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41.
An important aspect of earthquake loads exerted on extended structures, or structures founded on several foundations, is the spatial variability of the seismic motion. Hence, a rigorous earthquake resistant design of lifeline structures should account for the spatial character of the seismic input, at least in an approximate way. A procedure is proposed which enables addressing the problem of multiply supported structures, subjected to imperfectly correlated seismic excitations, by means of an extension to the response spectrum method. A modified response spectrum model is developed for the design of extended facilities subjected to single and multicomponent ground motion. The modification procedure is based on adjusting each spectral value of the given design response spectrum by means of a correction factor, which depends on the structural properties and on the characteristics of the wave propagation phenomenon. Finally, the theoretical model is validated through digital simulation of seismic ground motion, whereby model predictions are found to be in good agreement with exact results. 相似文献
42.
Ali?Ben Dhiab Mehdi?Ben Mimoun Jose?OterosEmail author Herminia?Garcia-Mozo Eugenio?Domínguez-Vilches Carmen?Galán Mounir?Abichou Monji?Msallem 《Theoretical and Applied Climatology》2017,128(3-4):541-549
Tunisia is the world’s second largest olive oil-producing region after the European Union. This paper reports on the use of models to forecast local olive crops, using data for Tunisia’s five main olive-producing areas: Mornag, Jemmel, Menzel Mhiri, Chaal, and Zarzis. Airborne pollen counts were monitored over the period 1993–2011 using a Cour trap. Forecasting models were constructed using agricultural data (harvest size in tonnes of fruit/year) and data for several weather-related and phenoclimatic variables (rainfall, humidity, temperature, Growing Degree Days, and Chilling). Analysis of these data revealed that the amount of airborne pollen emitted over the pollen season as a whole (i.e., the Pollen Index) was the variable most influencing harvest size. Findings for all local models also indicated that the amount, timing, and distribution of rainfall (except during blooming) had a positive impact on final olive harvests. Air temperature also influenced final crop yield in three study provinces (Menzel Mhiri, Chaal, and Zarzis), but with varying consequences: in the model constructed for Chaal, cumulative maximum temperature from budbreak to start of flowering contributed positively to yield; in the Menzel Mhiri model, cumulative average temperatures during fruit development had a positive impact on output; in Zarzis, by contrast, cumulative maximum temperature during the period prior to flowering negatively influenced final crop yield. Data for agricultural and phenoclimatic variables can be used to construct valid models to predict annual variability in local olive-crop yields; here, models displayed an accuracy of 98, 93, 92, 91, and 88 % for Zarzis, Mornag, Jemmel, Chaal, and Menzel Mhiri, respectively. 相似文献
43.
Vulnerability assessment of reinforced concrete bridge structures in Algiers using scenario earthquakes 总被引：1，自引：1，他引：0
Abderrahmane Kibboua Hakim Bechtoula Youcef Mehani Mounir Naili 《Bulletin of Earthquake Engineering》2014,12(2):807-827
Algeria has an inheritance of more than 11,000 bridges, with approximately 5,000 road bridges of which more than 30 % have a high probability to be exposed to major earthquakes and serious damages in the future. Therefore, it is of great importance to retrofit the existing bridges and assess their seismic vulnerability and set a permanent monitoring survey to follow the change of their dynamic characteristics such as natural frequency and modal damping. The assessment of the seismic vulnerability of existing RC bridges was carried out based on the consistent and complete post earthquake survey after the Boumerdes earthquake. The information on the damaged existing RC bridges was investigated and evaluated by the authors. This paper presents a simple and efficient inspection method for the preliminary evaluation of the seismic vulnerability of existing bridge structures. To assess the seismic damage of 148 existing bridges, two seismic scenarios were carried out using “Khair al Din” and the “Zemmouri” faults that are capable to generate earthquakes with a maximum acceleration of 0.8g. The main findings of this study are summarized in this paper. 相似文献
44.
The spatial and temporal characteristics exhibited by earthquake ground motions at points below the soil surface have important implications for both deeply embedded structures and for spatially extended constructed facilities. In most cases, the characteristics of the seismic motion are known only at the surface, since it is there where most (but not all) of the historical earthquake records have been obtained. While downhole arrays can provide valuable additional information on motion statistics below the surface, it is both possible and desirable to supplement the available database with predictive computational models. With this goal in mind, this paper presents an analytical model to estimate the statistical properties of seismic motions at any point in the ground on the basis of the statistical properties obtained from records on the surface. The emphasis is on the particular cases of stationary SH-waves propagating in a multi-layered soil, and of stationary P-waves propagating in a half-space. The stochastic deconvolution model considered here is based on a formulation with matrices of spectral density functions. Together with the existing formulation based on cross-correlation matrices proposed earlier by Kausel and Pais (J. Engng Mech. Div., ASCE 113 (2) (1998) 266–277), this stochastic deconvolution technique will be referred to as the Complete Stochastic Deamplification Approach (CSDA). The results obtained show that the reduction in the intensity of shaking with embedment is more pronounced when SH-waves propagate in a stratified soil than when they propagate in a homogeneous half-space. Also, it is found that incident P-waves exhibit greater coherency than incident SH-waves, an indication that it is important to distinguish between such wave types when developing coherence models from array data. 相似文献