Rain Loads Research Articles

Comparison of wind-driven rain load on building facades in the urban environment and open field: A case study on two buildings in Zurich, Switzerland

Wind-driven rain (WDR) is one of the largest moisture sources affecting the hygrothermal performance and durability of building envelopes. Accurate estimation of WDR loads on building facades as boundary condition is important for the hygrothermal analysis of building envelopes. In this work, computational fluid dynamics (CFD) simulations and semi-empirical models are used to compare WDR load on building facades in the urban environment and open field. The research focuses on two historical buildings in the city center of Zurich, Switzerland. There is a very large difference in terms of the local wind-flow fields around buildings in the urban environment and open field. Raindrop trajectories in the open field are more horizontal due to higher wind speeds around the building. In the urban environment, the wind speed is lower yielding droplets following trajectories that are more parallel to the facades. The building overhang is more effective at rain protection in the urban environment compared to the building in the open field due to a larger rain sheltering effect, since the rain trajectories are more parallel to the facades. There is a very large difference in WDR load and distribution on the facade of buildings in the urban environment and open field. WDR loads on buildings in the urban environment are much smaller than in the open field. When semi-empirical models are used for this case study, there is large uncertainty in the prediction and the predicted WDR load can be many times larger compared to the load predicted by CFD.

Representative meteorological data for long-term wind-driven rain obtained from Latin Hypercube Sampling – Application to impact analysis of climate change

Accurate estimation of wind-driven rain (WDR) load on building facades is of paramount importance for the assessment of moisture-induced damage risks. The response of the facade depends on the used meteorological data, which can show significant variation over time, especially considering climate change. In this study, a statistical approach based on a Latin Hypercube Sampling (LHS) is used to generate reduced samples, which accurately represent long-term meteorological conditions for WDR. Based on cumulative distribution functions, the generated samples with LHS are a subset of actual measured data, independent of the temporal information, and are clustered around values of highest frequency. Computational fluid dynamics (CFD) simulations of WDR are performed on a historical building located in Victoria, BC, Canada based on a previously validated methodology, determining the parts of facade receiving the highest WDR load. The sensitivity study shows that a sample size of 200 with LHS, corresponding to around 0.2% of the total measured data and 4.1% of the data during rainfall, is sufficient to replicate successfully the spatial distribution of WDR with a maximum discrepancy of 7%. The reduced samples can be easily modified to model various scenarios with respect to the climate change. The change in WDR load is presented for different scenarios in terms of rainfall intensity and wind speed as predicted by future climatic conditions. The results indicate that the future WDR load depends highly on the wind speed conditions, even when wind speed is kept constant and only rainfall intensity is varied.

The Spectral Approach of Love and Mindlin-Herrmann Theory in the Dynamical Simulations of the Tower-Cable Interactions under the Wind and Rain Loads

The paper presents the transmission line dynamic response considering tower-conductor cable coupling under wind and rain load is presented. The cable and the tower are modeled using the Spectral Element Method. The finite Element Method with different types of elements is used for verification. Excitations, such as wind and rain, are researched in the analysis and the results show the variation of the OTL displacements in each case. The tower modulates the dynamic cable response close to the coupling point and has a high influence in the response of the system. The application of the methodology based on spectral modeling, confirming good feasibility for the overhead transmission line, tower, and cable is the purpose of the study. The new approach of Love and Mindlin-Herrmann theory in the dynamical simulations and tower-cable interactions depending on the distance from the cable connection point is studied. Analysis of the wave number depending on the frequency is also shown.

Analisis Perkuatan Rangka Atap Baja pada Bangunan Gedung Heritage 1921 Menggunakan Software SAP 2000

Introduction: The roof truss construction used in the cultural heritage building in this analysis is a truss roof truss with 2L angle steel profiles (double elbow) 40.40, 50.50, 60.60, 70.70, IWF steel profile gording 150x150, and roof tile coverings, with a length ofroof 102 m, width 21.6 m, height 5 m, with a distance of 7.4 m and 4.1 m truss. The cultural heritage building discussed in this analysis is the roof, namely the horses. Method: The method used in this study is to collect data in the form of shop drawings. The purpose of the study was to identify the capability of the roof structure with the updated loading regulations RSNI 1727-2018. Results: This analysis uses the latest RSNI 1727-2018 loading regulations and the latest SNI 1729-2015 steel regulations, does not change the installed materials and existing shapes, and does not use earthquake and rain loads, only live/maintenance loads, heavy dead loads. roof coverings, ceilings and hangers, and compressed and suction wind loads. Conclusion: From the resultsof this analysis, it is assumed that the rusted steel profile has been replaced, there are two truss rods that need to be replaced with a 2L 80.80 double angled profile with initial data of a 70.70 2L profile. Analysis of the 3-dimensional roof structure with SAP2000 software by reviewing the dead load, the live load of workers according to the loading regulations of the RSNI 1727-2018, taking into account the compressed wind load of 75.82 m2, the suction wind load of 57.37 m2 according to the wind speed of 40 m/s

Hydrophobic Antiwetting of Aquatic UAVs: Static and Dynamic Experiment and Simulation

The adhesion of water to the surfaces of unmanned aerial vehicles (UAVs) adversely affects the function. The proposed UAVs will have underwater as well as flight capability, and these aquatic UAVs must shed water to resume flight. The efficient separation of the adhering water from aquatic-UAV surfaces is a challenging problem; we investigated the application of hydrophobic surfaces as a potential solution. Using aquatic-UAV models, one with hydrophilic surfaces and the other with superhydrophobic anisotropic textured surfaces, the antiwetting mechanism of the hydrophobic surfaces was investigated using a simulated-precipitation system and instrumentation to measure the load of the water adhering to the aquatic UAV, and to measure the impact energies. When the model was stationary (passive antiwetting), no adhesion occurred on the superhydrophobic surfaces, while continuous asymmetric thick liquid films were observed on the hydrophilic surfaces. The superhydrophobic surfaces reduced the rain loading by 87.5%. The vibration and movement of the model (dynamic antiwetting, simulating flight motions) accelerated the separation process and reduced the contact time. The observed results were augmented by the use of computational fluid dynamics with lattice Boltzmann methods (LBM) to analyze the particle traces inside the droplets, the liquid phase velocity-field and pressure-field strengths, and the backward bouncing behavior of the derived droplet group induced by the moving surface. The synergy between the superhydrophobic surfaces and the kinetic energy of the droplets promotes the breakup of drops, which avoids the significant lateral unbalance observed with hydrophilic surfaces during simulated flight.

DESIGN PHASE OF A CYLINDRICAL LONG-SPAN COAL SHED WITH STEEL ARCH SPACE-TRUSS STRUCTURE

<p class="Text">This paper discusses the structural design phase of a long-span coal shed structure in a 2x50 MW steam power plant. This study aims to share knowledge on how to design a long-span coal shed structure safely based on the design standards. The main structural system of the coal shed roof is a steel arch space-truss with 120 m of span and 31 m of height above supporting 12.5 m height of reinforced concrete columns. The superstructure contains a roof system and reinforced concrete system. The substructure system consists of a tie beam, pile cap, and bore pile. In the numerical model, all structural members were idealized as frame elements, except the pile cap that to be idealized as shell elements. Then, the soil springs were assigned to the bore pile element nodals with a 1 m interval to simulate the soil-structure interaction. The gravity loads due to dead loads, additional dead loads, live loads, rain loads, and lateral loads due to wind action and earthquakes to be considered. Furthermore, the structural analysis was conducted with non-linear geometric to simulate the large displacement effects and tension only element of the wind bracing. In addition, a simplified method to estimate the structural stability under lateral load was conducted. Based on the structural analysis and structural design, the coal shed structure could fulfill the safety criteria in terms of ultimate and serviceability limit based on the design code criteria. Furthermore, the non-linear geometry and stability issue should be considered with an appropriate structural analysis method.</p>

On extreme ground snow depth and ground snow load at Canadian sites

The roof snow load in the National Building Code of Canada (NBCC) is expressed as the sum of the snow and rain components. A probabilistic analysis of the components was carried out by using the recorded historical meteorological data. Probabilistic characterizations of the annual maximum ground snow depth SA, ground snow load SL, and snowpack bulk density were given. By considering the commonly adopted probabilistic models for SA, it was found that the use of the lognormal distribution, Gumbel distribution, and generalized extreme value distribution (GEVD) for SA is preferred for 46%, 35%, and 19% of the considered meteorological stations. A similar observation was made for SL. Snow hazard maps in terms of return period values of SA and SL were developed. Also, the hazard maps of (winter) rain load, SR, were developed. It was found that the correlation coefficient between SA and SR is negligible; the implication of this is discussed.

Response of 5 MW Floating Wind Turbines to Combined Action of Wind and Rain

For 5 MW floating wind turbines, the load response is significantly affected by wind and rain conditions. In order to reveal the relevant regularity of windblown rain and analyze the load response after being affected by the wind and rain, the rain phase is regarded as a continuous phase to be simulated. The self-compiled solver WARFoam (Wind and Rain Foam) is used to simulate the 5 MW wind turbines under wind and rain conditions. It is based on the Euler multiphase-model theory and the algorithm of unidirectional coupling of wind and rain. In this paper, the results of aerodynamic loads under WAR conditions are compared with the results of using the Lagrange particle-tracking model in order to prove that the Euler multiphase model can accurately calculate rain loads. On the basis of comparative verification, the convergence of the self-compiled solver is verified, which proves that the load-response analysis of the wind turbines under wind and rain conditions is accurate and efficient. The results show that rain has a significant impact on the load response of the wind turbines. Finally, the simulation results obtain the envelope diagram of the influence coefficient of rain-induced loads, which provides a quantitative reference standard for the calculation of the loads under wind and rain conditions.

Research on Calculation Method of Rain Load on Structures Based on Discrete Particle Model

With the frequent occurrence of extreme weather, the rain load of structures under high wind speeds accompanied by heavy rainfall conditions has become a hot issue for research. In this paper, based on the discrete particle model, the raindrop impact load correction formula is proposed. A rapid calculation method for the rain load of structures is formed through experimental verification. And the forecasting program is developed independently to complete the calculation of rain load per unit flat plate under different wind speed and rainfall intensity combination states. The rain load correction coefficient ΔCw is defined as the dimensionless coefficient of the rain load per unit area of the flat plate in a fully developed rain field driven by wind speed. The rain load is factored into the wind load calculation formula by way of the correction coefficient ΔCw to form the calculation formula for the rain load of structures. The results show that ΔCw has little correlation with wind speed but is closely related to rainfall intensity R. The calculation formula for ΔCw about rainfall intensity is fitted. When rainfall intensity R = 709.2 mm/h, ΔCw is approximately 22.3%. The research results in this paper provide theoretical and technical support for guiding the rapid calculation of rain load on structures.

Analysis of moisture risk in internally insulated masonry walls

Due to the need to preserve the façades of valuable historical buildings, internal thermal insulation is often the only measure for energy retrofitting for such class of buildings. However, internal thermal insulation may lead to moisture damage risks. In this study, the influence of seven parameters, namely water absorption coefficient and diffusion resistance of the exterior render, wind-driven rain load, brick type, masonry structure, thermal insulation type and thermal conductance (U-value), of the internally retrofitted wall on moisture risk is analyzed. Two parameters, water absorption coefficient and wind-driven rain load, have a much larger influence on moisture risk. By comparison, brick type and masonry structure have a very small influence on moisture risk. The influence of U-value on moisture risk is dependent on the insulation system. An artificial neural network (ANN) model is trained based on hygrothermal simulation results. The results predicted by the ANN model are very close to the hygrothermal simulation results. The ANN model enables fast and reliable evaluation of moisture risks. Towards guidelines, the development of an index which would consider jointly render properties and wind-driven rain loads could support a more accurate evaluation of moisture risk in internally insulated masonry walls.

Hygrothermal assessment of internally insulated historic solid masonry walls with focus on the thermal bridge due to internal partition walls

This study investigated the hygrothermal performance of five insulation systems for internal retrofitting purposes. Focus was on the hygrothermal performance near partition brick walls compared to the middle of the wall. The setup comprised two insulated reefer containers with controlled indoor climate, reconfigured with several holes containing solid masonry walls with interior embedded wooden elements, an internal brick partition wall and different internal insulation systems, with and without exterior hydrophobisation. Relative humidity and temperature were measured over five years in the masonry/insulation interface and near the interior surface, in the centre of the test field and near the partition wall. In addition, calibrated numerical simulations were performed for further investigation of the thermal bridge effect. Findings for the masonry/insulation interface showed higher temperatures and lower relative humidity near the partition wall in comparison with the central part of the wall. Near the interior surface, measurements showed only minor differences between the two locations. The relative effect of the thermal bridge was smaller in the case of a high driving rain load on the exterior surfaces. The numerical simulations showed that the hygrothermal conditions were affected further away from the partition wall than what could be measured in the experimental setup.

Impact of climate change on the wind-driven rain exposure of a historical building

Due to climate change, considering future rain event patterns and increased average temperatures, wind-driven rain exposure of buildings can increase. In order to assess the future damage risk related to moisture, it is essential to take the future wind-driven rain load into account. Computational fluid dynamics simulations of wind-driven rain are performed on a historical building located in Victoria, BC, Canada using the current and future weather data. The results show an increased wind-driven rain exposure of the building by up to 20%, especially in façade regions which are already exposed to a higher amount of rain.

Combined Use of Wind-Driven Rain Load and Potential Evaporation to Evaluate Moisture Damage Risk: Case Study on the Parliament Buildings in Ottawa, Canada

Parts of the building envelope that frequently receive high amounts of rain are usually exposed to a higher risk of deterioration due to moisture. Determination of such locations can thus help with the assessment of moisture-induced damage risks. This study performs computational fluid dynamics (CFD) simulations of wind-driven rain (WDR) on the Parliament buildings in Ottawa, Canada. Long-term time-varying wetting load due to WDR and potential evaporation are considered according to several years of meteorological data, and this cumulative assessment is proposed as a fast method to identify critical locations and periods. The results show that, on the Center Block of the Parliament buildings, the façades of lower towers facing east are the most exposed to WDR, together with the corners of the main tower. Periods of high WDR wetting load larger than the potential evaporation are observed, indicating that deposited rain may lead to moisture accumulation in the envelope. During these critical periods of up to several months, air temperature may repeatedly drop below freezing point, which poses a risk of freeze–thaw damage. First assessment on future freeze–thaw damage risks indicates an increase in such risks at moderate increases in temperature, but a lower risk is found for larger increases in temperature.

Deep renovation of an old single-family house including application of an water repellent agent – a case story

The 145 year old rural case building presented in this paper has undergone a deep renovation including internal insulation of the external walls to reduce the heat loss and improve the indoor thermal comfort. The internal insulation was a PUR-based insulation with channels of calcium silicate, experiencing to some extent capillary active behaviour. Sensors were installed between the existing wall and the internal insulation to monitor the development of hygrothermal conditions. The external façade was later hydrophobized with a water repellent agent to minimize the wind driven rain load. Measurements show that it takes time to get rid of the built-in moisture due to the application of internal insulation, however the moisture content expressed in relative humidity is slowly decreasing, although still high about two years after hydrophobizing the wall. Simulations show that the order of hydrophobizing the wall and applying internal insulation is important to promote drying of the wall.

Using hygrothermal simulations to define safe and robust energy retrofit solutions: interior insulation of a mountain hut with extreme climate conditions

Interior insulation is a crucial retrofit measure to improve the energy performance of historical building while preserving their exterior appearance. However, it affects the hygrothermal behaviour of the wall and for this reason it must be planned with a very detailed and careful approach. This becomes even more important when dealing with buildings that are subject to extreme climate conditions such as mountain huts. They are typically exposed to very cold temperatures for all year and to an elevated driving rain load. This paper presents the methodology followed to design the interior insulation intervention of a mountain hut located in Trentino-Alto Adige (Italy). The methodology is centred around the use of hygrothermal dynamical simulations at component level, but several other tools are used to identify the right input for these simulations: the analysis of monitoring data of nearby weather stations to define the exterior climate, simulations at the building level to calculate the interior climate and laboratory measurements to identify the correct material properties.

Feasibility of Vertical Rainwater Harvesting via In-situ Measurement of Wind-driven Rain Loads on Building Facades in a Tropical Climate

Rainwater is an alternative water resource to fulfill sustainable management of freshwater particularly in the regions receive abundant annual amounts of precipitation such as tropical Malaysia. To collect and store rainwater, rainwater harvesting system has been practiced since ancient from horizontal surfaces mostly rooftop of buildings in urban areas. Nowadays, this method in modern urban areas with tall buildings is considered inadequate and uneconomical because the ratio of facade surface areas is much higher than the ratio of roof surface areas. On the other hand, all rain has a horizontal velocity due to wind acting upon rain droplets which is called wind-driven rain (WDR). Growing tall buildings and the presence of WDR phenomenon make building façade surfaces the available promising surfaces to harvest substantial rainwater vertically and more efficiently. This article presents a one-year field measurement results that aims at quantifying the WDR loads impinged on the vertical facade areas of a pilot building located at the main campus of the University Malaya in Kuala Lumpur, Malaysia. Detailed descriptions of the gauge design, building, the measurements of on-site WDR, rainfall duration time, and weather data are presented. Records show that monsoon winds characteristics have significant influence on the WDR loads on the building facades compare to horizontal rainfall intensity. Finally, the collected in-situ data are exploited to validate data and determine WDR coefficient (γ) to estimate the amount of WDR on a building façade via an empirical WDR relationship. Results show the feasibility of each square meter of vertical façade area to supply 12% of non-potable or 4.9% of potable water-usage per capita per day.

An analysis of historical wind-driven rain loads for selected Canadian cities

The performance and durability of wall assemblies are greatly affected by the moisture load to which they may be subjected, in particular those arising from Wind-Driven Rain (WDR). Standard approaches for estimating such moisture loads assume 1% of the WDR load, whereas these loads have also been assessed from watertightness tests, although these assumed loads have been determined based on limited climate information. To more accurately estimate the moisture loads to which wall assemblies may be subjected over their service life, an analysis of historical WDR loads was completed for 11 cities across Canada. The magnitude, probability of occurrence of WDR loads in different cities and correlations between WDR related climate parameters, are discussed in this paper. Also, a novel WDR severity index is introduced, referred to as the Wind-Driven Rain Pressure Index, to permit quantifying the real-time and simultaneously occurring effects of WDR intensity and Driving Rain Wind Pressure (DRWP). To estimate the WDR intensity and DRWP with a specific probability of occurrence, an Extreme Value Analysis (EVA) was completed for a climate dataset of 31 years (1986–2016) using the Generalized Extreme Value and Gumbel distributions. • There is no correlation between the Wind-Driven Rain (WDR) load and concurrent Driving Rain Wind Pressure (DRWP). • A novel Wind-Driven Rain Pressure Index (WDRPI) is proposed. • Current watertightness test protocols are not reflecting most of the WDR conditions. • Gumbel distribution is a better option to generate the Intensity-Duration-Frequency curve for the WDR and WDRPI. • WDR conditions in different cities varies greatly.

Intelligent Prediction Method for Operation and Maintenance Safety of Prestressed Steel Structure Based on Digital Twin Technology

The operation and maintenance stage of the long-span prestressed steel structure is the core link of the whole life cycle. At present, there are few studies on the change law of safety risk in the whole process of operation and maintenance, especially the research on the analysis and prediction of the change law of safety risk in the whole process of structural operation and maintenance by effectively using the abundant monitoring data and relevant safety risk information in the operation and maintenance stage, which also affects the prestressed steel, which also affects the efficiency of judgment and control decision-making of operation and maintenance safety state of prestressed steel structure. Taking the spoke-type cable truss as an example, this paper proposes a new concept of integrating the digital twin model (DTM) with steel structure operation and maintenance safety. Through the combination of real physical space dimensions and digital virtual space dimensions, it is based on a hypothetical analysis model. In the above, a theoretical framework is proposed, and a case analysis of a prestressed steel structure is carried out from big data, and the feasibility of applying this method in the prestress loss and uneven rain and snow load conditions is evaluated. This method can provide guidance for operation and maintenance management and formulate strategies in time.

Mechanism and erosion resistance of internally cured concrete including super absorbent polymers against coupled effects of acid rain and fatigue load

This study explored a novel method for inhibiting the effects of acid rain erosion and fatigue loading in concrete by incorporating super absorbent polymers (SAP). Three different dosages and four particle sizes of SAP were considered to evaluate the erosion resistance to a simulated acid rain solution (pH = 3.0) for eight test cycles. The mass loss, compressive strength, flexural strength, and erosion depth as well as the results of X-ray diffraction (XRD) and the mercury intrusion porosimetry (MIP) testing were employed to explore the erosion behavior and mechanism of the internally cured concrete with SAPs. The results show that the coupled effects of acid rain and fatigue loading has a remarkable influence on the performance degradation of concrete. The erosion of concrete by acid rain was delayed and weakened with the addition of SAP, particularly when 0.10% SAP was added with a particle size of 100–120 mesh. Moreover, the SAP promoted hydration, which lessened the deterioration caused by pore deformation and improved the internal pore structure.

Understanding and modelling future wind-driven rain loads on building envelopes for Canada

Wind-driven rain (WDR) is the amount of rainfall that passes through a vertical plane due to its co-occurrence with wind, which can adversely impact the performance of building façades. Hygrothermal and durability analysis of façades require quantification of future WDR loads for a changing climate. This study evaluates projected changes to WDR loads across Canada for the end of century using regional climate model simulations for the Representative Concentration Pathway scenario 8.5. WDR loads are quantified in terms of omnidirectional and directional WDR amounts over periods of interest, which are relative indicators of WDR exposure and potential moisture content of absorbent surfaces, respectively. Furthermore, return levels of annual maximum WDR spell amounts, which are representative of the risk penetration through the façade, are also used to develop WDR risk category maps for Canada and specifically for 16 Canadian cities.Future projections suggest increases in WDR loads for Arctic Canada, due to increases in both rainfall and wind magnitudes, while for other regions with increased loads, it is mostly due to increases in rainfall. Results suggest a shift in the timing of the highest monthly WDR loads from summer to fall, which is suggestive of higher WDR penetration through wall systems, given the relatively low evaporation rate in fall compared to summer even in a warmer climate. Furthermore, the developed WDR risk category maps show changes to critical façade orientations with elevated risk in future climate. This information is crucial in the development of detailed guidelines to ensure climate-resilient buildings.