Elsevier

Marine Structures

Volume 74, November 2020, 102789
Marine Structures

Strength evaluation of intersection between stiffeners and primary supporting members in double hull structure

https://doi.org/10.1016/j.marstruc.2020.102789Get rights and content

Highlights

  • The effect of the shear force is clarified, and the difference between double hull and single hull structures are clarified.

Abstract

In this previous study, a consistent theoretical formula was established in single hull structure, taking account of all the structural components affecting the load share of each member, in combination with the combined load effect of direct force from the longitudinal stiffener and shear force on the primary supporting member. What's more, it has been known qualitatively that the bending moment at the root of the web stiffener in double hull structure is less than that in single hull structure. However, the difference between double hull and single hull structures has not been achieved. In this study, the authors develop a theoretical formulation to represent the stresses at the root of the web stiffener due to the load from both the longitudinal stiffener and the shear force on the primary supporting member in the double hull structure. Then, the results calculated by the derived formulae are compared with the results obtained by finite element analysis, and good accuracy of the proposed formula was verified. Finally, the calculated stresses were compared between double hull and single hull structures. On one hand, the share of loading born by the web stiffener is almost comparable between the double hull and single hull structures. On the other hand, the bending moment at the root of the web stiffener is smaller in the double hull structure than in single hull structure, and therefore, the maximum stress is smaller.

Introduction

Fatigue damages have great influence on the life and property safety. The first massive appearance of fatigue damages that the maritime industries experienced was coincident with rapid increase in the size of crude oil tankers during 1960's. According to Okumoto et al. [1], most commonly observed cracks initiated at the round weld toe in way of the attachment of the web stiffener to the face plate of the longitudinal stiffener, as shown as CRACK-A and CRACK-B in Fig. 1. Therefore, to prevent this kind of damages, it is important to conduct theoretical calculations of the stress distribution in the intersections between the web stiffener and the face plate of the longitudinal stiffener.

Since then, a lot of research works have been conducted [[2], [3], [4], [5], [6], [7]], and in the authors’ previous paper [8], a consistent theoretical formula was established, taking account of all the structural components affecting the load share of each member, in combination with the combined load effect of direct force from the longitudinal stiffener and shear force on the primary supporting member. In this previous study, the formula was derived assuming the single hull structural configuration. On the other hand, it has been known qualitatively that the bending moment at the root of the web stiffener in double hull structure is less than that in single hull structure. Therefore, the maximum stress at the root of the web stiffener tends to be smaller in the double hull structure, and slot cut-out structures in double hull is less vulnerable to fatigue damages. The purpose of this study is to establish a theoretical formula for double hull structures and to confirm the difference between double hull and single hull structures quantitatively through theoretical analysis and to verify it through FE analysis.

In this paper, the authors firstly establish the theoretical formulation to represent the stresses at the root of the web stiffener due to the load from both the longitudinal stiffener and the shear force on the primary supporting member in the double hull structure. Then, the results calculated by the derived formulae are compared with the results obtained by finite element analysis. Using the derived theoretical formula, stresses at the root of the web stiffener are calculated, and the comparison are made between the results of double hull and single hull structures.

Section snippets

Derivation of share of loads among web stiffener, primary member web and collar plate

In this section, we derive the formula to calculate share of loads among web stiffener, primary member web and collar plate in the similar way as Ref. [8], assuming a structural configuration of the intersection of longitudinal stiffener and primary supporting member as shown in Fig. 2.

To simplify the derivation of theoretical formulas, the load from the longitudinal stiffeners is decomposed into the symmetrical load and anti-symmetrical load as shown in Fig. 3.

Finite element analysis

Finite element analysis is now conducted for the structures and loading as shown in Fig. 13, where the 3-dimensional finite element model, loading and boundary conditions are shown. Fig. 13 (1) shows the structural arrangement, boundary conditions and loading to be modeled in the finite element analysis. Five longitudinal stiffeners are arranged on both the upper shell plate and the lower shell plate. Fig. 13 (2) shows the details around the slot cut-out. Loading case 1 corresponds to

Comparison of stress magnification due to web stiffener bending

In this chapter, the authors deal with a typical double hull structure with parameters as shown in Table 3.

To obtain the main differences and similarities between single hull structure and double hull structure, four typical cases are chosen to make comparisons as shown in Table 4. The force PB is working at the connections between the longitudinal stiffener and the web stiffener, which is obtained by a linear combination of the anti-symmetric component, PM, and the symmetric component, P0.

In

Conclusions

In this paper, the authors established a theoretical formula to represent the stresses at the root of the web stiffener due to the load from both the longitudinal stiffener and the shear force on the primary supporting member in the double hull structure. The derived formulas were validated through comparison of the calculated results with those applying the finite element method. Then, the calculated stresses were compared between double hull and single hull structures. As a result, the

Declaration of competing interest

The authors declared that they have no conflicts of interest to this work.

We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.

Acknowledgement

The authors would like to thank Mr. Masahiro Fujiwara for his valuable advice with regard to the derivation of theoretical formulae on slot cut-out structures.

References (9)

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