• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.4
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• pp.435-443
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• 2010

This study presents key parameters for the structure installed with MR controller in reducing its responses. MR controller is regarded as Bingham model of which control forces are frictional and viscous ones. The parameters are identified as friction force ratios, $R_f$ and $R_h$ which are, respectively, ratio of MR controller friction force to static restoring force for free vibration and ratio of the friction force to amplitude of harmonic force. Structure-MR controller system shows nonlinear response behavior due to friction force. Energy balance strategy is adopted to transform the behavior to linear one with equivalent damping ratio. Finally, proposed equivalent linear process is compared to the nonlinear one, which turns out to give acceptably good results.

• Earthquakes and Structures
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• v.7 no.1
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• pp.83-99
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• 2014

This study is devoted to estimate higher-mode effects for multi-story structures with considering soil-structure interaction subjected to decomposed parts of near-fault ground motions. The soil beneath the super-structure is simulated based on the Cone model concept. Two-dimensional structural models of 5, 15, and 25-story shear buildings are idealized by using nonlinear stick models. The ratio of base shears for the soil-MDOF structure system to those obtained from the equivalent soil-SDOF structure system is selected as an estimator to quantify the higher-mode effects. The results demonstrate that the trend of higher-mode effects is regular for pulse component and has a descending variation with respect to the pulse period, whereas an erratic pattern is obtained for high-frequency component. Moreover, the effect of pulse component on higher modes is more significant than high-frequency part for very short-period pulses and as the pulse period increases this phenomenon becomes vice-versa. SSI mechanism increases the higher-mode effects for both pulse and high-frequency components and slenderizing the super-structure amplifies such effects. Furthermore, for low story ductility ranges, increasing nonlinearity level leads to intensify the higher-mode effects; however, for high story ductility, such effects mitigates.

• Earthquakes and Structures
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• v.2 no.2
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• pp.149-169
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• 2011

Dynamic response of two adjacent single degree-of-freedom (SDOF) structures connected with friction damper under base excitation is investigated. The base excitation is modeled as a stationary white-noise random process. As the force-deformation behavior of friction damper is non linear, the dynamic response of connected structures is obtained using the equivalent linearization technique. It is observed that there exists an optimum value of the limiting frictional force of the damper for which the mean square displacement and the mean square absolute acceleration responses of the connected structures attains the minimum value. The close form expressions for the optimum value of damper frictional force and corresponding mean square responses of the coupled undamped structures are derived. These expressions can be used for initial optimal design of the friction damper for connected structures. A parametric study is also carried out to investigate the influence of system parameters such as frequency ratio and mass ratio on the response of the coupled structures. It has been observed that the frequency ratio has significant effect on the performance of the friction damper, whereas the effects of mass ratio are marginal. Finally, the verification of the derived close from expressions is made by correlating the response of connected structures under real earthquake excitations.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3A
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• pp.473-484
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• 2006

The capacity spectrum method (CSM) can be used to simply estimate the maximum displacement response of the nonlinear structures. To evaluate seismic performance of multi-span bridges using the CSM, the representative response for structural system should be derived from the multi-degree-of-freedom (MDOF) responses by using the equivalent single-degree-of-freedom (ESDOF) method. The ESDOF method is used to calculate the capacity curve of the structural system from the pushover curves of all piers or structural members estimated by the pushover analysis. In order to evaluate an accuracy of ESDOF methods used in the CSM, the maximum displacements estimated by the CSM incorporating the several ESDOF methods are compared to those by the inelastic time-history analysis for several artificial earthquakes corresponding to the design spectrum.

• Earthquakes and Structures
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• v.12 no.3
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• pp.271-284
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• 2017

This paper presents a multimodal adaptive nonlinear static method of analysis that, differently from the nonlinear static methods suggested in seismic codes, does not require the definition of the equivalent Single-Degree-Of-Freedom (SDOF) system to evaluate the seismic response of structures. First, the proposed method is formulated for the assessment of r.c. plane frames and then it is extended to 3D framed structures. Furthermore, the proposed nonlinear static approach is re-elaborated as a displacement-based design method that does not require the use of the behaviour factor and takes into account explicitly the plastic deformation capacity of the structure. Numerical applications to r.c. plane frames and to a 3D framed structure with inplan irregularity are carried out to illustrate the attractive features as well as the limitations of the proposed method. Furthermore, the numerical applications evidence the uncertainty about the suitability of the displacement demand prediction obtained by the nonlinear static methods commonly adopted.

• Smart Structures and Systems
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• v.2 no.1
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• pp.1-24
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• 2006

The optimal design of multiple tuned mass dampers (multiple TMD's) to suppress multi-mode structural response of beams and floor structures was investigated. A new method using a numerical optimizer, which can effectively handle a large number of design variables, was employed to search for both optimal placement and tuning of TMD's for these structures under wide-band loading. The first design problem considered was vibration control of a simple beam using 10 TMD's. The results confirmed that for structures with widelyspaced natural frequencies, multiple TMD's can be adequately designed by treating each structural vibration mode as an equivalent SDOF system. Next, the control of a beam structure with two closely-spaced natural frequencies was investigated. The results showed that the most effective multiple TMD's have their natural frequencies distributed over a range covering the two controlled structural frequencies and have low damping ratios. Moreover, a single TMD can also be made effective in controlling two modes with closely spaced frequencies by a newly identified control mechanism, but the effectiveness can be greatly impaired when the loading position changes. Finally, a realistic problem of a large floor structure with 5 closely spaced frequencies was presented. The acceleration responses at 5 positions on the floor excited by 3 wide-band forces were simultaneously suppressed using 10 TMD's. The obtained multiple TMD's were shown to be very effective and robust.

• Structural Engineering and Mechanics
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• v.45 no.6
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• pp.741-758
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• 2013

In this study, inelastic displacement ratios are investigated for existing systems with known lateral strength considering soil structure interaction. For this purpose, SDOF systems for period range of 0.1-3.0 s with different hysteretic behaviors are considered for a number of 18 earthquake motions recorded on soft soil. The effect of stiffness degradation on inelastic displacement ratios is investigated. The Modified Clough model is used to represent structures that exhibit significant stiffness degradation when subjected to reverse cyclic loading and the elastoplastic model is used to represent non-degrading structures. Soil structure interaction analyses are conducted by means of equivalent fixed base model effective period, effective damping and effective ductility values differing from fixed-base case. For inelastic time history analyses, Newmark method for step by step time integration was adapted in an in-house computer program. A new equation is proposed for inelastic displacement ratio of system with SSI with elastoplastic or degrading behavior as a function of structural period ($\tilde{T}$), strength reduction factor (R) and period lengthening ratio ($\tilde{T}$/T). The proposed equation for $\tilde{C}_R$ which takes the soil-structure interaction into account should be useful in estimating the inelastic deformation of existing structures with known lateral strength.

• Earthquakes and Structures
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• v.16 no.2
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• pp.165-175
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• 2019

Incremental dynamic analysis (IDA), as an accurate method to evaluate the parameters of structural performance levels, requires many non-linear time history analyses, using a set of ground motion records which are scaled to different intensity levels. Therefore, this method is very computationally demanding. In this study, a new method is presented to estimate the summarized (16%, 50%, and 84% fractiles) IDA curves of a first-mode dominated structure using discrete wavelet transform and bees optimization algorithm. This method reduces the number of required ground motion records for the prediction of the summarized IDA curves. At first, a subset of first list ground motion records is decomposed by means of discrete wavelet transform which have a low dispersion estimating the summarized IDA curves of equivalent SDOF system of the main structure. Then, the bees algorithm optimizes a series of factors for each level of detail coefficients in discrete wavelet transform. The applied factors change the frequency content of original ground motion records which the generated ground motions records can be utilized to reliably estimate the summarized IDA curves of the main structure. At the end, to evaluate the efficiency of the proposed method, the seismic behavior of a typical 3-story special steel moment frame, subjected to a set of twenty ground motion records is compared with this method.

• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.2
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• pp.69-80
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• 2008

In this study, improved capacity spectrum method (CSM) is proposed. The method can account for higher mode contribution to the seismic response of MDOF systems. The CSM has been conveniently used for determining maximum roof displacement using both demand spectrum and capacity curve of equivalent SDOF system. Unlike the conventional CSM, the maximum roof displacement is determined without iteration using inelastic displacement ratio and R factor calculated from demand spectrum and capacity curve. Three moment resisting steel frames of 3-, 9- and 20-stories are considered to test the accuracy of the proposed method. Nonlinear response history analysis (NL-RHA) for three frames is also conducted, which is considered as an exact solution. SAC LA 10/50 and 2/50 sets of ground motions are used. Moreover, this study estimates maximum story drift ratios (IDR) using ATC-40 CSM and N2-method and compared with those from the proposed method and NL-RHA. It shows that the proposed CSM estimates the maximum IDR accurately better than the previous methods.

• Structural Engineering and Mechanics
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• v.51 no.3
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• pp.447-470
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• 2014

Numerical simulation of the non-linear behavior of (RC) structural walls subjected to severe earthquake ground motions requires a reliable modeling approach that includes important material characteristics and behavioral response features. The objective of this paper is to optimize a simplified method for the assessment of the seismic response and damage development analyses of an RC structural wall building using macro-element model. The first stage of this study investigates effectiveness and ability of the macro-element model in predicting the flexural nonlinear response of the specimen based on previous experimental test results conducted in UCLA. The sensitivity of the predicted wall responses to changes in model parameters is also assessed. The macro-element model is next used to examine the dynamic behavior of the structural wall building-all the way from elastic behavior to global instability, by applying an approximate Incremental Dynamic Analysis (IDA), based on Uncoupled Modal Response History Analysis (UMRHA), setting up nonlinear single degree of freedom systems. Finally, the identification of the global stiffness decrease as a function of a damage variable is carried out by means of this simplified methodology. Responses are compared at various locations on the structural wall by conducting static and dynamic pushover analyses for accurate estimation of seismic performance of the structure using macro-element model. Results obtained with the numerical model for rectangular wall cross sections compare favorably with experimental responses for flexural capacity, stiffness, and deformability. Overall, the model is qualified for safety assessment and design of earthquake resistant structures with structural walls.