Introduction to tension members Slenderness ratio design strength pf tension members

1. Sanjivani Rural Education Society's
Sanjivani College of Engineering, Kopargaon 423603.
-Department of Civil Engineering-
By
Mr. Sudhir B. Gayake (Assistant Professor)
Mail Id- gayakesudhircivil@sanjivani.org.in

2. Prof. Sudhir B. Gayake,SCOE Kopargaon.
(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.
Defination- 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 doesnot buckle therefore no need
of classifying type of section.

3. Prof. Sudhir B. Gayake,SCOE Kopargaon.
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
sctions with gusset plate are commonly
used for truss members.
3. Rods or flat plates may be used for
bracing system in truss or builtup
columns.
4. Wire ropes and cables are used in case of
suspension bridges.

4. Prof. Sudhir B. Gayake,SCOE Kopargaon.

5. Prof. Sudhir B. Gayake,SCOE Kopargaon.
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 stregth due to yeilding of gross section (Tdg)
• Design stregth due toRupture of critical section (Tdn)
• Design strngth due to block shear (Tdb)
(1) Design strength due to yeilding of gross section (Tdg)-
Tdg=(Ag × Fy/m0)
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 (Table No.5 IS 800:2007 Pg.No. 30)

6. Prof. Sudhir B. Gayake,SCOE Kopargaon.
(2) Design strength due to Rupture of critical section (Tdn)-
a) Plates & threaded rods-
Tdn = 0.9fu.An/m1
where,
fu = Ultimate tensile strength of material (410MPa)
An = Net area of cross section after deduction for bolt holes=(b-n×dh)t
m1= partial safety factor for ultimate tension failure by
rupture = 1.25 (Table No.5 IS 800:2007 Pg.No. 30)
b) Single Angles-
Tdn = (0.9Anc×fu/m1)+(Ago×fy/mo)
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)(fy /fu)(bs/Lc) < (fu.  mo)/fy.  m1) but  > 0.7
w= outstand leg width

7. Prof. Sudhir B. Gayake,SCOE Kopargaon.
bs= Shear lag width
Lc= distnce between outermost bolts /equivalent length of welding in load direction.
t= thickness of leg
(3) Design strngth due to block shear (Tdb)-
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;
Tdb1 = ( Avg fy/(√3γm0) + 0.9Atn fu /γm1 )
or
Tdb2 = (0.9Avn fu /(√3γm1) + Atg fy /γm0 )
Lc
p

8. Prof. Sudhir B. Gayake,SCOE Kopargaon.
where,
Avg and Avn = minimum gross and net area in shear along a line of transmitted force
respectively
Atg and Atn = minimum gross and net area in tension from the hole to the toe of the angle
perpendicular to the line of transmitted force
Tension area
Shear area
e p p p
e