CCB – Security is A Very Dirty Word
Doing a Guz “two-fer.”
I’ve been working, briefly, on another renovation. An old laboratory built in the 60’s which is now to have some very heavy server equipment put in it. I say briefly because I’ve been kicked off the project by the client, annoyingly.
The request was to assess whether or not the existing floor could facilitate the server equipment loading. A preferred loading arrangement was given, along with the loads of the individual server equipment. The existing floor is a composite slab, 16″ deep steel beams with a 4″ thick slab on top. The slab should be 5″ but destructive testing proves otherwise. The beams are 10″ o.c and span 30′. I calculated that the capacity of the system was around 240kip.ft [325kN.m] and that an increase in capacity would be required due to the loads imposed by the new equipment. I proposed (or at least I would have) a simple framing system which could either a) tie into the existing steel columns, above the existing floor level thereby effectively suspending the equipment above the slab, which wouldn’t see any of the additional load or b) sit on top of the slab tying in structurally – forming (for want of a better phrase) a concrete sandwich between two steel beams. Both have various pros and cons that I could think of, but what I was surprised about was the magnitude of the additional capacity provided by a steel plate which had been welded to the base of the existing composite beam arrangement. It was a lot! It was an accidental discovery made from messing around with simple hand calcs, and an error I made in missing out the base plate initially. Fortunately I recognised that things were off and I went back to check why, otherwise I might never have thought twice about the numbers. The plate itself is welded to the bottom of the existing steel beam and is .5″ (12mm) deep by 8″ (203mm). So not insignificant. The reason it increases the capacity so much though is because of the change it makes to the second moment of inertia (I) of the whole composite section. The original composite section minus the plate has I of c. 975inch^4. The composite section plus the plate has I of c.1985inc^4. When you apply this to the MIFY equation you can no doubt see the gain in moment capacity; The I has pretty much doubled for a very minor change in y. This could be a neat trick to remember if additional capacity is required but other methods of engineering (say replacing beams, or installing propping) are not viable.
Anyway, like I say I’ve been kicked off the project for being Australian. This was discovered when I called the client to ask for specifics about the server equipment; exact weights, how the loads are transmitted to the ground, sizes etc. Clearly alarmed as to why there was an “Alien” poking about he fobbed me off to somebody else, who wouldn’t pick up his phone and presumably called USACE. Turns out its a classified project. Shouldn’t be a problem thinks my line manager, who knew this. Well it is.
Alan. I’ve said it before, you are entering a foreign country. Brace yourself.
And also:
Since hearing that local Dunkin Do’nuts is closing me and Henry have been doing our bit to increase their take.
Holdfast Training Services Trial Blog 
On the security side I have had a similar issue with being allowed into USACE HQ’s server rooms to conduct a survey as they hold ‘classified data’. Presumably these are the secret air conditioning settings for the White House etc. I meant to mention it on Friday Brad, but have they considered moving the heavy computer equipment down onto the ground floor, negating the need for an to upgrade this structure again.
Good blog and a valuable tip for future reference.
How is your time accounted for? Do you bill your hours against projects like us in the world of civvies do?
How have you conducted destructive testing? Does your proposed solution allow for extra axial load in columns? I assume the lower beam reduces effective height in one direction, what about out of plane? Thanks for the conversions otherwise I would struggle!
Destructive testing was conducted by a contractor to American Society of Testing and Materials (ASTM) codes. (ASTM 42 covers obtaining and testing of drilled cores). Basically they would have taken the cores away and crushed them, however it does state that the strengths reported in testing are typically lower than those of samples poured specifically for testing. Most results were as expected. I didn’t get as far as checking the columns but that would have been a major consideration yes. Out of plane could be considered braced by the floor slab, so braced in both directions.
Hi Brad, thanks for the reply. I have heard the oppositeb with cores and compression tests in that the insitu strength would be higher than say a cube or cylinder because of the higher temperature of the concrete. That obviously assumes the cubes were not under temperature controlled/matched curing. Out if interest how did they avoid any rebar and how was repair done? We are trying to get some cores of river walls crushed and have to be careful about replacing the original face stone with the stone disc cored out.
Damo – I just had to re-check the ASTM, I thought I had mis-spoke! It says “measured compressive strength of a core will
generally be less than that of a corresponding properly molded
and cured standard cylinder tested at the same age.”
The outcome is affected by original strength specification, moisture and temperature history, and the manner with which the core was taken. (ie carefully or ham-fistedly) I wonder if there is a difference in testing? There is a strength correction factor applied here to samples based on the diameter of the core and the length of the sample. In samples where sufficient L/D is not possible results are reduced by between 2-13%.
I wasn’t present at the sampling but speaking to the guy who was repair and patching was fairly rough and ready – the project is to gut out and refurbish the building anyway.
Henry – Directly below is the mechanical and boiler room so that’s a no go. Presumably if upgrades turn out un-favourable then this may well be an option elsewhere in the building footprint.
Guz – The design office here is operated pretty much like a profit generating enterprise, however the level of profit allowed is restricted to +/- 1%. Anything over that 1%. This means that yes, the normal people in the office charge to labour codes even though it is a military organisation. Everything has to be accounted for, including training, site visits etc. I log my hours in work but USACE isn’t allowed to charge me out. Therefore any work output (direct labour cost) from me is a saving to the client.
Guz. On the billing affair I have found myself put onto a couple of projects with tight budgets to alleviate them, this has the advantage of them being small enough that I can assume responsibility for them too.
Brad, Conscious that I am out of lane, if the room below is a mechanical room surely no one is going to mind a couple of strategically placed columns if they would reduce the cost of works? Clearly equipment maintenance distances have to be considered.
That’s fine – I meant a no go in terms of putting all the server equipment down there. Columns could be a sensible option, assuming they can go in the right place.