Steel Buildings in Europe

Part 5: Detailed Design of Trusses 5 - 26 Figure 3.12 Passage of a duct – Broken diagonal Development of stress in the modified area is represented on the section diagrams in Figure 3.13. Axial force (kN) Bending moment (kNm) Initial structure Axial force (kN) Bending moment (kNm) Modified structure Figure 3.13 Effects of a broken diagonal under ULS gravity loading The effects of modification on the calculated stresses are mainly:  A noticeable increase is observed in the axial force in the second lower chord member from the right hand support (in the panel with the broken diagonal): the tension calculated increases from 818 to 1350 kN.  A significant increase is also observed in the compression force in the broken diagonal compared with the rectilinear diagonal of the initial structure: compression increases from 624 to 1090 kN.  As far as the additional triangulation member is concerned, this supports a normal compression force of 755 kN.  In the lower chord, as well as an increase in the normal tension force, an increase in “secondary” moments is also observed on the three right panels