Principal static wind loads

in Journal of Wind Engineering & Industrial Aerodynamics (2013), 113

In current wind design practice, static wind loads are usually defined to obtain, by simple static analyses, the extreme values of any structural response that would be formally obtained with a strict ... [more ▼]

In current wind design practice, static wind loads are usually defined to obtain, by simple static analyses, the extreme values of any structural response that would be formally obtained with a strict dynamic buffeting analysis. The minimum and maximum values that may reach any response define the envelope. Equivalent static wind loads (ESWLs) allow to recover extreme responses in the envelope. As a first objective, this paper formalizes a general method to determine ESWL, in a nodal basis, by extending the concept of load-response correlation, which is only valid in the background range. The general method, the displacement-response-correlation (DRC) method, covers the background and resonant contributions of the considered response. As a second objective, the paper addresses the problem of building a set of static wind loads that adequately reconstructs the envelopes of responses. The concept of principal static wind loads (PSWL) is introduced to form a reduced basis of representative loads well-suited for envelope reconstruction. Its optimality is demonstrated both analytically and with a detailed illustrative example. [less ▲]

Efficient uncoupled stochastic analysis with non-proportional damping

in Journal of Sound & Vibration (2012), 331(2012), 52835291

The use of normal modes of vibration in the analysis of structures with nonproportional damping reduces the size of the resulting set of governing equations, but does not decouple them. A common practice ... [more ▼]

The use of normal modes of vibration in the analysis of structures with nonproportional damping reduces the size of the resulting set of governing equations, but does not decouple them. A common practice consists in decoupling the equations by disregarding the o -diagonal elements in the modal damping matrix. Recently, an approximation based on an asymptotic expansion of the modal transfer matrix has been proposed in a deterministic framework to partially account for o -diagonal terms, but still with a set of uncoupled equations. This paper aims at extending this method in a stochastic context. First the mathematical background is introduced and the method is illustrated with a simple example. Then its relevance is demonstrated within the context of the structural analysis of a large and realistic structure. [less ▲]

Optimal processing of wind tunnel measurements in view of stochastic structural design of large flexible structures

Book (2011)

Stochastic analysis of a stadium roof from deterministic wind tunnel measurements

in 13th International Conference on Wind Engineering (2010)

Dynamic analyses of structures under buffeting wind loads can be performed in a deterministic (Clough and Penzien, 1997) or stochastic (Preumont, 1994) context, both with a modal approach for ... [more ▼]

Dynamic analyses of structures under buffeting wind loads can be performed in a deterministic (Clough and Penzien, 1997) or stochastic (Preumont, 1994) context, both with a modal approach for computational efficiency reasons. In the first option, the forces are deterministically given, and the uncoupled modal equations of motion are solved either in the time domain with a stepby- step method, either in the frequency domain, with Fourier transformation. In the second option, the analysis relies on the determination of the Power Spectral Density (PSD) matrix of the structural response given that of the loading. The choice of one or another method usually depends on whether the loading is provided in the time or frequency domain and as a deterministic (a single time history) or stochastic manner. From a designer’s point of view, the wind loading can be defined using design codes (e.g. Eurocode, 2005) where analytical expressions of (i) the PSD of wind velocities (Davenport, Von Karman, etc) (ii) the coherence functions and (iii) the pressure coefficients are given to compute, finally, (iv) the PSD of the aerodynamic pressures. Design engineers are usually familiar with this probabilistic approach. Alternatively, the design may be conducted from aerodynamic pressures measured in a wind tunnel. This approach is more realistic than the aforementioned codified procedure since a number of phenomena as (a) the aerodynamic instabilities, (b) aerodynamic admittance (Scanlan and Jones, 1999), (c) site effects are taken into account. Pressures are thus given as unique (deterministic) time histories at each sensor. In a Finite Element context and a modal analysis, the generalized forces are computed from the measured pressures. With the firm wish to perform the analysis in a stochastic manner (for a number of good reasons mentioned next), we suggest to fit a probabilistic model to the measured data. Such a model could be fitted to the measured pressures right away, or any other subsequent quantity such as the generalized forces. The following discussion is about the most favorable quantity that has to be fitted and how to do it appropriately in view of typical measurement imperfections. [less ▲]