Section 3 Longitudinal Strength

301. Longitudinal hull girder strength

Longitudinal strength is to be based on Pt 3 and Pt 12 of Rules for the Classification of Steel Ships. The total hull girder bending moment, ÀŹ is the sum of the maximum still water bending

moment for operation on site or in transit combined with the corresponding wave-induced bending

moment (Mw) expected on-site and during transit to the installation site. In lieu of directly calcu- lated wave-induced hull girder vertical bending moments and shear forces, recourse can be made to the use of the Environmental Severity Factor (ESF) approach described of this guide. The ESF ap-

proach can be applied to modify the Steel Vessel Rules wave-induced hull girder bending moment and shear force formulas. Depending on the value of the Environmental Severity Factor, ØŽẄŶ , for vertical wave-induced hull girder bending moment (see this Guide), the minimum hull girder section modulus, Cmin , of unit may vary in accordance with the following:

Table 5.1 Minimum hull girder section modulus

* Environmental Severity Factor

Environmental Severity Factors are adjustment factors for the dynamic components of loads and the expected fatigue damage that account for site-specific conditions as compared to North Atlantic unre- stricted service conditions.

(1) ESFs of the Beta (Ø) Type

This type of ESF is used to introduce a comparison of the severity between the intended envi-

ronment and a base environment, which is the North Atlantic unrestricted service environment.

In the modified formulations, the Ø factors apply only to the dynamic portions of the load com-

ponents, and the load components that are considered “static” are not affected by the in- troduction of the Ø factors.

Ø G ÁZ

JÁŹ

where

ÁZ : most probable extreme value based on the intended site (100 years return period), transit (10 years return period), and repair/inspection (1 year return period)

environments for the dynamic load parameters specified in Table 5.2.

ÁŹ : most probable extreme value base on the North Atlantic environment for the dynamic load parameters specified in Table 5.2.

A Ø of 1.0 corresponds to the unrestricted service condition of a seagoing vessel. A value of Ø

less than 1.0 indicates a less severe environment than the unrestricted case.

(2) ESFs of the Alpha (Ø ) Type

This type of ESF compares the fatigue damage between the specified environment and a base

environment, which is the North Atlantic environment. This type of ESF is used to adjust the

expected fatigue damage induced from the dynamic components due to environmental loadings at the installation’s site. It can be used to assess the fatigue damage accumulated during the histor- ical service either as a trading vessel or as a unit, including both the historical site(s) and his- torical transit routes.

ǼŹZ

ŊĦ ÈÈ

where

ǼŹ : annual fatigue damage based on the North Atlantic environment (unrestricted service) at the details of the hull structure

ǼZ : annual fatigue damage based on a specified environment, for historical routes, ical sites, transit and intended site, at the details of the hull structure

histor

Table 5.2 Dynamic Load Parameters

302. Hull girder ultimate strength

1. The hull girder ultimate longitudinal bending capacities are to be evaluated in accordance

12 of Rules for the Classification of Steel Ships.

with Pt

2. The vertical hull girder ultimate strength for the unit design environmental condition (DEC) is to satisfy the limit state as specified below. It need only be applied within the 0.4L amidship region.

ÀÃ

ǾÅÀZŽ ĞǾBØÃAÀÀŽŽ GZŴX ≤ JǾ Ą

ÀZŽ

: permissible still-water bending moment, in kNm

ÀŽŽGZŴX

: sagging vertical wave bending moment, in kNm, to be taken as the midship sag-

ging value defined in Pt 12, Sec 7/3.4.1.1 of Rules for the Classification of Steel Ships.

ÀÃ : sagging vertical hull girder ultimate bending capacity, in kNm, as defined in Pt 12, Appendix A/1.1.1 of Rules for the Classification of Steel Ships.

ØÃAÀ : ESF for vertical wave-induced bending moment for DEC

ǾÅ : load factor for the maximum permissible still-water bending moment, but not to be taken as less than 1.0

ǾB : load factor for the wave-induced bending moment, but not to be taken as less than below for the given limits

= 1.3

= 1.2

(ÀZŽ Ĥ ŊĦËÀŹ 또는 ÀZŽ I ŊĦÈÀŹ ) (ŊĦËÀŹ ≤ÀZŽ ≤ŊĦÈÀŹ )

ÀŹ : total bending moment, in kNm

= ÀZŽ ĞØÃAÀÀŽŽ GZŴX

ǾĄ : safety factor for the vertical hull girder bending capacity, but not to be taken as less than 1.15