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Approximate closed-form maximum interstory drifts under the critical pseudo-double impulse (PDI) are derived for undamped multi-story shear building models with bilinear hysteresis by using the proposed updated mode-controlled energy-based approach (UMEA). PDI was proposed in the previous paper to simulate the critical responses of elastic-plastic MDOF models under near-fault fling-step motions. Although a double impulse (DI) is treated as a ground motion, PDI is treated as a set of impulsive lateral forces. PDI excites only the fundamental-mode responses of elastic proportionally-damped MDOF models because the fundamental participation vector is applied to the influence coefficient vector of PDI. UMEA is a kind of displacement control analyses, and the displacement increment, which is proportional to the fundamental mode evaluated by the tangent story stiffnesses, is given to the model. It is demonstrated that UMEA effectively captures the main characteristics of the maximum interstory drifts under the critical PDI and the critical one-cycle sine wave because most of the kinetic energy, which the fundamental mode has just before yielding, is given to the plastic fundamental mode just after yielding except for the case that the post-yielding stiffness is almost zero. The use of UMEA leads to much more efficient estimation of the maximum interstory drifts than the time-history response analysis because UMEA requires only 2 N -time evaluations of the elastic and plastic fundamental modes at most for N -story shear mass models with bilinear hysteresis. It is shown through numerical examples that the maximum interstory drifts under the critical PDI and the corresponding one-cycle sine wave correspond well to those evaluated by the proposed method. It is also shown that the correspondence of the responses of elastic-plastic MDOF models under recorded near-fault motions and the estimated responses by the proposed method is fairly good. • Approximate closed-form maximum drifts under critical pseudo-double impulse (PDI) are derived for bilinear models. • Closed-form maximum drifts of MDOF hysteretic models under sinusoidal motion are derived for the first time. • Updated mode-controlled energy-balance approach (UMEA) is proposed for closed-form expressions. • UMEA can reduce computational time drastically compared to conventional time-history response analysis. • Maximum drifts under critical PDI and the corresponding one-cycle-sine wave correspond well. [ABSTRACT FROM AUTHOR]

The recent huge earthquake ground motion records in Japan result in the reconsideration of seismic design forces for nuclear power stations from the view point of seismological research. In addition, the seismic design force should be defined also from the view point of structural engineering. In this paper it is shown that one of the occurrence mechanisms of such large acceleration in recent seismic records (recorded in or near massive structures and not free-field ground motions) is due to the interaction between a massive building and its surrounding soil which induces amplification of local mode in the surface soil. Furthermore on-site investigation after earthquakes in the nuclear power stations reveals some damages of soil around the building (cracks, settlement and sand boiling). The influence of plastic behavior of soil is investigated in the context of interaction between the structure and the surrounding soil. Moreover the amplification property of the surface soil is investigated from the seismic records of the Suruga-gulf earthquake in 2009 and the 2011 off the Pacific coast of Tohoku earthquake in 2011. Two methods are introduced for the analysis of the non-stationaiy process of ground motions. It is shown that the non-stationary Fourier spectra can detect the temporal change of frequency contents of ground motions and the displacement profile integrated from its acceleration profile is useful to evaluate the seismic behavior of the building and the surrounding soil. [ABSTRACT FROM AUTHOR]

The input energy and energy input rate to a base-isolated (BI) building during an earthquake are considered and formulated in the frequency domain. The frequency-domain approach for computation of input energy and energy input rate has different remarkable advantages compared with the conventional time-domain approach. It is demonstrated that the input energy can be of a compact form via the frequency integration of the product between the input component (squared Fourier amplitude spectrum of acceleration) and the structural model component (so-called energy transfer function). Furthermore, the energy input rate can also be of a similar form via the frequency integration of the product between the instantaneous power spectrum and the energy transfer function. With the help of this compact form, it is shown that the formulation in the frequency domain is essential for deriving arbitrary-order closed-form sensitivities of the input energy and energy input rate with respect to uncertain stiffness and damping coefficients in the BI storey. The closed-form sensitivity expressions provide us with information on the most unfavourable variation of the uncertain parameters that leads to the maximum input energy and input rate. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The response and damage assessment of engineering structures under near-field ground motions is currently of great interest. Near-field ground motion with directivity focusing or fling effects produces pulse-like ground motion that has characteristics different from those of ordinary records. This paper develops simple deterministic and probabilistic models for near-field pulse-like ground motions. These models belong to the class of engineering models that aim to replicate some of the gross features observed in near-field records. The ground velocity is expressed as a steady-state function or a stationary random process modulated by an envelope function. Both models account for the non-stationarity and the multiple pulses in the ground velocity. While the deterministic model is similar to some of the models developed earlier, the probabilistic model facilitates handling uncertainties in the ground motion and variability in the structure''s properties. For instance, this model combined with structural reliability methods can be used for reliability assessment of structures under near-field random ground motion. The reduction of the structural response by adding supplemental dampers is also investigated. [Copyright &y& Elsevier]

Temporal variation of dynamical modal properties of a base-isolated building is investigated using earthquake records in the building. A batch processing least-squares estimation method is applied to segment-wise time-series data. To construct an input-output system, an auto-regressive model with exogenous input (ARX) of second-order including a forgetting coefficient as a weighting coefficient is used for the estimation of modal parameters. The fundamental and second natural frequencies and the damping ratios of the fundamental and second natural modes of the base-isolated building are identified in the time domain. The identified results are consistent with the results obtained from the micro-tremor vibration data, forced-vibration test data and earthquake records in the present base-isolated building in the case of taking into account the amplitude-dependency of the isolators and viscous dampers. It is finally pointed out that several factors, e.g., amplitude dependency of the isolator and damper system and special characteristics of the series-type viscous damper system, may be related complicatedly with the temporal variation in modal properties of the above-mentioned system. [ABSTRACT FROM AUTHOR]

This study introduces measures to identify resonant (concentration of energy in a single or a few frequencies) or unfavorable earthquake ground motions. Probabilistic measures based on the entropy rate and the geometric properties of the power spectral density function (PSDF) of the ground acceleration are developed first. Subsequently, deterministic measures for the frequency content of the ground acceleration are also developed. These measures are then used for identifying resonance and criticality in stochastic earthquake models and 110 acceleration records measured at rock, stiff, medium and soft soil sites. The unfavorable earthquake record for a given structure is defined as the record having a narrow frequency content and dominant frequency close to the structure fundamental natural frequency. Accordingly, the measures developed in this study may provide a basis for selecting records that are capable of producing the highest structural response. Numerical verifications are provided on damage caused to structures by identified resonant records. [ABSTRACT FROM AUTHOR]

• Efficient and effective use of transformation of a moment frame into the 1st-mode equivalent shear mass system. • Damper optimization in shear mass system can be performed using the local search-based optimization. • Added damping coefficients of the shear mass system is inversely transformed into the added dampers of the moment frame. • Models designed for large-amplitude ground motions (GMs) can reduce the maximum response for various levels of GMs. A new method of optimal damper design is presented for elastic–plastic planar frame structures under large-amplitude earthquake ground motions. The transformation of a moment frame into the 1st-mode equivalent shear mass system leads to an efficient search of the optimal damper placement along the building height for the elastic–plastic moment frame. In the optimization procedure, a linear elastic bare frame is transformed into the 1st-mode equivalent shear mass system first. Then the optimization of the damper placement is conducted for the elastic shear mass system. After that, the damped shear mass system is inversely transformed into the elastic–plastic moment frame with the added dampers. This inversely transformed damper system in the moment frame is employed as an initial design and the local search-based optimization is conducted for the efficient distribution of dampers not only along the building height, but also among the different bay. The proposed method greatly reduces the computational task in the whole optimization procedure because only a limited number of time-history response analyses is required for elastic–plastic moment frames. It is demonstrated through numerical examples that the proposed method efficiently provides the damper designs with high accuracy. Finally, the importance of using the large-amplitude ground motions for damper optimization is demonstrated through the incremental dynamic analysis (IDA) for the optimally designed models. [ABSTRACT FROM AUTHOR]

A pseudo-double impulse (PDI) is proposed as an extension of the ordinary double impulse (DI) as a substitute of a one-cycle sine wave. PDI is treated as a set of impulsive lateral forces while the ordinary DI was introduced as an impulsive ground acceleration. The deformation and acceleration responses of multi-degree-of-freedom (MDOF) models under DI largely exceed those under the corresponding one-cycle sine wave as a main part of a near-fault ground motion. This is because DI has multiple frequency components and the higher-mode responses are excited. While the influence coefficient vector of the ordinary DI consists of 1 at every component, the influence coefficient vector of PDI is set to be proportional to the undamped fundamental natural mode. Therefore, the fundamental-mode response is mainly excited and the higher-mode responses are hardly excited by PDI. The displacement responses, the velocity responses and the input energy under DI and those under PDI are derived here for both elastic proportionally and non-proportionally damped MDOF models. The critical timing under PDI is also derived. The critical timing can be obtained by the time-history response analysis without repetition. It is demonstrated through the time-history response analysis that the distributions of interstory drifts and floor accelerations under the critical PDI correspond well to those under the critical one-cycle sine wave. Moreover, it is shown that, as far as the input level is large, the critical input period of PDI and that of the one-cycle sine wave correspond well. Since this procedure is not limited to elastic models, the proposed procedure helps to efficiently estimate the critical responses under the one-cycle sine wave for elastic-plastic MDOF models. Finally, the responses under recorded near-fault ground motions are compared with those under PDI. It is shown that the correspondence of the response under PDI and that under the recorded ground motions is fairly good although recorded ground motions are not always critical inputs for elastic-plastic MDOF models. • A pseudo-double impulse (PDI) is proposed as an extension of the ordinary double impulse (DI). • The fundamental-mode response is mainly excited and the higher-mode responses are hardly excited by PDI. • The critical PDI can efficiently estimate the critical responses of elastic-plastic MDOF models and the critical period. • PDI can capture the critical input period of a one-cycle sine wave without repetition and evaluate the maximum acceleration. [ABSTRACT FROM AUTHOR]

We propose a new flexible technique for accurate vision-based seismic displacement measurement of building structures via a single non-stationary camera with any perspective view. No a priori information about the camera's parameters or only partial knowledge of the internal camera parameters is required, and geometric constraints in the world coordinate system are employed for projective rectification in this research. Whereas most projective rectifications are conducted by specifying the positions of four or more fixed reference points, our method adopts a stratified approach to partially determine the projective transformation from line-based geometric relationships on the world plane. Since line features are natural and plentiful in a man-made architectural building environment, robust estimation techniques for automatic projective/affine distortion removal can be applied in a more practical way. Both simulations and real-recorded data were used to verify the effectiveness and robustness of the proposed method. We hope that the proposed method could advance the consumer-grade camera system for vision-based structural measurement one more step, from laboratory environments to real-world structural health monitoring systems. [ABSTRACT FROM AUTHOR]

The effectiveness of the optimal viscous damper placement for elastic-plastic multi-degree-of-freedom (MDOF) structures under the critical double impulse is demonstrated through the comparison with the optimal damper placement for elastic MDOF structures designed with respect to transfer function amplitudes at natural frequencies. The method for optimal viscous damper placement was proposed for elastic-plastic MDOF structures subjected to the critical double impulse as a representative of near-fault ground motions in the previous paper [1]. The double impulse is composed of two impulses with opposite directions and the critical interval is determined by using the criterion on the maximum input energy. The critical timing of the second impulse was found to be the timing which requires the vanishing of the sum of the restoring force and the damping force in the first story. Three models with different story stiffness distributions of main structures are treated to demonstrate the effectiveness of the optimal viscous damper placement under the critical double impulse. The double impulse pushover (DIP) procedure proposed in the previous paper for determining the input velocity level of the critical double impulse is examined further in this paper. It is demonstrated that the optimal viscous damper placement for elastic-plastic MDOF structures under the critical double impulse is more effective for pulse-type recorded earthquake ground motions than the optimal damper placement designed with respect to transfer function amplitudes at natural frequencies because several higher modes arising in the elastic-plastic response under pulse-type recorded earthquake ground motions can be well controlled by the design for the double impulse. • Investigation on optimal viscous damper design for elastic-plastic MDOF systems in view of harmonic input and double impulse. • Optimal damper design for elastic-plastic MDOF under critical double impulse is more effective than harmonic input design. • Higher modes in elastic-plastic response under pulse-type motions can be well controlled by the design for the double impulse. [ABSTRACT FROM AUTHOR]

Summary: Structures are usually subjected to some specific local damages or weaknesses, which cannot be explained by uniformly distributed stiffness or mass changes, especially when the local damages or weaknesses have slight influences on global natural periods or vibration modes. Furthermore, large amounts of measurement positions are in need to capture the damage location and severity in traditional damage identification, and results easily depend on the initial estimates of the unknown parameters for the iterative update. To circumvent the above problems, a novel framework is proposed, involving strategies for physical‐based parametrization and local damage identification for frame‐type structures. The novelty of this research lies in the careful integration of the physical‐based parameterization and the identification techniques to robustly quantify commonly encountered local damages, namely, the weakness in exposed column base and partially fractured beam end. In this framework, the guidance for the application of physical‐based parametrization is provided, and thus, the above‐mentioned local damages of structures could be parametrized in an appropriate and convenient way. The response sensitivity approach is employed to derive the parameters by directly using time domain data. Derivatives of the stiffness matrix with respective to the newly introduced physical parameters are directly proposed so that no finite difference method is involved. Furthermore, trust‐region restriction is adopted to enhance the efficiency and stability of the identification approach when facing strong convergence difficulty or way‐out initial estimates. Two case studies are presented to validate the effectiveness and accuracy of the proposed framework. The shell element‐based models with intentional damage and weakness are built in ABAQUS to provide the data source. Two corresponding beam element‐based models are developed in MATLAB as physical‐based parametrized models. Results show that damages are accurately and efficiently estimated by the proposed framework, and the original dynamic responses are well reproduced by the identified models. Comparisons to the results by Bayesian estimation are also discussed. [ABSTRACT FROM AUTHOR]

This paper presents a novel sparse‐regularized minimum constitutive relation error (min‐CRE) approach for structural damage identification with modal data. In this approach, the inverse identification problem is treated as a nonlinear optimization problem whose objective function is just the constitutive relation error (CRE). To circumvent the ill‐posedness of the inverse problem that is caused by use of the possibly insufficient modal data and enhance the robustness of the identification process, the sparse regularization is introduced where a sparse (or ℓ1‐norm) regularization term is added to the original CRE function. In regard to the minimum solution of the sparse‐regularized CRE objective function, a two‐step substitution algorithm is established. The attractive feature of the present damage identification approach is that no sensitivity analysis is involved herein and the additional introduction of the sparse regularization term introduces little computational complexity. The approach is applied to damage identification of one‐ or two‐dimensional beam structures with experimental or simulated modal data. Results show that the sparse regularization indeed improves the effectiveness and robustness of the min‐CRE approach under measurement noises and initial model errors, even in the case of large damages. [ABSTRACT FROM AUTHOR]

Practical damage identification often suffers from the ill-posedness and the unavoidable model errors. On the one hand, the regularization techniques including the Tikhonov regularization and the sparse regularization have been well recognized as effective tools to circumvent the ill-posedness. On the other hand, the model errors render the established baseline/analytical model inconsistent with the real structural and thereof, would introduce unexpected errors into damage identification. To deal with the model errors, the two-step strategy is often adopted for damage identification in practice: firstly update the baseline model so as to minimize the inconsistence and secondly, identify the damage upon the updated baseline model; Another empirical and not-yet-widely-recognized way is to use the measurement changes and motivated by this, a new MC (Measurement Changes) strategy that simply revises the measured data with measurement changes is developed in this paper for sensitivity-based damage identification. This work aims to present experimental investigations and comparative studies on the possible remedies for the difficulties in damage identification: the Tikhonov or sparse regularization for the ill-posedness and the two-step or MC strategy for the model errors. Final results show that the MC strategy is rather effective and efficient for damage identification and synthesis of the sparse regularization and the MC strategy is found as the appreciated way to practical damage identification. [ABSTRACT FROM AUTHOR]

A novel static identification approach to beam damage is presented. It is based on the minimum constitutive relation error (CRE) principle where the exact stiffness, the exact displacement and the exact bending moment are shown to make the CRE functional minimal. For practical implementation, two cases regarding full-field displacement measurements and finite-point displacement data, respectively, are considered. For full-field displacement measurements, the CRE functional is directly treated as the objective functional while in case of finite-point measurement data, the CRE functional along with additional penalty terms for treatment of the finite-point displacement measurements is defined as the objective functional. Multiple loads and associated sets of measurements are also considered to improve the identifiability and robustness of the procedure. Convergence is finally verified through numerical examples. [ABSTRACT FROM AUTHOR]

Abstract The objective of this paper is to provide a new damage identification method using frequency response data. In this approach, the inverse identification problem is treated as a nonlinear optimization problem whose objective function is just the constitutive relation error (CRE). To circumvent the ill-posedness of the inverse problem which is caused by use of the possibly insufficient data and enhance the robustness of the identification process, the sparse regularization is introduced where the ℓ 1 -norm regularization term is added to the original CRE function. In regard to the minimum solution of the sparse-regularized CRE objective function, the alternating minimization (AM) method is established. The attractive features of the present damage identification approach are: (a) while coping with the sparse regularization, a closed-form solution is obtained due to the decoupling of the CRE function with respect to the damage parameters and hence the sparse regularization term would introduce little computational complexity; (b) the sparse regularization parameters are directly determined by a simple threshold setting method; (c) no sensitivity analysis is involved herein. Numerical examples are conducted to verify the proposed approach and the results show that the sparse regularization obviously improves the accuracy and robustness for the identified damages. [ABSTRACT FROM AUTHOR]

The article offers a discussion on optimum placement and characteristics of velocity-dependent dampers under seismic excitation. It mentions a study led by the authors in which they reviewed the research development in passive damper optimization. It adds that the authors introduced a drift-based formulation in to deal with the interstory drift.

A sophisticated story-wise stiffness identification method for a shear building structure is applied to the case where the shear building is subjected to an actual micro-tremor. While the building responses to earthquake ground motions are necessary in the previous method, it is shown that micro-tremors can be used for identification within the same framework. This enhances the extended usability and practicality of the previously proposed identification method. The difficulty arising in the limit manipulation at zero frequency in the previous method is overcome by introducing an ARX model. The weakness of small SN ratios in the low frequency range is avoided by using the ARX model together with filtering and introducing new constraints on the ARX parameters. [ABSTRACT FROM AUTHOR]

Highlights: [•] A new interpretation of large earthquake accelerations is provided. [•] Non-linear interaction between an embedded building and its surrounding soil is a key. [•] A bi-linear restoring-force characteristic with a gap-slip process is used for analysis. [•] Ricker wavelet and a continuous sweep sinusoidal wave are adopted as input. [•] The amplification is induced by a higher mode due to the change of a support condition. [Copyright &y& Elsevier]