design considerations for aluminum hull structures - Ship Structure ...

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-56-at the deck and keel. This stress should be assumed to taper to 6.7J KSI atthe neutral axis for the hull envelope and its framing, and tO ze~o foT O~h@rinternal structure to account for stresses at an angle of heel.Limitations on -platepanel deflections are no% considered necessary, sincethe increase in plate thickness in converting from mild steel to aluminum willgenerally provide a sufficient increase in inertia to offset the effects ofdifferences in elastic moduli.Design Criteria for Stiffeners - The design procedu~e for converting mildsteel stiffener scantlings to aluminum consists of increasing the sectionmodulus of the steel mem~er by the relative strength ratio noted previouslyfor plahes:Equation (4): Malum .WIteel 97,000( )Y+u/Where Y and U are asnoted previously for Equation (1).Corrosion allowances arebut are neglected to providedtechnically applicable to the above equation,an additional margin for member stiffness andhigh residual stresses in way of end connections. The additional weightresulting from this simplification is negligible, since the added areagenerally contributes to hull girder section modulus for longitudinallyframed ships.It is noted that longitudinal stiffeners on the shell and deck aresubjected to a combination of axial load from hull girder bending andsecondary bending from normal loads. Fortunately, however, the ratio ofhull girder primary design stress to the quantity (Y + U) of steel andaluminum bulk carriers are essentially identical at about 0.20, so thatthis combined loading condition affects both materials similarly, andEquation (4) remains valid.In addition to the foregoing, stiffeners should be checked for columnbuckling strength under the effects of longitudinal bending loads, andagainst local instability of flange and web as discussed in the previoussection. Ii is suggested that the L/r ratio of the plate-stiffener combinationbe sufficiently low that the safety fackoT on column buckling failurewould be 1 .67, and that the web and flange proportions would permit developmentof full welded yield stresses in the member without local instability.The deflection of aluminum stiffeners should be kept within reasonablelimits, so that vibration problems and secondary bending effects are minimized.However, it is difficult to establish a specific deflection limitation, sincethis is a somewhat arbitrary decision, with little technical justification.Until a valid technical foundation for such a limitation can be developed,it is proposed to limit deflections of Primarv framinp members (girders. webframes, ~tch end beams, etc.) to l-1/2-times-’thatof-the equiva~ent st~elsection, with no limits on the deflection of secondary stiffening. Equation(s) specifies the inertia required for primary hull framing members:Equation (~): Ialum = 2 Isieel (primary members only)
-57-Stanchions - Aluminum stanchions should have the same sSfety factor onThe end connections,column buckling as the equivalent Rules steel stanchion.considered.which will be at O temper, should be speciallyPROPOSEO CRIT~IA- SECONDARY HULL STRUCTUREh designing suck secondary structures asdeckhouses, structural bulkproposed,which are essentiallyheads, tanks, etc., the following criteria arethe same as those far primary hull structures:For Plates:Equation (6): talum = tsteel 97,000 ny+u‘( )Where n = 1 for plates loaded primarily on the edges(tension, compression or shear)For Stiffeners:n = 1/2 for plates loaded laterallyEquations (~) and(5)apply.Crack Arresting - The various Regulatory Bodies and design activities withwhom crack arresting requirements were discussed, indicated t~at aluminum alloysappear to possess sufficient fracture toughness, ductility and tear resistancethat mechanically fastened crack arrestor seams may not be required for analuminum hull. The investigation of fracture toughness and tear resistanceof aluminum which was conducted for this study did not provide sufficient datato justify such a conclusion for a large, highly stressed hull subjected tocyclic loading. The data is particularly sparse in the area of crack propagationin way of the heat affected zone when subjected to high intensity cyclic loading.Therefore, it is concluded that a minimum number of mechanically fastenedseams should be incorporated in the design of large aluminum hulls.For this study, it is proposed to incorporate a single mechanically fastenedseam at the lower edge of the shear strake port and starboard. This locationreflects the fact that the deck is more highly stressed than the bottom, andsubject to high stress concentrations at hatch corners. Mechanically fastenedseams are not desirable below the water line due to possible stress corrosionproblems at the faying surface.Thermal Stresses - The thermal stresses induced h the hull of an aluminumship with S083 alloys will be no more critical than with an equivalent steelhull, based upon the following logic:Thermal elongationEthe length of the memberthe coefficient of linear.00128 for aluminum—- .00065 for mild steelexpansion per IOO”F
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CONTENTSI.. II.III.Iv.v.VI ●VII.I
Page 9 and 10:
LIST OF FIGURES(Cent’d)FIGURE NO.
Page 11 and 12:
I. INTRODUCTIONThis report summariz
Page 13:
art in fabricating and maintaining
Page 16 and 17: MONTEROSSO GRANA /17VALGRANA / CARA
Page 18 and 19: -8-Numerous references have been re
Page 20 and 21: .10.TABLE 2. Mechanical Properties
Page 22 and 23: TABLE 2 Mechanical Properties of Al
Page 24 and 25: TABLE 3 Mechanical Property Limits
Page 26 and 27: -16-l?igures5, 6, 7 ati 8 present f
Page 28 and 29: -18-ti-’”’-”-””””-L
Page 30 and 31: -20-60 .r---.— ..,.— -——,L-
Page 32 and 33: .22-each stress level, rate of load
Page 34 and 35: -24-!Z456-H321 = 0.485083-H321 = 0.
Page 36 and 37: -26-(c)Members with partial or cont
Page 38 and 39: -28-AllOyS 5083 and 54.56(~ content
Page 40 and 41: -30-The previous paragraphs have de
Page 42 and 43: -32-The problem of cargo hold abras
Page 44 and 45: -34-The question of residual stress
Page 46 and 47: .36-Each alloy was given a relative
Page 48 and 49: -38-GENERAL OBSERVATIONSFYior to a
Page 50 and 51: -40-The question of comparative imp
Page 52 and 53: -42-(d)(e)Poor quality welds due to
Page 54 and 55: -44-The ABS criteria noted above we
Page 56 and 57: -46-DNV would consider fatigue in e
Page 58 and 59: -48-is less, for the exposed side s
Page 60 and 61: Equation (2):-50-Hu1l SMa~um = Hull
Page 62 and 63: -52-Another aspect of vibrations wh
Page 64 and 65: -54-000000000Bottom Shell PlateSide
Page 68 and 69: -58-AT is the change inUT= Thermal
Page 70 and 71: -60-SUl@!ARYAll parties contacted f
Page 72 and 73: -62-(c)(d)(e)(f)T~e exterior side o
Page 74 and 75: TABLE 12 Aluminum Bulk Carrier - Su
Page 76 and 77: .66-INSUT.ATION AND SHEATHINGShell8
Page 78 and 79: -68-(b)(c)(d)(e)(f)(g)(h)(i)(j)At l
Page 80 and 81: -70-IIF.INSTALLATION OF SYSTEMS AND
Page 82 and 83: Rudder Assembly -carrier should be
Page 84 and 85: -74-(b)MechanicalTensile Strength 6
Page 86 and 87: -76-(e)The steel piping must be of
Page 88 and 89: -78-Other Piping Systems and Valves
Page 90 and 91: -80-struetion for the aluminum hull
Page 92 and 93: -82-Large heavy type machine~ must
Page 94 and 95: suffers attack in an alkaline envir
Page 96 and 97: -86-REPAIRSObtaining proper repairs
Page 98 and 99: -88-The design of the midship s~cti
Page 100 and 101: -90-assuming the increase is applic
Page 102 and 103: LIGHT SHIP WEIGHT ESTIMATE-92-In or
Page 104 and 105: -94-TABLE 20 Aluminum Bulk Carrier
Page 106 and 107: TABLE 22 Trim and StabilityFull Loa
Page 108 and 109: -98-TABLE 24 Price of Steel Bulk Ca
Page 110 and 111: GaseNumber. . . -.,- .TABLE 27 Comp
Page 112 and 113: -1o2-TABLE 28CarriersComparison of
Page 114 and 115: 12 ---n..T.[T7%l,=LEGS IU ORF=ErY
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-106-such as iron ore, on two of th
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-108-7)is,zg~ gg~5e mzz~E’4E!~K2j
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-11o-(a)(b)(c)(d)Inerting system fo
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-112-fatigue, particularly in the p
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-114-2k* Installation of Systems an
Page 126 and 127:
-116-LIST OF REFERENCES(7)Fatigue P
Page 128 and 129:
-11.8-LLST OF REFERENCES(Cent’d)(
Page 130 and 131:
-120-ADDITIONAL SOURCES OF INFORMAT
Page 132 and 133:
-122-redistribution of the still wa
Page 134 and 135:
-124-APPENDIX BEXCERPTS FROMRULES A
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-126-92.07-10(d)(~) Interior stairs
Page 138 and 139:
-128-~gE1+0102030- .. ..—405060
Page 140 and 141:
ectintyclassification4KEYWORDSROLEL
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SHIP STRUCTURE COMMITTEE PUBLICATIO
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