Search

The paper presents a study on the evaluation of seismic fragility of cylindrical ground-supported steel silos intended for storing solid material. Silos are a key facility in industrial processes. For example, cylindrical steel silos constitute the main structural component for several industrial activities, such as the ones aimed at the production of food and beverage, and seismic actions can cause high economic losses and long functionality interruptions. Thus, the main goal of this paper is to propose a numerical procedure aimed to assess the seismic fragility of different cylindrical steel silos, accounting for varying geometries and service conditions (i.e., filling level of granular-like material), and observing different failure modes. In detail, a set of smooth steel silos was selected, considering different geometrical configurations (i.e., varying from squattest to slenderest structures). Different service conditions were simulated, with the aim to observe the behaviour of empty and filled silos (30%, 60%, and 90% of filling degree with respect to the maximum capacity). For each configuration, a detailed numerical model was developed under proper boundary conditions, adequately simulating the shell structure, the solid material inside, and the interactions between them. After validating the numerical models against existing literature data, three different failure modes were identified and assessed, accounting for the most recurrent post-elastic buckling type (i.e., elephant foot) and considering the possible occurrence of the elastic ones (i.e., diamond or similar shape failures at the middle and top of the structures). Both static and dynamic analyses were performed to identify the most probable failure modes and evaluate the probability of exceeding each one. As the output of the proposed approach, the seismic performance of each silo under a specific limit state was provided in the form of fragility curves. The results highlight some novel aspects, starting from the role that service conditions assume in the silos seismic performance up to the possible differences in terms of failure modes for different silos geometrical structural configurations. [ABSTRACT FROM AUTHOR]

Studied are the hysteretic force–deformation response of large-scale nonlinear viscous dampers and model of the response for use in numerical simulations and seismic design. The force–deformation response of nonlinear viscous dampers with a force capacity of 600 kN are characterized under sinusoidal loading. A wide range of amplitudes and frequencies are used in the characterization tests. A nonlinear Maxwell model is presented for modeling the force–deformation response of large-scale nonlinear viscous dampers for use in nonlinear response history analyses. This paper also presents an equivalent linear model for the force–deformation response of a nonlinear viscous damper in-series with the elastic bracing and connection components needed to connect the damper to a building structure. The equivalent linear model enables the effects of the elastic flexibility of structural components on the response of the damper-brace component to be considered in seismic design. Results from tests on a 0.6-scale three-story structure with nonlinear viscous dampers validated the predictive accuracy of the equivalent linear model. Also evaluated are the effects of the elastic flexibility of structural components (e.g., bracing and connection) on the effective stiffness and damping ratio of a building structure with nonlinear viscous dampers. [ABSTRACT FROM AUTHOR]

Bridges are the most critical and usually the most vulnerable structural component of a road network exposed to various hazards. Damage due to recent earthquakes worldwide highlighted the substantial direct and indirect financial losses related to partial or total collapse of critical bridge components and pointed to the need for reliable assessment of their seismic performance. This paper presents a 'toolkit' developed for bridge-specific fragility analysis of bridges; it is implemented on a "two-track" online platform, including ad-hoc developed software for online bridge-specific fragility curve derivation, as well as the option to select an appropriate set of generic fragility curves from a database including a broad range of bridge classes. Three alternative options for the estimation of component-specific limit state thresholds are provided; selection from extensive lists with available thresholds for piers, bearings and abutments, and calculation of limit state thresholds for as-built and retrofitted piers based on (a) closed-form relationships, or (b) inelastic pushover analysis and capacity assessment of a parametrically defined pier model (carried out online). Details regarding the software developed, the methodology for bridge-specific fragility curves, and all critical features are presented and discussed herein. The application of the online software is illustrated through two case studies involving the derivation of fragility curves for bridges with different structural systems and properties. [ABSTRACT FROM AUTHOR]

This paper investigates the seismic loss assessment of seismically isolated and non-isolated buildings with steel moment or braced frames, designed by the seismic design standard of ASCE/SEI 7-16. The seismic loss is calculated from the damage to structural and non-structural components, as well as the demolition and the collapse of buildings. This study demonstrates that the expected annual losses for seismically isolated buildings are half or less than half of those calculated for non-isolated buildings. These losses depend on the types of seismic isolation systems and seismic force resisting systems used. Among the cases of isolated buildings studied in this paper, the most cost-effective systems are found to be the buildings designed by minimum strength requirement in ASCE/SEI 7-16 and with isolators which have displacement capacity 1.5 times larger than the minimum required in ASCE/SEI 7-16, in terms of expected annual losses. This study also compares the results obtained from different approaches of selection and scaling of ground motions. The following research finds that when Incremental Dynamic Analysis approach with far-field ground motion set in FEMA P695 is used, the computed expected total annual losses become doubled from the Conditional Spectra approach. [ABSTRACT FROM AUTHOR]

Timber structures are important components of the architectural and cultural heritage. To enrich literature on reconnaissance and heritage preservation, this paper provides a comprehensive damage survey and assessment of the Shuanghe Confucian temple after the 2019 Changning earthquake Series. Confucian temple is a temple for the veneration of Confucius and the sages and philosophers of Confucianism in Chinese folk religion and other East Asian religions. The Shuanghe Confucian temple, which sits in southwestern China, was first built at about 1241, but have been gradually deteriorating and refurbished for 600 years. It has the supreme structural grade in ancient Chinese architecture and delicate local characteristics. On June 17th, 2019, an Ms 6.0 earthquake stroke Changning County, and another four earthquakes (aftershocks) with magnitude larger than Ms 5.0 took place in the next 20 days. The Shuanghe Confucian temple experienced very distinctive damage during the earthquake series. The paper first present sufficient ground motion information. Characteristics of the all the major structural components are also introduced along with their mechanical functions. Next, the damage of all the typical timber structural components, like roof overhangs drop, column rupture, column bottom lateral residual displacement, and non-structural components failure are carefully documented and assessed. The paper reveals two important aspects that some major damages of the Shuanghe Confucian temple occurred in aftershocks, and that the columns bottom lateral residual displacement was caused by eternal impact induced by adjacent wall collapse, instead of structural inner forces. Thus, this paper helps better understand the seismic performance of traditional timber structures and identify potential weaknesses which might have adverse influences on timber structures. Lessons learnt from the Shuanghe Confucian temple can be used in future to better protect other historical timber structures from earthquakes. [ABSTRACT FROM AUTHOR]

In this paper, empirical fragility curves for reinforced concrete buildings are derived, based on post-earthquake damage data collected in the aftermath of earthquakes occurred in Italy in the period 1976–2012. These data, made available through an online platform called Da.D.O., provide information on building position, building characteristics and damage detected on different structural components. A critical review of this huge amount of data is carried out to guarantee the consistency among all the considered databases. Then, an in-depth analysis of the degree of completeness of the survey campaign is made, aiming at the identification of the Municipalities subjected to a partial survey campaign, which are discarded from fragility analysis. At the end of this stage, only the Irpinia 1980 and L'Aquila 2009 databases are considered for further elaborations, as fully complying with these criteria. The resulting database is then integrated with non-inspected buildings sited in less affected areas (assumed undamaged), to account for the negative evidence of damage. The PGA evaluated from the shakemaps of the Italian National Institute of Geophysics and Volcanology (INGV) and a metric based on six damage levels according to EMS-98 are used for fragility analysis. The damage levels are obtained from observed damage collected during post-earthquake inspections through existing conversion rules, considering damage to vertical structures and infills/partitions. The maximum damage level observed on vertical structures and infills/partitions is then associated to the whole building. Fragility curves for two vulnerability classes, C2 and D, further subdivided into three classes of building height, are obtained from those derived for specific structural typologies (identified based on building height and type of design), using their frequency of occurrence at national level as weights. [ABSTRACT FROM AUTHOR]

The reliable estimation of seismic losses due to damage to buildings is paramount for the post-emergency management and the planning of recovery activities. For residential reinforced concrete (RC) infilled buildings, a significant role in the computation of seismic loss is played by non-structural components, above all infills, partitions and services, as shown in past earthquakes. In this work, a component-based methodology is proposed to assess seismic losses for residential RC buildings in Mediterranean region. The attention is focused on the repairing activities for masonry infills (typical enclosure or partitions elements in Italian and Mediterranean RC buildings), and for services (plumbing systems, electric equipment, floor/wall tiles...), commonly enclosed within the infill panels for the considered building typology. The described methodology can be used starting from the expected damage level to infills and partitions. It adopts given repair unit costs at different damage states of infills. The loss estimation methodology has been, first, validated by comparing predicted and actual repair costs for specific case-study buildings damaged by L'Aquila (Italy) 2009 earthquake. Then, the methodology has been applied to a wide dataset of RC buildings (about 2500 residential buildings) damaged by L'Aquila earthquake available from the literature, to show its possible application at a large-scale level. A good agreement between observed and predicted costs is obtained both for specific case-study buildings and for the wider building stock, especially when damage to structural components is very limited. [ABSTRACT FROM AUTHOR]

An improved response surface method (RSM) for the seismic fragility analysis of base-isolated structures is proposed so that the correlation of seismic demands on the structural components can be effectively considered. In addition, the performance levels of base-isolated structure as well as the associated quantitative indices for various structural components are discussed and defined. Taking a typical base-isolated reinforced concrete plane frame with lead-rubber-bearings as an illustrative example, the seismic fragility analysis following the computational procedure based on the improved RSM are conducted. Through the illustrative example, it is demonstrated that the obtained response surface models for the seismic demands on the components as well as the correlation of components are accurate and reliable; moreover, the computational cost for the system seismic fragility analysis is significantly reduced due to the use of Monte Carlo simulation; finally, it is indicated that it is necessary to take into account the correlation of components in order to obtain more accurate system fragility curves of base-isolated structure. [ABSTRACT FROM AUTHOR]

This article presents an approach to rapidly predict the seismic vulnerability existing of low-to mid-rise residential reinforced concrete (RC) buildings. In this procedure, Capacity Index is computed considering the cross-sectional orientation and size and material properties of the components of the structural system. This index is modified considering the several coefficients of possible negative impacts of structural irregularities, which are frequently found in RC buildings. Accuracy of the proposed approach has been tested considering 196 RC buildings subjected to earthquakes. The procedure categorizes the buildings either as safe or as unsafe according to whether they meet the life-safety target performance requirement. The analytical results indicate that the consistency of the proposed approach in this paper is about over 90%. Therefore, the proposed approach can be used to asses the seismic performance and vulnerability levels of existing RC buildings. [ABSTRACT FROM AUTHOR]

The need for proper nonlinear modelling of the structural damage resulting from strength and stiffness degradation observed at different levels of seismic intensity is essential in a comprehensive response assessment of a structural system. A nonlinear model based on plastic and damage mechanisms is presented here for seismic analysis of inelastic structures. To begin with, piecewise linearization of the initial backbone curve is carried out, each segment being defined by an in-parallel combination of elastic-perfectly plastic and elastic-softening damage mechanisms. The deterioration of the plastic and damage mechanisms is controlled by a damage index, which involves an accumulation rule of a damage parameter. Then, simulation of structural components is used to exemplify the reproduction of some hysteretic models with different types of degradation. Comparison with experimental results is subsequently carried out to calibrate the proposed model. Cyclic histories, with variable amplitude, are also considered to illustrate the effects of the plastic-damage mechanisms on the hysteretic response. Finally, nonlinear seismic analysis of a single-degree-of-freedom system, equivalent to an r.c. framed structure, is used to highlight the capability of the proposed approach in order to generate the capacity boundary curve starting from the initial backbone curve. [ABSTRACT FROM AUTHOR]

The columns and the supporting foundations are invariably subjected to the interacting axial force, V, shear force, H and moment, M. It is quite common to consider the interaction of these forces in design of structural components, but the available standards and literature usually ignore the effect of interaction in case of foundations on slopes. Further, very little information is available about seismic capacity of foundations located on slopes. This article presents a numerical study on evaluation of the V–H–M capacity envelopes of strip foundations placed on top and face of slopes and subjected to earthquake action, with an objective of enabling a direct comparison with the capacity of the supported columns. Nonlinear 2D finite element limit analyses are performed for this purpose. Modified 'Probe' analyses are carried out for two representative c-ϕ soil slopes to develop the V–H–M capacity envelopes. The computed capacity envelopes are compared with their counterparts on flat ground. The characteristic features of the capacity envelopes are identified and explained considering the failure patterns under different combinations of V, H and M. A comparison of the capacity envelopes of counterpart foundations on flat ground and of columns is presented to highlight the relative hierarchy of strength of columns and foundations of a typical building on slope. [ABSTRACT FROM AUTHOR]

Due to the brittle nature of wood material, the dissipation of seismic energy in timber structures is typically ensured through yielding of the mechanical connectors, where plastic deformations are developed in fasteners that have adequate ductility and cycle-fatigue strength. These structural components are denoted dissipative zones, whereas all other structural elements are assumed to behave elastically. Such elements are designated as non-dissipative zones and are designed with sufficient over-strength, to meet the requirements of capacity-based design (CD). Despite the general consensus that using the principle of CD could lead to safe buildings, where brittle failures are avoided, the applicability of such approach to light frame timber (LFT) and cross laminated timber (CLT) buildings has lacked analytical expressions that depend on the structural typology and failure mechanism. The current paper aims to fill this gap in knowledge by proposing an analytical approach that incorporates the CD philosophy to LFT and CLT buildings at the substructure (wall) and super-structure (building) levels. A simplified approach is adopted for structures with a low-to-medium energy dissipation capacity whereas a more rigorous approach is presented for structure with a high energy dissipation capacity. An experimental comparison and design example is included to present the applicability of the proposal. [ABSTRACT FROM AUTHOR]