Tension member

Design of Tension member

1. Sanjivani Rural Education Society’s
Sanjivani College of Engineering, Kopargaon-423 603
( An Autonomous Institute Affiliated to Savitribai Phule Pune University, Pune)
NAAC ‘A’ Grade, NBA Accredited, ISO 9001:2015 Certified



Unit I : Tension members







By

Prof V M Mahajan (Asst. Professor)
Department of Civil Engineering
Email Id: [email protected]

2. (i) Various cross sections such as solid threaded rod, cable and angle
sections.
(ii) Limit strength due to yielding of gross section, rupture of critical section and
block shear failure.
(iii) 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. 3
1. A tension member may consist of
single rolled section or
combination of sections as a
built up section.

2. Usually single angle and double
angle sections with gusset plate are
commonly used for truss members.

3. Rods or flat plates may be used
for bracing system in truss or built
up columns.

4. Wire ropes and cables are used
in case of suspension bridges.

4. 4

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)

5
fy × Ag
T
m0
dg



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
for staggered or zig-zag bolting

m1 = partial safety factor for ultimate tension failure by
rupture = 1.25 (IS 800:2007, Table No.5 Pg. No. 30)

6 m1
dn
fu ×An ×0.9
T

  tdhnbnA    t
g
Pn
dhnbnA 
















4
'
2

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

7   
m0m1
dn
fy×Ago× fu×Anc×0.9
T





8. bs = Shear lag width, t= thickness of leg
Lc = distance between outermost bolts /equivalent length of welding in load
direction.






(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;

8
Lc
p m01
db2
m1m0
db1
fy×Atg
×3
fu ×Avn×0.9
T
fu ×Atn×0.9
×3
fy×Avg
T


m
OR

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