CHAPTER 3 STRUCTURES

101. General

1. The structures of WIG ships are to be satisfied with the operating requirements in either the water surface and the air.

2. The scantling of each structural members are to be determined by direct strength analysis, and the material and results from the calculation should be submitted to the Society. The hull, each mem- ber and primary attachment to the hull like wing to maintain the longitudinal strength, other im- portant strength and local strength may be applied to the Korean Airworthiness Standard if deemed necessary by the Society.

3. The design life of WIG ships is to be minimum 25 years.

102. Materials and Weldings

1. The requirements in Pt 2, Ch 1 of Rules for Classification of Steel Ships are to be applied to steels, aluminium alloys or composite materials intended to be used for hull construction of a WIG ship.

2. The welding, rivet connection and FRP bonding are to be carried out in accordance with the proce- dures for welding, rivet connection and FRP bonding previously approved, with the materials quali- fied by the Society. Welding is to be carried out by the welders qualified by the Society and rivet connection and FRP bonding are carried out by competent personnel on methods.

103. Structures

1. General requirements of structure

(1) The factor of safety is design factor considering the possibility of very large loads and the un- certainty from materials and design. Unless otherwise provided, a factor of safety of 1.5 should be used.

(2) Limit loads are maximum loads with foreseeable operation conditions and ultimate loads are ob- tained from limit loads multiplied by the factor of safety.

(3) The air and water loads should be placed in equilibrium with inertia forces, considering each

item of mass in the WIG ships. These loads should be distributed to conservatively approximate or closely represent actual conditions. If the deformation due to the loads change the distribution of external or internal load considerably, this change should be considered and acceleration and loads based on full scale measurements may be considered to apply the actual loads.

(4) The structure should be able to support limit loads without permanent deformation. At any load

up to limit loads, the deformation may not interfere with safe operation. And the structure should be able to support ultimate loads without failure for at least three seconds, except local failures or structural instabilities between limit and ultimate load are acceptable only if the structure can sustain the required ultimate load for at least three seconds. However, when proof of structural strength is shown by dynamic tests simulating actual load conditions, the three sec- ond limit does not apply.

(5) If structural safety is not confirmed by structural analysis, substantiating load tests should be carried out. Dynamic tests, including structural flight tests, are acceptable if the design load con- ditions have been simulated.

2. Emergency landing conditions

The structure should be designed to protect the passenger, although it may be damaged in emer- gency landing condition. Proper use is made of safety belts and shoulder harnesses provided for in the design. All objects in structure are fixed to prevent the damage of passenger.

3. Fatigue evaluation

(1) Damage tolerance criteria for fatigue evaluation should be approved through the test for material and use of structural member of WIG ships. Particularly in case of composite materials, diver- sity and environmental effects of damage tolerance criteria should be considered. Unless fatigue

Guidance for WIG ships(Wing-In-Ground Effect Ships) 2012 5

Ch 3 Structures Ch 3

strength for hull structures and other structures are verified according to damage tolerance cri- teria, evaluations in detail design and construction are to be in accordance with followings:

(A) A fatigue strength investigation in which the structure is shown by tests, or by analysis sup-

ported by test evidence, to be able to withstand the repeated loads of variable magnitude expected in service.

(B) A fail safe strength investigation, in which it is shown by analysis, tests, or both that cata-

strophic failure of the structure is not probable after fatigue failure, or obvious partial fail- ure, of a principal structural element.

(C) The member subjected to fatigue strength evaluation is to be determined by test and operat-

ing experience, and evaluation should be performed according to damage tolerance criteria considering the simultaneous damage. The residual strength evaluation should show that the remaining structure is able to withstand critical limit loads, even though the structures are damaged partially according to damage tolerance evaluations.

(D) Each evaluation required should be;

(a) typical loading spectra (e.g., taxi, ground-airground cycles, maneuver, gust)

(b) any significant effects due to the mutual influence of aerodynamic surfaces

(c) any significant effects from propeller slipstream loading, and buffet from vortex impinge- ments

(2) Where bonded joints are used in each wing(including canards, tandem wings, and winglets), em- pennage and relating structures, moveable control surfaces and their attaching structure, made by

composite materials, composite structure should be evaluated as following:

(A) The maximum disbonds of each bonded joint consistent with the capability to withstand the loads should be determined by analysis, tests, or both. Disbonds of each bonded joint great- er than this should be prevented by design features.

(B) Proof testing should be conducted on each production article that will apply the critical limit design load to each critical bonded joint.

(C) Repeatable and reliable non-destructive inspection techniques should be established that en-

sure the strength of each joint.

(3) Structural components for which the damage tolerance limit is shown to be impractical should be shown by component fatigue tests, or analysis supported by tests, to be able to withstand the

repeated loads of variable magnitude expected in service.

104. Hull Openings and Tightness test

1. Hull tightness and opening

(1) The hull structure below flooding point in intact stability calculation is to be kept watertight, except where the structure is composited by independent(separate) structure and not effected to maneuvering, stability or flooding of hull, like as main wing, tail or etc.

(2) The hull structure above flooding point (including main wing and tail) are to be kept weathertight. Each weather opening on hull and wing, including external doors, windows and hole covers, is to be kept weathertight, except where the structure is composited by in- dependent(separate) structure and not effected to maneuvering, stability or flooding of hull, like as main wing, tail or etc.

2. Tightness test

(1) After completion of hull, hose testing is to be carried out to each exposed part of hull required to be watertight and weathertight as well as watertight transverse bulkhead to verify structural tightness. The hose test is to be carried out in accordance with Pt 3, Ch 1, Sec 2 of Rules for Classification of Steel Ships.

(2) When hose test cannot be performed without damaging possible machinery, electrical in- stallations, insulation or outfitting already installed, it may be replaced by a careful visual in-

spection of all the crossings and welded joints, where necessary, dye penetrant test or ultrasonic

leak test may be required.

6 Guidance for WIG ships(Wing-In-Ground Effect Ships) 2012

Ch 4 Equipment Ch 4