One of the first questions we receive from potential customers is how a Legacy building will perform in their area – whether the concern is snow, wind, seismic activity or another regional concern.
The answer is that Legacy buildings are engineered to approved, replicable engineering standards. Every aspect of the building design or potential pressure is calculated using generally accepted guidelines, and the building design is adjusted accordingly.
As permanent and semi-permanent buildings, fabric buildings should be held to the same engineering standards as metal buildings. You wouldn’t want to take unwarranted shortcuts with an important asset like a building – or risk the health and safety of the people in and around the building.
Before starting any building construction project, ensure your building designer has calculated each of the following considerations.
Snow places significant pressure on the building roof. The building’s ability to shed or withstand snow depends on the shape and angle of the roof, the building’s exposure, thermal factors, obstructions on the roof such as vents, and of course, the roof cladding.
Fabric has a smooth surface, which makes the snow slide off it more quickly. In snow locations, Legacy buildings have at least a 4/12 roof slope, which accelerates the slide off.
Some fabric building manufacturers incorporate reductions in roof snow load based on the snow slide characteristics of snow on fabric. However, applying the full snow load requirement as stated in building code ensures that the building is fully compliant and provides a high level of safety to the building design.
Wind exposure is dictated by the surface obstructions around the building. For example, buildings in densely built or wooded areas will have different wind exposure factors than buildings not protected by other buildings or trees.
Ensuring that the proper wind exposure category is used for the site location of the building is an important part of the design engineering for a building. Buildings that will be constantly exposed to strong winds will need appropriate bracing to protect each element of the structure.
Seismic ratings are determined by the occupancy rating of the building as well as the expected level of building movement during seismic events.
Tension fabric buildings are a great option for areas and applications with seismic concerns. The flexible nature of the fabric allows for some movement of the frames without damaging the cladding. Fabric panels are permanently welded together, so there is no risk of fasteners coming out of place or damaging the fabric.
Even with the advantages of fabric during seismic events, Legacy does not use the fabric as a lateral brace, but it is an additional safety feature that isn’t calculated in the building design.
The building’s use will determine collateral loads, which consist of anything added to the building frame. This includes systems like lighting, heating and cooling, conveyors and catwalks, overhead cranes, and fire suppression systems.
These loads are in addition to the required environmental loads, and the building designer will need to account for the total of all live and dead loads.
Supporting collateral loads is one area where rigid frame fabric buildings have a clear advantage over buildings using open web trusses. Trusses are fabricated in standard sizes, leaving you to choose between an under‐engineered truss or a more expensive over‐engineered truss.
Because trusses are more prone to movement under environmental loading such as wind or snow than rigid frame designs, this often leads to increased maintenance and downtime on systems with moving parts such as conveyors or overhead cranes.
Some collateral loads are not distributed evenly among the building frames – for example, stairs, jumbotrons, conveyors or cranes. Trusses typically can be designed to accommodate these point loads only where the web meets the cord. With rigid steel beams, these loads can be placed anywhere on the building or along the beam for truly custom placement.
Soil Type and Foundation
The type and quality of the soil beneath the building will have a significant impact on the foundation. Soils high in peat or clay may not have the strength to support a fully loaded building, and changing the soil type is prohibitively expensive.
The entity designing the building foundation should complete soil testing. An experienced building engineer will design a building foundation that will support the weight of the building on your site.
Fabric buildings are comparable to pre‐engineered metal buildings, and they have nearly identical foundation requirements. If a fabric building manufacturer is claiming that a permanent or semi‐permanent building does not require a foundation, ask them to back that up with accepted engineering calculations.
Occupancy rating is determined by the building’s use. A structure that is designed for regular use by the public will have a higher occupancy rating than a storage building. A higher occupancy rating allows for easier permitting of public events and keeps everyone inside the building safer in case of disaster.
One caveat to remember related to occupancy rating – it is much easier to get event permits in a building that is rated for higher occupancy. If you plan on ever holding public events, please make the investment in a higher‐occupancy building before construction begins. Retrofitting an existing building for a higher occupancy rating can be expensive and time‐consuming.
Fabric buildings are a significant investment. Ensuring that your building is compliant to all local building codes and requirements will help your investment last longer. Building longevity and safety is not one area to compromise.