How is the strength of the double angle checked in rupture?

Each angle carries half the load (200 kN) and its Tdn is doubled

Both angles are treated as one with the full area at fu

Rupture is ignored for double angles

Why are tack bolts with packing provided between the double angles?

To make the two angles act together and limit slenderness of individual angles

To increase bolt shear capacity

To reduce shear lag factor beta

2075 Bhadra · 10 marks

Double angle tension member 400 kN, M20

Short answer

Use 2 ISA 75×75×8 placed on opposite sides of gusset plate. Connect with 4 M20 grade 5.6 bolts at 60 mm pitch (double shear). Bolt capacity 477 kN and section capacity 517 kN both exceed 400 kN.

Design a double angle section to carry a tension of 400 kN. The end connection to be made using M20 bolts at product class C and property class 5.6. Assuming the angle sections are provided on the both sides of gusset plate. The steel used are E 250.

Given: factored tension 400 kN; two angles on opposite faces of the gusset (bolts in double shear); M20 bolts, product grade C, class 5.6 ( $f_{ub}=500$ , $f_{yb}=300$ ); E250; gusset plate assumed 12 mm; $d_0=22$ mm.

1. Bolts

$V_{dsb}=\dfrac{500}{\sqrt3\times1.25}(245+314)\times10^{-3}=129.1$ kN (one plane in threads)
Bearing on gusset 12 mm ( $e=40$ , $p=60$ ): $k_b=\min(0.606,0.659,1.22,1)=0.606$ ; $V_{dpb}=119.3$ kN
Bolt value $119.3$ kN → $n=\dfrac{400}{119.3}=3.35$ → 4 bolts, pitch 60 mm, end distance 40 mm; capacity $477.1$ kN.

2. Section

$A_g\ge\dfrac{400\times1.10}{250}\times10^3=1760$ mm². Try 2 ISA 75×75×8 ( $A=1138$ mm² each, $2276$ mm²), bolt gauge 40 mm from the heel.

Yielding: $T_{dg}=2\times\dfrac{1138\times250}{1.10}\times10^{-3}=517.3$ kN (258.6 kN per angle)
Rupture per angle (load 200 kN): $A_{nc}=(75-4-22)\times8=392$ mm², $A_{go}=(75-4)\times8=568$ mm², $b_s=w+w_1-t=75+40-8=107$ mm, $L_c=180$ mm, $\beta=1.142$ → $T_{dn}=263.1$ kN
Block shear per angle: $\min(287.6,258.6)=258.6$ kN
Strength of one angle $=\min(258.6,\ 263.1,\ 258.6)=258.6$ kN; pair $=517.2$ kN $>400$ ✓ (member length not given; check $L/r\le400$ : with $r_{min}\approx23$ mm this allows $L\le9$ m).

Provide tack bolts at no more than 1000 mm centres, with packing.

Answer: 2 ISA 75×75×8 (one on each side of the gusset) with 4 M20 bolts (5.6) at 60 mm pitch.

✓ Answer checked by Claude Opus 5.5 (high effort)

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Double angle tension member 400 kN, M20

1. Bolts

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