Towards a Better Understanding of the Fundamental Period of Metal Building Systems

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Virginia Tech


Metal buildings account for over 40% of low-rise construction in the US. Despite this, predictive fundamental period equations that were obtained empirically for mid-rise construction are used in seismic design. Analytical modeling of metal building frames implied that these equations significantly underpredict the period, which led to the development of a new predictive equation. However, experimental tests showed that these models may overestimate the measured period.

In this work, further tests were carried out in order to single out possible causes. Buildings were tested during different stages of construction to evaluate how non-structural elements could affect the behavior. Both planar and three-dimensional models were developed to determine if design assumptions are accurate for the purpose of estimating the period.

The results from tests showed that, unlike other single-story buildings, non-structural components seem to have negligible effect on the structural behavior. However, several buildings seemed to exhibit signs of fixed conditions at the column base. This assertion was corroborated by updating the analytical models. The two modeling approaches showed good agreement with each other as well, validating the use of planar models to predict the period.

Finally, new predictive equations are proposed that take into account the type of cladding, as it was found to be an important variable not previously considered. However, low mass participation ratios coupled with the stiffness provided by the secondary framing put the use of the equivalent lateral force procedure into question.



Metal Buildings, Seismic Design, Operational Modal Analysis, Equivalent Lateral Force, Non-Structural Elements