Our amazing architect left the firm, and the firm are being hopeless at covering the work with her gone. As a result I am trying to cover some bits off myself. 

 

We have some galleries/Mezzanines going in, which span the 3.1m width of the room, with 400mm centeed cross spans. To keep the Mezzanine as slim as possible I want the main cross beam to be 150mmm x 145mm in effect. 

 

This is outside normal span tables, can anyone point me to something building control would recognise? 

 

Thanks

 

 

The stress in a bending beam can be expressed as

σ = y M / I                                     (1)            

where

σ = stress (Pa (N/m²), N/mm², psi)

y = distance to point from neutral axis (m, mm, in)

M = bending moment (Nm, lb in)

I = moment of Inertia (m⁴, mm⁴, in⁴)

 

https://www.engineeringtoolbox.com/beam-stress-deflection-d_1312.html

Brings me back to my headache of an engineering degree I struggled for years, made a success of it... But also made a habit of being the most non engineer engineer ever!

 

Timber joists, I should have added! 

Your Architect would have thrown all of this at a Structual Engineer 

In any case BC will want SE calcs for anything load baring 

 

 

You need a structural engineer. They will give you all the calcs and the spec to satisfy Building Control and they will have PI cover to satisfy the warranty provider too.  150mm is quite slim so they may suggest some steel.

Thanks all, I can do that worse case, just trying to avoid the cost if I can help it.

 

Pictures might help....  We have had 3 of these mezzanines/galleries built. using 220mm x 45mm joists joined together to form a 220 x 90mm master beam. This has left us with a lip, that is a trip hazard near the staircase we will install.

 

As a result, I want them to trim this lip down, and add a third sistered joist to form the ultimate 150mm x 135mm master beam.

 

Online span calculations show that for a joist of  72mm x 145mm will pass a room width of up to 3.4m at medium loading (400mm joist spacing, as ours are).

 

With our desired joist being 150 x 135mm, this should far exceed the minimums, surely?#

Free UK Span Table for Domestic Floor Joists to BS 5268-7.1 (C16, 1.5 kN/m² load) - Timber Beam Calculator

 

[img]https://i.imgur.com/KfWZnfZ.jpg[/img]

[img]https://i.imgur.com/IWyJYjk.jpg[/img]

 

 

I can’t open the images and struggling to visualise the problem. Have you got a quote for the joists and trusses? The supplier will do all the calculations for BC. I asked mine to do a couple of changes, they did another set of calcs without complaint. Two minutes work on their design software.

Is the sistered joist going to sit on the blocks as the other pair of joists are, if so, looking at the table and your pictures I can't see why there would be a problem, but then I'm not a SE.

A solution to keep it slim is to fix plywood on top, with lots of ringshank nails. The plywood converts the joists into T beams. You need an SE to give you the design to hand to bc.

Then you don't need any steel.

A flitch beam might be a solution here. 

The pictures from an earlier post for those that can't open them

 

 

 

So you want to notch part of the deeper joists just where the stairs come up?