ISO 19902 Connections (1^st 2007)

ISO 19902 Connections (1^st, 2007) checks the strength of tubular joints (connections) according to chapter 14 of the standard.

To add the standard execute Standards - Main - ISO - ISO 19902 Connections (1^st 2007) 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.

By default, all supported Connections are included in the selection but it can be changed by pressing . If connections were not recognized press to run Connection Finder tool.

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

Constants are set to Standard default values. It is not necessary to change them.

Options

Extra Partial Resistance Factor is used to ensure that members fail before the joint yields (chapter 14.2.3). Default value is 1.17, giving a total resistance factor of 1.23. The value can be relaxed to a value within the range 1.00 to 1.17 only if justified by the designer;

Brace Utilization - the utilization of the brace at the end adjoining the joint. It is used in the interaction check Equation (14.3-13) to ensure joint strength exceeds brace member strength;

Is Critical Brace - According to chapter 14.2.3, all joints, except those identified as being non-critical, shall additionally be checked to ensure that joint strength exceeds the brace member strength, using Equation (14.2-2). Non-critical joints are joints that do not influence the reserve strength or response of a structure and do not cause significant safety or environmental consequences if they fail. Set value to Yes for critical joints (default) and No for non-critical joints. For non-critical joints, the interaction check Equation (14.3-13) is not applied;

Is Load Transfer defines the braces for which chapter 14.3.5 (Y- and X-joints with chord cans) is applied. When set to Yes and the chord contains a can, the joint representative axial strength is calculated accounting for the chord can length;

Brace Type Method - use brace type of selected method that are calculated by Brace Classification Tool.

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°

τ ≤ 1.0

f_y ≤ 500N/mm²

gT > -1.2γ

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. 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 following equations:

where

P_d - is the design value of the joint axial strength, in force units;

M_d - is the design value of the joint bending moment strength, in moment units;

Υ_Rj - is the partial resistance factor for tubular joints, Upsilon;_Rj = 1,05 ;

Strengths for simple tubular joints are calculated by following formulas:

where

P_uj - representative joint axial strength, in force units;

M_uj - representative joint bending model strength, in moment units;

f_y - representative yield strength of the chord member at the joint (SMYS or 0,8 of the tensile strength, if less), in stress units;

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

d - brace outside diameter;

θ - included angle between brace and chord;

Q_u - strength factor;

Q_f - chord force factor;

Strength factor Qu

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

where

f_y,b - representative yield strength of the brace at the intersection of the chord, in stress units;

t - brace wall thickness at the intersection of the chord;

For -2.0 < ^g/_T < 2.0, gap factor Q_g is calculated as linear interpolation between formulas 14.3-7 and 14.3-8:

Note: g - 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

where

λ = 0,03 for brace axial stress

  = 0,045 for brace in-plane bending stress

  = 0,021 for brace out-of-plane bending stress

q_A parameter is calculated by the following formula:

where

P_c - axial force in the chord member from factored actions;

M_c - bending moment in the chord member from factored actions;

P_y - representative axial strength due to yielding of the chord member not taking account of buckling, in force units:

P_y = A*f_y

f_y - representative yield strength of the chord member, in stress units;

A - cross-sectional area of the chord or chord can at the brace intersection;

M_p - representative plastic moment strength of the chord member;

M_p = W_e* f_y,

- plastic modulus;

D - chord member diameter;

T - chord member thickness;

ϒ_Rq - partial resistance factor for yield strength, ϒ_Rq = 1,05;

ipb - in-plane bending;

pb - out-of-plane bending;

C₁ and C₂ coefficients are taken from the table:

q_A parameter is calculated for each chord member from the left and right side of intersection of a respective brace. Furthermore, axial forces are calculated for each brace type separately:

Maximum of left and right side chord members are taken into account:

Q_faxial = Q_faxial(K joint)* brace percentage(K joint) + Q_faxial(Y joint)* brace percentage (Y joint) + Q_faxial(Cross joint)* brace percentage (Cross joint)

Q_fipb = 1- 0.045 * q²_A(bending)

Q_fopb = 1- 0.021 * q²_A(bending)

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

where

P_uj- joint axial strength, in force units;

P_uj,c - is the value P_uj,c from Equation (14.3-1), based on the chord geometrical and material properties, including Q_f calculated from chord can properties and dimensions;

Note: r cannot be taken greater than 1;

L_c - effective total length;

Y_n - the lesser chord member thickness on either side of the joint;

T_c - chord can thickness;

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 - can diameter;

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

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

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

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

Strength check

Each brace in a joint that is subjected to an axial force or a bending moment alone, or to an axial force combined with bending moments, shall be designed to satisfy the following conditions:

for all joints except those identified as non-critical

where

U_j - joint utilization;

P_B - axial force in the brace member from factored actions;

M_B - bending moment in the brace member from factored actions;

P_D - design value of the joint axial strength (see 14.3.2);

M_D - design value of the joint bending moment strength (see 14.3.2);

ipb - in-plane bending;

opb - out-of-plane bending;

U_b - brace utilization. Can be set manually to critical joints. Default value is

Υ_zj - extra partial resistance factor. Can be set manually to critical joints. Default value is 1.17;

Overlapping joints

The strength of 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.

b) Section 14.3.5 (can calculations) does not apply to overlapping joints.

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

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

Area₁ = 2 * p₁* t₁ - area of the through brace; Area₂ = 2*(p₂-q) * t₂ - area of the overlapping brace;

where

t₁ - thickness of the through brace;

t₂ - thickness of the overlapping brace;

p₁ = d₁/sin(θ₁);

p₂ = d₂/sin(θ₂);

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

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

q - overlapping distance (negative gap);

Applied shear force is taken as 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

c) If axial forces in the overlapping and through braces have the same sign (both in compression or both in tension), the check of the intersection strength of the through brace on the chord shall use the combined axial force representing the force in the through brace plus the portion of the overlapping brace force(s). The portion of the overlapping brace force may be calculated from the ratio of the cross-sectional area of the brace that bears onto the through brace to the full area of the overlapping brace.

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 / P_uj;

P_uj - joint axial capacity from formula (14.3-1);

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 intersection strength of the through brace on the chord. This combined moment shall account for the sign of the moments.

M_d1, M_d2 - respective in-plane and out-of-plane bending moments of the through and overlapping brace;

Modified moment UC= (Modified ipb moment / M_uj(ipb))²+Modified opb moment / M_uj (opb)

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

e) The overlap onto the through brace shall be checked by using the through brace as the chord in the equations in 14.3. The through brace strength shall also be checked for combined axial force and bending moment in the overlapping brace in accordance with 14.3.6 using the value of Qf calculated for the through brace.

Note:

• Through brace is taken as a chord and overlapping brace is calculated once again with TY=100% classification to obtain axial, bending and combined UFs;
• Through brace is recalculated once again using the overlapping brace element;
• If a brace is overlapping/through at the same time for few braces – absolute maximum value is taken into account;

f) Where nominal thicknesses of the overlapping and through braces differ by more than 10 %, the thicker brace shall be the through brace

Note: through brace is a brace with a maximum diameter, or maximum thickness if equal or minimum angle if equal.