Ioannis Zisis

Large-Scale Experimentation Using the 12-Fan Wall of Wind to Assess and Mitigate Hurricane Wind and Rain Impacts on Buildings and Infrastructure Systems

AbstractEngineering research is undergoing dramatic changes with novel, large-scale research facilities being developed to help reduce the growing economic losses associated with natural disasters....

Wind-Induced Pressures on Patio Covers

A wind tunnel study has been carried out to assess wind loads on patio covers attached to low-rise buildings. A 1:100 geometric scale building and patio cover model was constructed and tested for open exposure conditions. The patio cover model was instrumented with pressure taps on both top and bottom surfaces, allowing the simultaneous measurement of wind pressure/suction on each side of the patio cover. The effect of building/patio height was considered by testing three different model configurations. Local surface and net wind pressure and force coefficients are presented for each model configuration. Correlation analysis was carried out to demonstrate how wind flow on the top and bottom of the patio cover affects the total wind load. The findings are also compared to the limited design guidelines derived by current building codes. Finally, recommendations for design wind load standards and codes of practice are made.

Wind-induced loads on the foundation of a low-rise building: full-scale and wind tunnel experimentation.

Structural monitoring of an instrumented experimental single-storey wood building provided important information regarding the behaviour and response of low-rise buildings subjected to wind loads. Foundation wind-induced loads were captured by twenty-seven three-dimensional load cells simultaneously with the envelope pressures and weather characteristics. The distribution of the total wind load to each wall is examined and normalized to the wind speed for each direction. The correlation between loads acting on different wall segments is also quantified in the form of participation factors. In parallel with full-scale findings, a scaled model of the experimental building and its surroundings is tested in a boundary layer wind tunnel. The detailed pressure distribution information for thirty-six wind angles of attack obtained through three different upstream terrain simulations is used to generate expected total uplift wind force. The findings are compared to data acquired directly from the foundation load cells located in the test house. The comparison revealed that in most cases wind tunnel values are within the range of the field results. Discrepancies are somewhat higher for wind tunnel tests conducted using the open/suburban terrain compared to the urban terrain simulation. The results are significant for the improvement of the wind tunnel testing and simulation procedures, for the development of code and standard provisions, as well as for the verification of the finite element numerical model of the test house.

Large-Scale Wind Tunnel Tests of Canopies Attached to Low-Rise Buildings

AbstractCanopies attached to residential and other buildings are predominantly lightweight structures with both surfaces exposed to the wind; therefore, their design is mostly governed by wind-induced loads. Currently, only limited information exists for the design of attached canopies against wind action in building codes and wind standards, which justifies the need to further investigate the wind effects on these structures to establish reliable design recommendations. The pressure distribution on the canopy surfaces, as well as the net component, is highly affected by the wind field around the canopy; therefore, its dimensions, location, and wind direction need to be considered. To investigate the effects of these parameters, in this study, a set of six 1:6 scaled model configurations of a low-rise building with different attached canopy dimensions and locations were tested at boundary-layer flow in the Wall of Wind Research Facility at Florida International University. The results are presented as loc...

Experimental Assessment of Wind Loads on Vinyl Wall Siding

Wind-induced damage to multi-layer building wall systems, such as systems with vinyl siding, is common, especially in hurricane-prone areas. Wind load distribution through these multi layered walls and the amount of load reduction due to pressure equalization is expressed through Pressure Equalization Factors (PEF). The ASTM D3679 standard suggests a PEF of 0.36, which means a 64% reduction in the net pressure on the siding. This paper presents results from an experimental study conducted on a low-rise building subjected to realistic wind loading conditions at the Wall of Wind (WOW) experimental facility at Florida International University (FIU). Results from area averaged mean and peak pressure coefficients indicated that a very small portion of the total wind load is carried by the vinyl siding. However, PEF’s were found to be much higher when individual taps were considered. For instance, PEFs ranged from 71% to 106% for the case of pressure coefficients with negative sign (suction) and 39% to 110% for the case of pressure coefficients with positive sign (pressure). When a combined set of taps was considered, PEFs ranged approximately from 50% to 80% for the case of ‘suction’ and 15% to 75% for ‘pressure’. Based on the 1 m2 of tributary area used in ASCE 7-10 Standard, results show that the net load on vinyl wall siding can be obtained by reducing the net design load for the entire wall assembly by 25% and 60% for suctions and pressures, respectively. However, a smaller tributary area (< 1 m2) can experience a local peak load that can induce damage to connections, especially in the case of relatively flexible wall coverings, with no or very little load sharing between connection points. Results indicate that for smaller areas (~ 0.2 m2) the allowable percentage reductions should not be more than 15% and 25% for suctions and pressures, respectively. This study shows that the suggested ASTM PEF of 0.36 may lead to the underestimation of loads for the design of details affected by local loads. However, further research is needed to consider more cases when developing adequate design load guidelines for vinyl wall sidings.

Wind Loading on Attached Canopies: Codification Study

AbstractA wind tunnel study was performed to examine wind loads on canopies attached to the walls of low-rise buildings. A model of a building with an attached canopy of geometric scale of 1∶100 was constructed and tested in a simulated open terrain exposure. The attached canopy model was equipped with pressure taps at both upper and lower surfaces to allow for simultaneous monitoring of wind pressures and evaluation of the overall load. A total of 63 different building/attached canopy configurations were tested for 28 wind directions. Pressure and correlation coefficients were generated to provide a better understanding of how the wind-loading patterns at upper and lower surfaces of the attached canopy contribute to the net loading effect. Current design guidelines and building code and standard provisions are assessed and compared with the experimental results of the present study. The influence of the geometry of each configuration on the experimental net pressure coefficients was assessed and recommen...

An Experimental Study on the Wind-Induced Response of Variable Message Signs

Variable Message Sign (VMS) systems are widely used in motorways to provide traffic information to motorists. Such systems are subjected to wind-induced structural vibration that can lead to damage due to fatigue. The limited information that is available on the safe wind design of VMS motivated a large scale testing that was conducted at the Wall of Wind (WOW) Experimental Facility at Florida International University (FIU). One of the objectives of the present study was to experimentally assess the wind-induced force coefficients on VMS of different geometries and utilize these results to provide improved design guidelines. A comprehensive range of VMS geometries were tested and mean normal and lateral force coefficients, in addition to the twisting moment coefficient and eccentricity ratio, were determined using the measured data for each model, for wind directions of 0o and 45o. The results confirmed that the mean drag coefficient on a prismatic VMS is smaller than the value of 1.7 suggested by American Association of State Highway and Transportation Officials (AASHTO). An alternative to this value is presented in the form of a design matrix with coefficients ranging from 0.98 to 1.28, depending on the aspect and depth ratio of the VMS. Furthermore, results indicated that the corner modification on a VMS with chamfered edges demonstrated a reduction in the drag coefficient compared to sharper edges. Finally, the dynamic loading effects were considered by evaluating the gust effect factor, using the ASCE 7 formulations, for various VMS weights and geometries. The findings revealed a wide range of possible gust effect factors, both above and below the current AASHTO specification of 1.14. Future research may include different geometries of VMS and a wider range of wind directions.

Wind loading and building exposure: Are we still on A, B, C?

Wind-induced pressures for the design of components and cladding, as well as primary structural systems of rigid buildings are calculated by using provisions of ASCE 7 [ASCE/SEI 7-05, 2006] or the National Building Code of Canada [NBCC 2005] depending on the building roof shape and location. In general, these pressures are the product of a dynamic velocity pressure (q), an exposure factor (Ce) and a gust pressure coefficient (CpCg). For simplicity, gust pressure coefficients used to originate from extreme values obtained in boundary layer wind tunnel experiments under conditions of open country upstream exposure and were reduced by directionality arguments by a factor of 0.80 or 0.85. Regardless of the actual exposure of the low building, the conservative assumption of open upstream exposure warranted very good results, at least in most, if not all, cases. The paper reviews some of the rationale behind the values provided in wind standards and codes of practice and compares experimentally measured vertical uplift and horizontal thrust coefficients on an end bay of gabled roof low buildings in suburban terrain roughness with Canadian, American and European corresponding provisions. Some recent work on the influence of exposure on wind loading of low buildings is also presented.

Wind Loads on Patio Covers

A common characteristic of North American low-rise residential buildings is the patio, a very active and eventful part of familys living space, with a number of activities to take place on it. For most home owners and unfortunately for many retailers, the patio cover is assumed to be a structure of minor importance which can be constructed without any special design. Patio covers are structures that have not fully been examined and evaluated by the present building codes. Very few studies have been carried out and it is questionable whether the performance of these structures is underestimated or, in the contrary, these are over-designed due to the lack of appropriate knowledge. Like every engineering problem, the dilemma vacillates between safety and cost. The current study presents the methodology and findings of a set of wind tunnel tests on a building model with a patio cover attached to it. Both the testing procedure and the data analysis are discussed and detailed results are presented. Although these structures are relatively simple, they occasionally form part of an existing building, subjected to same loads and accommodating the same number of people — or even more — as that building. Patio covers are often treated as a subsection of canopies. Sometimes they are even assumed to be an extension of the roof. In most cases though, patio covers cannot fall under any of the above categories. Canopies are used as covers and are not usually surrounded by walls. The specifications, use and geometry of canopy roofs though, defers significantly of those of patio covers. Moreover, patio covers are often at a lower level than that of the roof, thus they cannot be treated as roof extensions or overhangs. The only wind codes that clearly refer to attached patio covers are the International Building Code [IBC 2000], the International Residential Code [IRC 2000] and the Australian Wind Standard [AS/NZS 1170.2:2002]. Various other national building codes include wind provisions for canopy roofs or open buildings.

Field and Wind Tunnel Experiments to Evaluate Wind-Induced Cladding and Structural Loads on a Low Wooden Building

Full-scale studies, wind tunnel experiments and finite element modeling were used for the study of a wooden low-rise building subjected to wind loads. The conclusions of this study can be summarized as follows: 1) The pressure distribution comparison between the wind tunnel and the full-scale results shows good agreement. Some discrepancies can be justified by the high fluctuations of the wind direction in the full-scale records. The peak pressure coefficient comparison is characterized by higher discrepancies. 2) The wind tunnel / full-scale general agreement allows the use of wind tunnel data for numerical simulation. 3) The comparison between the full-scale load cell readings and the base reactions computed by the finite element analysis made in the form of force coefficients shows good agreement, as far as mean values are concerned. Higher values of forces have been found by using the measured pressure coefficients on the building envelope in comparison with those recorded directly by load cells placed on building foundation. 4) The experimental critical local pressures (suctions) tend to be higher (lower) in comparison to the code suggested values. Topography and surrounding structures effects can justify these discrepancies. 5) Field pressure data are, in some cases, significantly higher than the corresponding ASCE 7 values for components and cladding. The study confirms that full-scale structural monitoring is very difficult, time-consuming, yet necessary task. The ongoing collection of data will lead to more complete outcomes. Furthermore, roof load cells have been installed on the base of roof trusses and a more detailed picture of the structural response will be available in the near future.