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1、 COMMENTARY ON THE GUIDE FOR BUCKLING AND ULTIMATE STRENGTH ASSESSMENT FOR OFFSHORE STRUCTURES MARCH 2005 American Bureau of Shipping Incorporated by Act of Legislature of the State of New York 1862 Copyright 2005 American Bureau of Shipping ABS Plaza 16855 Northchase Drive Houston, TX 77060 USA Cop
2、yright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:30:08 MDTNo reproduction or networking permitted without license from IHS -,-,- This Page Intentionally Left Blank Copyright American Bureau of Shipping Provided by I
3、HS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:30:08 MDTNo reproduction or networking permitted without license from IHS -,-,- ABS COMMENTARY ON THE GUIDE FOR BUCKLING therefore, uncertainties in loads and resistances are not specially addressed, but are inhere
4、ntly incorporated into the maximum strength allowable utilization factors. The formulations proposed are generally based on the premises that: They should not depart significantly from the formulations presented in ABS existing Rules and Guides and be consistent throughout the whole Guide; Where dep
5、artures from existing ABS formulations are recommended, they should tend towards a formulation presented in other widely used design standards, such as API RP 2A-WSD; Where appropriate, improvement in formulation accuracy, whether the starting point is ABS MODU Rules1, ABS Steel Vessel Rules2 or API
6、 RP 2A-WSD3, should be included in the proposed formulations. In order to validate the two- or three-dimensional interaction equations of buckling and ultimate strength proposed in the Guide, a modeling uncertainty is introduced, which was suggested by Hoadley and Yura(1985)4. The modeling uncertain
7、ty is the ratio of the distance from the origin to the test data point in question, L1, over the distance from the origin to the interaction curve, L2, and is written by: Modeling Uncertainty = L1/L2 An example of the modeling uncertainty is shown in Section C1, Figure 1. From this definition, the b
8、uckling and ultimate strength prediction is conservative if modeling uncertainty is greater than 1.0. The modeling uncertainty is especially useful because it can be used in one, two and three dimensions, and it is not a function of the exponent of each term in the interaction equation. In addition,
9、 it can be used to determine the amount of conservatism in a state limit when the experimental points are outside the range of the interaction equation when excluding factors of safety. Copyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for
10、 Resale, 08/07/2008 20:30:08 MDTNo reproduction or networking permitted without license from IHS -,-,- Section C1 Introduction 2 ABS COMMENTARY ON THE GUIDE FOR BUCKLING 2 on seamless pipe, Smith et al19; and 70 on ERW pipe, Steinmann and Vojta20 and Yeomans21. This is considerably larger than that
11、previously used to validate offshore tubular strength formulations. The increase is primarily due to the inclusion of relevant results from a large CIDECT test program (Yeomans21). The figure confirms that the ABS MODU Rules1 and API RP 2A-WSD3 formulations are identical. However, the statistics of
12、the comparisons between the formulations and the test data indicate that differences do arise. For example, the means for the two formulations are 1.0736 and 1.0743 respectively. An examination of the calculation details reveals that differences arise because of an API RP 2A-WSD local strength requi
13、rement. This applies for D/t 60; whereas the ABS MODU Rules local buckling limit is in excess of 60 (or using ABS MODU Rules1 definitions, D/t 59) for yield stresses up to 386 N/mm2. The mean and COV of modeling uncertainty of various codes are given in Section C2, Table 2 TABLE 2 Mean/COV of Modeli
14、ng Uncertainty for Column Buckling ABS MODU Rules API RP 2A WSD ABS Buckling Guide Mean 1.0736 1.0743 1.0547 COV 7.56% 7.51% 5.28% Copyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:30:08 MDTNo reproduction or netw
15、orking permitted without license from IHS -,-,- Section C2 Individual Structural Members ABS COMMENTARY ON THE GUIDE FOR BUCKLING the higher level of failure usually leads more severe consequence than the preceding level. Therefore suitable scantling proportions between plates, stiffeners and girder
16、s are necessary to guarantee the sufficient safety of the stiffened panels. Theoretically, plate panels exhibit a continued increase of resistance after the bifurcation point, before they finally reach the ultimate load carrying capacity. In other words, the plate panels have stable postbuckling beh
17、avior. Therefore, it is acceptable that plate panels are designed to reach the buckling state but not the ultimate state. The nominal load-deflection relationship of plate panels is shown schematically in Section C3, Figure 4. FIGURE 4 Load-Deflection Relationship of Plate Panels There are three typ
18、es of buckling mode for stiffeners and girders, i.e., beam-column buckling, torsional-flexural buckling and local flange/web plate buckling. The buckling of stiffeners and girders is restricted because their resistance decreases quickly if any one of these three types of buckling occurs. Their buckl
19、ing strength is regarded as the ultimate strength. If the associated plating of a stiffener buckles, but is below its ultimate state, the platings effective width acting with the stiffener is to be applied. Corrugated panels are self-stiffened panels. There are three levels of failure mode, i.e., fl
20、ange/web plate buckling, unit corrugation buckling and entire corrugation buckling. Depending on the loading type, corrugated panels may collapse into the different failure modes. For examples, axial compression mainly induces the flange/web buckling, lateral pressure induces the buckling of unit co
21、rrugation, and edge shear force leads to the buckling of entire panels. The buckling strength is the least value obtained from those established for the three failure modes considering any load type and load combination. Copyright American Bureau of Shipping Provided by IHS under license with ABS Li
22、censee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:30:08 MDTNo reproduction or networking permitted without license from IHS -,-,- Section C3 Plates, Stiffened Panels and Corrugated Panels 30 ABS COMMENTARY ON THE GUIDE FOR BUCKLING comparisons of results using the ABS Buckling Guide and DnV
23、CN 30.1 are presented. The other example is a converted FPSO in C3A2/3. In the latter example, comparsions between the ABS Buckling Guide and the SafeHull Criteria meant for ship structure are given. 1 Spar Appendix C3A2, Figure 1 provides examples of buckling and ultimate strength assessments for p
24、late panels and stiffened panels used in a Spar design. All plate panels satisfy the ultimate strength criterion. The results of ultimate strength assessment for plates from the ABS Buckling Guide and DnV CN30.1 are remarkably close. FIGURE 1 Design Practice of Spar 0 0.2 0.4 0.6 0.8 1 1.2 00.20.40.
25、60.811.2 ABS Buckling Guide DnV CN30.1 (a) Ultimate Strength of Plate Panels Copyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:30:08 MDTNo reproduction or networking permitted without license from IHS -,-,- Sectio
26、n C3 Appendix 2 Design Code Examples and Comparisons 60 ABS COMMENTARY ON THE GUIDE FOR BUCKLING the higher level of failure usually leads more severe consequence than the preceding level. Therefore suitable scantling proportions between shell plates, rings and stringers are necessary to better assu
27、re the safety of ring and/or stringer stiffened cylindrical shells. Theoretically, the resistance of a cylindrical shell decreases after the bifurcation point is reached, so the buckling strength is equal to the ultimate strength of the cylindrical shell, as shown in Section C4, Figure 3. However, i
28、nitial imperfections have a detrimental effect on load-carrying capacity due to the very unstable postbuckling behavior of cylindrical shells. Therefore initial imperfections should be monitored carefully during fabrication, assembly and installation. Copyright American Bureau of Shipping Provided b
29、y IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:30:08 MDTNo reproduction or networking permitted without license from IHS -,-,- Section C4 Cylindrical Shells ABS COMMENTARY ON THE GUIDE FOR BUCKLING thus emphasizing the importance of the proportioning criteri
30、a in the design of offshore structures. C7 Ring and Stringer Stiffened Shells Stringers together with ring stiffeners form the main stiffening elements of fabricated cylinders used as compression members in steel offshore structures. Bay buckling is characterized by the stringer stiffener/panel junc
31、tion deflecting between the end supports or ring stiffeners. The positioning of stringer stiffeners has a significant influence on buckling behavior. Externally stiffened shells have higher buckling strength and increased imperfection sensitivity compared to their internally stiffened counterparts.
32、C7.1 Bay Buckling State Limit In the ABS Buckling Guide, the interaction equation for the bay buckling of a ring and stringer stiffened cylindrical shell between adjacent ring stiffeners subjected to combined loading is consistent with the ultimate strength interaction equation for plate panels in S
33、ection 3 of the ABS Buckling Guide. It is also similar to the one in API Bulletin 2U. The equation is written as: Copyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:30:08 MDTNo reproduction or networking permitted
34、without license from IHS -,-,- Section C4 Cylindrical Shells ABS COMMENTARY ON THE GUIDE FOR BUCKLING the critical stress is made up of two parts: inelastic buckling stress of an unstiffened shell and plastic collapse stress of the stringers acting compositely with effective shell plating. The sum i
35、s then modified by an effective correction factor. The formulation is written as: CB = (CR + sp)Kp where CR = critical buckling stress of an unstiffened shell sp = collapse circumferential stress of a stringer stiffener with its associated shell plating Kp = coefficient to account for the strengthen
36、ing effect of ring stiffener The database for ring and stringer stiffened shells subjected to external pressure only contains 12 test datasets. Section C4, Table 12 gives the statistical characteristics of the modeling uncertainty, and Section C4, Figure 12 shows the distribution of modeling uncerta
37、inty. TABLE 12 Modeling Uncertainty of Bay Buckling: External Pressure API Bulletin 2U DnV CN30.1 ABS Buckling Guide Mean 1.1781 1.4113 1.1900 COV 0.1584 0.3717 0.1745 Copyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/200
38、8 20:30:08 MDTNo reproduction or networking permitted without license from IHS -,-,- Section C4 Cylindrical Shells 84 ABS COMMENTARY ON THE GUIDE FOR BUCKLING Foundations and Analysis, Delft, 31 Mar-2 Apr 1980. 115. Steen, E, Xirouchakis, P and Valsgard, S. (1982). “Design Proposals for Buckling of
39、Stringer-stiffened Cylindrical Shells under Axial Compression and External Pressure”, Det Norske Veritas, Report 82-0268. 116. Steen, E and Valsgard, S (1981). “General Buckling of Orthogonally Stiffened Cylindrical Shells under various Load Conditions”, Det Norske Veritas, Report 81-0611. 117. Syng
40、ellakis, S and Walker, A C (1981). “Elastic Local Buckling of Longitudinally Stiffened Cylinders”, Stability Problems in Engg Structures and Components, Ed. T.H. Richards and P. Stanley, Essex: Applied Science Publishers, 159-178. 118. Valsgard, S and Steen, E (1980). “Simplified Strength Analysis o
41、f Narrow-paneled Stringer- stiffened Cylinders under Axial Compression and Lateral Load”, Det Norske Veritas, Report 80-0590. 119. Valsgard, S and Foss, G (1982). “Buckling Research in Det Norske Veritas” Buckling of Shells in Offshore Structures, Ed. J.E. Harding et al., London: Granada, 491-548. C
42、opyright American Bureau of Shipping Provided by IHS under license with ABS Licensee=Boeing Co/5910770001 Not for Resale, 08/07/2008 20:30:08 MDTNo reproduction or networking permitted without license from IHS -,-,- Appendix C2 References ABS COMMENTARY ON THE GUIDE FOR BUCKLING & ULTIMATE STRENGTH
43、ASSESSMENT FOR OFFSHORE STRUCTURES . 2005 137 120. Videiro, P M (1980). “Reliability-based Design of Marine Structures”, Doctoral Thesis, Department of Marine Structures, Faculty of Marine Technology, The Norwegian University of Science and Technology, NTNU, Trondheim, Norway, 1998. 121. Walker, A C
44、 and Sridharan, S (1980). “Analysis of the Behavior of Axially Compressed Stringer-stiffened Cylindrical Shells”, Proc. ICE., Part 2 69, 447-472. 122. Walker, A C, et al (1982). “Theoretical Analysis of Stringer and Ring Stiffened Shells”, Buckling of Shells in Offshore Structures, Ed. J.E. Harding,
45、 et al., London: Granada, 183- 208. 123. Walker, A C and Sridharan, S (1979). “Buckling of Longitudinally Stiffened Cylindrical Shells”, BDSS “79, Paper 72, London, 341-356. 124. Weller, T, Singer, J and Batterman, S C (1974). “Influence of Eccentricity of Loading on Buckling of Stringer-stiffened C
46、ylindrical Shells”, Thin Shell Structures: Theory Experiment and Design, Ed. Y.C. Fung, and E.E. Sechler, New Jersey: Prentice-Hall, 305-324. 125. White, J D and Dwight, J B (1977). “Weld Shrinkage in Large Stiffened Tubulars”, Proc. of Conference on Residual Stresses in Welded Structures, Welding I
47、nstitute, Cambridge, December. 126. AWS D1.1(2000), “Structural Welding Code Steel”, American Welding Society, 17th Edition. 127. HSE(1990). Offshore Installations: Guidance on Design, Construction and Certification, Fourth edition, HMSO. 128. BOMEL(1999). Tubular Joints Design Guide - Chapter 2: St
48、atic Strength. Dec. 1999. Confidential to Sponsors (including ABS). 129. Hoadly, P A and Yura, J A (1983). “Ultimate strength of tubular joints subjected to combined loads : Phase II”. PMFSEL Report No. 83-3. University of Texas at Austin. 130. Weinstein, R M and Yura, J A (1985). “The effect of chord stresses on the static strength of DT tubular connections”. PMFSEL Report No. 85-1. University