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CONTENTS
Volume 21, Number 4, October 2021
 


Abstract
Masonry structures are relatively inexpensive and easier to construct compared to other types of structures such as steel and reinforced concrete buildings. However, they are relatively heavier, less ductile, and more vulnerable to damages in earthquakes. In this research, a new proposed low-cost seismic isolator made of rubber and steel rings (SISR) was used to reduce the seismic vulnerability of masonry walls. Two specimens of the proposed SISR were fabricated (placed on top of each other) and tested for horizontal displacement under a fixed vertical load condition according to ASCE 7-16 loading protocol. The proposed SISRs which out-performed the standard loading protocol of ASCE 7-16 were evaluated in a numerical study of the concrete block walls under Erzincan and Imperial Valley-06 earthquakes. ABAQUS finite element software was used for the structural modeling of the walls. The results showed the proper performance of the proposed SISRs in reducing the acceleration and preventing cracks in the masonry walls.

Key Words
base isolation; dynamic analysis; earthquake/seismic isolation; earthquake/seismic vulnerability; inelastic response; unreinforced masonry structures

Address
Habibollah Kakolvand: Department of Civil Engineering, College of Engineering, West Tehran Branch, Islamic Azad University, Tehran 14687-63785, Iran

Mohammad Ghazi: Department of Civil Engineering, College of Engineering, West Tehran Branch, Islamic Azad University, Tehran 14687-63785, Iran

Behnam Mehrparvar: Department of Civil Engineering, College of Engineering, West Tehran Branch, Islamic Azad University, Tehran 14687-63785, Iran

Soroush Parvizi: Department of Materials Engineering, Shahid Rajaee Teacher Training University (SRTTU), Tehran 16788-15811, Iran


Abstract
The present study focuses on estimating the effects of dynamic soil-structure-interaction (DSSI) on the earthquake response of a high-rise reinforced concrete (R/C) building with semi-ductile structural system having shear walls and column-beams under the vertical earthquake motion. For this aim, a set of comparative studies between the DSSI model with soft/firm soils and fixed support (FS) model under both only horizontal (H) and horizontal+vertical (H+V) earthquake motion are conducted. The soft (SS) and firm soil (FIS) properties specified with the standard penetration test are adopted for the DSSI model. Finite element model considerations are also detailed for the DSSI and FS models. The linear time-history analysis (LTHA) is performed to practically understand DSSI effects on structural response considering the vertical earthquake motion based the considered global monitoring parameters. The outcomes show that the DSSI model yields to more significant results than the FS model, but the most critical ones are obtained as the base shear force, the overturning moment and the base axial force. The vertical earthquake motion has a noticeable impact on the increase in the base axial force, the overturning moment and the top story vertical displacement. This study underlines that the consideration of the vertical earthquake motion and DSSI is required to make a reliable advanced estimation on structural damages and earthquake performance levels of R/C building structures.

Key Words
direct method (DM); dynamic soil-structure interaction (DSSI); finite element model (FEM); linear time-history analysis (LTHA); vertical earthquake motion

Address
Selcuk Bas: Department of Civil Engineering, Faculty of Engineering, Architecture and Design, Bartin University, 74100 Bartin, Turkey

Abstract
Seismic isolation is a remedy for providing earthquake resistant features for structural components, nonstructural components, and contents of building systems. However, its performance may become counterproductive under the effect of near-field ground motions, which may cause an increased structural response due to resonance. In this paper, the responses of a high-rise building and a low-rise building, which are isolated with lead core rubber bearing (LCRB) subjected to near-field pulse period ground motions, are investigated. The results indicate that the selected isolation system and base-isolated buildings are period-dependent, making them vulnerable to near-field pulse-period ground motions as a result of resonance. For this investigation, several ground motions are generated synthetically with a specific pulse period, which is set close to the fundamental period of the subjected base-isolated high-rise building to facilitate resonance. To mitigate the responses of the subjected base-isolated buildings and since the fundamental natural period of a structure is not affected by fluid viscous dampers (FVD), FVD was implemented with LCRB forming a fluid viscous damper-base isolation system (FVD-BIS). Note that some investigations have suggested that FVD can improve the performance of base-isolated buildings, but the impact of FVD-BIS on base-isolated high-rise and low-rise buildings at the time of resonance remains ambiguous. This study has illustrated that the intensity of the resonance phenomenon can be sharply mitigated in a base-isolated high-rise building using FVD-BIS.

Key Words
Fluid Viscous-Base Isolation System (FVD-BIS); Fluid Viscous Damper (FVD); Lead Core Rubber Bearing (LCRB); pulse-like ground motions; resonance phenomenon

Address
Mohammad Reza Bagerzadeh Karimi: Civil Engineering Department, Cyprus International University, Nicosia, Cyprus Via Mersin 10, Turkey

Mehmet Cemal Geneş: Civil Engineering Department, Eastern Mediterranean University, Famagusta, Cyprus via Mersin 10, Turkey

Abstract
The unexpected effect of a distant earthquake is studied in this paper, which caused a landslide at the eastern part of the hotel "Atrium" in Thassos Island, Northern Aegean Sea in Greece. The area is geologically located in the tectonic active fault damage zone of gneiss and sandstone. The movement of the fault was activated by the earthquake and accelerated the slope sliding. In order to describe the mechanism of the sliding and decide the appropriate restoration, the rock mass classification of Blastability Quality System (BQS) is used. The results are combined with those of the classical Slope Mass Rating (SMR) classification system and it is showed that both estimates are really close. Considering the presence of the active fault and the rock mass quality as it was estimated by the above classifications, the restoration can be a flexible system with gabions and benches which follow the geometry of the potential critical sliding cycle so, it can absorb the fault movement during future earthquakes. The cracked small wedges can be prevented from sliding by wire mess. In addition to all of them, a drainage system and toe ditch needs to drive the water of the rainfall out of the slope.

Key Words
earthquake damage; earthquake performance; earthquakes; stability; wave propagation

Address
Maria A. Chatziangelou: Department of Geology, Aristotle University of Thessaloniki, University Campus, 54124 Thessaloniki, Greece

Abstract
Seismic isolation is used worldwide to protect a myriad of structures from traditional use to industrial applications. Its success evolves from the use of rigid body motion reducing the demand on the structure especially in terms of drifts. Nonstructural damage refers to the loss of content of a structure including equipment and machinery that can be deemed necessary for facility operation. In many cases, this content is acceleration sensitive especially for machinery with fundamental frequencies above 2 Hz. Most work to date has focused on either nonstructural damage or isolated buildings with little known about the relationship between them. With this in mind, the study herein explores the performance of nonstructural content in seismically isolated structures in the near-fault region with vertical excitation. Using floor level time histories and response spectra, the presence of high frequency content is observed along with areas of decreased performance for the seismic isolation system. The results reinforce the complex relationship between the performance of nonstructural content, seismically isolated structures, and near-fault excitations.

Key Words
floor response spectra; near-field; seismic isolation

Address
Jenna B. Wong: School of Engineering, San Francisco State University, 1600 Holloway Ave, San Francisco, CA, U.S.A.

Lakshmipriya Lakshmipathy: School of Engineering, San Francisco State University, 1600 Holloway Ave, San Francisco, CA, U.S.A.

Abstract
Selection of appropriate ground motion records for dynamic analysis has uttermost importance since it significantly affects structural responses which are used for seismic performance assessment of buildings. This study focuses on probabilistic assessment of several record selection strategies that apply different level of constraints for spectrally matched real ground motion records. For this purpose, single degree of freedom (SDOF) systems with various lateral strength capacity ratios, vibration periods and hysteretic models were considered to cover broad type of structural systems and maximum displacement demands of SDOF systems were obtained by nonlinear dynamic analyses. Using the analysis results, central tendency of maximum displacement demands was evaluated. Confidence intervals of the demands were also estimated in probabilistic manner. In addition, non-exceedance probability curves of the displacement demands were constructed. Results indicate that using supplementary constraints about spectral matching, it is possible to control the variation of spectral accelerations and hence the variation of seismic displacement demands. In conclusion, displacement demands can be obtained for code- or probability-based design/performance assessment with appropriate selection approach considering desired variation which can be determined from either probabilistic or deterministic seismic hazard analysis.

Key Words
dynamic analysis; real earthquake record selection; seismic response; spectral compatibility; statistical evaluation

Address
Ahmet Demir: Department of Civil Engineering, Bolu Abant Izzet Baysal University, Bolu, Turkey

Mehmet Palanci: Department of Civil Engineering, Istanbul Arel University, İstanbul, Turkey

Ali Haydar Kayhan: Department of Civil Engineering, Pamukkale University, Denizli, Turkey

Abstract
Recent papers have investigated the contribution of structural and secondary elements in the overall damage of structures due to seismic effects. The present paper improves such methods by investigating also the marginal contribution of the geotechnical disorders and geometric regularity, in addition to the combined effect of structural and secondary elements. An adapted artificial neural networks (ANNs) method is proposed for this purpose. In this approach, three groups of parameters are considered for the quantitative evaluation of post- earthquake damage of structures: the structural group, the secondary group and a qualitatively evaluated group consisting observed geotechnical disorders and building regularity. Principal-component analysis is used in order to evaluate the effects of each input variable on the global structural damage. The ANN model is trained and validated for a collected database corresponding to 27,601 of buildings (Boumerdes earthquake, Algeria: M=6.8; May 21, 2003) and tested for 1,000 damaged buildings, located near the hypocentral zone (Bordj-El Bahri city, near Algiers), inspected during a post-quake damage survey. The assessment of the overall damage of structures based on the whole combination of three groups indicates that the developed model provides more accurate theoretical global damage predictions (98% accordance) that render it a promising tool for the inspector to decide about the final damage category.

Key Words
damages; earthquake; geotechnical disorders; neural network; post-disaster; structures

Address
Hichem NOURA: University Djilali Bounâama, Khemis Miliana, Laboratory of Acoustic and Civil Engineering, Algeria

Mohamed ABED: University Djilali Bounâama, Khemis Miliana, Laboratory of Acoustic and Civil Engineering, Algeria

Ahmed MEBARKI: University Gustave Eiffel, Laboratory Multi Scale Modeling and Simulation (MSME UMR 8208 UGE/UPEC/CNRS),
5 Bd Descartes, 77454, Marne-La-Vallée, France

Abstract
This study aims to show the efficiency of a proposed spectral matching technique for the reduction of required ground motions in the dynamic time history analysis. In this non-stationary spectral matching approach, unconstrained optimization is employed to adjust the signal to match a target spectrum. Adjustment factors of discrete wavelet transform (DWT) coefficients associated with the signals are then considered as decision variables and the Levenberg-Marquardt algorithm is employed to find the optimum values of DWT coefficients. This matching algorithm turns out to be quite effective in the spectral matching objective, where matching at multiple damping ratios can be readily achieved. First, the efficiency of the spectral matching procedure is investigated in a case study earthquake record and then compared with two conventional spectral matching methods. Results show considerable improvement in the matching accuracy which is accompanied by minimal changes in shaking characteristics of the original signal. In addition, it is shown that earthquake records matched with the proposed method can noticeably reduce the essential number of ground motions that are normally required for the dynamic analysis of a concrete dam as well as a shear wall system being considered here as the case study models. In this regard, it has been found that the number of required motions can be reduced by more than 80% when matched motions are selected to be used as the seismic inputs for the dynamic analysis.

Key Words
concrete dam; discrete wavelet transform; non-stationary spectral matching; numerical optimization; time history analysis

Address
Mojtaba Harati: Department of Civil and Environmental Engineering, Colorado State University, Fort Collins, U.S.A.

Mohammadreza Mashayekhi: Faculty of Civil Engineering, K.N. Toosi University of Technology, Tehran, Iran

Hamid Mohammadnezhad: Faculty of Civil, Water and Environmental Engineering, Shahid Beheshti University, Tehran, Iran

Hanieh Jaberi: School of Railway Engineering, Iran University of Science and Technology, Tehran, Iran

Homayoon E. Estekanchi: Department of Civil Engineering, Sharif University of Technology, Tehran, Iran


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