Footfall Induced Vibration Analysis on Concrete Floor Slab

Hello,

I am wondering if it is possible to calculate footfall induced vibration across a floor plate using Karamba. I know there is a "natural vibrations" component that takes in a model and outputs frequency in Hz, however I am a bit confused on some of these other inputs and outputs, such as "NModes" for example.

Essentially, what we are trying to do is take a floor slab and:

1) Assign zones, such as corridors to the slab (presumably subdivided meshes)

2) Give that slab/zones a walking criteria (footfall in steps/minute) - corridors have a greater walking criteria for instance

3) Output the Mips (micro-inches per second) value for particular affected areas/zones on the slab - can be represented in some color range for the respective values accross the mesh.

4) Assign slab thickness based on optimized zones of vibration

So, to summarize - based on an input slab, we would like to calculate the mips produced on a floor-slab based on pedestrian footfall in steps/minute, then use this data to determine specific slab thicknesses. I am not sure if this can be achieved using the natural vibrations component or not, or if there are other tools that can achieve this calculation in Karamba.

Unfortunately I don't think I can provide an image at this moment, but it is basically a simple 30'x30' column grid in a 6x6 matrix, and more speculative at this point.

Either way, amazing tool! Cheers!

Replies to This Discussion

Permalink Reply by Karamba3D on March 5, 2017 at 1:54pm

Hello Alan,

the normal way to assure that a floor slab does not excessively vibrate is to assure that its first natural frequency is larger than 3Hz (in case of a dance hall 5Hz), so that the users are not able to excite that frequencey by jumping.

In Karamba the 'Natural Vibrations'-component gives you the modal mass for each vibration mode. With this and an assumption regarding the damping properties of the structure one could calculate the maximum displacement response of the structure under a dynamic load.

However I do not think that the effort of such a refined analysis pays off, since in case of pedestrian footfall there is a large degree of uncertainty involved in determining the governing loads. So a rough procedure like giving a lower limit for the first eigenfrequency seems to be more justified.

Best,

Clemens

Permalink Reply by Alan Cation on March 23, 2017 at 9:20am

Hey Clemens,

Thank you for your feedback, I will give this a try. It is for a lab space so this is an attempt to be economical about reducing as much vibration as possible for controlled experiments in certain zones. Perhaps this will be an effort not worth the payoff, so I will see.

Best,

Alan

RSS