Pergola Advice

[Agent_zed]

If they want to keep the big span open one option could be canter levering. If you extended the joists out backwards towards the fir trees by 3ft and then brought ties down to a fixed point there would be very little weight held by the front beam.

Not quite this extreme but to illustrate my point http://www.rifemachine.us/wp-conten...ergolas-take-flight-blackline-designbuild.jpg

 

[HOJ]

That beam was doomed from the start!



And that's under its own weight

 

[Massimiliano Mancino]

Been tasked with replacing this 3.6m 47 x 150 joist. The sagging has occurred over 20 years ( not my work!) and I was considering attaching a metal bar to the inside face to add some strength along it’s length.
Questions
How long should that bar be on 3.6m span ?
Is screwing it to the face enough or should it be routed in?
Easy enough to get 1m bars from Screwfix or similar or should I source just 1 bar of the recommended length if the view is that the bar needs to be longer than 1m?
Thanks

You could make a slightly upward curved wood laminated arc, the way the romans used to do. Roman stone arcs are still standing after a couple of millennia, there must be a good reason.... In this case the posts might be tensioned with a steel cable under the arc, to avoid them from collapsing outward because of the weight and outward momentum... I think that if you copy the geometry of timber roofs you'd get a good stable structure...

 

[dizjasta]

That beam was doomed from the start!

View attachment 180526

And that's under its own weight

The beam mentioned lasted over 20 years. The report provided overlooks that torsional resistance was provided by the supporting cross beams along the span.

 

[mc281]

Unless the metal bar is deep 100mm l+ and preferably a L section it's not going to help sagging.

Tbh for the price of £20 for some timber I'd be replacing it!

You are incorrect as a flat strip works perfectly. A structural engineer advised this 20 years ago and it has been solid ever since on a floor support in a listed building.