Seismic Safety Of Structures Research Articles

Effects of Spatial Variation in Relative Density on Seismic Behavior of Saturated Sandy Ground

Proper consideration of variations in soil properties and their effects is necessary to enhance the seismic safety of structures. In this study, the effect of spatial variations in the cyclic resistance ratio on seismic ground behavior was investigated. Initially, dynamic centrifuge model tests were conducted on sandy ground featuring a 20% mixture of weak zones with low relative density and on homogeneous sandy ground with no mixture of weak zones. Subsequently, an effective stress analysis was performed by modeling the distribution of weak zones in the centrifuge model tests. Finally, after confirming the validity of the parameter settings, several analytical models with different weak-zone distributions were generated and numerically analyzed using random field theory. The results indicate that a local mixing of approximately 20% weak zones has only a limited effect on overall ground behavior. However, differences were observed in the rate of increase and dissipation of the excess pore water pressure ratio and in the residual horizontal displacement.

Influence of near‐field ground motions with fling‐step and forward‐directivity characteristics on seismic response of stilted buildings in mountainous area

SummaryNear‐field ground motions with fling‐step and forward‐directivity characteristics contain large‐amplitude pulses in velocity history, causing severe damage to stilted buildings in mountainous areas. In this study, three groups of 20 near‐field ground motions with fling‐step and forward‐directivity characteristics and 10 far‐field ground motions were selected as seismic inputs. Nonlinear response history analysis (NLRHA) was performed on plane finite element models of two seven‐story stilted frame structures, one with steel braces in the stilted story and the other without steel braces in the slope direction. Structural seismic response obtained from NLRHA was discussed in terms of inter‐story drift ratio (IDR) and peak floor acceleration (PFA). In addition, damage to two structures was assessed using the modified Park–Huang damage model. The results show that stilted structures exhibit greater inter‐story ratios and damage index values under near‐field ground motions with fling‐step characteristics and forward‐directivity characteristics than far‐field ground motions, where the stilted story has the highest amplification ratio in both IDR and damage index among floors. Designers should pay sufficient attention to the influence of ground motions with fling‐step and forward‐directivity characteristics on seismic demands and damage to stilted structures. The peak inter‐story ratio and damage index of stilted structures with steel braces were significantly lower than that of stilted structures without braces, proving the validation of setting steel braces on reducing the seismic demands of stilted structures and improving structural seismic safety. Additional NLRHA performed using artificial pulses shows that the seismic response of stilted buildings is related to pulse periods of near‐field ground motions and the greatest seismic demands and damage are obtained when the pulse period is 1.5–1.6 times the fundamental period of the stilted building.

Research on the effectiveness of a new-type bearing for structural seismic and vibration dual control

The burgeoning expansion of subway systems has heightened the significance of subway-induced vibrations and their impact on nearby structures. Addressing the dual challenges of mitigating subway-induced vibrations and ensuring structural seismic safety is garnering increasing attention. This study introduces a new-type seismic and vibration dual control isolation bearing that leverages the deformability of rubber. This bearing consists of a thick rubber bearing and a traditional horizontal rubber bearing, which are decoupled in motion and responsible for vertical vibration isolation and horizontal seismic isolation, respectively. A scaled model was constructed of an actual structure to assess the effectiveness of this bearing, conducting shaking table tests with inputs simulating typical subway-induced vibrations and seismic motions. Our findings reveal that the bearing successfully meets predefined isolation and vibration control objectives. Regarding subway-induced vibration loads, it markedly diminishes peak vertical acceleration responses. Frequency-wise, it effectively attenuates high-frequency responses while amplifying low-frequency ones. Notably, increasing damping does not significantly improve vertical vibration isolation. Regarding seismic loads, by aptly configuring the horizontal seismic isolation parameters, the bearing achieves targeted seismic isolation objectives. Furthermore, this new bearing demonstrates certain vertical isolation capabilities, distinguishing it from traditional horizontal rubber isolation bearings.

Efficient seismic fragility assessment method for a frictional isolated bridge constrained by shape memory alloy cables under pulse-like ground motion

Utilizing shape memory alloy (SMA) cables to constrain frictional isolated bridges is considered an efficient approach to limit bearing displacement and prevent serious earthquake damage. Accurate seismic fragility assessments of this kind of structure are crucial for aseismic decision making. However, traditional assessment methods cannot quantitatively describe the impact of the pulse effect on pulse-type seismic motions, which may lead to inaccurate assessment results. Therefore, this study deduced a novel equation for seismic fragility assessment that considers the pulse effect. Firstly, the impact of the pulse effect is quantified. Then, a multivariable probabilistic seismic demand model (MV-PSDM) is developed that is conditioned on the pulse period, peak ground velocity, structural period, maximum friction coefficient and SMA consumption. Based on the MV-PSDM, an effective approach for predicting structural seismic vulnerability is recommended, which does not require finite element modeling or nonlinear time-history analysis. Finally, a novel equation for calculating the intensity measure corresponding to 50% damage probability is deduced. The results indicate that increased friction coefficients and SMA consumption can enhance structural seismic safety under pulse-type ground motions. However, when the ratio of pulse period to structural period is too small, increased friction coefficients or SMA consumption have no meaningful effect on the seismic fragility of the structure.

A Review of Nanotechnology for Seismic Safety in Structures

Many earthquakes have occurred worldwide in recent decades, resulting in massive destruction and structure collapse due to poor seismic design. The goal is to design structures so that damage to them is minimized and to construct structures that are safe, sustainable, and durable for future generations. Nanotechnology is one of the most promising technologies of the twenty-first century, and it is gaining traction in the building industry. The main goals of this work are to provide a quick review of the possible benefits of nanotechnology before discussing nanotechnology innovation for structural seismic safety. Several studies and analyses have shown that using nanotechnology could improve traditional construction materials like concrete and steel performance and properties. During the review, it was discovered that nanotechnology has the potential to revolutionize the traditional engineering business and aid in meeting the demand for sustainable development.

Seismic vulnerability assessment of reinforced concrete bridge piers exposed to chloride-induced corrosion

Existing reinforced concrete (RC) bridge piers located near the sea are vulnerable to corrosion phenomena that might negatively affect the load-bearing capacity of the overall bridge, especially under seismic loading. It is of primary importance to assess the seismic vulnerability of existing RC bridge piers under different corrosion scenarios, in order to quantify the reduction of the seismic structural safety induced by these frequent material degradation phenomena. This contribution deals with an experimental-numerical procedure for the seismic vulnerability assessment of corroded bridge piers. The procedure is illustrated in the context of the Zappulla multi-span viaduct (Sicily, Italy), whose RC piers are experiencing chloride-induced corrosion. A comprehensive quality control is conducted, including carbonation tests, corrosion potential mapping and extraction of corroded steel bars for tensile tests, in conjunction with SonReb tests and concrete coring. The test results are critically interpreted to calibrate a numerical fiber-hinge model of the bridge pier, through which numerical seismic analysis is performed under two different corrosion scenarios. It has been found that the seismic safety margin of pier structures is reduced of up to 20-40% by taking into account a mass loss in percentage of the steel bars equal to 20-30%, as suggested by experimental findings.

On the influence of seasonal changes in the resonant properties of surface soils on seismic safety of structures

Field experiments were carried out to assess the possible changes of the seismic safety of buildings due to seasonal variations in the resonant properties of the near-surface soils. The natural frequencies of a ten-storey building and the surface soil layer were determined from passive seismic measurements. The observations were carried out at the end of January when the top soil layer was frozen because of prolonged exposure to negative temperatures, and at the end of June after the ground was completely thawed. The results of the experiments showed that in areas characterized by alternation of long periods of positive and negative temperatures, the natural frequencies of surface soils can change significantly more than the natural frequencies of the buildings built on them. In certain periods, such changes can lead to the coincidence of some natural frequencies of the soil layer and the buildings standing on it, which ultimately reduces the latter seismic safety.

A Novel Whale Optimization Algorithm for the Design of Tuned Mass Dampers under Earthquake Excitations

This paper introduces a novel methodology for the optimum design of linear tuned mass dampers (TMDs) to improve the seismic safety of structures through a novel Whale Optimization Algorithm (WOA). The algorithm is aimed to reduce the maximum horizontal peak displacement of the structure, and the root mean square (RMS) response of displacements as well. Furthermore, four additional objective functions, derived from multiple weighted linear combinations of the two previously mentioned parameters, are also studied in order to obtain the most efficient TMD design configuration. The differential evolution method (DEM), whose effectiveness has been previously demonstrated for TMD applications, and an exhaustive search (ES) process, with precision to two decimal positions, are used to compare and validate the results computed through WOA. Then, the proposed methodology is applied to a 32-story case-study derived from an actual building, and multiple ground acceleration time histories are considered to assess its seismic performance in the linear-elastic range. The numerical results show that the proposed methodology based on WOA is effective in finding the optimal TMD design configuration under earthquake loads. Finally, practical design recommendations are provided for TMDs, and the robustness of the optimization is demonstrated.

Fatality rates implied by the Italian building code

AbstractThe project Rischio Implicito – Norme Tecniche per le Costruzioni (RINTC) assessed the seismic structural reliability, in terms of the annual rate of earthquakes causing failure, of a large set of code‐conforming buildings, designed to be located in three different sites, representative of low, mid, and high seismic hazard in Italy. It was found that seismic reliability tends to decrease significantly as the site's hazard increases, despite the design actions having the same return period at all sites. Because this is a consequence of the code's approach, the simple study presented in this paper aims to contribute to the discussion on whether the code‐implied safety is yet acceptable. To this end, the annual fatality rates due to the seismic failure of the buildings from the mentioned project are computed, in a simplified manner, and compared with the annual risk from other common causes of death in Italy; the latter obtained based on data from the Italian Statistical Institute. The results, although subjected to the conventionality of the working assumptions, seem to indicate that seismic fatality risk is generally lower than that of other causes of death, by one or more orders of magnitude at the lower hazard sites. This can contribute to the discussion on seismic structural safety due to the characteristics of the Italian code that are common to state‐of‐the‐art codes internationally.

Seismic fragility assessment of ductile reinforced concrete building frames

Purpose Increasing awareness of the society and complying with design requirements of building codes for seismic safety of structures and inhabitants during severe earthquakes are the primary purpose of seismic analysis. This study aims to present the variability in seismic fragility functions for frames of different heights for the most vulnerable condition of structure using nonlinear time history analysis. Design/methodology/approach A total of 4, 8 and 20 stories reinforced concrete (RC) moment-resisting two-dimensional frames are considered for this study. Ground motions (GM) are selected as per the conditional mean spectrum and these are conditioned on a target spectral acceleration at the concern time period. RC frames are designed and detailed as per Indian standards. A concentrated plasticity approach is adopted for non-linear analytical modeling of the RC frames. Deterministic capacity limit states in terms of maximum inter-story drift ratio are considered for different damage states. Fragility functions have been derived following a lognormal distribution from incremental dynamic analysis curves. Finally, the maximum likelihood estimation of the response is obtained for fitting curves with observed fragility. Findings The fragility functions of the three structures reflect that under critical or extreme conditions of GM the taller buildings have higher fragility than the shorter buildings for each level of limit states even though both are designed to meet their code-level design forces. Research limitations/implications The study is conducted on the extreme scenario of GM conditioned on the fundamental time period of each building, whereas comparison can be developed by selecting various methodologies of GM set. The probabilistic capacity model can be developed for future studies to check the fragility variation with deterministic and probabilistic capacity. Originality/value The investigation endeavors to present a comprehensive fragility assessment framework by analytical method. The outcome will be useful in the development of a disaster management strategy for new or old buildings and the response of seismic force with a variation of the building’s height. The findings will also be useful for updating the earthquake-resistant building codes for the new building construction in a similar context.

Seismic fragility functions for Portuguese RC precast buildings

Fragility functions are fundamental for the assessment of seismic safety of structures or the loss assessment of a portfolio of assets. The present paper describes a procedure to derive fragility functions representative of Portuguese reinforced concrete precast buildings. This goal was achieved following an analytical methodology considering the result of hundreds of nonlinear static analyses, whose building models reflect both mechanical and geometrical characteristics of the Portuguese industrial building stock. Considering the specificities of this typology, and in particular the connections between the structural members, a recently developed macro-element was employed, which enables the explicit simulation of friction and dowel mechanisms. The fragility analyses considered both structural and non-structural limit states, and the findings indicate a poor seismic performance, even under low seismic demand.

Identification of joint structural state and earthquake input based on a generalized Kalman filter with unknown input

Accurate and real-time information of structural states and earthquake input is the prerequisite for structural seismic safety assessment and vibration control. When the earthquake input to a structure is not measured, it has been tried to identify structural state and the unknown earthquake input using the measured structural responses as an inverse problem. However, only structural absolute acceleration responses instead of the relative ones can be measured in this case, which limits the real-time performance of the existing Kalman filter with unknown input (KF-UI). In this paper, a generalized Kalman filter with unknown input (GKF-UI) is proposed to identify structural states and unknown earthquake inputs in real-time. Structural motion equations are established in the relative coordinate system and the observation equations are structural absolute acceleration-only measurements. The analytical derivation of the proposed GKF-UI is a direct extension of the classical Kalman filter (KF). It is also proven that the identification by the proposed GKF-UI using the absolute acceleration-only measurements under unknown earthquake excitation does not lead to the so-called drifted results in the previous identifications under unknown external excitations. Moreover, structural modeling errors can be considered in the identification by the proposed method. Then, it is extended to investigate the identification of the structural state of high-rise shear buildings and unknown earthquake inputs by combining the proposed GKF-UI with the modal expansion. Hybrid dynamic motion equations in modal space and observation equations in physical space are established to both reduce the state dimension and keep the one-dimension of unknown earthquake input instead of the increased number of unknown modal inputs. In addition, absolute accelerations are used in the observation equations, which avoids the dilemma that absolute accelerations cannot be converted into relative modal accelerations in the relative coordinate system under unknown earthquake input. Some numerical examples are used to verify the proposed method. Moreover, a shaking table test is adopted to further validate the performances of the proposed method.

Generalized algorithms for the identification of seismic ground excitations to building structures based on generalized Kalman filtering under unknown input

The exact information of seismic excitation and structural state is a prerequisite for structural seismic safety assessment and vibration control. When the seismic excitation to a structure is not measured, the seismic excitation can be identified as an inversed problem from measured structural responses. Although some relevant approaches have been developed, there are certain limitations or drawbacks in the existing approaches. To circumvent these problems, two generalized algorithms are proposed for the identification of seismic ground excitation to multi-story and tall buildings, respectively. When the seismic ground excitation to a structure is not measured, the data measured by a structural health monitoring system are structural absolute responses. So the structural motion equation in the absolute coordinate system is derived, in which the unknown seismic ground excitation is treated as unknown external force acting on the structure. First, the identification of unknown seismic excitations to multi-story building structures is studied. A generalized Kalman filtering under unknown input is proposed for the identification of structural state and unknown seismic excitation without the observation of structural absolute acceleration responses at the location of unknown external force. The derivation of the proposed generalized Kalman filtering under unknown input is based on the classical Kalman filter, but is more general than the existing identification approaches based on Kalman filter with unknown input in the deployments of accelerometers in the building structure. Then, it is extended to explore the identification of unknown seismic excitations to tall building structures. To avoid substructural identification from the top to bottom in a sequential manner, the motion equation in absolute coordinate system is reduced by modal expansion. Moreover, instead of the identification of unknown modal forces in previous approaches, the seismic excitation is directly identified without increasing the number of unknown forces. To demonstrate the proposed algorithms, numerical examples of identifying seismic excitations to a 6-story shear building and an 18-story tall building are investigated.

Fragility analysis of high CFRDs subjected to mainshock-aftershock sequences based on plastic failure

Numerous earthquake disasters have demonstrated that secondary damage to structures induced by aftershocks may seriously threaten the seismic safety of structures since the mainshock may have already weakened structural integrity. This paper investigates the fragility of a 200-m high concrete face rockfill dam (CFRD) subjected to mainshock-aftershock sequences based on multiple stripes analysis (MSA). A modified generalized plasticity model and a plastic-damage model are used to describe the nonlinearity of the rockfills and the concrete face slabs, respectively. A series of nonlinear dynamic time history analyses for the CFRD under mainshock-aftershock sequences with different intensity combinations are conducted. The analysis focuses on the deformations, the shear strains and the damage index (DI) of the face slabs. According to the analysis results, the vertical deformation is the best indicator of the cumulative damage inflicted by aftershocks on the high CFRD. Then, considering the importance of face slab damage to the integrity and performance of the CFRD, the influences of aftershocks on the probability of the CFRD reaching a specific limit state are discussed based on vertical deformation and DI. The results reveal that aftershocks can significantly increase the fragility of the CFRD when it has been damaged by mainshocks.

THE USE OF DAMPER SYSTEMS IN BUILDINGS WITH REINFORCED CONCRETE STRUCTURES

This study aims to emphasize, by means of a comparative study, the efficiency of some damper systems as modern variants of consolidation / seismic structural safety enhancement used for buildings with reinforced concrete structure designed and erected according to the P13-type standards (from 1963) and considering this as an alternative possibility instead of retrofitting with reinforced concrete jackets (with significant implications for most of the structural elements at all levels of buildings). Damper devices are elements that can be easily replaced later in case of damage. Case studies were made, based on structural calculations in the linear elastic field, using the ETABS program.

The Use of Tuned Mass Dampers for Reducing Structural Vulnerabilities During the Side Movements of Buildings with Reinforced Concrete Frames

Abstract The present article aims to point out, with the help of a comparative research, the efficiency of tuned mass dampers, modern variants of consolidation ensuring seismic structural safety, used for buildings with a reinforced concrete structure, designed and produced according to the new codes. Case studies were based on structural computations in the linear elastic field using the ETABS program.

О ВЛИЯНИИ СЕЗОННЫХ ИЗМЕНЕНИЙ РЕЗОНАНСНЫХ СВОЙСТВ ВЕРХНЕЙ ЧАСТИ РАЗРЕЗА НА СЕЙСМОБЕЗОПАСНОСТЬ СООРУЖЕНИЙ

The results of experiments to assess the possible influence on seismic safety of structures of seasonal changes in the natural frequencies of the underlying soils are given. It is shown that the resonance properties of the surface soil layer during the year can vary more significantly than the properties of the structures built on them. This can lead to the coincidence of natural frequencies of the soil layer and the structures standing on it, which ultimately reduces their seismic safety.

Patented inventions of Serbian scientists in the field of seismic reliability of structures and landslide remediation with application

Having in mind that on the territory of the Republic of Serbia patent protection of domestic inventions has been at the level of 20% of the total number of patents granted by the European Patent Office to inventors from Europe in the past twenty years in the area of seismic reliability of structures and landslide remediation, this work complements research on the continuity in the application of exceptional technical solutions of Serbian scientists in the field of civil engineering, that has been started with the work with title: Common characteristics of main contributions of Roger Boscovich, Milutin Milanković and Branko Žeželj to the development of civil engineering, 2017. Bearing in mind that Žeželj has been active in patent protection of his numerous inventions, during second half of the 20th century, this paper presents systematic overview of patented inventions created in 21st century by Serbian scientists and inventors in the field of seismic safety of structures and landslide remediation, as well as examples of their specific application.

A novel bat algorithm based optimum tuning of mass dampers for improving the seismic safety of structures

Metaheuristic algorithms are effective for optimization with diverse applications in engineering. The optimum tuning of tuned mass dampers is very important for seismic structures excited by random vibrations, and optimization techniques have been used to obtain the best performance for optimally tuned mass dampers. In this study, a novel optimization approach employing the bat algorithm with several modifications for the tuned mass damper optimization problem is presented. In the proposed method, the design variables such as the mass, period and damping ratio of tuned mass damper are optimized and different earthquake records are considered during the optimization process. The method is then applied to a ten-story civil structure and the results are then compared with the analytical methods and other methods such as genetic algorithms, particle swarm optimization, and harmony search. The comparison shows that the proposed method is more effective than other compared methods. Additionally, the robustness of the optimum results was evaluated. The proposed approach for optimizating tuned mass dampers via the bat algorithm is a feasible and efficient approach.

Why School Resilience Should Be Critical for the Post-Earthquake Recovery of Communities in Divided Societies

From pre-disaster to recovery, education is a fundamental key in reducing the impacts of disasters on children, people, and communities. This article aims to highlight the key components that are necessary for building school resilience to earthquakes and to demonstrate that promotion of the seismic resilience of schools is not only critical for children’s safety and the continuity of their education but also for the effective post-earthquake recovery of communities. It is shown that promoting social cohesion through the improvement of the seismic structural safety of school buildings and the capabilities of school administrators with regard to shifting to an online teaching and learning mode during school dysfunctions or closures are key to the post-earthquake recovery of vulnerable communities in divided societies. This article can be of practical significance to educational administrators interested in school protection and in the continuity of educational services in the aftermath of disasters.