Clause 11.3.1.1 (NEN 6770): Class 1 and Class 2 I-section profiles

Class 1 and class 2 I section profiles must satisfy the interaction formulae given in tables 10 & 11 of NEN 6770.

Table 10 Provides interaction checks for bending about the major axis (All necessary terms and formulae are described below):

1. If V_z;s;d ≤ 0.5·V_z;pl;d and N_s;d ≤ 0.5 · a₁ · N_pl;d , check equation 11.3.1
2. If V_z;s;d ≤ 0.5·V_z;pl;d and N_s;d > 0.5 · a₁ · N_pl;d , check equation 11.3.2
3. If V_z;s;d > 0.5·V_z;pl;d and N_s;d ≤ 0.5 · a₂ · N_v;u;d , check equation 11.3-3
4. If V_z;s;d > 0.5·V_z;pl;d and N_s;d > 0.5 · a₂ · N_v;u;d , check equation 11.3-4

where

Vz;s;d	=	Actual Shear force in the section along Z- axis
Vz;pl;d	=	Shear capacity of section  along Z - axis = Aw · fy;d / √3
fy;d	=	yield stress
Aw	=	A - 2 (bf - tw - 2r) tf Definition of Aw
Ns;d	=	Axial force in the section
Npl;d	=	Axial capacity of section = A · fy;d
My;s;d	=	Bending moment about major axis
My;pl;d	=	Plastic moment capacity of section = fy;d · Wy;pl
Wy;pl	=	Plastic section modulus
a1	=	min( A-2bfx tf)/A , 0.5) - used in tables 10 & 11
a2	=	see eqn 11.3-10- used in tables 10 & 11
Mv;y;ud	=	see eqn 11.3.12
N;v;u;d	=	see eqn 11.3-13

Table 11: Provides interaction formulae for bending about the minor axis

1. If V_y;s;d ≤ 0.25 · V_y;pl;d and N_s;d ≤ 1.0 · a₁ · N_pl;d check equation 11.3-5
2. If V_y;s;d ≤ 0.25 · V_y;pl;d and N_s;d > 1.0 · a₁ · N_pl;d check equation 11.3-6
3. IfV_y;s;d > 0.25 · V_y;pl;d and N_s;d ≤ 1.0 · a₁ · N_v;u;d check equation 11.3-7
4. If V_y;s;d > 0.25 · V_y;pl;d and N_s;d > 1.0 · a₁ · N_v;u;d check equation 11.3-8

where

Vy;s;d	=	Actual Shear force in the section along Y-axis
Vy;pl;d	=	Shear capacity of section along Y-axis $2b{t}_f\frac{f_{y;d}}{\sqrt{3}}$
Mv;z;u;d	=	q · Mz;pld =  q · fy;d · Wpl;z;d
Wpl;z;d	=	plastic section modulus about minor axis) & q as per eqn 11.3-14
Nv;u;d	=	Npl;d – 2·(1 - q)·bf · tf · fy;d

Clause 11.3.1.3 ( NEN 6770) : Class 1 and Class 2 Square and rectangular hollow sections

This clause requires class 1 and class 2 square and rectangular tube profiles to satisfy the interaction equations in Table 13.

1. If V_z;s;d ≤ 0.25 · V_z;pl;d and N_s;d ≤ 0.5 · a₃ · N_pl;d check equation 11.3.22
2. If V_z;s;d ≤ 0.25 · V_z;pl;d and N_s;d > 0.5 · a₃ · N_pl;d check equation 11.3.23
3. If V_z;s;d > 0.25 · V_z;pl;d and N_s;d ≤ 0.5 · a₄ · N_v;u;d check equation 11.3-24
4. If V_z;s;d > 0.25 · V_z;pl;d and N_s;d > 0.5 · a₄ · N_v;u;d check equation 11.3-25

where

Vz;s;d	=	Actual Shear force in the section along Z-axis
Vz;pl;d	=	Shear capacity of section along Z-axis
b	=	breadth of section
h	=	height of section
A	=	area of section
Vz;pl;d	=	$V_{z;cl;d}=\frac{h}{b+h}A\frac{f_{y;d}}{\sqrt{3}}$
a3	=	min{ (A - 2 · b · t)/A or 0.5}
a4	=	from equation 11.3.27

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