Design of steel structure Tension member.pptx

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1. Design of Tension Member

2. (i) Various cross sections such as solid threaded rod, cable and angle sections. Limit strength due to yielding of gross section, rupture of critical section and block shear failure. Design of tension member: using single and double angle sections, connections of member with gusset plate by bolts and welds. Definition- Tension members are linear structural members subjected to axial forces which will elongate (yield) the member. Eg. Wire rope of a cable stayed bridge supporting deck. or A bottom chord of a truss member. As the member is subjected to axial pull force it elongates and does not buckle therefore no need of classifying type of section. 2

3. A tension member may consist of single rolled section or combination of sections as a built up section. Usually single angle and double angle sections with gusset plate are commonly used for truss members. Rods or flat plates may be used for bracing system in truss or built up columns. Wire ropes and cables are used in case of suspension bridges. 3

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5. The design strength (Td) of the member shall be greater than factored tensile force (Tu) acting on it: Td>Tu , The design strength (Td) of tension member is least of Design strength due to yielding of gross section (Tdg) Design strength due to Rupture of critical section (Tdn) Design strength due to block shear (Tdb) (1) Design strength due to yielding of gross section (Tdg)- where, fy = yield strength of material (250MPa) Ag = gross area of cross section  m0 = partial safety factor for failure in tension by yielding = 1.10 (IS 800:2007, Table No.5, pg. No. 30) T 5 m0 dg   Ag × fy

6. (2) Design strength due to Rupture of critical section (Tdn)- a) Plates & threaded rods- (IS 800:2007, Cl. No. 6.3.1, Pg. No. 32) where, fu = Ultimate tensile strength of material (410MPa) An = Net area of cross section after deduction for bolt holes for chain bolting An = Net area of cross section after deduction for bolt holes  m1 = partial safety factor for ultimate tension failure by rupture = 1.25 (IS 800:2007, Table No.5 Pg. No. 30) m1 dn T   0.9× An ×fu An   b  n  dh   t      t    An    b  n  dh    4  g  n '  P 2   for staggered or zig- zag bolting 6

7. b) Single Angles- (IS 800:2007, Cl. No. 6.3.3, Pg. No. 33) where, Anc = net area of connected leg Ago = gross area of outstanding leg fy and fu = yield and ultimate stress respectively  = 1.4 - 0.076(w/t)(f y /f u )(b s /L c ) < (f u ×  mo )/f y ×  m1 ) , but  > 0.7 w= outstand leg width m1 m0 dn T     0.9× Anc ×fu     × Ago ×fy  7

8. 8 bs = Shear lag width, t= thickness of leg Lc = distance between outermost bolts /equivalent length of welding in load direction . Lc p (3) Design strength due to block shear (Tdb )- ( IS 800:2007, Cl. No. 6.4.1, pg.no. 33) The failure of the end connection as a unit along the centers of the bolt holes in tension and shear plane is termed as block failure. The block shear strength (Tdb) is least of the below; db2 m1 m0 db1 T  3 ×   3 ×   Avg ×fy  0.9× Atn ×fu  0.9× Avn ×fu  Atg ×fy m0 m 1 OR T

9. where, A vg and A vn = minimum gross and net area in shear along a line of transmitted force respectively A tg and A tn = minimum gross and net area in tension from the hole to the toe of the angle perpendicular to the line of transmitted force 9 Tension area Shear area e p p p e