Strength evaluation of intersection between stiffeners and primary supporting members in double hull structure
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)
- et al.
Strength evaluation of intersection between stiffeners and primary supporting members considering the effect of shear force on the primary member web
Mar Struct
(2018) - et al.
Design of ship hull structures – a practical guide for engineers
(2009) - et al.
Strength around slot for penetration of longitudinals
IHI Eng Rev
(1971) Surveillance study for ship structural damages (2) – damages around slot structure in tanks -. Research report No.13 of the West-Japan Society of Naval Architects
(1971)
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2022, Ocean EngineeringCitation Excerpt :The collar plate is a welded plate on the transverse and longitudinal element and the purpose is to replace the material of the transverse element removed for the passage of the longitudinal element (and thereby re-establish the shear strength) and reduces the stress concentration factor. Theoretical formulations have been developed that allow the fatigue life of the structural detail to be established, Gu et al. (2020) obtained a theoretical formula (validated by the finite element method) to represent the stresses in the web frame stiffener in double hull and single hull structures. Okada and Kawamura (2018) presented a theoretical formula (validated by the finite element method) to represent the stresses in the web frame stiffener under a critical review of the International Association Classification Societies (IACS) rules.
QUASI-STATIC RESPONSE
2022, Proceedings of the 21st International Ship and Offshore Structures Congress, ISSC 2022