Structural Load Capacity of a RC Slab 1

[Humam Al Sebai]

I have a Slab that is 250 mm thick. Has T16-150 mm Bottom mesh and T12-150 mm top mesh. The slab is on a rectangular grid that is 9m x 8.5 m. supported on columns. The beams between each slab panel are 600 mm x 600 mm with 5-T25 top and bottom.

It is required to check if a demolition equipment that weighs 1120 kg can safely operate on the slab. The equipment moves on two trackers that are 200 mm wide and 933 mm long. I already applied the weight of the equipment on the SAFE model and checked reinforcement required before and after the load. I did not notice any change in reinforcement.

I still feel that is not enough to validate the safety of the use of the equipment. The attached file shows the equipment.

 

[JAE]

So what is your question?
Are you asking us to perform the engineering to tell you it's OK?
Not really what this site is for.

 

[Humam Al Sebai]

Dear JAE

My question is simply to the experienced in the field of demolition. What are the required documents that would show that this equipment is safe to operate on the slab? And please do not speculate and accuse based on mere speculations. That is not really what this site is for.

 

[jayrod12]

To OP,

Be careful who you, as a new member with only two total posts, try to tell tenured members what the site is for. JAE has been around here far longer than you, and has provided some of the best advice many of us have seen consistently.

You've given a bit of information, more than a lot of first posters, but at the same time, there actually isn't a question in your first post. When that happens we often assume the worst, being that someone is coming to the site for free engineering, not discussion between professionals.

That being said, regarding the analysis, did you account for the equipment as a moving load? If not, you may be surprised at the outcomes. The equipment being in one area may cause hogging in other areas where there is insufficient top slab reinforcing.

Did you safe model have the actual reinforcing input, or are you running it as a design where the program gives your required reinforcing?

Did you account for other materials being stored/moved during the demolition process?

Where are they stockpiling the demolished materials?

Those are just a few questions/scenarios that I would be evaluating if it were my project.

 

[JAE]

What are the required documents that would show that this equipment is safe to operate on the slab?

Well, first you should do an on-site investigation of the slab to verify that its current condition is not diminished in any way by cracking, rust, spalling, or other deterioration.
If the slab is damaged or deteriorated, then your SAFE analysis isn't valid unless you adjust the capacity to reflect the loss of competence.

Second, you would then need to perform a structural analysis and design check of the slab - as it is currently reinforced and configured - to see whether it can support your equipment.

It appears that you have done an analysis and design check using SAFE and it appears OK.

As jayrod12 suggests, there is also the issue of impact loading and demolition sequencing - how does the slab move across the slab.
Is the slab the thing to be demolished or something else? Is the slab simply the floor on which the equipment is supported while it demolishes something else?
Does the demolition material come falling down on the slab (impact)?

As far as required documents go - typically I would write a report outlining the following:
1. OBSERVATIONS - what is the current condition. What source documents did you use to allow verification of load capacity (reinforcing, concrete strength, etc.). What are the features and data on the demolition equipment. How is the equipment located on the slab. What forces are anticipated on the slab.
2. ANALYSIS - Describe your analysis and design checks. Include all your assumptions (very important). Use tables, diagrams or images to help communicate your results.
3. CONCLUSIONS - From the above, list what conclusions to you come to with regard to use of the proposed equipment on the slab. This is the meat of your report and what your client is ultimately asking for from you.
4. LIMITATIONS AND RECOMMENDATIONS - You made assumptions to derive whether this equipment can be used on the slab - you need to include these in your report and specify to your client (who may not be an engineer) in clear and plain language what they need to do to ensure the equipment use remains safe. This might include a list of "do's" and "don'ts" such as "do not allow the equipment to operate closer than X distance from the center 1/4 of the slab area" or "Demolition contractor shall ensure that material is not piled up on the slab higher than X". This is where you try to think through all the possible bad things that could go wrong and list them out - this list will cover you somewhat in case something goes bad. If any temporary shoring or bracing is required then you should include it here.

If the demolition requires a specific sequence or series of phases, then a series of drawings or diagrams may be required.
If the demo contractor needs to have temporary items designed then you can either do them yourself (if a party to the contractor) or delegate the design to the contractor with you there to review the resulting engineering designs.

 

[Lomarandil]

Keep in mind that if the Brokk is operating while on that slab (demolishing the slab or something adjacent), when that arm is extended it will shift the distribution of weight. Brokks are better balanced than excavators, but we often see weight split 70%-30% between tracks or up to 50% of the gross weight in a single outrigger (if extended). If operating a hydraulic hammer, you might also get some impact effects from that.

 

[Humam Al Sebai]

Dear JAE

Thank you for the elaborate answer. The slab condition seems fine and I already did a on-site investigation and reported the results. The demolishing work is for the flooring tiles and not for the slab itself. I exaggerated the loads by a factor of 2.5 and it is still safe.
I instructed the contractor to make a mockup test under supervision and the test was successful.

I thank you once again and I apologies if I have offended you. I am a very decent person but I hate when people talk to me with a descending language.

Regards

 

[Humam Al Sebai]

Dear jayrod12

Thank you for your answer. I will take the dynamic effects into account.

 

[Humam Al Sebai]

Dear Lomarandil

Many thanks.