TENSION MEMBERS

DESIGN OF TENSION MEMBERS Teaching Resources for Steel Structures DESIGN OF TENSION MEMBERS Introduction Behaviour of Tension Members Plates Under Tension Threaded Rods Angles Under Tension Code Provisions Summary © Dr S R Satish Kumar IIT Madras © IIT Madras, SERC Madras, Anna Univ., INSDAG Calcutta

Tension Members in Buildings suspenders (b) Suspended Building tie (a) Roof Truss rafter (c) Roof Purlin System purlin Sag rod Top chord (d) Braced frame © Dr S R Satish Kumar IIT Madras

Uniform stress over the cross section Very Efficient Member INTRODUCTION Characteristics Members Experience Axial force Stretching Uniform stress over the cross section Very Efficient Member Strength governed by the material strength Bolt holes affect the strength © Dr S R Satish Kumar IIT Madras

Cross Sections Used for Tension Members INTRODUCTION Cross Sections Used for Tension Members Channel Angle Double Angle Rod Cable Built up sections © Dr S R Satish Kumar IIT Madras

BEHAVIOUR IN TENSION Material Properties T fy c  High Strength Steel Mild Steel High Strength Steel T  a b c d e fy 0.2% Yield Plateau © Dr S R Satish Kumar IIT Madras

BEHAVIOUR IN TENSION Plates with a Hole u y (a) Elastic (b) Elasto-Plastic (c) Ultimate u y © Dr S R Satish Kumar IIT Madras

b d BEHAVIOUR IN TENSION Plates with Holes (Cl 6.3) (a) (b) P = pitch g = gauge 1 4 p g 2 3 b d Case a: Net Area: = t (b - 2*d) Case b: Net Area: = t (b – d) Case c: t (b - 2*d)<Area< t (b –d) (a) (b) (c) © Dr S R Satish Kumar IIT Madras

An = [ b – n d + (p2 / 4 g)]t BEHAVIOUR IN TENSION Plates with Holes © Dr S R Satish Kumar IIT Madras

BEHAVIOUR IN TENSION ANGLES Eccentrically Loaded Through Gussets Gusset plate © Dr S R Satish Kumar IIT Madras

SECTION 6 DESIGN OF TENSION MEMBERS Revised IS 800:2007 SECTION 6 DESIGN OF TENSION MEMBERS 6.1 Tension Members 6.2 Design Strength due to Yielding of Gross Section 6.3 Design Strength due to Rupture of Critical Section 6.3.1 Plates 6.3.2 Threaded Rods 6.3.3 Single Angles 6.3.4 Other Sections 6.4 Design Strength due to Block Shear 6.4.1 Plates 6.4.2 Angles © Dr S R Satish Kumar IIT Madras

Revised IS 800:2007 CODAL PROVISIONS 6.1 Tension Members The factored design tension T, in the members T < Td 6.2 Design Strength due to Yielding of Gross Section The design strength of members under axial tension Tdg, Tdg = fy Ag /m0 mo = 1.1 6.3 Design Strength due to Rupture of Critical Section 6.3.1 Plates  The design strength in tension of a plate, Tdn, Tdn =0.9 fu An / m1 m1 = 1.25 An = Cont… © Dr S R Satish Kumar IIT Madras

Revised IS 800:2007 CODAL PROVISIONS 6.3.2 Threaded Rods  The design strength of threaded rods in tension, Tdn, Tdn =0.9 fu An / m1 Ultimate elastic elastic -Plastic droot dgross f < fy fy fu © Dr S R Satish Kumar IIT Madras

Revised IS 800:2007 CODAL PROVISIONS 6.3.3 Single Angles  The design strength, Tdn, as governed by tearing Tdn = 0.9 fu Anc / m1 + Ago fy /m0  = 1.4 – 0.076 (w/t) (fu/fy) (bs/L ) [≈ 1.4-0.52(bs/L)] Alternatively, the tearing strength of net section may be taken as Tdn =  An fu /m © Dr S R Satish Kumar IIT Madras

Revised IS 800:2007 CODAL PROVISIONS bs=w w w1 bs=w+w1 Fig. 6.2 Angles with end connections © Dr S R Satish Kumar IIT Madras

Revised IS 800:2007 CODAL PROVISIONS 6.4 Design Strength due to Block Shear 6.4.1 Plates –The block shear strength, Tdb, of connection shall be taken as the smaller of Tdb = ( Avg fy /(3 m0) + fu Atn /m1 ) or Tdb = ( fu Avn /(3 m1) + fy Atg /m0 ) 1 2 3 Fig 6.3 Block Shear Failure of Angles 4 Fig 6.2 Block Shear Failure of Plates 1 2 4 3 © Dr S R Satish Kumar IIT Madras

DESIGN OF TENSION MEMBERS Efficiency  = Pt /(Ag * fy / M0) Design Steps An = Pt / (fu / M1) Ag = Pt / (fy / M0) Choose a trial section Analyse for its strength © Dr S R Satish Kumar IIT Madras

DESIGN OF TENSION MEMBERS Stiffness Requirements Designed for compression under stress reversal /r < 250 Not designed for compression under stress reversal /r < 350 Members under tension only /r < 400 © Dr S R Satish Kumar IIT Madras

DESIGN OF TENSION MEMBERS Summary Efficient load carrying members Efficiency may reduce due to bolt holes shear lag block shear Thank You © Dr S R Satish Kumar IIT Madras

Structural Engineering Laboratory, Dept. of Civil Engineering, www.steel-insdag.org Dr S R Satish Kumar Asso. Professor & Head, Structural Engineering Laboratory, Dept. of Civil Engineering, IIT Madras, Chennai 600 036. sr.satishkumar@gmail.com © Dr S R Satish Kumar IIT Madras