Catnic Steel Angle lintel - deflection

[GoodDIYjob]

Would you expect a catnic Ang 1500 single leaf steel lintel to show 4mm deflection at each end compared to centre?

Used to install in a 1100mm window aperture on external leaf. Concrete lintel already in place on internal leaf. 1920s semi, two floor plus loft space. Pitched clay tile roof. Brick cavity walls.

No lintel replaced when original timber framed windows replaced with uvpvc windows >10 years ago b4 I owned house.

 

[tony1851]

Did you mean deflects in the middle rather than the ends?

All lintels deflect no matter what the load - the issue is how much deflection is acceptable.

Normally, deflection is measured relative to the span and the maximum deflection is usually taken as something like span/300 or thereabouts. So your deflection may not be that much out.

Having said that, as it is a retro-fit lintel, it will deflect slightly more than it would have had it been built-in with the wall as a whole. This is because it will be supporting a slightly greater weight of brickwork.

 

[GoodDIYjob]

Yes, if you put a straight edge up against the underside of the installed lintel, where it is visible from the outside, it shows a bow in the horizontal plane.

With gaps of approx 4mm at either end compared to the centre "bow" using the straight edge.

I suppose I was also surprised how light weight the lintel looked.

Would it be better practice to install only the soldier and maybe one horizontal course course above the lintel and allow mortar to harden before building up anything above? Or would that be worse in leaving it susceptible to further flex at a latter stage?