RSJ and hollowcore

pat m

Hi

i'm currently putting the blocks up on my self build, the ceiling will be Hollow core, i have a window 2m wide over which the HC will rest on. Where will the RSJ actually be postioned ?, ie will it rest on top of the window( on the lentils or block work beside the window) or will it rest on top of the wall over the blocks which are over the window so that the hollow core will directly rest on the RSJ. i saw in a friends house that the HC rested directly on the RSJ under which was the blocks which rested on standard lentils with the hallway opening underneath. I can't see the advantage of this as the rsj just seems to transmit the HC load down through the blocks to the lentils ie the lentils are bearing the loads over the opening. pherhaps I'm wrong, I'l take any any help i can get. I do'nt want to go near my engineer yet without any knowledge. thanks

RKQ

Engineers question specific to your design. (Have a chat will the hollowcrete suppliers Engineer also).

I've seen rsj over all window and door opes with blockwork over supporting floor - no conc lintols. RSJ takes loads.

Discuss your design with your Engineer.

Mellor

pat m wrote: »

i saw in a friends house that the HC rested directly on the RSJ under which was the blocks which rested on standard lentils with the hallway opening underneath.

The reason for that was likely the required head height.
The hollowcore has a fixed height/position, due to ceiling/floor height. As does the RSJ, due to the HC position. Now, if the underside of your RSJ gives you the required head height, all well and good, but it may not. And a door head might be lower, say 225mm lower. In this case a row of blocks would go in on a lintol, to give the req head height (as the RSJ can't be dropped).
Another option would be a studed out head.


Above all, your situation is specific to you, so you should sonsult your engineer

pat m

Hi mellor

Thanks for the reply

But that brings me back to the orginal question is'nt the lentil bearing all the load from above including the weight of the rsj for that matter. what use is the rsj if it just transmits the load of the HC down through blocks to the lentils over the hallway opening.

muffler

The RSJ should be at least the same width and preferably wider than the lintels. There should be a couple of courses of blocks between them and by the time the loading spreads from the ends of the RSJs its well clear of the lintels.

As advised above you should talk to your engineer as this is only a rule of thumb and not case specific.

Carlow52

pat m wrote: »

Hi mellor

Thanks for the reply

But that brings me back to the orginal question is'nt the lentil bearing all the load from above including the weight of the rsj for that matter. what use is the rsj if it just transmits the load of the HC down through blocks to the lentils over the hallway opening.

The rsj is doing virtually all the work here and it could quite easily be used instead of the lintel with blocks above: the boxing out of the rsj is a pain so hence not noramally done this way.
In order for the lintels to carry any appreciable load from the HC via the rsj, the rsj would have to deflect enough under the weight of the HC, which apply a uniform distributed load on the rsj.
I expect that the rsj is sized for carrying the hc plus other loads assuming no lintel.