The interconnection of longitudinal frames at transverse bulkheads in tankers, International Ship Structure Congress, Glasgow, September 1961

REPORT

SSL 77

March 1961

SHIP STRUCTURE LABORATORY

TECHNOLOGICAL UNIVERSITY

- DELFT

THE INTERCONNECTION OF LONGITUDINAL

FRAMES AT TRANSVERSE BULKHEADS IN TANKERS

Xntenationa). Ship: Structure ConFreas,.

19-21. stember 1961».

Glasgow.

The interconnection of longitudinal frames at

transverse bulkheads in

tankers..

by Ire J. J. W.Nibberin&.

Ship Structure Lbora'tory, Delft

The Nethei lands.

When the first aeriôus brittle fractures occured in T2-tan-kers it was already known

that

not only

welding but also

quality of steel and design' greatly influence the brittle

behaviour of etitures. Much. iorkbas since been done in

order to improve shipbuilding steels.

The influence of design hasonly incitexitally been

investi-gated. This is paztly due

to the scientifically right con-'ception that fundamental research must precede experiments

with large structural components0 It i however e;uully

true that the theories emerging from fundamental research

must find an opportunity to prove their valúe. Further, as» a matter of fact1 shipbuilders like to have direct indica-. fiona as to the design of structures.

One of the Lirst :experimenta with large structural compc nents bas been executed by' Irwin and Cabel1 .i).

Speci-mens representing the intersection of a bottom longitudinal with a transverse bulkhead were pulled to rupture at low

lu Japan, TakahaBbi, Akita and Yokoy8ra investigated the

tres8es and strains inscale node1a of longitudinals tri

Whio)thtckne88 and size. of the bracketp1ìtes were

eyste-matically varied

('2).

The result of both inveStigations cannot directly be

used for

htps.

'irstly the American test pieces were only

subjected t:O

unique elongation till rupture, whereas

longi-tudinale in ships are aeverely dynamically loaded in axial

dircotlønas well asin bending. Purthermore the order of

merit of the specimens has mainly been obtained by using

öpergy

t 11. fracture as the criterion of strength.

It i

shown

(3) that this will lead to errneoue cunclusions if the

in-fluence

of the boundary conditions of the test pieces is

not carefully taken into account. This particulurly applies

tò the length of the specimens and the breadth of the

bot-tomplate. Take for

instance two types of specimens;; in one

type plastic deformation is supposed to. occur only in the

imnie

diatevicinity of the fracture and in the

other type

every-where outside tbe

fracture-region. When these

test pieces are

short, the aniounta of

energy till rupture can be about equa],

but whin they are long the secônd type will seem to be the

best.

It is-iniportsnt--to--realtze__tbat_l.ength also determines to a

large extent the amount of elastic energy

that can be

aeumu-lated in a structure. As a

consequence long

test pieces

are

more.indanger of brittle fracture than

short ones..

The breadth of the bottoinpiates of the American test pieces

.acuounted to 60%

of the longitudinal l'rame apacing.The

influ-encé.ofbreadth on the bebaviourof the specimens can be

lar-3

, but numerical

corrections axe difficult to make.

The above mentioned

considerations bave led to

the opinion

tbat an exteneioof the investigìtions on longitudinal

con-ùections is necessary. This will be done tri the Ship Str.uc-turé'Laboratory of the Technological

University atDelft.

The influence of boundary conditions on the behaviour of the specimens.

The influence of loads

perpendicularto the plane of the

bottomplat:e on the longitudinal strength of the

speci-.menb.

The interrelations between local deformations, static

strength at low teperaturea ond dynamic strength.

cl. Notch sensitivity of the material in the: vicinity of

frac'-tures before and after the

statical and dynamical testa. In. consequence of the general character of the

investiga-tion it is sufficient to test only two or three. types of structures. They must corréspond to specimens typical for the American and Japanese tests and must h easily

compara-ble to each other. Nevertheless they

iiust represent opposite

design trends. The old, rigid T2-design and its flexible mo-difications with semi-circular,cut-outs come satisfactorily up to these requirements (fig. 1). Furthermore some

speci-mens will be tested in which the longitudinal uninterrupted:-ly passes. through the bulkhead without the Use of.bxackets. They will serveas e basis for strength comparison and will further be used för an investigation of

the

influence of

'low temperatures

on .the low cycle high tress fatigue strth

o structures..

Ail the specimens will be t'ested in the 500 tons tenaie-cowprcssion machine of the Ship Structure Laboratory at Deift. (fig. 2).

The program will start in May 1961.

Deift, March 1961.

/

Refer erices:

(ei). Tensile te:ts of large specimens representing the

intì-section of s bottom loiigitudinal with a trriEv%r

bulk-heid in tankers.

L.K. Irwin znd Campbell. Ship Structure Commite

Report No. SSC-68, JanuAry 18,

_1954.

(2.

Experiments on ttiestiength of the connection of

bot-tom longitudinale and transverse bulkheads in tankers. K. Takahashi, L. Akita, LI. Yokoyama.

International Shipbuilding ProgLe6s No. 1:.

_1955.

(3).

Jnige beschouwingen over breukverscbijnselen,

tena en constructieve vormeving, in het bijzonder ut

betre1king tot schecpsconstructies.

Ir. .J.J.W. Nibbering, Schip en Vert, 12 juni

_1959.

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