DESIGN EQUATIONS FOR TRIPPING OF STIFFENERS UNDER INPLANE AND LATERAL LOADS
A series of design oriented equations to predict the tripping (lateral-torsional instability) of stiffeners under inplane and lateral loads has been developed which will allow this mode of failure to be more comprehensively addressed in the early stages of structural design. This type of failure is characterized by a twisting of the stiffener about its line of attachment to the plating and has been demonstrated by some recent British grillage tests to have serious potential as a primary mode of failure. The solutions developed take into account the effects of (1) the rotational resistance provided by the plating to which the stiffener is attached, (2) nonlinear material and structural behavior by means of a tangent modulus type approach, and (3) stiffener web deformations (for inplane loading). The equations are suitable for manual calculations but particularly powerful applications are possible when they are teamed up with a desk-top type mini-computer. A number of comparisons between tripping predictions made using these equations and numerical finite element results in general show very good agreement. For the case of lateral loading the agreement is less consistently acceptable, primarily because of the more complicated nature of the tripping mode shapes and the inability at present to include the effects of web deformations for this loading. Comparisons are also made with experimental collapse data from two of the British grillages which failed by tripping and the agreement is quite good. Unfortunately, the mean tripping failure stresses (the basis of these comparisons) are quite sensitive to the estimates of plating effectiveness and thus wide variations in predicted mean stresses are possible. Thus, this limited experimental validation is not as conclusive as might be hoped for. The development of these design equations is quite timely in view of the current interest being shown in the use of bulbs and flat bars as stiffening members (for reasons of economy). Such members are inherently weak with respect to tripping and their application would require that careful attention be given to tripping behavior.
David Taylor Naval Ship R&D CenterDevelopment Center
Bethesda, MD United States 20084
- Adamchak, J C
- Publication Date: 1979-10
- Features: Figures; References; Tables;
- Pagination: 99 p.
- TRT Terms: Axial loads; Buckling; Failure; Plate bearing test; Stiffened plates; Structural analysis; Structural design; Structural mechanics; Torsion; Web stiffened structures
- Uncontrolled Terms: Axial loading; Structural failures
- Old TRIS Terms: Failure mode
- Subject Areas: Marine Transportation; Materials;
- Accession Number: 00301879
- Record Type: Publication
- Report/Paper Numbers: DTNSRDC-79/064 Final Rpt.
- Files: TRIS
- Created Date: Nov 7 1979 12:00AM