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Seismic risk assessment of new and existing structures has a long history, which is based on the development of specific methods for seismic hazard and vulnerability analyses. Performance-based earthquake engineering is the natural evolution and integration of all these aspects that is nowadays implemented in several precodes. However, some critical aspects are not yet completely clarified. As a matter of fact, the vulnerability analysis suffers the so-called record-to-record variability, which is usually controlled through different parameters used as seismic intensity measures (IMs), whose significance is still under discussion. Moreover, this variability represents an additional source of uncertainty, which is added to the dispersion derived from the ground motion prediction equation(GMPE), leading to an overconservatism. For these reasons, the present paper aims to propose a novel framework for the seismic risk assessment of structures, which is found on the idea to control the response variability in evaluating seismic hazard curves without taking into account the randomness (ε) of the GMPE, which instead is transferred to fragility curves. These latter are built by using groups of accelerograms, whose median and 84% fractile spectra fit well, for different return periods, the uniform hazard spectra for ε= 0 and 1, respectively. For this purpose, a new search algorithm for selecting natural records is formulated. The proposed method offers considerable advantages as it is no longer necessary to refer to a specific IM, and allows to select pairs of spectrum-compatible natural records, which is enable to solve the problem of the seismic assessment of three-dimensional structures. The procedure is then applied to assess seismic risk of a typical reinforced concrete frame, whose results demonstrate the robustness of the method and the practical independence from the record setused.

The results of an experimental study of four infilled frames with brick masonry walls subject to reversal cyclic lateral load are presented. The variables studied were the height to length aspect ratio of the wall and the use of joint reinforcement. The investigation was motivated by the fact that the Mexican code establishes the same specifications about the use of joint reinforcement for infill walls as for confined walls, because there is not enough experimental evidence on joint reinforced infill walls. To investigate the possible interaction of the study variables in the seismic performance of the walls, two pairs of specimens, scaled 1:2, with different aspect ratios (H/L = 0.75, 0.41) were tested. The specimens in each pair were identical except that one of them included steel bars into the bed-joints as reinforcement leading to amount phfyh=0.6 MPa. The infill walls with H/L = 0.41 were included from a previous study. The behavior of the specimens was defined in terms of lateral strength, ductility, displacement capacity, deformation of the joint reinforcement and crack pattern. The results indicate that joint reinforcement increases the strength of the system; however, the increase was more pronounced in longer walls. Ductility was reduced with horizontal reinforcement and this behavior was more important for longer walls. As occurred in confined walls, the joint reinforcement generates a more distributed cracking and reduces the width of the cracks. The experiments are described and this and other results are discussed in detail.

An earthquake of magnitude 6.4 occurred in Yangbi County, Yunnan Province on 21 May 2021, with a focal depth of 8 km, and strong ground motion with vertical components was monitored by Yangbi station (53YBX). A total of 14,122 houses were damaged in Yangbi in the earthquake, and 232 of them collapsed. Vertical components of ground motions have been gained more attention for its effect on structure’s seismic response in epicenter or near-fault regions at present. Taking the three earthquake ground motions of Yangbi, Chi-Chi, and Loma Prieta as inputs, and modeling based on Perform-3D, this research carried out the seismic dynamic time history analysis of an RC (reinforced concrete) frame structure and a brick-concrete structure under both horizontal and vertical working conditions. The results showed that vertical components of the three ground motions had no evident impact on the top horizontal displacement and acceleration of the two types of structures. Among the three ground motions, the vertical component of Yangbi ground motion has largely influenced the top vertical displacement, acceleration, and axial force of the frame column bottom (or masonry wall bottom). The vertical component had different amplification effects on the axial pressure and the bending moment of a single column at the bottom of the RC frame structure, thus causing resonance amplification effect of the brick-concrete structure floors and amplifying the vertical acceleration of the top floor. In addition, it considerably increase the maximum axial tensile strain of masonry walls and the possibility of faster tensile failure of the brick-concrete structure. Influence of vertical ground motion on the bearing capacity of RC frame structure’s columns and the brick-concrete structure’s masonry walls should not be ignored. The results of the research may provide a reference for the earthquake-resistant design of building structures, especially the earthquake-resistant design considering the vertical seismic effect.

This paper presents an experimental and numerical study on the dynamic performance of an RC frame structure crossing a ground fissure. Shake table tests were conducted with a 1/15-scale model of an RC frame structure crossing a ground fissure and the same structure on unfissured ground under earthquake excitations. Both surface and bedrock waves were taken into account in the study. Dynamic characteristics and seismic responses of the structure were recorded. Using LS-Dyna software, numerical analyses were conducted to investigate the influence of ground fissure on the structure considering the soil-structure-interaction (SSI). Good agreement was observed between the simulation and the test results. The results showed that the presence of a ground fissure changed the propagation characteristics of seismic waves for the common site, formatting the nonuniform excitation for the structure crossing the ground fissure. Moreover, structural members on the hanging wall suffered more serious damage than those on the footwall, because the dynamic amplification effect of the hanging wall was greater than that of the footwall. It was also found that the uneven settlement caused by the ground fissure moderately increased the seismic response of the structure. Furthermore, the settlement had a limited influence on the structural response, but the synthesis of the settlement and the earthquake had a more evident influence on it Refereed/Peer-reviewed

A series of shaking table tests on a scaled model were conducted to investigate the effect of steel braces on reinforced concrete frame structure across earth fissure under earthquake. In the test, a 1/15 scaled model structure taking into account soil–structure interaction was designed on the basis of similarity theorem. Seismic response data, including acceleration responses, displacement responses, shear force distributions, and strain amplitudes of column reinforcement were obtained and analyzed by comparing the results of unbraced and braced structure. Results show that with the peak ground acceleration of input motions increased, maximum of inter‐story drifts, shear forces, and strain amplitudes increased, whereas the acceleration amplification factors decreased. Steel braces could obviously reduce the seismic response of the structure, indicating that this retrofit method is an effective control measure for structures across the earth fissure under earthquake. These results are significant for studying the effect of earth fissure on seismic responses of structures. Refereed/Peer-reviewed

To investigate the behavior of a reinforced concrete (RC) frame structure across earth fissure under strong earthquake, a series of shaking table tests on a scaled model were designed and conducted. Three earthquake motion records were selected as input excitations, and the Jiangyou motion has a dramatically greater dynamic effect on the structure mainly due to its inherent rich low‐frequency component. The structural acceleration amplification factor gradually decreased as the peak ground acceleration of input motions increased, implying the progressive degradation of the structure stiffness. The results indicated that the earth fissure site has amplification effect on acceleration of the soil, and the displacement response of frame across the earth fissure was different to that of a typical RC frame structure. The ground floor was the most vulnerable story of the RC frame across the earth fissure. Refereed/Peer-reviewed

U radu je analizirano seizmičko ponašanje armiranobetonskih okvirnih konstrukcija različitih katnosti, projektiranih prema EC 8 i EC 2. Pri ovoj analizi primijenjen je probabilistički pristup gdje su u proračun uzete sve identificirane slučajnosti i neodređenosti. Ponašanje AB okvirnih konstrukcija prikazano je pomoću maksimalnog pomaka katova (engl. drift), dok je kao mjera intenziteta uzet spektralni odgovor ubrzanja. Rezultati provedenih analiza pokazali su da se seizmički odgovori uvećavaju za 31% do 54% ako se proračunom obuhvate slučajnosti i neodređenosti., The seismic performance of reinforced concrete frame structures of varying numbers of storeys, designed according to EC 8 and EC 2, is analyzed in the paper. The analysis is based on the probabilistic approach in which all identified incidental and indeterminate occurrences are taken into account. Performance of reinforced concrete frame structures is presented through maximum inter-storey drift values, while intensity is defined through spectral response of acceleration. The analysis results show that seismic response values increase by 31 to 54 percent if incidental and indeterminate occurrences are taken into account.