A Numerical Assessment to Estimate the Dynamic Factor for Wind Excited Façade Elements Having a Natural Frequency Smaller Than 5 Hz

Wind is the major action affecting a façade and local effects are governing the behaviour. The European standard (EN1991-1-4, 2005) follows and equivalent static approach, taking in consideration possible resonances by means of a structural factor, which should account for the effect of along wind actions deriving from the non-simultaneous occurrence of peak wind pressure on the surface and the effect of the vibrations of the structure due to turbulence. According to the standard, for façade and roof elements having a natural frequency greater than 5 Hz, the structural factor can be taken as 1. However, the 5 Hz value is not accepted as an adequate limit by the entire scientific community and no justification is provided about the choice of this value. The authors have investigated how the natural frequency influences the response of a Single Degree of Freedom (SDOF) system excited by the Wind Power Spectrum, comparing the outcomes with the structural factor proposed by the standard.