5 point load on a truss

[hadyn]

I'll soon be hanging a 26m long truss on hopefully 5 points, but I need the formula to calculate the point loads on each motor. I know the calculations for 2 and 3 points, but not 5.

 

Can anyone help out here please?

 

Thanks in advance,

 

Hadyn.

[trussmonkey]

hadyn,

 

I got this from one of Chris Higgs courses. I tried this calc based on a 500kg load.

 

1 2 3 4 5

.098 .286 .232 .286 .098

 

 

the 1/2/3/4/5 are the five lift points. the decimal numbers are the percentage of load taken by that point. So if you base it on a 500 kg load you get the following

 

1 2 3 4 5

49kg 143kg 116kg 143kg 49kg

 

which adds up to 500kg.

 

I hope this helps

[hadyn]

hadyn,

 

I got this from one of Chris Higgs courses.  I tried this calc based on a 500kg load.

 

  1              2                  3              4              5         

.098          .286              .232          .286          .098

 

 

the 1/2/3/4/5 are the five lift points.  the decimal numbers are the percentage of load taken by that point.  So if you base it on a 500 kg load you get the following

 

  1                2          3            4          5

49kg          143kg    116kg    143kg    49kg

 

which adds up to 500kg.

 

I hope this helps

<{POST_SNAPBACK}>

 

Cheers for that, just what I was looking for. Never thought to look in the course notes.

 

Hadyn.

[Chris Higgs]

Applies only where:

 

It is a uniform load

The end pick ups are at the ends (or very, very close)

The other points are equally spaced between them.

 

Don't forget to:

 

Add the weight of the truss to the uniform load before you do the factor sum.

Add the weight of the motor per point to the point load you calculate.

Allow an extra 25% to each point load to account for turning the motors on or off.......

 

Check that the load/span you are using is within the design of the truss.

The truss is correctly assembled and the right way up.

The truss is correctly and safely slung or supported.

The truss is in good nick and has been inspected by a competent person.

(Prefereably an engineer or manufacturer/authorised rep, with weld inspection experience and an understanding of what trusses do and how they do it)

 

HTH

[hadyn]

Applies only where:

 

It is a uniform load

The end pick ups are at the ends (or very, very close)

The other points are equally spaced between them.

 

Don't forget to:

 

Add the weight of the truss to the uniform load before you do the factor sum.

Add the weight of the motor per point to the point load you calculate.

Allow an extra 25% to each point load to account for turning the motors on or off.......

 

Check that the load/span you are using is within the design of the truss.

The truss is correctly assembled and the right way up.

The truss is correctly and safely slung or supported.

The truss is in good nick and has been inspected by a competent person.

(Prefereably an engineer or manufacturer/authorised rep, with weld inspection experience and an understanding of what trusses do and how they do it)

 

HTH

<{POST_SNAPBACK}>

 

Cheers for that Chris. I'd already done most of the above, when doing the calculations. The only one I hadn't taken into account was the 25% when starting stopping motors. Which leads me to potentially recalculate and add extra points as 2 of the points are about 5 kg below their rated load of 200Kg (it's a clearspan marquee). I suppose the next question I need to ask is what's the formula for 6 points? And is there a way of working out the % loads per x number of points so I don't have to keep asking on here??

[david.elsbury]

And is there a way of working out the % loads per x number of points so I don't have to keep asking on here?? :P

<{POST_SNAPBACK}>

I'd be interested in this too, if that's okay. And if the answer is "take a rigging course", I'm looking for one. The airfare to the UK is a touch too expensive for me at the mo. :o

Thanks

David

[hadyn]

And is there a way of working out the % loads per x number of points so I don't have to keep asking on here?? :o

<{POST_SNAPBACK}>

I'd be interested in this too, if that's okay. And if the answer is "take a rigging course", I'm looking for one. The airfare to the UK is a touch too expensive for me at the mo. ;)

Thanks

David

<{POST_SNAPBACK}>

 

I did take a rigging course with a certain forum member (which I can thoroughly recommend, best course I've ever done) , but can't remember if this was covered specifically. :P

[DSA]

I know the calculations for 2 and 3 points, but not 5.

Sorry, but surely if you know the calcs for 2 and 3, you could apply the same principles to find the results for 5 or 6 points. Or do you mean the answers?

 

Any good structures book should help you to work out loadings for a 'beam' subjected to a UDL (which is essentially what you are talking about). However, if you are unsure ask an engineer/other qualified person to check.

 

HTH,

David

[Pete McCrea]

It does come down to engineering basics. I should, and can just about remember the lectures that covered it, but not going to put my neck on the line cos it's been over a year since I (narrowly) passed my BEngs structures exams.....