How accurate (rigorous) should we be with site inspections of concrete structures? My question concerns, bar lengths, concrete cover, hairpin ties size, etc.
Rigorous? It's either right or not (with tolerances, of course). If you are asking about frequency, it depends on the criticality of the structure and the diligence of the contractor. I usually start out checking everything, then back off a bit if I see that the contractor is doing a good job. I also select areas of the construction to give a good check, while doing a cursory check on others. This introduces a bit of randomness to the process without having to measure each rebar spacing, cover, etc.
Documentation is important. If you find something, write it down. Keep a "non-compliance" list and delete the items as they are corrected.
If you are the engineer of record, or if you have responsibility for compliance, don't be shy. Employ the authority of the local building official if necessary to get the project on course if you find deficiencies.
thanks Ron and Qshake, but I'm asking if I need to look at bar lengths or just count the number of bars and bar size in a beam for example?
thanks a lot
In some manner you need to check the bar length, splice lengths, etc. If bars are not hooked, development length can be critical, so a few inches makes a difference.
Do you actually need to measure the length of the bar? Not really...there are other ways to see if it is correct. Where the bar terminates relative to the outside face of the form, for instance, tells you what you need to know.
One of the things we have to be careful of in our inspections is not to assume responsibility for items we cannot control. As an example,if you measure one horizontal control distance, are you expected to measure them all? It might then be assumed that you are responsible for horizontal LOCATION (different than horizontal distance).
Our goal in the specific inspection is to see if we or the engineer of record got what was wanted, based on the filed or officially changed plans, specs, or code requirements.
When I do inspections, I check clearances, correct rebar (you'd be surprised how many contractors use #5's instead of #6's) at the correct spacing, lap distances, etc. Obviously, you don;t have the time to check EVERY clearance, spacing, etc. If the job was OK, then I would write in my inspection report something like "..the reinforcing steel spacing APPEARS to be acceptable." The reason for "appears to be" is because of liability issues. Unless you actually checked EVERY bar, then you shouldn't write "...rebar IS acceptable."
While at the site, check the formwork, afterall, that is important too. In doing so you will know the relative dimensions of the reinforcing laying inside from the clearance required. Another good point by Ron is the terminal ends especially at lap splices. Always measure splices. Since the bars are generally close enough you can evaluate the whole set rather than measure each one.
Similarly, you can gauge the clearance by using a cheater. A cheater would be a piece of wood on a long stick (length as required). The length of the wooden end piece is the required clearance and you place the stick down the forms to quickly assess the areas of concern.
Check bar ties as well. You don't want rebar moving all over when concrete is being placed.
And as mentioned above, DO check bar size. Many times the job is littered with bars of all shapes and sizes. Not everyone is paying attention when they go and grab something!
Also, one concept that is not well documented is the difference between observation and inspection.
The purpose of observation is - to inspect to such a degree that the engineer has confidence that the plans and specs are being correctly interpreted and implemented into the construction. In other words: Are you as an engineer successfully COMMUNICATING to the contractor. By reviewing rebar (perhaps to the extent that Ron suggested) do you begin to have confidence that the contractor has the ability, knowledge and know-how to correctly interpret all the other beams/details that you indicate.
Liability under observation: Did you have reasonable evidence to suggest that the contractor had the ability to interpret your plans? It then remains the contractor's responsibility to ensure that the bars are all in place correctly.
The purpose of inspection is not an attempt to determine the efficiency of your communication, but rather to exhaustively check ALL the work.
