The optimal design of elastic perfectly plastic steel frames with or without suitable protection devices and subjected to static as well as seismic loadings is studied. Two minimum volume problem ...formulations are proposed, on the grounds of the so-called statical approach, accounting for three different resistance limits: the purely elastic limit, the (elastic) shakedown limit and the instantaneous collapse limit. The adopted load combinations are characterized by the presence of fixed loads, of quasi-static perfect cyclic loads and dynamic (seismic) loads. The linear elastic effects of the dynamic actions are studied by utilizing a modal technique. The proposed treatment is referred to the most recent Italian code related to the structural analysis and design. The solution of the optimization problem is reached by using an appropriate linearization iterative technique specialized to the proposed formulations. Flexural frames and cross-braced frames are studied, and the related minimum volume structures are reached for assigned features of the base isolation device. The Bree diagrams of the obtained optimal designs are also determined in order to characterize their structural behaviour.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Based on the horizontal slice method (HSM) and assuming a log spiral slip surface, a method to analyze the stability of a reinforced retaining wall under seismic loads was established in this study ...by calculating the tensile force of the reinforcement. A parametric study was conducted on the normalized tensile force of the reinforcement, and it was observed that the normalized tensile force tends to increase with acceleration of the seismic load and the height of the backfill. Moreover, it also increases with soil unit weight, while it decreases with increased friction angle of the backfill soil, and the influence of soil cohesion on the normalized tensile force is not significant. The HSM method is proved to be suitable for analyzing the tensile force of reinforcement in retaining walls under seismic loads.
Die grundlegenden seismischen Lastannahmen für den neuen Nationalen Anhang DIN EN 1998‐1/NA resultieren aus der vom Deutschen Institut für Bautechnik geförderten Neueinschätzung der ...Erdbebengefährdung Deutschlands. Sie gründet sich auf eine umfassende Einbeziehung aller zu berücksichtigenden Unsicherheiten in Eingangsmodellen und ‐parametern und die Bereitstellung eines rationalen transparenten Rahmens zu deren Umsetzung. Das Vorgehen ermöglicht die solide und robuste Berechnung sowohl von Mittelwerten als auch jeglicher Quantile von geforderten Parametrisierungen seismischer Lastannahmen. Wesentliche Verbesserungen des Gefährdungsmodells beruhen auf aktualisierten und erweiterten Datenbeständen, umfassenden Unsicherheitsbereichen von Modellen, stabilen Methoden und ausgewählten Bodenbewegungsmodellen jüngster Generation. Die berechneten Gefährdungsparameter entsprechen den nutzerbezogenen Anforderungen und wurden für Felsuntergrund (vS30 = 800 m/s) und mittlere Wiederholungsperioden von 475, 975 und 2 475 a berechnet und in Form von gefährdungskonsistenten Antwortspektren, seismischen Gefährdungskarten für spektrale Antwortbeschleunigungen und für makroseismische Intensitäten standardmäßig als Mittelwerte, Mediane und 84 %‐Quantile bereitgestellt. Die resultierenden Unsicherheiten der Gefährdungsparameter werden analysiert und die Stabilität der Gefährdungskarten bezüglich früherer Versionen sowie ihre Kompatibilität zu Gefährdungseinschätzungen von Nachbarstaaten diskutiert.
Reappraisal of the seismic hazard assessment of Germany – version 2016 – for DIN EN 1998‐1/NA
The basic seismic load parameters for the upcoming national design regulation for DIN EN 1998‐1/NA result from the reassessment of the seismic hazard supported by the German Institution for Civil Engineering (DIBt). This study is based on a comprehensive involvement of accessible uncertainties in models and parameters. It includes the provision of a rational framework for integrating epistemic uncertainties and aleatory variabilities in a comprehensive way and incorporates significant improvements. It is based on updated and extended databases, robust methods to evolve sets of models representing epistemic uncertainties and a selection of latest ground‐motion prediction equations.
The output specifications were designed according to the user oriented needs. Seismic load parameters are calculated for rock conditions, mean return periods of 475, 975 and 2 475 yrs and delivered as uniform hazard spectra, seismic hazard maps for peak ground acceleration, spectral response accelerations and macroseismic intensities. Results are supplied as mean, median and 84th percentile. Resulting uncertainties of calculated seismic load parameters are analyzed. The stability of the hazard maps with respect to previous versions and cross‐border comparisons are emphasized.
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The purpose of this article is to describe the Bouc–Wen model of hysteresis for structural engineering which is used to describe a wide range of nonlinear hysteretic systems, as a consequence of its ...capability to produce a variety of hysteretic patterns. This article focuses on the application of the Bouc–Wen model to predict the hysteretic behaviour of reinforced concrete bridge piers. The purpose is to identify the optimal values of the parameters so that the output of the model matches as well as possible the experimental data. Two repaired, retrofitted and reinforced concrete bridge pier specimens (in a 1:6 scale of a real bridge pier) are tested in a laboratory and used for experiments in this article. An identification of Bouc–Wen model's parameters is performed using the force–displacement experimental data obtained after cyclic loading tests on these two specimens. The original model involves many parameters and complex pinching and degrading functions. This makes the identification solution unmanageable and with numerical problems. Furthermore, from a computational point of view, the identification takes too much time. The novelty of this work is the proposal of a simplification of the model allowed by simpler pinching and degrading functions and the reduction of the number of parameters. The latter innovation is effective in reducing computational efforts and is performed after a deep study of the mechanical effects of each parameter on the pier response. This simplified model is implemented in a MATLAB code and the numerical results are well fit to the experimental results and are reliable in terms of manageability, stability, and computational time.
•Wood has been used to strengthen stone ashlar buildings in the ancient monuments, such as Qasr el-Bint, Petra, Jordan.•Wood was used in a form of flexible string-courses that held the brittle stone ...ashlars together.•Use of wooden beams imbedded in stone ashlars increase the strength of buildings and function as an anti-seismic device.•Study proved the role of the imbedded wooden beams in reducing the shear stress of the structure by up to 50%.•Study shows that monument has survived moderate earthquakes because of these beams that functioned as anti-seismic devices.
Wood has clearly been used to strengthen stone ashlar buildings in the ancient monuments in Petra, Jordan. However, to date, no analysis has been made of how wood works from structural engineering point of view, especially during earthquakes. Wood was used in a form of flexible string-courses that held the brittle stone ashlars together. This study analyses how this technique increases the strength of buildings and to what extent it functions as an anti-seismic device. Conducting such study requires the multidisciplinary collaboration of scholars with knowledge of architecture, architectural history and structural engineering. The result of this analysis proved the role of the imbedded wooden beams as anti-seismic device in reducing the shear stress of the structure by up to 50%. Repairing and preserving these beams are to strengthen the structure against possible earthquakes. The simulation results showed that the monument under study; which is Qasr el-Bint, has survived moderate earthquakes because of these beams that functioned as anti-seismic devices, and can continue to do so if these beams are retrofitted and strengthened.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Offshore triceratops is one of the alternate structural forms that is desirable for the deep-sea oil exploration. It consists of a deck and buoyant leg structures (BLS) that are positively buoyant ...and the platform is position-restrained by tethers. Ball joints, which connect the deck and the BLS units, restrain the transfer of rotations between them. These platforms experience a significant tether tension variation under the vertical seismic excitations that are caused at the seabed. In the present study, response analyses of triceratops to seismic activity in the presence of waves are examined. Records of the El Centro earthquake and the artificially generated earthquake using Kanai-Tajimi (K-T) power spectrum are considered for the study. Earthquake excitations are imposed on the tethers to determine the dynamic tether tension variations caused by the seismic excitations. Triceratops is then analysed numerically for these tether tension variations in the presence of regular waves. Based on the numerical studies conducted, it is seen that the heave and pitch responses of the BLS units and the deck are significantly high under these tether tension variations. It is also seen that the response amplitude operator of the deck in the pitch degree of freedom is lesser than that of the BLS units. This study quantifies the response variations of the triceratops under seismic activities, which is useful for the design and development of new generation offshore platforms for deep waters.
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This commentary covers the significance for practical design of the Architectural Institute of Japan's Recommendations for Loads on Buildings revised in 2015 and includes an overview of the changes ...made from the previous edition, providing an introduction to, among specific types of loads, seismic loads, and the newly added tsunami loads and impact loads. In terms of their significance, these Recommendations are distinguished by the fact that they present “appropriate design load values” from the viewpoint of society, building owners, and designers, as opposed to the “minimum values” to which laws and regulations are limited to. Another distinguishing feature of these Recommendations is that they organize the various types of loads in a unified manner and that they provide load setting methods that do not depend on the design method used and the target building, along with the latest objective data.
The aim of the present work is to evaluate the effectiveness of viscoelastic-damped braces (VEDBs) to improve the wind and earthquake responses of fire-damaged steel framed buildings, where a ...significant reduction of stiffness and strength properties of the structural elements following exposure to fire is highlighted. To this end, a ten-storey steel office building, designed for a low-risk zone under the former Italian seismic code and in line with Eurocodes 1 and 3, is considered as test structure. The dynamic response of the test structure in a no fire situation is compared with what would happen in the event of three fire scenarios, on the assumption that the fire compartment with a uniform temperature is confined to the area of the first (i.e. F1), fifth (i.e. F5) and tenth (i.e. F10) level, with the parametric temperature–time fire curve evaluated in line with Eurocode 1. Two retrofitting structural solutions are examined to upgrade the fire damaged test structures, by inserting diagonal steel braces with or without viscoelastic dampers. Frame members are idealized by a bilinear model, which allows the simulation of the nonlinear behavior under seismic loads, while an elastic linear law is considered for diagonal braces. Finally, viscoelastic dampers are idealized by means of a frequency-dependent model.
•Time–temperature curve of the fire-compartment and fire scenarios.•Damage of steel framed structures due to fire loading.•Design of diagonal steel braces with or without viscoelastic dampers.•Along-wind response of fire-retrofitted steel framed structures.•Seismic response of fire-retrofitted steel framed structures.
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GEOZS, IJS, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
This paper presents a structural analysis of a masonry chimney, which is being catalogued as local interest heritage, according Eurocode 8. The chimney, located in Alicante (Spain), is severely ...damaged, and it shows several longitudinal cracks, and mortar loss between bricks. In order to guarantee the structural safety under seismic forces, the chimney was retrofitted with composite materials. This reinforcement comprised an internal textile reinforced mortar (TRM) layer, i.e. glass fiber mesh and cement matrix, and local reinforcement with longitudinal carbon fiber bands. This study consisted of two stages: first, numerical and experimental analyses of the original chim- ney were done. Second, design of an internal reinforcement scheme was done. The experimental text includes acceleration measures under ambient vibration for an operational modal analysis. And laboratory test for bricks and mortar to study the mineralogical composition and mechanical properties. The numerical analysis includes, preliminary pushover analysis before and after the reinforcement was done, and second, linear response spectrum analysis to evaluate the structural stability under the seismic demand.
There is a lack of knowledge on the wind and seismic responses of steel framed structures in the case of fire and an amplification of the structural response is expected in the case of existing ...structures exposed to fire: i.e. acceleration and deformability thresholds, under wind loads, and damage and buckling thresholds, under seismic loads, can be exceeded at the serviceability and ultimate limit states, respectively. To evaluate the wind and earthquake responses following a fire, a numerical investigation is carried out with reference to the steel framed structure of a 10-storey office building, which was designed for a low-risk zone under the former Italian seismic code and in line with Eurocodes 1 and 3. More specifically, the dynamic response of the test structure in a no fire situation, along the in-plan principal directions, is compared with what would happen in the event of fire, at 500°C, 550°C and 600°C fire temperatures, hypothesising a reduction of stiffness and strength due to fire. Four fire scenarios have been considered on the assumption that the fire compartment is confined to the area of the first level (i.e. F1), the first two (i.e. F1/2) and the upper (i.e. Fi, i=5, 10) levels, with the parametric temperature–time fire curve evaluated in accordance with Eurocode 1. Dynamic analyses are carried out in the time domain using a step-by-step initial stress-like iterative procedure. Along-wind loads are considered assuming, at each level, time histories of the wind velocity based on an equivalent spectrum technique. Real accelerograms, whose response spectra match those adopted by Italian seismic code for a medium-risk seismic zone, are considered to simulate the seismic loads.
•Time–temperature curves of the fire-compartment and fire scenarios.•Reduction of mechanical properties due to fire loading before wind and earthquake.•Along-wind response of fire-damaged steel framed structures.•Seismic response of fire-damaged steel framed structures.
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GEOZS, IJS, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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