# V. GB500017-2017 Double Angle section with Axial Force

Verify the slenderness, strength, and stability of a double-angle section subject to axial force per GB50017-2017.

## Reference

MOHURD. 2017. GB 50017-2017 Standard for design of steel structures . Beijing, China: Ministry of Housing and Urban-Rural Development

## Problem

The section is a 2 x L100x100x7 SP 0 with a length of 3.005 m. The structure is a truss model. Member #32 assigned with double angle section (2 x L100x100x7 SP 0) is designed per GB 50017-2017. The governing load combination (#4) is 1.2 DL + 1.4 LL and the ultimate force on the member, N, is 416.2 kN of axial compression.

Material Properties

The material is Q235 type steel.

• Design strength in tension, compression, and flexure: fy = 215 MPa
• Design strength in shear: fv = 125 MPa

Section Properties

• Side length, b = h = 100 mm
• Thickness, t = 7 mm
• Cross-sectional area, A = 2,760 mm2
• Moment of inertia about x, Ix = 2,631,000 mm4
• Moment of inertia about y, Iy = 4,732,000 mm4
• Area moment about x, Sx = 36,700 mm3
• Area moment about y, Sx = 37,280 mm3

## Calculations

Slenderness Ratio

According to Table 7.4.1-1 of GB50017-2017, effective length of double angle is:

lox = lx = 3,005 mm

loy = ly = 3,005 mm

According to formula 7.2.1-1 and 2 of steel structures code, slenderness ratio of double angle with X axis and Y axis is:

$λ x = l 0 x i x = 3,005 30.87 = 97.33$
$λ y = l 0 y i y = 3,005 41.41 = 72.57$

According to formula 7.2.2-7 of steel structures code, torsional buckling equivalent slenderness ratio of double angle is:

$λ z = 3.9 × b t = 3.9 × 100 7 = 55.71$

Calculate the equivalent slenderness ratio of symmetry axis. Since $λy>λz$, the formula 7.2.2-5 should be used to get the $λyz$:

$λ y z = λ y 1 + 0.16 λ z λ y 2 = 72.57 × 1 + 0.16 × 55.71 72.57 2 = 79.42$

The maximum slenderness ratio of the double-angle section, $λ max = 97.33$

The limit of slenderness ratio of compression member is 150 according to table 7.4.6 of steel structures code.

The limit of slenderness ratio of tension member is 300 according to table 7.4.7 of steel structures code.

Tension or Compression Strength

According to formula 7.1.1-1 and 7.1.1-2 of steel structures code, the stress of double angle with gross cross-section area is:

And the ratio is:

$σ f = 150.8 215 = 0.70$

The stress of double angle with net cross section area is:

And the ratio is:

$σ 0.7 f u = 150.8 259 = 0.58$

The steel type is Q235. According to note 1 in table 3.5.1 of Standard for design of steel structures and table 1 of Standard for design of steel structures. Commentary 2.2, the steel grade correction coefficient is εk = 1.

Compressive Strength

According to table 7.2.1-1 of steel structures code, the double angle section class is b.

The slenderness ratio of double angle on X axis, $λ x = 97.33$. So,

$λ ε k = λ x = 97.33$
$λ n = λ x π f y E = 97.33 π 235 206,000 = 1.046$

Class b, so, the coefficients are α1 = 0.650, α2 = 0.965, and α3 = 0.300.

Since $λ n = 1.046 > 0.215$ , then the stability factor in x:

$ϕ x = 1 2 λ n 2 α 2 + α 3 λ n + λ n 2 - α 2 + α 3 λ n + λ n 2 2 - 4 λ n 2$
$= 1 2 × 1.046 2 0.965 + 0.300 × 1.046 + 1.046 2 - 0.965 + 0.300 × 1.046 + 1.046 2 2 - 4 × 1.046 2 = 0.572$

The slenderness ratio of double angle on symmetry axis is $λ y z = 79.42$. So,

$λ ε k = λ x = 79.42$
$λ n = λ xy π f y E = 79.42 π 235 206,000 = 0.854$

Class b, so, the coefficients are α1 = 0.650, α2 = 0.965, and α3 = 0.300.

Since $λ n = 1.046 > 0.215$ , then the stability factor in xy:

$ϕyz=12λn2α2+α3λn+λn2-α2+α3λn+λn22-4λn2$
$=12×0.85420.965+0.300×0.854+0.8542-0.965+0.300×0.854+0.85422-4×0.8542=0.692$

The minimum stability factor is 0.572.

From GB50017-2017 Clause 7.3.1-5, when λ > 80εk, the formula 7.3.1-7 should be used to get the value of width thickness ratio of compression member. Here, 97.33 > 80×1.

Limit value of width to thickness ratio = 5εk + 0.125λ = 5 + 0.125 × 97.33 = 17.17.

According to Clause 7.3.2 of GB50017-2017, ϕAf = 0.572 × 2,760 × 215 = 339.4 kN < N = 416.2 kN

Therefore, the limit value of width to thickness ratio without magnification.

According to formula 7.3.1-7 of GB50017-2017, w = b - 2t = 100 - 2× 7 = 86 mm

$w t = 86 7 = 12.29 < 17.17$
$Actual value Limit value = 12.29 17.17 = 0.72 < 1.0$

The double angle members are composed of equilateral single angle. So, the check process of the height thickness ratio of compression web is consistent with that of width thickness ratio of compression flange. Thus, OK.

Stability of the compression member: according to formula (7.2.1) of GB50017-2017:

Shear Strength

According to formula (7.2.7) of GB50017-2017,

Then, according to formula (6.1.3) of GB50017-2017,

Therefore, the ratio is:

$τ f v = 6.957 125 = 0.06$

## Comparison

Table 1. Comparison of results
Result Type Reference STAAD.Pro Difference Comment
Compression Slenderness 0.64 0.65 none
Tension Slenderness 0.32 0.32 none
Truss Strength 0.70 0.70 none
Compression Flange Slenderness 0.72 0.72 none
Compression Web Slenderness 0.72 0.72 none
Compression Stability 1.23 1.23 none
Shear strength 0.06 0.06 none

The file C:\Users\Public\Public Documents\STAAD.Pro CONNECT Edition\Samples\ Verification Models\09 Steel Design\China\GB500017-2017 Double Angle section with Axial Force.std is typically installed with the program.

STAAD SPACE
START JOB INFORMATION
ENGINEER DATE 11-Aug-18
END JOB INFORMATION
INPUT WIDTH 79
UNIT METER KN
JOINT COORDINATES
1 0 0 0; 2 1.66667 0 0; 3 3.33333 0 0; 4 5 0 0; 5 6.66667 0 0; 6 8.33333 0 0;
7 10 0 0; 8 1.66667 2.5 0; 9 3.33333 2.5 0; 10 5 2.5 0; 11 6.66667 2.5 0;
12 8.33333 2.5 0; 13 0 0 2; 14 1.66667 0 2; 15 3.33333 0 2; 16 5 0 2;
17 6.66667 0 2; 18 8.33333 0 2; 19 10 0 2; 20 1.66667 2.5 2; 21 3.33333 2.5 2;
22 5 2.5 2; 23 6.66667 2.5 2; 24 8.33333 2.5 2;
MEMBER INCIDENCES
1 1 2; 2 2 3; 3 3 4; 4 4 5; 5 5 6; 6 6 7; 7 8 9; 8 9 10; 9 10 11; 10 11 12;
11 1 8; 12 8 3; 13 3 10; 14 10 5; 15 5 12; 16 12 7; 17 2 8; 18 4 10; 19 6 12;
20 3 9; 21 5 11; 22 13 14; 23 14 15; 24 15 16; 25 16 17; 26 17 18; 27 18 19;
28 20 21; 29 21 22; 30 22 23; 31 23 24; 32 13 20; 33 20 15; 34 15 22; 35 22 17;
36 17 24; 37 24 19; 38 14 20; 39 16 22; 40 18 24; 41 15 21; 42 17 23; 43 1 13;
44 2 14; 45 3 15; 46 4 16; 47 5 17; 48 6 18; 49 7 19; 50 8 20; 51 9 21;
52 10 22; 53 11 23; 54 12 24;
DEFINE MATERIAL START
ISOTROPIC STEEL
E 2.05e+008
POISSON 0.3
DENSITY 76.8195
ALPHA 1.2e-005
DAMP 0.03
TYPE STEEL
STRENGTH FY 253200 FU 407800 RY 1.5 RT 1.2
END DEFINE MATERIAL
MEMBER PROPERTY CHINESE
1 TO 10 22 TO 31 43 TO 54 TABLE ST PIP152X8.0
12 15 17 TO 21 33 36 38 TO 42 TABLE ST L80X80X6
11 16 32 37 TABLE SD L100X100X7
13 14 34 35 TABLE ST L100X100X6
CONSTANTS
MATERIAL STEEL ALL
MEMBER TRUSS
11 TO 21 32 TO 42
SUPPORTS
1 7 13 19 PINNED
2 TO 6 8 TO 12 14 TO 18 20 TO 24 FY -20
8 TO 12 20 TO 24 FY -40
8 TO 12 20 TO 24 FY -30
LOAD COMB 3 F : 1.20DL
1 1.2
LOAD COMB 4 F : 1.20DL+1.40LL
1 1.2 2 1.4
LOAD COMB 5 F : 1.00DL
1 1.0
LOAD COMB 6 F : 1.00DL+1.40LL
1 1.0 2 1.4
LOAD COMB 7 F : 1.20DL+0.98LL
1 1.2 2 0.98
LOAD COMB 8 F : 1.00DL+0.98LL
1 1.0 2 0.98
LOAD COMB 9 F : 1.35DL
1 1.35
LOAD COMB 10 F : 1.35DL+0.98LL
1 1.35 2 0.98
PERFORM ANALYSIS
FINISH


Chinese steel design parameters (.gsp file):

[version=2207]
*{ The below data is for code check general information, please do not modify it.
[CodeCheck]
BeamBendingStrength=1
BeamShearStrength=1
BeamEquivalentStress=1
BeamOverallStability=1
BeamSlendernessWeb=1
BeamSlendernessFlange=1
TrussStrength=1
TrussStability=1
TrussShearStrength=1
ColumnStrength=1
ColumnStabilityMzMy=1
ColumnStabilityMyMz=1
PressedTrussSlenderness=1
TensionTrussSlenderness=1
ColumnSlendernessFlange=1
ColumnSlendernessWeb=1
BeamDeflection=1
SelectAll=0
GroupOptimize=0
FastOptimize=0
Iteration=0
SecondaryMembers=
SectCollectionOrder=0
[CheckOptionAngle]
PrimaryAxis=60.000000
SecondaryAxis=60.000000
ExtendLine=10.000000
*{ The above data is for code check general information, please do not modify it.

[GROUP=1]
Name(Parameter Name)=DOUBLEANGLE
Type(Member Type)=2
Principle(Principle Rules)=0
SteelNo()=Q235
Fatigue(Fatigue Calculation)=0
Optimization(Perform optimized design)=0
MaxFailure(Failure Ratio)=1
MinTooSafe(Safety Ratio)=0.3
BeamBendingStrength()=1
BeamShearStrength()=1
BeamEquivalentStress()=1
BeamOverallStability()=1
BeamSlendernessFlange(b/t on beam)=1
BeamSlendernessWeb(h0/tw on beam)=1
TrussStrength(Axial Force Strength)=1
SecondaryMoment(Secondary Moment of Truss)=0
TrussStability(Solid-web Axial Compression Stability)=1
TrussShearStrength(Axial Shear Strength)=1
PressedTrussSlenderness(Pressed Member Slenderness)=1
TensionTrussSlenderness(Tension Member Slenderness)=1
ColumnStrength(Column Member Strength)=1
ColumnStabilityMzMy(Column Stability In-plane)=1
ColumnStabilityMyMz(Column Stability Out-plane)=1
ColumnSlendernessFlange(b/t on column)=1
ColumnSlendernessWeb(h0/tw on column)=1
CheckItemAPPENDIX_B11(Beam Deflection)=1
lmdc(Slenderness Limit of Compression Member)=0
lmdt(Slenderness Limit of Tension Member)=0
Lmd831(Slenderness of Seismic Column)=0
Lmd841(Slenderness of Seismic Brace)=0
Lmd9213(Slenderness of Seismic Single-story Plant)=0
LmdH28(Slenderness of Seismic Multi-story Plant)=0
rz(Plastic Development Factor in Major Axis)=0
ry(Plastic Development Factor in Minor Axis)=0
gamaSharp(Plastic Development Factor of sharp side)=0
betamz(the equivalent moment factor in Major Axis plane)=0
betamy(the equivalent moment factor in Minor Axis plane)=0
betatz(the equivalent moment factor out Major Axis plane)=0
betaty(the equivalent moment factor out Minor Axis plane)=0
DFF(Deflection Limit of Beam)=400
DJ1(Start Node Number in Major Axis)=0
DJ2(End Node Number in Major Axis)=0
Horizontal(Check for Deflection in Minor Axis)=0
Cantilever(Cantilever Member)=0
fabz(Overall Stability Factor in Major Axis of Bending Member)=0
faby(Overall Stability Factor in Minor Axis of Bending Member)=0
StressFeature(Select the Stress Feature to calulate stability factor of beam)=1
faz(Overall Stability Factor in Major Axis of Axial Compression Member=0
fay(Overall Stability Factor in Minor Axis of Axial Compression Member)=0
lz(Unbraced Length in Major Axis)=0
ly(Unbraced Length in Minor Axis)=0
miuz(Effective Length Factor for Column in Major Axis)=1
miuy(Effective Length Factor for Column in Minor Axis)=1
Lateral(Member in Frame Without Sidesway or not)=1
APZ(Gyration Radius Calculation as Z-Axis Parallel Leg)=1
rFlange(Limit Ratio of Width to Thickness for Flange)=0
rWeb(Limit Ratio of High to Thickness for Web)=0
BucklingStrength(Axis forced member bulking strength)=0
ZSectType(Section Type in Z-Axis)=0
YSectType(Section Type in Y-Axis)=0
HSectWebInTrussPlane(Web of H in Truss Plane)=0
rAn(Net Factor of Section Area)=1
rWnz(Net Factor of Resistance Moment in Z-Axis)=1
rWny(Net Factor of Resistance Moment in Y-Axis)=1
CapReduce(Seismic Reduction Factor of Load-bearing Capacity for Brace)=1
AngleReduce(Angle Strength Reduce)=0
LAglConSta(Connect Type of unequal single angle)=0
LAngleStrength(Reduction Factor of Angle Strength)=0
LAngleStability(Reduction Factor of Angle Stability)=0
rTrussSectReduce(Effective Factor of Axial Force Section)=1
Members(Member Number)=32