vibration for dancing and concert
vibration for dancing and concert
(OP)
I need to do vibration analysis for dancing and concert. Attached is my problem.
Structure consists of the following
- big trusses at lines A and B (L span = 6x28ft) with support at line 1 and 7.
- 7 columns at line C
- 7 lines of trusses spanning between big trusses and columns at line C
- Floor loads supported by filler beams and then transferred to trusses.
I'm thinking to simplify my problem assuming a bay of 168ft (= 6x28ft) by 70ft with trusses at line 1 to 7 as a beam and big trusses at line B as girder. I will follow the design guide 11 procedure with these assumptions. Is this the right approach? Need some inputs. Thanks.
Structure consists of the following
- big trusses at lines A and B (L span = 6x28ft) with support at line 1 and 7.
- 7 columns at line C
- 7 lines of trusses spanning between big trusses and columns at line C
- Floor loads supported by filler beams and then transferred to trusses.
I'm thinking to simplify my problem assuming a bay of 168ft (= 6x28ft) by 70ft with trusses at line 1 to 7 as a beam and big trusses at line B as girder. I will follow the design guide 11 procedure with these assumptions. Is this the right approach? Need some inputs. Thanks.






RE: vibration for dancing and concert
I did vibration looks for similar framing not long ago - it was 20' deep trusses spanning 140' supporting two floors. I will just say that it is exceptionally difficult to get the trusses stiff enough to work for vibrations. I'd be interested in your results when you work through this.
RE: vibration for dancing and concert
RE: vibration for dancing and concert
RE: vibration for dancing and concert
You use the FEM program to get the natural frequency? My first time to do this kind of vibration analysis. What size of the top and bottom chords do you use?
RE: vibration for dancing and concert
I sized the chords based on strength, while neglecting the composite slab action. We weren't counting on that for strength, but you can count on it for vibrations even if it isn't a true composite slab because the loading at which vibrations are considered is much lower than ultimate strength levels and deck welds and friction will do the trick. I had very heavy W14's for the chord. Somewhere in the nieghborhood of W14X500 (I don't think 500 is a real weight, but it was VERY heavy).
RE: vibration for dancing and concert
RE: vibration for dancing and concert
The second is accelerations. The acceleration needs to be checked regardless of fn. It is a function of fn and of the forcing function (somewhere in the neighborhood of 7psf for a lively concert) - which I believe to be a bit conservative for your condition (and the condition I was dealing with). I believe it's difficult to get 7psf acting together over such a large area.
I'm surprised we haven't heard from 271828 yet. He must not have logged in recently. He is the resident vibrations expert.
RE: vibration for dancing and concert
When in doubt, just take the next small step.
RE: vibration for dancing and concert
Do you have any papers that sugges this? For a truss this long, with this much load at full service level loads, I would expect to see piles or some other deep foundation for which the stiffness would not be an issue.
RE: vibration for dancing and concert
The design guide 11 has a small but significant revision can't remember when it happened now, but for rhythmic excitation column deflection and foundation parameters were included in the basic equations. If the building has deep piles these need to be treated as columns and included in cals. My rule of thumb is if you have column/pile lengths in excess of 15m then you need to included this deflection, more from experience than anything.
When in doubt, just take the next small step.