Seismic soil-structure interaction analysis of wind turbine support structures using augmented complex mode superposition response spectrum method

In this study, the seismic soil-structure interaction (SSI) of wind turbine support structures is investigated using response spectrum method (RSM) based on the complex eigenmodes. Seismic loadings on wind turbine support structures are newly derived by complex mode superposition RSM. To improve the prediction accuracy of the shear force acting on footings, this method is augmented by introducing the upper limit of modal damping ratios of 10 %. In addition, the bending moment at the hub height due to the mass moment of inertia of rotor and nacelle assembly is considered as an additional loading. The proposed method is validated by comparison with time history analysis (THA) accounting for different types of foundations and different tower geometries. Seismic loadings acting on the towers and footings by the proposed method show favourable agreement with the mean results by THA of several input acceleration time histories, while the original complex mode superposition RSM strongly underestimates shear forces acting on footings.

Performannce Base Analysis of Multy Storied Building

In India multistoried buildings are widely designed with the method suggested by Indian Standard IS1893: Part-1:2016, Criteria for the Earthquake resistance design of the structures: General Provision and Buildings for the calculation of equivalent horizontal load generated during earthquake. Response Spectrum method is widely used for the multistoried buildings with base shear scaled to get the equal value as calculated with the time period obtained by the empirical formula of time period of the buildings. The approach of the dynamic analysis is basically a linear approach. In this scenario we are totally relying on ductility of the structure. The concept for performing the Pushover Analysis is to analyze a structure with non linear approach and to find the behavior of structure beyond its ductile limit. Pushover analysis can help to demonstrate how progressive failure in building really occurs and to identify the mode of final failure of the buildings. Pushover analysis is commonly used to evaluate the seismic capacity of existing structures and appears in several recent guidelines for retrofit seismic design. It can also be useful for performance-based design of new buildings that rely on ductility or redundancies to resist earthquake forces. So basically Pushover analysis is non linear approach to estimate the strength capacity of the structure beyond Limit State. In this analysis we can predicts the weak areas in the building and keeping track of the sequence of damages of each and every member in the building/structure, thus can be performed for existing structure and also for performance base design, similarly for progressive collapse analysis. The approach is easy to understand, when we designed or analyze a moment resisting frame as per IS 1893:2016 by Response Spectrum method with response spectrum method with the response reduction factor 5 i.e. R=5, we are basically designing the structure with 1/5th horizontal load (calculated with the empirical formula given in IS 1893:2016), the rest 4/5th load is basically taken care by the ductile behavior of the building. The ductile detailing suggested by the 13920:2016 will resist the full impact of seismic load without collapse. The distribution and impact of the full horizontal load can be analyzed with the non linear approach, and pushover analysis is one of them. METHODLOGY: A pushover analysis is performed by subjecting a structure to a monotonically increasing pattern of lateral loads, representing the inertial forces which would be experienced by the structure when subjected to ground shaking. Under incrementally increasing loads various structural elements may yield sequentially. Consequently, at each event, the structure experiences a loss in stiffness. Using a pushover analysis, a characteristic non linear force displacement relationship can be determined. Key elements of the pushover analysis 1) Definition of plastic hinges, it includes hinges for uncoupled moment, hinges for uncoupled axial load, hinges for uncoupled shear force, hinges for coupled axial force and hinges for biaxial bending moment. 2) Definition for control node, the node used to monitor the displacement of the structures. Pushover curve is obtained from the displacement verses base shear. 3) Developing the pushover curve which includes the elevation of the forces distribution 4) Estimation of the displacement demand. 5) Evaluation of performance level for the structure