Posi joist direction help

[Vijay]

Wondering if anyone can give me some advice on my joist direction for my landing. It's a gallery landing, so there are 3 different parts to it. The S.E showed their directions, but different joist suppliers have done them in different directions. So I wondered if there is any advice on which way to go, long or keep them short (and use more joist hangers). My concern with going long is deflection, but are you allowed to support a posi joist through the web to reduce deflection?

 

I've attached a copy of the plan, the S.E drawing and a pic showing the steels and load bearing walls. 

 

The distance of the landing parts 1 & 2 (top to bottom) are approx 5.8m. The distance between them (3 - left to right)) is approx 4.5m. The yellow lines are beams and the blue lines show the load bearing block walls.

 

Another thing is the joist suppliers are keen to use beams (I believe doubled) to replace the steels. In my mind using beams will give me the least deflection out of the two, is that right?

 

I appreciate any advice on this.

 

Vijay

 

 

[Mr Punter]

Keep them short.

 

Steel v timber beam deflection can be the same.  Depends on the specs.  It is simpler to fit stuff to beams.

 

Specify a maximum deflection of 8mm or 0.002 x span (whichever is least) and the floor will feel really solid.

[Big Jimbo]

I can't help with the engineering side, but i have used timber i beams lots of times. I personally would dump all the steels i could, and go with the timber.

[jamieled]

Strong backs can (and should generally) be fitted through the  posi web and this reduces deflection I think. What to use and where depends on the span.  There was a thread recently about this.

[Vijay]

2 hours ago, Mr Punter said:

Keep them short.

 

Steel v timber beam deflection can be the same.  Depends on the specs.  It is simpler to fit stuff to beams.

 

Specify a maximum deflection of 8mm or 0.002 x span (whichever is least) and the floor will feel really solid.

 

Well that's opened my mind. I've no experience with any engineered joists, so in my mind steel beams are solid.  Do you mean stuffs easier to fit in steel or timber beams?

 

2 hours ago, Big Jimbo said:

I can't help with the engineering side, but i have used timber i beams lots of times. I personally would dump all the steels i could, and go with the timber.

 

Cos of ease of fitment or running services through them?

 

 

Edited April 24, 2020 by Vijay

[Vijay]

1 hour ago, jamieled said:

Strong backs can (and should generally) be fitted through the  posi web and this reduces deflection I think. What to use and where depends on the span.  There was a thread recently about this.

 

I believe strongbacks are normally fitted between joists, connecting them, but can they go through a single posi joist and fix to walls/steels? (so making a t cross)

[jamieled]

I might have misinterpreted the original post. Not sure about through a single posi. I'm only aware of strong backs connecting posi's.

We have some pretty wide posi's due to the span, and this was also to minimise deflection.

[Mr Punter]

Strong backs run at right angles to the posi joists and work a bit like herringbone strutting or blocking in that they stiffen the joists.  They can interfere with services like ventilation and drainage.