Earthquake Engineering & Structural Dynamics

doi: 10.1002/eqe.3927pmid: N/A

Magliulo, Gennaro; D'Angela, Danilo

doi: 10.1002/eqe.4080pmid: N/A

The paper investigates the seismic response of nonstructural elements (NEs), focusing on acceleration‐sensitive components housed in buildings, modelled as inelastic Ibarra–Medina–Krawinkler (SDOF) systems. Incremental dynamic analysis (IDA) is carried out considering (a) representative suites of building floor motions (real loading histories recorded within reinforced concrete (RC) buildings and table testing protocol inputs) and (b) a wide range of NE models (with elastic frequencies ranging within 1–9 Hz). The Ibarra‐Medina‐Krawinkler (IMK) model was implemented in OpenSees, defining the key modeling parameters according to the formulations provided by Lignos and Krawinkler. Both IDA curves and component (acceleration) amplification factor (CAF) are characterized, also considering statistical measures. The seismic capacity of the investigated NEs is estimated through fragility curves, accounting for five incremental damage states (DSs). The fragility parameters are correlated with the frequency of the NE models, and (statistical‐based) closed‐form capacity criteria are provided. The study provides a robust technical and scientific methodological framework for assessing the seismic capacity of NEs that can be modeled by inelastic SDOF systems. The findings have a potential major impact on both research and practice, enriching scientific knowledge and providing useful applicative tools. In particular, quantitative response and capacity measures are supplied, and the developed capacity criteria can be particularly useful for expeditious but reliable design and assessment, as well as for comparison purposes.

Vicencio, Felipe; Alexander, Nicholas A.; Málaga‐Chuquitaype, Christian

doi: 10.1002/eqe.4076pmid: N/A

Frequently, buildings in urban areas are designed by considering their stand‐alone response, that is, as single structures with no neighboring buildings. Nevertheless, the existence of a high density of buildings in large metropolitan areas inevitably results in the likelihood of an important seismic interaction between adjacent buildings through the underlying soil. This paper explores the effects of Structure‐Soil‐Structure Interaction (SSSI) on the seismic response of two yielding structures embedded in a linear elastic soil. A simple two‐dimensional nonlinear reduced‐order parametric model is proposed, where different building parameters are considered. A nonlinear phenomenological Bouc–Wen model is assumed for the buildings. A database of 15 strong ground motion records and an additional spectrally matched seismic ground motion are considered. An extensive parametric study comprising over two million nonlinear cases is conducted. The results show important differences between nonlinear SSSI and nonlinear SSI for particular parameter configurations. Nevertheless, due to energy dissipation and increases in damping in the nonlinear case, the effects of SSSI are less relevant compared with the linear case.

Mayorga, C. Franco; Tsampras, Georgios

doi: 10.1002/eqe.4073pmid: N/A

This paper assesses the effects of (1) the gravity load‐resisting system (GLRS) modeling approach, (2) the seismic force‐resisting system (SFRS) modeling approach, and (3) the uncertainty of the model parameters of the constitutive law of the longitudinal reinforcing steel of the SFRS on the seismic responses of a 12‐story reinforced concrete wall building with force‐limiting connections. This is achieved by conducting nonlinear numerical earthquake simulations. The seismic responses of the building models with force‐limiting connections using two GLRS modeling approaches, (1) a moment frame system and (2) a pin‐base lean‐on‐column system, are compared. The seismic responses of the building models with conventional connections and force‐limiting connections, respectively, using two SFRS modeling approaches, (1) a distributed‐plasticity modeling approach and (2) a lumped‐plasticity modeling approach, are compared. A joint probability density function for the ASTM‐A615 Grade 60 steel available in the literature is used to conduct an uncertainty propagation analysis through Monte Carlo simulation. The uncertainty in the steel model parameters is propagated to the seismic responses of the building models with conventional connections and force‐limiting connections, respectively. The distributions of the mean values of the peak structural responses of the building models are studied. The effects of the GLRS modeling approach on the seismic responses are not significant in the context of seismic performance‐based design and assessment of buildings with force‐limiting connections. The effects of the SFRS modeling approach and the uncertainty in the steel model parameters on the floor total acceleration and force responses are reduced by including force‐limiting connections.

Esposito, Francesco; Faiella, Diana; Mele, Elena

doi: 10.1002/eqe.4079pmid: N/A

Vertical extensions of existing buildings can be realized through Intermediate Isolation System (IIS): the extension, equipped with a base isolation system on the rooftop of the existing building, can work as a mass damper, thus reducing the seismic demand on the old structure. The idea proposed in this paper is to predict the elastic or inelastic response of the existing structure in the IIS configuration by means of the results of simple linear analyses. Parametric response spectrum analyses are performed on simplified two degree‐of‐freedom models by varying the mass ratio and the periods of both the existing building and the new isolated vertical extension. So‐called IIS design spectra are derived, and the results are provided as design charts. Given the period of the existing building and the mass ratio, the period of the new isolated vertical extension is selected to obtain the required/desired response of the existing building. For existing buildings working in the elastic field, the designer can derive the response of the existing building by utilizing the IIS design spectra as design charts. For existing building working in the inelastic field, the design charts can still be adopted, though within a more complex procedure, which accounts for two limit behaviors that the extended building exhibits in the inelastic field. The outlined design procedure is applied to some case studies and validated through the comparison with the results of nonlinear time history analyses.

Xu, Ming‐Yang; Lu, Da‐Gang

doi: 10.1002/eqe.4082pmid: N/A

This study proposes an extended generalized conditional intensity measure (EGCIM)‐based approach to selecting aftershock ground motions that match the target aftershock EGCIM distributions. The main purposes of the proposed methodology are threefold: (a) to consider the multiple characteristics of aftershock ground motions (e.g., amplitude, frequency contents, cumulative effects, and duration), (b) to account for the correlations between mainshocks (MS) and aftershocks (AS) as well as cross‐correlations between AS IMs, and (c) to associate with the conventional mainshock GCIM approach to enforce mainshock‐consistency for practical applications. For these purposes, three components of the EGCIM methodology for aftershock ground motion selection are utilized: (1) the multivariate aftershock EGCIM distributions of any vector of aftershock intensity measures (IMs) are constructed conditioned on two MS‐AS IMs, (2) the correlations between mainshocks and aftershocks as well as the cross‐correlations between AS IMs are considered, and (3) the random realizations of aftershock IMs are generated as a target using the aftershock EGCIM distributions to select aftershock ground motions from the specific database. The proposed methodology is applied to a case study in the LPCC station in New Zealand, whose aftershock EGCIM distributions of the considered 18 IMs are constructed for the case scenario. Among them, the correlations between mainshocks (MS) and aftershocks (AS) as well as the cross‐correlations between AS IMs are determined using the total residuals (epsilons) based on 662 real MS–AS ground‐motion pairs. Several examples are then discussed to illustrate the application of the proposed aftershock EGCIM approach, including the comparison of the aftershock acceleration spectrum with the ASK14 model and the effects of different components of the aftershock IM weight vector. Then, the proposed approach is compared with the conventional aftershock synthesis methods. It is observed that the conventional methods perform biased representations of different aftershock characteristics, of which the limitations are improved in the proposed approach. Moreover, a sensitivity study is performed for a typical midrise structure to investigate the effects of aftershock ground motion selection on the aftershock fragility analysis. The results indicate that the selection of aftershock records considering different AS characteristics has a notable impact on the aftershock fragility assessment. The uncertainties associated with record‐to‐record variations in aftershock fragility analysis can be effectively reduced by using the proposed selection approach that incorporates the comprehensive ground motion characteristics. The findings in this study promote the extension of the existing methods for aftershock ground motion selection, which can be applied to structural design or seismic risk analysis considering the aftershock effects.

Park, Jamin; Park, Minseok; Chae, Yunbyeong; Kim, Chul‐Young

doi: 10.1002/eqe.4085pmid: N/A

The material properties of steel and concrete vary depending on the loading rate to which they are subjected. To realistically evaluate the seismic performance of reinforced concrete (RC) columns, it is necessary to simulate the loading rate that structures will experience during seismic events as accurately as possible. Real‐time dynamic testing is preferred over quasi‐static testing for this purpose. On the other hand, the seismic performance of RC columns also depends on the axial force applied to the column. However, due to the large axial stiffness of RC columns, accurately controlling the axial force during the test, particularly in real‐time testing, is challenging. Consequently, only a few component‐level dynamic tests have been conducted for RC columns. This study aims to explore the influence of axial force and loading rate on the seismic performance of RC columns. To this end, both slow and fast cyclic loading tests were conducted on square cross‐section RC columns subjected to four different axial forces. By utilizing a robust actuator control method along with a specially designed load transfer element, the axial force was successfully controlled, while the lateral displacements were imposed on the columns in real‐time. The results include lateral strengths, postyield responses, damage patterns, rebar strains, and their rates, all of which constitute unique experimental data that can contribute to a deeper understanding of the actual seismic response of RC columns.

Destro Bisol, Giacomo; DeJong, Matthew J.; Liberatore, Domenico; Sorrentino, Luigi

doi: 10.1002/eqe.4074pmid: N/A

When subjected to earthquakes, many objects or structural elements behave like rocking rigid blocks. Computer servers, medical shelves, art objects, statues, and electrical transformers are frequently included in this category. Protection of these objects is an important task, considering that their value could be inestimable or their operation crucial during earthquakes; base isolation technology has been proven to be a viable option for this purpose. Initially, the dynamic model of a rocking rigid block placed on a base isolation device is reviewed. Then, two equivalent‐static displacement‐based procedures for designing the isolators for these types of objects are proposed, and the main steps are illustrated. The first procedure aims to determine isolator characteristics to prevent the initiation of rocking motion during the code‐level earthquake event. The second procedure is aimed at designing isolators that allow a specified maximum rotation of the block during seismic events. The proposed procedures are validated by means of time‐history analyses for a suite of spectrum‐compatible accelerograms. The first displacement‐based procedure appears particularly suitable for objects of small to medium size. The validation of the second procedure demonstrates that the equal displacement rule can be applied for this kind of systems, despite their softening. The results also indicate that the approach is particularly effective for medium to large structures/objects, if small oscillations are acceptable. The controlled rocking procedure offers a significant advantage by allowing for a reduction in the maximum displacement and period of the isolator, compared to situations where rocking motion must be prevented entirely.

Chen, Jinnan; Xu, Chengshun; Du, Xiuli; El Naggar, Hesham M.; Han, Runbo

doi: 10.1002/eqe.4078pmid: N/A

This paper presents the design and commissioning of a novel pseudo‐static test apparatus for underground structures that accounts for soil‐structure interaction by simulating the soil with suitably designed springs. The developed apparatus was employed to conduct 1:10 large scale tests on a two‐story three‐span prefabricated subway station structure. Two comparative cyclic load tests were conducted: one involved the developed springs‐structure system; and one involved the structure alone (no springs). The test results demonstrated important differences in the damage location, damage degree, bearing capacity, and deformation capacity of the prefabricated subway station structure under the two loading conditions (i.e., with and without springs). The presence of springs (i.e., soil‐structure interaction) enhanced the lateral collapse resistance of the underground structure and affected the inter‐story displacement ratio (IDR) between the upper and lower layers of the two‐story prefabricated subway station structure. However, it did not affect the deformation coordination of the walls and columns of each layer. A finite element model of the prototype station was also established to conduct dynamic time history analysis simulating the soil‐structure interaction. The results from the dynamic analysis validated the effectiveness of the pseudo‐static test method employing the spring‐structure system. The excellent agreement between the calculated dynamic responses and the responses obtained from the pseudo static tests confirmed the ability of the developed apparatus to conduct seismic tests on complex large‐scale underground structures such as prefabricated subway stations. Thus, this test methodology might be utilized to attain valuable insights into the seismic performance of prefabricated subway stations at a relatively low cost and effort.

Huang, Yu‐Tzu; Loh, Chin‐Hsiung; Chou, Chung‐Che; Chen, Wen‐Hui

doi: 10.1002/eqe.4084pmid: N/A

Structural health monitoring is conducted to ensure the structural integrity of a building during earthquakes. This study aimed to improve our understanding of the dynamic response of buildings subjected to a series of earthquake excitations, focusing on interpreting structural dynamic characteristics and identifying potential seismic damage subjected to a series of earthquake excitations. To this end, a series of seismic response data of a 13‐story reinforced‐concrete/steel building were collected through long‐term monitoring over 2 years. A systematic approach for monitoring the health of the building was established by integrating several algorithms for vibration‐based (both output‐only and input–output parametric nonparametric feature‐discrimination algorithms) and model‐based feature extraction techniques. Furthermore, the time‐varying dynamic characteristics of the building were determined, including its modal frequency, mode shape, and stiffness, as extracted from features obtained over the monitoring period of 2 years. Safety assessment of this newly compound high‐rise building is investigated to explore the system dynamic characteristics through long‐term seismic monitoring.