A performance based approach for site response analysis requires a probabilistic approach accounting for the observed variability in soil stratification and engineering properties of the soil layers. ...The major variability in site-specific response analysis arises from the uncertainties induced by the (a) local seismic hazard assessment, (b) selection and scaling of the hazard compatible input earthquake time histories, (c) soil stratification and engineering properties of encountered soil and rock layers, and (d) method of site response analysis. Even though the uncertainties related to first item, local seismic hazard assessment, has primary importance on the outcome of the site-specific response analyses, the discussion in this article focuses on the possible uncertainties in selection and scaling of the hazard compatible input earthquake time histories, soil stratification, thickness, type and their engineering properties, depth of ground water table and bedrock and properties of the engineering bedrock. One alternative may be to conduct site response analyses for large number of soil profiles generated by Monte Carlo simulations using relatively large number of hazard compatible acceleration time histories to assess probabilistic performance based design acceleration spectra and acceleration time histories calculated on the ground surface with respect to different performance levels. A remaining issue may be considered as the variability induced by 1D, 2D, and 3D site response analysis.
•Definition of performance based site response analysis.•Comparison of 1D, 2D, and 3D site response analysis.
•Effect of excitation spectrum shape on the mechanical damage of pears was obvious.•Vibration resulted in the change of physiological and mechanical properties of pears.•Pear damage is related to the ...stacked position.•Links between pear damage and vibration level were developed.
Mechanical damage of the horticultural produce during postharvest transportation is an important criteria for fruit sorting and grading. The vibration during transportation has a significant effect on the mechanical damage of the fruit. In this study, the effect of different vibration spectrum shapes on mechanical damage of Huangguan pear (Pyrus bretschneideri Rehd, cv. Huangguan) was investigated. Four acceleration spectrums (spectrum Ⅰ, spectrum Ⅱ, spectrum Ⅲ, and spectrum Ⅳ) with same vibration level and different shapes were evaluated. The power spectral density (PSD) amplitude in the resonant region was in the order of spectrum Ⅰ > spectrum Ⅱ> spectrum Ⅲ > spectrum Ⅳ. The change in appearance, physiological properties (respiratory rate and weight loss), and mechanical properties (firmness and elastic modulus) of the pears were evaluated after vibration. Results showed that vibration resulted in quality deterioration of pear. Compared to the control group, respiratory rate and weight loss of the pears increased while the flesh firmness and elastic modulus of the pears decreased after vibration. The mechanical damage became more serious as stacked position increased. The effect of spectrum shape on the mechanical damage of pear was also obvious. Different degree of mechanical damage was observed under spectrum Ⅰ, spectrum Ⅱ, spectrum Ⅲ, and spectrum Ⅳ vibration. The higher the acceleration PSD in resonant region, the more serious the mechanical damage of pear. In comparison with the control group, pear under spectrum Ⅰ effect showed the most mechanical damage and the pear under spectrum Ⅳ effect had the minimum mechanical damage. Furthermore, S−Grms curves (damage area - vibration level) showed a clockwise rotation from spectrum Ⅰ to Ⅲ vibration. This study reveals the mechanical damage mechanism of pears based on acceleration spectrum shape and provides guidance for postharvest loss reduction using simulated test.
A novel assessment method for rapid structural safety state assessment is developed based on state-of-the-art machine learning technology. In this paper, a deep neural network (DNN), which originated ...in computer science, is first introduced, including its concept, structure and related training algorithms. Then the evaluation procedure to determine the structural safety state based on the DNN is developed. In the procedure, the pseudo-acceleration spectra and the structural safety states are selected as the input and output of the DNN model, respectively. Finally, the procedure of the novel assessment method is illustrated using a five-story reinforced concrete (RC) frame as an example. The effectiveness and accuracy are validated, and the influence of the number of hidden layers and size of the training data on the performance of the DDN is also investigated. The results demonstrate that the proposed method can evaluate the structural safety state rapidly based on the DNN. The most appropriate number of hidden layers is two considering both training accuracy and test accuracy. The training accuracy and test accuracy were 93.45% and 93.14%, respectively, using the two-hidden-layer DNN model trained on a training dataset of size 66,612.
AbstractThe seismic safety of acceleration-sensitive secondary elements rigidly connected to the primary structure can be ensured in the case of ordinary structures by simply and accurately ...estimating the largest peaks in the floor accelerations consistent with a given seismic hazard. A new modal combination rule is developed in this study to estimate the peak floor accelerations in the case of lumped mass, classically damped, multistoried structures. The formulation is based on stationary random vibration theory and the use of nonstationary peak factors together with the amplitudes of the specified design spectra. The proposed formulation is supported by the development of (1) an expression for estimating the peak factor for floor acceleration from the peak factors for modal displacement responses and peak modal contributions to the peak floor response, wherein both floor acceleration and modal peak factors are normalized by the (nonstationary) peak factor for input ground acceleration, and (2) a two-parameter power function for estimating the normalized modal peak factors for relative velocity from the oscillator period, together with the scaling equations for the two parameters in terms of ground-motion characteristics. A numerical study using five example buildings and six example ground motions shows that the proposed modal combination rule works well, with the absolute error averaged over all floors of the structure being less than 10% for 90% of the cases. Also, the proposed rule works better compared to when various peak factors are taken to be identical.
The implementation of fluid viscous dampers has been proven as a feasible method to improve the seismic performance of buildings. However, the different variables involved in the damper's design ...affect the structural response, especially in terms of seismic demand on non-structural elements. This paper presents a parametric study on the floor acceleration response of three case study buildings equipped with fluid viscous dampers through nonlinear time-history analysis. The results show that the different design parameters of fluid viscous dampers significantly modify the floor acceleration response, with some damper configurations yielding floor accelerations larger than those of the buildings without dampers.
The engineering purpose of designing resistant structures in seismic areas goes through the modeling of the earthquake ground motion. To design complex earthquake-resistant structures, above all if ...the structural non-linearities must be considered, dynamic analysis of the response of the structure is highly recommended instead of the response spectrum analysis. Therefore, the need to generate artificial accelerograms for structural design arises. This paper proposes a stochastic procedure that, based on the seismological point-source model, allows to generate artificial accelerograms. Therefore, the artificial accelerogram generated incorporates the "source," "path" and "site" characteristics. For each term of the seismological model, a corresponding best approximating filter transfer function has been given. Therefore, a new quadruple-filter system has been derived. The proposed approach is used to generate various earthquake records that occurred in Italy. The outcomes of the numerical examples demonstrate the suitability of the proposed study.
In the seismic design and assessment of acceleration-sensitive equipment installed in buildings, floor acceleration spectra, which are based on an uncoupled analysis of the structure and the ...equipment, are usually used. However, in order to obtain an “accurate” determination of floor spectra, a complex and quite demanding dynamic response-history analysis is needed. Recently a method for the direct generation of floor acceleration spectra from ground motion spectra, taking into account the dynamic properties of the structure, has been developed and validated. It is based on the theory of structural dynamics, in combination with empirically determined values for the amplification factors in the resonance region. The method can be used for both elastic and inelastic multi-degree-of-freedom structures and equipment modelled as an elastic or inelastic single-degree-of-freedom oscillator. In the case of inelastic primary structures, the method is coupled with the pushover-based N2 method. The variant of the method which is presented in this note is intended for practical applications, e.g. for implementation in guidelines and codes, and it represents a simplified version of the original method. In addition to some simplifications, the option of taking into account the inelastic response of the equipment was added. In the note, the method is summarized, and all the formulae needed for the calculation of floor acceleration spectra are provided. A description of all steps of the analysis, together with all the relevant numerical data, is presented in a test example.
Spectra of the two official GLEs of solar cycle 24 Perez-Peraza, Jorge A.; Márquez-Adame, Juan C.; Caballero-Lopez, Rogelio A. ...
Advances in space research,
01/2020, Volume:
65, Issue:
1
Journal Article
Peer reviewed
Open access
Based on ground-level data and on satellite data we determine in this work the observational spectrum of both, the Ground Level Enhancement of May 17, (2012) the so-called GLE71 and the Ground Level ...Enhancement of September 10, 2017 (GLE 72). We describe a simplified method to obtain the experimental spectrum at ground level. Data of the GLE71 and GLE72 indicate the presence of two different populations, each one with a different energy spectrum. On the other hand, we explore the kind of phenomena that take place at the source in these two particular events. In contrast with other methods based on the temporal synchronization between electromagnetic emissions of flares and coronal mass ejections (CME), here we develop an alternative option based on the study of the accelerated particles, by adjusting our theoretical spectra to the observational spectra. The main results of this work are the derivation of the source and acceleration parameters involved in the generation process. These results lead us to construct possible scenarios of particle generation in the source for each one of the two studied GLEs.
Base isolation is an effective way to protect structures from earthquake-induced damage. However, near-fault (NF) earthquakes may seriously damage base isolation structures. Viscous dampers can ...control the isolation displacement and enhance the energy dissipation of base isolators. Therefore, a series of shaking table tests were conducted to investigate the influence of nonlinear viscous dampers (VDs) on the seismic performance of base-isolated structures under NF ground motion. A 1/4 scaled frame model structure with four base isolation systems was designed for the shaking table tests. Laminated natural rubber bearings (LNRB) or lead rubber bearings (LRB) were selected as two base isolation systems. Additional nonlinear viscous dampers (NLVDs) were installed at the base-isolation level of the LNRB- and LRB-isolated structures to add two additional base-isolated systems. Three ground motions, including one far-fault (FF) and two NF, provide seismic inputs to the base-isolated structures. The effects of supplemental NLVDs on the dynamic properties and seismic performance of the superstructures were investigated. The floor acceleration spectrum and energy dissipation of the isolation level were considered to evaluate the ground motion characteristics on the seismic performance of the base-isolated structures. The test results show that the pulse-like NF ground motion caused the greatest deformation and shear force in the isolation bearings while inducing the largest drift and floor acceleration. The NLVDs were effective when the base-isolated structure experienced pulse-like NF ground motion. The supplemental NLVDs amplified the inter-story drift and floor acceleration response of the superstructure under FF ground motion, especially for the LRB-isolated structure.
This study aimed at proposing a new ground motion scaling method for precise spectral matching between the response accelerations and the standard design spectrum regarding the normalization ...procedure. In this method, the dispersion in acceleration and displacement responses were decreased significantly. Moreover, 11 parameters were used for normalizing response accelerations, including peak ground acceleration, peak ground velocity, peak ground displacement, Arias intensity, Housner intensity, cumulative absolute velocity, maximum incremental velocity, energy index, acceleration spectrum intensity, velocity spectrum intensity, and specific energy density. Three sets of non-pulse-like, near-field pulse-like and non-pulse-like long-duration ground motions were taken into account to investigate the effect of earthquake characteristics on normalizing parameters. Hence, by performing sensitivity analysis, suitable parameters were determined for normalizing response accelerations. Statistical results illustrated that normalizing response accelerations to acceleration spectrum intensity, Housner intensity, and peak ground displacement led to minimum dispersion at acceleration-sensitive, velocity-sensitive, and displacement-sensitive regions, respectively. Moreover, the results showed that suitable normalizing parameters could be determined considering the period of vibration. It was concluded that normalizing response accelerations and scaling of them could lead to appropriate spectral matching and low dispersion. Finally, drift dispersion for four, eight, and twelve-story steel special concentrically braced frame structures under nonlinear fiber-element time-history analysis was evaluated carefully. The results indicated that the inter-story drift dispersion decreased acceptably in all structures.
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