Week 2 Challenge

Aim:

To calculate net area of given sections at critical failures, design strength of Sag rods & Tension member.

1. Net area calculation for tension member design

(a)

20mm thick plate & 20mm bolt size

An = (260x20) - (4x20x20) = 3600 mm2

(b)

Plane 1 An = (260x20) - (2x20x20) = 4400 mm2

Plane 2 An = (260x20) - (3x20x20) = 4000 mm2

Choosing the least area An = 4000 mm2

(c)

From clause 6.3.1,

An = (300-(3x20) + (50^2/4x90) + (50^2/4x130))x12

= (240 + 6.9 + 4.8)x12

An = 3020 mm2

2. Design of Sag rod

It is understood from the plan that 1 panel load will transfer to a sag rod (8/3 x 1.2 m panel)

Roof weight = 60 kg x 8/3 x 1.2 = 192 kg (or) 1.92 kN

Wind pressure = 150 kg x 8/3 x 1.2 = 480 kg (or) 4.8 kN

Live load = 75 kg x 8/3 x 1.2 = 240 kg (or) 2.4 KN

Purlin weight = 100 kg x 8/3 =266 kg (or) 2.7 kN

Total load = 11.8 KN gravity load

Resolving it to horizontal load = 11.8 x cos 75 = 3 kN

Assume yeild strength 350 N/mm2 & Ultimate strength 490 N/mm2

From clause 6.3.1,

Td = 0.9 An Fu / Ym1

3000 = 0.9 x An x 490 / 1.25

An = 8.5 mm2

3. Determination of section size for given Tensile load

Data:

Length = 5 meter

Axial load = 500 KN

Yield strength of material Fy = 350 N/mm2

As per IS-800 Table-1, The ultimate strength of corresponding material Fu=490 N/mm2

From clause 6.2,

Td = Ag Fy / Ymo

500x1000 = Ag x 350 / 1.1

Ag = 1571 mm2

From IS808, Choosing Angle ISL 110x110x10 (Ag = 2110 mm2)

Hence okay

Just assuming 10 bolts of dia 20mm resisting the given factored loads, that are arranged at equal spacing as below

Net area = 220x10 - (2x20x10)

An = 1800 mm2

From clause 6.3.1,

Td = 0.9 An Fu / Ym1

= 0.9 x 1800 x 490 / 1.25

Td = 635 KN

Hence okay

From clause 6.4.1,

Gross shear area Avg = 2x(55+150+150+150+150) x 10 = 13100 mm2

Net shear area Avn = 13100 - (10x20x10) = 11100 mm2

Gross tension area Atg = 2110 mm2

Net tension area Atn = 2110 -(2x10x20) = 1710 mm2

Tdb1 = (13100x350/v3x1.1) + (0.9x490x1710/1.25) = 2406 KN + 603 KN = 3009 KN

Tdb2 = (0.9x490x11100/v3x1.25) + (2110x350/1.1) = 2260 KN + 671 KN = 2931 KN

Hence okay

From Table-3,

Maximum Slenderness limit for Tension member kL/r = 400

kL = 5000 mm

r = 33.7 mm (From IS-808 steel book)

kL/r = 148 Hence okay.