A Performance-Based Design Approach for Balancing Risks and Construction Cost in Vibration-Sensitive Labs

Julia Graham, Motioneering Inc.

Specialized laboratory equipment often requires low-vibration environments for proper functionality. On elevated floors, occupant footfalls are often the most critical source of vibration. Individual footfall forces depend primarily on the weight of the walker and on his or her pace frequency. Traditional methods for predicting footfall-induced vibration recommend using the weight of an average person and a range of expected walking frequencies. However, no consideration is given to the probability of occurrence of each walking frequency. Enveloping the worst-case of all possible walking frequencies can result in an overly conservative design, especially in cases in which occasional exceedances of vibration criteria are tolerable.

This presentation will highlight a novel performance-based design approach in which known statistical distributions of various walker parameters (e.g., walker weight and pace frequency) are used to determine statistical representations of expected floor vibrations (e.g., vibration levels expected to be exceeded 10% of the time the floor experiences footfall excitation). This allows for a cost-effective and sustainable design in cases where occasional vibration-criteria exceedances are tolerable. This statistical representation also allows for risk-based decision making in which costs are weighed against vibration risks. Cases in which traditional versus the novel statistical approach might be most appropriate will be discussed.

Learning Objectives

• Understand how vibration can affect sensitive equipment;
• Understand how various parameters influence predictions of footfall vibration;
• Understand the trade-off between floor construction costs and vibration performance; and
• Understand the differences between traditional worst-case and risk-based decision making.

Biographies:

Julia is a Senior Engineer specializing in structural dynamics with Motioneering, a sister company to RWDI. With 12 years of experience, she has worked on more than 100 building projects providing vibration control for a wide range of projects from landmark residential towers to laboratories containing advanced vibration-sensitive equipment.

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