Service Moment (KNm)

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'.

"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

Reply to
David WE Roberts
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It's a good job you're not a structural engineer then.

mark

Reply to
mark

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Reply to
David WE Roberts

snip

And you are of course.

Reply to
Roger Chapman

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

Reply to
mark

snip

It must be nice to be able to resort to insults without the need to check your facts.

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Reply to
Roger Chapman

I think that was possibly ambiguous. It certainly didn't say what I intended to mean. 1 Kgf is 9.81 N. I just got it the wrong way round for which I am sorry. Blame it on my education that didn't include SI metric, just Imperial units and cgs and mks metric.

Reply to
Roger Chapman

Reply to
mark

So how do you calculate the bending moment?

Reply to
Bruce

Wrong. A kgf (kilogramme force) is the force exerted by one kg due to gravity. There is no 9.81 involved. 1 kg exerts 1 kgf.

These units are no longer used for structural design - kgf has not been in general use since the 1970s. Absolute units of force are used instead, based on the Newton, which is the force required to accelerate 1 kg by 1 m/s per second (1 m/s^2).

The acceleration due to gravity is approximately 9.81 m/s^2. So the force exerted by one kg due to gravity is 9.81 N.

A kilonewton (kN) is 1000 Newtons, or the force exerted by 102 kg due to gravity, because 1000 divided by 9.81 is approximately 102.

Reply to
Bruce

"So one kilogram-force is by definition equal to 9.80665 newtons"

As stated, its a good job you aren't a structural engineer, or a scientist, or an engineer, etc.

Reply to
dennis

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)

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.
Reply to
John Rumm

snip

I did, as you well know since as you had plenty of time to read my subsequent message before taking the opportunity to gloat.

Can't you ever post anything without resorting to a lie.

Reply to
Roger Chapman

Bugger! Maths 101 again for me!

Reply to
David WE Roberts

Do you think people read to the end of a thread and then reply?

No lie, just an opinion based on your previous posts.

Reply to
dennis

snip

Sensible people do as do the devious and deceitful which is the category you qualify under.

Just because you lie at the drop of a hat is no excuse for believing that others are equally dishonest.

And if it is opinions you want to exchange it is my opinion that you are dishonest scumbag who would never stoop to telling the truth when a lie would serve your purpose better. IIRC you claim to be some sort of scientist but what scientist could be so absolutely clueless about statistics as you have proved yourself to be?

So who cares what you think.

Reply to
Roger Chapman

Ah well I understand more about UseNet than you do. To start with its asynchronous. Messages propagate to different servers at different times. You can never be sure someone hasn't posted another reply that hasn't arrived your server. I am surprised you haven't looked it up on wiki so you can understand why someone might not see your second post even if they have read the whole thread. PS. there is no guarantee that you will see this message as UseNet can lose messages between servers.

Your general lack of understanding about most things, like UseNet, makes me think you are not educated enough to be an engineer/scientist.

Probably about as many as care what you try to think.

Reply to
dennis

You might think that (and I freely admit I don't know very much about its inner workings) but your reply shows that you have a very superficial view yourself.

Yes, so?

And how long does that usually take? Your message was timestamped 119 minutes after my second message.

Quite right but very much a red herring. Seems we will have to add probability to the long list of things you don't understand.

Those two messages where probably close enough for the second to have turned up first on your server but the odds of it being delayed for so long that it didn't arrive till after you posted yours is remote.

In which case I would be able to reply to it and all you pearls of wisdom would have been wasted.

Unlike you I have never claimed to be be a scientist and also unlike you I base my case on observation and not by palely reflecting my comments back at me which smacks of schoolboy yah-boo on your part.

Sometimes I think you are a retard. Doesn't take much effort given your track record.

Reply to
Roger Chapman

Well last week it was taking two days for them to arrive on datemas. I have no idea how long it took to arrive as I only do manual downloads to my system so it could sit there for hours if i wonder of and make dinner or sand down a table or have a bath. As i said you don't have a clue.

Reply to
dennis

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.

Reply to
Roof

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