Exercise 7

NTNUNorwegian University of Science and Technology.

Faculty of Marine Technology

Department of Marine Structures. TMR4205 Buckling and Collapse of StructuresUse of Nauticus spreadsheet: Buckling of stiffened plates according to DNV-RP-C201/oct. 2002________________________________________________________________________________________Date: March 2011 Signature: EKim Distributed Date: 17.03.11 Due Date 24.03.11PROBLEM 1

A stiffened panel shall be checked with respect to buckling according to DNV-RP-C201. The spreadsheet included in Nauticus shall be used (Open XL spreadsheet named StiffenedPlateBuckling_RP-201 located in C:\Program Files\DNVS\NauticusHull\*\). The panel has the following properties:

t =15 mm

s =650 mm

l =1800 mm

LG =6500 mm

Lp =3250 mm

Long stiffeners HP profile 240x12

Girders:

htot = 800 mm

tw =18 mm

bf =400 mm

tf =35 mm

It is subjected to the following design stresses

x =150 MPa

y =50 MPa

=25 MPa

External lateral pressure 0.3 MPa

The yield strength is 235 MPa

a) What is the maximum utilization factor (UF) for the unstiffened plate?b) What is UF with respect to lateral pressure for the unstiffened plate? What do the factors x and y represent? What is the influence of these factors? (Calculate the required thickness giving the same UF when x = yn =1)

c) What is the UF for buckling of unstiffened plate? Is this failure mode really a true buckling event? How can you explain the UF for longitudinal compression alone is larger than the UF for combined loading? Can you propose a UF expression, which is more consistent with that of uniaxial compression? How much can the stresses be increased to get a usage factor of 1? ( increasing 1) only x,, 2) only y, 3) increasing both)d) Check the UF for the stiffened panel. What does the factor P0 represent and how important is it in the present case? Why is tension field action not taken into account? What is the effective plate width? Why is the characteristic material strength different for the plate and stiffener side of the stiffened panel?

What kind of failure do the critical point(s) for the plate_stiffener represent?

e) What does the factor z* represent? Reduce the axial stress by 90% and check the UF. Comment the result. Is the change in usage factor as expected? If not, try to explain why it does not change much.