ABSTRACT Current seismic damage classification standards do not adequately capture the distinctive damage characteristics inherent to base‐isolated buildings. To bridge this gap, this study collects and analyzes empirical damage observations from 52 base‐isolated buildings affected by 11 destructive earthquakes globally. Operating within the framework of current Chinese seismic damage classification standards, the typical damage patterns of critical and vulnerable components in base‐isolated buildings are summarized, including isolation bearings, supplemental energy‐dissipation devices, nonstructural elements within the isolation layer, and the superstructure. On this basis, we propose a seismic damage classification framework for base‐isolated buildings, which incorporates postearthquake functionality, the conditions of the isolation layer, and the extent of nonstructural damage. The damage state of the isolation layer is derived from discrete damage states and damage rates of its constituent parts, which is subsequently integrated with the state of the superstructure to determine the overall building damage state. It offers a practical foundation for postearthquake field survey, damage statistical analyses, and the future revision of relevant standards.
ABSTRACT Buildings on hillside slopes have complex structural systems due to the existing topographical limitations. The seismic behavior and the failure pattern of these buildings are also observed to be peculiar in the past earthquakes such as Sikkim (2011) and Nepal (2015). Therefore, the mitigation strategy for such buildings must be delineated based on the detailed understanding of the typical damage characteristics exhibited. This study is focused on identifying the effect of critical parameters of configuration such as aspect ratio and slenderness ratio, that are usually imposed due to the topographical limitations, on the seismic response of the buildings on hill slopes. A total of 40 buildings are numerically modeled with varying aspect and slenderness ratios and the correlation between various member‐level parameters such as beam axial stresses, columns shear stress etc., are studied with the help of correlation matrices. Based on the observations, these parameters are categorized into three sets namely system parameters, behavior control parameters, and behavior verification parameters. Further, a suite of 11 ground motions recorded during the past earthquakes are utilized to verify the observations through nonlinear dynamic analysis. The response along the valley is predominantly governed by shear‐force concentration in the uphill columns, whereas the response across the valley is associated with differential flexible‐ and rigid‐edge deformations and the resulting torsional behavior. Lastly, three mitigation strategies are suggested and verified to improve the response and reduce the brittle failure modes, viz., (a) to limit the shear failures, (b) to improve the base shear distribution along the valley, and (c) to regulate the deformation of flexible edge that leads to reduction in the overall twist. Nonlinear analysis of the proposed model showed substantially reduced concentrated shear in short columns and improved deformations along and across the valley. The proposed methodology produced a more balanced structural response by improving stiffness distribution, deformation compatibility, torsional behavior, and force redistribution, with the flexible‐to‐rigid edge deformation ratio moving closer to unity.
ABSTRACT Resilient seismic design requires that structures exhibit excellent seismic performance and small residual deformation. Unbonded prestressed reinforced concrete (UBPRC) columns, with prestressed strands serving as self‐centering components, can effectively reduce residual displacement, which is of great significance for the seismic resilience of bridges. Compared with a traditional reinforced concrete column, the presence of prestress may change the failure mode of the UBPRC column. To quantitatively study the failure mode of UBPRC columns, two failure modes in the complete damage state were defined, and a matrix‐based analytical model was proposed. First, two failure modes were defined: crushing of the core concrete and tensile fracture of the longitudinal steel bars. On this basis, the uniform‐failure state was defined as the two failure modes occurring almost simultaneously. Then, an analytical model for the failure mode, including eight structural and material parameters, was proposed. The failure mode can be identified by inputting the values of these parameters into the analytical model. According to the proposed analytical model, the effects of various parameters on the failure mode of UBPRC columns were investigated. The parameter design was carried out using transverse and longitudinal reinforcement ratios, and the prestressing force ratio as examples, based on the uniform‐failure state. The proposed analytical model can be applied to identify the failure modes and to perform preliminary parameter design of the UBPRC column.
ABSTRACT This paper investigates the dynamic instability of pile foundations subjected to real seismic excitation through numerical analysis. The seismic input is extracted from ground motion records of the 1966 Peru earthquake, specifically the PER01 station record obtained from the official database of the Instituto Geofísico del Perú. The recorded ground acceleration was processed using the SeismoSignal software and then incorporated into the equation of motion of the pile foundation as a parametric excitation. Because the time‐varying coefficient in the equation of motion is represented by digitally recorded discrete data, conventional methods are not directly applicable. To overcome this limitation, a novel numerical method is proposed for evaluating the dynamic instability of systems whose equation coefficients are available only as digital discrete data. The method approximates the state transition matrix using a cascading matrix technique, enabling accurate stability analysis under arbitrary recorded excitations. A series of parametric studies is then conducted to investigate the effects of key parameters—including static load, soil damping, soil stiffness, excitation frequency, pile elastic modulus, and pile length—on the boundaries of the dynamic instability regions.
ABSTRACT The behavior of Cold‐Framed Steel (CFS) frames under earthquake loads must be examined before CFS building systems can be integrated fully into the construction market. Over the past 20 years, studies have focused on the subsystem level, while system‐level performance has been less studied. This paper aims to bridge the gap between subsystem and system‐level performance. In this regard, a full‐scale shake‐table test is conducted using results from subsystem‐level tests to provide experimental insight into the behavior of real 3D CFS‐framed structures under seismic excitation. The CFS‐framed building is designed in accordance with the Iranian Cold‐Formed Light Steel Structures Design and Construction Code. The building's structural system comprises CFS, CFS‐framed shear walls with two‐sided and one‐sided sheathings, and a k‐brace for lateral force‐resisting shear walls. The CFS test structure features a rectangular floor plan measuring 2.9 m × 3.10 m, with a uniform story height of 2.4 m throughout all levels. Using signal‐processing techniques, the frequency response function of the CFS specimen is determined to identify its natural frequencies and damping ratios. The structure is subjected to ground motion tests on the shake‐table. Then, simplified numerical models are developed in OpenSees. Nonlinear time‐history analyses were performed on finite element models of the CFS building, with results systematically compared with shake‐table test data to validate the proposed simplified modeling approach. The developed model demonstrates excellent agreement with experimental results, showing: (1) close correlation in natural period between the numerical model and physical structure, and (2) nearly identical peak story absolute acceleration responses.
