Three calculators are on the website: chain link, welded wire mesh and expanded metal. TryourSkyCiv Free Wind Tool. The "Guide Specifications for Design of Metal Flagpoles" includes a map showing maximum wind speeds in the United States. << The formula to calculate the wind pressure on external surfaces is. This information also appears on the last page of the order process. Chain Link Fence: Line Post Calculator: Wind Analysis Method: Design Wind Loads - Solid Free Standing Walls: ASCE 7-10 Sec. Summary of the MWFRS Pressure Visualizations in the Pro and Ultimate versions. v b, 0, where v b is the basic wind velocity in m/s, c d i r is directional factor [-], c s e a s o n is seasonal factor [-], v b, 0 is basic fundamental value of wind velocity. Advertisement cookies are used to provide visitors with relevant ads and marketing campaigns. For this example, since the wind pressure on the windward side is parabolic in nature, we can simplify this load by assuming that uniform pressure is applied on walls between floor levels. ASCE 7 offers several methods to use for the wind pressure calculator on components and cladding. /Type/ExtGState \(G\) = gust effect factor\({C}_{p}\) =external pressure coefficient\(({GC}_{pi})\)= internal pressure coefficient\(q\)= velocity pressure, in psf, given by the formula: \(q = 0.00256{K}_{z}{K}_{zt}{K}_{d}V^2\) (3), \(q\) = \({q}_{h}\)for leeward walls, side walls, and roofs,evaluated at roof mean height, \(h\)\(q\)=\({q}_{z}\) for windward walls, evaluated at height,\(z\)\({q}_{i}\)=\({q}_{h}\)for negative internal pressure, \((-{GC}_{pi})\)evaluation and \({q}_{z}\)for positive internal pressure evaluation \((+{GC}_{pi})\)of partially enclosed buildings but can be taken as \({q}_{h}\)for conservative value.\({K}_{z}\) = velocity pressure coefficient\({K}_{zt}\)= topographic factor\({K}_{d}\)= wind directionality factor\(V\) = basic wind speed in mph. Read More Types of Loads on Beams [Full Guide]Continue, Load combination generator lets you automatically generate all possible load combinations needed in structural design., Read More Load Combination Generator [How-To Guide]Continue, Last updated: April 30th, 2023 In this blog post we will show how the characteristic snow load of a pitched roof is calculated according to Eurocode. For this example, since the wind pressure on the windward side is parabolic in nature, we can simplify this load by assuming that uniform pressure is applied on walls between floor levels. Forces on solid signs with openings shall be permitted to be multipled by the following reduction factor: e = Solidity Ratio = Solid Area / Gross Area. American Society of Civil Engineers. We also use third-party cookies that help us analyze and understand how you use this website. The document is reviewed and updated every 6 years, the most recent designation, ASCE/SEI 7-10. In this figure there are up to three different loading conditions that may need to be considered, Case A, B, and possibly C. In figure 29.3-1 it states that Case A and B must be considered for all S/h < 1, which basically covers the range of nearly all possiblities. Moreover, we will be using the Directional Procedure (Chapter 30 of ASCE 7-10) in solving the design wind pressures. Fortunately, MecaWind makes this process easy since its all handled automatically once the overhang is modelled. Lets work an example to illustrate this method. The total horizontal wind force is calculated from the force coefficient corresponding to the overall effect of the wind action on the structure. << Then the wind pressure coefficient will be as follows. This article describes the method followed for the calculation of wind loads on free standing walls. K. zt = 1.00. This cookie is set by GDPR Cookie Consent plugin. /ca 1 stream We like to explain it with examples. The Pro version makes the L-Shaped building easy, with just a few simple inputs the entire analysis is performed by the MecaWind software. External pressure coefficient with two values as shown in Tables 7 and 8 shall be checked for both cases. What is the Process of Designing a Footing Foundation? Identify the ice exposure level for your project: a. heavy ice storms, b. moderate icing c. no icing 3. This is shown in Table 26.6-1 of ASCE 7-10 as shown below in Figure 4. We did not include the walls on the roof top in the following picture due to better visualization. Does the program have a help manual?A help manual is provided with the program in the form of a pdf file. <>>> The recorded wind gust data is plotted on maps of the United States so one can see the expected wind gusts in a particular area. American Society of Civil Engineers. According to the parameters entered for the structure, certain methods will be available for use to the designer, and what criteria he is passing and failing for each of the C&C methods. Learn the basics of load combinations and how they are used in structural engineering to ensure the strength and safety of a building or structure. Figure 3. endobj There is even a default for solid fence which is described within ASCE/SEI 7-10 as any surface area having greater than 70% closure such as privacy slats and wind screens. A helpful tool in determining the exposure category is to view your potential site through a satellite image (Google Maps for example). ASD DESIGN LOAD COMBINATION CALCULATOR FOR CANOPY & PERGOLA DESIGNS For At-Grade Freestanding or Host Attached Canopies & Pergolas Using ASCE 7-16 BETA: Verify results with a design. In my many years of experience in the fence industry, I have visited countless sites and seen photos of fences bent anywhere from 30 degrees or more to just about flat to the ground. SkyCiv simplifies this procedure by just defining parameters. endstream Specific states that we know reference ASCE 7 include: California, Texas, Oklahoma, North Carolina, Hawaii. The following picture shows only the structural elements. To determine if further calculations of the topographic factor are required, see Section 26.8.1, if your site does not meet all of the conditions listed, then the topographic factor can be taken as 1.0. Moreover, the values shown in the table is based on the following formula: , are the values we would need in order to solve for the design wind pressures. endobj A wind load is a measure of the force exerted on a surface by the wind, which can be expressed as a force on the whole surface or a pressure (which is simply force per unit area). hbbd```b`` " - /BM/Normal ASCE 7-22 introduced a procedure for calculating Tornado wind loads on structures. used to calculate wind loads and/or wind pressures utilizing the ASCE 7 Standards & IBC Codes. Table 9. The positive and negative \(({GC}_{p}\)) for the roof can be approximated using the graph shown below, as part of Figure 30.4-2B: Figure 11. Table 6. Then, using exposure category B, a 3-foot fence height, and a maximum wind speed of 90 mph, get the wind load value q of 11.10 pounds per square inch from Table 14. /AIS false Florida Department of Business & Professional Regulation, 836 W. Jasper St., Broken Arrow, OK 74011, FBC 2020 (IBC 2018 with amendments) (Pro & Ultimate Only), FBC 2017 (IBC 2015 with amendments) (Pro & Ultimate Only). Copyright 2004-document.write(new Date().getFullYear()) | Meca Enterprises LLC, Wind loads on Signs and Freestanding walls is covered in. <>/ProcSet[/PDF/Text/ImageB/ImageC/ImageI] >>/MediaBox[ 0 0 612 792] /Contents 4 0 R/Group<>/Tabs/S/StructParents 0>> /SMask/None Will the wind blow down a fence? , for each surface using table 27.4-1 of ASCE 7-10. In addition, MecaWind Pro offers the ability to calculate the total reactions at the base of the structure. These calculations can be all be performed using SkyCivs Wind LoadSoftware for ASCE 7-10, 7-16, EN 1991, NBBC 2015, and AS 1170. , can be calculated using Table 27.3-1 of ASCE 7-10. 29.4 Fence Height (strength) Line Post Spacing S = Cf = B/h = B/h 0 to .05.05 to .1.1 to .2.2 to .5 . Common Types of Trusses in Structural Engineering, Truss Tutorial 1: Analysis and Calculation using Method of Joints, Truss Tutorial 2: Analysis and Calculation using Method of Sections, Truss Tutorial 3: Roof Truss Design Example, Calculating the Centroid of a Beam Section, Calculating the Statical/First Moment of Area, Calculating the Moment of Inertia of a Beam Section, Calculating Bending Stress of a Beam Section. Some sites allow you to enter inputs and then display the output. This is shown in Table 26.6-1 of ASCE 7-10 as shown below in Figure 4. Naturally, fence is subjected to wind gusts and therefore more and more contract specifications and codes require the fence to be designed to structurally meet the local wind load criteria. Please let us know here why this post is inappropriate. Some sites allow you to enter inputs and then display the output. For a height to width ratio h/d = 17.1m/20.2m = 0.85 which is < 1 and > 0.25 we get the following coefficients. Find an Internet site for calculating wind load on the type of permeable fence you selected. Wind Loads on Fence MVPs Wbruseski (Structural) (OP) 12 Mar 02 18:20 Any suggestions for designing wind load forces on a 6' aluminum fence (2x2 posts with (15) 5/8" square pickets)? Decide on the type of permeable fence you want. For a partially enclosed building with a gable roof, use Figure 27.4-1. 2023 Structural Basics - WordPress Theme by Kadence WP. The maximum wind speed there is 90 mph. Users would need to conduct manual calculations of this procedure in order to verify if the results are the same as those obtained from the software. Usually, velocity pressure coefficients at the mean roof height, \({K}_{h}\), and at each floor level, \({K}_{zi}\), are the values we would need in order to solve for the design wind pressures. This cookie is set by GDPR Cookie Consent plugin. Depending upon the specific analysis methods chosen, some of these roofs are not handled by ASCE 7. MecaWind Allows for calculations utilizing both the Main Wind force Resisting System (MWFRS) and Components and Cladding (C&C). Based upon the Florida Building Code used throughout Florida for design loads, which is published by the. How to Determine the Depreciation of a Fence. Or maybe a runaway motor vehicle! SkyCiv Engineering. Force on Post P' = 1/Cf1 = P' = P/Cf1 Cf1 = Steel Post Type Group 1A Grade 30 Group 1A Grade 50 Group IC Grade 50 The ASCE 7-10 provides a wind map where the corresponding basic wind speed of a location can be obtained from Figures 26.5-1A to 1C. Moreover, since the roof is a gable-style roof, the roof mean height can be taken as the average of roof eaves and apex elevation, which is 33 ft. Table 4. Using ASCE 7-98, I ran numbers using the Trussed Tower coefficient but Cf comes out to 3.02 which gives me a pressure of 30psf on the solid area. Location of calculated C&C pressures. SkyCiv released a free wind load calculator that has several code references including the ASCE 7-10 wind load procedure. Those wind area loads we can now visualize in a floor plan. Follow the instructions on the site to obtain the wind load. of notable changes to the wind load provisions. 4 0 obj Ess holds Bachelor of Science degrees in computer science and civil engineering. endobj In many locations, fencing must comply with local ordinances and/or homeowners' association rules. % One time I visited a tennis court site at Montauk Point on Long Island; unfortunately, the wind screens were left on during a storm and I couldnt believe my eyesone 120-foot side of the court fence was blown a full 60 feet to the other! This gives the user all of the flexibility to customize the graphic to suit the needs of the designer. Does your client also want you to check it out for a falling palm tree, or a projectile at 110 mph too? IMO, seems a bit ridiculous or a least impractical for such a condition. Out of these, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website. Fortunately, MecaWind makes the process of calculating wind loads on parapets relatively simple. This parameter depends on the height above ground level of the point where the wind pressure is considered, and the exposure category. Your email address will not be published. Note any other inputs required by the site. The wind direction shown in the aforementioned figures is along the length, L, of the building. The concrete was poured in a 12 inch in diameter concrete tube. Many fence manufacturers have such sites. , is 1.0. Directionality Factor. The exposure to be adopted should be the one that will yield the highest wind load from the said direction. For our example, the external pressure coefficients of each surface are shown in Tables 6 to 8. Wheatland, PA 16161 Can I get a fully functioning demo to try out the software?We offer a limited capability demos, but we do not offer a fully functioning demo. Figure 6. <> ASCE 7-10 Fig. /ca 1 Although there are a number of software that have wind load calculation already integrated into their design and analysis, only a few provide a detailed computation of this specific type of load. \(({GC}_{p}\)) can be determined for a multitude of roof types depicted in Figure 30.4-1 through Figure 30.4-7 and Figure 27.4-3 in Chapter 30 and Chapter 27 of ASCE 7-10, respectively. Figure 2. /CA 1 From 30.4-2B, the effective wind pressures for Zones 1, 2, and 3 can be determined. %PDF-1.4 /AIS false For our example, the external pressure coefficients of each surface are shown in Tables 6 to 8. There is a value for a surface area of 1 $ m^2$ and 10 $m^2$. I used a strong concrete mix in the ratio 3:2:2. Figure 8. >> Graphically see all Main Wind Force Resisting System (MWFRS) pressures on each surface. Figure 7. The 7 Types of Loads on Structures & Buildings (Practical Guide), Load Combination Generator [How-To Guide], Snow Load Calculation Of Pitched Roofs {Step-By-Step Guide}. You will be using the software in minutes after purchase. . Internal Pressure Coefficient, \(({GC}_{pi})\), from Table 26.11-1of ASCE 7-10. So lets apply the wind loads (for 10 $m^2$) on our building. 3 0 obj 1 0 obj Well, you are right, that is almost never the case for beams and slabs. An urban area with numerous closely spaced obstructions having the size of single-family dwellings or larger For all structures shown, terrain representative of surface roughness category b extends more than twenty times the height of the structure or 2600 ft, whichever is greater, in the upwind direction. The software helps navigate through those issues, but it still requires some familiarity with the ASCE 7 standard. 2. The designer must first work through a flowchart to determine if tornado loads must be considered, and then if Tornado loads must be considered there is a procedure for calculating those loads. The cookies is used to store the user consent for the cookies in the category "Necessary". Wheatland has made this very complicated structural design process easy by developing and including within their website an interactive Fence Post Wind Load Calculator. In most cases, including this example, they are the same. Enter the dimensions and porosity of the parapet, and then the wind pressure calculator will clearly display the results on all surfaces in the analysis output. , for our structure are both equal to 0.85 since the building is the main wind force resisting system and also has components and cladding attached to the structure. /OP true Those areas depend on where the wind comes from and can be seen in EN 1991-1-4 Table 7.1. Take note that a positive sign means that the pressure is acting towards the surface while a negative sign is away from the surface. (If you know other states that should be added, let us know and we will add it). Take a fence in a midwestern area as an example. In this article we are going to calculate the wind load on vertical elements like walls and facades according to EN 1991-1-4:2005. The answer is no, you must meet the criteria specified for each method in order to use that procedure. endstream endobj 581 0 obj <>/Metadata 8 0 R/Outlines 12 0 R/PageLayout/SinglePage/Pages 578 0 R/StructTreeRoot 15 0 R/Type/Catalog>> endobj 582 0 obj <>/Font<>>>/Rotate 0/StructParents 0/Type/Page>> endobj 583 0 obj <>stream /OPM 1 ASCE 7-16, 120 mph, Exp. The output results match exactly those which we have calculated here. In our ASCE 7-10 wind load example, design wind pressures for a large, three-story plant structure will be determined. Okay, now lets go back to the formula for the wind pressure for external surfaces and derive the values. The distance a from the edges can be calculated as the minimum of 10% of least horizontal dimension or 0.4h but not less than either 4% of least horizontal dimension or 3 ft. a : 10% of 64ft = 6.4 ft > 3ft0.4(33ft) = 13.2 ft 4% of 64ft = 2.56 fta = 6.4 ft. Based on Figure 30.4-1, the \(({GC}_{p}\))can be calculated for zones 4 and 5 based on the effective wind area. Here is a summary of the major differences between the Standard, Pro, and Ultimate versions. This calculation will be in accordance with IS 875-3:2015 wind load calculations. /SMask/None This parameter depends on the height above ground level of the point where the wind pressure is considered, and the exposure category. Take note that the definition of effective wind area in Chapter C26 of ASCE 7-10 states that: To better approximate the actual load distribution in such cases, the width of the effective wind area used to evaluate \(({GC}_{p}\). Table 8. For our example, since the location of the structure is in farmland in Cordova, Memphis, Tennessee, without any buildings taller than 30 ft, therefore the area is classified as Exposure C. A helpful tool in determining the exposure category is to view your potential site through a satellite image (Google Maps for example). Depending upon whether the overhang has a soffit or not determines when the building internal pressure must be taken into account. Case 1: Full wind loads in two perpendicular directions considered separately. Since the location of the structure is in flat farmland, we can assume that the topographic factor, \({K}_{zt}\), is 1.0. Wind pressure on external surfaces w e The formula to calculate the wind pressure on external surfaces is w e = q p c p e Where The coefficient c p e has 2 different values depending on the wind loaded area. You will also need to ensure that the fence erectors follow this design also. /Type/ExtGState External Pressure Coefficients for the walls and roof are calculated separately using the building parameters L, B, and h, which are defined in Note 7 of Figure 27.4-1. Site location (from Google Maps). /Type/ExtGState The wind load calculator enables you to compute the wind force on any structure. Design wind pressure for roof surfaces. SkyCivnow automates the wind speed calculations with a few parameters. With these values we can then calculate the forces: The forces are applied at the center of each of the spans. See the table below for a detailed summary for what is included in each version. FBC (Florida Building Code)Based upon the Florida Building Code used throughout Florida for design loads, which is published by the Florida Department of Business & Professional Regulation. Will work on physical PC but not virtual machines, Use by only one user at a time per license (additional seats can be added for simultaneous use), Install on unlimited multiple computers within company, Install at unlimited physical locations within company, Use by unlimited multiple users within company, Will work on physical PC or virtual machines. A hurricane with wind speed 35 m/s is acting on a 10 m2 wall. During her shorter career in engineering she wrote EPA operating permits. /ca 1 How to Determine the Reactions at the Supports? Close this window and log in. In this paper, the effect of non-normal wind loads on the performance of a porous fence was numerically investigated using computational fluid dynamics (CFD) techniques. By clicking Accept All, you consent to the use of ALL the cookies. This seems excessive, but what other coefficient should I use? Suburban residential area with mostly single-family dwellings Low-rise structures, less than 30 ft high, in the center of the photograph have sites designated as exposure b with surface roughness Category B terrain around the site for a distance greater than 1500 ft in any wind direction. Check out the article to read about the other 9 loads. From Equation (3), we can solve for the velocity pressure, \(q\) in PSF, at each elevation being considered. This guide is issued by the American National Standards Institute and the National Association of Architectural Metal Manufacturers and is available online. See Table 1.5-1 of ASCE 7-10 for more information about risk categories classification. I have used 12 foot 4 x 4 pressure treated posts set in 4 feet of concrete spaced 8 feet apart. This is no simple calculation, given the complexity of the pressure distributions on the roof. Figure 6. Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Others provide documents describing how to do the calculation. Note: Topography factors can automatically be calculated using SkyCiv Wind Design Software. will be found using Figure 30.4-1 for Zone 4 and 5 (the walls), and Figure 30.4-2B for Zone 1-3 (the roof). Examples of areas classified according to exposure category (Chapter C26 of ASCE 7-10). from the edges can be calculated as the minimum of 10% of least horizontal dimension or 0.4. but not less than either 4% of least horizontal dimension or 3 ft. Based on Figure 30.4-1, the \(({GC}_{p}\), can be calculated for zones 4 and 5 based on the effective wind area. Many fence manufacturers have such sites. We request that questions be limited to the use of the software, we can not provide interpretations as to how to apply the code to various situations. << Any structure which is not a building, is classified as an Other Structure by the standards. The customer will need to email [emailprotected]with their refund request with proof of purchase attached. The lever arm distance for each of the horizontal loads will be: One-third of the wall's height from the bottom of the base for the resultant of the active pressure distribution of the retained soil. endobj Those are basement walls and surrounded by soil. Additional design information includes: Section modulus, S = 159.9 in./ft (0.009 m/m) Net area, An = 36 in./ft (0.08 m/m) >> 4 0 obj The software adds the forces and moments about the origin of the building and summarizes those in the output. Learn what loads act on roofs, how to calculate them & how they are applied on the structure (Dead load, wind load + 3more). 29.4: Basic Wind Speed (ultimate) 135.00; MPH. The Main Wind Force Resisting System (MWFRS) is the assemblage of structural elements that are assigned to provide support and stability for the overall building or other structure. Calculated C&C pressures for purlins. The input file can be obtained here, and the output file here. For this example, since this is a plant structure, the structure is classified as Risk Category IV. According to EN 1991-1-4 7.2.2 (3) the wind loads can be reduced in the direction of the wind (Areas D and E) if they meet the following criteria. Familiarize yourself with the American Society of Civil Engineers, ASCE 7-10, wind load exposure categories, B, C and D listed in Table 1 below. Fig. Its difficult to keep up with all state requirements, but as far as we know all states are now following ASCE 7. The circles next to each method are either Red (Not valid) or Green (Valid) giving the user a quick overview of which methods can be used based on the structure parameters entered. Required fields are marked *. >> What is a Truss? Learn what loads act on structures and buildings and how to apply them (Dead, snow, live load + 4 more). But for smaller elements like cladding elements of the facade or fixings, $c_{pe.1}$ comes into play (EN 1991-1-4 7.2.1 Note 1). Since trusses are spaced at 26ft, hence, this will be the length of purlins. Read More The 7 Types of Loads on Structures & Buildings (Practical Guide)Continue. You can also purchase our EBook which is a great tool to explain wind load calculations and how to use the software to calculate wind loads. << In this section, we are going to demonstrate how to calculate the wind loads, by using an S3D warehouse model below: Figure 1. Wind Force / Side Load Calculator Our Wind Force / Side Load Calculator generates the wind load factor according to UBC 97 formula of Force = A x P. P = Wind pressure (lb/ft2) = Ce Cq Qs info here close ABOUT US SPECIES SIDING DECKING TIMBERS FENCING TRIM MORE. Take note that for other locations, you would need to interpolate the basic wind speed value between wind contours. The description of each exposure classification is detailed in Section 26.7.2 and 26.7.3 of ASCE 7-10. These cookies will be stored in your browser only with your consent. Calculated external pressure coefficients for roof surfaces (wind load along L). A picket fence is an example of a permeable fence. Clicking on these circles then gives the color coded summary of what criteria has been met. /Type/ExtGState Risk Category I Structure. , is 120 mph. This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Click Here to join Eng-Tips and talk with other members! This time, we will calculate the wind forces on facade elements for a precast concrete office building. Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a parts function at the center of their design considerations. From Chapter 30 of ASCE 7-10, design pressure for components and cladding shall be computed using the equation (30.4-1), shown below: \(p = {q}_{h}[({GC}_{p})-({GC}_{pi})]\) (6), \({q}_{h}\): velocity pressure evaluated at mean roof height, h (31.33 psf)\(({GC}_{pi}\)): internal pressure coefficient\(({GC}_{p}\)): external pressure coefficient. *Eng-Tips's functionality depends on members receiving e-mail. The positive and negative \(({GC}_{p}\)) for walls can be approximated using the graph shown below, as part of Figure 30.4-1: Figure 10. 2. The Pro & Ultimate Versions of MecaWind offers a template specifically for a wind load calculator on L-Shaped buildings. When wind hits either a solid or permeable fence, it puts a force on the fence known as wind load. Copyright 2004-document.write(new Date().getFullYear()) | Meca Enterprises LLC, Supports multiple standards & codes (ASCE 7, IBC, & FBC) (both current & historical), Supports Main Wind Force Resisting System (MWFRS), Supports Components and Cladding (C&C) (doors, windows, roofing, etc. Table 2. Use the Hoover Fence Company site in Reference 2 for the example. K. d Some sites allow you to enter inputs and then display the output. /Type/ExtGState Since the sign is not double-faced, we dont have the special conditions indicatedin Fig 29.3-1, Note 3. Internal Pressure Coefficient, \(({GC}_{pi})\), From these values, we can obtain the external pressure coefficients, \({C}_{p}\). Basic design wind speed, V, miles per hour and allowable stress design wind speed, Vasd, as determined in accordance with Section 1609.3.1. in PSF, at each elevation being considered. Once the design wind pressureis determined then the resultant forcefor each panel of fence is calculated by multiplying the design windpressure by the tributary area (fence post spacing and height). All Reports will utilize the referenced ASCE Standard. Table 10. \(q\)= velocity pressure, in psf, given by the formula: for leeward walls, side walls, and roofs,evaluated at roof mean height, \(h\), for windward walls, evaluated at height,\(z\), for negative internal pressure, \((-{GC}_{pi})\), for positive internal pressure evaluation \((+{GC}_{pi})\), \({K}_{z}\) = velocity pressure coefficient, The first thing to do in determining the design wind pressures is to classify the risk category of the structure which is based on the use or occupancy of the structure. need not be taken as less than one-third the length of the area. Hence, the effective wind area should be the maximum of: Effective wind area = 10ft*(2ft) or 10ft*(10/3 ft) = 20 sq.ft.
wind load on fence calculations
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