There’ve been a flurry of emails going out to all tenants of my company’s main office building (where I don’t work, so it’s moot to me anyway) that at such-and-such date / time (middle of the night) they will be X-raying a couple of floors of the buiding and you can’t be in the building at all (or maybe not on those floors).
What sort of things would prompt the need to X-ray a building? Structural concerns? locating pipes?
This is a relatively new place - just a couple of years old at most - so one would think they know the pipe locations etc.
In addition to concrete, X-rays can be used to detect poor welds in steel elements, as discussed here.
I believe X-rays can also be used to measure stress in steel elements.
If the building is new, this makes a lot of sense. Concrete takes time to fully cure, even after the rapid initial hardening. Stress on steel elements might change from the intended levels if there’s any settling or faulty elements.
The building probably has a new tenant and is soing a tenant improvement. That is remodeling a space. If there is going to be any cutting through the floors for sink drains, HVAC ducts or what ever and the building has prestressed cementit will have to be X-rayed before any cutting can be done. What they are looking for are any stress cables, they do not want to cut through any of those.
I have worked in brand new buildings where the first tenant in an area requires major changes during the TI.
I worked in a company where we wanted to run some network cable to the floor under the boardroom table. Doing so required drilling a hole in the concrete floor through which to run the cable, and this required x-rays prior.
The prestress cables are on the prints as a description of the cable placed every 6", 8", 10", or what ever inches.l they are not drawn on the prints. And any mistake could cause a major repair and bracing to be done.
As a structural engineer with extensive experience in building modifications and repairs, including nondestructive testing, allow me to offer several points:
It is very rare to x-ray in buildings. Very, very rare. The most common of the rare reasons is to check the quality of welds, as previously discussed. On very rare occasion, x-rays are used on concrete, but the development of ground penetrating radar (GPR) has almost eliminated this usage.
It is common for building owners to use the term x-ray to refer to any type of non-destructive investigation.
The fact that your are being ask to leave the building implies that they are actually x-raying.
In summary, it is almost certainly a steel framed building, and there are concerns about quality of the welds.
Correct. Elements with post-tensioned or prestressed tendons (cables) are never cored, drilled or cut without identifying the locations of the cabled first using GPR or metal detectors. Cutting a tendon is a very expensive mistake and could cause a failure.
X-Ray diffraction and similar methods are used only in the laboratory to identify problems with the cement chemistry. It would not be performed in the field.
To my knowledge, and I would expect to know, x-rays cannot be used for this purpose. However, people are always coming up with something new, and I may be wrong.
As an Architect I think it would be unusual for an office building to be a Post Tensioned slab, although it isn’t unheard of. I have seen them x-ray PT slabs to locate the PT cables but usually that is on a retail floor or a residential floor when a new toilet location, etc. has to occur.
Or as culture mentioned it could be a weld situation, but I personally have no experience with that aspect of xraying. But I concur that it most likely is a structural steel frame and thus not likely a PT slab (but again it could be). What area of the country is this building located in?
My experience.
1st retail store saw cut through the floor to b ring plumming through. Did not X ray. Twang they found and went through a PT cable.
2nd 4 story garage building. X rayed slab before drilling for anchor bolts on new doors.
3rd 4 Brand new 5 story office building. X rayed before doing major TIs.
4th 14 story office building. If we are going to drill in the slab in anypart of the building we are not to drill deeper than 2 inches, with out getting a x ray first.
I believe this is a very new building - my company has only been occupying it for about 6 months and we may have been the original tenants on the floors we occupy (which don’t include the ones being X-rayed, as far as I know).
Well then it is possible it is a concrete building rather then steel. I worked in the DC area for about 5 years and as I recall PT concrete wasn’t uncommon there. One reason is that DC has a height limit and a steel building has a higher floor to floor then a PT concrete slab. Thus you might be able to squeeze one more floor into the vertical measurement and that would make the economics work out. If I recall in general steel is cheaper then concrete (depends on a whole bunch of factors and what is happening globally), goes up faster and is more flexible and thus makes sense for an office building.
Most of my work is in high rise residential and that is almost exclusively PT concrete (but there are a few steel residential hi rises). Concrete is easier to finish and to deal with acoustics then steel is and thus makes more economic sense. Money and time is often what typically drives these decisions.
The odd thing is that in general the toilet rooms, etc are part of the core and typically placed as part of the original shell and core. However say a tenant wanted to put showers in or something like that, then they might need to xray the floor to find the post tensioned cables. Other then something like that I can’t imagine a need to xray a concrete slab.
I think culture has it, that they are calling something that is not an xray and xray. I mean people call it a cement floor all the time and damn it, it is a concrete floor! If it was cement it would blow away! Just a pet peeve of mine.
