ABS 75-1995 Safehull System for Tankers Guide on Improvement for Structural Connections and Sample Structural Details - Service Experience and Modifications - for Tankers《油轮修改及运行经验.pdf
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1、ABS TITLE GISCSSDSEMT 95 065LL02 DOL0793 9T5 FOUNDED :862 - AMERICAN BUREAU OF SHIPPING such as locations at the bracket toes, cut-outs, terminations of heavily loaded members, the connection of flexible elements with much stiffer members, the ends of unbalanced structural members, just to name a fe
2、w. For ship structures designed with relatively low working stresses and high safety margins, the 1 ABS T%TL,E GISCSSDSEMT 95 Ob5LL02 0030777 5YO detrimental effects of such stress concentrations may not be readily apparent. On the other hand, for structures designed with relatively high working str
3、esses and low safety margins, damaging effects of such stress concentrations could appear sooner than the anticipated period of time. Appropriate stress concentration factors (SCFs) obtained from either experimental data or structural analyses are required to evaluate the design of structural detail
4、s. 2.3 Weld Effects and Fatigue Strength Another important factor to be considered is the effects of welding on the properties of material (heating effects) and on structural continuity (profile of the weld deposit and under- cuts). This factor which highly depends on the welding methods, processes
5、and workmanship is vital for assessing the fatigue strength of the joint. To date, the welding effects on the fatigue strength are primarily determined by experimental data presented in the form of S-N curves and characteristics of the test specimens, as shown in the Appendix 52AA of the Rules. 3.0
6、CONSIDERATIONS FOR DESIGN OF STRUCTURAL DETAILS In light of the discussions given in Y2A5.4, it is apparent that the necessary criterion for the design of structural details is simply to offer a well balanced joint which is compatible with the anticipated working stresses. To this end, the solution
7、is to be tailored to a specific location of a specific design. In addition, there is no unique solution to the problem. Many alternatives may exist. The designerdbuilders would have to exercise their judgment based on their fabrication facilities, techniques and experience. The information offered b
8、elow is provided for reference. 3.1 Structural Configuration and Arrangement of Brackets When selecting the structural configurations and sizing the brackets connecting primary supporting members, due consideration is to be given to the bad transmission and the 2 AR5 TITLE GISCSSDSEMT 95 Ob51102 OOL
9、0798 487 W 3.2 relative stiffnesses of the members to be connected. A smooth pattern of load transmission is essential. The connecting bracket is to be of sufficient size to withstand the highly concentrated loads and to shift the critical spots (bracket toes) to the lower stressed regions. An appro
10、priate stiffening system is also required for large brackets to prevent local structure instability and tripping. Sample illustrations are shown in Fig. 1 and Fig. 2 for damages experienced in existing tankers with recornmended modfications. Installation of Brackets and Collar Plate To prevent local
11、 distortions and to minimize the magnifying effects of structural notches, consideration is to be given to additional brackets and collar plates (or lugs) at the criitical joints and cut-outs, respectively. Sample illustrations are shown in Fig. 3 for local damages recorded and the recommended modif
12、ications. Alternatively, different stiffening systems may be considered to minimize the critical spots in highly stressed regions. For example, utilization of the horizontal stiffeners with appropriate tripping brackets for floors in the double bottom, instead of vertical stiffeners would eliminate
13、the critical spots at the face bar toes on the flange of longitudinal as shown in Fig. 342. 3.3 Softening Hard Spots To minimize the stress concentration at hard spots, such as bracket toes, tapered face plate, and welded connections of the face plate of transverses and bulkhead plating, the welded
14、joints may be softened by providing a large radius at bracket toes or a cope hole with proper reinforcement of the surrounding panel to prevent local instability. Some sample illustrations are shown in Fig. 4. To minimize the detrimental effects of knuckles in structural elements, sample illustratio
15、ns are shown in Fig. 5. 3 ABS TITLE GISCSSDSEMT 95 = Ob51102 0010799 313 3.4 Improvement of Fatigue Strength At crkal structural joints, the fatigue strength can be improved, as discussed in the previous paragraphs, by reducing the magnitudes of nominal stresses (working stresses) andor minimizing t
16、he stress concentrations. In addition, it may also be advisable to consider the following improvements on the fatigue strength: 1) Utilizing better contour shapes for cut-outs, such as the cope holes shown in Fig. 6. 2) Having bracket toe and the surrounding weld deposit ground smooth with an approp
17、riate radius as shown in Fig. 7. 4.0 SAMPLE STR UCTURAL DETAIL S These examples are divided into the following five groups: Figure 1 - Examples for Bracket Enlargement a) Connection of Bottom Girder and Vertical Web b) Bottom Girder End Bracket c) Bottom Transverse End Bracket d) Reinforcement at Co
18、nnection of Bottom Girder and Oil Tight Bulkhead Figure 2 - Examples for Bracket Modification a) Connection of Centerline Girder and Oil Tight Transverse Bulkhead b) Connection of Horizontal Girder and Side Longitudinal c) Longitudinal End Bracket Figure 3 - Examples for Additional Brackets and Coll
19、ar Plate a) Connection of Bottom Girder and Swash Bulkhead b) Tripping Bracket on Transverse Web c) Connection of Longitudinal to Floor in Double Bottom d) Connection of Longitudinal to Transverse Web Figure 4 - Examples for Hard Spot Effects a) Tapered Face Plate of Horizontal Girder b) Connection
20、of Transverse Face Plate and Bulkhead Plating c) Bracket Toe on Bottom Transverse d) Bracket Toe on Longitudinal e) Sniped Tripping Bracket on Horizontal Girder Figure 5 - Examples for Knuckle Effects 4 Modification II! ! i Existing Figure l(a) Connection of Bottom Girder and Vertical Web 5 ABS TITL
21、E GISCSSDSEMT 95 Ob5LL02 OOLOBOL BTL I Modification I& WAY Existing /- Figure l(b) Bottom Girder End Bracket 6 ARS TITLE GISCSSDSEMT 95 m Ob5LL02 OOLO802 738 Modification PENETRATION SERTED PLATE ITH INCREASED THICKNESS * LUGS Existing - .- LONGITUD I NAL BULKHEAD II Figure l(c) Bottom Transverse En
22、d Bracket 7 ABS TITLE GISCSSDSEMT 95 Ob51102 0010803 674 = Modification Existing Figure l(d) Reinforcement at Connection of Bottom Girder and Oil tight Bulkhead 8 ABS TITLE GISCSSDSEMT 95 m Ob51102 0010804 500 H Modification Existing 0.T. BULKHEAD BOTTOM TRANSVERSE I - , FRACTURE y BOTOM SHELL FRACT
23、URE 7 VIWA-A Figure 2(a) Connection of Centerline Girder and Oil tight Trans Bulkhead 9 ABS TITLE GISCSSDSEMT 95 m Ob5LL02 OOL0805 447 m Modification Existing TRANSVERSE BULKHEAD FRACTURE - f SIDE SHELL Figure 2(b) Connection of Horizontal Girder and Side Longitudinal 10 ABS TITLE GISCSSDSEMT 95 Ob5
24、1102 OOL080b 383 Modification Existing t I Figure 2(c) Longitudinal End Bracket 11 ABX TITLE GISCSSDSEMT 95 = Ob51102 0010807 21T Modification Existing I il Figure 3(a) Connection of Bottom Girder and Swash Bulkhead 12 ABS TITLE GISCSSDSEMT 95 m Ob51102 OOLOBOB 156 = Modification el - TRANS. CUTOUT
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