5 Things to Look for When Inspecting a Suspended Concrete Slab | Palantir Consulting

5 Things to Look for When Inspecting a Suspended Concrete Slab

Here are 5 critical aspects to be checked in a suspended concrete slab:

(IMPORTANT: Engineers and Builders, remember that an inspection of a suspended concrete slab should ALWAYS be done in person – never by Facetime or with photos!)

1. Reinforcement at Maximum Moment

At the most basic level, one has to check that the reinforcement placed in the suspended slab is in accordance with the design engineer’s plans.

That is the minimum standard and any structural engineer should be aiming for better than that. Yes, things change on-site and maybe the communication between the engineer and the builder hasn’t been perfect. But that’s no excuse. One cannot just check for compliance with the drawings.

• Always consider the shape of the bending moment diagram when inspecting a suspended slab.
• Is the maximum amount of suspended slab reinforcement located to correspond with the highest bending moments?
• If one doesn’t know what a bending moment diagram is and/or you don’t know where the maximum moments are in a span, there is no reason for that individual to be inspecting a suspended slab. It is just too critical.

It's not to say that one MUST be a registered engineer to inspect a suspended slab, but before attempting to check slab reinforcement on-site, one should know where the most amount of reinforcement should be. The one conducting the inspection acts as the builder’s and engineer’s backup plan and the last chance to pick up any errors.

If something wrong or at the very least unusual has been observed,– an inspector should be able to make the call. The engineer and builder need to confirm that they are working off the latest set of plans.

2. Supports are Where the Drawings Say They Are

When walking around on top of a suspended slab deck, check the slab supports to see that they are where the design engineer thinks they are.

It’s all too common for misunderstandings about half-height walls to make it through to construction and for a builder to blindly build a slab with fewer supports than anticipated by the engineer.

• Check the loadbearing walls are built to the underside of the suspended slab.
• Make sure the slab and walls are engaged or isolated in accordance with the design engineer’s drawings.
• Check the reinforcement coming out of columns is handled as per the drawings.

These are basic things that need to be done before a suspended slab is poured.

3. What Concrete Strength has the Builder Ordered?

The drawings will be fairly explicit about what concrete strength the design engineer needs the suspended slab concrete to be.

Concrete strength is important because it affects things like bending strength, shear strength, durability, and propping times.

One way of ensuring the right concrete is going to be poured is to ask the builder, “What grade of concrete are you ordering?”

If the builder can’t answer this question, then it should be reason to worry.

Go to the drawings, point out the concrete grade to the builder and make sure they understand.

The concrete grade is the basis of so many aspects of the concrete pour. Surface durability, porosity, beam and slab strength, shear strength, serviceability, and creep are all affected by concrete grade.

Using the right grade of concrete is so important that it could very well be number one on this list.

4. Which Reinforcement Layers Were Placed First and Last?

Design engineers know that the closer the steel reinforcement is to the tension face the more effective it is.

When a design engineer specifies the order that slab reinforcement layers are placed it is an inspector's job on site to ensure the builder has placed the steel in the right order.

A different amount of cover affects the forces in the steel reinforcement. This is item number four because if the layers are done wrong extra steel can be added before the pour to fix any mistakes.

Check the drawings. Ensure which layers of steel reinforcement were meant to be placed first and last. Then make sure the builder got it right.

5. Suspended Concrete Slab Reinforcement Cover

Last, but certainly not least in the list of things to check when checking a suspended concrete slab before a concrete pour, is to ensure that the correct cover is achieved to the slab reinforcement.

This is the last item of importance because it can easily be rectified on-site. However, it is super-critical to check that suspended slab reinforcement is positioned correctly in the slab.

Too close to the surface and the steel could corrode and fail the slab prematurely.

Too far from the concrete surface and the steel reinforcement may be overloaded or the slab could crack before the steel takes up the tensile forces in the concrete.

Don’t be afraid to pull the tape measure out and check the top and bottom covers. Ask where the top of the concrete slab is. Get down low and look for slab mesh that is sticking up higher than the top of the slab.

Don’t forget to check the cover to the edge forms, the under slab formwork, and the drop beams too. Slab reinforcement hanging out of a slab is a bad look and you are singularly responsible for getting it right.

Get it right.

?Palantir Consulting has the expertise and experience to check a suspended slab before pouring

These 5 things are critical aspects of checking a suspended concrete slab. If these elements are beyond you or your team, then don’t be afraid to put your hand up and say you’re not experienced in checking suspended concrete slabs.

It is far better to get an experienced structural engineer out to check a suspended concrete slab before it is poured than to be out of your depth and pass a slab that is not ready to be poured.

Send us an email at [email protected] or call us at 02 9037 6422 and to our team of experts.

??PLUS! Builders, get a copy of our in-demand resource, "Building Crack-Free Concrete Structures" and be on top of your construction game. Link here: https://campaign.palantirconsulting.com.au/crack-free-structures/