Procedure de dimensionnement au vent des bardages et vetures: approches experimentale et numerique

Abstract

Wind loads on porous claddings of buildings depend on the external pressure wind fields and on the induced internal pressure field of the air trapped between the wall and the outer sheeting. The external pressure field can be determined directly from reduced scale simulations of buildings, surroundings, and wind configurations, using current techniques in boundary layer wind tunnels. But it is practically impossible to reproduce to the same scale the flows through porous cladding, and from one region to another behind the cladding, so that the internal pressure field is correctly modelled as well. Research at CSTB shows that scale facades may be over-designed by as much as 60% if the role of the internal pressure is neglected. This paper presents a method for optimal design of cladding taking into account the external pressure fields known from wind tunnel investigations and the porosity of cladding measured on a test rig at full scale. Cladding porosity for a given cladding is used along with the external pressure field to calculate the internal pressure field using a numerical procedure described in the paper. To validate and perfect the numerical model, a test house 29 m × 5.2 m in plan was built on a turntable at an exposed site. One facade, with slate cladding covering an area 3.24 m × 2.52 m high, was instrumented with 15 external pressure taps and 12 internal ones. Of the many 20-minute records taken so far, three 50-second excerpts illustrate the net loads on the slates, and also the calculated internal pressures, for individual taps. After complete validation of the numerical procedure for several types of typical claddings, a catalogue of permeabilities for claddings in common use will be established with the help of the test rig.