huangyhg

effects of vibration
i am currently investigating if a 1600 kgs embroidery machine can be placed on the third level of a factory building.
note:
1)10 units will be distributed to an area of about 150 sq.m.
2) the embroidery machine vibrates when operated
3) the machines are operated continuously and simultaneously for 24 hrs.
i would like to inquire:
a)the percentage of weight to be added for investigation/design?
b)what factors should i consider in the investigation/design?
c)assuming the building can structurally carry such machine, what is the long term effect on the structure due to frequent vibration?
d)how can we lessen the effect of vibration on the structure? can rubber pads help? what type of pads are advisable? others?
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i don't understand what you mean by part (a)but there are two ways to take care of vibration in a structure. the first is to make the existing structure stiff so that the vibration goes direct thru to the foundation. (heavy up the connections/beams/columns, etc.) the second is to make the foundation heavy so the vibration is absorbed. i like to try to run in the middle between these two. i size the foundation to a factor of the sum of the moving parts. i then get the equipment manufacture to discuss the application of vibration isolation pads. for a raised application further investigation of the building structural components are required. ie what is the building constructed of? steel/concrete.etc. let me know if you need more specifics.
thanks for your reply.
(1) part (a) would mean the required factor of weight in addition to its weight. would 80% of weight be enough for effects of vibration? ie total load due to machine is equal to 1.8 times 1600kgs.
example :
in concrete design, liveloads are multiplied by 1.7
(2) the existing building is a concrete structure with a liveload capacity of about 100psf.
(3) for investigation of an existing structure what are the factors to be considered?
(4) what are the short and long term effects on the structure due to frequent vibration?
best regards.
hi ksdphillippines
it depends on the excited frequencies of your machines and vibration characteristics (phase) during their operations. i suggest you investigate the dynamic response factor which depens on eigenfrequency of your structure , damping and excited frequency. the serviceability of building during operation should be taken care of.
bests,
i'm going to respond to d) only:
you will need to change the natural period of the structure to account for the vibration. this is done by changing the stiffness and/or adding an offsetting mass to the system (increasing the mass of the foundation). dampeners can also be incorporated.
the information on the machines should be available from the manufacturer. a word of advice: check the complete range of frequencies from the machines. for example, all on at full speed, all on at half speed, half on at full speed, etc. you get the idea. even though you say all on for 24/7 make sure. a coworker ran into a situation where the structure was checked at 50% of maximum output but the machines were actually running at 100% of max and it started to tear the beams apart.
as a rule of thumb for generator pads i use 2 to 3 times the weight of the generator to take care of this. very simple example but it is based on increasing the mass of the foundation.
miked
append to canyonrat
if vibration characteristics of machines are complicated by phase lag, unsimultaneous operations, and different excited frequencies, it will be more convenient to investigate your structural response in frequency domain by using ft or fft technique in order to control some eigen mode proned to resonance. the dynamics response factor cannot be imaged by only one's experience because it depends on several variables specifically case by case.
bests,

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