Floor vibration analysis: Truss Girder

[dollarbulldog]

Dear all,

I am curious in investigation of floor vibration for a 14m long span ballroom truss (static designed LL = 5 kpa) . It supports concrete plank without composite action. I've found that lowest natural frequency of such floor is about 3.7 Hz which does not meet 5Hz minimum as required by NCA code.

Investigation of floor acceleration hence needs to be performed. Is there any code referred to full model simulation ? , and which kind of dynamic test at which loading level shall I simulate in case no area functionality is a priori known?

sincerely

 

[rob768]

Whatever you do, a full model will not make that particular beam stiffer, hence, your vibraton will not increase.

 

[archeng59]

increasing the stiffness of the truss, or adding partitions or other means of damping, will help increase the natural frequency. are you using AISC design guide 11 as a reference?

 

[rob768]

Sorry, but adding damping does not alter the natural frequency. Increase the stiffness (easiest) or loose weight (which isn't always pratically possible).

 

[archeng59]

damping doesn't change natural frequency of the framing but affects the way people perceive the vibrations in the system.

 

[ArneG]

You typically take members (even non composite ones) as being partially composite, provided they are attached in some manner.

Make sure your taking advantage of things like actual load vs. design load, and if the space has partitions, etc.

Read AISC design guide 11 thouroughly and make sure you understand the equations prior to troubleshooting a vibration issue.