Structural design for ponding of rainwater on roof structures

Ponding of rainwater is a special load case that can lead to roof collapse. In Dutch building practice the most frequently occurring damage cases are failures of flat roof structures caused by ponding of rainwater. In the Dutch code for loadings and deformations NEN6702 [1] and the Dutch guidelines for practice regarding ponding NPR 6703 [2], principles and guidelines for the determination of rainwater loads are given. The Dutch code [1] prescribes a complex iterative procedure for ponding of rainwater. Today, there are a number of computer software programs available to support the structural designer in this iteration method. However, to keep insight in the process of rainwater ponding, a simple design method for ponding of slightly sloping flat (steel) roof structures was developed. The method is described in the first part of this article. In the second part a sensitivity analysis for design and construction inaccuracies is presented. It is shown that roofs, that are seemingly stiff enough to withstand ponding, need partial safety factors substantially greater than normally used to account for construction inaccuracies. A proposal for the partial safety factor related to roof stiffness and construction inaccuracies is given

Segmented Barrel-Vaulted Glass Roof

A structural system for segmented barrel-vaulted glass roofs has been developed,aiming at maximum transparency due to structural optimization. This has led to astructural system with small connections, integrated into the glass, as well as clear,transparent joints. Finite element analysis and a full-scale test has been performed,showing PVB-laminated glass, 101010.4, could be sufficient to create spans up to20 meters with slightly prestressed cables measuring just 3 mm in diameter

VACUUMATICS; Systematic Flexural Rigidity Analysis

The structural integrity of vacuumatics relies on the principle of prestressing unbound particles inside an enclosed membrane. By introducing a negative pressure (partial vacuum) inside this airtight flexible enclosure, the membrane is tightly wrapped around the outer particles, hence effectively bonding the particle filling to create (adaptable) load-bearing structures. Analytical and numerical studies on the fundamental prestress derivation of vacuumatically prestressed structures have shown that the effective prestressing forces between the particles largely depend, apart from the differential in (air) pressure differential, on the elastic properties of the skin material. The flexural rigidity of vacuumatics is mainly determined by the material properties of the particles and membrane used. Variations in elasticity of the skin and particle filling, and with this the shape, size, compressiveness, roughness, and packing density of the individual particles, highly influence the structural behaviour of vacuumatic structures. In order to explore the influence of different particle and skin characteristics (or parameters) on the flexural rigidity, experimental research has been carried out by means of four point bending tests. Different types of particles were used to discover behavioural trends dependent on the parameters varied. The results of this study provide an enhanced understanding of the true overall structural response of vacuumatics. By systematically elaborating the different parameters, we are able to determine what specific material properties are desired to design the ‘most efficient’ vacuumatic structure for every application

Bracing Steel Frames with Adhesively Bonded Glass Panes - Mechanic Models

Circumferentially adhesive bonded glass panes in steel frames of facades can take over the structural function of steel braces for the stabilization of one-storey buildings. A system, built up of a steel frame, a single glass pane and a flexible adhesive bonded joint across the full thickness of the glass pane was subjected to a concentrated horizontal in-plane load at the top. Experiments with square glass pane sizes showed that the system had a very small inplane stiffness, a glass-steel contact at large horizontal in-plane loads and a good residual capacity. The parametric studies by means of finite element models only focused on the variation of the geometry of the glass pane. The behaviour of the system mainly depends on the stiffness of the adhesive bonded joint. At larger horizontal in-plane displacements, systems with rectangular glass pane sizes have two glass-steel contacts. The mechanic models well predict the in-plane stiffness of the system, the largest maximum principle stress and the maximum normal and shear stresses in the adhesive bonded joint. The horizontal in-plane load and the horizontal in-plane displacement at the top at the first glass-steel contact are also well predicted. The criteria are the limitation of the horizontal in-plane displacement at the top (serviceability) or the strain rate of the adhesive bonded joint (strength). To guarantee the stability of a building all glass panes in the facade have to be mobilized to transfer in-plane load

Parametric Studies on Bracing Steel Frames with Glued Glass Panes

Glass panes structurally bonded to a steel framework can be used as a stability system for buildings. A system built up of a single glass pane, a steel frame and a glued joint is only loaded by a concentrated monotonic in-plane load at the top. Three glued joint types are defined, namely a flexible joint on the end, a two-sided and a one-sided rigid joint. A finite element model was developed and calibrated with the experiments followed by varying the geometry of the glass pane. The applied criteria are the strength of glass for failure and the restricted in-plane displacement at the top. The system with a flexible joint on the end can be characterized by small loads, large inplane displacements and small stiffnesses. The stiffness is the criterion. Systems with two-sided and one sided rigid joints can be characterized by larger loads, much smaller ,in-plane displacements and larger stiffnesses. The strength of glass is the criterion and is located on the glass pane's surface in the vicinity of the glued joint which anchors the tensile diagonal of the glass pane. These tensile stresses increase by the different in stiffness of the glued joint (rigid) and the less shear stiffness of the bolts between beadwork and outside beam of the frame. However, the stress distribution in the glass pane as well as in the glued joint is unfavourable for systems with one-sided rigid joint. The two-sided rigid glued joint is a promising joint type based on the geometric parameters of the glass pane and the good residual capacity after the first cracks as observed in the experiments

Bracing Steel Frames with Adhesively Bonded Glass Panes - Mechanic Models

Circumferentially adhesive bonded glass panes in steel frames of facades can take over the structural function of steel braces for the stabilization of one-storey buildings. A system, built up of a steel frame, a single glass pane and a flexible adhesive bonded joint across the full thickness of the glass pane was subjected to a concentrated horizontal in-plane load at the top. Experiments with square glass pane sizes showed that the system had a very small inplane stiffness, a glass-steel contact at large horizontal in-plane loads and a good residual capacity. The parametric studies by means of finite element models only focused on the variation of the geometry of the glass pane. The behaviour of the system mainly depends on the stiffness of the adhesive bonded joint. At larger horizontal in-plane displacements, systems with rectangular glass pane sizes have two glass-steel contacts. The mechanic models well predict the in-plane stiffness of the system, the largest maximum principle stress and the maximum normal and shear stresses in the adhesive bonded joint. The horizontal in-plane load and the horizontal in-plane displacement at the top at the first glass-steel contact are also well predicted. The criteria are the limitation of the horizontal in-plane displacement at the top (serviceability) or the strain rate of the adhesive bonded joint (strength). To guarantee the stability of a building all glass panes in the facade have to be mobilized to transfer in-plane load

Parametric Studies on Bracing Steel Frames with Glued Glass Panes

Glass panes structurally bonded to a steel framework can be used as a stability system for buildings. A system built up of a single glass pane, a steel frame and a glued joint is only loaded by a concentrated monotonic in-plane load at the top. Three glued joint types are defined, namely a flexible joint on the end, a two-sided and a one-sided rigid joint. A finite element model was developed and calibrated with the experiments followed by varying the geometry of the glass pane. The applied criteria are the strength of glass for failure and the restricted in-plane displacement at the top. The system with a flexible joint on the end can be characterized by small loads, large inplane displacements and small stiffnesses. The stiffness is the criterion. Systems with two-sided and one sided rigid joints can be characterized by larger loads, much smaller ,in-plane displacements and larger stiffnesses. The strength of glass is the criterion and is located on the glass pane's surface in the vicinity of the glued joint which anchors the tensile diagonal of the glass pane. These tensile stresses increase by the different in stiffness of the glued joint (rigid) and the less shear stiffness of the bolts between beadwork and outside beam of the frame. However, the stress distribution in the glass pane as well as in the glued joint is unfavourable for systems with one-sided rigid joint. The two-sided rigid glued joint is a promising joint type based on the geometric parameters of the glass pane and the good residual capacity after the first cracks as observed in the experiments