huangyhg

vibrations and laboratory equipment
hello all,
let me give you some context...
i am in the design of a two story building that is to be used as a laboratory for a fairly large university in the midwest us. we went through 3 months of planning and design development, even a large piece of the final design. two weeks left in the design [2 wks until 100% cd's], the project was halted because the early budget numbers were coming in high. anyway, during a value engineering stage we found out what kind of equipment would be put into the lab. we had asked early on what equipment was to be used, but since they didn't know who would get the lab space, they said to design for something reasonable - we read that to be economical. we wrote the client a letter, specifically detailing the design criteria, including vibration criteria we would use.
our original design was for a composite slab on steel beams. [5 inches of normal wt conc on 2" deck]. our criteria called for a building using dr. murry's analysis of the floor for vibrations (steel design guide). we would design a floor for office occupancy, but have a modal damping of 0.2 (normal office can easily justify 0.3 or better). the client accepted this, but i have to say, i don't think they knew what they were looking at. we asked them to get a lab consultant to look at the criteria - to give us a better idea of what to design for. they hired someone, but not a structural consultant - an interior lab layout person.
okay now my dilema:
the type of equipment that they are going to use include mass spectrometers, ultraviolet and infrared spectrometers, and a laser lab. (also, the client, who is not the university but will lease the univ. the building wants future flexibility to move the lab's around.)
according the dr murry's research (along with dr unger and others) says mass spectrometers need to be designed for a maximum velocity of 250 micro-inches/second. when i use my vibration design software i require a 22 inch thick conrete floor, with w40x183 beams at 16 ft on center. i tried to optimize the mass/stiffness interaction - and this is the best combination i get.
and finally, my question:
i don't work as a scientist, and this is the first lab building i have built where sensitive lab space is on an elevated floor. are the listed equipment specifications in the steel book accurate? are vibration isolators for equipment a cost effective alternative? what can i do to remediate the vibrations and still meet the client's requirements? since i am writing my own vibration criteria and designing to it, i am on the hook for everything. so if it doesn't work, i'm the only source of blame. i know the owner/contractor will laugh if i tell them i need an almost 2 foot floor - on top of 40 inch beams!
ps. sorry for the long post - and before you suggest it - i don't have equipment manufacturers to speak to since they don't have specific equipment selected. i have called around to 3 manuf's and got 3 different answers.
1) in my experience, the vibration limits in the steel book are consistent with what a knowledgeable lab consultant or vibration consultant would give you.
2) unless on slab-on-grade, electron microscopes are almost installed with their own vibration isolation mounts. presumably that would also hold true for a mass spectrometer.
3) remediation: what you have found is true - with a vibration criteria of 250 micro-inches per inch, there is no reasonable solution other than putting the equipment on slab-on-grade. selecting the right vibration criteria for this project is something that your client will need to resolve with the tenant. you and the vibration consultant (and i would strongly recommend that you lobby to get one on board) can provide the data for the decision, but ultimately you do not want to be the one setting the criteria. as you can see, it can have a huge impact on the project economics.
as an aside, i would say that it seems like floors supporting sensitive equipment generally perform better than the numbers indicate, but i would not rely on that.
i should have also pointed out that this is not just an issue for the structural consultant. the murray criteria is only considers footfall induced vibration. the lab equipment is also susceptible to vibrations induced from other sources like mechanical equipment. the mep consultants will need to include the appropriate details and specifications to properly isolate their equipment, piping, etc. so that it doesn't create problematic vibrations. (again, a vibration consultant could help sort through these issues.)

__________________
借用达朗贝尔的名言：前进吧，你会得到信心!
[url="http://www.dimcax.com"]几何尺寸与公差标准[/url]