A vibration study to protect the performance of sensitive laboratory equipment
The Louis A. Simpson and Kimberly K. Querrey Biomedical Research Center is a 600,000-square foot facility located in Northwestern University’s academic medical district. Designed to act as a central hub for the university’s medical research activities, upon completion the facility will feature nine laboratory floors of 40,000 square feet each, with more lab capacity being added over time. Among other functions, the Perkins + Will-designed Simpson Querrey Center will provide facilities for pediatric medical researchers studying childhood conditions that carry into adulthood, including sickle cell anemia, early metabolism of obesity, asthma, cystic fibrosis, and cardiovascular disease.
The footfalls of building occupants are often the most significant source of floor vibration on the upper floors of research and healthcare facilities. Movement in the floors of such facilities can cause discomfort to occupants and interfere with the performance of vibration-sensitive equipment. In order to ensure that their laboratories support effective clinical work and research, advanced facilities must make precise design adjustments to create low-vibration environments.
Our team was engaged to conduct a study that would quantify the vibration performance of a sensitive area of the Simpson Querrey Biomedical Research Center, to ensure that its floor structure would be sufficiently stiff and massive to resist the forces exerted by occupant traffic. The ultimate goal of this work was to provide optimal conditions for both people and advanced equipment.
Our process began with an activity we would sustain throughout the project: working closely with the structural engineers to understand the research functions and design imperatives of the spaces we were studying. After ensuring that we had the right contextual information to ground our technical analysis, we proceeded in two phases:
Setting vibration criteria.
To develop recommendations for vibration mitigation, we first needed to establish the levels of vibration that would be acceptable at various locations on the floor under study. The limits would vary from place to place according to intended usage and the sensitivity of the equipment at work there. For instance, the laboratory areas of the building were required to achieve a more stringent criterion that ensures the performance of microscopes to 100 X magnifications. Once we had a detailed map of the acceptable vibration criteria at each location, we could then proceed with our footfall analysis, determining whether anticipated vibrations fell within or outside of acceptable ranges.
Analyzing footfall effects.
As a person walks along a floor, the forces their footfalls exert depend primarily on the person’s weight and walking speed. To computationally predict footfall vibration effects, we used analytical methodologies grounded in published design parameters. We used nonlinear analysis software to develop a finite element model that represented the portion of the building under study, and then used that model to represent the dynamic behavior of the floor--to show how the floor would vibrate. The next step was to feed the output of the finite element model into our proprietary floor analysis software, FASTmapTM, which produced estimates of vibration responses at all locations across the area of the floor.
Once we had completed the full analysis, we illustrated the results using contour plots showing the vibration effects that would result from someone walking at each of the speeds we considered. These plots let us illustrate for the designers where the existing design might fail to achieve the required level of performance given the sensitivity of nearby equipment; these simple visualizations captured detailed and complex information.
Once we had identified specific sites of concern, we were able to propose specific changes to the floor framing--either the addition of structural members or increases in members’ stiffness. As we worked closely with the structural engineers to iteratively incorporate these adaptations into the design and verify their performance, the floor’s structural system evolved to achieve the appropriate vibration levels at all relevant walking speeds.
Our analysis helped the designers refine and move forward with their design, confident that it was capable of controlling the effects of footfalls at a range of speeds. This collaborative work ensured both the efficiency of the design, and its ability to perform at the level necessary for the Louis A. Simpson and Kimberly K. Querrey Biomedical Research Center to function as a top research facility. We were proud to contribute to this project, which had kept the research center’s important scientific function at the heart of its design considerations from the beginning. As Ralph Johnson, design director at Perkins+Will put it, the design was never a matter of “creating a sculpture and fitting in the [lab] plan. It’s all about the research and the labs, and that’s the generator of the idea. When you do that, the shape of the building starts to happen.”