QC 20110616

The development of the construction industry brought the new methods of structural design, which have been introduced to engineers, although overall this phenomenon has increased building costs. A cost-effective construction is one of the major decision points during the definition of any engineering project, therefore, due to the opposing concepts of these two statements, revising design standards and codes are essential in order to provide adequate and cost-effective design requirements. A single-ply roof system is a relatively new method of roof construction that has been used in the building industry in recent decades, which seems to have undergone dramatic changes due to significant structural failures that have occurred through the years. Wind-induced damage on flat roofs is a common problem for low-rise buildings and much of this damage is initiated when the steel deck roof fails, leading to the overall roofing system collapse. The FM (Factory Mutual) design recommendations, which is a standard that recommends allowable dimensions and wind rating for the roofing products, have provided tabulated steel deck span dimensions and fasteners distance for many years. To update the FM design recommendations extensive experimental and analytical investigations are required. In the current study an experimental program was conducted at the National Research Council of Canada (NRC) on flat roofing systems, for simulating the wind uplift effect on several roofing systems samples, as recommended by FM design recommendations. A Finite Element Model (FEM) of the same roofing systems as those used in the experimental cases was developed and different loading patterns were analysed for providing a better simulation of the deflection, moments and forces responses, as measured during the experiments. The FEM was validated with the experimental results and was further employed for applying the FE analysis for more steel deck span dimensions and wind rating cases, as provided in the FM design recommendations tables. These results were reported to the Single Ply Roof Industry (SPRI) Committee where the updating of the FM design tables is currently under discussion.

An experimental study was carried out on a single-ply low-slope roof using a series of different underlayment layers to test and understand distributional characteristics of negative air pressure throughout the roof assembly, when subjected to suction pressure corresponding to different wind speeds. Various underlayments were tested at the Research & Demonstration Facility at Virginia Polytechnic Institute and State University to develop design guidelines for the installation of recently developed omni-directional roof vent on low slope membrane roofing systems. The newly designed and patented low-pressure roof vent works on Bernoulli and Venturi air flow principals and helps prevent uplift and detachment of the roofing membrane during storm or high wind conditions by creating a negative pressure zone underneath the roof membrane. The objective of this research is to further develop the Pressure Equalizing Vent System by testing the wind vent in combination with different underlayments and to determine the appropriate tributary area of each vent under dynamic wind conditions. The determined area of influence of each wind vent therefore serves as a guideline for appropriate spacing of the vents on the roof. It will also suggest the wind speed at which the pressure is lowered and its ability to weather storm events. The pressure sensors permanently installed beneath the membrane will continuously monitor the pressures in and around the wind vent. An additional objective of the research project is to understand the distributional characteristics of negative pressure in various layers of roof assembly in combination with varying underlayment membranes under different suctionals pressure to further develop the Pressure Equalizing Vent System. The proposal seeks to develop a cost effective roof assembly method, which can withstand the effect of extreme wind through improved understanding of air movement through different layers of roof assembly. The study explores the effect of various underlayments on spatial and distributional character of pressure field on the single ply flat roof deck in combination with omni-directional roof vent system. / Master of Science

Greenroof systems have been shown to be an environmentally friendly alternative based on various factors; such as, reduced lifecycle cost, improved air quality, ambient temperature reduction, stormwater management credit, sustainability and preservation of the environment. Recent research studies attempt to determine the construction methods of an ideal greenroof for environmental purposes, yet there is an absence of standards for the best design required to achieve acceptable structural performance and sustainability under wind loads. As a result, there is a need to document the effectiveness of greenroofs under high wind events by addressing the following questions: Do winds have an effect on greenroof material loss? Do greenroof materials modify local pressure conditions that would need a modification to current design codes? Does the level of vegetation establishment affect the material loss and pressure distribution? This thesis first focuses on vegetated greenroof construction techniques and issues along with some of the most recent studies conducted by UCF researchers. Then, the literature focuses on wind uplift of vegetated roofs constructed using different wind erosion control methods with respect to vegetation cover, geosynthetic liners, and wind breaks. As part of this research, two monitoring systems with a grid of very low differential pressure transducers and a high speed anemometer were designed and implemented on the East and West coasts of Florida to collect data for the pressure distribution across the greenroofs in relation to wind direction and speed. In addition to this, the design of this monitoring system with specific information about the sensing and data acquisition systems is presented. Subsequently, the analysis of the monitoring data compares the peak wind gusts for each time interval to their corresponding pressure measurement to obtain pressure coefficients identified at each pressure node on the roof. Based on this analysis, pressure changes for hurricane speed winds are predicted to have an overall average uplift pressure envelope within ASCE Code 7-05 design standards with vegetation cover enhancing sustainability under wind events. For future studies, controlled field investigations to reduce in situ limitations due to natural climatic conditions as well as long term monitoring are discussed as recommended studies for the evaluation of wind effects.

The aim of this thesis is going to concentrate on the issues associated with the technology of mechanically anchored coating waterproofing of roofs. Today the mechanical anchoring belongs to the most widespread way of how to stabilize the layers of roofing material against the effects of wind uplift particularly in indoor buildings. However some malfunctions occur more and more frequently which cause leaking into the constructions or even the destruction of the whole roof in the worse cases. The practical part of this thesis is going to concentrate on the fasterners which belong to the most important elements of the mechanical anchored system. The aim of the experimental measurement is to draw a comparison of the quality of fasteners which are distributed on the Czech market. Thereafter the obtained figures are going to be compared with the theoretical calculating procedures according to the valid designed standards.

The performance of building envelopes and roofing systems significantly depends on accurate knowledge of wind loads and the response of envelope components under realistic wind conditions. Wind tunnel testing is a well-established practice to determine wind loads on structures. For small structures much larger model scales are needed than for large structures, to maintain modeling accuracy and minimize Reynolds number effects. In these circumstances the ability to obtain a large enough turbulence integral scale is usually compromised by the limited dimensions of the wind tunnel meaning that it is not possible to simulate the low frequency end of the turbulence spectrum. Such flows are called flows with Partial Turbulence Simulation. In this dissertation, the test procedure and scaling requirements for tests in partial turbulence simulation are discussed. A theoretical method is proposed for including the effects of low-frequency turbulences in the post-test analysis. In this theory the turbulence spectrum is divided into two distinct statistical processes, one at high frequencies which can be simulated in the wind tunnel, and one at low frequencies which can be treated in a quasi-steady manner. The joint probability of load resulting from the two processes is derived from which full-scale equivalent peak pressure coefficients can be obtained. The efficacy of the method is proved by comparing predicted data derived from tests on large-scale models of the Silsoe Cube and Texas-Tech University buildings in Wall of Wind facility at Florida International University with the available full-scale data. For multi-layer building envelopes such as rain-screen walls, roof pavers, and vented energy efficient walls not only peak wind loads but also their spatial gradients are important. Wind permeable roof claddings like roof pavers are not well dealt with in many existing building codes and standards. Large-scale experiments were carried out to investigate the wind loading on concrete pavers including wind blow-off tests and pressure measurements. Simplified guidelines were developed for design of loose-laid roof pavers against wind uplift. The guidelines are formatted so that use can be made of the existing information in codes and standards such as ASCE 7-10 on pressure coefficients on components and cladding.