Is This Support Adequate?

When one buys a property, one takes on "all encumbrance" in England and Wales. Did the Surveyor not carry out this assessment as part of the Structural Survey of the building prior to contracts being exchanged for the purchase? That would be surprising as now there is no redress available!

No matter. Consult a qualified Building Structural Engineer locally, who will be in a better position to review the installation with sight of it, report and advise accordingly. Yellow Pages, perhaps?

No advice here.

Except, I'd hire a civil or mechanical engineer, if you are worried about being sued if something happens.

Your insurance company will definitely have an opinion about floor loading.

There are a number of sites on the net that will guide you. Here is one such site:

How to Calculate Floor Load Capacity | eHow.com

It is impossible to say without looking at the site as it could have been modified (support beams removed), the wood degraded by termites (you don't say what country it is in), etc.

The comment about 'home made I beams', no support pillars and no load bearing support in the walls has me worried that the floor may not be strong enough for your (commercial?) needs without building modification.

Consult a local building inspector (or similar) and get a site inspection first just in case.

The floor is in excellent shape.The walls are standard 2X4 studs on 16 Inch centers,the floor joist are 2X8's on 16 inch centers,the roof is a truss type on 16 inch centers, which puts no weight on inside walls.All weight is on outside walls,which rest on lower floor outside walls, which are 8 inch thick reinforced concrete walls.

It really seems to be overbuilt,except for my concern about the I beams.Making I beam from channel is fairly common, but paralleling two such beams is hard to calculate for me.

Perhaps there is a mechanical engineer in the house that can help?

Do you have any drawings of the structural floor plans for us to look at and offer comment for general interest (you should still get in a building inspector or similar to be sure).

The reason I say it seems to be overbuilt is that a 2X8 can span 10 feet and conform to code, These span only 5 feet.Floor joists,by code only need to be 24 inches on center,these are on 16 inch centers.Roof trusses only need to be on 24 inch centers to meet code requirements, these are on 16 inch centers.The truss type roof does not need any inside walls for support.All weight of roof is bearing on outside walls.

Perhaps the guy was putting it together with materials on hand,but he seemed to have a penchant for overkill.Perhaps the steel beams, although not standard fare, are more than adequate for the purpose.I could always run a row of posts down the center, but I prefer to leave it open if possible.

I may perform a pull test with my hoist on the center of a beam to see how much it sags when weight is applied.Stack block on pallet attached to beam and measure sag as each block is added.

Crude, I know, but it may give me some info I can use.

Using the formula referenced in the link above, the wooden floor structure can support 269 pounds per square foot,which is definitely overbuilt,so no worries there.

The beams are not currently sagging, and the building is 30+ years old,and the top floor was heavily loaded with mechanics tools by previous owner: V8 motors,blocks,trannies,differentials,gears,axles, etc.

Seems to me if they were going to sag, they would have done so by now.

Perhaps I am worrying over nothing.

The depth of the beam being less than the width leads me to believe whoever did this job didn't know much about structures. Sounds like a slap together with whatever is at hand job. I would consult a structural engineer.

The making of an I beam from channel is pretty common, giving a 3w X 4 deep I beam,which is mechanically logical,being taller than it is wide.

The main stresses would appear to me to be in the center of the beam where the 2 I beams are joined.The weld is continuous on both sides of all beams, and the bead looks very good..(I do know how to weld.)12 feet of 60XX or 70XX filler rod bead is very strong.

Perhaps it was done this way to reduce any skewing of the frame laterally?Just guessing, don't know for sure.

Guess if you wanted to hook onto something outside and drag it in, that would be the trick.

Any ideas?

The nature of these responses seems to be in pursuit of justifying doing nothing using anonymous responses to a global internet forum by readers that cannot see the installation.

The correct approach is to consult a local Structural Engineer and obtain a report. Then, should it fail, the building's insurance company has a document to justify not paying out and for reducing the premiums payable to it.

Abandon hope all who venture further.

I have no idea if this is a sturdy enough jury rig to support your unknown mass of cabinet shop tools. I'm not a civil engineer. Obviously you are not a civil engineer, too. There are no load bearing inside walls on top floor. Unless this building has no roof like the top floor of a parking garage, there is a load on these walls. The roof, its pitch and nominal weather conditions of your also unknown region will likely be dominant loading concerns of these walls. Even if this is a roofless floor, wind loading will happen with these walls.

Since you are obviously not a civil engineer, I do not trust any of your information to attempt an evaluation.

You need a local licensed civil engineer to inspect your building and tell you if you purchased a disaster waiting to happen, a sound construction with a load limit of XX pounds per square foot on any floor, or a building brilliantly designed that can take anything you load it with.

There is an obvious misunderstanding of the term "Inside Wall". It means walls that are not on the perimeter of the building,like divider walls between rooms.Perimeter walls of course,as you stated, bear all the roof weight , and all associated loads.These loads will have little effect on the beams below in this case.

Perhaps I should have explained it better.

Sorry for the confusion.

Post #2 by Lynn gives a link to calculate floor loading.Not as simple as it sounds.It is referencing as if this load were applied to every square foot of the floor area equally.

The shop has 800 square feet, so 800 X 269 = 215200 lbs. total weight support rating, all building materials and contents supported by floor.Other words, it could could support a tank of water over 4 feet deep covering the whole floor area.A swimming pool.That is just the wooden part, the weak link would be the steel beams underneath,but I feel pretty good about them since I have been pointed in the right direction for study.Not going to put in a pool or giant hot tub.

Generally accepted loading is around 50 lbs sq ft,so this floor is way over code requirements even for commercial usage.

I may put in a steel I Beam with rollers for a chain hoist right down the center,supported at both ends by steel columns.

Cutting span in half gives 8 times the strength.

Thanks to everyone for the feedback.

You are scaring me. I still cannot "see" the arrangement. You say that the beams are doubled up at the center and that beyond that they only span seven feet. Actually, this sudden change of section can be dangerous although it sounds as though the welding on yours is satisfactory. When you say they only span seven feet, are you saying that the beams are supported in the center? It doesn't sound like it. Span goes from support to support by definition.

I don't see where the 269 lbs/sqft came from. It sounds very high.

M=wL²/8. Cutting L in half reduces the moment to one quarter, not one eighth. That is if you cut the beam over the center support, if you run it continuously over the support, it is the same one quarter of the original moment but over the support with the tension on top. In some cases this can be a problem because the compression flange is not laterally restrained.

This is a standard way to provide area loading limits.

I installed a mezzanine at work that was rated for 100 lb/ft. This metric gives the total load limit and cautions against piling too much weight in a given area.

Example: Although the entire deck might be able to hold 10,000 lb, this does not mean you can put 8,000 lb in one corner.

I don't recall this requiring a detailed explanation to the EE's, ME's, or even the CemE's that I work with.

Everyone knows a small girl in heels will get stuck in the grass while us big guys walk just fine. Strange that no one brought this up. . .

-A-

<...should have explained it better...>

Explain it to a Stuctural Engineer who has sight of it and whose time has been paid for in order to do a formal assessment!

Your description of the "I beam" gives me no picture at all! An I beam is rolled that way at the mill, you appear to have a fabricated girder, and it doesn't sound like an "I" shape.

When starting a structural steel design, we start by looking at 1/2" of depth per foot of span for doubly symmetric beam shapes, this usually puts us in range for acceptable deflections, but not always, it is just a starting point.

Turn 2 pieces of C4 x 5.4 Channel back to back and weld together.The center is double thickness where the 2 pieces join.It is a fabricated girder by your definition,but a redneck I beam by common usage.

Thanks for the rule of thumb

Correction to above post::should be C4x7.25 not C4x5.4.

OOPS!

Before you start estimating wood or steel strengths, you should first evaluate the condition of the materials as they exist in their current locations (ie: ''in-place'').

You've given us no relevant information other than the shop is ''old''...

It would be best to have your (old shop) evaluated by a structural engineer who specializes in evaluating comparable structures ''in-situ''. and there are not that many of them around. then wait as long as it takes to recieve his detailed, written evaluation report. Be sure to fully inform said engineer exactly what you plan to do with the (old shop) in complete detail first, not during or afterwards...

So, look first, before you commit any more of your time and/or money...

A little smart patience can pay big dividends, if you give such a process enough of a chance...

How about replacing just a few of the beams with correctly specified ones?
Just a few, which align with the loading points of your upper floor equipment.
Or, some angled corner braces? Also maybe ties bars, floor up to roof beams?

Could give you peace of mind at minimal cost, may save an accident and,
be sufficient to get the building passed the inspector / insurance company.

It's not good doing only half a job, but less of a risk, and could save lives.
Belt and braces never hurt anyone.

jt.

A man round our way has been stabbing people with knitting needles,

There are 6 victims so far. Police warn he seems to be following a pattern!

First of all your question itself is very confusing. You should have shown drawing or photo of your shop. Your original seller must be possessing original drawings approved by local authorities. If you are looking for any free advise on CR4 then you are taking great risk.

Just because the center of the beam is "doubled up" by it's homemade box construction, it does not qualify as an end point of span. Your post is confusing, but it seems as though the span is 18 feet, and that you have composite beams (joists) made of steel and wood. I suspect the steel acts as a stiffiner. Make us a section drawing, identify fasteners, and even I could get close. I suspect they are undersized for the 80 lbs sf load I like in a shop.

I'm sure you know what YOU are talking about. I am saying you don't know what HE is talking about. So why pontificate on structural design?

BTW, 2x4 stud walls with sheathing are frequently responsible for supporting 3 stories of typical construction. Why would you say that you doubt that a 2x4 wall could possess adequate strength?

To your continued suggestion that 2x4 walls are not likely to be structurrally sufficient, are you saying that each of the stories has no floor load? I'm sure I don't have to point that out to you, but "three stories of just exterior wall" seems to imply that you do not consider this. So you are suggesting that these houses have another dynamic at play to transfer floor loads? Now I am wondering.

I have built structures. I like engineering. That's it. If the entire floor structure is appropriatley fastened, it could be a tremendously strong monolithic platform, bearing on four walls insted of two. I just can't visualize it. What do you see?

The op said the reinforcing is at 5' centers, but that the joists are above, on 16" centers. Are they perpendicular to the steel, or parallel above it. I still don't know "exactly" what he's talking about. That's all.

I have to ask this.

If you do not know "exactly" what someone is talking about, how can you offer any valid opinion or criticism?

A refining question seems at first plausible but without a qualified eye (no offense to HTRN) to provide an answer nothing useful can come from posing the question.

That is my point. Moosie said he knew "exactly" what the op was talking about. I don't know exactly what the op is referring to. Do You? He has not supplied drawings or even sketches, much less any technical data.

Okay, let me demonstrate something here regarding the load capacity of a 2x4 wall stud that is laterally supported by the exterior wall sheathing only.

Let's assume that the wood is a good one, say Douglas Fir Larch, #1 Grade. That's a rare wood species, but this is only for argument sake. Most likely the wall studs are a lesser strength species like Southern Pine or Hem Fir, Construction Grade.

Therefore, per the National Design Standard (NDS) for Wood Construction that Allowable Compressive Axial Load = 2.1 Kips, or 2,100#. Please note: I have not included any lateral loading such as wind acting against the exterior wall. If I had done so, that allowable axial load would drop dramatically because there is Combined Bending and Axial loading occurring in the 2x4.

Now, if we have one of those existing double steel channels bearing directly on the wall top plate and oriented directly above a single 2x4 wall stud:

Let's assume 50 psf Design Live Load (per BOCA), as well as a 8 psf dead load (for wood joists and 1" plywood only. The Dead Load = Self load of the double channel is 15 PLF.

Using a 5' o.c. beam spacing will give us a maximum Design Total Load Beam Reaction, as follows:

R = (0.5 * 19') * ((5.0' *58 psf) + 15 PLF) = 2,897.5#, which is greater than the safe Load Carrying Capacity of the wall stud of 2,100#. This would result in a 38% (+/-) Compressive OVERSTRESS. There's no doubt in my mind that the existing exterior wall studs would fail under applied Design Total Load, per Building Code.

Therefore the wall studs require bolstering. You will notice that I did not include the roof load and the 2nd story exterior wall loads in this scenario. If I had, the resulting TOTAL LOAD acting on the wall stud that is located between the foundation wall and the underside of the 2nd floor framing would be in excess of 2,100# by more than a factor of 2X...depending on the Design Roof Snow Load for RedNeks' location.

If the information is needed, I too am a Registered P.E. Retired now but still licensed.

Consider the steel members to be girders, if they are in the center, they pick up 5/8ths of the load per joist but at 5' centers they do not spread the load over all of the studs, they concentrate it on one or two. In normal framing, the loads are spread evenly along the wall.

If the beams are as Drew sketched, there is more trouble.

Almost everyone here has suggested you get an expert in to look at it. The reason is because we don't know you (other than reading your posts for the past few years) and we can't see the structure. Pictures and drawings would help but I wouldn't bet your life on an assesment I made just based on pictures. You seem credible and intelligent so you are getting lots of advice.

I can't really give much advice on the load (because I don't have that textbook in my office and would really like a drawing to work from (even just a back of the envelope drawing)).

I can explain how to set up the system. The way load capacity is calculated is by finding what amount of force will cause the beam to fail with a given load situation. With a standard beam floor you can look at it and know where the weakest point is. You know it right in the middle.

So you set up a worst case scenario of a point load in the middle of one of your (redneck) I-beams and calculate how much force it will take to yeild. Then you set up a distributed load and do it again.

Then you apply that force to the fittings that secure the beam to the supporting (wall, column etc) and calculate what amount of force would buckle the column (to make sure your load is smaller).

Once you find the critical failure device you apply a factor of safety to that load. The factor of safety is set based upon often an educated guess by the expert based upon age, quality of materials and welding and just a gut sense of how much you trust the structure.

The calculations for determining all this are not too difficult and you can probably find them online or in a Mechanics of Materials textbook.

Drew K

The problem with all of that advice is that these floor beams are NON-PRISMATIC due to the very nature that they have been spliced (cobbed?) together. There is no continuity, plus we haven't a clue how they were attached to one another and if it was done correctly at all. I have my doubts, because it is a very demanding and complicated design procedure to get the welds and bolting right, let alone construct it correctly in the field. Even most steel fabricators get the entire design process wrong, unless they have an experienced PE on staff or the hire one from the outside.

My gut feeling is that the previous owner or the one before him just cobbed the entire thing together with not structural design whatsoever.

No way would I design such floor beams the way these came out, especially for that span. They're too slender (not enough MEAT), spaced too far apart @ 60" o.c., and have too large a span for their net Section Modulus. The welds are probably undersized too and would become overstressed under full Design Load (LL+DL).

Add to all of the above the stress concentrations at the end of each splice (where we go from two "beams" to one), and I'd keep everything heavy close to the outside walls.

Not qualified to expound further.

By cabinet shop, I mean a carpenter shop that builds cabinets,tables, bars, etc,

Tools will be table saw,planer,jig saws,wood lathe,plus storage for materials,(Which will mainly be racked along outside walls) exterior 1st floor walls are 8" reinforced concrete.

What size and design of bar joist would be required to replace the beams?Same span length,standard commercial PSF loading?

Or,alternatively, an I beam of proper dimensions.

Would a 12 inch( or greater) mobile home subframe I beam suffice?At what spacing?

I want to make this floor right, but at the same time,of course,minimize costs.Mobile home I Beam steel is readily available due to a nearby mobile home manufacturer shutting down.I can get it for scrap steel prices while it lasts.

I realize this material is very thin, but I have no objection to placing them closer together.

Thanks

RedNek, I just took a quick look at using Light Gage Cold-Formed Steel joist for your floor. These would be the lightest, strongest and most economical structural floor system that you could install.

Because of the joist spans that are nearly 19 feet, you're going to need at least 12"deep joists with at least 3 parallel rows of joist bridging, equally spaced.

From the Marino Industries/Ware Floor Joist catalog, I chose their 12SW16 joists using 19 foot spans (center-to-center of wall bearings). These are 16 ga. joists with a Yield Strength (Fy) = 50 Ksi. Other Cold-Form steel joist manufacturers will have equivalent members. I can provide you with the required minimum structural properties so you can match them with the Marino/Ware joists specified herein.

@ 16" o.c. joist sp.: the Allowable Total Load = 84 psf; the Allowable Live Load = 75 psf w/ a L/240 LL Deflection Limitation = 0.95".

or,

@ 24" o.c. joist sp.: the Allowable Total Load = 56 psf; the Allowable Live Load = 50 psf w/ a L/240 LL Deflection Limitation = 0.95".

The joists need to bear fully on the 2x4 stud wall top plate the entire 3.5-inches. Also, you need to install Light Gage Steel (16 ga.) Web Stiffeners at end bearing end to prevent "Web Crippling". These can be secured using self-tapping sheet metal screws (#8).

The good news is that you can remove the existing heavy 2x_ wood floor joists and reuse them some other day for another project. You won't be needing them during reconstruction. Additionally, if the existing 1-inch plywood is in good shape, you can reuse it by securing it to the new steel joists with #8 or #10 self-tapping sheet metal deck screws sp. @ 6" o.c. maximum. Make sure that you stagger the plywood joints during the re-install.

I highly recommend that you double-up the existing 2x4 wall studs that are located between your foundation wall and the underside of your 2nd floor.

Congrats, you just received a Freebie design service! LOL

So, is this about what the beams look like? With the 2 x 8 joists on top?

This looks like a Mechanics of Materials homework nightmare...

Drew K

To be honest, I cannot visualize your description.

How about a picture or a diagram?

I do recall seeing a gardening show in England where they were putting roof gardens on houses in London. They put a temporary column in the center of the room beneath the roof and measured the deflection of the celing. They said that if the deflection was too great they wouldn't be able to install the garden. I don't recall how they loaded the roof to measure the deflection.

I still think your best (cheapest) bet is to get an expert in to look at what you have already. If you have been up there jumping around and it feels 'firm' then perhaps the modified beams are sufficient and an expert can verify for you. This would be much cheaper than rebuilding it.

Drew K

May or may not be helpful but...

Another "Rule of Thumb" which I was given some years back by a Fitter who did safety inspections on Girder Cranes etc, was that the allowable sag was 1/360th of the span.

i.e. on 18ft span 216"/360 = 0.6"

So in your proposed "Load Test" from the space below, you could load the floor until you got 0.6" sag.

Doing this while you are underneath may also be subject to a certain amount of risk, though?

That ratio varies with the usage. We used L/600 when designing crane girders because we don't want to have to run the crane uphill. L/360 is often used for Live Load deflection in most buildings, the floors tend to feel like trampolines otherwise. It is the limit to avoid cracking plaster ceilings.

Red Nek, if you want, you could install 10K1 Open Web Steel Joists, spaced @ 24" o.c. for that 18'-8" clear span. Deducting the joist weight, the plywood weight, and the 2x8 wood joists weight, leaves you with an approximate Live Load Capacity = 100 psf based on the Total Load Capacity.......the LL Capacity = 56.5 psf when the LL deflection is limited to Span (L)/360 or 0.63".

Please be advised that the bearing depth at the joist ends is 2.5", so you'll need to install a wood bearing block to make up the difference (4" channel beam depth - 2.5" new joist depth = 1.5" new wood blocking depth. Make sure you have FULL 3.5" bearing on the walls.

By using the steel joists you can remove the existing steel built-up channel beams one at a time while still maintaining the existing wood construction above them. You will need to have some buddies over to help erect them into place since they weight 5.0 pounds per lineal foot.....so each joist will weigh = 95# for a total 19' of length.

Open Web Steel Joists can be ordered through your local steel fabricator. You're going to have to provide them with actual clear span dimensions (face-to-face of wall interiors)...make sure you measure this dimension several times throughout the building.

Good luck!

Thanks,CaptMoosie,

I guessed right on the 10K1 joist,but I was not sure of the proper spacing of them.

An old saying down south:"Even a blind hog will sometimes root up an acorn."

The hog in this case is me.

Your reply was exactly what I needed.This will be the most economical and expedient method of bringing the support up to standard.

Should I bolt the ends down to the concrete wall after applying load, (Removing old steel) or before.Will it make a difference?

As always, your advice is highly respected.

You're very welcome! I was glad to help you out w/ your problem.

There's two ways that you can secure the joists to the existing concrete wall:

1. Use appropriately sized expansion anchor bolts (2 of them minimum) with at least 2.5" minimum embedment into the top of the concrete wall. I hope that you don't have concrete masonry walls, otherwise you will need to fill the block cells with pea gravel concrete. There may be a problem accessing the top of the wall without removing some of the exiting wood flooring structure. Same holds true with drilling 2 anchor bolt holes.....access problems!

2. You could install manageable sections of L 4 x 4 x 1/4 ASTM A36 steel angle to form a continuous joist bearing ledge, bolted alternately to the inside face of the concrete wall and the top of the wall, again w/ expansion anchor bolts....or you could use a 2-part construction epoxy to glue it to the wall if you have substantial access problems. After you finalize the placement of the joists, you could tack weld the joist bearing seats to the top of the L4x4's. The problem with welding is that it will be a fire hazard as well as position problem. you will need to protect the existing wood flooring and the exterior stud wall.

Don't forget that you will need to install bridging between the new floor joists as well as the last joists and the existing building end walls.

Okay, I gotcha now, as I was unaware that the exterior walls were resting on the 2x8 floor joists and plywood. I do have an elegant solution for you, and you can forget carving out beam bearing pockets into the CMU walls!!! Ain't that grand!!! hehehehhe

You already have a 4" gap now between the top of the CMU walls and the underside of the 2x8 floor joists due to the existing 4" deep steels, so the solution to your dilemma is a real snap!

All you need to do is weld L3x3x3/8 x 6" long angles to the beam ends. The angles must have one leg pointed down which will be welded to the end of the new beam web, whilst the other leg (the outstanding, ie horizontal, leg) will rest atop the existing CMU wall. The top of the angle must be held 4" lower than the top of the new beam, less the angle thickness of 3/8", or 2 5/8" difference. Hold the ends of the new beams 1/2" clear (no more than that!) of the inside faces of the CMU walls to give you some "wiggle room" for final adjustment.

The "Bearing Angles" shall be ASTM A36 steel, which are readably available from Steel Fabricators. The thickness and length of the angles as I have given you is to limit the bending stresses in the outstanding leg at the angle "root". I wish they could be thinner, but that would require a longer angle length and possibly stiffeners, which defeats economy.

Make sure that the welds are at least 3/16" x 3" long vertical E70XX Fillet welds each side of the new beam webs.

Also, make sure the top of the existing CMU walls are level and free of defects to ensure that you have full angle bearing and load transfer from the floor to the existing wall. If needed, apply a thin low slump masonry grout to aide in levelness and full bearing area.

All you have to do is slowly jack up a portion of the existing wooden floor so as to facilitate the removal of the existing steel beams and insertion of the new steel beams!!!!

Good luck with your project!!!!

RedNek, all you really need is 2-1/2" dia. expansion anchors with hex heads, and 5/8" thick washer/plugs in the vertical leg to fill the gap. You can most likely make the plugs from steel pipe cut on a chop saw equipped with a metal cutting blade bought at a Big box store. A good horiz. spacing for the anchors would be 3" minimum to 3.5" o.c. max.. You'll have better access to that vertical leg for drilling (use a good hammer drill with diamond encrusted masonry bit) and anchor installation, as compared to installing anchors in the horizontal leg that's resting on top of the CMU wall.

Yeah, I don't trust that existing steel either to support much of anything stored on that floor framing. The previous owner was extremely lucky that it did not fail!

Make sure that you take lots of pics and share them with us later, okay!!????

By the way, exactly what items do you plan on putting up the second story, and how much does each weigh?...

Ok, but what kind walls and/or colomns and/or pilasters do you have holding up the second floor? The second floor joists/beams/etc. won't do you much good if the walls, etc., can't hold up the entire second story, including roof, attic, etc., does it?...

Best guess is that at one time there were two garages side by side with a wall or beam between and someone removed the center section and added "I" beams. The size of the current beams sounds odd to me. I would have a local structural engineer in to look into this situation as no one can give you advice from here without actually coming to your building and taking a hands on approach.

when I was young my father had a two story two car garage. The previous owner of the property had worked at a plant where aircraft carriers were built and was able to attain 4X12 rough cut beams that span the entire depth of the garage. They were 16" centers and the upper floor was made of 2 courses of 1" plywood. Dad had an engineer friend look at it. This guy took pictures and brought equipment in and in the end stated that we could hang cars from the rafters below and park a semi tractor on the second floor and not see an appreciable bowing of the floor. I still want to try that . (but how to get that semi up there???)

I knew exactly what RedNek has for shop framing (mostly, that is), as I've seen it done before by homeowners and "Happy Happy Woodchuck Carpenters" who thought they knew betterbecause the LAST GUY got away with it w/o any Structural Engineering input or permitting.

I have already determined (above) and informed him that the welded-up double channels with a mid-span splice was inadequate......I'm actually quite surprised that there hasn't been a structural overload failure yet.