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Summary: Cross concentrically braced frames (X‐CBFs) are commonly used as primary seismic resisting system, owing to their large lateral stiffness, simplicity of design, and relatively low constructional cost. Current EN 1998‐1 provides design rules theoretically aiming at developing ductile global plastic mechanism, namely enforcing plastic deformations in the diagonal members, while the remaining structural members and connections should elastically behave. However, as widely demonstrated by many existing studies, the design and the corresponding seismic performance of EC8‐compliant X‐CBFs are generally affected by several criticisms, eg, difficulties in sizing of diagonal members, massive and non‐economical structures, and poor seismic behavior. In light of these considerations, the research activity presented in this paper is addressed to revise the design rules and requirements given EN 1998‐1 for X‐CBFs to simplify the design process and to improve the ductility and the dissipative capacity of this structural system. Hence, design rules are proposed for the next version of EN 1998‐1 and numerically validated by means of nonlinear dynamic analyses. [ABSTRACT FROM AUTHOR]

Highlights • The impact of the target spectrum on the acceleration causing collapse is investigated. • The impact of the number of ground motions on structural response is investigated. • Several MDOF and SDOF models are considered in the study. • A minimum of 15 ground motions should be used for time-history analysis. • The CS offers 1.2–2.3 times larger accelerations causing collapse than the UHS. Abstract The impact of the type of target response spectrum and the number of ground motions on the response of buildings is investigated. The parametric study involves the selection of ground motions based on the Eurocode 8 spectrum, a conditional spectrum using the official seismotectonic model of Slovenia, a uniform hazard spectrum based on the seismotectonic model of the SHARE project, and the corresponding conditional spectrum. In addition to the variation of the target response spectrum, the number of selected ground motions was varied from 7 to 60. Selected sets of ground motions were used to investigate the seismic response of eight reinforced concrete buildings with fundamental vibration periods from 0.15 s to 1.76 s. The aim of the study was to analyse the variation of target displacements obtained by a pushover-based method, i.e. the median displacement corresponding to a seismic intensity with a return period of 475 or 2475 years, and the median spectral acceleration causing collapse, which was estimated by incremental dynamic analysis. It was found that the target spectrum and the number of ground motions have a limited impact on the target displacement, especially if it corresponds to seismic intensities with a return period of 475 years. Additionally, the impact of the number of ground motions on the median spectral acceleration causing collapse is much lower than the impact of the target response spectrum. When the conditional spectrum was used as the target spectrum for ground motion selection instead of the design response spectrum prescribed by Eurocode 8, the resulting median spectral acceleration causing collapse increased by a factor of between 1.2 and 2.3. [ABSTRACT FROM AUTHOR]

This paper proposes a new fuzzy logic controller, which is designed for seismic protection of base-isolated structures utilizing piezoelectric friction damper against near-fault earthquakes for different ground sites. According to the elastic design spectrum that Eurocode 8 recommends, one 5% damped elastic design spectrum for Chi-Chi earthquake is proposed to generate artificial earthquakes of different ground sites. The proposed controller employs a hierarchic fuzzy control algorithm, in which a supervisory fuzzy controller governs a sublevel fuzzy controller by altering its input normalization factors according to current level of ground motion. In order to simultaneously reduce the base displacement and superstructure responses of the base-isolated structure during seismic excitations, genetic algorithm is employed to optimize the supervisory fuzzy controller and the preload of piezoelectric friction damper. The efficiency of the proposed controller is also compared with passive controller and a linear quadratic Gauss optimal controller. Numerical results show that the proposed fuzzy logic controller has favorable performance in mitigating the responses of the base-isolated structure. [ABSTRACT FROM AUTHOR]

This paper presents the results of a series of shake-table tests on a half-scale, four-storey building with reinforced concrete and unreinforced masonry walls. Due to the lack of reference tests, the seismic behaviour of such mixed structures is poorly understood. The test unit was subjected to several runs of increasing intensity yielding performance states between minor damage and near collapse. Before the test, the expected peak table accelerations leading to different limit states were estimated using the capacity spectrum method, and the predicted values corresponded rather well to actual sustained accelerations. Next to these analyses, the paper describes the test unit, instrumentation and input motion, and comments on the response of the mixed structure in terms of damage evolution and global response quantities, such as force-displacement response and drift and acceleration profiles. The raw and post-processed data sets are made publically available, and all relevant information with regard to data organisation and post-processing procedure is described in an appendix to this paper. The test serves therefore as a benchmark for the validation of numerical models of such mixed structures. The project aims at providing a foundation for the development of seismic design and assessment methods of mixed structures, which are currently not covered by structural codes, including Eurocode 8. [ABSTRACT FROM AUTHOR]

The seismic assessment of existing buildings is an essential issue of seismic engineering. This work is focused on the evaluation of the seismic performance of existing RC buildings according to the current Italian Technical Code, which almost coincides with the European Eurocode 8. Alternative types of analyses, all consistent to the Code provisions, have been performed with reference to a case-study, that is a real RC hospital building. An accurate knowledge of the building has been achieved, as a result of a collaboration between the University of Florence and the Regional Government. Both elastic and inelastic modeling, as well as static and dynamic ones, have been adopted in the analysis. The global response-with special attention to torsional effects-and the seismic performance of each single member have been found with all the performed analyses. The comparison among the analyses has been performed in terms of both global and local response parameters, and the reliability of each analysis has been pointed out. [ABSTRACT FROM AUTHOR]

Time history analyses have been preferred commonly in earthquake engineering area to determine earthquake performances of structures in recent years. Advances in computer technology and structural analysis have led to common usage of time history analyses. Eurocode 8 allows the use of real earthquake records as an input for linear and nonlinear time history analyses of structures. However, real earthquake records with the desired characteristics sometimes may not be found, for example depending on soil classes, in this case artificial and synthetic earthquake records can be used for seismic analyses rather than real records. Selected earthquake records should be scaled to a code design spectrum to reduce record to record variability in structural responses of considered structures. So, scaling of earthquake records is one of the most important procedures of time history analyses. In this paper, four real earthquake records are scaled to Eurocode 8 design spectrums by using SESCAP (Selection and Scaling Program) based on time domain scaling method and developed by using MATLAB, GUI software, and then scaled and real earthquake records are used for linear time history analyses of a six-storied building. This building is modeled as spatial by SAP2000 software. The objectives of this study are to put basic procedures and criteria of selecting and scaling earthquake records in a nutshell, and to compare the effects of scaled earthquake records on structural response with the effects of real earthquake records on structural response in terms of record to record variability of structural response. Seismic analysis results of building show that record to record variability of structural response caused by scaled earthquake records are fewer than ones caused by real earthquake records [ABSTRACT FROM AUTHOR]