I acquired an ordinary national certificate in mechanical engineering
some 40+ years ago, unused since.

Can some kind person direct me to a source for understandable formulae
for working out approximate purlin loading on a simple pitched roof? I
assume the existing trusses will be adequate.

I am replacing a time expired corrugated steel roof and am considering
using composite roof panels which are much heavier:-)

The original building is Victorian/agricultural but I can't see any
evidence of an earlier slate covering and the truss/purlin spacing is
only suitable for rigid sheeting.

Having just glanced at a chapter on theory of structures (Mitchell,
building construction) I fear I may be heading for deep water:-)

regards
--
Tim Lamb

Tim Lamb wrote:
I am replacing a time expired corrugated steel roof and am considering
using composite roof panels which are much heavier

Why not just replace the "corrugated iron" sheets? Last for ages,
cheap, easy to put up.

wrote:

Best advice if it's just for information, not for building control,
is to get the demo version of Superbeam (its free). I worked out my
roof design using that, and put it on plans for building control.
They then demanded some structuiral calculations for which I had to
pay 80 quid, which showed that my design was OK (which I knew).
The calcs by a qualified structural engineer took up about 15 pages
and gave me a nasty flash-back to A-level physics.

Would have almost been cheaper[1] to cough up for Superbeam so you could
have printed them off yourself!

[1] well not quite, but at least you would have a nice bit of software
to play with after ;-)

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

In message , Chris Bacon
writes
Tim Lamb wrote:
I am replacing a time expired corrugated steel roof and am
considering using composite roof panels which are much heavier

Why not just replace the "corrugated iron" sheets? Last for ages,
cheap, easy to put up.

Yes. These have lasted around 60 years. I suspect they were good quality
at the time.

Unfortunately moist air condenses on the underside of cold steel sheet.
This is particularly apparent when such buildings house cattle on deep
litter and there is a frost.

Anyone repairing or modifying traditional farm buildings has to consider
future alternative uses. My intention is to convert what was a milking
shed with standings for 12 cows to house the farm woodwork shop. Gluing
at less than 10 centigrade is a problem and I may need to put in some
heat.

The proposed panels have 80mm of insulation and weigh 11.75kg/m2.

regards

--
Tim Lamb

In message . com,
writes

Best advice if it's just for information, not for building control,
is to get the demo version of Superbeam (its free).

OK ta. I'll have a look this evening. If the building ever comes up for
a change of use, I will have to sort this out properly.

regards

--
Tim Lamb

On Wed, 8 Mar 2006 09:22:42 +0000, Tim Lamb
wrote:

I acquired an ordinary national certificate in mechanical engineering
some 40+ years ago, unused since.

Can some kind person direct me to a source for understandable formulae
for working out approximate purlin loading on a simple pitched roof? I
assume the existing trusses will be adequate.

I am replacing a time expired corrugated steel roof and am considering
using composite roof panels which are much heavier:-)

The original building is Victorian/agricultural but I can't see any
evidence of an earlier slate covering and the truss/purlin spacing is
only suitable for rigid sheeting.

Having just glanced at a chapter on theory of structures (Mitchell,
building construction) I fear I may be heading for deep water:-)

regards

Seems like a fine opportunity for combined roofing and solar heating
panels, depending on your orientation. Good luck with the calcs.
--
Regards,
Mike Halmarack

Drop the EGG to email me.

wrote in message
ups.com...
Best advice if it's just for information, not for building control,
is to get the demo version of Superbeam (its free). I worked out my
roof design using that, and put it on plans for building control.
They then demanded some structuiral calculations for which I had to
pay 80 quid, which showed that my design was OK (which I knew).
The calcs by a qualified structural engineer took up about 15 pages
and gave me a nasty flash-back to A-level physics.
Simon.

A friend has a garage with a flat roof. He wants to put a pitched roof on.
The roof is merely for looks as the flat roof is waterproof. The garage
roof will not be big at all as the garge can just about fit a Cavalier car.
Would Building Control need to be notified and would they require stress
calcs for such a simple small roof? A cut roof using 2x4s would be well
strong, and I can't see the need for calcs in this instance as rule of thumb
is more than good enough.

"John Rumm" wrote in message
...
wrote:

Best advice if it's just for information, not for building control,
is to get the demo version of Superbeam (its free). I worked out my
roof design using that, and put it on plans for building control.
They then demanded some structuiral calculations for which I had to
pay 80 quid, which showed that my design was OK (which I knew).
The calcs by a qualified structural engineer took up about 15 pages
and gave me a nasty flash-back to A-level physics.

Would have almost been cheaper[1] to cough up for Superbeam so you could
have printed them off yourself!

[1] well not quite, but at least you would have a nice bit of software to
play with after ;-)

How much is Superbeam?

Doctor Drivel wrote:

How much is Superbeam?

£149+VAT

http://www.sda.co.uk/sbw.htm

(Still waiting for Tony to do us the uk.d-i-y special discount version
though! ;-)


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Wed, 08 Mar 2006 13:20:48 +0000 John Rumm wrote :
(Still waiting for Tony to do us the uk.d-i-y special discount
version though! ;-)

I'm am forever being told that we sell it too cheap so everyone is
getting the discount price!

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm
[Latest version QSEDBUK 1.12 released 8 Dec 2005]

Tony Bryer wrote:

On Wed, 08 Mar 2006 13:20:48 +0000 John Rumm wrote :

(Still waiting for Tony to do us the uk.d-i-y special discount
version though! ;-)


I'm am forever being told that we sell it too cheap so everyone is
getting the discount price!

To be honest, I agree! ;-)

(I would not have been suprised if it came with a price tag in the £300
to £600 range)

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Wed, 08 Mar 2006 14:22:26 +0000 John Rumm wrote :
To be honest, I agree! ;-)

(I would not have been suprised if it came with a price tag in the £300
to £600 range)

Thanks! Knowing what to charge is hugely problematic with something that
has a minimal marginal cost per extra unit supplied. I have no doubt that
the vast majority of those who have bought it and use it regularly would
*now* feel that it is worth more, but keeping the price lower encourages
the less certain to take a chance - £149 is not nothing but it's not a
disaster if it doesn't work out. And, more importantly, we haven't left
much of a price hole for someone else to come in and fill - a few have
tried over the years but never lasted.

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm
[Latest version QSEDBUK 1.12 released 8 Dec 2005]

In message , Mike Halmarack
writes

Seems like a fine opportunity for combined roofing and solar heating
panels, depending on your orientation. Good luck with the calcs.

Thanks.

East/West so OK but...

With a largish river 20m away I'm more inclined to a heat pump.

I don't know if o/p temperatures would be high enough for under floor
heating but I will bear it in mind for any future change of use.

regards

--
Tim Lamb

In message .com,
writes
Mike Halmarack wrote:
On Wed, 8 Mar 2006 09:22:42 +0000, Tim Lamb
wrote:

I am replacing a time expired corrugated steel roof and am considering
using composite roof panels which are much heavier:-)

Seems like a fine opportunity for combined roofing and solar heating
panels, depending on your orientation. Good luck with the calcs.

Yes, this is when it can really be cost effective. Panels and roof
covering are one and the same thing. How much hot air could it produce
during winter? at what cost? How much more is this than plain roofing
cost?

Current estimate for a roof 4.5m x 13.5m (in plan) around £1500 using
*seconds*. A lot of the cost is in the fixings, ridge, gap closers,
barge boards etc.

I have no idea what the cost would be if half were in solar panels.
Presumably I would still need a conventional heat source as a back up?

regards


NT


--
Tim Lamb

We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember Tony Bryer
saying something like:

On Wed, 08 Mar 2006 13:20:48 +0000 John Rumm wrote :
(Still waiting for Tony to do us the uk.d-i-y special discount
version though! ;-)

I'm am forever being told that we sell it too cheap so everyone is
getting the discount price!

Superbeam and Superheat are really excellent items. The demo versions
will do me for just now, but if I start needing them seriously I'll have
no hesitation in paying for them.
--

Dave

"Tim Lamb" wrote in message
...
In message , Mike Halmarack
writes

Seems like a fine opportunity for combined roofing and solar heating
panels, depending on your orientation. Good luck with the calcs.

Thanks.

East/West so OK but...

With a largish river 20m away I'm more inclined to a heat pump.

I don't know if o/p temperatures would be high enough for under floor
heating but I will bear it in mind for any future change of use.

A water sourced heat pump extracting from a moving stream or river is by far
the best system.

Tim Lamb wrote:
Chris Bacon writes
Tim Lamb wrote:
I am replacing a time expired corrugated steel roof and am
considering using composite roof panels which are much heavier

Why not just replace the "corrugated iron" sheets? Last for ages,
cheap, easy to put up.

Unfortunately moist air condenses on the underside of cold steel sheet.
This is particularly apparent when such buildings house cattle on deep
litter and there is a frost.

Lay the iron over 1/2" Sterling board. This works well. Then again,
you're adding weight...

In message , Chris Bacon
writes
Tim Lamb wrote:
Chris Bacon writes
Tim Lamb wrote:
I am replacing a time expired corrugated steel roof and am
considering using composite roof panels which are much heavier

Why not just replace the "corrugated iron" sheets? Last for ages,
cheap, easy to put up.
Unfortunately moist air condenses on the underside of cold steel
sheet. This is particularly apparent when such buildings house cattle
on deep litter and there is a frost.

Lay the iron over 1/2" Sterling board. This works well. Then again,
you're adding weight...

The nice thing about steel sheeting is that the ribs confer rigidity.
This allows the construction of a weatherproof roof without much
supporting structure. My trusses are 3m apart and the purlins 1.5m.
Compare this with a conventional roof!

regards

--
Tim Lamb

In message ews.net,
Doctor Drivel writes

With a largish river 20m away I'm more inclined to a heat pump.

I don't know if o/p temperatures would be high enough for under floor
heating but I will bear it in mind for any future change of use.

A water sourced heat pump extracting from a moving stream or river is
by far the best system.

So what exit temperature could I expect from the heat exchanger and is
this high enough for under floor space heating?

There is also the issue of Environment Agency consent. I have not
investigated their views on this particular river (the Lea) but know
they normally expect a licence/payment to abstract and return water.

It may be acceptable to draw from a shallow well and return via a soak
at some distance.

regards


--
Tim Lamb

Would have almost been cheaper[1] to cough up for Superbeam so you could
have printed them off yourself!
I wondered about that.Aparently a superbeam printout is OK for bulding
control.
But surely garbage-in, garbage-out.
The structural engineer analyses the load on the structure as well as
analysing the
structure itself.
How is that sorted out if you use superbeam for building control ?
Simon.

"Tim Lamb" wrote in message
...
In message ews.net,
Doctor Drivel writes

With a largish river 20m away I'm more inclined to a heat pump. I don't
know if o/p temperatures would be high enough for under floor heating
but I will bear it in mind for any future change of use.

A water sourced heat pump extracting from a moving stream or river is by
far the best system.

So what exit temperature could I expect from the heat exchanger

Depends on the compressor, but enough to supply DHW, so 55-60C is achievable
all year round.

and is this high enough for under floor space heating?

It will run rads, as long as the stream
or river never drys up.

There is also the issue of Environment Agency consent. I have not
investigated their views on this particular river (the Lea) but know they
normally expect a licence/payment to abstract and return water.

You are just extracting heat. Making the water cooler, to therm, may affect
wildlife. If the river moves quite well, then this should not a be a problem
at all. Also, a reversible heat pump can dump heat into the river too, and
cool the house.

It may be acceptable to draw from a shallow well and return via a soak at
some distance.

If you can do this without permission and there is enough water being
replenished in the well, all fine and dandy. All you need is a pump to
extract the water and all the heat pump equipment can be on the surface.
None of this is cheap at all. Look into insulating the place up to the
rafters and making the house air-tight. Then only a small LPG, or electric
heating system cost £50 ayear or so to run, may be required just to raise
the temp.

Doctor Drivel wrote:

"Tim Lamb" wrote in message
...
In message , Mike Halmarack
writes

Seems like a fine opportunity for combined roofing and solar heating
panels, depending on your orientation. Good luck with the calcs.

East/West so OK but...

With a largish river 20m away I'm more inclined to a heat pump.

I don't know if o/p temperatures would be high enough for under floor
heating but I will bear it in mind for any future change of use.

A water sourced heat pump extracting from a moving stream or river is by far
the best system.

Umm, no.

It's by far the best way if you can only heat with electricity.
Anything else, and things become lots less clear.

You're unlikely to get very close to about 6 times the input power in
electricity out as heat.
As electricity is about 3 times the price of gas, this means the maximum
saving is 50%.
Add to that, even with the high price of gas, the extremely high capital
cost, and it may well not pay back over a reasonable period.

Combining enough solar to reduce your heating needs by 50%, with
efficient gas, and maybe some low temperature water storage to run UFH
as background heat, in addition to gas fired radiators, may work out
dramatically cheaper to install, and have the same running costs.

On 9 Mar 2006 01:56:21 -0800 wrote :
I wondered about that.Aparently a superbeam printout is OK for
bulding control.
But surely garbage-in, garbage-out.

Absolutely: SuperBeam is a classic GIGO program. In the early
versions the disclaimer said "If you don't know what you're doing
this program will help you design dangerous structures even more
quickly" but on legal advice I had to delete this - some people have
no sense of humour!

Barely a week goes by without me talking someone out of buying
SuperBeam - they seem to believe that buying a copy will enable them
to dispense with the services of their structural engineer even
though they know next to nothing about the subject. Re Tim's comment
about the gap in knowledge in filling in the data this is deliberate:
if you need your hand held here please don't use the program.

The structural engineer analyses the load on the structure as well
as analysing the structure itself.
How is that sorted out if you use superbeam for building control ?

First and foremost it is of course the responsibility of the person
doing the design. But back in my BCO days one had to continually
remember not to get so hung up on checking what had been submitted
that you failed to notice the omissions. The SuperBeam disclaimer
says

"... Do NOT use this program unless you have enough knowledge and
experience to correctly assess the loads on members, the suitability
of the proposed construction, the overall performance of the
structure and the reasonableness of the program output ..."

and all these things matter.

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm
[Latest version QSEDBUK 1.12 released 8 Dec 2005]

The message
from Tim Lamb contains these words:

The sheeting is rigid so I find it difficult to visualise how the load
would be shared between the wall plate, an intermediate purlin and the
ridge. More study:-)

No one seems keen to help you out so I thought I would at least try
using some rusty knowledge that hasn't been gainfully employed for at
least some 35 years. No doubt someone better acquainted will then come
along and tear holes in what I have to say.

I think it is easiest to start by considering a flat roof. A flat roof
with no intermediate supports and uniform roofing has a uniformly
distributed load along the length of each rafter and bearing loads of
50% of the total weight at each end. Put an intermediate support in the
centre and the weight distribution becomes 25% at each end and 50% on
the intermediate support. If the intermediate support is not central
then the loadings will be such that the moments about any point are
zero. The stiffness of a rafter would have very little effect on this
except in extremis (purlin failure) as it is positioned unstressed and
probably not even allowed to sag under its own weight. This conveniently
allows us to ignore the extra stiffness that might be imparted by a
rigid roofing sheet.

If the roof is at an angle not a lot changes. The weight distribution
remains the same and the weight continues to act downwards but what
might be called the ladder effect needs to be considered. At the upper
(ridge) end on a symmetrical structure each rafter would be opposed
horizontally by another but it is only the ridge pole that is supporting
the upper ends and that is carrying the same loading as the purlins
(rafter each side). Any sag at the ridge pole will result in some sort
of spreading movement in both purlin and wall plate.

--
Roger Chapman

In message , Roger
writes
The message
from Tim Lamb contains these words:

The sheeting is rigid so I find it difficult to visualise how the load
would be shared between the wall plate, an intermediate purlin and the
ridge. More study:-)

No one seems keen to help you out so I thought I would at least try
using some rusty knowledge that hasn't been gainfully employed for at
least some 35 years. No doubt someone better acquainted will then come
along and tear holes in what I have to say.

There's brave:-)

I think it is easiest to start by considering a flat roof. A flat roof
with no intermediate supports and uniform roofing has a uniformly
distributed load along the length of each rafter and bearing loads of
50% of the total weight at each end. Put an intermediate support in the
centre and the weight distribution becomes 25% at each end and 50% on
the intermediate support. If the intermediate support is not central
then the loadings will be such that the moments about any point are
zero.

OK to here.

The stiffness of a rafter would have very little effect on this
except in extremis (purlin failure) as it is positioned unstressed and
probably not even allowed to sag under its own weight. This conveniently
allows us to ignore the extra stiffness that might be imparted by a
rigid roofing sheet.

Umm..

If the roof is at an angle not a lot changes. The weight distribution
remains the same and the weight continues to act downwards but what
might be called the ladder effect needs to be considered. At the upper
(ridge) end on a symmetrical structure each rafter would be opposed
horizontally by another but it is only the ridge pole that is supporting
the upper ends and that is carrying the same loading as the purlins
(rafter each side). Any sag at the ridge pole will result in some sort
of spreading movement in both purlin and wall plate.

OK again. So provided the rafters/sheets are rigid and the wall plate
prevented from spreading by the truss tie, the purlin and ridge are
mainly decorative?

In reality they are not fully rigid. The manufacturer will supply data
sheets on span/deflection/loading but I don't know how to apply this to
the Superbeam software.

regards


--
Tim Lamb

The message
from Tim Lamb contains these words:

OK again. So provided the rafters/sheets are rigid and the wall plate
prevented from spreading by the truss tie, the purlin and ridge are
mainly decorative?

That is not what I intended to impart. Looking at one side of the roof
in isolation the wall plate and the ridge will take 25% of the total
weight of the roof and the purlin 50%. As the ridge is also supporting
the other side of the roof its actual loading is the same as the purlin.

You didn't quote any actual dimensions and I was assuming the rafters
were bound to be strong enough if the purlin was. I have 3" or more of
stone on my barn roof with 2 purlins each side but the rafters are only
4" by 2" at 18" centres. If you want to check a rafter consider the
rafter in 2 parts with a uniformly distributed load. Initially as a
simply supported beam but if you want to model it more closely as one
end built in and one end simply supported.

I have no knowledge of Superbeam but I assume it will allow that sort of
calculation.

--
Roger Chapman

This is an interesting thread. Although I studied engineering and
mechanical structures, I simply can't remember much of it. I want to
look at a loft conversion for our mid terraced house and will need to
consider strengthening the ceiling joists. I have a feeling that this
is a little more straight forward than you problem and has been done
100's of thousands of time across the UK so there should be lots of
info out their.

At the moment all I want to consider is strengthening the
floor/ceiling. The full conversion with stair will come a little later.

"swinster" wrote in message
oups.com...
This is an interesting thread. Although I studied engineering and
mechanical structures, I simply can't remember much of it. I want to
look at a loft conversion for our mid terraced house and will need to
consider strengthening the ceiling joists. I have a feeling that this
is a little more straight forward than you problem and has been done
100's of thousands of time across the UK so there should be lots of
info out their.

At the moment all I want to consider is strengthening the
floor/ceiling. The full conversion with stair will come a little later.

At its simplest, lay additional joists the at least the same size as the
ones supporting the floor below (which presumably have the same span)
alongside the ceiling joists - I would actually go up a size as the floor
joists below may now be under specified. They will rest on the wall plates.
Pack them up with plywood plocks about 15mm. This will ensure the ceiling
floats separately to the new loft floor above and doesn't crack when you
hump stuff about.. In addition, cables can be run without drilling (although
that's not the main point) they go over the old and under the new. Fire (and
noise) requirements will be met by laying mineral fibre (rockwool or
similar, not glass fibre) insulation between the joists (80mm plus), nailed
to the joists either side (to prevent gaps) This, with the normal ceiling
below and the eventual flooring (18/24mm t&g chipboard) *should* provide the
30min fire protection that will eventually be needed if a full conversion is
done. Mind you it would then have to be inspected. These are general
opinions based on my loft conversion and are only opinions and should not be
regarded as fact - no liability accepted etc.


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

In message , Roger
writes
The message
from Tim Lamb contains these words:

OK again. So provided the rafters/sheets are rigid and the wall plate
prevented from spreading by the truss tie, the purlin and ridge are
mainly decorative?

That is not what I intended to impart. Looking at one side of the roof
in isolation the wall plate and the ridge will take 25% of the total
weight of the roof and the purlin 50%. As the ridge is also supporting
the other side of the roof its actual loading is the same as the purlin.

I was writing in jest:-)

My construction is such that there are no rafters. The building has
three trusses at roughly 3m intervals. There is no ridge board but a
purlin close to the ridge and a second midway (it may not be proper to
call these *purlins* as they are load carrying members). I can secure
the ridge such that a rigid triangle is formed taking all the load to
the wall plates. Assuming snowloading, windloading and thrust on walls
are not issues (the building has withstood these for the last century) I
am concerned that there will be some sagging midway between the trusses
with the additional sheeting weight.

The agricultural solution is to try it and see: beefing up the structure
if necessary.

I have no knowledge of Superbeam but I assume it will allow that sort of
calculation.

Yes. Probably:-)

regards


--
Tim Lamb

Bob Mannix wrote:

that's not the main point) they go over the old and under the new. Fire (and
noise) requirements will be met by laying mineral fibre (rockwool or
similar, not glass fibre) insulation between the joists (80mm plus), nailed

You can actually use glass fibre - it has the same grade A fire rating.
(our BCO wanted it laid on chicken wire which was fixed to the joists)

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

The message
from Tim Lamb contains these words:

OK again. So provided the rafters/sheets are rigid and the wall plate
prevented from spreading by the truss tie, the purlin and ridge are
mainly decorative?

That is not what I intended to impart. Looking at one side of the roof
in isolation the wall plate and the ridge will take 25% of the total
weight of the roof and the purlin 50%. As the ridge is also supporting
the other side of the roof its actual loading is the same as the purlin.

I was writing in jest:-)

I am afraid that passed me by.

My construction is such that there are no rafters. The building has
three trusses at roughly 3m intervals. There is no ridge board but a
purlin close to the ridge and a second midway (it may not be proper to
call these *purlins* as they are load carrying members). I can secure
the ridge such that a rigid triangle is formed taking all the load to
the wall plates. Assuming snowloading, windloading and thrust on walls
are not issues (the building has withstood these for the last century) I
am concerned that there will be some sagging midway between the trusses
with the additional sheeting weight.

I am not 100% convinced I understand your explanation but my current
assumption is that you have a barn some 40 feet long and at every
intermediate 10 feet there is a triangular roof truss which supports 4
horizontal timbers (2 at approximate mid points, 2 near the ridge) to
which the original roof sheeting was fixed.

If that is the case and your only worry is the new sheeting sagging
there is a very simple solution. Ask the supplier what the maximum
allowable clear span is. If the roof is shallow enough to be walked on
it might also be worth establishing whether that would require a shorter
clear span.

AIUI you were also worried about the strength of the horizontal supports
but not of the supporting trusses. In the above set-up the horizontal
members should be relatively lightweight* but the rafter (for want of a
better word) sections of the truss would probably have to be more
substantial (carrying more load than the purlin), considerably more
substantial if there is little or no cross bracing.

The agricultural solution is to try it and see: beefing up the structure
if necessary.

Doesn't work too well if failure precedes beefing up. :-)

*I have a gut feeling that 6" x 2" (floor joist for 10 feet span) might
be overkill, 4" x 2" would need checking out but to do that you would
need to know what to add for weather and safety constraints and there I
can't help.

--
Roger Chapman