertical load, the HDRB start to show the instability transient and for about 7 times, the CSS is about 350%.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.1
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• pp.59-67
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• 2013

Complex-shaped tall building causes many structural challenges due to its structural characteristics regarding inclined members and complexed shape. This paper is aimed at development of design process using computational-platform which is effective design tool for responding frequent design changes, particularly as to overseas projects. StrAuto, a parametric structural modeling and optimizing system, provides the optimized alternatives according to design intent and realize a swift process converting a series of structural information necessary to nonlinear analytical models. The application of the process was to a 45-story hotel building in Ulanbator, Mongolia adopting shear wall and special moment frame with outrigger systems. To investigate the safety of lateral force resisting system against maximum considered earthquake(MCE), nonlinear response history analysis was conducted using StrAuto.

• Journal of the Korean Geotechnical Society
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• v.32 no.9
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• pp.51-62
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• 2016

Parametric studies for various site conditions by using 3d numerical model were carried out in order to estimate dynamic behavior of soil-pile-structure system in dry soil deposits. Proposed model was analyzed in time domain using FLAC3D which is commercial finite difference code to properly simulate nonlinear response of soil under strong earthquake. Mohr-Coulomb criterion was adopted as soil constitutive model. Soil nonlinearity was considered by adopting the hysteretic damping model, and an interface model which can simulate separation and slip between soil and pile was adopted. Simplified continuum modeling was used as boundary condition to reduce analysis time. Also, initial shear modulus and yield depth were appropriately determined for accurate simulation of system's nonlinear behavior. Parametric study was performed by varying weight of superstructure, pile length, pile head fixity, soil relative density with proposed numerical model. From the results of parametric study, it is identified that inertial force induced by superstructure is dominant on dynamic behavior of soil-pile-structure system and effect of kinematic force induced by soil movement was relatively small. Difference in dynamic behavior according to the pile length and pile head fixity was also numerically investigated.