purlin on top of beam create purlins on the selected support 4 2 purlin connection prostructures correct purlin for roof framing steel structure h section beam purlin retrofit roofing systems steel hall with z purlins r model secondary framing pebbers structures girder joist purlin assignment rules c purlin tubular beams retrofit roofing systems simply supported lattice purlin best purlin connection over trusses or script archive consteel statewide steel contact retrofit roofing systems girder joist purlin assignment rules best fabrication method for z sections purlin offerings by aep span e purlin lvl s wesbeam wesbeam mitek residential construction z purlin and z girt structural steel purlin and girts tata bluescope steel steel building insulation systems column purlin rafter prefab steel utils js light weight utility belt web local yielding