Numerical modeling of the seismic performance of monopile supported wind turbines in sandy soils susceptible to liquefaction.

Since 1980, as wind farms have moved from coastal to offshore areas, the wind energy industry has been completely transformed which in turn has led to the increase in the construction of wind turbines. On the other hand, harsher offshore environmental conditions have led to larger lateral loads and anchorages applied to the wind turbines and specifically to their piles than other coastal and offshore structures. Thus, more solid piles are required to ensure proper rigidity and bearing capacity. Liquefaction is one of the most important seismic hazards through which various damages caused to different parts of wind turbines. In order to develop coastal and offshore structures in Iran, a study of liquefaction is of great importance due in part to the high risk of seismicity. In this study, the effect of liquefaction on seismic response of offshore wind turbines is examined taking advantage of a finite element model. To this end, all analyzes have been carried out in both occurrence and non-occurrence of the liquefaction, so that by comparing these two modes, the mechanisms affecting the seismic behavior of wind turbines are understood. As depth increases, the possibility of liquefaction is reduced due to higher pressure. Liquefaction is considered to a depth of 20 m and structural behavior is evaluated based on the level of seismic hazard, the thickness of the susceptible layers, soil compaction, the non-fluidizing top layer, the gradient of the earth, the thickness of the monopole, the dimensions of the wind turbine and different soil layering conditions. According to the mentioned factors, a comprehensive and parametric study of the behavior of wind turbines in seismic zones, and in different loading conditions, pile diameters and soil layering is carried out in soils prone to liquefaction. Since analyzes are performed in both occurrence and non-occurrence of the liquefaction, the number of analyzes and computational cost in this research becomes enormous. Therefore, there is a need for a highly effective software and a practical modeling method that will allow for this comprehensive study. Open Sees software and beam on nonlinear Winkler foundation approach are used to model the soil-pile-structure interaction. The minor differences observed in the laboratory values compared to the numerically calculated ones may refer to the fact that the chamber is not modeled. In the bottom layer, as the depth decreases, the elastic response spectra record larger values which are due to the resonance in the structure.

Free-Field Seismic Response Analysis

This paper shows the results of free-field seismic response analyses (SRA), that were performed for the subsoil conditions of Piazza dei Miracoli in Pisa. The site investigation and in particular the shear wave velocity profile is extended down to 120 m below the ground level. One-dimensional SRA were carried out by using three computer codes, EERA, STRATA and ONDA. The first two codes perform the analyses in the frequency domain considering a linear-equivalent soil model. ONDA analyses the problem in the time domain assuming a true non-linear soil behaviour. In particular, the Ramberg-Osgood constitutive model, coupled with a modified Masing criterion was assumed. The computed elastic response spectra were compared to those prescribed by the Italian Building Code, which represents the Italian implementation of Eurocodes. Some details concerning the response spectra prescribed by Italian Building Code are also given.

Control spectra for Quito

The Metropolitan District of Quito is located on or very close to segments of reverse blind faults, Puengasí, Ilumbisí–La Bota, Carcelen–El Inca, Bellavista–Catequilla and Tangahuilla, making it one of the most seismically dangerous cities in the world. The city is divided into five areas: south, south-central, central, north-central and north. For each of the urban areas, elastic response spectra are presented in this paper, which are determined by utilizing some of the new models of the Pacific Earthquake Engineering Research Center (PEER) NGA-West2 program. These spectra are calculated considering the maximum magnitude that could be generated by the rupture of each fault segment, and taking into account the soil type that exists at different points of the city according to the Norma Ecuatoriana de la Construcción (2015). Subsequently, the recurrence period of earthquakes of high magnitude in each fault segment is determined from the physical parameters of the fault segments (size of the fault plane and slip rate) and the pattern of recurrence of type Gutenberg–Richter earthquakes with double truncation magnitude (Mmin and Mmax) is used.

Control Spectra for Quito

The Metropolitan District of Quito is divided into five areas: south, south-central, central, north-central and north. It is located on or very close to segments of reverse blind faults: Puengasí, Ilumbisí-La Bota, Carcelen-El Inca, Bellavista-Catequilla and Tangahuilla as indicated in Alvarado et al. (2014), making it one of the most seismically dangerous cities in the world. For each of the urban areas of Quito, elastic response spectra are presented in this paper, which are found using some of the new models of the PEER's NGA-West2 Program, models developed by: Abrahamson et al. (2013), Campbell and Borzognia (2013), and Chiou and Youngs (2013). These spectra are calculated considering the maximum amount that could be generated by the rupture of each fault segments, and taking into account the soil type that exists in each zone according to the Norma Ecuatoriana de la Construcción 2015 (NEC-15). Subsequently, the recurrence period of earthquakes of high magnitude in each fault segment is determined from the physical parameters of the fault segments (size of the fault plane and slip rate), and considering that the fault can break in earthquakes of magnitude less than the expected maximum (minimum size 5.0 Mw). For this, the pattern of recurrence of type GR earthquakes (Gutenberg and Richter, 1944) with double truncation magnitude (Mmin and Mmax) proposed by Cosentino et al. (1977) is used.

Recorded Ground Motion and Estimated Soil Amplification for the 11 May 2011 Lorca Earthquake

On 11 May 2011 an earthquake of magnitude 5.2 ( M w) hit the Murcia region of Spain causing significant damage to buildings in the town of Lorca. Accelerograms were recorded by stations of the Instituto Geográfico Nacional, and high-amplitude ground motions were observed at the Lorca station, with a peak ground acceleration (PGA) of 0.37 g. The contribution of a near-field component of ground motion is shown in time histories and in elastic response spectra. Features of near-field ground motions such as directivity could have significantly enhanced the ground shaking caused by this event. Local amplification effects in Lorca were investigated by the H/V spectral ratio technique and an array method. Information obtained from the geophysical field survey allowed the definition of representative soil columns and site classifications according to Eurocode 8. Modeling of site response is conducted for an example location. The aftershocks recorded at different sites confirm the soil amplification at these locations.

Influence of Seismic Behavior Factor on the Design of Building Structures for Low Seismic Demands Regions

The use of reduced seismic forces obtained from elastic response spectra analysis is a common practice for structural design purposes. This procedure is used: (a) To take advantage of the nonlinear behavior of the structural elements that conform the entire structure, and (b) To reduce the initial cost of the construction, allowing certain degree of damage if a severe earthquake occurs, but trying to avoid collapse with good structural design and construction detailing. In this paper, structural analyses were performed using several seismic reduction coefficients and the considered structures were designed for low seismic design regions according to the Mexico construction codes for both, serviceability limit states and ultimate limit states. Results show that the final design is strongly dependent on allowed interstory drift, associated to lateral displacements. Results also showed that, reducing significantly the seismic forces is not directly associated with a reduction in the initial cost of the structure, i.e., the final design for different seismic behavior factor may have similar seismic vulnerability.

Seismic Analysis of High Pier Three-Span Continuous Bridge

In this paper, SAP2000 and ANSYS software are used to modeling and analysis athree-span continuous beam bridge with high piers case study.By using differentbearing types and combinations to form different options, create two finiteelement models.Analysis dynamic characteristics ,elastic response spectra,linear time history and nonlinear time history .And focus on comparing dynamiccharacteristics of the earthquake response of the two programs .Running outputdata processing and comparison results show that the application of thedifferent parameters of the rational combination of rubber bearing basin bridgearrangement has better seismic performance.

DESING SPECTRUMS FOR THE CENTRAL NORTH OF QUI-TO AND SEISMIC ANALYSIS OF STEEL STRUCTURES USING THE CAPACITY SPECTRUM METHOD.

The city of Quito lies on geological faults that have no surface outcrop but are moving with a speed of 2-4 mm per year. The last strong earthquake associated with these thrust faults, was rec-orded in 1587 and had a magnitude of 6.4; so it has been more than 400 years, there is a large amount of stored energy, and the probability of an earthquake occurring is very high. Therefore, this article presents, firstly, the periods of recurrence of these faults; then a microzoning of the north central part of the city and the elastic response spectra for 5% damped associated to the Llumbisi- La Bota segment fault, ILB. And subsequently, an analysis of nine steel structures from one to nine storeys assuming that they are situated in the following three areas of north central Quito: the old Quito Tenis; La Gasca and Benalcazar High School. Using the Capacity Spectrum Method MEC, the seismic response is found with the presence of three spectrums as prescribed in the Ecuadorian Construction Regula-tions NEC-11; the recommendation in the study of the seismic microzoning of Quito ERN-12 and those found in the seismic microzoning associated with the fault ILB. Three types of responses are indicated for each location, the structures situated in the old Quito Tenis present a performance point found using the Capacity Spectrum Method MEC; for those in La Gasca, a maximum lateral displacement is indicated in each storey; and the structures situated in the Benalcazar High School present maximum interstorey drifts. It should be highlighted that the lateral displacements and interstorey drifts are reaching the end of their performance, thus the conclusions to be found in this study about which spectrum the maximum response has could be inferred from any of the three structural parameters.