‍The ClearCalcs Wind Load Calculator for MWFRS (Main Wind-Force Resisting System) provides a streamlined and accurate solution for calculating wind loads in accordance with ASCE 7-16. This calculator helps structural engineers quickly determine wind pressures and forces acting on buildings, taking into account a wide range of building configurations and exposure conditions. It offers comprehensive analysis for different design scenarios, including partially enclosed, and enclosed buildings. The calculator determines the corner zone width, wind pressure for the basic load cases and provides the option to link loads to the other ClearCalcs calculators.

Project Defaults

You can select whether the calculator will use the project defaults in which you can set the building code used for your project, as well as wind, snow, seismic, deflection, and general criteria that will be used in your building. In particular if you provide the project address in the Project Details as well as theRisk category and Exposure Category, the basic wind speed will be automatically determined and will be used in your wind calculator. 

If you select to override project defaults, you must input the basic wind speed and exposure category

Key Properties

Under the key properties section, you can select the type of calculation for wind pressures (we will focus on MWFRS for this article), and see the properties set in the previous section.

Building Properties

This input allows you to define the roof type and its properties, taking into account that only flat and gable roof types are supported for the MWFRS calculations, selecting flat type allows you to define the height of the roof which is the height from the base of the building to the roof, and selecting gable allows you to define the roof pitch meaning how many inches the roof rises for every 12 inches in depth and roof top height from base of the building to the highest point of the roof. Also, you can define the width, length and enclosure type per the following descriptions:

• Partially Enclosed: A structure with large openings on one or more walls, creating internal pressure from wind (e.g., buildings with broken windows).
• Enclosed: A fully enclosed structure with no significant openings, maintaining controlled internal pressure (e.g., typical houses or office buildings)

A specific way to define the enclosure type can be found in the following table:

Terrain Properties

If you specified a location for your project you can select whether these properties are calculated automatically or you can specify custom ground elevation above sea level and if there is a hill or escarpment present. In this case you must select the hill shape as described in ASCE 7-16 Figure 26.8-1:

Then you have to input height of the hill or escarpment relative to ground (H), distance upwind of crest to mid-height of Feature (Lh) and Distance from Crest to Building Site (x)

Calculations and results

Once all of the site and wall properties have been inputted, we can look at our calculations and results. Wind load parameters and pressure coefficients are calculated as per ASCE 7-16, and include wind directionality and topographic factors, 3-s Gust-speed power law exponent, nominal height of the atmospheric boundary layer, ground elevation factor, velocity pressure and its exposure coefficient.

It also calculates the Internal pressure coefficient and the External pressure coefficient for the basic load cases.

The internal coefficient accounts for the pressure inside a structure, influenced by the size and location of openings (e.g., windows, doors) and the enclosure type. It reflects how wind pressure enters and affects the internal environment of the building.

The external coefficient represents the pressure exerted by the wind on the exterior surfaces of a structure, varying with factors like wind direction, surface shape, and zone (e.g., windward, leeward, roof). It defines how wind interacts with the outer surfaces of a building.

In the summary section you can see the corner zone width, the zones for each basic load case and the wind pressures for each zone. Wind pressure results are used to evaluate the structural performance of buildings and components under wind loads. These pressures, calculated for external and internal surfaces, are applied to walls, roofs, and other structural elements based on their zones. You can use our linking functionality in other calculators to add these pressures automatically. Watch our webinar on this here: https://www.youtube.com/watch?v=hN3AB3BE21c 

Lastly, the ASCE 7-16 imposes a minimum average wind pressure of 16 psf, so if the wind pressure in any zone is lower than that value, you should use the minimum value in your designs.