4. Structure and Strength

4.1 General

The dock gate is to have adequate strength and stiffness fit for the environmental condition and operational condition of water area in service.

4.2 Overall Strength

(1) Overall Strength of the dock gate is to be assessed by direct strength calculation method in ac- cordance with the following.

(2) Analysis method

(A) The Analysis methods and programs are to be capable of taking the effects of bending de- formation, shear deformation, axial deformation, and warping deformation into account.

(B) The analysis methods and programs are to be such that the behaviors of plane or space structures can be effectively expressed and displayed under the reasonable boundary

condition.

(C) The analysis program is to have a sufficient analysis accuracy. And if deemed necessary by the Society, the Society may require the submission of the data on the details of analysis method, verification of accuracy, etc.

(D) Where direct strength calculation is performed, documents describing the conditions of calcu- lation and the data summarizing their results are to be submitted to the Society.

(3) Load

(A) The design loads for the dock gate are to be such that the most severe load conditions tak- ing into account of the environment of water area in service are considered.

(B) The design loads are to be presented by the builder and to be specified in the drawings

and documents for approval.

(C) Where vehicles pass over the dock gate, the vehicle loads are to be considered and not to be less than 17.2 kN/m2.

(4) Structural model

(A) Structural modelling for analysis is to be in accordance with Pt 3, Annex 3-2 of Guidance Relating to the Rules.

(B) However, structural modelling is to be carried out based on the net thickness

thicknesses for corrosion margin.

(5) Allowable stress

(A) When structure analysis is carried out by overall model of steel-made dock gate, stress is to be in accordance with the following:

(i) Allowable stress when plate elements are used.

excluding

allowable

2

Normal stress : ſſC Ņ ÌĨJ Õ Å (N/mm )

Shear stress : ſſi Ņ ÌLL Õ Å (N/mm2)

2

Equivalent stress : ſſᾙ Ņ ÌKJ Õ Å (N/mm )

ſſᾙ : in accordance with the following formula:

Ī 2

←

ſſᾙ Ņ Ρ̓Üſſ ← Ň ſſ ← Ǿ ſſ← Ñ ſſĪ Ñ ĮſſiĪ (N/mm )

Å : material factor of used material as follows: A, B, D and E : 1.0

AH 32, DH 32 and EH 32 : 0.78 AH 36, DH 36 and EH 36 : 0.72 AH 40, DH 40 and EH 40 : 0.68

(ii) Allowable stress when beam elements are used;

Web of beam elements :

equivalent stress ſſᾙ Ņ ÌKJ Õ Å

(N/mm2)

shear stress Flange of beam elements :

ſſi Ņ ÌLL Õ Å

(N/mm2)

2

2

longitudinal stress of dock gate ſſᾨ Ņ ÌLL Õ Å (N/mm )

transverse stress of dock gate ſſᾼ Ņ ÌĨJ Õ Å (N/mm ) Equivalent stress is to be in accordance with the following:

ᾙ

ſſ Ņ Ρ̓Üſſ Ī Ñ ĮſſiĪ (N/mm2)

ſſ : in-plane normal stress, to be in accordance with the following:

ſſ Ņ ſſᾍ Ñ ſſᾎ

ſſᾍ : axial stress

ſſᾎ : bending stress

ſſi : mean shear stress

(iii) Where deemed necessary by the Society, fine mesh analysis may be required. In this case, the allowable stress is to be deemed appropriate by the Society.

(B) Allowable stress of dock gate made of special material other than steel is to be deemed appropriate by the Society.

4.3 Local Strength

Structural members used for deep tank are to comply with the following, in addition to the require- ments of 4.2. as above.

(1) Bulkhead plate of deep tank

The thickness(t) of the bulkhead plate of deep tank is not to be less than that obtained from the following formula;

ᾼ Ņ ĮǾĴ Ċ Ρ̓Üᾜ Ñ ĪǾJ (mm)

where,

Ċ : spacing of bulkhead stiffeners (mm)

ᾜ : the greater of the following

(A) vertical distance measured from the lower edge of each bulkhead plate to the mid-point of the distance between the top of tanks and the top of overflow pipes.(m)

(B) 0.7 times the distance measured from the lower edge of each bulkhead plate to the point of 2.0 m above the top of overflow pipes(m)

(2) Bulkhead stiffeners of deep tank

The section modulus (Ě) of bulkhead stiffeners of deep tank is not to be less than that obtained from the following formula;

Ě Ņ Ǽ Ċ ᾜ ᾨĪ (cm3)

where,

Ċ : as specified in (1).

ᾨ : span of the bulkhead stiffeners in meters

ᾜ : vertical distance given below, whichever is the greater, the lower end being regarded as the midpoint of ᾨ for vertical stiffeners and as the midpoint of distance between the adjacent stiffeners for horizontal stiffeners.

(A) vertical distance measured from the lower end to the midpoint of the distance be- tween the top of tanks and the top of overflow pipes(m)

(B) 0.7 times the vertical distance measured from the lower end to the point of 2.0 m above the top of overflow pipes

Ǽ : Coefficient given in following Table, according to the type of end connections

Values of Ǽ

(3) Strengthening girder

(A) The section modulus (Ě) of the strengthening girders(hereinafter referred to as girder) porting stiffeners is not to be less than that obtained from the following formula;

Ě Ņ KǾÌĮ Ċ ᾜ ᾨĪ (cm3)

sup-

where :

Ċ : breadth of the area supported by the girders in meters

ᾜ : vertical distance measured from the mid-point of Ċ for horizontal girders, and from the midpoint of ᾨ for vertical girders, to the top of ᾜ specified in (2) in meters

ᾨ : span of the girders in meters

(B) The moment of inertia (Ā) of girders is not to be less than that obtained from the following formula. However, the dept of girders is not to be less than 2.5 times the dept of slots for stiffeners.

Ā Ņ ĮL ᾜ ᾨĨ (cm4)

where,

ᾜ and ᾨ : as specified in the preceding paragraph (A)

(C) Thickness of the girder web is not to be less than that obtained from the following three formulas, whichever is the greatest.

Ǽ Ċ ᾜ ᾨ (mm)

ᾼÌ Ņ ĨÌǾK Ü Ì

Ñ ĪǾJ

ÜǼ Ċ ᾜ ᾨ Ċ Ī

Į

ᾼĪ Ņ LǾÌKĨ Ρ̓Üᾘ Ì

Ì Ñ ĪǾJ (mm)

ᾼĮ Ņ LǾLÌ ĊÌ Ñ ĪǾJ (mm)

where,

Ċ, ᾜ and ᾨ : as specified in the preceding paragraph (A)

ĊÌ : spacing of web stiffeners or the depth of girders, whichever is the smaller (mm)

ᾘÌ : depth of the girder at the location considered, reduced by the depth of slots for stiff- eners (mm)

Ǽ : Coefficient obtained from the following three formulas. However, it is not to be less than 0.5.

←

For horizontal girders : Ǽ Ņ ÔÌ Ň ĪÜᾨ Ô

Ì Ì

Ì ← ᾨ ← Ī

For vertical girders : Ǽ Ņ Ô Ì Ñ ÜJ Ǿ Üᾜ

Ñ

Ň NĪ Ñ ÜᾜŃᾨÜ

Ü← NᾨÜŃ Ô

← : Distance measured from the end of ᾨ for horizontal girders, and from the lower end of

ᾨ for vertical girders, to the location considered (m)

(D) The actual section modulus and moment of inertia of girders are to be calculated in accord- ance with Pt 3, Ch 1, 602. of the Rules.

(4) Cross Ties

(A) Where efficient cross ties are provided across deep tanks connecting girders on each side of the tanks, the span(ᾨ ) of girders specified in (3) may be measured between the end of gird-

er and the center line of cross tie or between the centerlines of adjacent cross ties.

(B) The sectional area(A) of cross ties is not to be less than that obtained from the following formula.

2

A Ņ ÌǾĮ Ċ ᾎᾯ ᾜ (cm )

where :

Ċ and ᾜ : As specified in (3)

ᾎᾯ : Breadth of the area supported by cross ties(m)

(C) The ends of cross ties are to be bracketed to girders.

(5) Top and bottom construction

The scantlings of the members forming the top or the bottom of deep tanks are to be in ac- cordance with the requirements of 4. of this Annex, regarding the members as the members forming the deep tank bulkheads at the location. For top plating of deep tanks, the thickness of plates is to be at least 1 mm greater than that specified in (1) above.

(6) Scantlings of members not in contact with sea water

The thickness of bulkhead plates and girders which are not in contact with sea water in service conditions may be reduced from the requirements in (1), (3) and (4) by the values given below:

For the plates of which only one side is in contact with sea water ------ 0.5 mm For the plates of which neither side is in contact with sea water -------- 1.0 mm

However, bulkhead plate in way of the location such as bilge wells are to be regarded as plates in contact with sea water.

(7) All structural members are to be sufficiently considered in respect of buckling.

4.4 Consideration for Deflection and Leakage

(1) The structural scantlings of the dock gate are to be determined taking into account negative(-) deflection(in the reverse direction against that of loading) due to reaction forces at longitudinal ends of the dock gate. the calculation results of negative(-) deflection at longitudinal ends are to be submitted to the Society.

(2) Seals are to be provided along the longitudinal ends and bottom of dock gate to prevent leakage. Details for the seal structure and its material property including compressive strength are to be submitted to the Society.

(3) Pump and drainage system are to be provided in dock gate to discharge sea water leaking from the dock gate into the dock.