Rain Loads Research Articles

Geographical variability in hygrothermal simulation results of historical building envelopes with interior insulation in Belgium

Thermal retrofits of existing buildings offer a great potential to reduce Europe’s energy use and CO2 emissions. The impact of these retrofitting strategies on the risk for degradation in building envelopes is assessed through hygrothermal simulations. Due to the lack of long term climate data, hygrothermal simulations are performed for a certain location, and the results are generalised over a large region. However, this generalisation may not be valid, since the hygrothermal performance of building envelopes is highly influenced by local climate conditions. Therefore, we assessed the geographical variability on degradation risks in building envelopes. This paper presents the results of 34560 hygrothermal simulations of solid masonry walls, with and without interior insulation, and including a range of other parameter variations, for 20 synoptic weather stations across Belgium. Generally, the risk for degradation is higher at locations with a higher elevation above sea level. For Belgium, the elevation correlates well with the mean temperature (invers correlation), and the annual precipitation and wind-driven rain load. For a known wall orientation, the impact of interior insulation on the risk for freeze-thaw damage is most determined by the elevation above sea level. Also the mould index in uninsulated walls correlates best with the elevation. On the contrary, the brick type is more important than the location when considering wood decay of embedded beam heads in retrofitted walls. To conclude, the risk for degradation cannot be generalised, especially over areas with complex variations in orographic and climatological conditions.

Impact of upstream buildings on Wind-Driven Rain Loading: Refining Obstruction Factor in ISO semi-empirical model based on CFD

CFD is a valuable tool for assessing Wind-Driven Rain (WDR) loading, one of the most important environmental loads for façade design. The majority of previous studies on this topic have primarily concentrated on simple building configurations, i.e., stand-alone buildings. Hence, prior findings may not be applicable to consider the impact of upstream buildings in urban areas, which significantly alter wind flow field, consequently, change WDR loadings on downstream building facades compared to the stand-alone building. Part A: four different steady-state RANS models (i.e., standard k−ω, realizable k−ε, RNG k−ε, and standard k−ε) coupled with the Eulerian Multiphase (EM) technique (RANS-EM) are compared and implemented using OpenFOAM-7. These models are validated and verified based on wind-tunnel and field measurement data obtained from the literature for a six-story mid-rise residential building located in an urban area in Vancouver, Canada. The study considers 13 distinct rainfall events, for the test building with/without overhangs. All four RANS models are deemed suitable for modeling WDR in urban areas, while the steady-state standard k-ω RANS-EM approach without incorporating turbulent dispersion showing slightly better performance, thus utilized for the reminder of the study. Part B: a sensitivity analysis is presented on how the upstream buildings influence the WDR loading on a downstream building, denoted as Obstruction Factor. A comparison between the CFD and ISO semi-empirical model shows significant discrepancies, potentially reaching up to factors of 5. Thus, updated Obstruction Factors are suggested to enhance the ISO model for more accurate estimation of WDR loads.

Impact of semi-empirical methods implemented in heat, air, and moisture (HAM) models on predicted wind-driven rain (WDR) loads and hygrothermal responses

The amount, duration, and intensity of wind-driven rain (WDR) are instrumental to the durability and sustainability of building components. Semi-empirical methods implemented in heat, air, and moisture (HAM) models have proved to be a practical and efficient approach to quantify WDR exposure of building components and to examine WDR's influence on hygrothermal responses of building envelopes. However, specific assumptions and simplifications in the implementations can cause discrepancies in WDR calculations and hygrothermal responses. While measured datasets or computational fluid dynamics (CFD) predictions are employed to validate WDR calculations in previous studies, few address the further influence on hygrothermal responses, particularly confronted with full-scale experimental datasets. This paper starts with a general formulation of semi-empirical methods for WDR calculation and elaborates the ASHRAE and ISO standards implemented in two representative HAM models, WUFI and DELPHIN. In the first phase of simulations, two full-scale experimental datasets at Leuven (Belgium) and Eindhoven (the Netherlands) are reproduced by the two models to compare predicted WDR loads. In the second phase, the predicted and measured WDR loads are imposed as boundary conditions of different scenarios of one benchmark case to further analyze the influence on the hygrothermal responses. The results indicate that both models roughly reproduce the semi-empirical methods. Because of disparity in algorithms and implementations and differences in weather and building conditions, the simulated WDR loads show similar trends with deviations to the measured datasets. The predicted hygrothermal responses show deviations to different extents, presumably due to disparity in WDR load predictions during certain periods.

Development of Prefabricated Additional Insulation Elements for the Renovation of High-Rise Apartment Buildings

Prefabricated additional insulation elements have demonstrated success in renovating up to 5-storey apartment buildings. However, the unique challenges posed by high-rise buildings necessitate a closer examination of installation and long-term performance. In this study, we developed an additional insulation element specifically tailored for renovating high-rise apartment buildings and analysed its hygrothermal performance. To test the performance of the insulation elements, we installed a prototype and measured its performance at critical points along the external envelope. We calibrated a calculation model and applied building performance simulation software to explore various combinations of prefabricated elements. Our goal was to compare the associated risks and the key hygrothermal properties of these different material combinations within the insulation element. Critical points between the insulation layer and the wind barrier, as well as between the surface of the existing concrete panel wall and the vapour control layer of the additionally insulated exterior wall were analysed. The study's results indicate that the thermal resistance and water vapour permeability of the wind barrier layer, and the presence of an appropriate vapour control layer primarily influence the performance and moisture dry-out of a structure. Additionally, the study results indicate that the weather component has a higher impact than in lower buildings as the wind-driven rain loads are considerably higher in the upper parts of the high-rise buildings. The initial moisture (w = 110 kg/m3 at the height of the 9th storey and w = 117 kg/m3 at the height of the 16th storey) dry-out can last more than 3 years depending on the building type and materials used. This study underscores the importance of tailored solutions and vigilant moisture safety management in high-rise apartment building renovations, particularly when utilizing prefabricated additional insulation elements.

Precipitation Simulation and Dynamic Response of a Transmission Line Subject to Wind-Driven Rain during Super Typhoon Lekima

Typhoons bring great damages to transmission line systems located in coastal areas. Strong wind and extreme precipitation are the main sources of damaging effects. Transmission lines suffered from wind-driven rain exhibit more susceptibility to damage due to the coupled effect of wind and rainwater. This paper presents an integrated numerical simulation framework based on mesoscale WRF model, multiphase CFD model and FEM model to analyze the motions of a transmission line subjected to coupled wind and rain loads during typhoon events. A full-scale transmission line in Zhoushan Island is employed to demonstrate the effectiveness of the proposed framework by simulating typhoon evolution in terms of wind fields and rainfall, solving the coupled wind and rain fields around the conductor and predicting the dynamic responses of the transmission line during Super Typhoon Lekima in 2019. The results show that the horizontal displacements of the transmission line under the joint actions of wind and rain increase approximately 17–18% compared to those of wind loads only. It is important to consider the coupled effects of wind-driven rain on conductors in the design of transmission lines under typhoon conditions.

Safety Factor and Settlement Analysis of Borepile Foundation in Warmadewa Gianyar Hospital Building

Building structure planning must be distinct from foundation structure planning. The foundation plays an important role in transferring building loads to the ground. The Warmadewa Gianyar Hospital building consists of 5 floors with a building area of 8323. 471 m2 on a granular soil location where there are three layers of soil types, namely sandy silt soil, silty sand, and sand mixed with rock grains. The Borepile foundation is installed at a depth of 12 m with an N SPT value of 60. This building carries dead loads, live loads, rain loads, wind loads, and earthquake loads. This building will use a bore pile foundation by modeling bore pile piles in GEO5 software to obtain safety factor values and installed reinforcement. Based on the analysis results, the pile diameter used is 450 mm and has a length of 12 m. The analysis obtained the carrying capacity with a safety factor of 2.1> 2 and a maximum settlement of 4.77 mm.

Drying of an aerogel-based coating system in Swedish climates: Field tests and simulations

Aerogel-based coating mortars (ACM-systems) introduce new solutions for energy-retrofit of uninsulated building envelopes, preserving their characteristics while minimizing the material thickness. However, when introducing new solutions, the long-term durability needs to be investigated. The hygrothermal (heat and moisture) performance is one aspect that needs to be secured. The aim of this study is to investigate the hygrothermal performance, with specific focus on moisture drying, of an ACM-system for external applications in Swedish climates. A field test was conducted where an ACM-system with 40 mm of ACM was applied on the exterior of a brick masonry wall partition. The temperature and relative humidity in the wall were monitored for 15 months. Furthermore, numerical hygrothermal simulations were used to predict the early stage drying and long-term performance of the ACM-system in four Swedish climates. The field measurements showed that the built-in moisture dried out after approximately 6 months, after which the ACM-system followed the variations in the surrounding climate for the remaining period. The simulations predicted that the early stage drying time ranged from 134 to 336 days, depending on climate and time of application. Furthermore, the elevated relative humidity in the ACM due to rainwater absorption resulted in an average thermal conductivity of up to 9 % above the rated value. Consequently, mitigating water absorption at the exterior is crucial for enhancing the long-term thermal performance in high rain load scenarios.

CFD modeling of Wind-Driven Rain (WDR) on a mid-rise building in an urban area

Wind-Driven Rain (WDR) loading on building facades is a crucial factor for designing sustainable and climate-resilient buildings and preserving historical buildings. WDR loading on buildings has been studied previously but results for such a multi-parameter problem are not generally conclusive. Thus, the relevant provisions of ISO semi-empirical model cannot be applied with confidence for complex building configurations, such as those in urban areas given that the estimated WDR can be more than twice of the field measurements. This paper aims to evaluate the effectiveness of two WDR techniques, namely Lagrangian Particle Tracking (LPT) and Eulerian Multiphase (EM), combined with the steady-state standard k-ω RANS turbulence model (referred to as RANS-LPT and RANS-EM). The results obtained from the RANS-EM approach are compared with the RANS-LPT results reported in the literature for a six-story mid-rise residential building located in Vancouver, Canada. The study considers 13 distinct rainfall events, including stand-alone and urban area configurations with and without overhangs. The RANS-EM and RANS-LPT approaches are evaluated by comparing modeled wind and WDR against wind-tunnel and on-site WDR measurements, respectively. The study found that the RANS-EM requires less computational time and provides more accurate results for the test building situated in an urban area compared to the RANS-LPT.

Risk assessment and electrical control of high-permeability renewable energy photovoltaic system under extreme weather conditions

Abstract High-permeability photovoltaic (PV) systems are a key technical way to bring about new energy changes in electric power networks. Risk assessment and electrical regulation during extreme weather can make PV systems with high permeability work much more efficiently during severe weather. We establish an operational risk model for a high penetration rate PV system using the PV probability model, load parameter model, and probabilistic trend calculation model. Based on the results of the tidal current calculation, the risk assessment indexes of PV systems are constructed, including the voltage overrun risk index and branch circuit tidal current overrun risk index. The Monte Carlo simulation method using the Latin hypercubic sampling method is used to simulate the operational loads of PV systems under extreme weather conditions such as windy, rainy, and snowy conditions and to form a fault simulation set. Finally, we implement the QMC method to assess the risk of PV systems with high permeability and use the RBF neural network design to achieve automatic control of PV electrical equipment. When the weather is the same extreme, the risk of overrun at each node goes up with the number of nodes. When the weather is different, the risk of voltage overrun at each node under ice-covered load goes up by about half compared to rain load, and the risk of active overrun at each branch goes up by almost six times compared to rain load.

A Kriging-based probabilistic framework for multi-hazard performance assessment of transmission tower-line systems under coupled wind and rain loads

A Kriging-based probabilistic framework for multi-hazard performance assessment of transmission tower-line systems under coupled wind and rain loads

Assessment of wind-driven rain (WDR) on buildings in an urban area: comparison of different CFD frameworks

The study of Wind-Driven Rain (WDR) loading on building facades is essential to design more sustainable and climate-resilient buildings, as well as to prevent further damage to old and historical buildings. Both WDR loading on buildings and façade responses to impinging raindrops have been studied previously but results for such a multi-parameter problem are not generally conclusive. Thus, the relevant provisions of ISO semi-empirical model cannot be applied with confidence for complex building configurations, such as those in urban areas since the WDR prediction can be more than twice that of the experimental data. In this paper, the Eulerian Multiphase (ME) technique is coupled with the RANS model to simulate the WDR loading on a six-story building under steady rainfall event conditions. Wind and WDR results are compared with the available wind-tunnel and on-site field measurement results, respectively. The field measurements were carried out on a six-story mid-rise residential building, located in Vancouver, Canada. The results show that the Euler-Euler framework (RANS-EM) predicts wind and WDR in such an urban area configuration more rapidly and accurately compared to the more traditional Euler-Lagrange framework (RANS-LPT) for both stand-alone and urban area configurations.

Wind-driven rain load in Finland in present and future projected climates

The amount of wind-driven rain (WDR) has been shown to have a major effect on the different deterioration mechanisms of outdoor exposed structures. For example, in recent studies of Finnish existing concrete element buildings the amount of WDR has been shown to have strong correlation with the corrosion rate of reinforcements in carbonated concrete and the freeze-thaw damage of concrete. The latter can be related to all porous stone-based materials (e.g., bricks and mortars). In addition, the amount of WDR has a major effect on mould growth potential in different materials or structures sensitive to it. Thus, the effect of the amount of WDR in present climate has been studied comprehensively. In this study, the amount of WDR is calculated for a new 30-year period (1989-2018) presenting the present climate among with two future periods presenting 2050 and 2080 climates. In future climate projections, three different CMPI5 based scenarios are used: RCP2.6, RCP4.5 and RCP8.5. All calculations take into account the wind directions and they are made for four different locations presenting Finland: coastal area, southern Finland, inland and northern Finland (Lapland). Based on the results, the WDR load in the form of rain or sleet is increasing in all locations and from every direction regardless of the used scenario. The highest relative increase is in inland and Lapland, though, the load is still significantly higher in coastal and southern parts of Finland. With all the scenarios the WDR load is still focusing on southern directions, but it will be more evenly divided for other directions than in present climate. In addition, the WDR load is increasing during autumn and wintertime, i.e., during the periods when in the latitudes the drying conditions are weak because of the lack of solar radiation and the high-level relative humidity.

Modelling Rain Water Ingress in Hygrothermal Simulations

The hygrothermal response of building envelope components is often studied by means of numerical Heat-Air-Moisture (HAM) simulation models. There models aim to capture the most important physics that affect the transport and storage of heat and moisture due to climatic excitations. For a lot of climates and components the wind driven rain load is the main driver for moisture uptake in the construction, and as well, the trigger of important degradation phenomena e.g., freeze-thaw damage, mold growth, wood decay, corrosion, salt transport, algae growth. When building components are subjected to wind driven rain loads and driving rain wind pressures, capillary uptake in porous materials is typically considered in models, but rain water often infiltrates directly into different layers of the construction and these infiltrations may have a significant impact on the hygrothermal behavior. This paper offers a straightforward methodology to take the rain water management of building envelope components into account in hygrothermal simulations. For different types of façade systems a categorical approach is presented to simulate rain water ingress into the different layers. Next to that, also the drainage and retention is discussed in detail. Finally, this methodological approach is embedded in the SAMiRA-framework, which comprises 3 performance levels for each input parameter of the simulations: (i) Superior, (ii) Advanced, (iii) Minimum Requirement Approach. Hence, 3 different levels are offered to implement rainwater infiltration in hygrothermal simulations.

Back analysis of a building collapse under snow and rain loads in a Mediterranean area

Abstract. At the end of February 2018 the Mediterranean area of Montpellier in France was struck by a significant snowfall that turned into an intense rain event caused by an exceptional atmospheric situation. This rain-on-snow event produced pronounced damage to many buildings of different types. In this study, we report a detailed back analysis of the roof collapse of a large building, namely Irstea Cévennes. Attention is paid to the dynamics of the climatic event, on the one hand, and the mechanical response of the metal roof structure to different snow and rain loads, on the other hand. The former aspect relies on multiple sources of information that provide reliable estimates of snow heights in the area before the rain came into play and substantially modified the load on the roof. The latter aspect relies on detailed finite-element simulations of the mechanical behavior of the roof structure in order to assess the pressure due to snow and rain loading, which could theoretically lead to failure. By combining the two approaches, it is possible to reconstruct the most probable scenario for the roof failure before its full collapse. As an example of building behavior and vulnerability to an atypical rain-on-snow event in the Mediterranean area of France, this detailed case study provides useful key points to be considered in the future for a better mitigation of such events in non-mountainous areas.

ANALYSIS AND DESIGN REINFORCED CONCRETE CONSTRUCTION STRUCTURE OF 4 FLOOR HOTEL IN KUNINGAN

Planning for a 4-storey hotel in Kuningan is projected to support supporting facilities for the tourism sector in Kuningan Regency, supporting facilities like this are really needed by Kuningan Regency which has great potential in the tourism sector and is proven by the continuing increase in the number of tourists every year, with the development of Kuningan Regency and the increasingly widespread the construction of multi-storey buildings is needed planning in order to make efficient use of land. To support the availability of tourism support facilities, this research will examine the planning of hotel building structures based on SNI 2847-2019, SNI 1727-2020 and SNI 1726-2019 and calculate the budget plan for the structural work. Referring to these rules, the dimensions of the structural elements and the need for structural reinforcement can be produced that meet the rules and can also support the work force and loads received on a building including earthquake loads, wind loads and rain loads. The cost of building a 4-storey hotel building in this study is Rp. 26,712,400,000.00 (Twenty Six Billion Seven Hundred Twelve Million Four Hundred Thousand Rupiah), and the cost of building a one square meter building is Rp. 4,345,716.00 (Four million three hundred forty-five million seven hundred and sixteen thousand rupiah).

Research on the control limits of cable length errors of cable-strut tensile structures for prestressed relaxation under load effect

Cable-strut tensile structures (CSTS) are mainly composed of cables, and the cable length errors are bound to exist in the manufacturing of cables. The cable length errors have significant impacts on the mechanical properties of CSTS under load effects. Meanwhile, CSTS generally uses flexible membrane material as roofs, therefore cable length errors will result in the wrinkle of roofs and then cause the secondary accumulation effects of rain and snow load. Therefore, it is necessary to reasonably control the manufacturing errors of cable length. In order to solve the problem, the method of solving the control limits of cable length errors of CSTS is proposed due to the prestressed relaxation under load effects. The reliability index of CSTS is firstly given based on the reliability theory. Then, based on the reliability index and the criterion of prestress relaxation under load effect, the critical state equation and constraint inequality group are constructed, and the coefficient matrix of constraint inequality group is derived. Meanwhile, the nonlinear finite element method for solving the coefficient matrix of constraint inequality group is proposed. The procedure of solving the control limits of cable length errors of CSTS is given based on the proposed method. The crossed spoke cable-truss structure is taken as an example to verify the feasibility of the new method. The research contents provide an effective solution for controlling cable length errors of CSTS for prestressed relaxation under load effect.

Projected changes of wind-driven rain and moisture load in wall assemblies across Canada

The changing climate is affecting many aspects of the built environment. In respect to the wall assemblies of buildings, any change in the moisture load to the wall would influence its long-term moisture performance. Given that Wind-Driven Rain (WDR) is the primary source of the moisture load to the wall and that this load may also change as a result of changes to the climate in the future, it is expected then, that such changes will subsequently affect the moisture performance of wall assemblies. In this study, changes in moisture load of a vinyl-clad and a brick veneer-clad wall assemblies, located in 11 selected Canadian cities, subjected to climate data for two future projected climate scenarios, 2.0 °C (2034–2064) and 3.5 °C (2062–2092), as generated from the Canadian Regional Climate Model (CanRCM4), were assessed. Climatic parameters such as, WDR and Driving Rain Wind Pressure (DRWP), as well as their Intensity-Duration-Frequency (IDF) curves were analyzed and produced to determine boundary conditions for watertightness testing. The two analyzed wall assemblies were thereafter subjected to such tests, and the results of which were used to establish a two-step approach to estimate the moisture loads in these two wall assembly types based on hourly WDR load and hourly DRWP. Moisture loads of each wall assembly type during future projected climate scenarios were compared to those of the historical baseline periods. Increase in moisture load to both wall assembly types were found for most of cities analyzed in this study.

Review of Methods to Create Meteorological Data Suitable for Moisture Control Design by Hygrothermal Building Envelope Simulation

Hygrothermal simulations have become essential for sustainable and resilient building design because moisture is the major cause of problems in buildings. Appropriate meteorological input data are important to obtain meaningful simulation results. Therefore, this article reviews different methods to create Hygrothermal Reference Years (HRY) as severe or average climate inputs. The current standards define HRYs solely based on outdoor temperature, although moisture problems are caused by a combination of climate parameters, including driving rain and other loads. Therefore, there are also methods considering several impact parameters. The existing methods can be classified into two categories: construction-independent and construction-dependent methods. The former determines HRY based on a weather data analysis and is useful for large-scale parametric studies comprising many climatic parameters acting on buildings. The latter is based in addition to computer simulations to verify the HRY also in the context of specific construction types. It is a more comprehensive approach since the moisture responses of constructions are the decisive outcome for performance predictions. The advantages and disadvantages of the different methods are summarized and compared. Lastly, further research questions and simplifications aimed at practitioners are pointed out to arrive at reliable hygrothermal building performance predictions.

Interaction of open-top, short, cylindrical tank with wind-driven rain

Driving rain or wind-driven rain (WDR) is defined as rain, falling in an inclined manner due to the driving force of the wind, inflicting damage to the envelope of building, due to rain droplet impingement, hygrothermal effect, and, rain water ingress. When rain is driven by wind, especially high wind (during storm, cyclone, etc.), the rain droplet impact can increase. There is no availability of literatures on the interaction of shell structures with driving rain, which incurs damage to the thin wall of the tank through droplet impact. This scope is the main motivation behind the present study, which is focused on fluid–structure interaction analysis of an open-top, ground-supported, cylindrical tank with a slenderness ratio of 1.0, affected by wind driven rain. The thickness of the tank wall is varied, and, open terrain condition is considered. The study exhibits that the force coefficient (Cf) of WDR is higher between 0° to 53° peripheral position and decreasing upto 140° circumferential location. Maximum 28% increase of force coefficient of WDR noticed for 45° position in comparison to the wind force coefficient. Also, the top of the tank wall exhibits greater deformation and vulnerable under the effect of wind-driven rain load. Also, it is evident that 0° to 18°, and, 0° to 27° circumferential area exhibit higher deformation for radius: thickness (R/t) ratios 500, and 250, respectively. In case of R/t ratios 125, and 166.67, the higher deformation zone is distributed 0° to 15° and 77° to 82° peripherally. This deformation behaviour of the tank wall, shows that the open-top tanks need to be stiffened at the top to withstand the wind-driven rain force. The magnitude of deformation exhibits increments with the decrease in the thickness of wall of the tank. Maximum deformation is observed for lowest thickness of the tank wall.

Assessment of frost damage risk in a historic masonry wall due to climate change

Abstract. Historic masonry buildings are an integral part of human cultural heritage, and they need to be preserved for future generations. Brick is susceptible to frost damage which is common in regions with cold and humid climates. The frost damage on the masonry walls is accumulated over the years becoming more and more critical for the integrity of the historic buildings and it is also affected by climate change (CC). In the current research, the focus was placed on a coastal region in southern Norway with a significant number of historic masonry buildings. The frost damage risk of the masonry walls was assessed by using data from a climate reanalysis for the present conditions and from a climate model under past, present, and future conditions. Two climate-based (CB) indices accounting for the air temperature and one material response-based (MRB) index considering the temperature and moisture content inside a simulated masonry wall were used for the frost damage risk assessment. The inputs for the MRB index were calculated by heat, air, and moisture (HAM) transfer simulations. Within the HAM simulations, the indoor climate was in one case representative of an unconditioned building with air leakages and many openings, while in the second case it was representative of a small, conditioned room. The overall impact of CC was a decrease in the frost damage risk of the masonry walls. However, an increased frost damage risk was observed from the present to the future conditions according to the MRB index for the walls of small, conditioned rooms with higher driving rain load and lower solar radiation gains. The (i) number of freeze-thaw events, (ii) periods during which freeze-thaw events occur, and (iii) CC-related trends varied based on the considered index with the most explicit risk assessment being the MRB one. Moreover, the freeze-thaw events experienced by the masonry walls of unconditioned, leaky buildings were 20 times more than the ones for the small, conditioned rooms. Significant differences were observed between the results from the climate model and the climate reanalysis which were mainly linked to the underestimation of the air temperature and the overestimation of the precipitation by the climate model. The outputs of the MRB index were translated into certain damage categories while suggestions on improving the limitations of the current research were made.