Why Hardiflex (Cement board) can't be used on hot-rolled steel section? 1

[lager]

http://www.jameshardie.co.nz/productfiles/0054864001404956645.pdf

The cement board Hardflex manual says "Sheets must not be fixed directly to drawn steel or hot-rolled steel sections"?

May I know the reason for it? Are there chemical reactions between cement board and hot-rolled steel sections?

But most steel sections are hot rolled.. is it not?

 

[hokie66]

In perusing that manual, I didn't find your quote, but am sure it is there. What page?

No, chemical reactions wouldn't be the reason.

Hot rolled steel sections are generally a lot thicker than cold formed steel sections. Even if allowed, fastening to hot rolled sections would be impractical due to the difficulty of doing so.

I think the main reason for such a provision is that fibre cement sheets are relatively brittle, so any movement of the fasteners needs to be in the supporting members (timber or light gauge cold formed steel). You will note that there is a similar prohibition to attaching the sheets directly to the bottom chord of roof trusses. Battens must be used.

 

[lager]

Oh no. I have dozens of 9mm thick Hardiflex cement boards at site ready to be installed to 1.6mm thick purlins. The web site shared earlier was about sidings and eaves.. it's in page 11. But in the general Hardiflex frame installation guide,

http://www.jameshardie.com.au/uploads/files/Bracing Sheet Application Guide - Jan 2012 - LR.pdf

it says:

"8.2 FRAMING
8.2.1 General
HardieBrace sheet bracing can be fixed to either timber or domestic steel
framing. The framing used must comply with the relevant building
regulations and standards and the requirements of this manual.

8.2.3 Steel
The base metal thickness (BMT) of a steel frame must be between
0.55mm and 1.6mm."

But it seems HardieBrace sheet bracing is itself cement board.. in the site

http://www.jameshardie.com.au/products/external-cladding/hardieflex-sheet/

it says:

"6mm HardieFlex base sheet can also be used as bracing."

So how would my 9mm Hardiflex cement board act in the 1.4mm Hot-rolled steel section? Since the cement board is 1.2 meters width.. we plan to install purlin every 0.6 meter.. so how do you put extra bracing.. and what do you mean by fasheners? Are they screws or another framing over the purlins? How.. we don't have local Hardiflex technical support. Thank you.

 

[Ingenuity]

Your "1.6mm thick purlins" have a BMT of 1.6mm and are cold formed so you appear to comply with the stated requirements.

 

[hokie66]

Ingenuity is correct. Your purlins are cold formed, not hot rolled. The Hardie manual which you referenced gives you the requirement for fasteners, which would be screws in your case. Follow the manual in all cases, but I assume you have telephones. Hardie reps can be consulted worldwide. The word "fasteners" means screws, nails, bolts...

 

[lager]

Your "1.6mm thick purlins" have a BMT of 1.6mm and are cold formed so you appear to comply with the stated requirements.

Up to what thickness are purlins cold formed? Are there no 1.6mm purlins that is hot formed? how about 2mm or 1.8mm because the delivery has mixture of 2mm and below?

 

[hokie66]

Not sure about where you are, but in Australia we have cold formed purlin availability up to 3.0 mm thick, at least. To the best of my knowledge, no Cee and Zed type purlin sections are hot rolled.

 

[MikeHalloran]

Now I'm confused by Hardie's recommendations as cited.

Cold formed articles, e.g. purlins, are roll-formed or brake-formed, commonly from cold rolled steel.
I think some people refer to cold rolled as cold drawn, but the processes are different.

Cold drawn steel is fat wire that is pulled through a series of tapered dies to make thinner wire, or other roundish product.

Cold rolled steel is thick sheet or plate that is passed through multiple sets of rollers that squeeze it normal to its thickness to make thin sheet.

In both cases, the reduction in area is accomplished 'cold', below the recrystallization temperature, so the mechanical properties are improved, but in the case of drawing, the primary driver for deformation is tension in the product, and in the case of rolling, the primary driver for deformation is compressive stress applied through the thickness, which of course induces tensile stress along the products length indirectly.

If Hardie means 'cold rolled' when they say 'drawn', then contact with common purlins would be contraindicated, I'm not sure why.

You really need to call Hardie, somewhere, and escalate your question until you find some technical person to explain what they mean, exactly.

Please report back with the results; now I'm curious.





Mike Halloran
Pembroke Pines, FL, USA

 

[lager]

The company i bought the 1.6mm cee purlins said they were hot rolled. I need to know. If purlins are 1.6mm hot rolled vs cold rolled. Do they have similar hardness or stiffness or is the hot rolled harder or stiffer than the cold rolled (but same thickness)??

 

[MikeHalloran]

I won't say it's impossible, but I don't recall ever seeing a hot-rolled shape that was thinner than ~4mm.
Of course they could be cold-formed (by roll forming or brake bending) from hot-rolled sheet, which can be thin.

Stiffness must be the same.



Mike Halloran
Pembroke Pines, FL, USA

 

[hokie66]

You are making too much of this, lager. How would you hot roll a purlin shape? The sheet which they are made from can be hot or cold rolled, as Mike said. Either way, the process of rolling makes the sheet very hot. But purlins are cold formed from the sheet. What company told you they were hot rolled? Even if somehow they are, I am sure Hardie's requirement is based on the thickness of the steel. Like Mike, I wonder about the "drawn" bit, as I wonder what application is considered.

 

[lager]

I think the main reason for such a provision is that fibre cement sheets are relatively brittle, so any movement of the fasteners needs to be in the supporting members (timber or light gauge cold formed steel). You will note that there is a similar prohibition to attaching the sheets directly to the bottom chord of roof trusses. Battens must be used.

The following is the recommended pattern for the nailing...

With so much nails.. won't it crack during seismic movement if they are attached directly to hot rolled 1.6mm C-section?

The C-section is 2x4 inch and 0.063" (1.6mm thickness). The 9mm hardiflex were supposed to be connected to the 2 inch side.. but I'm afraid they may be so rigid... anyone has idea how to connect the hardiflex to battens instead that is connected to the C-section (purlin)? Maybe the purpose of connecting it to battens is during seismic activity.. the battens would flex and this would avoid brittle failure of the Hardiflex?

The Hardiflex technical crews were not structural engineers so they can't answer my question. They don't even know the difference between hot rolled steel vs cold rolled steel. The technical said it shouldn't be connected to frozen support (her understanding of cold rolled steel)

Has no one here installed Hardiflex over C-sections before??

 

[John2025]

The manual that restricts direct connection is for soffits and eaves. Is it a venting and condensation issue? I seem to remember a discussion about condensation in un-conditioned spaces due to temperature swings from day to night in humid climates. Maybe the hot roll/cold roll issue isn't really what they mean?

 

[lager]

In the same url shared in the first message. It was mentioned

"Steel framing members must be fabricated from light-gauge sheet steel 0.55mm thick minimum to 1.6mm maximum. If heavier sections are used difficulties may be experienced in fixing the
self-drilling, self-tapping fasteners. Refer to specific details for the minimum flange width requirements.

Sheets must not be fixed directly to drawn steel or hot-rolled
steel sections. These must first be battened out with ex 50mmthick
(40mm minimum) timber battens or light-gauge metal furring
channels."

Hardiflex refers to light-gauge sheet steel as from 0.55mm to 1.6mm thick.
Does it refer to hot-rolled as above 1.6mm thick? Or are there really light-gauge sheet that is 1.6mm and this is different from hot-rolled that is 1.6mm?

I mean.. I read somewhere that hot-rolled are greyish blue in the surface texture and cold-rolled are more smooth.. so there must be difference in the fabrication? maybe some cold-rolled are produced from different kind of hot-rolled than those directly hot-rolled?

 

[hokie66]

Hot rolled, cold rolled, it is all steel. Structural sections are generically called hot rolled, while light gauge like 1.6 mm is cold rolled. I thought these sheets were being installed horizontally, but now see they are wall cladding or lining. Follow the Hardie directions for number and type of fasteners, which won't be nails if you are fastening to steel. Yes, if you have an earthquake, there will be damage to the sheets. So what?

 

[lager]

hokie.. the philosophy in seismic design is ductility and not brittle failure.. in the event of earthquakes.. the Hardiflex must not break apart and fall down.. instead the fasteners or studs inside it is the one that must move.. isn't this what you mentioned too..

when we think of hardiflex.. we imagine thin sheet of concrete.. but isn't it there is a fibre component to these cement board that makes them tougher?

Usually how big an earthquake before they break down? It's just more difficult to replace them from the outside.. so it's better to have ductile elongation and bending of the studs than brittle failure of the cement board.

But then.. my senior designer didn't make the C-sections thinner than 1.6mm because he said if they are lesser in thickness, the wind force may bend them...

 

[hokie66]

I couldn't answer your question about how big of an earthquake it would take to damage the sheets. That depends on a lot of variables involving the magnitude, location, and type of earthquake. It also depends on the structure of your building. But suffice it to say, large earthquakes almost invariably cause damage to building facades.

 

[lager]

I think you can recognize between hot and cold rolled steel.. the following site says cold rolled still are smooth grey while hot rolled steel are bluish-grey..

Why does Cold Finished Steel have a smooth grey finish, while Hot Rolled Steel has a rough, blue-grey finish?

http://www.metalreference.com/INFO_Cold_Finished_Steel.html

Last week we had delivery of cold rolled steel purlins which I took as galvanized or galvalume.. so I rejected it because you are not supposed to have galvalume contact with other metal, concrete because the zinc-aluminum can oxidize.. so I rejected all the items delivered.. in the following picture.. the 4 purlins on the left are cold-rolled (see the smooth grey).. the 5 purlins on the right are hot rolled (just delivered a while ago).. final caliper thickness says 1.7mm..

Quoting from the above url which says it's fragile to bend any existing hot rolled into cold rolled purlins.. then how can you say purlins below 3mm are cold rolled.. they can break if bent cold so I think purlins below 3mm and above 1mm are hot rolled.. the url says:

"Why does Cold Finished Steel have a smooth grey finish, while Hot Rolled Steel has a rough, blue-grey finish?
Cold Finished Steels are just that - the final rolling is done when the steel is cold (room temperature), the whole operation bathed in oil, so the finished product is unoxidized, the grey of the actual steel, and as smooth as the rollers that do the processing.

Hot Rolled Steels are just that - They are heated up red-hot and pushed through rollers that squeeze the metal, literally squishing it into a particular profile, depending on the shape of the rollers. The process takes a long time, and because the steel is so hot for so long in th open air of the steel mill, the surface of the metal has has a long time to oxidize, producing a thick, tough oxide scale with the characteristic blue grey finish of the final product.

Why are there so few shapes available in Cold Finished Steel and so many in Hot Rolled Steel?
Steel is a very tough material when it is “cold” (meaning “room temperature”). When it is bent, hammered (such as in cold forging), or deformed in any way steel can actually harden in the area of distortion and begin to crack or weaken. Only if it is heated past a particular temperature (usually a red-heat) does it become plastic enough to be bent, formed hammered, and squeezed with relative ease and without damaging the metal. For example, few of us would be able to bend a bar of 1” thick steel at room temperature no matter how hard we tried, but if the middle of the bar were heated with a torch until it glowed a healthy cherry red color, most of us would have very little trouble bending the bar back upon itself until both ends touched. And when it cooled it would regain its toughness and strength in that bent condition and we would no longwr be able to bend it.
This means that the intricate profiles apparent in, say, a Hot Rolled beam or channel is only possible to form if the steel is iin the red-hot condition. If these types of profiles were attempted in the cold condition both the metal and the equipment used to shape the metal would be ruined.
This means that only relatively simple shapes like flats, hexagons or rounds are available in Cold Finished Steels. However, one of the great advantages of this process is that the resulting products is a much finer surface (that is bare of oxidation) and sharp corners to the profiles of Cold Finished products as opposed to the rounded and rough finish of Hot Rolled Steels."

Anyway. I have one problem.. the hardiflex limit is 1.6mm base metal thickness.. my purlins or C-sections are 1.7mm base metal thickness when measured using accurate caliper.. can you give a metal object that is 0.1mm thick for comparison.. how thin is 0.1mm thick.. how much percentage can it affect when you insert teksscrews??

 

[hokie66]

Get real. Steel is steel. You are wasting our time, and the only reason I am commenting is that I have had a few glasses of nice red wine. Good night.

 

[lager]

Steel is steel.. but for the same diameter say 3/8" rebar, there are grade 40 and grade 60. Likewise the impression they are giving is that cold rolled steel are like grade 40.. hard rolled steel are like grade 60.. they are same diameter but the grade or compressive strength may differ.. what was what I had in mind since start of thread..

unless you meant rebar is not pure steel so the grade can vary but cold and hard rolled steel are pure steel so the grade is similar (or ungraded).. I just thought of this at this moment.. hmm...