# Forum Home Renovation Pergolas, Gazebos, Strombellas & Rotundas  Join Beams and maintain a "continuous span"

## Daggs455

Hi  
  I am designing a new pergola which will be 10m long. Based on 4 posts,  my span calcs indicate I can use a 190 x 45 KD TP F7 Beam. The only  catch is these dont come in 10m lengths!  
  So, I am wondering how can I join shorter beams together and still maintain a continuous span categorisation? 
  One way I have been told is to rebate one beam top and the other  bottom, then bring them together and sandwich the join and a bit beyond  between a 6mm steel plate either side. The whole assembly is then bolted  together. This assembly would then not need to be supported over a  post. 
  Eg.
  ______________ .....................                                               __________________ ....................B1 |_______                    ........|______  B2
_____________________|....... ...........                                          |___________  
  _________________________________________ ................| ...*     *    |_______ .......            *   * .     |
_________|__*_*________|____*_* _|__________ ..............^----------Plate Area -------^ 
(Not sure about bolting arrangement)  
Does the Standard give any guidance on how beams should be joined? 
  Any thoughts or ideas welcome! 
  Thanks  
  Darren

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## Pulse

This has to be engineered. Try a truss manufacturer or just pay a few bucks more for the next size !

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## Daggs455

> This has to be engineered. Try a truss manufacturer or just pay a few bucks more for the next size !

  Hi, 
Thanks for your reply, 
I'm assuming you mean a bigger size that will qualify them for single spans of that length?
I was hoping to avoid this as the yard climbs up away from the beam so you always look up into that beam when looking out into the yard. 
Perhaps I will go down the engineering path or maybe some some sections of LVL that can take the load but keep size down. 
(The reason i'm not just going for a 10m LVL beam in that case is the delivery is a killer ...$250 for one beam. Not saying this is over priced, as they would need a semi, but on top of the beam cost this option is a little cost prohibitive)

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## Moondog55

Why not just do a quick redesign to put a post under the join?

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## METRIX

You can join them with a plate if you like but it will look ugly, why not change the spec of the timber, use something like a SmartLam GL18, with 3 posts and spaced at 5m apart ? 
You are better to join the beam on a post.
What is the specifications of the pergola ?, 
RLW
Rafter Spacing
Roof or no roof ?, if roof what type of roof
 Where are you located, in AUS ?

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## Daggs455

> You can join them with a plate if you like but it will look ugly, why not change the spec of the timber, use something like a SmartLam GL18, with 3 posts and spaced at 5m apart ? 
> You are better to join the beam on a post.
> What is the specifications of the pergola ?, 
> RLW
> Rafter Spacing
> Roof or no roof ?, if roof what type of roof
>  Where are you located, in AUS ?

  Thanks for your reply. 
For reasons similar to wanting to keep the beam small (the view) I am wanting to stick to even numbers of posts. This means that when we look out of the main area of the house and up into the back yard, we don't have a post in the middle or a big beam to look at. 
I think you are right that a join would look ugly, so I'm happy to find another solution. 
The details of the design are as follows:
Rectangle shape pergola running along rear of the house for 10m 
There will be extenda brackets on house roof to support 1 beam (5 or 6 ... not sure at this stage) and 4 posts as discussed above supporting the other beam. There will be an 800mm cantilever on one end of the roof mounted beam in order to avoid tile ridge.  
Span between the beams will be 3.9m. Roof will be center pitched trusses @ 900mm spacing pitched at 23 deg with clear polycarbonate sheeting.
Outer side will have 400mm overhang which gives a RLW of approx 2519mm allowing for pitch (Hope I just calculated that right...) 
Other .... Location Vic, Wind Classification N1 (Have been designing around N2 though don't see much change from N1 in this application) 
One of my only other hesitations with LVL is that a lot of the product sheets (eg tillings)  indicte that though they are treated, they are not suitable for exposure especially horizontal surfaces, which given the ends of the roof will be open to allow for air movement, this may be an issue. 
I am still going through other products though. 
Maybe I will go with a some LVLs like the gl18 joined on the posts and just treat them a single spans in my calcs. 
Hope this paints a clearer picture of my situation. 
Regards, 
Darren

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## Daggs455

> You are better to join the beam on a post.

  An additional question, 
Is there a recommended way to join beams on a post. (Say 190 x 45 join over a 90 x 90 post)
Again, I have seen a few ways including 45 miter then bolted through top and bottom, but I have seen these pull apart due to not enough bite left in the mitered timber. 
I'm sure the suppliers/manufacturers could tell me this anyway, but do construction methods such as this differ with laminated products versus solid timber? 
Thanks!

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## METRIX

Hi Darren. 
Working on your situation, 4 posts with approx 3300 span between each, and a RLW of, 2519 (I put it at 2600), 900 spacings, N2, using 25kg/m2 roof dead load, you could use 190 x 45 MGP12 and it will only be loaded to 48%, or a 190x45 F7 Softwood would be loade to 74%.
If you wanted to use a GL, then a GL17C of 130 x 65 will be loaded to 57%, or a GL18 of 150 x 65 will be loaded to 36%. 
Altrenative LVL of 200 x 45 will be loaded to 42%, you can use the LVL in this situation, just be sure to paint all exposed sides with a few coats of weatherproof exterior paint. 
I would choose the GL series, as these come pre primed, and DAR, plus you can use smaller members for your view concern.
Just use 3 lengts of around 3300, and bolt ono 4 posts using a half lap joint as shown in your picture B. 
Keep the lap short, so both sides of the beam can rest in the shoulders of the posts, this makes for a stronger connection, I would go up to a 112 post rather than the 88 / 90mm variety if you ae using GL due to thw thickness of the GL Beam required, you can treat the GL just as you would  solid piec of timber.

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## Daggs455

> Hi Darren. 
> Working on your situation, 4 posts with approx 3300 span between each, and a RLW of, 2519 (I put it at 2600), 900 spacings, N2, using 25kg/m2 roof dead load, you could use 190 x 45 MGP12 and it will only be loaded to 48%, or a 190x45 F7 Softwood would be loade to 74%.
> If you wanted to use a GL, then a GL17C of 130 x 65 will be loaded to 57%, or a GL18 of 150 x 65 will be loaded to 36%. 
> Altrenative LVL of 200 x 45 will be loaded to 42%, you can use the LVL in this situation, just be sure to paint all exposed sides with a few coats of weatherproof exterior paint. 
> I would choose the GL series, as these come pre primed, and DAR, plus you can use smaller members for your view concern.
> Just use 3 lengts of around 3300, and bolt ono 4 posts using a half lap joint as shown in your picture B. 
> Keep the lap short, so both sides of the beam can rest in the shoulders of the posts, this makes for a stronger connection, I would go up to a 112 post rather than the 88 / 90mm variety if you ae using GL due to thw thickness of the GL Beam required, you can treat the GL just as you would  solid piec of timber.

  Thanks for checking that for me. Spans are actually 3400 (I had to dodge some other existing infrastructure) 
Seems I'm doing something wrong when checking my spans as I found I couldn't use the 190 x 45 F7? (In a single span scenario)  In fact I seem to get different answers from 3 different software (Hyne Design, design it and now I have just checked design pine). This is a bit confusing as shouldn't F7 (What I am looking at) be of the same min standard and have the same spans? Were you using one of these products  for your calculations? 
Of course I hadn't even considered MGP12, probably because everyone around me seems to use/supply F7 when talking treated pine.
Is this because MGP12 is not available in treated? 
I agree the bigger posts would be a good choice so I'll probably use the 115 x 115 DAR Cypress Gold posts as they seem quite nice.
I think if I do that and use the 190 x 45 I'll be quite happy.  
Thanks for your helpful input to my questions!

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## METRIX

There are span tabels on the forums, check these for the right advice.
I would deffinetly go the bigger posts, MGP12 is a little harder to find but can be sourced from timber merchants, Melbourne has heaps of timber merchants, and at much better prices than Sydney. 
It is strange you are getting different results from the programs, as they should be obiding by the standards for the timber specs derived from AS 1684.
No, I am not using one of the programs you mentioned we use PROKON, it is a pay program not a free one. 
Let me clarify your specifications. 
Length of pergola 10.2m
3.4m between each post (4 posts in total)
RLW of 2.6m (which means your roof depth from the pitching beam to the verndah beam is 5.2m), ((pitcing beam is the one you attach to the Roof Extendas)) ?
Rafter spacing 900
Laserlite roofing material ? 
You mentiond something about trusses ? 
Can you post a sketch of what it is you are building, it's much more helpful to see what it is you are after. 
Also, Any information provided here is free, and should be used as a guide for you to do further investigation, or seek professional advice from a qualified engineer or Builder to ensure what you are building is in accordance to the Australian Standards, and meets all safety requirements.

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## Daggs455

> There are span tabels on the forums, check these for the right advice.
> I would deffinetly go the bigger posts, MGP12 is a little harder to find but can be sourced from timber merchants, Melbourne has heaps of timber merchants, and at much better prices than Sydney. 
> It is strange you are getting different results from the programs, as they should be obiding by the standards for the timber specs derived from AS 1684.
> No, I am not using one of the programs you mentioned we use PROKON, it is a pay program not a free one. 
> Let me clarify your specifications. 
> Length of pergola 10.2m
> 3.4m between each post (4 posts in total)
> RLW of 2.6m (which means your roof depth from the pitching beam to the verndah beam is 5.2m), ((pitcing beam is the one you attach to the Roof Extendas)) ?
> Rafter spacing 900
> ...

  Hi, 
I understand your last comment. I will be using a builder down the track and I am already getting some engineering advice on the footings for the posts given the nearby retaining wall. I am just trying to understand how we can put this together, what my options are and how things are done (I like to learn as I do projects like this rather than just sit back and watch) 
I will attach a couple of sketches which I hope will clarify where I'm heading. I have rechecked everything and made allowances for the bigger posts and placed measurements in the pics. All other details are correct. 
The RLW I gave was based on the fact that there is a 400 overhang on one side, so took this as worst case.
Is the beam across the posts not also a pitching beam? (Have I confused this by giving the perception this was to be a flat roof ? If so, sorry) 
I think the span table issue might be a case of operator error... but I need to play a bit more to be sure. :Blush7:   
I was thinking of going for trusses rather than pitched roof to save mucking around with a long ridge beam(s) and to simplify putting it up. 
I was even considering getting the trusses fabricated, though some recent checks indicate this may not be so cost effective! 
P4 shows my thoughts on what a truss might look like in this case though these are just based on some quotes I have received and designs of friends pergolas that I have looked at. (point being they may not be suitable for my application) I will need to seek some more advise on this, as I notice a number of site built trusses (ie not pre-fab) seem to be mostly like the top or bottom examples, where as prefab of this size seem to be more of the middle example.  
Thanks.

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## raul07

Metrix,
With a Pergola like this do you think pryda stirrups are ok to support the posts?  Just the normal full stirrup type? 
Also,   would a butt join (and not a half lap join) be ok over the post if it a 115 x 115 post?  Maybe with a plate over the join?

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## METRIX

If you go to the reference below , you will find the info you are after for your situation. 
The reason the trusses you see made on site are of the non triangular design is it is easier to make these, the traditional truss with the 5 triangles are made by machines, your truss drawing is slightly different to the normal one used in houses, they consist of 5 triangles, the truss timbers are stressed when they are created so when the roof load is put on them they flex back into place to create a straight plane across the roof, this is why you cannot cut any chords on a pre made truss as they are under pressure and you will destroy the truss if cut, yes you will probably find pre made ones expensive as you wil lonly require around 10, this is too short a run for them to justify a reasonable price, when mr AVJennigs orders 6000 of them  :Sneaktongue:  
Its good you are investigating all the options, and then seeking assistance to build it, as a lot of people won't investiage, instead they take a guess, and build their pergola or deck completely wrong, therefore making it an unsafe structure to be on or under.  http://www.google.com.au/url?sa=t&rc...Kjm6ig&cad=rja

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## METRIX

> Metrix,
> With a Pergola like this do you think pryda stirrups are ok to support the posts?  Just the normal full stirrup type? 
> Also,   would a butt join (and not a half lap join) be ok over the post if it a 115 x 115 post?  Maybe with a plate over the join?

  Of course Pryda Stirrups are ok, this is what thay are made for, you can either bolt them to the concrete footing, or embed them into the wet concrete when pouring the footings, the choice is yours. 
Yes you can join the beams using a butt join and 4 x M12 bolts, there is no need to lap the joins, we do both depending on the timber being used.

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## raul07

> Of course Pryda Stirrups are ok, this is what thay are made for, you can either bolt them to the concrete footing, or embed them into the wet concrete when pouring the footings, the choice is yours. 
> Yes you can join the beams using a butt join and 4 x M12 bolts, there is no need to lap the joins, we do both depending on the timber being used.

  
Thanks Metrix..  I enjoy reading the advice you give everyone!

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## METRIX

Also forgot no need to use a plate at the join, just bolt through the timbers but remember to use washers with the nuts

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## Daggs455

Thanks Metrix.
Your help is appreciated. 
I think Im sorted now with the beams and spans etc. .. many thanks! 
I know I am straying off my original topic here  but I do seem to have caused myself some confusion with the whole truss issue though.
 I will try and explain my thoughts and would be happy for yours or anyone elses input. 
As previously stated, I thought that a simple quick and easy way to put this roof up would be to use trusses that could be lifted in to place and not have to worry about ridges. I was thinking that I would either use prefab trusses or make them on site.
As you indicated, my 10 are no match for Mr Jennings so I have given prefab away as too expensive. But in reading some other posts and looking at requirements from council etc they seem to indicate that any truss will need to be commercially manufactured or have manufacturers design criteria. 
So my questions are: 
Does this mean that builders cannot manufacture a truss on site? (This could be bolted not nail plates if required) 
Thinking of an alternative  Does a coupled roof have to have ridge plate ? Ie could I have assemblies consisting of 2 opposing  rafters coupled by a joist at ceiling level, with a collar tie? These would then be fixed to the top of the beams , with diagonal bracing added followed by battens and sheeting (all of which would provide stability for these assemblies) not dis-similar to how a truss would be installed?  
Maybe I am confusing what a truss is and is not and coupled roofs for that matter? (I understand the concept of a truss but perhaps not where requirements sit in residential building) 
Perhaps I need to source some more reading material on roof construction

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## barney118

Daggs, you have confused me with your first sketch dimensions and topic of forum. 
When you join over a number of posts (3 min) the section is classed as continuos. If its 2 posts then single span.
Trusses give a larger span for section size, with roofs etc special attention is needed for tie down and if you are using light material then you will have XX speedbrace in your view looking under. Truss manufacturers provide all this info, it's up to you to install as per instructions.
So in answer to your original post, joining can be done a number of ways as per lap join, or butt join, it comes down to what are you joining with? Bolts or type 17 bugle screws, and abiding by the min bearing on post for beam. 
Sent from my iPhone 4s using Tapatalk

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## Daggs455

Hi Barney, 
Thanks for your input. 
Not being a pro in this field I may not communicate my issues so clearly or use incorrect terminology so my apologies if I come across a bit confusing. I also realise I have strayed away from my original topic with truss issues so perhaps I should move those questions to a new thread??  **looking over his shoulder for an irritated moderator** 
While I have solved my span issue, your comments actually get back to something I still dont understand.
I get the difference between single and continuous span, but I didnt know if there were any requirements in joining of the beams. Single size spans are less than continuous for a given size of beam. I am guessing this is because in a continuous span the forces exerted on one section act in opposition to another across the support (kind of like a pivot point)??? Or am I really off point? 
So anyway, if I have 3 posts/extenda brackets  and a single beam bolted between the left and centre one , this is a single span. If I add another beam between the centre and right post and also bolt this to the centre post, this is now continuous? 
If so, what I dont understand is how this affects the structure in a way that allows for an increase in span? While both beams are joined to the centre support, they are not joined to each other so I dont understand how any load or force can be passed to the other beam (all we have done is increase the load on any centre posts/supports). OR is it more about sideways forces on the supports? Just trying to understand the logic behind different max span sizes for the two configurations In reality I don't need to understand why, just the what, but I like to understand what is behind it all.   
As for my joins, I have decided they should be bolted with the addition of a plate across the back. 
Thanks for your input to the truss issue. I think I need to rethink the way Im asking all this and put it in under another topic. Maybe I should post my requirements/wish list for what I want to do and ask for build options that might work. Given my level of understanding that may be less confusing to all. 
Thanks!

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## barney118

> Hi Barney, 
> Thanks for your input. 
> Not being a pro in this field I may not communicate my issues so clearly or use incorrect terminology so my apologies if I come across a bit confusing. I also realise I have strayed away from my original topic with truss issues so perhaps I should move those questions to a new thread??  **looking over his shoulder for an irritated moderator** 
> While I have solved my span issue, your comments actually get back to something I still dont understand.
> I get the difference between single and continuous span, but I didnt know if there were any requirements in joining of the beams. Single size spans are less than continuous for a given size of beam. I am guessing this is because in a continuous span the forces exerted on one section act in opposition to another across the support (kind of like a pivot point)??? Or am I really off point? 
> So anyway, if I have 3 posts/extenda brackets  and a single beam bolted between the left and centre one , this is a single span. If I add another beam between the centre and right post and also bolt this to the centre post, this is now continuous?

  Moderators sneak around looking for troublemakers, so I would say you are safe  :Biggrin: . Correct, a simple structure 2 post, self explanatory, 3 posts now continuous, loads are assumed distributed uniformly, unless known point loading. Loads, ie roof spread over an area and supported by posts/walls through members to the foundation/ground. (vertical) also sideways loading is applied i.e wind (racking forces) hence use of bracing with noggins/studs metal XX, cladding etc. 
So the forces of the timber in sideways is taken in shear, sideways through bolts,screws, so imagine trying to push over something with 2 post or 3 posts?    

> If so, what I dont understand is how this affects the structure in a way that allows for an increase in span? While both beams are joined to the centre support, they are not joined to each other so I dont understand how any load or force can be passed to the other beam (all we have done is increase the load on any centre posts/supports). OR is it more about sideways forces on the supports? Just trying to understand the logic behind different max span sizes for the two configurations In reality I don't need to understand why, just the what, but I like to understand what is behind it all.

   

> As for my joins, I have decided they should be bolted with the addition of a plate across the back. 
> Thanks for your input to the truss issue. I think I need to rethink the way Im asking all this and put it in under another topic. Maybe I should post my requirements/wish list for what I want to do and ask for build options that might work. Given my level of understanding that may be less confusing to all. 
> Thanks!

  Truss, yep go for a new post, plates across the back are not going to make it any stronger than the bolts already used, (thats why I am thinking type 17 bugles may be a better option than bolts. 
Being a mech engineer, I recall how steel fails when too many holes in the one plane etc, and how it reduces the strength of a join too many bolts etc. I have finished stage 3 of carpentry and looking at getting into cert 4 next year. 
So surprising how it is houses basically are built with nails and joined well, thats why pay attention to bearing of members, ie 30mm min etc, and dont check out too much in posts.

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## shauck

> Hi Barney, 
> So anyway, if I have 3 posts/extenda brackets  and a single beam bolted between the left and centre one , this is a single span. If I add another beam between the centre and right post and also bolt this to the centre post, this is now continuous?

  Both of those beams as you describe, are single span. If it was one beam from left to centre to right, that would be continuous.

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## Pulse

> So anyway, if I have 3 posts/extenda brackets  and a single beam bolted between the left and centre one , this is a single span. If I add another beam between the centre and right post and also bolt this to the centre post, this is now continuous?

  No, continuous span is one beam, supported in the middle by a third post. To get back to your original point, AS1684 is pretty clear on this. 
You were right with the "pivot point" comment, the reason it spans further is because the deflection in one span is resisted by the opposite deflection in the other span. 
Cheers
Pulse

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## Daggs455

> No, continuous span is one beam, supported in the middle by a third post. To get back to your original point, AS1684 is pretty clear on this. 
> You were right with the "pivot point" comment, the reason it spans further is because the deflection in one span is resisted by the opposite deflection in the other span. 
> Cheers
> Pulse

  Hi Pulse, 
Thanks, this makes sense to me and my mind can now rest  :Biggrin:  
Thanks for your input!

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## barney118

I stand corrected. Can't wait to get into the course, just looked it up, even crippling a bearer makes it single span.  
Sent from my iPhone 4s using Tapatalk

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