Elsevier

Thin-Walled Structures

Volume 88, March 2015, Pages 48-57
Thin-Walled Structures

Ultimate shear strength of intact and cracked stiffened panels

https://doi.org/10.1016/j.tws.2014.12.001Get rights and content

Highlights

  • Crack is considered as a parameter affecting the strength of stiffened panels and the ultimate shear strength characteristics of intact and cracked stiffened panels are investigated based on parametric analysis.

  • Three types of cracks are considered, namely vertical crack, horizontal crack and angular crack.

  • The formula for the ultimate shear strength of cracked stiffened panels is derived, which can be valuable for life assessment of aged ship structures.

Abstract

The present paper focuses on the ultimate shear strength analysis of intact and cracked stiffened panels. Several potential parameters influencing the ultimate shear strength of intact panels are discussed, including the patterns and amplitudes of initial deflection, the slenderness and aspect ratios of the plates, and the boundary conditions defined by the torsional stiffness of support members. An empirical formula for the ultimate shear strength of intact stiffened panels is proposed based on parametric nonlinear finite element analyses in ANSYS. Furthermore, the ultimate shear strength characteristics of cracked stiffened panels are investigated in LS-DYNA with the implicit method. Three types of cracks are considered, namely vertical crack, horizontal crack and angular crack. A simplified method is put forward to calculate the equivalent crack length. And the formula for the ultimate shear strength of cracked stiffened panels is derived on the basis of the formula for intact stiffened panels.

Introduction

Ship and offshore structures now tend to be designed based on the ultimate strength. Significant progress has been made on the ultimate strength characteristics of various types of structural components under typical load conditions as axial compression and edge shear [1]. Comparing to axial compression, less attention has been given to the shear loading [2], [3]. Though several empirical formulae have been developed and applied in industry, most of them are based on the elastic buckling strength of the individual plate [e.g. [1], [2]. In order to accurately assess the limit-state-based capacity of ship structures, systematic study on the ultimate shear strength of stiffened panels should be carried out further.

Moreover, failure due to shear loads will arise particularly for damaged structures [2]. Fatigue cracks are among the most typical damage or defect forms, which would be initiated in the concentration area of the structure. The importance on assessing residual ultimate strength of cracked ship structures under monotonically increasing extreme load has been highlighted [4], [5]. Some studies have been paid on buckling characteristics of the cracked plates under shear [6], while the study on post-buckling or large-deflection regime is still not enough.

The aim of this paper is therefore to investigate the ultimate shear strength of intact and cracked stiffened panels. Since the deflection pattern of the plates under edge shear in the post-buckling or large deflection regime is quite complex, the analytical approach may not be straightforward to use [1]. In this case, nonlinear FEA softwares, ANSYS [7] and LS-DYNA-implicit [8] will be used for carrying out analyses on intact and cracked stiffened panels respectively, while cracked panel models used in LS-DYNA with initial deflection are preprocessed by ANSYS. Based on the computed FEA results, an empirical formula for estimating the ultimate shear strength of stiffened panels will be derived. And it will provide the basis for the residual shear strength assessment of cracked panels. Factors for shear strength reduction due to typical cracks will be put forward at the same time.

Section snippets

Ultimate shear strength of intact stiffened panels

The one-bay SPM (stiffened panels model) shown in Fig. 1 will be adopted for calculation in the present study. The plate dimension is a×b×tp; the stiffener web dimension is hw×tw; and the stiffer flange dimension is bf×tf. The Young׳s modulus is E; the material yield stress is σY; and the Poisson ratio is ν. The shear modulus can be expressed by G=E/2(1+ν); and the shear yield stress can be expressed by τY=σY/3. The plate slenderness ratio representing the degree of plate thickness is defined

Ultimate shear strength of cracked stiffened panels

Defects of cracks are inherent in structural components; they are either present during production or developed under service load [10]. Ultimate strength can be weakened by the cracking defects significantly. The ductile cracks with large-scale yielding zone are usually regarded as new free surface for residual strength assessment under monotonic extreme loading. However, cracks may also grow under some cases of monotonically increasing extreme loads, which will further decrease the strength

Concluding remarks

The aim of the present paper is to investigate the ultimate shear strength of the intact and cracks stiffened panels. Nonlinear finite element analyses in ANSYS and LS-DYNA-implicit are carried out for this purpose. Several potential parameters influencing the ultimate shear strength of intact panels are discussed. Three types of cracks are considered, namely vertical crack, horizontal crack and angular crack. And the possibility of crack propagation is checked with shear load increasing. Based

Acknowledgments

The present paper was undertaken at the Ship and Offshore Structural Mechanics Laboratory, Pusan National University, that is a National Research Laboratory funded by the Korea Science and Engineering Foundation (Grant no. ROA-2006-000-10239-0). Part of the study was also supported by the Lloyd׳s Register Education Trust (LRET) through the LRET Research Centre of Excellence at Pusan National University.

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