Bco git

[ETC]

First things first:

Anyone who installs an UVHWS needs to be competent. His/or her ID card will prove this to your BCO.

Secondly:

Check with your local British Gypsum representative - a standard first floor construction will - in my opinion - not give fire resistance to steelwork within the floor void. I would not accept this argument unless evidence is provided by British Gypsum and to date I have never received this - structural steel within a floor void should be painted with intumescent paint - I can of course be persuaded otherwise.

[saveasteading]

Let's go back.

Red oxide gives no protection.

Self applied fire paint works as well as professionally done. You do need to prove the thickness.

Not all steels need protection if very chunky.

How much is exposed?

Lengthwise

Cross section.

There are several means of achieving this.

Bco has done an hour on fire. I've done a serious course and argued on such several times. I might have forgotten of course.

The bco never admitted to being wrong, but found some getout. Same result.

Is it behind a ceiling , as mentioned? Cables are a potential source of ignition not of conflagration.

 

I assume you'd like to say: no further protection is required.

[ETC]

30 minutes FR required to structural steel in a house.

[Pocster]

24 minutes ago, saveasteading said:

Let's go back.

Red oxide gives no protection.

Self applied fire paint works as well as professionally done. You do need to prove the thickness.

Not all steels need protection if very chunky.

How much is exposed?

Lengthwise

Cross section.

There are several means of achieving this.

Bco has done an hour on fire. I've done a serious course and argued on such several times. I might have forgotten of course.

The bco never admitted to being wrong, but found some getout. Same result.

Is it behind a ceiling , as mentioned? Cables are a potential source of ignition not of conflagration.

 

I assume you'd like to say: no further protection is required.

Lots of stuff here .

Remember bco has called this irrespective of his ‘knowledge ‘ ( or lack of )

Steels are about 350% over spec  ( as SE told me ) so we can safely say “ chunky “ .

How much is exposed ? Depends on which steel . Worst case 2 faces I.e the flat underside and 1 web .

The steel does not support walls or roof etc - purely exists for stairwell .

Above 30 min fire rated ceiling . No cables ( only low voltage lighting anyway ) cross the steel . Light cables go to perimeter lighting ring I.e not back to CU and hence across the steels .

Edited November 12 by Pocster

[saveasteading]

Sounds to me as if that needs no further treatment.  What is behind the ceiling that might burn?

I would need to know the steel section reference.

 

I'd be cheeky and ask bco to answer the query from your fire engineer: what risk he perceives (where is the fuel behind the ceiling and the likely ignition.

 

Given the HP/A why does he think it needs more protection.?

 

[Pocster]

3 minutes ago, saveasteading said:

Sounds to me as if that needs no further treatment.  What is behind the ceiling that might burn?

I would need to know the steel section reference.

 

I'd be cheeky and ask bco to answer the query from your fire engineer: what risk he perceives (where is the fuel behind the ceiling and the likely ignition.

 

Given the HP/A why does he think it needs more protection.?

 

Nothing . Beam and block !

I’m unlikely to antagonise my bco further !!!

[Oz07]

I've been thinking about this and its puzzling me. Howcome electric wires are ok running around or through joists and trusses, including big boy trimmers or triple girder trusses holding up massive loads. But if you have wires running around a non combustible rsj its deemed a risk?!

Is it something to do with roof or floor allowed to collapse into the building but rsj and walls failing could cause building to collapse outwards?!

[ETC]

On 12/11/2024 at 19:56, Pocster said:

Lots of stuff here .

Remember bco has called this irrespective of his ‘knowledge ‘ ( or lack of )

Steels are about 350% over spec  ( as SE told me ) so we can safely say “ chunky “ .

How much is exposed ? Depends on which steel . Worst case 2 faces I.e the flat underside and 1 web .

The steel does not support walls or roof etc - purely exists for stairwell .

Above 30 min fire rated ceiling . No cables ( only low voltage lighting anyway ) cross the steel . Light cables go to perimeter lighting ring I.e not back to CU and hence across the steels .

- Structural steel in a house that supports an element of structure needs fire protection - steel trimming a floor for a staircase needs fire protection. Steel supporting a roof does NOT need fire resistance.

- Ceilings in a two storey dwelling will not - generally on their own - provide fire protection. The complete floor construction gives the fire resistance.

[Pocster]

1 hour ago, Oz07 said:

I've been thinking about this and its puzzling me. Howcome electric wires are ok running around or through joists and trusses, including big boy trimmers or triple girder trusses holding up massive loads. But if you have wires running around a non combustible rsj its deemed a risk?!

Is it something to do with roof or floor allowed to collapse into the building but rsj and walls failing could cause building to collapse outwards?!

I think it’s rather a lot of nonsense in a domestic . Fireman getting tangled in cables so needs a cable tray - hmmmmmmm . Massive rsj not fire resistant? . How hot is the fire ? Burning for how long ? - until it fails . Going to be quite a wait I think .

[Gordo]

1 hour ago, Pocster said:

I think it’s rather a lot of nonsense in a domestic . Fireman getting tangled in cables so needs a cable tray - hmmmmmmm . Massive rsj not fire resistant? . How hot is the fire ? Burning for how long ? - until it fails . Going to be quite a wait I think .

A lot of research on bendy steel steelwork following a fire supports the need for fire resistance to any steel works supporting floors or any fire resistant element / system. The fire resistance need only equal the FR of the element it supports. Never debated the issue of falling cables entangling fire fighters but I am aware of it. I didn't think it applied to domestic work TBH.

[bassanclan]

It took me a while to realise that it is my job as the builder to prove to the building inspector that my work complied with building regs, rather than assuming that the inspector can see that the work meets the regs.

[Gordo]

7 minutes ago, bassanclan said:

It took me a while to realise that it is my job as the builder to prove to the building inspector that my work complied with building regs, rather than assuming that the inspector can see that the work meets the regs.

Exactly. The BCO is only an inspector. if unsure they have a duty to ask for evidence to prove it complies. It is the builders responsibility to prove they have complied with the substantive requirements of the regulations. If shit goes wrong the courts/investigators will look at the evidence.

Edited November 26 by Gordo

[Gordo]

On 12/11/2024 at 19:56, Pocster said:

Lots of stuff here .

Remember bco has called this irrespective of his ‘knowledge ‘ ( or lack of )

Steels are about 350% over spec  ( as SE told me ) so we can safely say “ chunky “ .

How much is exposed ? Depends on which steel . Worst case 2 faces I.e the flat underside and 1 web .

The steel does not support walls or roof etc - purely exists for stairwell .

Above 30 min fire rated ceiling . No cables ( only low voltage lighting anyway ) cross the steel . Light cables go to perimeter lighting ring I.e not back to CU and hence across the steels .

If your steels are behind an adequate FR system the steels are protected and require no further protection. Usually this would require 12.5mm fireline or similar lining for a ceiling. 12.5mm regular plasterboard wouldn't cut it. To prove this to the BCO go to british gypsum or whoever your board manufacturer is and get a copy of their declared fire performance for your system.

Edited November 27 by Gordo

[Pocster]

7 hours ago, Gordo said:

If your steels are behind an adequate FR system the steels are protected and require no further protection. Usually this would require 12.5mm fireline or similar lining for a ceiling. 12.5mm regular plasterboard wouldn't cut it. To prove this to the BCO go to british gypsum or whoever your board manufacturer is and get a copy of their declared fire performance for your system.

The steels are behind a 30min rated ceiling . This I think is what convinced him .

[saveasteading]

8 hours ago, Gordo said:

To prove this to the BCO go to british gypsum or whoever

No. As an earlier post says.....to prove this the builder must present the proof to the bco.

 

It is easy enough to find the solution to suit the circumstances.

 

By the time a steel beam has melted there isn't much left of the house or the people upstairs. But a good ceiling stops it all.

 

[SteamyTea]

Just an engineering point.

 

This is not about structures 'melting' or burning though.

It is all about how they fail over time.  Very few things fail explosively, thankfully, most deform in a predictable manner (cars are a good example).

 

This is a good, basic, tutorial.

https://feaforall.com/failure-modes/

Failure Modes: Understand the 5 most common failure types

February 15, 2017 by Cyprien 31 Comments

 

Many engineers I meet don’t know there are several failure modes…

http://feaforall.com/wp-content/uploads/2017/02/cracked-beam-300x171.png

Beam failure (not intended to be realistic ;-) )

They think:

« That’s pretty simple… you apply a load, the load is too heavy, so your system fails and breaks… »

Ok. I acknowledge that this is obvious… systems can break under a heavy loading.

In fact… even a 3 years old would understand this logic.

BUT…

That’s not all!

Don’t wait to have a big security problem in your system to finally try to understand what’s going on…

Let’s discuss together some of the major failure modes.

Just a note before starting with failure modes:

That’s a LARGE topic with an awful amount of crazy knowledge to understand.

That’s why I’ll only be mentioning the most obvious things… because my purpose is only to make you AWARE that those problems even exist

…Hoping that if you are concerned by one of these failure modes , you will do your own research to understand.

Why do you need to know about failure modes?

If you are still wondering that, here’s the most straightforward answer in the world:

You have to be able to see how a system can fail to improve it and protect it against potential failure modes.

Don’t wait for it to break down to take action.

(That’s what most companies do though… and that’s when they start to realize they might need to use FEA to find out the cause.)

What are the typical failure modes?

Let’s see that now

1) Fracture: When cracks appear

I guess that everyone saw some cracks in a bridge or in a wall… well, that’s a sign that the structure has a problem!

http://feaforall.com/wp-content/uploads/2017/02/Crack-in-the-wall-300x279.png

When a new cracks appear or existing cracks are extended, you are basically looking at a fracture mechanism.

Not every part fractures in the same way:

Some parts fracture slowly and deform plastically before seeing a sign of a crack… that’s because those parts are built in a ductile material.

http://feaforall.com/wp-content/uploads/2017/02/ductile-failre.png

Ductile fracture with characteristic distortion and shear lip

Steel is basically a ductile material. It extends and deforms before failing.

That’s why the stress-strain curve is like this:

http://feaforall.com/wp-content/uploads/2017/02/stress-strain-curve.png

Now… you have also brittle materials!

Those are much more « sneaky » if I dare say

Those materials tend to fail suddenly and abruptly without showing any sign of plastic deformation.

Concrete and glass are 2 examples of brittle materials.

Note that you have also materials which a ductile up to a point and then become brittle.

Some materials like bone can be ductile or brittle in function of the strain rate ( Source)

Here’s a picture that shows the difference between brittle, ductile and semi-ductile materials:

http://feaforall.com/wp-content/uploads/2017/02/brittle-and-ductile.png

Want to see how a real beam fractures?

Watch this video (you can skip just to watch the interesting moments):

How do you simulate fracture with FEA?

Well, that’s a difficult topic so I won’t talk about it now, but that’s really something that deserves your attention to study.

You will find fascinating theories and algorithms to solve fracture problems… a lot of them being still very experimental.

(If you have something to add to that or experience with fracture simulation, please write it in the comment section, that will be useful for everyone reading)

2) Yielding: When a body experience stresses

Yielding is probably the most common type of failure analyzed with FEA

It describes a body which experiences stress in excess of the yield stress.

Yielding is only called yielding when it actually compromises the integrity or function of the part that yields.

Why do I need to precise that?

Sometimes you may observe a « localized » yielding that cause strains near stresses concentrations in your part, but then… the stress in redistributed and the yielding actually stops.

How to simulate that with FEA?

The most simple type of analysis, the « linear static » analysis, deals with this kind of failure mode.

Nothing too complex, just normal FEA… and a lot of engineering judgment.

3) Insufficient Stiffness (Deflection): When flexibility causes failure

Whatever the mechanical system you build, it must be stiff enough to resist the loads.

Seems pretty basic, but that’s really a notion at the heart of mechanical engineering.

It was also probably one of the first lessons I learned when I used FEA for the first time in my life.

http://feaforall.com/wp-content/uploads/2017/02/Capture-d%E2%80%99%C3%A9cran-2017-02-14-%C3%A0-12.10.15-1024x685.png

The system you see here is a mechanical system I was building for a student project when I was in the Ecole Centrale of Lille in France in 2006-2008.

If you are wondering what it was supposed to do…well, a scanner was placed at the center on a mobile platform and a rotating arm was supposed to take the sheet going out of the scanner and store it in a removable tray.

The part on the top-right picture was supposed to support a big ring of steel of 50 cm diameter and around 3 kg.

I designed it the most simple way I could at that time… a sheet of metal simply folded in 3 pounded to make a big hole.

Then when I had to BUILD this system, I realized that this part was bending with a deflection of something like 10 cm…

How I used FEA to solve the problem

The consultant supervising my team of 6 people told us something I still remember back now:

« Your part is bending because it is not stiff enough, if you fold it again a second time in other direction, it will become much more stiffer…. »

That’s when I had the (brilliant) idea to come up with a new CAD model design that would solve the problem…

I didn’t have much time because the project was due in 2 weeks… so I decided to use FEA to solve this problem (before doing the testing… gaining around 1 week of time)

I simulated the part and the FEA software told me that the maximum deflection would be 2mm … probably not the best I could get, but acceptable…

I built the new part and tested on the system…and it actually WORKED.

Man, I was stunned.

I thought to myself: «  This FEA stuff is quite something, I’ll have to dive deeper into it when I get the time »

By the way, If you don’t believe that I built this system, here’s an actual proof ;-)

http://feaforall.com/wp-content/uploads/2017/02/cyprien-armadocs.png

If someone tells me how I can get back this hair, I’ll pay you a beer! (Don’t tell me surgery, haha…)

Ok, I was on the road to explain you the different failure modes… back on the road

3) Buckling: When a loss of stability creates big damages…

http://feaforall.com/wp-content/uploads/2017/02/04ecca04-30ec-4a79-ac9f-eb4429265117.jpg

In a nutshell, buckling a kind of failure that happens to certain types of slender geometries because of the inner instabilities that occur in the loading.

In it very dangerous because buckling failure can happen much before the material failure (Yielding).

I won’t talk too much about this failure mode because I already wrote some much more detailed article just about it here:

http://feaforall.com/buckling-simple-explanation/

Another important point about buckling is that it is not detectable in FEA if you are just performing a linear static analysis. You will have to perform an actual « buckling » analysis to see its effects (and that’s why knowing about it is important)

4) Fatigue: When time causes a loss of strength

When you hear a story in your family that they were driving the same car they drive for more than 10 years and suddenly a part failed and they didn’t know why…

That’s probably because of Fatigue!

Fatigue is a failure mode that takes a lot of time to happen.

Basically, you can understand it like that…

When you use a system, even if it is designed to be resistant enough to the loads applied to it… after some cycles of loading, the parts start to lose strength and become weaker.

A typical fatigue failure of a part looks like that:

http://feaforall.com/wp-content/uploads/2017/02/Fatigue-cut-300x218.png

Part which failed due to fatigue

 

How do you simulate Fatigue with FEA??

I have an old guide that explains simply the principles behind Fatigue analysis.

Join my newsletter here and I’ll send it to you (along with other free material and courses)

[optin-monster-shortcode id=”aereopxpatfcxnuc”]

 

5) Creep: When a body deforms over time

Those analyzing concrete structures like bridges or buildings know this mode of failure very well.

Creep is simply the natural tendency of some solid materials to move slowly or deform permanently under stress.

It is increased when the materials are heated (the extreme example is when steel is melt under high heat to make it change shape)

http://feaforall.com/wp-content/uploads/2017/02/12059701-email-dsc00332-2-300x225.jpg

Creep failure of a pipe

Creep is far from being negligible as it is involved in many accidents around the world.

For example, some experts say that the collapse of the world trade center was due to Creep

(Search for the word « creep » in the article to find the explanation)

How do you simulate Creep with FEA??

Creep is generally handled by a special type of material model in your FEA software and is still very experimental.

There are many different creep models available which depend on the kind of model you have.

Creep generally happen over a very long time period, thus it is very difficult to observe in reality or to make theories about it because the scientist will have to wait years before seeing results.

Same for FEA, even if you have creep models and you can theoretically simulate creep, you have to be very careful about the accuracy of those results without any experiment coming to prove that they are correct.

(If by some chance you have some experience in creep and you have something to add, please enlighten everyone by leaving a comment about your experience.)

Can several failure modes happen at the same time??

Yes, it most engineering problems, that is what happens… that’s why it’s alway important to review the data and try to spot all the possible signs of any failure.

Good luck with that!

///////////////////////////////////////////////////////////////////////////////

You maybe noticed that I wrote a lot of great educational article… that’s because I really want to contribute and help engineers who are new to FEA to understand those concepts better and faster!

I am not hiding that it takes a lot of efforts to write all that, so…

[Pocster]

It’s a bit like my HMO’s . The emergency lighting has to last 3 hours …. In an emergency e.g fire - I reckon most people would be out in a bit less than 3 hours .

Why 3 hours ? Who knows … more overkill I think .

[Gordo]

15 hours ago, saveasteading said:

No. As an earlier post says.....to prove this the builder must present the proof to the bco.

 

It is easy enough to find the solution to suit the circumstances.

 

By the time a steel beam has melted there isn't much left of the house or the people upstairs. But a good ceiling stops it all.

 

Anyone can provide the proof. BCO doesn’t care who provides it and a good FR ceiling only works for a set period of time before it’s compromised and bendy steel time.

Edited November 28 by Gordo

[Gordo]

8 hours ago, Pocster said:

It’s a bit like my HMO’s . The emergency lighting has to last 3 hours …. In an emergency e.g fire - I reckon most people would be out in a bit less than 3 hours .

Why 3 hours ? Who knows … more overkill I think .

Most codes / guidance are based on a worst case scenario for simplicity. This allows the codes to be used by the “less expert”. If you employed a certified fire engineer they can provide a bespoke solution to argue lower standards than the codes quote. Building control generally bow to the experts (unless they are talking nonsense. For example in a HMO they generally designed for simultaneous evacuation ie every one out and with max 1/2 hr fire resistance elements. so I would imagine it wouldn’t be hard to argue that 3hr battery back up to emergency lights is not necessary.

Edited November 27 by Gordo