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DDSS - Build-Up Section

Design of Build-Up Section:
Design and Drawing of Steel Structures

This is a compression member. The slenderness ratio of the each member between the connections should not be greater then 40 nor greater than 0.6 times the most unfavorable slenderness ratio of the whole strut.
In no case should the spacing of tackling rivets in a lined exceed 600 mm for such members like tee angles, channels or tees placed back to back.
For other type of Build-Up Compression Members say where cover-plates are used, the pitch of tackling rivets should not exceed 32.t or 300 mm, whichever is less.
When plates are exposed to the weather, the pitch should not exceed 16.t or 200 mm whichever is less.

Design Steps:

Step 1: Selection of Section
  • Selection of Section
Pd = Ae.fcd
where, 
Ae is Effective Area
Pd = 1.5*P

#Assumption of fcd, when Pd is given:
1. When Pd > 10 kN
   Then fcd 25 MPa to 50 MPa
2. When 100 < Pd < 250 kN
   Then fcd 75 MPa to 150 MPa
3. When 250 < Pd < 350 kN
   Then fc 100 MPa to 150 MPa (Yes Same)
4. When Pd > 350 kN
   Then fc 150 MPa to 250 MPa
  • Select Section From Steel Table: 
1. For Back-To-Back Section, it is directly given in Steel Table,
2. For Toe-To-Toe, we need to develop using single sections.
  • Spacing Between Channel Section:
Ixx = Iyy
  • Check for Limiting Width To Thickness Ratio (Table 2 IS 800 - 2007)

  • Check Strength of Provided Section:
Pd = Ae.fcd
Find fcd fom Table 9(A) to 9(D), using buckling class and slenderness ratio.

Step 2: Design of Lacing System
PART 1:-
  • Decide angle of inclination:
40 < Angle < 70
  •  Effective Length and Total Length of Lacing Bar (Leff):
  • Min Width (Bmin):
  • Thickness of Lacing Bar (t):
PART 2:-

  • Local Buckling:
a1/r1 <= 50 <= 0.7 Slenderness Ratio
  • Slenderness Ratio:
Slenderness Ratio < 145

PART 3:-

Check Compression and Tensile Strength of Lacing:
  • Compression Strength:
For this Check Out Here: DDSS - Compression Member
  • Tensile Strength:
For this Check Out Here: DDSS - Tensile Member

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