C. Kramer

Wind loads on permeable roofing systems

Abstract The paper presents conclusions on the critical wind loads of two different types of roofing systems: tiles on pitched roofs and paving slabs on flat roofs. Because of gaps between those roofing elements these types of roof coverings are wind permeable. The net wind load on an element is determined by the external pressure distribution on the roof surface and the internal pressure distribution underneath the roof covering. The external pressure distribution depends on the building flow field and changes in the local flow due to the shape of the roofing elements. The internal pressure distribution is influenced by the local flow direction with respect to the gaps between the elements and the resistance of the flow underneath the permeable covering. The critical loading on a roofing element does not necessarily occur for the critical external pressure distribution on the roof surface.

On the wind-loading mechanism of roofing elements

Abstract The outer, wind-exposed layer of many roofing systems is wind permeable. The wind load on a roofing element of such systems is determined by the pressure difference across the roofing element. Only the external pressure distribution induced largely by the building flow field is given in wind-loading codes. The application of the codes to wind-permeable roofing systems usually leads to very conservative wind loads. This paper describes the wind-loading mechanism for three widely used roofing elements. The experimental results obtained give a reliable basis for designing more economic roofing systems.

Wind induced loading cycle and fatigue testing of lightweight roofing fixations

Abstract The paper presents information on the load cycle for flat-roofed and pitch-roofed low-rise buildings and of a testing procedure to determine the fatigue strength of mechanical fixation elements. Roofing membranes and roofing elements for lightweight roofs are normally fixed mechanically to the roof structure. The fixings are subjected to time-varying loads. The fatigue limit of the fixings depends on the load cycle and the dynamic behaviour of the roof system. A proposal for testing fixings and first results of tests will be presented.

Wind pressures on roofs of very low and very large industrial buildings

Abstract This paper deals with the windload on block-type buildings with very low relative heights (i.e. building height related to the building width). Such buildings correspond to most industrial building complexes. It is shown by wind tunnel studies comprising flow visualization on the building surfaces and pressure measurements on the model roof, that there are significant differences between the requirements in the windload codes and the experimental findings. For this type of building the height/width ratio is the most important factor concerning the roof windload. The effect on parts of the building protruding from the main roof surface is demonstrated in case studies. The windload on the surface of the protrusions is strongly influenced by the position of the protrusions with respect to the main building.

Interference effects for groups of stacks

Abstract Since code information concerning the static wind loads and wind-induced vibrations of groups of stacks is scarce, a basic study in this field of building aerodynamics is currently in progress in the Fluid Mechanics Laboratory of the Fachhochschule Aachen. For some standard configurations the static wind load in high Reynolds number flow simulated by roughening the model surfaces has been obtained. The experiments for measuring the wind-induced vibrations were conducted in subcritical Reynolds number flows. The influence of platforms on the vibrations of in-line stacks has been investigated.

Wind loading on loosely laid pavers and insulation boards for flat roofs

Abstract The paper gives results of experiments and calculations concerning the safety against wind lift-off of loosely laid pavers and insulation boards on flat roofs. The experiments are aimed to derive information concerning the underelement pressures depending on the external pressure distribution and the windpermeability of the layer consisting of pavers or insulation boards. Theoretical considerations lead to a simple equation for determining the failure wind speed depending on the external pressure, the relative element size and the area weight of the elements. The results of the calculations are given as diagrams which may help the designer to choose the best possible solution when using loosely laid insulation boards as additional thermal insulation or when using pavers as roof ballast.

Wind loads on wind-permeable building facades

Abstract This paper describes some significant results of a comprehensive study of wind loads on wind-permeable facades of low-rise buildings. The investigation was undertaken to provide wind load information for the design of elements of wind-permeable facades and the design of their fixation to the wind-impermeable building walls. The wind loading mechanism, the experimental methodology and some results have been presented elsewhere (1) and will be discussed only very briefly. The emphasis of this paper is on the probability distribution of pressure coefficients obtained for the critical areas of the building facades and for the critical flow situations. In particular the sensitivity of the peak pressures to the initial flow conditions and the relative building dimensions will be discussed.

On aerodynamic sealing for industrial applications

Abstract This paper describes a new device for aerodynamic sealing of openings for the passage of striplike material in chambers, e.g. in industrial furnaces, dryers, and for clean rooms. A numerical prediction procedure for the flow generated by the sealing device is presented. The influence of the relevant flow parameters upon the sealing efficiency is systematically analysed. Theoretical predictions are validated through concentration measurements in a physical model of a strip flotation furnace. The advantages of the new device—contactless sealing and minimized leakage of the atmosphere from inside the chamber to be sealed—are discussed in detail.

Surface flow field around three-dimensional bluff bodies

Abstract The influence of the relative dimensions of a three-dimensional bluff body on the flow pattern at the ground plane is investigated. Two cases are considered: (i) the approach flow is rectangular and uniform (ii) the body is placed in a boundary layer. From the extensive flow-visualisation studies made, both qualitative and quantitative results are obtained which show how the near wake length and the general flow pattern vary with the relative dimensions in case (i). The results in case (ii) show the influence of the dimensions of the body relative to the boundary layer on the horse-shoe vortex generated in front, the changes that occur in the extent of the near wake and the variations in the general flow pattern around the body. A comparison between cases (i) and (ii) is presented which brings out the comparative influence of the boundary layer on the flow near the ground plane.

Calculations of pressure equilibration underneath loose-laid, flow permeable roof insulation boards

Abstract The flow underneath a loosely laid insulation board or a paver is approximated by a two-dimensional laminar flow in a very shallow channel having a porous upper roof. The momentum theorem and flow continuity are used to determine a set of non-linear differential equations which are solved numerically to obtain the pressure distribution underneath the paver for a given outer pressure distribution on a roof top. The important parameters that influence the flow and pressure equilibration are identified. Considering the critical case where the separated flow reattaches within the length of the paver it is found that the pressure distribution underneath a flow impermeable paver is linear and depends on the ratio of the flow resistance in the joints of adjacent pavers to the resistance underneath the paver. The flow rate underneath the paver is, however, directly proportional to the inverse of the sum of the resistances. For a flow permeable paver the additional influencing parameters are the flow resistance within the porous medium of the paver and the ratio of the effective flow area of the paver to the cross-sectional flow area underneath the paver. Two cases of outer pressure distribution, sinusoidal and uniform distributions, are investigated. The results presented are also applicable to flow permeable building claddings.