How to Perform a Structural Check on an Existing Roof Slab, Baghdad.

i've been in the building industry for years and have dealt with testing labortories at the federal level. i can assure you that the infomation that you are looking for is beyond most civil engineers and testing labs. doubt that anyone has that knowlege other than the defense department. i would'nt think that they would be willing to share it withl you.

I would not even consider certifying an existing concrete roof. If you have the drawings showing the reinforcement, you could check the theoretical capacity of the roof as designed but you have no assurance that it was built in strict accordance with the drawings. My advice is...don't do it.

If the original villa is from the 1960s-1970s, would any of the mortar fire protection schemes been present back then? I'm guessing that the roof would have been designed only for its own weight plus conventional live loads. If so, there probably wouldn't be enough surplus strength to support the heavy IDF structure.

I remember when a hole fell though the floor of the local .. new.. rugged.. convention center from dirt being brought in for a show.. I can't imagine it was considered possible at the time.

No way would I expect to be able to put all of that steel and sand on anybody's roof..

That's like parking cars end up and next to each other.. ... (Which may actually be lighter and afford reasonable protection)..

How thick? although it would be a nice insulator from the heat..

A better insulator from the ravages of war? peace

Hello Baghdadlad,

In regard to theoretically determining the load carrying capacity of the existing concrete roof you need to do the following:

1. You can have a certified testing agency perform a non-destructive test called a Windsor Probe test. In this test a steel penetrator is shot into the slab and the depth of the penetration is measured to determine the in-situ compressive strength of the concrete. You should have a minimum of 3 test shots conducted per every 100 square feet of area. It is fairly accurate (within a few % points of actual core sample test results) in the hands of an experienced testing technician/inspector. Either that,or you're going to have to conduct some destructive testing such as full depth concrete coring that are to be tested later in the laboratory....concrete core compressive strength testing. Again, perform a good number of these tests so that you have a good statistical Mean Average....I recommend that no less than 5 cores be done per 1000 square feet of roof slab area. Do a Google search to learn more about the Windsor Probe testing and the testing procedure.

2. I highly recommend that you obtain the services of a qualified lab that has electronic sonic (or other type) locating equipment (and trained certified operators) available which are capable of determining the size, depth and location of the steel reinforcing steel in the existing roof slab. This is a non-destructive test as well and functions much like Ground Penetrating Radar (GPR). You should really run the equipment over the entire roof. Most equipment is capable of storing the data electronically and you're able to retrieve it of a stored electronic media such as USB or CD.

Q: You DO know how to perform the analysis calculations of the existing slab based on the rebar and concrete compressive strength findings, don't you?

Good luck!

A roof in Baghdad, in the past, would not have been made for deep snow and ice, and so would only be strong enough to support itself and its use as an open air patio or sleeping

I doubt it would support the weight that the sandbags/plate would add.

You need to calculate the weight of this extra load, and then add an explosive burst safety factor, and then add to the structure to properly support this load, worst case

Look here for hints

I recommend that they move.

Having lived and worked in Iran in the 60's I would suspect your roof structure is not concrete. Why not consider adding a gable or shed roof (depending on spans, of course) to bypass the concerns about the load bearing capability of the existing roof?

Having researched a bit further and from my observation of the Iraqi contractors and previous villas that have been hit by incoming rounds, i would say the roof is constructed of approximately 300mm of concrete, reinforced with non-deformed bars.

However, the client has no information on the construction of the villa and there are no testing labs with the ability to perform the relevant non destructive tests. I advised the client that i would not perform any structural analysis based on the assumptions of what has previously been the normal villa construction in Baghdad. They had also declined to let me core the roof. (and yes i am capable of calculating the safe load bearing capacity of a reinforced concrete slab ;)

Thank you for all your comments

On the same matter, there is a lot of different opinions over here on what design of IDF cover provides the best protection, it seems to vary from organisation to organisation and country to country. The general rule is that you have a detonation layer then a minimum of 1m below, a catchmant area for the fragments. Hence the steel plate with a layer of sandbags underneath. However, i have heard of other ways, one being where you construct a series of concave arches perpendicular to the main point of incoming fire (usually Sadr City etc to the West of the International Zone). The point being that any IDF that impacts the structure will be deflected from the vertical to a more horizontal projection, thus saving anyone below. (unless it happens to fall directly into the centre if the arch). There seems to be very little information on these type of structures, other than Military regulations about building bunkers.

So, i would be really interested to hear from anyone that has been involved in the design of IDF protection for existing buildings. I have details of the various rounds that are used here and the explosive charge of each.

Thank you again.

I could give you suggestions having once been an US Army Engineer (USACE) with previous experience design regarding these types of constructs, but I cannot do so because they remain Classified. Sorry about that Lad!

You may want to search whatever is available on the USACE websites that is not Classified or has been de-classified. Look for USACE Engineering Manuals (ER), okay? That's starter for you.

If you have any trouble locating the necessary ER's just say so and I can provide the URLs for you. It's a long long listing.

One thing to think about.....provide the necessary structural support spanning across the existing slab and directly resting on opposing bearing walls instead of the roof structure. It'll avoid all of the hassle of conducting an extensive engineering testing and subsequent analysis which can get quite costly for your client. You gain a void space possibly helping in deflecting the rounds as well as providing additional storage space for your client. Just a suggestion...

Good luck with the project!

4000 lb per sq inch what most concrete can theoretically handle when the member is a concrete column or solid concrete wall. Using 1000 lb per sq inch will give you a 4x safty factor. if your concrete looks weak better have its crushing streangth tested. This assumes that your walls are perpendicular to the ground and that you are placing extensions directly ontop of them.

load bearing capacity is to know how much weight per sq ft the roof can tolerate.

You are basically adding another level. You need to know the bearing capacity of your walls and columns that are supporting your existing roof and how much of that capacity is already used (existing live and dead loads). Then if they can support the additional loads. Decide how you are going to extend those or join through the roof to distribute the loads of the new structure to the existing columns or load bearing walls.

Perhaps your roof is strong enough to suport all sorts of weight but you will still be better off placing loads onto columns or load bearing walls that are in effect extended through the existing roof.

Thank you, I do think the idea of loading the supporting walls is a much safer option than risking over loading the existing concrete roof slab. There was an incidence of this type of structure collapsing last year. There was no testing done in any way, which happens quite frequently over here, and although the structure seemed fine with the sandbags at first, when it rained during the winter the water was absorbed by the sand and the additional load caused the roof to collapse on those underneath.

As much as this may seem like a project not to get involved in, i would rather it was carried out by me than some of the other contractors here, basically because i know the client that will be sleeping underneath.

I think the parameters outlined in your original post are correct and functionally effective principals.

I would build this as two arches, upper and lower, to preserve the plenum (expansion area) and to apply the mass loading to the walls, not the roof slab.

Additional reasons for this dual arch span, rather than sitting on the roof, are;

A. flexibility, so shock absorption, by the 'fragmentation barrier'

B. even if the slab is 'good', shocks are not 'enhancing' a large pre-load force. I.e. the slab is more free to flex independently.

C. due to the two (3) 'independent layers' above, the slab becomes an additional layer under a second plenum space.

Or he could make up a "shock absorber" of 4" slabs of styrofoam laminated with woollen blankets to form a laminate approx 6 feet thick (deep) around which a containment barrier of formply sheets is fastened so's it won't blow off in a wind. ( See last night in Mission Beach)

No?

Cheers,

Stu.

I see you have a good grasp of the principals of armor and the structural conundrum Stuey, but I think that might be a bit "soft" in terms of things with a bit of inertia and/or shaped charges.

Some of these things could take out an armored vehicle.

But of course vehicle armor is limited by compactness - whereas this application has plenty of space to employ the same principals, ideally using common materials.

So; I suggest you harden up the skin to assure detonation (by contact or deceleration) add a layer of hard stuff somewhere mid-ish, and maybe sub Kevlar for wool.

But good positive suggestion.

So OK,

To help dissipate the forces of deceleration ( sorry, for us Inj's,negative acceleration) of the 'bomb' place a sheet of 3/4" corten steel over, and on top of, the lot.

It'll help with the local industry and employment by having teams of welders fixing the damage.

Cheers,

Stu.

An there I was thinking maybe a few layers of chain link mesh, or woven matting.

But if my input is annoying you - just say so, as I'm happy to quit the thread for other reasons. None of which include you, or other posters who are being constructive.

Maaaate,

Quite the contrary!

It I who is grasping.

I actually thought you and I had a little 'rapport', as they say in the classics.

Moosie came in from left field. I didn't see he was pulling my leg.

And , by the way, chain-link armour IS a good idea. I was working on the principle of flexible , resilient covering being able to dissipate the forces better by being suitable to cheap and plentiful materials.

But I'm no armory expert at all. But I believe we could fix this problem, right here.

You ready?

We did do an experiment half a lifetime ago by substituting the front bumper of one of my vans for a big wadge of very stiff flexible foam plastic covered in a thin GRP shell just so it wouldn't flop all over the place. It was more effective absorbing the day-to-day knocks than all the 'crumple zones'. If you've ever driven an 800cc Suzuki Carry van loaded with tools you'll appreciate the need for protection. There's nothing between the shins and the accident, but coke-can thin sheet steel.

I'd always thought about it, but the urgency came on day when I "leaned" on the rear end of another car, suddenly stopping, in traffic. Crumpled metal, but thankfully no crumpled legs.

Cheers,

Stu.

I thought we did too - hence my concern over annoying you.

But understandable if you did think I was "joining in" in posting "left field advice" aimed at misleading the OP into killing off his client family.

As for the topic of protecting them;

A mortar or missile, could be military issue or home made. So I think the speed, mass, cross sectional area, "pointyness", hardness and charge position and type, are huge variations to design against.

There is also the variable of a sand rod, which is used to detonate above ground in soft ground or sand, but that would help rather than hinder, is this application.

For an overview of the military stuff, some of which you might expect.

I think using Ceramic tile painted with ZECTRON /or a similar sand based silicon

and vulcanized rubber product could be worth checking into. Sand Bags are sort of

Rustic.

You could always install Chobham Armor on the existing roof slab, but somehow I seriously doubt that your clients would be able to purchase it due to it's incredibly astronomical cost and unavailability to civilians + it's classified by the UK and USA military. Would be nice to have it installed as it'd stop any mortar rounds.

Sooooo sorry!

So,

Why would you suggest it?

Styrofoam and woollen blankets are ubiquitous. And cheap.

And if you do the math you'll find this 'sandwich' will perform nearly as well (but only once) as will a popular, although much smaller, stack of aramid fibre sandwich, which again is certainly not ubiquitous in the Baghdad environs.

Cheers,

Stu.

Stuey, I was just pulling the guy's leg.....the idea just popped into my gray matter and I just had to share it...it's so far the ultimate armor protection yet devised pound for pound. No problem stopping a mortar round.

As far as I know, no US Army, USMC, or Israeli M-1 or M-1A1 Abrams Main Battle Tank (MBT) and UK MBTs that are equipped w/ the Chobham armor (which, BTW, was developed in the UK) has ever been penetrated by an opposing force's HEAT or Sabot round, and that includes Soviet built T-72 and T-80 MBTs.

Cheers!

You could always install the poor man's armor atop of the roof, Reactive Armor. Second best to Chobham composite armor. It'll stop almost any mortar round.

I'm sure you can find it in the Black Market in the appropriate neighborhoods in Baghdad or any large Iraqi city. No doubtafter nearly 8 years of war there the theives have pilffered loads of the stuff off of Iraqi and IFOR armor vehicles!

Ummm, what kind of neighborhood is this place located in anyhow? If you ask me, it sounds like it's high time to pull up stakes and head for the hills! LOL

Just a thought.

Gentlemen,

You should perform two types of testings as desribed below:

1. Analytical

As suggested by some other feollw, get cores (3 min.) and get tested from a good lab to find out the current compressive strength of concrete. This core can also identify what dia and spacing of rebars have been used. Based on the reults you check the structural design of the slab for the loads it is subjected to.

2. NDT/LOAD TEST

Per this procedure, you have to load the slab with sand bags and before doing that you must put teh gages for mesuriung deflection of the slab at centre. You need to load the slab in increments of say 20% and after each loading wait for 6 hours and measure the deflection. Similarly for another increment of load, measure the deflection. ACI Code allows certain deflection under dead load and live load. Compurte the deflection analytically and if your actual deflection is within 80% of that deflection, your slab is safe. 20% margin is for safety for additional lonf term deflection under sustained loads.

Akhtar Naviwala

Hello Baghdad Lad

The best and the cheapest way to do this is (assuming that you are a PE or a structural Engineer), get a Hilti ReBar Locator, this is a simple & easy to use MRI device which can give you correct data for the slab reinf, sizes and depths.

Second part is to get a Schmidt Hammer (NDT too), the rebound tests can give you very reasonable results for the (remaining, minimum can be 10mPa) concrete strength. Once you have this data you can go with analysis of the slab. Not to forget that concrete when properly casted & cured can grow very stronger with age.

If you use mathcad I can forward some spread-sheets for this sample calculations - fareed.siddique@yahoo.com.