Splices to long span portal frame rafters
Splices to long span portal frame rafters
(OP)
Hi all,
I have designed a 20m bay portal structure which is currently about to go into fabrication. 20m rafters can be transported to site, but the steel fabricators have requested a splice in the rafters so that they can store them more easily in their yard.
The rafters have been designed very close to full utilisation, and I am nervous about allowing them to provide a splice as I feel it would invalidate the plastic hinge history calculations (to British Standards) by not providing a uniform section.
I am aware that rafter splices are used on portal frames - has anyone given any consideration to their effect on the rafter design calculations? Do you provide a bit of fat in your rafter size to make up for it? Or would you be happy with a rafter designed to 100% utilisation to be spliced?
I have already queried the additional weight of the connection, which is negligible, and would only allow the splice near the points of contraflexure (which however will move around with different load cases)
Thanks for any help!
I have designed a 20m bay portal structure which is currently about to go into fabrication. 20m rafters can be transported to site, but the steel fabricators have requested a splice in the rafters so that they can store them more easily in their yard.
The rafters have been designed very close to full utilisation, and I am nervous about allowing them to provide a splice as I feel it would invalidate the plastic hinge history calculations (to British Standards) by not providing a uniform section.
I am aware that rafter splices are used on portal frames - has anyone given any consideration to their effect on the rafter design calculations? Do you provide a bit of fat in your rafter size to make up for it? Or would you be happy with a rafter designed to 100% utilisation to be spliced?
I have already queried the additional weight of the connection, which is negligible, and would only allow the splice near the points of contraflexure (which however will move around with different load cases)
Thanks for any help!






RE: Splices to long span portal frame rafters
RE: Splices to long span portal frame rafters
RE: Splices to long span portal frame rafters
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Splices to long span portal frame rafters
RE: Splices to long span portal frame rafters
CivEng80 - I'd be more worried about the stiffness throwing the plastic hinge hierarchy, not the capacity. Say you got a couple of degrees slip out of the splice - wouldn't that throw your calcs? Or if the splice was significantly stiffer that the rest of the section, again that might throw your hinge formation away from an assumed position?
RE: Splices to long span portal frame rafters
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Splices to long span portal frame rafters