Service Moment (KNm)

Page 3 of 3  


Why is shear force a complication? What do you think governs the design of a beam or lintel?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Well, at least something has finally sunk in
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

For the avoidance of doubt, fuck off, and don't come back.
Meanwhile, congratulations on your restoration to my kill file.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

You seem to be mis-reading the manufacturers data. They've provided a table giving the safe uniform working load a lintel can take for a particular lintel size and clear span. If the load isn't uniform then they've provided the equivalent service moment. If you don't understand the figures then it probably means you need someone to assist you.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Roof wrote:

Here you go roof, your chance to actually help the chap and explain it all!
--
Cheers,

John.

/=================================================================\
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
David WE Roberts wrote:

What is your actual application here?
In many cases you don't need to deal with service moments since often the lintel will be carrying a uniformly distributed load - or at least a series of point loads that can be treated as a UDL e.g. floor joists spanning a room that are supported on a wall into which you are installing a lintel and creating an opening. Hence you can use the figure from the body of the table directly.
--
Cheers,

John.

/=================================================================\
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

At last a voice of sanity. I trust the squabbling kids have moved on.
*********************** Firstly, I hadn't seen the row at the bottom of the PDF which gave a load in Kg per metre. This would have made things a lot easier.
The application is a lintel to go over the top of two doors and two windows in the Mother of all Sheds. They will be part of the ultimate block course and so be bearing little more than the weight of the roof and joists. The window span is 900mm. The door span is 1650mm. The loading figure given for P100 is 14.27 Kg/metre. This suggests that it would bear the weight of roof joists and roof but might not be adequate on its own to support the load of an 80Kg adult on a single joist hung above the lintel.
************************************** Edit - I've left the above in to show what I thought on first re-read.
Looking at it again this is the weight of the lintel itself, per metre, 'to be subtracted from the load given'.
Interesting - the volume of a 2.1 metre lintel is just under 1.5 * volume of a concrete block. Concrete block weighs 3 stone or 19Kg. So for equivalent density the lintel would weigh just under 30Kg. At 14.27Kg/metre a 2.1 metre linte wighs just under 30Kg. So a period of mature reflection would have concluded that this couldn't be a figure for the load bearing strength!
So, given that Roof said:
"You seem to be mis-reading the manufacturers data. They've provided a table giving the safe uniform working load a lintel can take for a particular lintel size and clear span. If the load isn't uniform then they've provided the equivalent service moment. If you don't understand the figures then it probably means you need someone to assist you. " where is this information about the safe uniform working load? Or has Roof mis-read the table?
All I can see at the moment are figures for lintel weight and Service Moment. I presume that in taller walls a lintel has to support the triangle of blocks/bricks directly ove the lintel which are not self-supporting. In this case there would be 2/3 of a block course then a wall plate above the lintel. The joists would be on hangers off the wall plate. So for the door the combined strength spreading the load would be the wall plate above 2/3 row of blocks above the lintel (which isn't quite touching the top of the door frame otherwise that would provide some additional support).
I now have two other pieces of advice:
"Multiply weight in Kg by 9.81 to get Newtons" "One KN is about the force you get from 100Kg weight" Which don't seem to agree.
100Kg * 9.81 is approximately 10 Newtons? Which would be 0.01kN?
Or 100Kg = 1kN?
For the 2.1m P100 on a 1650mm span with a figure of 3.33 kN this is either:
100 * 3.3/0.01 = 33,000Kg (!) or 100 * 3.3 = 330Kg.
Hopefully the lower figure is still accurate because a load of 330Kg per metre should support even my weight. This is about 17 concrete blocks per metre and I think a course would become self supporting at less than 8 courses high over 1.65 metres.
If there is another order of magnitude difference then 33Kg is just about useless given that an individual concrete block weighs 19Kg and you lay just over 2 to a metre!!.
So, bottom line is the lintel is across a void and intended to support a metal sheet roof on wooden joists with the ability to support an adult male on the roof above the void. About 2/3 of a course of blocks and a wooden wall plate will be above the lintel.
Assuming the 330Kg/metre is accurate then the P100 should be fine, especially with the additional strength of the wall plate.
And it is, afer all, only a f*cking shed.
Cheers
Dave R
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

The two pieces of 'advice' do pretty much agree.
100kg *9.81 = 981Newtons , rounding to 1000 newtons which is 1kN
Thus: 100Kg equates to 1kN
mark
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thu, 22 Apr 2010 12:27:06 +0100, "mark"

So how do you calculate the bending moment?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Bugger! Maths 101 again for me!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
David WE Roberts wrote:

Careful - that's the weight of the lintel itself per meter. So for example a 2.1M long P150 lintel (65x140mm) would be 2.1 x 19.38 kg for the lintel. However its load carrying capacity over a 1.8m span would be 4.23kN or about 423kg. From that you need to subtract the weight of the lintel itself - or about 40 odd kg (being conservative using the full width rather than just the span).

;-) ok - I have left in the first bit I typed to show that I did not read this far down until now!

In general Roof is being as helpful as always.
The main slab of figures in the grid gives you the maximum uniform load for various combinations of lintel profile and length.

You should be able to see a table with length down the left hand column, and lintel profile across the page...
(is your PDF viewer doing something funny)

yup
The lack of courses of bricks/blocks above the lintel means technically you don't get the full load spreading effect of the point loads from the joist ends, but in this non critical application I can't see that being a problem.

lets round the 9.81 up to 10 for the mo...
so 100kg x 10 = 1000N = 1kN

I think your decimal point went walkies somewhere!

yup.
The latter...

Note - that is a TOTAL uniform distributed load of 330kg - not a load of 330kg per meter.

If you start from the span, you can calculate the weight of blocks you will support. Then you need to know the weight per square meter of roof, including any anticipated extra loads like snow etc (for flat roof apps they typically[1] use about 0.75 kN/m^2 for snow and "access" (i.e. you etc)).
From there you can multiply the area load by your joist spacing and length to get a UDL per joist. Under normal circumstances half the total load on each joist will bear on the support at each end. Take that and multiply by the number of joists sitting on the lintel to get the total loading from the roof, and add to the block loading.

If your span is 1.65m, then that means say 80kg of blocks etc, and say 30kg of lintel, leaves you 220kg to play with. I can't see your roof weighing much if its just corrugated tin sheets - say 15kg m^2 tops. Add an effective 75kg/m^2 for snow, wind uplift, and people etc. If the shed is say 2.5m deep and the joists are on 400mm spacings then :-
2.5 x 0.4 x (15 + 75) x 10 = 900N / joist.
So four joists on the lintel at most, with 450N each - that is another 180kg.
Adjust for your actual spans and spacings etc.

Indeed. This is where structural engineers can come a bit unstuck - they sometimes forget to check why the question is being asked.
[1] may want some adjustment if you are in a very windy area. There are tables in one of the approved docs IIRC on what is considered not unusual for each area.
--
Cheers,

John.

/=================================================================\
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

John, you let yourself down in a big way when you make those sorts of meaningless statements.
I have been nothing more than consistent in the advice I have given regarding structural matters on this newsgroup; if you don't know what you are doing, then get paid-for professional advice from a structural engineer. Bruce understands this simple principle and now sings from the same hymn sheet.
In the second part, you are trying to be too helpful and in doing so, it worries me that you going to fall into the pooh.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Roof wrote:

How is that? I was just commenting on your consistency. ;-)

Seriously, for building a shed?
Like most folks I come here for discussion, information, answers etc, and have over the years been astounded at quality and quantity of information that people are prepared to share - it is what makes this group a formidable source of learning on a diverse range of topics, at least if you are prepared to invest enough time to get the best from it.
Even when posted with the best of intentions, posts that are (or at least appear to be) condescending, willy waving, self serving, holier than thou etc, I personally find only serve as an irritation. I dislike "closed shops" with a passion. As I see it, we are grown-ups here, free to make our own cockups.
I work on a principle counter to yours it seems. Generally I see no reason not to share what I know about something (be that on usenet or with clients paying for my professional advice). I appreciate that there are times when one can read between the lines of a question and realise that the asker is in danger of getting themselves into a potentially dangerous situation - and in those cases I would also back away from a direct answer. However I expect again there we differ in approach, normally at that point I would probe a bit further for more background first to better gauge the question and questioner, rather than moving straight to a "you need to seek professional help" type of response.
Hence even if a questioner concludes that a subject is indeed too "deep" and professional advice should be sought, they at least get to seek it better informed.

I would be interested to know what "pooh" you perceive that one might fall into?
This is usenet, and I know that Dave and most other folks around here have been communicating this way plenty long enough to understand the realities of the situation. People ask for advice, they get answers, some might be good, some will be crap, plenty will be unrelated etc. No money has changed hands, there is no contractual nexus in place, so you use any advice you receive entirely at your own risk, understanding that it may be nothing more than hearsay from someone entirely uneducated and without experience in the domain.
Personally that is a risk I am content with when seeking advice - since I find its not too difficult to work out what advice is useful, what is questionable and what can be discounted out of hand, and to learn the strengths and weaknesses of regular contributors. Its also a risk I am content with when offering advice. Generally I try to give decent quality information, and will not usually resort to invention or guess work without making this clear. I do make mistakes, and post stuff in error from time to time, and presume that readers won't be too disillusioned to realise that ultimately this is their problem, since there are no guarantees offered!
--
Cheers,

John.

/=================================================================\
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote in message >

<snip>
John, I know who supplies more value per posting :-) [Although zero isn't hard to beat] Thanks again for your help.
Dave
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Roof wrote:

Does this mean you've been less than consistent?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Gib Bogle wrote:

less than or equal ;-)
--
Cheers,

John.

/=================================================================\
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It's dennis on the tiles
--
geoff

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Roof wrote:

I find that barely credible.
Tim
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Picture added to http://s817.photobucket.com/albums/zz92/LittleGreyCatUK/Mother%20of%20all%20Sheds/
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

    HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.