Norsok N004 Connections (Rev. 3, 2013)

Norsok N004 Connections (Rev. 3, February 2013) Standard - checks the strength of tubular joints (connections) according to chapter 6.4 of the standard.

This standard is applied to simple circular tubular joints with the following validity ranges: 0,2 ≤ β ≤ 1,0; 10 ≤ γ ≤ 50 and 30° ≤ θ ≤ 90°.

To add the standard execute Standards - Main - Other - Norsok N004 Members (Rev. 3, 2013) from the ribbon:

Press to Set Standard Custom Settings

Connection Checks are calculated on Connections. With the help of Connection Finder tool, it is possible to automatically recognize Chords and Braces with their dimensions.

Standard uses material data (Yield/Tensile) in calculations. Wizard checks if the values are defined for all materials.

Options

Material Factor, Gamma_M is used as a divisor in the joint design axial resistance (Formula 6.52) and bending resistance (Formula 6.53) calculations to account for material uncertainties;

Is Load Transfer defines the braces for which chapter 6.4.3.5 (Y- and X-joints with chord cans) is applied. When set to Yes and the chord contains a can, the joint design axial resistance is calculated accounting for the chord can length;

Brace Type Method - use brace type of selected method that are calculated by Brace Classification Tool. The Brace Type Method determines the method for classifying braces:

• Left-to-Right - classification is performed from the left brace to the right brace;
• Total Force - classification is based on the total force in the brace.

Calculations

Nomenclature and geometric parameters that are used in results:

The validity ranges of connection parameters:

0.2 ≤ β ≤ 1.0

10 ≤ γ ≤ 50

30° ≤ θ ≤ 90°

g/D ≥ -0.6 (for K joints)

f_y ≤ 500N/mm²

f_y - chord allowable static stress = Min(yield stress, tensile strength * 0.8).

For each brace connected to the chord, connection elements of the chord are taken into account. The minimum allowable stress is taken if elements are of different materials.

Note: If material yield stress > 500 Mpa - allowable static stress is taken equal to material yield stress.

Basic Joint Strength.

Joint axial and bending capacities shall satisfy the following equations:

where

N_Rd - the joint design axial resistance;

M_Rd - the joint design bending moment resistance;

f_y - the yield strength of the chord member at the joint;

ϒ_M = 1.15;

T - the chord wall thickness at the intersection with the brace;

d - the brace outside diameter;

θ - included angle between the brace and the chord;

Q_u - the strength factor;

Q_f - the chord force factor;

Strength factor Qu

Q_u is the strength factor which varies with the joint and the action type:

where

f_y,b - the yield strength of brace;

f_y,c - the yield strength of chord;

t - the brace wall thickness;

For -0.05 ≤ ^g/_D < 0.05, the gap factor Q_g is calculated as linear interpolation between the limiting values of the above expressions:

Note: g - the total gap of the brace. From the following picture g = 0.023076 * 0.1362 + 0.196152 * 0.8638 = 0.172579;

Chord force factor Q_f

σ_a,Sd - the design axial stress in chord, positive in tension;

σ_my,Sd - the design in-plane bending stress in chord, positive for compression;

f_y - the - yield strength;

C₁,C₂,C₃ - the coefficients depending on the joint and the load type:

The average of the chord loads and bending moments on either side of the brace intersection should be used in the formulas (6.54), (6.55). The chord thickness at the joint should be used in the above calculations.

Q_{f total} = Q_fK * brace percentage K + Q_fTY + brace percentage TY + Q_fX * brace percentage X -for the axial loading;

Extra joint axial capacity calculations are performed to the connections that contain increased thickness of the chord. The axial strength is calculated by following formula:

where

N_can,RD - N_RD from the equation (6.52) based on the chord can geometric and material properties including Q_f calculated with respect to the chord can;

T_n - the nominal chord member thickness;

T_c - the chord can thickness;

Note: r cannot be taken greater than 1;

Effective length L is calculated for each brace separately. It is a minimum distance from the end of can till the point of intersection of chord and brace multiplied on 2.

T_c ≥ T nominal;

L₁,L₂ ≤ 1.25 * D. If L₁ and L₂ and L₂ exceed 1.25 * D distance, can will not be recognized;

D - the can diameter;

L = 2 * L₁ - the effective length for the left brace;

L = 2 * L₃ = 2 * L₄ - the effective length for the middle brace;

L = 2 * L₂ - the effective length for the right brace.

Note: This section is applied to the connections with cans. If the brace L_c 0 section is not applied. If the brace is overlapping the section is not applied.

Strength check

Joint resistance shall satisfy following interaction equation for axial force and/or bending moments in the brace:

for all joints, except those, that identified as non-critical

where

N_Sd - the design axial force in the brace member;

N_Rd - the joint design axial resistance;

M_y,Sd - the - design in-plane bending moment in the brace member;

M_z,Sd - the design out-of-plane bending moment in the brace member;

M_y,Rd - the design in-plane bending resistance;

M_z,Rd - the design out-of-plane bending resistance;

Overlapping joints

The strength of the joints that have in-plane overlap involving two or more braces may be determined using the requirements for simple joints defined in 14.3, with the following exceptions and additions.

a) Shearing of the brace parallel to the chord face is a potential failure mode and shall be checked.

Shear capacity = fy * effective area /√3 - 1.05)

Effective area is the total area of two braces that overlap:

Area1 = 2 * p₁* t₁ - the area of the through brace;

Area2 = 2*(p₂-q) * t₂ - the area of the overlapping brace;

where

t₁ - the thickness of the through brace;

t₂ - the thickness of the overlapping brace;

p₁ = d₁/sin(θ₁);

p₂ = d₂/sin(θ₂);

d₁, d₁ - the original diameter of the through and overlapping braces respectively;

θ₁, θ₂ - the inclination of the through and overlapping braces respectively to the chord;

q - the overlapping distance (negative gap);

Applied shear force is taken as the summation of forces, perpendicular to the chord of the through and the overlapping braces;

Shear UC (Ultimate Capacity) is calculated as the relation of Applied shear force to shear capacity:

Shear UC = Applied shear force / Shear capacity

b) Section 6.4.3.5 (can calculations) does not apply to overlapping joints.

c) If axial forces in the overlapping and through braces have the same sign, the combined axial force representing that in the through brace plus a portion of the overlapping brace forces should be used to check the through brace intersection capacity. The portion of the overlapping brace force can be calculated as ratio of cross sectional area of the brace that bears onto the through brace to the full area.

Modified axial force= P_d1+P_d2 * ov;

where

P_d1 - the axial force of the through brace perpendicular to the chord.

P_d2 - the axial force of the overlapping brace perpendicular to the chord.

ov - overlapping percentage,

ov=q/p*100%;

Modified axial UC= Modified axial force / N_Rd;

N_Rd - the joint axial capacity from the formula (6.52);

d) For both in-plane or out-of-plane moments, the combined moments on the overlapping and through braces shall be used to check the through brace intersection capacity. This combined moment shall account for the sign of the moments.

M_y,Sd1, M_y,Sd2, M_z,Sd1, M_z,Sd2 - the respective in-plane and out-of-plane bending moments of the through and overlapping brace;

Modified moment UC= (Modified ipb moment / M_y,Rd)²+Modified opb moment / M_z,Rd

Modified axial and moment UC=Modified axial UC+Modified moment UC