• Structural Monitoring and Maintenance
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• v.7 no.4
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• pp.319-344
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• 2020

Inverse analysis of non-linear reinforced concrete bridge pier using recursive Gaussian filtering for in-situ condition assessment is the main theme of this work. For this purpose, minimum variance unbiased estimation using unscented sigma points is adopted here. The uniqueness of this inverse analysis lies in its approach for strain based updating of engineering demand parameters, where appropriate bound and constrained conditions are introduced to ensure numerical stability and convergence. In this analysis, seismic input is also identified, which is an added advantage for the structures having no dedicated sensors for earthquake measurement. First, the proposed strategy is tested with a simulated example whose hysteretic properties are obtained from the slow-cyclic test of a frame to investigate its efficiency and accuracy. Finally, the experimental test data of a full-scale bridge pier is used to study its in-situ condition in terms of Park & Ang damage index. Overall the study shows the ability of the augmented minimum variance unbiased estimation based recursive time-marching algorithm for non-linear system identification with the aim to estimate the engineering damage parameters that are the fundamental information necessary for any future decision making for retrofitting/rehabilitation.

• Structural Engineering and Mechanics
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• v.81 no.4
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• pp.395-409
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• 2022

The presence of infill generally neglected in design despite the fact that infill contribution significantly increase the lateral stiffness and strength of the reinforced concrete frame structure. Several experimental studies and computational models have been proposed to capture the rational response of infill-frame interaction at global level. However, limited studies are available on explicit finite element modelling to study the local behavior due to high computation and convergence issues in numerical modelling. In the current study, the computational modelling of RC frames is done with various configurations of infill masonry in terms of types of blocks, lateral loading and reinforcement detailing employed with material nonlinearities, interface contact issues and bond-slip phenomenon particularly near the beam-column joints. To this end, extensive computational modelling of five variant characteristics test specimens extracted from the detailed experimental program available in literature and process through nonlinear static analysis in FEM code, ATENA generally used to capture the nonlinear response of reinforced concrete structures. Results are presented in terms of damage patterns and capacity curves by employing the finest possible detail provided in the experimental program. Comparative analysis shows that good correlation amongst the experimental and numerical simulated results both in terms of capacity and crack patterns.

• International Journal of High-Rise Buildings
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• v.6 no.3
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• pp.227-235
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• 2017

This paper describes some of the challenges for structural design of a mid-story seismic isolated high-rise building, which is located near Tokyo station, completed in 2015. The building is a mixed-use complex and encompasses three volumes: one substructure including basement and lower floors, and a pair of seismic isolated superstructures on the substructure. One is a 136.5m high Main Tower (office use), and the other is a 98.5 m high South Tower (hotel use). The seismic isolation systems are arranged in the $3^{rd}$ floor of the Main Tower and $5^{th}$ floor of the South Tower, so that we call this isolation system as the mid-story seismic isolation. The primary goal of the structural design of this building was to secure high seismic safety against the largest earthquake expected in Tokyo. We adopted optimal seismic isolation equipment simulated by dynamic analysis to minimize building damage. On the other hand, wind-induced vibration of a seismic isolated high-rise building tends to be excited. To reduce the vibration, the following strategies were adopted respectively. In the Main Tower with a large wind receiving area, we adopted a mechanism that locks oil dampers at the isolation level during strong wind. In the South Tower, two tuned mass dampers (TMDs) are installed at the top of the building to control the vibration. In addition, our paper will also report the building performance evaluated for wind and seismic observation after completion of the building. In 2016, an earthquake of seismic intensity 3 (JMA scale) occurred twice in Tokyo. The acceleration reduction rate of the seismic isolation level due to these earthquakes was approximately 30 to 60%. These are also verified by dynamic analysis using observed acceleration data. Also, in April 2016, a strong wind exceeding the speed of 25m/s occurred in Tokyo. On the basis of the record at the strong wind, we confirmed that the locking mechanism of oil damper worked as designed.

• Tunnel and Underground Space
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• v.26 no.2
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• pp.59-67
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• 2016

In this paper, we perform a numerical analysis to evaluate the potential of fault reactivation during gas production from hydrate bearing sediments and the moment magnitude of induced seismicity. For the numerical analysis, sequential coupling of TOUGH+Hydrate and FLAC3D was used and the change in effective stress and consequent geomechanical deformation including fault reactivation was simulated by assuming that Mohr-Coulomb shear resistance criterion is valid. From the test production simulation of 30 days, we showed that pore pressure reduction as well as effective stress change hardly induces the fault reactivation in the vicinity of a production well. We also investigated the influence of stress state conditions to a fault reactivation, and showed that normal fault stress regime, where vertical stress is relatively greater than horizontal, may have the largest potential for the reactivation. We tested one simulation that earthquake can be induced during gas production and calculated the moment magnitude of the seismicity. Our calculation presented that all the magnitudes from the calculation were negative values, which indicates that induced earthquakes can be grouped into micro-seismic and as small as hardly perceived by human beings. However, it should be noted that the current simulation was carried out using the highly simplified geometric model and assumptions such that the further simulations for a scheduled test production and commercial scale production considering complex geometric conditions may produce different results.

• Journal of the Earthquake Engineering Society of Korea
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• v.15 no.4
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• pp.45-54
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• 2011

A simple model for reinforced concrete shear walls with boundary elements is proposed, which is a macro-model composed of spring elements representing flexure and shear behaviors. The flexural behaviour is represented by vertical springs at the wall ends, where the moment strength and rotational capacity of the wall are based on section analysis. The shear behaviour is represented by a horizontal spring at the wall center, where the key parameters for the shear behavior are based on the flexural behaviour since the shear walls with boundary elements are governed by the flexure. The proposed model was prepared with the results of hysteretic tests of the shear walls, and then the reliability of the hysteretic rule and variables was investigated by nonlinear dynamic analyses. Using parametric study with nonlinear dynamic analyses, the effect of the variables on demand and capacity, which are major parameters in seismic performance evaluation, are investigated. Results show that the measured and calculated shear forces versus the shear distortion relationships are slightly different, but the global response is well simulated. Furthermore, the demand and capacity are also changed in a similar way to the change in the major parameters so that the proposed model may be appropriate for reinforced concrete shear walls with boundary elements.

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.6
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• pp.59-70
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• 2003

We estimated the spectrum decay parameter $\chi$ and the stress parameter ($\Delta$$\sigma$) in southeastern Korea. Especially, we propose a procedure to compute site-independent $\chi$$_{q}$ and dependent $\chi$$_{s}$ values, separately, This procedure is to use the coda normalization method for the computation of site independent Q or corresponding $\chi$$_{q}$ value as the first step followed by the next step, the computation of $\chi$$_{s}$ values for each site using the given $\chi$$_{q}$ value evaluated at the first step, For the estimation of stress parameter, we used seismic data monitored from three earthquakes occurred near Gyeongju in 1999 with the method of Jo and Baag, In addition, we simulated strong ground motion using the $\chi$ value and the stress parameter, In this case, we calculated the $\chi$ value with conventional method. The $\chi$ value of 0.016+0.000157R and the stress parameter of 92-bar was applied to the stochastic simulation, At last, we derived seismic attenuation equation using results of the stochastic prediction, and compared these results with some others reported previously.ported previously.

• Journal of the Earthquake Engineering Society of Korea
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• v.15 no.2
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• pp.53-60
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• 2011

When designing building structures, dynamic serviceability is one of the most important items. Much research is being carried out on machine vibrations that affect inside residents and expensive equipment in the building structure. The vibration effect generally depends on the mass ratio, and an adequate mass ratio is determined by comparison with the serviceability limit according to the criteria. This study investigates the evaluation of vibration serviceability by using ISO 2631 to confirm the propriety of adequate mass ratios and it is verified that the application of a complicated FE model to model the real large shaking table facility with the mathematical model simulated as a SDOF system. The weighted RMS value is then compared with the comfort limit given by ISO 2631. As a result, the analysis of the numerical model is consistent with analysis of the FE model. Moreover, it is found that the adequate mass ratio of the concrete foundation and shake table, considering the self-weight of the real facility, should be less than 0.013. It is also confirm that the sample facility is satisfies the requirement of an adequate mass ratio.

• Journal of the Korean Geotechnical Society
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• v.38 no.11
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• pp.69-86
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• 2022

The railway is widely used to transport passengers and freight due to its punctuality and large transport capacity. The recent remarkable development in construction technology enables various subsea railway tunnels for continent-continent or continent-island connectivity. In Korea, design and construction experience is primarily based on the successful completion of the Boryeong subsea tunnel (2021) and the Gadeok subsea tunnel (2010). However, frequent earthquakes with diverse magnitudes, globally induced and continuously increased the awareness of seismic risks and the frequency of domestic earthquakes. The effect of an earthquake on the subsea tunnel is very complicated. However, ground conditions and seismic waves are considered the main factors. This study simulated four ground types of 3-dimensional numerical models, such as soil, rock, composite, and fractured zone, to analyze the effect of ground type and seismic wave. A virtual subsea railway shield tunnel considering external water pressure was modeled. Further, three different seismic waves with long-term, short-term, and both periods were studied. The dynamic analyses by finite difference method were performed to investigate the displacement and stress characteristics. Consequently, the long-term period wave exhibited a predominant lateral displacement response in soil and the short-term period wave in rock. The artificial wave, which had both periodic characteristics, demonstrated predominant in the fractured zone. The effect of an earthquake is more noticeable in the stress of the tunnel segment than in displacement because of confining effect of ground and structural elements in the shield tunnel. 

• Steel and Composite Structures
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• v.34 no.5
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• pp.743-767
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• 2020

Due to the impressive flexural performance, enhanced compressive strength and more constrained crack propagation, Fibre-reinforced concrete (FRC) have been widely employed in the construction application. Majority of experimental studies have focused on the seismic behavior of FRC columns. Based on the valid experimental data obtained from the previous studies, the current study has evaluated the seismic response and compressive strength of FRC rectangular columns while following hybrid metaheuristic techniques. Due to the non-linearity of seismic data, Adaptive neuro-fuzzy inference system (ANFIS) has been incorporated with metaheuristic algorithms. 317 different datasets from FRC column tests has been applied as one database in order to determine the most influential factor on the ultimate strengths of FRC rectangular columns subjected to the simulated seismic loading. ANFIS has been used with the incorporation of Particle Swarm Optimization (PSO) and Genetic algorithm (GA). For the analysis of the attained results, Extreme learning machine (ELM) as an authentic prediction method has been concurrently used. The variable selection procedure is to choose the most dominant parameters affecting the ultimate strengths of FRC rectangular columns subjected to simulated seismic loading. Accordingly, the results have shown that ANFIS-PSO has successfully predicted the seismic lateral load with R² = 0.857 and 0.902 for the test and train phase, respectively, nominated as the lateral load prediction estimator. On the other hand, in case of compressive strength prediction, ELM is to predict the compressive strength with R² = 0.657 and 0.862 for test and train phase, respectively. The results have shown that the seismic lateral force trend is more predictable than the compressive strength of FRC rectangular columns, in which the best results belong to the lateral force prediction. Compressive strength prediction has illustrated a significant deviation above 40 Mpa which could be related to the considerable non-linearity and possible empirical shortcomings. Finally, employing ANFIS-GA and ANFIS-PSO techniques to evaluate the seismic response of FRC are a promising reliable approach to be replaced for high cost and time-consuming experimental tests.

• Interaction and multiscale mechanics
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• v.2 no.1
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• pp.69-89
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• 2009

Reinforced and prestressed concrete (RC and PC) thin walls are crucial to the safety and serviceability of structures subjected to shear. The shear strengths of elements in walls depend strongly on the softening of concrete struts in the principal compression direction due to the principal tension in the perpendicular direction. The past three decades have seen a rapid development of knowledge in shear of reinforced concrete structures. Various rational models have been proposed that are based on the smeared-crack concept and can satisfy Navier's three principles of mechanics of materials (i.e., stress equilibrium, strain compatibility and constitutive laws). The Cyclic Softened Membrane Model (CSMM) is one such rational model developed at the University of Houston, which is being efficiently used to predict the behavior of RC/PC structures critical in shear. CSMM for RC has already been implemented into finite element framework of OpenSees (Fenves 2005) to come up with a finite element program called Simulation of Reinforced Concrete Structures (SRCS) (Zhong 2005, Mo et al. 2008). CSMM for PC is being currently implemented into SRCS to make the program applicable to reinforced as well as prestressed concrete. The generalized program is called Simulation of Concrete Structures (SCS). In this paper, the CSMM for RC/PC in material scale is first introduced. Basically, the constitutive relationships of the materials, including uniaxial constitutive relationship of concrete, uniaxial constitutive relationships of reinforcements embedded in concrete and constitutive relationship of concrete in shear, are determined by testing RC/PC full-scale panels in a Universal Panel Tester available at the University of Houston. The formulation in element scale is then derived, including equilibrium and compatibility equations, relationship between biaxial strains and uniaxial strains, material stiffness matrix and RC plane stress element. Finally the formulated results with RC/PC plane stress elements are implemented in structure scale into a finite element program based on the framework of OpenSees to predict the structural behavior of RC/PC thin-walled structures subjected to earthquake-type loading. The accuracy of the multiscale modeling technique is validated by comparing the simulated responses of RC shear walls subjected to reversed cyclic loading and shake table excitations with test data. The response of a post tensioned precast column under reversed cyclic loads has also been simulated to check the accuracy of SCS which is currently under development. This multiscale modeling technique greatly improves the simulation capability of RC thin-walled structures available to researchers and engineers.