Vapour resistance of wind barrier tape: Laboratory measurements and hygrothermal performance implications

In the building industry, the interest into adhesive tape to achieve a more tight and robust building envelope has increased rapidly in recent years. With an increasing demand for energy efficiency in buildings, national building authorities are strengthening building requirements to mitigate and adapt to future climate impacts. This paper studies the water vapour permeability of adhesive tape for building purposes. A water vapour permeable wind barrier is essential to enable drying of the external side of the building envelope. Laboratory measurements have been conducted to evaluate how the drying conditions of the wind barrier layer are affected by the use of wind barrier tape. The results show that all the wind barrier tapes tested can be defined as significantly more vapour tight than the wind barrier itself. The wind barrier used as reference was found to have an sd-value of 0.03 m while tape ranged between 1.1 and 9.24 m. To ensure adequate drying and minimize the risk of moisture damages, the wind barrier layer should be vapour open. In an investigated construction project, the amount of tape constitutes 13% of the area of the building’s wind barrier. Further simulations need to be conducted to accurately determine the drying conditions and the following consequences.

Can collected hygrothermal data illustrate observed thermal problems of the façade? – A case study from Greenland

Buildings are more vulnerable to faults in design and construction, when exposed to the extreme Greenlandic climate, however, most new materials and designs have not been tested for Arctic conditions. Thus even minor errors can result in failures like mould growth, discomfort, and unnecessary heat loss. Rekognizing the source of the error can be difficult, yet valuable. But how can it be identified whether the error lies in the design or quality of workmanship? This paper describes a case study from Nuuk, Greenland, where a new mineral wool insulation system was implemented. Residents were complaining about draft and cold areas. An investigation revealed that inaccurate use of the system caused several problems. Simulations of the exterior wall performance were conducted and compared to measurements. This paper discusses whether these measurements and simulations support the identified issues, and therefore if this kind of general surveillance of exterior walls can be used to determine the total performance of an exterior wall. The paper concludes that the collected data can support the issues of the complaints, and that the fundamental reasons for the problems are the design, the precision of the casted concrete and the lack of a wind barrier protecting the insulation.

Microclimate measurements in ventilated air gaps – instrumentation and first results

To achieve energy efficient buildings, the requirements for air tightness in Norway were strengthened in the recent years. Thus, the use of tape for tightening connections and overlaps in the wind barrier and vapour barrier layer has become more and more common. Since these products are covered by a façade cladding and hence difficult to access, they need to maintain their performance level over many years, usually 25 to 30 years. To design test methods to ensure the performance of tapes and other products used in the ventilated air gap, more knowledge on the climatic conditions, especially temperature conditions, is needed. The recently finished ZEB Lab building in Trondheim, Norway, has been instrumented with thermocouples to monitor the temperature conditions in the air gap. This study presents the instrumentation set up and first findings from the start of the experiment in summer 2020. First results show temperature levels up to 76°C in the upper part of the roof construction.

Influences of Wind Barriers on the Train Running Safety on a Highway-Railway One-Story Bridge

In this study, the influences of wind barriers on the aerodynamic characteristics of trains (e.g. a CRH2 train) on a highway-railway one-story bridge were investigated by using wind pressure measurement tests, and a reduction factor of overturning moment coefficients was analyzed for trains under wind barriers. Subsequently, based on a joint simulation employing SIMPACK and ANSYS, a wind–train–track–bridge system coupled vibration model was established, and the safety and comfort indexes of trains on the bridge were studied under different wind barrier parameters. The results show that the mean wind pressures and fluctuating wind pressures on the trains’ surface decrease generally if wind barriers are used. As a result, the dynamic responses of the trains also decrease in the whole process of crossing the bridge. Of particular note, the rate of the wheel load reductions and lateral wheel-axle forces can change from unsafe states to relative safe states due to the wind barriers. The influence of the porosity of the wind barriers on the mean wind pressures and fluctuating wind pressures on the windward sides and near the top corner surfaces of the trains are significantly greater than the influence from the height of the wind barriers. Within a certain range, decreasing the wind barrier porosities and increasing the wind barrier heights will significantly reduce the safety and comfort index values of trains on the bridge. It is found that when the porosity of the wind barrier is 40%, the optimal height of the wind barrier is determined as approximately 3.5[Formula: see text]m. At this height, the trains on the bridges are safer and run more smoothly and comfortably. Besides, through the dynamic response analysis of the wind–train–track–bridge system, it is found that the installation of wind barriers in cases with high wind speeds (30[Formula: see text]m/s) may have an adverse effect on the vertical vibration of the train–track–bridge system.

Investigation of wind loads on bridge decks: an experimental and numerical analysis

Wind tunnel testing is very expensive, especially due to the handmade models and the cost of building and operation of wind tunnels. Therefore, numerical modelling such as computational fluid dynamics can be a more cost efficient solution and is seen to take the leading position in the future. The following research contains the validation of the Computational Fluid Dynamics tool VXFlow by comparing the numerical results with values in literature, the Eurocode and wind tunnel measurements. The study includes the analysis of static wind loads for different wind barrier geometries for the example of the Suderelbebrucke in Hamburg. VXFlow is found to give good results in a short computational time but tends to overpredict the drag coefficient. The application is aligned for investigations in the preliminary design of bridge decks and can be also used for wind tunnel validation. Keywords: Bridge deck, CFD tools, VXFlow, static wind loads, wind barrier

Investigation of wind loads on bridge decks: an experimental and numerical analysis

Wind tunnel testing is very expensive, especially due to the handmade models and the cost of building and operation of wind tunnels. Therefore, numerical modelling such as computational fluid dynamics can be a more cost efficient solution and is seen to take the leading position in the future. The following research contains the validation of the Computational Fluid Dynamics tool VXFlow by comparing the numerical results with values in literature, the Eurocode and wind tunnel measurements. The study includes the analysis of static wind loads for different wind barrier geometries for the example of the Suderelbebrucke in Hamburg. VXFlow is found to give good results in a short computational time but tends to overpredict the drag coefficient. The application is aligned for investigations in the preliminary design of bridge decks and can be also used for wind tunnel validation. Keywords: Bridge deck, CFD tools, VXFlow, static wind loads, wind barrier

Aerodynamic Response and Running Posture Analysis When the Train Passes a Crosswind Region on a Bridge

Trains running on a bridge face more significant safety risks. Based on the Unsteady Reynolds-Averaged Navier–Stokes turbulence model, a three-dimensional Computational Fluid Dynamics computational model of the train–bridge–wind barrier was proposed in this study to measure the transient aerodynamic load of the train. The transient aerodynamic load was input into the wind–train–bridge coupling dynamic system to perform dynamic analysis of running safety. Significant fluctuations in the aerodynamic coefficients were found when the train entered and exited the wind barrier due to the dramatic change in flow pattern. The maximum value of the derailment coefficient decreased with the height of wind barriers, which hardly affected the wheel load reduction rate. The 2 m high wind barrier had no evident influence on the running posture of a general high-speed train, while the 4 m high wind barrier was proven to have better protection. Over-protection was found with an even higher wind barrier.