• Earthquakes and Structures
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• v.10 no.6
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• pp.1451-1465
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• 2016

The effectiveness of base isolation (BI) systems for mitigation of seismic vibration of bridges have been extensively studied in the past. It is well established in those studies that the performance of BI system is largely dependent on the characteristics of isolator yield strength. For optimum design of such systems, normally a standard nonlinear optimization problem is formulated to minimize the maximum response of the structure, referred as Stochastic Structural Optimization (SSO). The SSO of BI system is usually performed with reference to a problem of unconstrained optimization without imposing any restriction on the maximum isolator displacement. In this regard it is important to note that the isolator displacement should not be arbitrarily large to fulfil the serviceability requirements and to avoid the possibility of pounding to the adjacent units. The present study is intended to incorporate the effect of excessive isolator displacement in optimizing BI system to control seismic vibration effect of bridges. In doing so, the necessary stochastic response of the isolated bridge needs to be optimized is obtained in the framework of statistical linearization of the related nonlinear random vibration problem. A simply supported bridge is taken up to elucidate the effect of constraint condition on optimum design and overall performance of the isolated bridge compared to that of obtained by the conventional unconstrained optimization approach.

• Earthquakes and Structures
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• v.14 no.4
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• pp.337-347
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• 2018

This paper presents some shaking table tests conducted on a 1/4-scaled model with 5-story steel reinforced concrete (SRC) spatial frame with irregular section columns under a series of base excitations with gradually increasing acceleration peaks. The test frame was subjected to a sequence of seismic simulation tests including 10 white noise vibrations and 51 seismic simulations. Each seismic simulation was associated with a different level of seismic disaster. Dynamic characteristic, strain response, acceleration response, displacement response, base shear and hysteretic behavior were analyzed. The test results demonstrate that at the end of the loading process, the failure mechanism of SRC frame with irregular section columns is the beam-hinged failure mechanism, which satisfies the seismic code of "strong column-weak beam". With the increase of acceleration peaks, accumulated damage of the frame increases gradually, which induces that the intrinsic frequency decreases whereas the damping ratio increases, and the peaks of acceleration and displacement occur later. During the loading process, torsion deformation appears and the base shear grows fast firstly and then slowly. The hysteretic curves are symmetric and plump, which shows a good capacity of energy dissipation. In summary, SRC frame with irregular section columns can satisfy the seismic requirements of "no collapse under seldom earthquake", which indicates that this structural system is suitable for the construction in the high seismic intensity zone.

• Journal of Korean Association for Spatial Structures
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• v.19 no.3
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• pp.93-100
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• 2019

In this study, the retractable-roof spatial structure was chosen as the analytical model and a tuned mass damper (TMD) was installed in the analytical model in order to control the seismic response. The analysis model is mainly consisted of runway trusses (RT) and transverse trusses (TT), and the displacement response was analyzed by installing TMD on those trusses. The mass of the single TMD which is installed in the analytical model was set to 1% of the total structure mass and the total TMD mass ratio was set to be 8% or 6%. In addition, the mass of a single TMD was varied depending on the number of installations. As a result of analyzing the optimal number of installations of TMD, the displacement response was reduced in all cases compared to the case without TMD. Above all, the case with 8 TMDs was the most effective in reducing he displacement response. However, in this case, as the load on the upper structure of the retractable-roof spatial structure increases, the total mass ratio of TMD was maintained and the number of TMDs was increased to reduce the mass ratio of one TMD.

• Structural Engineering and Mechanics
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• v.48 no.5
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• pp.681-695
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• 2013

Performance-based seismic design allows a structure to develop inelastic response during earthquakes. This modern seismic design requires more clearly defined levels of inelastic response. The ultimate deformation of a structure without total collapse (target displacement) is used to obtain the inelastic deformation capacity (inelastic performance). The inelastic performance of a structure indicates its performance under excitation. In this study, a new energy-based method to obtain the target displacement for reinforced concrete frames under cyclic loading is proposed. Concrete structures were analyzed using nonlinear static (pushover) analysis and cyclic loading. Failure of structures under cyclic loading was controlled and the new method was tested to obtain target displacement. In this method, the capacity energy absorption of the structures for both pushover and cyclic analyses were considered to be equal. The results were compared with FEMA-356, which confirmed the accuracy of the proposed method.

• Journal of the Earthquake Engineering Society of Korea
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• v.24 no.2
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• pp.87-93
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• 2020

Seismic responses due to the dynamic coupling between a primary structure and secondary system connected to a structure are analyzed in this study. The seismic responses are compared based on dynamic coupling criteria and according to the error level in the natural frequency, with the recent criteria being reliant on the error level in the spectral displacement response. The acceleration responses and relative displacement responses of a primary structure and a secondary system for a coupled model and two different decoupled models of two degrees-of-freedom system are calculated by means of the time integration method. Errors in seismic responses of the uncoupled models are reduced with the recent criteria. As the natural frequency of the secondary system increases, error in the natural frequency decreases, but seismic responses of uncoupled models can be underestimated compared to that of coupled model. Results in this paper can help determine dynamic coupling and predict uncoupled models' response conservatism.

• Earthquakes and Structures
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• v.25 no.4
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• pp.269-282
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• 2023

This study investigates a rocking seismic isolation (RSI) system as a seismic protection measure against narrow-band ground-motions generated by earthquakes. Structures supported over RSIs are considered capable of reducing the lateral demands and damage of the main structural system through lifting and rocking. This lifting and rocking during earthquake activity is provided by free-standing columns. A single-degree-of-freedom (SDOF) system supported on a RSI system is subjected to narrow-band seismic motions and its response is compared to an analog system without RSI. The comparison is then extended to reinforced concrete linear frames with and without RSI; three-bay frames with 11 and 17 storeys are considered. It is found that the RSI systems significantly reduce acceleration and displacement demands in the main structural frames, more noticeably if the first structural mode dominates the response and for ratios of the predominant frequency of the ground motion to the predominant frequency of the main frame near one. It is also found that the RSI system is more effective in reducing lateral accelerations and displacements of the main structure when the aspect ratio, b/h, and size, R, of the free-standing columns decrease, although the rocking stability of the RSI system is also reduced.

• Earthquakes and Structures
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• v.23 no.2
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• pp.207-219
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• 2022

Seismic response control has always been a grave concern with the damage and collapse of many buildings during the past earthquakes. While there are several existing techniques like base isolation, viscous damper, moment-resisting beam-column connections, tuned mass damper, etc., many of these are succumbing to either of large displacement, near-fault, and long-period earthquakes. Keeping this viewpoint, extensive research on the application of smart materials for seismic response control of buildings was attempted during the last decade. Shape Memory Alloy (SMA) with its unique properties of superelasticity and shape memory effect is one of the smart materials used for seismic control of buildings. In this paper, an exhaustive review has been compiled on the seismic control applications of SMA in buildings. Unique properties of SMA are discussed in detail and different phases of SMA along with crystal characteristics are illustrated. Consequently, various seismic control applications of SMA are discussed in terms of performance and compared with prevalent base isolators, bracings, beam-column connections, and tuned mass damper systems.

• Computers and Concrete
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• v.20 no.6
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• pp.671-682
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• 2017

In this research, seismic response of pipes is examined by applying nanotechnology and piezoelectric materials. For this purpose, a pipe is considered which is reinforced by carbon nanotubes (CNTs) and covered with a piezoelectric layer. The structure is subjected to the dynamic loads caused by earthquake and the governing equations of the system are derived using mathematical model via cylindrical shell element and Mindlin theory. Navier-Stokes equation is employed to calculate the force due to the fluid in the pipe. Mori-Tanaka approach is used to estimate the equivalent material properties of the nanocomposite and to consider the effect of the CNTs agglomeration on the scismic response of the structure. Moreover, the dynamic displacement of the structure is extracted using harmonic differential quadrature method (HDQM) and Newmark method. The main goal of this research is the analysis of the seismic response using piezoelectric layer and nanotechnology. The results indicate that reinforcing the pipeline by CNTs leads to a reduction in the displacement of the structure during an earthquake. Also the negative voltage applied to the piezoelectric layer reduces the dynamic displacement.

• Structural Engineering and Mechanics
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• v.12 no.6
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• pp.573-594
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• 2001

A two-level displacement-based design procedure is developed. To obtain the displacement demands, elastic spectra for occasional earthquakes and inelastic spectra for rare earthquakes are used. Minimum global stiffness and strength to be supplied to the structure are based on specified maximum permissible drift limits and on the condition that the structure responds within the elastic range for occasional earthquakes. The performance of the structure may be assessed by an inelastic push-over analysis to the required displacement and the evaluation of damage indices. The approach is applied to the design of a five-story reinforced concrete coupled wall structure located in the most hazardous seismic region of Argentina. The inelastic dynamic response of the structure subjected to real and artificially generated acceleration time histories is also analyzed. Finally, advantages and limitations of the proposed procedure from the conceptual point of view and practical application are discussed.

• Earthquakes and Structures
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• v.4 no.4
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• pp.341-363
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• 2013

Earthquake response calculation, parametric analysis and seismic parameter optimization of base-isolated structures are some critical issues for seismic design of base-isolated structures. To calculate the earthquake responses for such non-symmetric and non-classical damping linear systems and to implement the earthquake resistant design codes, a modified complex mode superposition design response spectrum method is put forward. Furthermore, to do parameter optimization for base-isolation structures, a graphical approach is proposed by analyzing the relationship between the base shear ratio of a seismic base-isolation floor to non-seismic base-isolation one and frequency ratio-damping ratio, as well as the relationship between the seismic base-isolation floor displacement and frequency ratio-damping ratio. In addition, the influences of mode number and site classification on the seismic base-isolation structure and corresponding optimum parameters are investigated. It is demonstrated that the modified complex mode superposition design response spectrum method is more precise and more convenient to engineering applications for utilizing the damping reduction factors and the design response spectrum, and the proposed graphical approach for parameter optimization of seismic base-isolation structures is compendious and feasible.