Membrane Roof Research Articles

A radically new UV stabilizer for flexible PVC roofing membranes

Ultraviolet absorbers, such as those from the hydroxyphenylbenzotriazole and hydroxybenzophenone classes of compounds, are typically added to flexible PVC roofing membranes in order to protect the membranes during long-term exposure to sunlight. In this article a radically new UV stabilizer, one that is not just another UV absorber, is introduced. This new UV stabilizer, which is chemically a low-basicity hindered piperidine derivative, was found to dramatically increase the weatherability of PVC roofing membranes. The performance of the new light stabilizer is documented and compared to that of traditional PVC membranes containing just a UV absorber. Although the article focuses on PVC roofing membranes, examples are provided of other durable applications that could benefit from the new light stabilizer technology. J. VINYL ADDIT. TECHNOL., 11:91–94, 2005. © 2005 Society of Plastics Engineers

Numerical Investigation of the Interaction of Turbulent Wind Flow and Elastic Structures

AbstractThe Interaction between wind flow and structures plays an important role in the computation of civil engineering application. In case of gravity prestressed membrane roofs, the wind lifting forces may exceed the dead load leading to high amplitude structural oscillations, which interact with the flow field. To investigate the interaction a consistent discretization method based on stabilized space‐time finite elements is applied. The flow field is modeled with the incompressible Reynolds Averaged Navier‐Stokes (RANS) equations with an anisotropic eddy‐viscosity turbulence model. The structural motion is described with the theory for geometrically nonlinear elastic deformation behavior, a strong coupling algorithm for the time‐dependent fluid‐structure interaction is implemented. Two applications show the capability of the turbulence model in representing the anisotropic turbulence structure, the differences in the flow field over a bluff body between two configurations representing a rigid and an elastic membrane roof, discusses the structural responses of the roof at a high Reynolds number. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Simple reconstruction of frontal sinus opened during craniotomy using small autogenous bone piece: Technical note

Background Accidental opening of the frontal sinuses during craniotomy can lead to various postoperative complications. We report a simple and reliable reconstruction method using no exogenous or autogenous material obtained from another site. Methods This method involves packing a small wedge-shaped piece of bone obtained from the bone flap of the craniotomy into the nasal recess of the exposed sinus. The large opened frontal sinus is reconstructed as a new minimized frontal sinus with mucous membrane and bony roof in the nasal recess. Results Eleven patients with large frontal sinus opening during craniotomy (7 cases of bifrontal craniotomy for the basal interhemispheric approach) underwent frontal sinus reconstruction by packing of a small bone piece into the nasal recess. No patients suffered postoperative complications related to the opened frontal sinus such as pneumocephalus or cerebrospinal fluid rhinorrhea. Conclusion Packing of a small bone piece from the bone flap is a quick and reliable method to reconstruct the frontal sinus opened during craniotomy.

Computer Assistance in Managing the Maintenance of Low-Slope Roofs

Computerized roof management systems (CRMSs) are developed to assist building owners in minimizing their expenditures on roof maintenance while improving the safety and serviceability of their roof stock. Current CRMSs have some limitations that affect their ability to efficiently represent roof data at different manageable levels and to accurately predict the service life of various roof components. A new CRMS, called CBROOF, is developed within the Building Envelope Life Cycle Asset Management (BELCAM) research project to overcome these limitations. CBROOF has an object-oriented conceptual model that supports the hierarchical decomposition of roofs and the representation of their data at different levels of detail. CBROOF also incorporates the use of the case-based reasoning (CBR) approach to predict the future condition of roof components based on the recorded condition of similar components. The design and implementation of the relevant modules of CBROOF are presented, and the CBR deterioration model developed for the service life prediction of built-up roof membranes is validated.

Recycling of roofing membrane rubber by ultrasonic devulcanization

AbstractThe recycling of vulcanizates based on EPDM roofing membrane rubber using a new ultrasonic devulcanization reactor with a grooved barrel was carried out. This reactor provided continuous devulcanization at an output as high as 2.52 g/s. Die pressure and ultrasonic power consumption were measured as a function of processing conditions. The mechanical properties of virgin vulcanized and revulcanized roofing membranes were measured. Tensile strength of the revulcanized rubber was found to be similar to that of the virgin vulcanizate. Gel fraction, crosslink density, and dynamic properties of the virgin vulcanizate, the ultrasonically devulcanized rubber, and the revulcanized rubber were determined. Also, dynamic properties and the cure behavior of the virgin compound and of the devulcanized roofing membrane were investigated. All these properties were found to be dependent on processing conditions during devulcanization. The thermal stability of the virgin compound, virgin vulcanizate, and devulcanized and revulcanized rubbers were studied by means of TGA. It was found that the thermal stability of all the vulcanizates in air and nitrogen environments remained practically intact, while that of devulcanized rubber in air environment was a function of processing conditions.

Investigation of thermally-induced loads in modified bituminous roofing membranes

When exposed to various thermal conditions, installed roofing membrane experiences dimensional change, which creates induced, loads on the membrane material. These loads can cause a number of undesirable effects such as the membrane separating away from the parapet wall, seam components splitting, membrane tear at the vicinity of fasteners and membrane slag causing blistering. This paper deals with two kinds of thermally-induced loads, namely, reversible thermal expansion/contraction and irreversible stress releasing. The mechanisms for each type of induced load have been explored in detail on two membrane types of different internal structure. Thermal conditions are configured in the experiments to simulate typical Canadian summer and winter temperatures on a black roofing membrane surface. This study also explores the role of the membrane's length and pre-loading on the induced loads. Based on limited data, some practical recommendations are given, such as regarding the influence of the induced loads in the membrane and on the performance integrity of the roofing assembly constructions when subjected to various exposure conditions.

FRP形材を骨組とした膜構造のクランプ部破壊性状と光ファイバセンサによる内部損傷モニタリング

In the present paper, the failure behavior of the joint between fiber reinforced polymer (FRP) shapes and polytetrafluoroethylene (PTFE) roof membranes has been studied. The tensile test of the joint has been performed statically, then its failure mechanism has been discussed. The fiber Bragg grating sensors have been embedded into FRP materials. It has been successful in that not only strain quantities but also optical power spectra were measured in detail. Consequently it is shown that the optical power decreases as the load increases and its shape develops two peaks after reaching at a critical load due to the occurrences of small transverse cracks.

An attempt at engineering the bulk properties of blends of a bitumen with polymers

AbstractWe have taken blends of a bitumen with three homopolymers that produce systems softer than the bitumen, and to each have added small quantities of different semicrystalline polyolefins. The intention is to discover whether these will form an extensive network system within a blend with a low Tg in which crystallites create the cross‐links, as may happen with the isotactic polypropylene present in some atactic polypropylene systems. Such thermoplastic cross‐links might provide a useful feature for certain uses, such as in built‐up roofing membranes. These were found only within one blend based upon the polybutadiene, in two blends based upon chlorinated polyethylene, but in none based on the Lycra®, whose blends with LLDPEs and the HDPE flowed below the crystal melting temperature. The E′′ plots indicate the presence of many loss processes within the blends at low temperatures: the tan δ plots show other processes active up to 200°C within the soft matter. The behavior we discovered suggests that the properties of binary polymer blends are not associated solely with the components, but that, when the material is stiff or after heating, certain polymer—bitumen interactions may also be significant, and are sensitive to slight differences of structure between LLDPEs, even when present at the 3.4% level. © 2002 Wiley Periodicals, Inc. Adv Polym Techn 21: 275–286, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10032

Protection of Foam Plastic Thermal Insulation in Low Sloped Roofing Systems

Foam plastic thermal insulations have substantially replaced traditional insulations in low sloped roofing systems in North America. Foam plastic thermal insulations used in low sloped roofs are low density (typically 16–48 kg/m3) materials with low permeability to air and water vapour. In many roofs these materials have been directly substituted for traditional (wood and glass fibre) insulations without due attention to the different material characteristics. Moist air movement within roofs,condensation protection (air and vapour barriers),steel deck corrosion,roof membrane blistering and roof traffic damage are discussed. This paper discusses protection of foam plastic thermal insulations in roofing systems, why the protection is needed,and what consequences result if these materials are not protected. Case studies demonstrate the importance of condensation protection in reducing corrosion of galvanized steel in roofs containing closed cell phenolic foam roof insulation in Canada.

球形状の実大ドーム型膜構造物の積雪・滑雪性状に関する研究

On an actual domed structure with membrane roofs, changes with time and distributions in the. snow loads on the roof were investigated using a method based on estimations from the increase in membrane strain. And the sliding behavior of snow blocks was observed by combining video images with 3-dimensional CAD images. The following were confirmed :1. The accumulated snow on the Dome disappeared sooner than that deposited on the ground and on the flat roof model. This tendency was particularly marked on the middle and lower parts of the Dome, due to frequent snow sliding.2. Immediately after snowfall started, the distribution of snow load on the Dome was relatively uniform over its entire surface, then it gradually changed into a hill-shaped distribution by gradual accumulation of snow on the upper part and frequent sudden reductions of snow load on the lower part by sliding. When the snow load was at its maximum value, the load on the middle part was larger than that on the upper part, and the load on the lower part was extremely small.3. The shape coefficient of the Dome to the flat roof model was large initially without exceeding 1, and took the smaller value when the snow load was at its peak value.4. The course of the snow sliding on the Dome, which speed was relatively low, was close to the uniform motion.

Tension roofs and bridges

The term ‘Tension Structures’ is commonly used for those structures wherein one or more primary load bearing elements are in tension. Such structures include membrane roofs, cable roofs, cable bridges, guyed masts or towers, cooling towers though some of these are less common. The tension elements are strands, ropes or membranes, which have to combine with structural elements carrying compression, flexure or a combination thereof, such as, columns/towers/masts, arches, beams/girders/trusses. This review note confines itself to roofs and bridges, summarising the status of the various issues involved. The note covers a summary discussion on materials, analytical approach, illustration of forms, and the latest information and trends on cable technology and aerodynamics. Despite interesting developments that are taking place in the field of tension structures, this is not a subject of common attention. A brief historical perspective has therefore also been included in this note.

A boundary element solution to the soap bubble problem

The boundary element method (BEM) is applied to the soap bubble problem, that is to the problem of determining the surface that a soap bubble constrained by bounding contours assumes under the action of molecular forces. This is also the shape of a uniformly stretched membrane bounded by one or more non-intersecting curves. As the slopes of the membrane surface are finite, their square can not be neglected and the resulting governing equation is non-linear. The problem is solved using the analogue equation method (AEM). According to this method the non-linear membrane is substituted by a linear one subjected to a fictitious transverse load. The fictitious load is established using the BEM. Numerical examples are presented which illustrate the method and demonstrate its accuracy. This application of the BEM to non-linear problems shows that BEM is a versatile computational method for all-purpose use in engineering analysis. The solution of the problem at hand is very important in engineering, since the soap bubble surface can be used as the best initial form for membrane roofs.

メンブレン屋根防水層の耐久性試験方法および試験結果

What asked for durability test methods for roof membrane systems is durability of their performance, not durability of the individual materials that compose the systems. However, the most tests that have been adopted as durability tests only focus on roofing material itself. Therefore it has been difficult to estimate durability of roof membrane systems by the present test methods. In this study, new test methods to make clear performances of roof membrane systems were proposed from the idea of combining the performance tests for them described in JASS 8 with degradation conditions. The items for degradation are heat, ultraviolet irradiation, ozone and moisture. The durability of the four kinds of commercial roof membrane systems was experimentally estimated using the proposed test methods.

Roof membranes—The Swedish practice in light of EOTA TB 97/24/9.3.1 PT3 Durability

The practice for roof membranes for flat and low-slope roofs has substantially developed during the last two decades of the twentieth century. New technical solutions have been introduced and building codes and guidelines have been changed.

Modification of a Bitumen with Various Polymers for Use in Built-Up Roofing Membranes

Bitumen, a mixture of aromatics, paraffins, asphaltenes and resins that remain after crude oil has been fractionally distilled, finds applications in blends with a proportion of a polymer, in built up membranes for the roofing industry. Blends of three commercially used polymers with a 100 penetration grade Nynas bitumen at levels between 9% and 29% w/w were prepared using a Z-blade mixer. The morphology, thermal and dynamic mechanical properties of these blends were examined using fluorescence optical microscopy, differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). The blends prepared with these polymers displayed low temperature flexibility and an onset of flow at high temperatures. The former characteristic is required for use in cold environments the latter feature being a critical property when the membrane is manufactured and later when applied by the torching process on a roof. It may be seen how the different blends function in a manner that makes them suitable for the production of built-up roofing membranes.

Roof Surface Wind Speed Distributions on Low-rise Buildings

On low-rise buildings the damage to and destructive removal of small roofing elements forming a porous roof membrane, such as tiles, shingles and shakes, is largely controlled by the heal mean andpeak wind speeds that exist just above the roof surface. Some typical high speed regions have been identified by the selective removal of cladding elements during high wind events [Refs. 1 and 2]. Frequently these high speed regions close to the roof surface are comer or ridge vortices. This study endeavours to map the mean surface wind speeds in the wind tunnel on some typical house geometries at a scale of 1:25 with a robust hot-probe anemometer. In one configuration these data were confirmed by full-scale measurements. Some peak wind-speed data were also collected at selected locations with a highly responsive hot-film anemometer. Both sloped and near-horizontal roofs have been investigated. In all geometries, a locally increased mean wind speed of up to sixty percent above the approach flow value was found for particular wind azimuths at critical locations on the roof surface. The peak gusts close to the roof surface varied significantly with the flow regime present, but a useful design gust factor of 2.5 times the approach mean velocity was found to be an upper bound for most roof-surface wind speeds.

Wind tunnel measurements of cavity pressure dynamics in a low-rise flexible roofed building

Abstract Results are presented from a series of wind tunnel tests to measure the cavity pressure dynamics of a flexible roofed building with a single dominant opening. Tests were conducted in a simulated atmospheric boundary layer, representative of an open-country terrain, for the model configured with five different roof tensions, three internal volumes, two windspeeds and five opening azimuth angles. The ratio of air-to-building bulk moduli was used as a measure of roof tension and buildings with 0.02 Eq. (1) ) provided a convenient means of collapsing the unsteady cavity pressure data for those configurations where significant resonance occurred. A flow component into the opening was necessary to sustain large resonant oscillations and this occurred with an opening on both windward and leeward sides of the building. Increased flexibility of the roof membrane reduced the value of the Helmholtz frequency and also reduced the magnitude of the resonant response.

A New Dynamic Wind Load Cycle to Evaluate Mechanically Attached Flexible Membrane Roofs

Abstract In North America, at present, no test procedure exists for certifying roofing systems under dynamic wind loads. To develop such a dynamic test procedure, the National Research Council of Canada (NRC) formed an industry-based consortium during 1994. The consortium is known as the Special Interest Group for Dynamic Evaluation of Roofing Systems (SIGDERS). This paper reports SIGDERS' progress on dynamicload cycle development. Wind tunnel investigations were carried out using two flexible roofing membranes: poly(vinyl chloride) (PVC) and ethylene propylene diene monomer (EPDM). Using the wind tunnel pressure records as source data and comparing the membrane responses of PVC with EPDM, SIGDERS developed a dynamic load cycle. With input from industries, building owners, and roofing associations, the developed load cycle has been generalized and extended to evaluate the ultimate strength of flexible membrane roofs. To validate the newly developed load cycle, several membrane roofing systems were investigated and then reported separately. The SIGDERS load cycle in a laboratory mimics failure modes similar to those observed in the field.

Form Finding and Analysis of Tension Structures by Dynamic Relaxation

The paper describes numerical procedures, based on the method of dynamic relaxation with kinetic damping, for the form finding, analysis and fabrication patterning of wide-span cable nets and grid shells, uniform or variably prestressed fabric membranes and battened membrane roofs. The historical development of the method is briefly reviewed and a full description is then given which accounts for cable or strut elements, membrane elements and spline beam elements. All of these elements are implemented in their natural stiffness form allowing for gross geometrical and material non-linearities, with automatic controls to ensure stablility and convergence of the method.

Dynamic Evaluation of Thermoplastic Roofing System for Wind Performance

The effects of wind on roofing systems are dynamic, because of wind's fluctuation in time and space. Therefore, a dynamic means of evaluating roofing systems is beneficial in identifying the component of the system that has the weakest resistance against wind uplift forces. The Special Interest Group for Dynamic Evaluation of Roofing Systems (SIGDERS) has commissioned a unique North American facility, which has been used to evaluate a mechanically fastened thermoplastic membrane roof system under three different test methods: the Factory Mutual FM-4470 static test standard, the European Union of Agreement (UEAtc) procedure, and the SIGDERS-developed dynamic load cycle. Comparison of the data from these tests shows that UEAtc and SIGDERS tests produce failure modes similar to those observed in the field. The SIGDERS load cycle is completed in much less time than the UEAtc procedure.