A structural engineer is designing a steel-framed building in a hurricane-prone region. The building has a flat roof with a parapet. When calculating the wind pressure coefficients for the parapet, which of the following typically results in larger design pressures for the parapet itself, according to ASCE 7?
- AConsidering the parapet as a component and cladding element.
- BConsidering the parapet as part of the main wind force resisting system (MWFRS).
- CParapet height being greater than 3 feet.
- DParapet height being less than 3 feet.
Show answer & explanationAnswer & explanation
Correct answer: A. Considering the parapet as a component and cladding element.
According to ASCE 7, parapets are typically designed as components and cladding (C&C) elements. The C&C procedure (Chapter 30) generally yields significantly higher design pressures than designing it as part of the MWFRS (Chapter 28 or 29), especially in corners and edges, because C&C accounts for localized pressure variations and smaller tributary areas. Parapet height affects the specific C&C coefficients but the C&C approach itself results in larger design pressures for the parapet.
Why the other options are wrong
- B. Designing the parapet as part of the MWFRS (main wind force resisting system) would generally result in lower, more averaged pressures over larger areas, which is not conservative for the parapet itself.
- C. Similar to A, height is a factor within the C&C approach, not the approach itself.
- D. Parapet height influences the specific C&C coefficients but doesn't define the design approach that yields higher pressures.
Wind Design for Parapets (ASCE 7 C&C)
Parapets are typically designed as Components and Cladding (C&C) elements under ASCE 7, which applies localized, higher wind pressures to account for their exposed nature and smaller tributary areas.
- ASCE 7 Chapter 30 for C&C design.
- C&C pressures are generally higher than MWFRS pressures for the same element.
- Parapet height and location (edge/corner) are critical for C&C coefficients.
Memory trick: Wind design: MWFRS for the big picture, C&C for the details.