API RP 2A-LRFD Connections (1^st, 1993)

API RP 2A-LRFD checks the strength of tubular connections according to Section E of the standard.

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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.

Options

Yield Stress Resistance Factor, Phi_q - used in the calculation of the chord stress ratio A (Chapter E.3.1.1);

AISC Resistance Factor for Weld depends on the strength of welding. See Table J2.5 of AISC LRFD Specification for Structural Steel Buildings (December 27, 1999). This characteristic is used to calculate the nominal shear strength of the wel;

Is Load Transfer defines the braces for which chapter E.3.4 (joints in which load is transferred across the chord) is applied. When set to Yes and the chord contains a can, the joint axial capacity is calculated accounting for the chord can length and nominal chord properties.

Calculations

Geometric parameters that are used in calculations are obtained by the following equations:

The effective strength is defined as the buckling load for members loaded in either tension or compression, and as the yield load for members loaded primarily in tension:

where

F_y  = the yield strength of the cord member at the joint (or 2/3 of the tensile strength if less), in stress units

F_yb = the yield strength of the brace member in stress units

Note: When a chord is formed by different properties parameters for such connections are updated.

Strength check. Joint capacity shall satisfy the following:

P_D < φP_uj........(E.3-2)

M_D < φM_uj........(E.3-3)

where

P_D   = the factored axial load in the brace member, in force units

P_uj  = the ultimate joint axial capacity, in force units

M_D   = the factored bending moment capacity, in moment units

M_uj  = the ultimate joint bending moment capacity, in moment units

Φ_j   = resistance factor tubular joints taken from the table below

For braces which carry part of their load as K-Joints and part as T & Y or Cross joints, interpolate Φ_j is based on the portion of e ach in total:

Φ_j Total = (K percentage)* Φ_j + (T&Y percentage)* Φ_j + (Cross persentage)+ Φ_j

For combined axial loads and bending moments in the brace, Equation E.3.2 should be satisfied along with the following interaction equation:

where

Ipb - in-plane bending

Opb - out-of-plane bending

The ultimate capacities are defined as follows:

Calculations of A parameter are the following:

Axial and bending stresses.

Extreme Fiber Stresses.

Extreme Fiber stress is a difference between axial and bending stresses:

Elastic modulus.

Q_f is calculated for axial, in plane bending and out-of-plane bending parameters separately:

Q_uis the ultimate strength factor which varies with the joint and load type:

Note: In no case Q_g should be taken less than 1.

For braces which carry a part of their load as K-Joints and part as T&Y or Cross joints, interpolate Q_u is based on the portion of each in total:

Q_u total = (K percentage) * Q_u + (T&Y percentage) * Q_u + (Cross percentage) * Q_u

Load Transfer

Puj = P(1) + (L / 2.5D) * (P(2)-P(1)),	for L < 2.5D (E.3.4-1a)
Puj = P(2),	for L > 2.5D (E.3.4-1b)

where:

P(1) = Puj from equation E.3.5 using nominal element geometric parameters (diameter, thickness, area, Fy);

P(2) = P_uj from equation E.3.5 using can element geometric parameters (diameter, thickness, area, Fy);

Note: Load transfer calculations are applied when:

- Chord has increased thickness Tc;

- Effective length L matches the conditions like shown on the picture below;

- Brace chord diameters ratio (d/D) is less than 0.9, where D - diameter of a can element;

Note: Compression members are required to be checked on the load transfer, however it is possible to set the load transfer manually;

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.

Tc ≥ T nominal;

L1, L2 ≤ 1.25D. If L₁ and L₂ exceed 1.25D 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.

Overlapping joints

The factored axial Force component perpendicular to the chord P_D⊥ should satisfy the following equation:

where

v_w   = Φ_shF_y

Φ_sh  = the AISC resistance factor for the weld

t_w  = the lesser of the weld throat thickness or the thickness, t, of the thinner brace

l₁    = circumference for that portion of the brace which contacts the chord (actual length)

l   = circumference of the brace contact with the chord neglecting the presence of overlap

l₂   = the projected chord length (one side) of the overlapping weld, measured perpendicular to the cord

Note: Brace contacts chord under the angle creating elliptical intersection. SDC Verifier treats that kind of intersection as circular intersection so that l and l1 parameters are measured as circular circumferences:

d=2*r;

l=π*d;

q'=q*sin(θ₂);

∠AOB - angle in radians;

θ₁ - inclination of brace 1 to the chord;

θ₂ - inclination of brace 2 to the chord;

Resistance coefficient φ_sh depends on the strength of welding and is used in calculations of overlapping (Section E.3.2 API 2A RP LRFD). A table is taken from Load and resistance factor design specification for structural steel buildings December, 27 1999. The default value in SDC is set to 0.9.

The design strength of welds shall be the lower value of (a)φF_BMA_BM and (b)φF_wA_w, when applicable. The values of φ,F_BM, and F_w and limitations thereon are given in Table J2.5,

where

FBM	- nominal strength of the base material, ksi (MPa)
Fw	- nominal strength of the weld electrode, ksi (MPa)
ABM	- cross-sectional area of the base material, in.2(mm2)
Aw	- effective cross-sectional area of the weld, in.2 (mm2)
φ	- resistance factor

[a]	For definition of the effective areas, see Section J2.
[b]	For matching filler metal, see Table 3.1, AWS D1.1.
[c]	Filler metal is one strength level stronger than matching filler metal is permitted
[d]	For T and corner joints with the backing bar left in place during service, filler metal with a classification requiring a minimum Charpy V-notch (CVN) toughness of 20 ft-lbs. (27 J) @ +40° shall be used. If filler metal without the required toughness is used and the backing bar is left in place, the joint shall be sized using the resistance factor and nominal strength for a partial-joint-penetration weld.
[e]	Fillet welds and partial-joint-penetration groove welds joining component elements of built-up members, such as flange-to-web connections, are not required to be designed with regard to the tensile or compressive stress in these elements parallel to the axis of the welds.
[f]	The design of connected material is governed by Sections J4 and J5.
[g]	For alternative design strength, see Appendix J2.4