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Roof-mounted structures are increasingly in demand across the U.S., as there is often limited space in major metropolitan areas for fully developed tower sites. The key issue is providing adequate assurance to building owners that additional loads imposed by these structures can withstand the extra weight.
Importance of Design Considerations
There are various types of steel structures for antenna installations supported by building roof surfaces. For example, antennas can be mounted on pipes attached to the interior or exterior wall surface of the building. They can also be installed on self-standing penetrating or non-penetrating rooftop steel frame structures. In the event of design or analysis flaws, roof-mounted structures can cause significant damage or collapse during high wind events. These structural failures are likely to cause disruption in communications and can even lead to punctured roof membranes which could potentially cause fatalities.
Rooftop sled mount frame and tripod mount overturned as a result of not having enough CMU blocks
Current Code Applicability
ASCE and TIA codes do not provide specific guidelines for structural design of rooftop mounted steel structures. Typically, engineers and building officials look to the Appurtenance Mounting Systems section of TIA-222-H or ASCE 7 requirements for components and cladding guidance. Perhaps the most important step is to determine if the rooftop structure is a mount or individual structure.
Next, building officials should identify the appropriate code: ASCE or TIA. Typically, wall mount, penetrating or non-penetrating, sled mount and tripod mounts are classified as mount. These rooftops mounts are designed and analyzed as per Section 16 of TIA-222-H. Equipment platforms, triangular ballasted rooftop mount, custom built, and rooftop towers are classified as separate self-standing structures. These rooftop structures are designed and analyzed as per ASCE 7-16 chapter 29. Even though code applicability should be solely contingent upon each Engineer of Record’s analysis and judgement, sometimes jurisdiction and demand determine how the code is applied on structural analysis.
Telecommunication installations on rooftops vary from small pipe mounts to huge lattice tower structures. It is therefore important to properly classify the structures and provide the methodology for each classification. A comparative study between ASCE and TIA for roof top structures can provide more insights for following the necessary design processes. The key to any methodology should be sufficiently generalizing the results so that the worst-case scenarios are included in the TIA-222-H code analysis. Therefore, a descriptive section pertaining to roof mounted structures should be included in future TIA codes or Addendum II of the TIA-222-H code.