《欧规3 钢结构设计》基础教程 教程25计算案例参考文件.docx

1、欧规3 钢结构设计基础教程 教程25计算案例参考文件Structural Steelwork Eurocodes Development ofA Trans-national ApproachCourse: Eurocode 3 Module 7 : Worked ExamplesLecture 25 : Plastic Design of Portal frames References for the Worked ExampleRef 117.2 Plastic design - ultimate limit stateThe following procedure is suggest

2、ed:1) Define frame geometry, determine loads, load combinations, factors and factors (see Section 11).2) Choose trial sections and trial haunch lengths by selecting beam sections that have resistances at least equal to the following: Where w is the maximum ULS gravity load/unit length along the span

3、 and L is the span of the portal.The haunch length should be chosen to optimise the overall portal structure. A length of L/10 from the column face is a reasonable initial choice, but the proportions of the haunch generally depend of the characteristics of each individual building, especially the si

4、ze of the rafter (see Section 6.3). A haunch length of L/10 will normally place the first hinge in the top of the column. A rather longer haunch will place the first hinge at the sharp end of the haunch.3) Calculate frame imperfection equivalent forces, referring to ENV1993-1-1 Section5.2.4.3 and Se

5、ction 15 of this publication. This can be by a preliminary frame analysis (which is necessary for all but the simplest buildings) or by a suitable approximation.4) Perform plastic analysis of the frame (see Section 12.4) assuming:(a) no reduction in plastic moment of resistance from coexistent axial

6、 and shear forces. This approach may need modifying, where axial loads are high, e.g. in tied portals, in portals with steep slopes and in portals with heavy roofing loads. (b) Trial VSd/Vcr 0,12 unless a better estimate is possible.Note that in uplift cases, the members might be subject to axial te

7、nsion. In this case, there will be no destabilisation of the frame and VSd/Vcr can be taken as zero.5) Calculate an accurate value of VSd/Vcr. (See Section 12 and Appendix B).6) If accurate VSd/Vcrtrial VSd/Vcr or if a more refined design is required, return to Step 4.Note: For relatively slender fr

8、ames, it is often wise to check the deflections at the Serviceability Limit State, as explained in Section17.4, before checking the buckling resistance.7) For the columns check that:(a) The classification is Class 1 or Class 2 as appropriate, as explained in Section13 and AppendixC; Sections 13.1, 1

9、3.2, 13.3 and AppendixC.2 are particularly relevant.(b) The crosssectional resistance is adequate, as explained in Section13 and AppendixC; Sections13.4 and AppendixC.4 and C.6 are particularly relevant.(c) The resistance of the member to minor axis buckling between lateral restraints is adequate, a

10、s explained in Section13 and AppendixD, together with the appropriate parts of AppendixF; Section13.5 is particularly relevant. For elements with a plastic hinge within the length or at either end, AppendixD.4 should be used (which contains the same check as AppendixF.4). For elements resisting mome

11、nts and forces close to the plastic resistance, AppendixD.4 might need to be used, because AppendixD.3.4.2 cannot be satisfied. For elements without plastic hinges and not very highly stressed, AppendixD.3.4.2 should be used, together with AppendixF.2, with L taken as the distance between lateral re

12、straints, e.g. between purlins.(d) Resistance of member to minor axis buckling between torsional restraints is adequate, as explained in Section13 and AppendixD, together with the appropriate parts of AppendixF.The method of checking is similar to (c) above, but AppendixF.3 should be used instead of

13、 AppendixF.2.8) For the rafters check that:(a) The classification is Class 1 or Class 2 as appropriate, as step 7(a) above.(b) The crosssectional resistance is adequate, as step7(b) above, but without AppendixC.6.(c) The resistance of the member to minor axis buckling between lateral restraints is a

14、dequate, as step7(c) above.(d) The resistance of the member to minor axis buckling between torsional restraints is adequate, as step7(d) above.9) For the haunches check that: (a) The classification is Class 1 or Class 2 as appropriate, as step7(a) above, but using AppendixE where the web slenderness

15、 is Class3. (b) The crosssectional resistance is adequate, as step7(b) above, but checking at several crosssections within the length of the haunch (both ends, quarter, mid-span and threequarter points are recommended). AppendixE.2 or AppendixE.3 should be used where the web slenderness is Class3. (

16、c) The resistance of the member to minor axis buckling between lateral restraints is adequate, as Step7(c) above, but giving special attention to the effect of the taper. These effects are described in Section 13.5.4, AppendixD.3.4.2, AppendixD.5 and AppendixE.4. (d) The resistance of the member to minor axis buckling between torsional restraints is adeq