Journal: WCEE Online Proceedings

Abbreviation

Publisher

National Information Center of Earthquake Engineering

Journal Volumes

ISSN

Description

Filters

202114
Reset filters

Search Results

Publications 1 - 10 of 14
  • Seismic Assessment of an Existing Swiss Unreinforced Masonry Building with Flexible Floor Diapgragms
    Item type: Conference Paper
    Arslantürkoglu, Safak; Volken, Nicolas; Mojsilović, Nebojša; et al. (2021)
    WCEE Online Proceedings ~ Proceedings of the Seventeenth World Conference on Earthquake Engineering Japan 2021
    Switzerland is a country of low and moderate seismicity. Nonetheless, because unreinforced masonry (URM) residential buildings are a major portion of the built inventory, the seismic risk is not negligible. To meet a growing need for seismic evaluation of buildings, SIA 269/8, a Swiss code for seismic assessment of structures, was recently adopted. SIA 269/8 prescribes a risk-based seismic evaluation using the compliance factor concept, a factor that relates the seismic capacity of an existing building to the seismic capacity corresponding to the collapse safety requirement of a hypothetical (essentially) identical new structure. The goal is to achieve an acceptable low risk of casualties (between 10-5 and 10-6 individual annual casualty risk linked to compliance factor values between 25% and 100%). SIA 269/8 also defines a process on how to decide if a seismic retrofit is mandatory or not and how to select the retrofit measures that are commensurable to the actuarial value of the potentially saved lives. This paper presents a case-study investigation of a typical existing Swiss URM building with flexible floor diaphragms that features an in-depth analysis of both local failures and global building behavior. Prior to undertaking a global nonlinear static analysis, local failure modes such as the out-of-plane wall failure mechanism, support and resistance of the floor diaphragms, and the load transfer from the floor diaphragm to walls were examined. The main emphasis was on the interaction between the out-of-plane responding walls and the flexible floor diaphragms. The force-based method based on rigid-body motions and the Paulay & Priestley approach were considered. Being known for its conservatism, the latter is still the most common approach among the Swiss engineering community. Equivalent frame approach was then used to model the building globally, followed by the global seismic performance assessment using the N2 method that compares the displacement demand to the displacement capacity of the entire structure. The outcome of the SIA 269/8 evaluation procedure is that the governing compliance factor of 75% is dictated by the out-of-plane responding wall of the north façade, resulting in a corresponding cost limit of 7’500 USD. In other words, seismic retrofit is mandatory if the upgrade related cost does not exceed 7’500 USD. Following SIA 269/8, a seismic upgrade may be waived if the expected cost is higher than this threshold value as the achieved risk reduction is not reasonably justified. The findings of this case study indicate that an implicit assumption of global structural integrity may give a false sense of safety for URM buildings with flexible diaphragms as local failure mechanisms often govern the structural performance. Another distinct finding to emerge from this study is the importance of updating of geometric and material parameters of the existing structure for the seismic capacity assessment using in-site investigations and laboratory tests to improve the often limited knowledge of the current state of the building and reduce uncertainties.
  • Displacement-based Analysis and Design of Rocking Structures
    Item type: Conference Paper
    Vassiliou, Michalis F.; Reggiani Manzo, Natalia (2021)
    WCEE Online Proceedings ~ Proceedings of the Seventeenth World Conference on Earthquake Engineering Japan 2021
    Rocking can be used as a seismic isolation strategy for bridges and buildings. Letting a structure uplift works as a mechanical fuse and limits the design forces of both the foundation and the superstructure. Interestingly, there is no correlation between the rocking oscillator and the elastic one. Therefore, there is not any “equivalent linear system” and the elastic spectra are useless when it comes to rocking. Thus, there is no simplified design procedure that a practicing engineer could use. In order to create design rocking spectra, the rocking oscillator should be described with the simplest possible way and the least necessary parameters. Since Housner’s seminal paper in 1963 the traditional DOF chosen to describe the motion of a rocking block has been its tilt angle. This description uncovers that out of two blocks with the same slenderness ratio, the larger one is more stable. This tilt-based description is mathematically correct, but not optimal. This paper shows that the top displacement is a better descriptor of the rocking oscillator, because it uncovers a fundamental property useful for design: As long as the blocks are not close to overturning, the top displacements of a large and a small block of the same slenderness are going to be roughly equal. This property is proven for both analytical pulses and for recorded ground motions. In mathematical terms, the displacement demand on a rocking block is a unary function of its slenderness angle. In practical terms, this means that the displacement demand of any block can be computed by the displacement of a block of the same slenderness, yet very large size – likewise the displacement demand of a yielding oscillator can be computed based on the displacement of an equivalent linear system. Thus, the rocking-related seismic hazard can be computed by much simpler rocking spectra. As an example, the proposed method is applied for the preliminary design of a rocking frame having the dimensions of a typical overpass bridge.
  • Blind Prediction Contest on the Shake Table Tests of a 3D Rocking Structure
    Item type: Conference Paper
    Vassiliou, Michalis F.; Broccardo, Marco; Cengiz, Cihan; et al. (2021)
    WCEE Online Proceedings ~ Proceedings of the Seventeenth World Conference on Earthquake Engineering Japan 2021
    Rocking motion is sensitive to the boundary and initial conditions of a rocking structure. Thus, the claims that numerical rocking motion models are not only inaccurate, but that all rocking structures behave unpredictably. Hence, rocking is not used as a seismic design approach. This paper revisits the issue of rocking motion unpredictability. Seismic behavior of structures is inherently stochastic, because the loading is stochastic. Therefore, the question of interest is not whether models can predict the seismic response to a single ground motion, but if the statistical characteristics of the ensemble of responses to a set of ground motions that define the seismic hazard can be predicted. For this purpose, a rocking podium, which is a three-dimensional structure comprising an aluminum slab supported by 4 tubular steel columns, was tested on a shake table excited by two sets of 100 consistently generated ground motions. It was found that the Cumulative Distribution Function (CDF) of the experimentally obtained displacements is statistically stable. Next, a blind prediction contest was organized. The contestants were invited to predict the CDFs of the slab lateral displacement. They were able to predict the slab displacement CDF relatively well. Both finite element and discrete element modeling approaches were used, but no clear pattern emerged as it was found that the performance of either approach depends on the input parameters used and the assumptions made.
  • Best retrofit based on energy dissipation for a building subjected to various strong earthquake
    Item type: Conference Paper
    Guzman Lucatero, Erik; Ramirez Marquez, Victor; Macias Jaime, Jesus; et al. (2021)
    WCEE Online Proceedings ~ Proceedings of the Seventeenth World Conference on Earthquake Engineering Japan 2021
    A Mexico City building built in 1958 located on soft soil is analyzed, which has been damaged by the 1985 Mw 8.1 and 2017 Mw 7.1 earthquakes. Buildings in the same area and similar structural systems collapsed in these earthquakes (210 in 1985 and 38 in 2017). To perform the mathematical model, a structural identification was carried out using a rebar locator and a concrete rebound hammer. The response of the building subjected to these earthquakes was analyzed, finding the changes of the stiffness of the building when plastic hinges were formed, as well as the adjustment in the period of the structure. The analysis performed are nonlinear time-history. The response of the structure shows considerable damage to several elements being at risk of collapse with another earthquake, the reason why the building is uninhabited. Therefore, reinforcements are proposed with energy dissipation which gives the building the capability to resist another earthquake like the experienced in 1985 or 2017. To determine which system is the most convenient in this case, the response of the building is compared using several energy dissipation systems; those that only provide damping to the structure, and those that provide damping and also stiffness. An important point observed was that systems that provide stiffness and damping can lead the period of the structure to coincide with the site period (2 seconds), which would cause a resonance effect, the main reason of why many near-2-second period buildings collapsed in 1985 earthquake. Therefore, it is highly recommended to carry out an analysis of this type on all buildings that have been affected by more than one strong earthquake in Mexico City.
  • Analysis of the behavior of a flexible building with seismic isolation in various interfaces
    Item type: Conference Paper
    Ramirez Marquez, Victor; Guzman Lucatero, Erik; Macias Jaime, Jesus; et al. (2021)
    WCEE Online Proceedings ~ Proceedings of the Seventeenth World Conference on Earthquake Engineering Japan 2021
    In previous research presented in the 16WCEE, the seismic response of a typical 19-story building for residential use in Mexico was analyzed. The structural system of the structure is based on reinforced concrete frames and walls with a fixed base. Design alternatives were proposed adding seismic isolation at one and two interfaces, presenting uplift issues in the case of one-interface isolation system due to its high slenderness. This issue was solved with the two-interface isolation system setting, installing sliding isolators at the base and the seventh level, reducing the observed uplifting. The proposed solution was considered an effective way to reducing uplifting when applying base seismic isolation to slender medium rise buildings, however, this solution has not been studied for taller high-rise buildings with larger slenderness. In this paper, the response of the same building with the same structural settings is analyzed, but increasing to a 60-story building with a total height of 220 meters. Three configurations were studied: two 30-story block interface; three 20-story block interface; and four 15-story block interface. In each configuration the isolation interface consisted on sliding isolators. The responses of each model are analyzed to determine the optimal number (technically and economically) of stories of each rigid block that the building should be divided in order to obtain the desired performance. The response of the structure is obtained by nonlinear time-history analysis. The results obtained show a considerable energy-dissipation at each interface level, reducing seismic response, passing them from the first mode (fixed base building) to their nth mode according to the number of interfaces added.
  • Scenario-based Resilience Assessment of Communities with Interdependent Civil Infrastructure Systems
    Item type: Conference Paper
    Blagojević, Nikola; Kipfer, Janine; Didier, Max; et al. (2021)
    WCEE Online Proceedings ~ Proceedings of the Seventeenth World Conference on Earthquake Engineering Japan 2021
    Civil infrastructure systems (CISs) supply the communities with essential resources and services, such as electric power, potable water, telecommunication and transportation. Extreme events, such as earthquakes, can cause disruptions to these systems resulting in significant direct and indirect financial and societal losses. Increasing disaster resilience of CISs reduces the negative effects of such events on communities. However, in order to improve CIS and community disaster resilience, it first it needs to be quantified, so that various strategies for resilience improvement can be devised and evaluated. This paper presents a model for quantifying the seismic resilience of communities with interdependent civil infrastructure systems. The model comprises four modules: the hazard module, the vulnerability module, the functional recovery module and the resilience quantification module. The hazard module is used to assess the intensity measures of a considered scenario earthquake at the geographic locations of CIS components. Ground motion prediction equations, and transient and permanent ground deformation models are used to estimate the peak ground acceleration, peak ground velocity and peak ground deformation, respectively. The vulnerability module links these measures to component damage states using seismic vulnerability curves. Due to the suffered damage, functionality of the components decreases. Additionally, certain components rely on the resources and services provided by other CISs. For example, a water pump needs electric power to operate. Such interdependencies between CISs are explicitly modeled using an iterative flow-based approach as they can cause further decreases of component functionality through feedback loops and cascading effects. The functional recovery module simulates the component repair process and restoration of component and system functionality using pre-assigned repair rates. Finally, the Re-CoDeS method is used to compute the unmet demand for a CISs service over time and thereby quantify the resilience (or lack thereof) of the considered CISs. In this paper, a virtual community served by three interdependent CISs is exposed to a scenario earthquake. The presented model is then used to quantify the seismic resilience of this system of systems and evaluate the effects of CIS interdependency.
  • Probability-based Resilience Assessment of Communities with Interdependent Civil Infrastructure Systems
    Item type: Conference Paper
    Blagojević, Nikola; Kipfer, Janine; Didier, Max; et al. (2021)
    WCEE Online Proceedings ~ Proceedings of the Seventeenth World Conference on Earthquake Engineering Japan 2021
    Communities exposed to seismic hazards should make their infrastructure more resilient to minimize the potential damaging effects of earthquakes. To rationally decide on investments to improve infrastructure systems’ performance in future events, an estimate of potential consequences of such events is needed. A probability-based model that quantifies the seismic resilience of a community enables such rational performance-based decision making. A probability-based resilience assessment using a modular model of a community supplied by interdependent civil infrastructure systems is presented in this paper. The model simulates the hazard in the hazard module, then assesses the drop in the functionality of the community due to the suffered damage in the vulnerability module. Next, the functional recovery module simulates the increase of community functionality over time. Finally, seismic resilience is quantified in the resilience quantification module. Using the Re-CoDeS framework for resilience quantification, the proposed model measures the Lack of Resilience (LoR) of the community with respect to each resource or service provided by the civil infrastructure systems. The proposed model is applied to a virtual community supplied by three interdependent civil infrastructure systems: electric power supply, water supply system and cellular communication system. The expected LoR increases with the intensity of the earthquake. Loss curves, plots of the mean annual rate of exceedance of community LoR values for a given seismic hazard exposure, probabilistically quantify this trend. Interdependency effects are evaluated, by comparing two modelling cases: the independent case – where the drop in the functionality of a component is solely the consequence of its current damage; and the interdependent case – where the functionality of a component also depends on the availability of resources and services the component needs to operate. Interdependency effects amplify the LoR for all considered resources and services at all hazard intensities.
  • Sequential Experimental Design of Hybrid Simulations For Bayesian Calibration Of Computational Simulators
    Item type: Conference Paper
    Abbiati, Giuseppe; Marelli, Stefano (2021)
    WCEE Online Proceedings ~ Proceedings of the Seventeenth World Conference on Earthquake Engineering Japan 2021
    Hybrid simulation combines physical and numerical substructures interacting with each other in a real- time control loop to simulate the time history response of a prototype structure subjected to a realistic excitation. Research on hybrid simulation is limited to the coupling of physical experiments and numerical simulations, that is, ensuring compatibility and balance of interface quantities involved by the physics of the prototype structure. No effort has been made yet to link experimental design and hybrid simulation. experimental design can be broadly defined as the process of selecting a particular setup for an experiment, from the parameter space of all the admissible setups, so as to maximize the information obtained from a future experiment prior to data collection. From a hybrid simulation perspective, the experimental design includes the definition of numerical substructures and loading excitations. From this standpoint, this paper presents an experimental design procedure that aims at maximizing the convergence rate of the Bayesian calibration of a computational simulation against hybrid simulation experiments.
  • Dimensional Analysis of Negative Stiffness Bilinear Systems under Pulse Like Excitations
    Item type: Conference Paper
    Reggiani Manzo, Natalia; Gallacchi, Julien; Vassiliou, Michalis F. (2021)
    WCEE Online Proceedings ~ Proceedings of the Seventeenth World Conference on Earthquake Engineering Japan 2021
    Rocking has been proposed as a seismic design strategy for bridges and buildings, as rocking structures experience minimal residual displacements. In order to provide redundancy to rocking systems and to control their displacements, researchers in New Zealand and the USA have proposed to use unbonded restraining tendons within the rocking elements. In parallel, in the former USSR and currently in former USSR countries, a rocking solution has been used, where the rocking elements are extended with curved wedges to increase their displacement capacity, without increasing the design forces of the superstructure. In terms of their pushover curves, the above two systems are similar, as they present an initial relatively stiff branch followed by a linear branch that can be of positive or negative stiffness, depending on the stiffness of the tendon or the curvature of the curved wedge. Unloading follows the same branch without any hysteretic energy dissipation (unless the structure is equipped with extra energy dissipaters). Energy dissipation happens instantaneously during impact. Opting for positive stiffness is the current state of the practice. However, a negative stiffness design would lead to a smaller design moment for both the superstructure and the foundation, potentially not requiring piles. Therefore, there is a need to better understand the dynamics of negative stiffness systems with instantaneous damping. This paper studies the general bilinear negative stiffness oscillator. It uses dimensional analysis to determine the nondimensional quantities that better describe the problem, and presents response spectra for analytical pulses. It shows that for negative stiffness systems, the addition of flexible tendons or large curvature wedges increases the displacement capacity of the system, while it keeps the displacement demand almost constant. Moreover, it discusses the influence of the characteristics of the first branch of the bilinear curve on the overall response of the system.
  • Comparison of different risk measures for portfolio-level earthquake risk assessment
    Item type: Conference Paper
    Bodenmann, Lukas; Galanis, Panagiotis; Broccardo, Marco; et al. (2021)
    WCEE Online Proceedings ~ Proceedings of the Seventeenth World Conference on Earthquake Engineering Japan 2021
    A risk measure quantifies the risk associated with a single asset (e.g., an individual building) or a group of assets (e.g., a building portfolio of a region) exposed to one or more sources of hazard during a given time horizon. These risk measures serve as objective functionals that define subsets of “acceptable” and “unacceptable” risks. In performance-based seismic design, a new building should fulfill a set of performance objectives not only to protect human life in rare earthquakes but also to limit direct (e.g., repair cost) and indirect (e.g., downtime, business interruption) financial losses in more frequent seismic events. These performance objectives are commonly formulated as limits on risk measures for individual buildings. The potentially large spatial footprint of earthquakes and the increased concentration of population and values in dense urban areas call for an explicit consideration of seismic risk at a regional level, in particular when formulating performance objectives for new individual building structures. Subadditivity is a desired mathematical property of risk measures in this setting, because the sum of subadditive risk measures evaluated separately for each individual building is an upper bound on the joint risk measured for a portfolio of buildings. The present study reviews different risk measures commonly employed in earthquake engineering and in the financial industry and discusses their mathematical properties with special emphasis on subadditivity. To illustrate the importance of subadditivity for earthquake engineering, a seismic loss analysis is performed for a given portfolio of buildings situated in a virtual hazard environment. Financial losses due to earthquake-induced building property damage are quantified for the individual buildings and for the portfolio of buildings using a set of risk measures. Given the defined hazard, vulnerability and exposure, the results show that quantile-based measures, such as the loss with a certain mean annual frequency of exceedance, are subadditive only for losses with a recurrence interval longer than 200 years. As a consequence, using quantile-based measures could lead to underestimation of portfolio-level financial losses for more frequent events.
Publications 1 - 10 of 14