Floor vibration evaluations for medical facilities

Chad Himmel, PEChad Himmel, PEAssociate Engineer, Associate Engineer, JEAJEACOUSTICSCOUSTICS

EENGINEEREDNGINEERED VVIBRATIONIBRATION AACOUSTIC &COUSTIC & NNOISEOISE SSOLUTIONSOLUTIONS

Structural Vibration Disturbance

• Vibrating, rotating building systems equipment• Indoor foot traffic• Occupant activity• Occupant equipment• Vehicle traffic (speed bumps)• Building wind loads

Equipment causing structural vibration disturbance

• Centrifuges & shakers• Freezer & refrigerator

compressors• Glasswash & sterilization

equipment• MEP, HVAC and central

plant equipment– Fans– Chillers & pumps– Transformers

Structural Vibration Sensitivity

• Offices, patient rooms, meeting rooms, lecture halls• Operating rooms

and equipment

• Microscopes• Radiological imaging & research equipment• Magnetic resonance imaging equipment• Nanoscale research imaging equipment

Generic Criteria

• Colin G. Gordon, “Generic Criteria for Vibration-Sensitive Equipment”, Proceedings ofInternational Society for Optical Engineering (SPIE), Vol. 1619, San Jose, CA, November 4-6, 1991, pp. 71-85

MR Criteria ComparisonNarrow Band (Left) & Octave Band (Right) Approximated Conversions

Case #1Eye Clinic - Laser Surgery Room

• New construction• Pier & beam system• W12x22 beams• Steel channel joists @

24” o.c.• Plywood subfloor• “Bouncy”

Case #2Biomedical Research Facility

• Space planning• New building with

structure identical to existing building

• NMR spectroscopy equipment planned

• Centrifuges, shakers & ambient vibration

• Lab users reported occasional “streaks” in spectrometer imaging, but mostly “okay” performance

VC-C (approximated)

Mfr. Criteria

Case #3 - Proposed MRI Suite

• New platform above existing slab is proposed

• Platform stiffness can be “made to order”

• Existing floor slab cannot support weight of proposed MRI equipment

• Occupied space below precludes structural reinforcement from below

MRI #1 MRI #2Control Rooms

#1 #2

Structural FloorMRI Platform

Structure (above)

Pre-Design Evaluation Measurements

• Ambient vibration measurements on existing suspended structural floor slab:– 3 mutually perpendicular axes (X, Y & Z)– Narrow band (1/8 – 1.5 Hz)– 1/3 octave band– Long duration (3 minutes)

• Structural response to heel drop impact to determine apparent structural resonant frequency– Vertical axis only– Narrow band (1/8 – 1.5 Hz)– Short duration (10 seconds)

Existing ConditionAmbient Measurement Results

• Peak disturbance frequencies: 9.5, 15, 19, 23-24 and 29 Hz• Disturbance correlates with 19 Hz apparent resonance

Vibration Control Recommendations

Plan Section

• Control room bay dissimilar to magnet bay– Internal de-tuning to reduce operator disturbance

• Very stiff perimeter elements and beams– Minimize deflection and platform shape distortion

Noise Control Recommendations

• Partition Design– Perimeter framing decoupled from platform slab– Internal partitions not tied to building structure

Structural Design Implementation

• Structural engineer performed Murray “walker” analysis and dynamic analysis to confirm resonant frequency

• Joist spacing (MRI Rooms ≠ Control Rooms) and edge stiffening

Post-Construction Measurements

• Intent: confirm compliance with criteria• Scheduled before facility occupation and

equipment installation to allow for corrections, if necessary

• With unloaded, undamped floor• With weight-loaded simulation--weights stacked

on floor at magnet location

Vibration Measurement Results

• Amplitude was not reduced

• Peaks were shifted to meet specific criteria

Post-Occupancy Evaluation

• Equipmentmanufacturers’commissioning– vibration– noise

• Users’ evaluation– image quality– noise & vibration

Acknowledgements

• Baylor College of Medicine– Human Neuroimaging Lab: Read Montague– Facilities Design & Construction: Philip Dee

• Page Southerland Page, Architects: Scott Tucker, AIA

• OmniPLAN Architects: Key Kolb, AIA

• Walter P. Moore, Structural Engineers: Ram Gupta, PE

• Atkinson Engineering: Tim Atkinson, PE

• Siemens Medical Systems: David Draeger

• JEAcoustics: Jack Evans, PE and Daniel Kupersztoch