Impact Load from Falling Concrete 1

[Aytacoglu]

Hi Everyone,

We did a scaffolding design for a building to enable some works to be carried out at the roof level. Basically they need to create a structural opening for a new hatch and they need to remove some of the existing concrete from the roof.

The scaffolding platform under the roof is designed for 5kN/m2 loading. During the structural opening works, some concrete from the roof can fall to the scaffold platform. However, this hasn't been considered in the design as we do not anticipate big chunks of concrete falling to the platform.

A question has been raised from client from their technical engineer reviewing our design. He is basically asking whether a concrete pieces falling from 1.2m to the scaffold platform would cause any issues.

I tried to do a quick calc to check this, however, I am realising that calculating an impact load is not an easy task to do. I am currently conservatively assuming a 20kg concrete falling from 1.2m to the platform, and trying to calculate the force that will be exerted from this.

Doing some quick search, in order to calculate this, you need to know/assume the distance travelled after the impact. The platform is made of timber boards, and I am not sure how to calculate this value, even if I assume 1-2cm to assume that timber will deform 1-2cm during the impact, I am not sure of the accuracy of this approach.

Has anyone got an idea how to tackle this issue and how to do a quick check to ensure the platform will be okay with this impact load?

Many Thanks.

 

[human909]

If you know the height and know the weight then can easily calculate the energy.

Use energy methods on your beams and flooring to work out their capacity (an you can work backwards to work out the force.)

Better explained here:

Design Beam for Impact Absorption - Structural engineering general discussion

I am trying to figure out how to design a beam to absorb the impact from a falling object. A conveyor carries 13,000 lb. parts over an industrial enclosure that we are building. The customer wants the roof beams to protect the people inside if a part falls from the conveyor. The fall distance is...

www.eng-tips.com

5kN/m is as fair bit and 20kg from 1.2m isn't a heap of energy (unless it lands on your toe) so the majority of your members should be fine. The flooring possibly not because the force will be high and localised.

 

[Greenalleycat]

I suggest grabbing a paver stone from your local hardware store, propping up a plank between two supports, and dropping it while filming. Send result to their engineer.

 

[human909]

Lol @ greenalley cat! Yes. It will probably be a faster and cheaper solution than a calculated solution!