Hi All Could anyone advise me, If I have rectangle steel 65mm x 35mm x 2.5mm fixed one end 600mm long, what weight would it hold at the other end. Thanks Tom
-- Edited by Tom464 on Monday 14th of October 2019 09:43:34 AM
Possum3 said
10:18 AM Oct 14, 2019
Tom, The leverage at 600 mm is quite significant. The questions that need to be answered are how is the RHS (Rolled Hollow Section) attached at holding end ie. welded (butt or chamfered), is there a fulcrum effect at attached end ie does it lie over another piece of RHS? Is this (lever) holding a dead weight totally perpendicular to the length of RHS, or is it the load on an angle, is there any turning moment on the RHS? Is the RHS attached to a caravan or another RHS ie on tow bar, A frame or rear bumper? Will the load be totally static or is in on a moving vehicle? Describe the load you are desirous of placing at end of RHS. ie Spare wheel, tool box, bike rack, etc. The origin and type of the steel used in manufacture of RHS can also effect load carrying as can the heat treating result of any welding. A mud-map drawing of your proposal would help to get a good Engineering estimate of capacity.
Which side of RHS section is the RHS taking the load ie long side up or narrow side up?
-- Edited by Possum3 on Monday 14th of October 2019 10:22:15 AM
-- Edited by Possum3 on Monday 14th of October 2019 10:28:32 AM
Whenarewethere said
12:58 PM Oct 14, 2019
Steel has a specific gravity of roughly 8, so a 1 metre square sheet at 1 mm thick will weight 8kg.
So add up the perimeter of the section in metres, multiply that by the thickness in mm, multiply by the length in metres, multiply by 8.
It should be close enough for most calculations. You could calculate the radius in the corners if you need better accuracy.
Edit: I misread the question, you need an engineer to calculate the SWL.
-- Edited by Whenarewethere on Monday 14th of October 2019 12:59:52 PM
Peter_n_Margaret said
02:10 PM Oct 14, 2019
Tom464 wrote:
fixed one end 600mm long, what weight would it hold at the other end.
How is it fixed?
Is it a static load or on a vehicle?
Do you have a picture?
You need to be much more specific about what you have in mind and then, maybe, some of us might give a "seat of the pants" guess.
Cheers,
Peter
Tom464 said
05:20 PM Oct 14, 2019
I'm going to make a rear bumper bar for our caravan, the bar will carry a little bulldog folding boat trailer 67KG. the hollow section RHS will fit into the caravan chassis RHS which is much larger 130 x 50 x 3 and bolted, I'm replacing the pipe bumper. I'm not welding the bumper I will have it welded, the steel I gave will be by Two with a cross member of the same size. I'm checking if one side piece holds that weight I'm happy. Thanks
Possum3 said
06:00 PM Oct 14, 2019
40kg on each arm should be OK - the load will be at extremity of the fabricated towbar, so main concern would be vibration and shock load on dictated by road conditions. Ensure when you are clamping new towbar that you don't indent the load arm as it would cause a significant weakness. As I said before - the arms are acting as a lever. If possible have your fabricator weld on new cross bar sitting on top of the side arms and add an infill web from cross bar to top bar. Ensure you have it MIG welded to ensure minimum heat is placed on the fabrication.
Possum3 said
06:05 PM Oct 14, 2019
Just saw this on For Sale forum - another way to skin the cat;https://thegreynomads.activeboard.com/t65971331/boat-rack/
Tom464 said
08:54 PM Oct 14, 2019
Thanks possum 3 you have been a very good help. Tom464
Peter_n_Margaret said
07:53 AM Oct 15, 2019
Putting 67 kg at the end of a caravan (especially at the rear) is a very bad idea from a stability perspective.
It increases the yaw inertia and WILL make the van less stable.
Cheers,
Peter
yobarr said
09:11 AM Oct 15, 2019
Peter_n_Margaret wrote:
Putting 67 kg at the end of a caravan (especially at the rear) is a very bad idea from a stability perspective. It increases the yaw inertia and WILL make the van less stable. Cheers, Peter
Absolutely right.....putting 67kg on to the rear bumper of a caravan is stupidity in the extreme,in my opinion.My car is around 15% heavier than my van,and I decided to mount a 32kg generator on the back of the van "just because". Bad move....after a one hour trip through the countryside,I decided that it was unsafe,and the generator now lives in my shed.As Peter says,the yaw inertia made the van move around badly,even though all my axle weights, and towball weight,were good. The 67kg on your rear bumper also would take around 50kg (guess) off your towball weight.I would strongly suggest that you reconsider your decision,but I wish you only good luck. Cheers
Possum3 said
09:15 AM Oct 15, 2019
Tom, Peter is correct regarding extra weight on rear of Caravan affecting stability - I personally wouldn't do it. Your other consideration must be how do you do it and keep within your plated rate. Contact Caravan Council of Australia and get an opinion from Colin Young he is an Automotive Engineer whereas I am a retired Mechanical Engineer.
Caravan Council of Australia
3 Margaret Street
Parkdale VIC 3195
T: 0409 865 399
F: 03 9587 1828
It depends on the van as to the stability issue. I have had a van that was affected by the shift of 20kgs rearward and others totally unaffected by hanging 40 to 50 kgs off the back, but it really pays to be careful doing what you wish to do. I have seen people hang a generator off what looks to be a fairly substaintial rear bumper bar only to lose it and the bumper bar down the road due to failure of the bumper bar supports under that load. Generator was about 30kgs.
Eaglemax said
12:02 PM Oct 17, 2019
Greg 1 wrote:
It depends on the van as to the stability issue. I have had a van that was affected by the shift of 20kgs rearward and others totally unaffected by hanging 40 to 50 kgs off the back, but it really pays to be careful doing what you wish to do. I have seen people hang a generator off what looks to be a fairly substaintial rear bumper bar only to lose it and the bumper bar down the road due to failure of the bumper bar supports under that load. Generator was about 30kgs.
The problem Greg with "and others totally unaffected by hanging 40 to 50 kgs off the back" is that usually only when the caravan and tug is out of control that the extra rearward weight is apparent.
It is similar to a car enthusiast asking if a wrong transmission oil can be used on his car and some say "I used this oil or that oil and it has worked for me for 3 years" well maybe, but that doesn't mean it will last as long as the right oil for many years after.
To be specific the caravan's tendency to yaw more easily might not be detectable until it's too late.
As most know my home built only weighs 1000kg ATM. 16ft. Recently we slowed down to 70kph as it was roo country near Rushworth and at 11pm. One huge roo appeared and I reacted with the steering and just avoided it. The van didn't sway about at all, just followed the car. It surprised me but when I think about it the 7ft of van behind the axle weighs say 400kg...not enough to have any pendulum effect. If I had 40kg off the rear bumper???
Tony
-- Edited by Eaglemax on Thursday 17th of October 2019 12:07:26 PM
Baz421 said
08:01 PM Oct 17, 2019
Possum3 wrote:
Tom, Peter is correct regarding extra weight on rear of Caravan affecting stability - I personally wouldn't do it. Your other consideration must be how do you do it and keep within your plated rate. Contact Caravan Council of Australia and get an opinion from Colin Young he is an Automotive Engineer whereas I am a retired Mechanical Engineer. Caravan Council of Australia 3 Margaret Street Parkdale VIC 3195 T: 0409 865 399 F: 03 9587 1828
I challenge engineers to PROVE not just make statements that for example an extra 30kg on the rear of a van with ATM and loaded to ATM of 3000kg (say a genny in a box) is dangerous.
Please show how the dynamic stability is affected as this is only,,, 1% extra weight to the rear of the COG.
No one has ever demonstrated this to the best of my knowledge.
I worked for an engineer years ago who questioned this and he was the approving engineer for modified vehicles at MVR vehicle standards.
Thanks. Yes this has been circulated before, but doesn't answer my question. The change to ball weight will still be within recommended (wheter AUSY OR USA) RANGE it's the change to stability/yaw/inertia I'm getting at Possum. I'm no engineer, just trying to pin down a definitive answer by adding 1% of weight to back of van. Cheers
Still doesn't answer my question,,,, but good demo obviously.
Possum3 said
10:16 AM Oct 18, 2019
Baz, Did you note the bottom diagram and formulae on my previous post?
Note: Dimensions from the centre of the axle-group to the left are positive dimensions to the right are negative.
(Drawing would not transpose, see article for drawing if required)
Example: T = 30 kg; LC = 3.5 m; LF = 3.0 m; LR = 2.0 m
Ball-weight currently contributed by the spare wheel(s) being on the A-frame:
Ball-weight = (T x LF) / LC
= (30 X 3.0) / 3.5 = + 25.7 kg
Ball-weight decrease by the spare wheel(s) being on the rear of the van:
Ball-weight = (T x LR) / LC
= (30 X 2.0) / 3.5 = 17.1 kg
The overall effect on the ball-weight is a reduction of 48.2 kg
This formulae shows that a 30kg tyre exerts a mass of 25.7kg on ball, if mounted on rear it amounts to 48.2kg mass that will effect the Yaw potential, when transferred to rear - Although as pointed out in the article speed in major contributor to Yaw.
Baz421 said
06:30 PM Oct 18, 2019
Possum3 wrote:
Baz, Did you note the bottom diagram and formulae on my previous post?
Note: Dimensions from the centre of the axle-group to the left are positive dimensions to the right are negative.
(Drawing would not transpose, see article for drawing if required)
Example: T = 30 kg; LC = 3.5 m; LF = 3.0 m; LR = 2.0 m Ball-weight currently contributed by the spare wheel(s) being on the A-frame: Ball-weight = (T x LF) / LC = (30 X 3.0) / 3.5 = + 25.7 kg Ball-weight decrease by the spare wheel(s) being on the rear of the van: Ball-weight = (T x LR) / LC = (30 X 2.0) / 3.5 = 17.1 kg The overall effect on the ball-weight is a reduction of 48.2 kg
This formulae shows that a 30kg tyre exerts a mass of 25.7kg on ball, if mounted on rear it amounts to 48.2kg mass that will effect the Yaw potential, when transferred to rear - Although as pointed out in the article speed in major contributor to Yaw.
Yes got all that Possum but question was not about weight was it? Not trying to be a pain in the butt,,,, but looking for answer.... someone will know. Cheers Baz
-- Edited by Baz421 on Friday 18th of October 2019 06:43:32 PM
Tom464 said
08:46 PM Oct 18, 2019
Hi A
Thank U I have change the way I am thinking about the rear weight. Thank all of U Regards Tom
-- Edited by Tom464 on Monday 14th of October 2019 09:43:34 AM
-- Edited by Tom464 on Friday 18th of October 2019 08:47:43 PM
Hi All Could anyone advise me, If I have rectangle steel 65mm x 35mm x 2.5mm fixed one end 600mm long, what weight would it hold at the other end. Thanks Tom
-- Edited by Tom464 on Monday 14th of October 2019 09:43:34 AM
Tom, The leverage at 600 mm is quite significant. The questions that need to be answered are how is the RHS (Rolled Hollow Section) attached at holding end ie. welded (butt or chamfered), is there a fulcrum effect at attached end ie does it lie over another piece of RHS?
Is this (lever) holding a dead weight totally perpendicular to the length of RHS, or is it the load on an angle, is there any turning moment on the RHS? Is the RHS attached to a caravan or another RHS ie on tow bar, A frame or rear bumper? Will the load be totally static or is in on a moving vehicle?
Describe the load you are desirous of placing at end of RHS. ie Spare wheel, tool box, bike rack, etc.
The origin and type of the steel used in manufacture of RHS can also effect load carrying as can the heat treating result of any welding.
A mud-map drawing of your proposal would help to get a good Engineering estimate of capacity.
Which side of RHS section is the RHS taking the load ie long side up or narrow side up?
See http://sunsetpatios.com.au/beam-deflection-calculator.php
-- Edited by Possum3 on Monday 14th of October 2019 10:22:15 AM
-- Edited by Possum3 on Monday 14th of October 2019 10:28:32 AM
Steel has a specific gravity of roughly 8, so a 1 metre square sheet at 1 mm thick will weight 8kg.
So add up the perimeter of the section in metres, multiply that by the thickness in mm, multiply by the length in metres, multiply by 8.
It should be close enough for most calculations. You could calculate the radius in the corners if you need better accuracy.
Edit: I misread the question, you need an engineer to calculate the SWL.
-- Edited by Whenarewethere on Monday 14th of October 2019 12:59:52 PM
How is it fixed?
Is it a static load or on a vehicle?
Do you have a picture?
You need to be much more specific about what you have in mind and then, maybe, some of us might give a "seat of the pants" guess.
Cheers,
Peter
I'm going to make a rear bumper bar for our caravan, the bar will carry a little bulldog folding boat trailer 67KG. the hollow section RHS will fit into the caravan chassis RHS which is much larger 130 x 50 x 3 and bolted, I'm replacing the pipe bumper. I'm not welding the bumper I will have it welded, the steel I gave will be by Two with a cross member of the same size. I'm checking if one side piece holds that weight I'm happy. Thanks
Just saw this on For Sale forum - another way to skin the cat;https://thegreynomads.activeboard.com/t65971331/boat-rack/
Thanks possum 3 you have been a very good help. Tom464
It increases the yaw inertia and WILL make the van less stable.
Cheers,
Peter
Absolutely right.....putting 67kg on to the rear bumper of a caravan is stupidity in the extreme,in my opinion.My car is around 15% heavier than my van,and I decided to mount a 32kg generator on the back of the van "just because". Bad move....after a one hour trip through the countryside,I decided that it was unsafe,and the generator now lives in my shed.As Peter says,the yaw inertia made the van move around badly,even though all my axle weights, and towball weight,were good. The 67kg on your rear bumper also would take around 50kg (guess) off your towball weight.I would strongly suggest that you reconsider your decision,but I wish you only good luck. Cheers
Caravan Council of Australia
3 Margaret Street
Parkdale VIC 3195
T: 0409 865 399
F: 03 9587 1828
caravancouncil@optusnet.com.au
It depends on the van as to the stability issue. I have had a van that was affected by the shift of 20kgs rearward and others totally unaffected by hanging 40 to 50 kgs off the back, but it really pays to be careful doing what you wish to do.
I have seen people hang a generator off what looks to be a fairly substaintial rear bumper bar only to lose it and the bumper bar down the road due to failure of the bumper bar supports under that load. Generator was about 30kgs.
The problem Greg with "and others totally unaffected by hanging 40 to 50 kgs off the back" is that usually only when the caravan and tug is out of control that the extra rearward weight is apparent.
It is similar to a car enthusiast asking if a wrong transmission oil can be used on his car and some say "I used this oil or that oil and it has worked for me for 3 years" well maybe, but that doesn't mean it will last as long as the right oil for many years after.
To be specific the caravan's tendency to yaw more easily might not be detectable until it's too late.
As most know my home built only weighs 1000kg ATM. 16ft. Recently we slowed down to 70kph as it was roo country near Rushworth and at 11pm. One huge roo appeared and I reacted with the steering and just avoided it. The van didn't sway about at all, just followed the car. It surprised me but when I think about it the 7ft of van behind the axle weighs say 400kg...not enough to have any pendulum effect. If I had 40kg off the rear bumper???
Tony
-- Edited by Eaglemax on Thursday 17th of October 2019 12:07:26 PM
This argument has been going on for years.
I challenge engineers to PROVE not just make statements that for example an extra 30kg on the rear of a van with ATM and loaded to ATM of 3000kg (say a genny in a box) is dangerous.
Please show how the dynamic stability is affected as this is only,,, 1% extra weight to the rear of the COG.
No one has ever demonstrated this to the best of my knowledge.
I worked for an engineer years ago who questioned this and he was the approving engineer for modified vehicles at MVR vehicle standards.
I hope someone takes up the challenge
See link; https://www.outbacktravelaustralia.com.au/driving-towing-towing/towball-weight-and-trailer-stability
Note: Dimensions from the centre of the axle-group to the left are positive dimensions to the right are negative.
(Drawing would not transpose, see article for drawing if required)
Example: T = 30 kg; LC = 3.5 m; LF = 3.0 m; LR = 2.0 m
Ball-weight currently contributed by the spare wheel(s) being on the A-frame:
Ball-weight = (T x LF) / LC
= (30 X 3.0) / 3.5 = + 25.7 kg
Ball-weight decrease by the spare wheel(s) being on the rear of the van:
Ball-weight = (T x LR) / LC
= (30 X 2.0) / 3.5 = 17.1 kg
The overall effect on the ball-weight is a reduction of 48.2 kg
This formulae shows that a 30kg tyre exerts a mass of 25.7kg on ball, if mounted on rear it amounts to 48.2kg mass that will effect the Yaw potential, when transferred to rear - Although as pointed out in the article speed in major contributor to Yaw.
Yes got all that Possum but question was not about weight was it? Not trying to be a pain in the butt,,,, but looking for answer.... someone will know. Cheers Baz
-- Edited by Baz421 on Friday 18th of October 2019 06:43:32 PM
Hi A
Thank U I have change the way I am thinking about the rear weight. Thank all of U Regards Tom
-- Edited by Tom464 on Monday 14th of October 2019 09:43:34 AM
-- Edited by Tom464 on Friday 18th of October 2019 08:47:43 PM