Txhawb nqa lub luag haujlwm: purlins yog kab rov tav ru tsev ci rau lub ru tsev truss lossis rafters. Lub luag haujlwm tseem ceeb yog txhawb cov rafters lossis cov khoom vov tsev kom paub meej tias lub ru tsev tuaj yeem ua tau ruaj khov. Nyob rau hauv cov steel qauv nroj tsuag, purlins zoo sib qhia thiab hloov chaw thau khoom ntawm lub ru tsev mus rau cov pawg txhawb nqa lossis phab ntsa, ua kom muaj kev ruaj ntseg ntawm txhua lub tsev.
Thauj cov kabmob: Purlin tuaj yeem tiv thaiv lub nra hnyav, tshwj xeeb tshaj yog nyob rau hauv cov hlau txheem hluav taws xob, purlin feem ntau yog ua kom muaj zog thiab cov khoom siv hluav taws xob. Tsis tas li ntawd, purlins kuj tseem tuaj yeem sib npaug thiab txo cov deformation ntawm lub ru tsev los ntawm kev hloov kho kom zoo thiab txoj haujlwm, yog li ua kom muaj kev ruaj ntseg thiab kev nyab xeeb ntawm tag nrho lub tsev.