Vibration FAQ

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How is an accelerogram reading applied to specific structural joints?

ANSWER: An acceleration record may be applied to individual nodes by first converting the reading into its equivalent displacement record. This process is described in the Displacement time-history record article. As described in the Manual multi-support excitation article, support restraints are then applied to the DOF which correlate with applied displacement. Results are generated through time-history analysis.

How is an AISC beam analysis performed for a noncomposite truss which supports a composite floor slab and beam system?

ANSWER: AISC beam vibration analysis is available for composite beams by using the composite-design post processor. To study the entire floor system or local systems, such as with a supporting truss assembly, uncheck the Include Lateral Mass Only option through Define > Mass Source, then generate out-of-plane vibration modes. Design may then proceed such that resultant behavior meets the guidelines or requirements of relevant publications or code.