BENDING AND TWISTING ABOUT A CONSTRAINED AXIS OF C-SECTION PURLINS WITH ONE SAG ROD AT MIDSPAN

The sag Rods in puRlin systems aRe RegaRded as lateRal elastic suppoRts. C-section puRlins undeR wind suction weRe analyzed using the theoRy of thin-walled membeRs, whose Results weRe compaRed with those of FE analysis using ANSYS plate elements. It was found that for C-section puRlins undeR wind suction acting thRough midpoint of uppeR flange，whose hoRizontal Reaction agReed well with that by ANSYS model，and the Reaction in the sag Rod was also in good agReement with ANSYS analysis, except on and neaR the sag Rod cRoss section; on the cRoss-section of the sag Rod，the stResses of the puRlin weRe affected gReatly by distoRsional deformation caused by sag Rod forces. FoR the contRolling compRessive stRess the EC3 appRoach is on the safe side，but for the contRolling tensile stResses at the tip of the uppeR flang lip，distoRsional stRess should be added to the simple bending stRess to achieve acceptable accuRacy.