Membrane Roof Research Articles

Development of smart control system for leakage warning in compact roofs

Smart sensor technologies to monitor temperature and moisture conditions in building components can be used to give automatic warnings for abnormal high levels of moisture. Flat compact roofs are of particular interest in this context, especially due to their vulnerability to rain leakages through the roofing membrane. Installing moisture sensors in such roofs measuring relative humidity (RH) and free water may give an early warning of rain leakages or condensation owing to air leakages from indoors before damage occurs. One challenge is, however, that normal moisture redistribution in the insulation layer over the season or a day may give very high levels of RH in the top or bottom part of the insulation. A sensor system must be able to distinguish between these normal RH levels and leakage events. Together with a sensor technology and control system producer, a semi-quantitative system that defines typical or normal RH levels in the insulation layer of the roof during the year has been developed. To investigate the applicability of such a system, measurements from the compact roofs of two pilot buildings located in Norway have been analysed. The objective has been to identify connections between measured data, occurring climate conditions and seasonal variations. Results may be used to further develop and improve the algorithms of the leakage warning system.

Investigation on typhoon-induced aero-elastic response of membrane structures by wind tunnel test and numerical simulation

Extreme winds, such as typhoons, can lead to serious vibration and damage for flexible membrane roofs. An understanding of the aeroelastic behavior experienced by membrane structures during typhoons is therefore significant to allow well designed in practice. This paper investigates the aeroelastic response of umbrella shaped membrane structures under typhoon experimentally and numerically. The flexible scaled model is tested in typhoon field simulated in wind tunnel to investigate the aeroelastic characteristics varying with wind velocities and wind directions, including displacement response, non-Gaussian characteristics, frequency, modal shape and damping ratios et al. The full coupled fluid-structure interaction numerical model proposed is benchmarked and expanded in parameter discussions. The results indicate that non-Gaussian characteristics appear significant with positive skewness in pressure region and negative skewness in suction region. The probabilistic distribution proves leptokurtic type with kurtosis beyond three. The displacement response in statistics increases almost linearly with wind velocity while the non-Gaussian characteristics remain robust. The high-order mode shapes can be excited in typhoon, and their frequencies and damping ratios vary with wind velocities. The effects of both wind velocity and membrane pretension are proved to be more remarkable than rise-span ratio. This study can address the deficiency of current studies and provisions on the dynamic response of membrane structures in typhoons.

Overview of textile tensile surface structures with the largest uniform area

The innovative design of tensile surface structures is often a distinguishing feature of the entire construction project. The use of membranes gives buildings a sense of lightness and often a futuristic look. The construction materials used in the design of membrane roofing are, in addition to the steel cables tensioning and supporting the roof membrane, technical fabrics. This article focuses on describing structures made of continuous tensioned membranes spanning a rope or bar network with a total uniform area of more than 20,000 m2. Five structures with the largest uniform load-bearing area are described. The most commonly used yarn materials and coatings are described. The basic strength parameters of the most commonly used fabrics are summarized. The principles of shaping membrane surfaces were described. Attention was drawn to the difficulty of transferring laboratory test results to real objects. It is very likely that, for reasons of usability and manufacturing technology, continuous membrane surfaces with larger areas than described will no longer be designed.

Flow field characteristics and vibration responses of saddle-shaped membrane structures

Elastically mounted flexible membrane roofs exposed to flows are prone to vortex-induced vibrations and even aero-instability due to the strong fluid–structure interaction (FSI). This study is to investigate the FSI mechanism in the saddle-shaped membrane structure over a range of Reynolds numbers and wind directions in laminar flows, by bridging structural vibration responses and flow dynamics. The aeroelastic characteristics of membrane structures, including statistics of displacement responses, oscillation frequency, and oscillation damping ratios, were identified from the perspective of time and frequency domains. Simultaneously, the particle image velocimetry system was employed to visualize the flow features, including velocity vector, turbulence intensity, and vortex evolution in both space and time. The flow modes were further decomposed by proper orthogonal decomposition (POD) to capture the salient aspects of the flow. Three patterns of POD modes are identified, and the first mode plays the dominant role in POD modes. It showed that as the wind Reynolds number increases, the space between the shear layer and membrane surface would be narrowed, and resultantly the vortices turn out smaller in scale and closer in space. This trend leads to an increase in the frequency of vortex shedding and a stronger FSI effect. When the frequency of vortex shedding approaches the fundamental frequency of structures, the vibration of the membrane would be shifted from turbulent buffeting to vortex-induced resonance, featured with lock-in frequency, significant amplified displacement, and negative aerodynamic damping ratio.

Anomaly Analysis of PVC Roofing Membranes in Portugal

Anomaly Analysis of PVC Roofing Membranes in Portugal

Summer and winter performance evaluation of double layered PTFE dome with aerogel-glass wool thermal insulation- field experiments and numerical simulation

Achieving optimal thermal performance in large membrane-enclosed buildings presents a significant challenge. Aerogel mats offer potential for enhanced insulation, but their effectiveness in varying seasonal conditions is yet to be fully determined. The current study investigates the thermal performance of an enclosed dome with double-layered PTFE membrane roof integrated with aerogel-glass wool insulation mats. This research utilizes field experiments to assess indoor thermal comfort and numerical model to evaluate the effectiveness of the dome’s insulation capabilities during summer and winter conditions. The Aerogel integrated areas show a difference of 10.26/3.72 °C for summer/winter while that of 9.36/3.22 °C for glass wool-integrated areas. An online thermal comfort tool utilized maximum indoor temperature values during both seasons obtained from numerical results indicating that winter comfort falls within ASHRAE comfort range with PMV value −0.48 but summer conditions require enhancements. Additionally, the study assessed the insulation’s effectiveness using Maximum Reduction in Temperature (MRT), Decay Factor (DF), and Time Delay (TD) indicators. Results showed significant thermal lag, with peak temperature delays of up to 3.1 h in summer and 2.2 h in winter. Notable temperature differences between the dome’s inner and outer surfaces, alongside 28 % and 27 % DF reductions during summer and winter, respectively, demonstrated the roof insulation’s effectiveness. These findings support the use of both experimental and numerical methods to develop thermal management practices that improve sustainable building design, emphasizing occupant comfort and energy efficiency.

Serviceability analysis and feasibility study of ballasted rooftop PV system on existing concrete roof slab buildings

Solar Photovoltaic (PV) installation on existing structures became popular for the purpose of reducing carbon emission and improving energy efficiency of buildings. Ballasted PV systems which can impose an additional dead load are preferred by building owners as direct roof penetration method can pose a potential threat to the insulation, water proofing as well as the warranty of roof membranes. Ballasted PV systems have been questioned for structural capability, economic feasibility as well as sustainability stand points. This study focuses on determining an the optimal ballast number to resist uplift wind pressure. It additionally considers concrete roof slab serviceability with respect to long-term deflection, and provides a feasibility study of PV installation. Based on the results of the study, the ballasted PV system does not yield a significant influence on structural serviceability of building. The economic feasibility analysis considers the current level of incentives. Economically a ballasted PV system can be an attractive investment with approximate payback period of 7.6 years. Without incentives, the payback period is 24 years.

Estimating nonlinear wind-induced response of roof cable nets by aeroelastic experiments and ML modeling

The paper examines the structural engineering challenges related to the assessment of the wind-induced vertical displacements of lightweight, hyperbolic-paraboloid cable-supported membrane roofs. Analysis and comparisons are conducted using three distinct methods for calculating the roof vertical, out-of-plane displacements. Finite element method (FEM) analysis is employed using: (i) estimated static nodal forces obtained from wind pressure coefficients determined by aerodynamic wind tunnel tests on a rigid building model, and (ii) loads found from wind pressure coefficients, estimated through machine learning (ML) methods, and (iii) measured roof response found from aeroelastic wind tunnel tests on a flexible model. The study examines three different roof geometries (square, rectangular and circular) and two distinct membrane curvatures for each geometry. Furthermore, wind directionality (three mean-wind incidence angles) and Reynolds number effects (seven mean wind velocities) are studied. Comparisons show that the non-linear FEM analysis, based on estimated static wind loads, underestimates the roof displacements at the roof center, compared to the direct measurements on the aeroelastic model. The main contribution of the study consists of a novel application of ML models, and Artificial Neural Networks (ANNs) in particular, which are employed to correct roof displacement estimations, found by simplified aerodynamic test pressure measurements on rigid roof models. The goal is to better describe the complex fluid-structure interaction of the roof membranes, which can only be achieved by direct aeroelastic tests that are difficult to design and execute. Finally, the study demonstrates that ANNs can be used not only for the preliminary design of the full-scale structure but also for construction of wind tunnel scale models.

Experimental Study on Shear Strength of Roof–Snow Interfaces for Prediction of Roof Snow Sliding

The sliding of roof snow may result in surcharges of snow load on lower roofs or the injury of pedestrians on the ground. It is therefore of great significance to study the mechanism of roof snow sliding, such that prevention or control measures can be developed to manage the risk. Considering four commonly used roofing materials, glass, steel, membrane, and concrete, two types of experiments were carried out in this study to possibly reveal the influence of roofing materials on the shear strength of the roof–snow interface: one is the critical angle tests where the angle at which the snow starts to slide off from the roof is tested, and the other is the shearing tests which aim to test the shear strength of the roof–snow interfaces at specific temperatures. The results showed that the critical angle for roof snow sliding, as well as the shear strength of the roof–snow interface for the four considered roofing materials, show a U-shape trend with the increase in surface roughness and that the shear strength of the roof–snow surface ranges from 0.15 kPa to 2 kPa for the cases considered, while the strength reaches its maximum at certain temperatures near −5 °C for a specific roofing material and snow thickness. These findings could be a useful reference for future experimental or simulation studies on roof snow sliding.

Thermo-structural analysis and design for multi-functional membrane roofs of airport terminals

The utilization of large-span membrane structures in airport terminals has attracted considerable attention due to their excellent building aesthetics, reasonable structural behavior and multi-functional applications. Integrating structure and function is useful to improve thermal performance of such buildings. This study focuses on a scaled two-layer membrane roof in accordance with a newly-built aerogel-membrane airport roof and investigates the dynamic building thermal performance. The two-layer membrane roof is composed of an outer membrane layer as structural element, an air gap for ventilation and an inner membrane layer integrating aerogel mats. The effects of aerogel thickness, ventilation velocity and gap height are analyzed with multi-physics numerical tools. The structural behavior of the aerogel-membrane roof structure is examined in agreement with the building standards. The comparison between numerical and experimental results on solar irradiance is performed to demonstrate the reliability of numerical results under the typical environmental conditions. The thickness of the aerogel layer and the ventilation velocity are shown to have a significant effect while the air-gap height plays a minor role. A maximum temperature reduction of 4.7 °C demonstrates that using the proposed approach can improve building thermal performance. Moreover, temperature curves with small fluctuations indicate an efficient control of the indoor temperature. Therefore, the thermo-structural analysis method of the multi-functional membrane roofs can guarantee structural safety and facilitate building thermal performance control.

Fluid-structure interaction behaviors of tension membrane roofs by fully-coupled numerical simulation

This study aims to investigate fluid-structure interaction (FSI) behaviors of an enclosed-type tension membrane flat roof. The roof with rectangular shape is chosen as the object because of its relatively idealized geometry for FSI analysis, which is a simplified shape compared to typical membrane roofs. Fully-coupled numerical simulations are performed to obtain the wind induced vibration, aerodynamic forces and surrounding flow field of the tension membrane roof structure, where large-eddy simulation (LES) is used for solving of the flow field, non-linear membrane elements are adopted for the structure field and partitioned algorithm is applied for the coupling between the flow and membrane vibration. The numerical simulations are validated by the aero-elastic experimental results. The characteristics of the wind-induced displacements and aerodynamic forces of the tension membrane roof are investigated in both time and frequency domains. The energy transfer characteristics between wind and the vibrating roof are investigated based on the phase analysis between the generalized forces and displacements of the membrane roof. The underlying mechanism of the modal-jump phenomena that the vibration mode of the membrane jumps from the first mode to the second mode with increasing wind velocity, as well as the instability mechanism of the tension membrane roof, are revealed by flow visualizations and unsteady aerodynamic forces identifications. It is found that the aero-elastic instability of the flat membrane roof is a kind of vortex-induced vibration (VIV), where the modal-jump phenomena and unstable vibration of the membrane roof occur with the occurrence of negative aerodynamic damping, induced by the interaction between the vortex transporting and the roof motion.

Development of smart control system for leakage warning in compact roofs

Smart Sensor technologies to monitor temperature and moisture conditions in building components, can be used to give automatic warnings for abnormal high levels of moisture. Flat compact roofs are of particular interest, especially due to their vulnerability to rain leakages through the roofing membrane. Installing moisture sensors in such a roof measuring relative humidity (RH) or free water may give an early warning of rain leakages or condensation due to air leakages from indoors – before they start to get problematic. One challenge is, however, that normal moisture redistribution in the insulation layer over the season or day may give very high levels of RH in the top or bottom part of the insulation. The sensor system must be able to distinguish between these normal levels and leakage events. Together with a sensor technology and control system producer we have previously developed a semi-quantitative system that defines typical or normal RH levels in the insulation layer during the year. This system was based on hygrothermal simulations for various conditions, such as different exterior climate and levels of built-in moisture. This paper presents the preliminary findings from the further development of the system using real measurements from two pilot buildings located in Norway.

Transparent Sol-Gel-Based Coatings Reflecting Heat Radiation in the Near Infrared.

Thin, flat textile roofing offers negligible heat insulation. In warm areas, such roofing membranes are therefore equipped with metallized surfaces to reflect solar heat radiation, thus reducing the warming inside a textile building. Heat reflection effects achieved by metallic coatings are always accompanied by shading effects as the metals are non-transparent for visible light (VIS). Transparent conductive oxides (TCOs) are transparent for VIS and are able to reflect heat radiation in the infrared. TCOs are, e.g., widely used in the display industry. To achieve the perfect coatings needed for electronic devices, these are commonly applied using costly vacuum processes at high temperatures. Vacuum processes, on account of the high costs involved and high processing temperatures, are obstructive for an application involving textiles. Accepting that heat-reflecting textile membranes demand less perfect coatings, a wet chemical approach has been followed here when producing transparent heat-reflecting coatings. Commercially available TCOs were employed as colloidal dispersions or nanopowders to prepare sol-gel-based coating systems. Such coatings were applied to textile membranes as used for architectural textiles using simple coating techniques and at moderate curing temperatures not exceeding 130 °C. The coatings achieved about 90% transmission in the VIS spectrum and reduced near-infrared transmission (at about 2.5 µm) to nearly zero while reflecting up to 25% of that radiation. Up to 35% reflection has been realized in the far infrared, and emissivity values down to ε = 0.5777 have been measured.

Parametric investigation of the solar-thermal performance of tensile membrane roofs in hot-desert climates

Parametric investigation of the solar-thermal performance of tensile membrane roofs in hot-desert climates

Wind loading on commercial roof edge metals: A full-scale experimental study

Roof edge metal systems provide an effective interface between the roof of a building to its walls and are used to secure and protect the edge of the roof membrane. Previous studies show that damage involving roof systems mostly occurs because of their failure at perimeter edges under high winds. This study presents an effort to evaluate wind loads on these edge metal elements by conducting full-scale experiments at the NHERI Wall of Wind (WOW) Experimental Facility (EF) at Florida International University. In addition to full-scale aerodynamic and failure assessment test protocols, the experimental campaign, for the first time to the authors’ knowledge, consisted of investigating the effect of wind-induced vibrations on these dynamically sensitive systems. Pressure measurements were conducted at different layers of the edge metals systems by considering the most common installation practices in the industry. The results showed that these roofing elements experience high suctions due to near-parallel wind flows and are susceptible to significant vibration even at low wind speeds, which is a phenomenon not captured in current static pull testing. Moreover, peak pressure coefficients were also observed to increase with wind speeds due to increased dynamic contributions which may amplify the aerodynamic loads by more than about 25%. Furthermore, utilization of edge metal configurations with a higher degree of flexibility was observed to possibly reduce suction on roofing components and appurtenances.

Experimental and theoretical study on cooling performance of membrane roof with circulated water film

Membrane roofs are widely used in buildings for excellent daylight and visual effects. Nevertheless, excessive solar penetration results in an overheated indoor thermal environment. The experimental and theoretical study on the cooling performance of circulated water film technology on membrane roofs was conducted. The scale experiment results indicated that with circulated water film the membrane surface temperatures decreased rapidly to a level slightly above the water temperature, where the polyvinylidene fluoride (PVDF) and ethylene tetrafluoroethylene (ETFE) membranes were 0.4 and 2.4 °C higher than water temperature. While the indoor air temperature gradually decreased in instances where PVDF roofs were utilized, the application of ETFE roofs did not yield a significant decrease in temperature. Subsequently, we derived an analytical solution for the dynamic two-dimensional heat and mass transfer process of the water film flowing on the membrane with incident solar radiation, which was validated by experiment. The analysis of influential factors indicated that the temperature drop increased with absorbed solar radiation and outdoor dry-bulb temperature, and decreased with the ambient wet-bulb temperature. Conversely, the cooling performance exhibited minimal sensitivity to variations in water film thickness. The indoor operative temperature dropped by 0.5–0.8 °C in the membrane roofed atrium with water film. The water film effectively cools the indoor thermal environment with membrane roofs.

Irradiation Analysis of Tensile Membrane Structures for Building-Integrated Photovoltaics

A dynamic development in building-integrated photovoltaics (BIPVs) has been observed in recent years. One of the manifestations of this trend is the integration of photovoltaic cells with tensile membrane structures, including canopies. Such solutions bring mutual benefits—the roofs provide a potentially large area for the application of photovoltaic cells while contributing to the improvement of the energy efficiency of the building. However, what is lacking is thorough research on the most favourable photovoltaic cell exposure within these roofs. This paper investigates the optimal position of photovoltaic cells in terms of energy gains related to exposure to solar radiation. Hypar geometries were simulated as the most characteristic of tensile membrane roofs and, simultaneously, the least obvious in the research context. Simulations were performed for 54 roof samples with the following geometric variables: roof height (1.0, 3.0 m) and membrane prestress (1:3, 1:1, 3:1). The research was conducted for three roof orientations defined by azimuth angles of 0, 22.5, and 45 degrees and three geographic locations, Oslo, Vienna, and Lisbon, representing Northern, Central, and Southern Europe, respectively. The Sofistik and Rhino + Ladybug software were used to create models and simulations. The study results show significant differences in the roof irradiation and, consequently, the optimal location of BIPVs depending on the above variables. Generally, it is the curvature that is the most important variable-less curved roofs are more irradiated and thus more suitable for BIPVs. Prestress and the azimuth angle are of lesser significance, but defining the optimal use of a BIPV depends on the adopted scenario regarding the percentage of membrane coverage with PVs—other recommendations concern the strategy of total or partial roof coverage with PV cells. The difference between optimally and incorrectly designed roofs may amount to a 50% electricity gain from PV cells.

Forensic Analysis of Roof Deterioration Due to Condensation

Corrosion of the structural steel roof deck of large warehouses resulted in several invasive forensic investigations to determine the cause and mechanism of the corrosion. The warehouse roof investigation presented in this paper is one of many similar warehouses located near the Gulf of Mexico and along the Southern Atlantic Seaboard experiencing corroded roof decks when constructed using fiberboard roof insulation made from sugarcane fiber called bagasse. Consensus exists among individuals studying this phenomenon that the fiberboard became saturated with water, which dissolved formic and acetic acid from the fiberboard. The steel deck corroded when it came in contact with the acidic solution. There was little consensus regarding the mechanism by which water intruded into the roof assembly. Invasive investigation of the low-slope roofs of buildings with various types of insulation (including bagasse fiberboard) and observation of physical commonalities between the instances led to the following conclusion: Water in the roof assemblies did not result from leaks through a compromised roof membrane but rather from humid air infiltrating the roof assembly and condensing on the underside of the roof membrane.

Vapor-permeable PP membranes – Tensile properties and surface structure

This paper presents the results of identification strength tests of selected vapor-permeable membranes together with an evaluation of their surface structure before and after failure. Polypropylene three-layered membranes of randomly chosen Polish manufacturer – windproof membrane (MB) and roof membrane (MG) – were chosen for research. Both membranes are made of two layers of polypropylene fabrics, between which there is a functional layer (film), ensuring proper operation of the product. The results obtained for tensile parameters and resistance to tearing (nail shank) are within by the manufacturer’s declared values (MDV). Tensile strength of membrane MB was equal 275 ± 11 N/50 mm in machine direction (MD) and 154 ± 5 N/50 mm in transverse direction (TD) while membrane MG characterized by tensile strength 209 ± 9 N/50 mm in MD and 126 ± 4 N/50 mm in TD. Resistance to tearing was more repeatable for membrane MG – the standard deviation did not exceed 3 N. Although the resistance to tearing of membrane MB was more than three times higher, the standard deviation was 17 N on average. Resistance to tearing of membrane MB was equal 212 ± 21 N in MD and 293 ± 14 N in TD, while membrane MG characterized by resistance to tearing 66 ± 3 N in MD and 62 ± 4 N in TD. Unfortunety, in the case of the membrane MG the mass per unit area was not within the MDV range. It was equal 90 g m−2 and together with the expanded uncertainty ± 2 %, was completely outside the lower tolerance limit. Structure analysis allowed to conclude that digital images are sufficient to observe the changes occurring in the microstructure of membranes and to make a preliminary assessment of their structure before or after failure. The results presented in paper emphasize the importance of maintaining the usable features declared by manufacturers, especially mass per unit area, and of continuously monitoring the quality of materials with use of relatively simple tests at the stage of factory production control (FPC).

Sensitivity analysis and practical application of an automatic snow-melting membrane roof

In recent decades, numerous membrane structures have been built in the cold regions of China. Nevertheless, uneven snow distribution and snow sliding from the edge of roofs cause frequent collapsing, which threatens people's lives and properties. To prevent the collapsing of membrane structures, we present an automatic snow-melting membrane roof based on an electrical–thermal system (ASMR-ETS) in this paper. ASMR-ETS is environmentally friendly, clean, and can be used for eliminating snow that accumulates on membrane roofs. The most important task in designing ASMR-ETS is the determination of its feasibility. A thermal simulation method for the snow-melting process is described in this paper. The surface temperature was obtained using the commercial software ABAQUS. The applicability and rationality of the thermal simulation were verified via snow-melting experiments. The heating wire spacing and heating wire power were set as heating wire parameters. The wind velocity, solar irradiation, ambient temperature, and snow thickness were selected to be the climatic conditions. The surface temperature of ASMR-ETS was simulated, and the snow-melting performance (snow-free area ratio and coefficient of variation of temperature) was analyzed for different heating wire parameters and climatic conditions. According to the simulation results, increasing the wind velocity and snow thickness decreases the snow-free area ratio and improves the coefficient of variation of temperature, whereas solar irradiation and ambient temperature showed an opposite effect. Furthermore, the snow-melting performance of the membrane structure was studied, and different layout schemes of the heating wire were considered. The results show that ASMR-ETS is practical and can therefore be used to clear snow on membrane structures.