Important Question And Problems With Answer: Tension Members
1. Tie member - Explain.
Tie member or a tension member is a structural element carrying an axial tensile force. For the tensile force to be axial it is necessary that the load be applied through centroid of the section of the member. But under axial tension the member gets straightened and eccentricity of the force decreases. The member is almost straight at the yield point and the distribution of the stress over the section becomes uniform.
2. How the tension members are classified?
It is classified according to its shape and size and it depends upon the type of structures.
Wires and cables - Used in hoists, derricks, suspenders in suspe nsion bridges
Rods and bars - Used in radi o tower, small spanned roof trusses with differe nt cross-sections such as round, rectan gular or square
3. What is meant by single section member?
Structural sections such as I-section, T-section, angle, and channel are used as tension
members. As the structural shapes provide more rigidity than cables or r ods, their buckling tendency under compression load is reduced and so can be used where reversal of stress takes place.
4. Under what circumstanc es you would go for Built-up members?
When single structural secti ons fail to provide required strength and stiffness to carry tension as well as compression in case of reversal of stresses, built-up members are used.
5. How the tension members are selected? It depends upon the various factors such as type of fabrication, type of structure, type of loading, i.e. whether the member undergoes reversal of stresses, and the maximum tension to be carried by the member.
6. Sketch the different form s a single section member
9. What is net sectiona l area of a tension member? How it is calculated in chain riveting?
The gross sectional area of the tension member minus the sectional area
of the maximum nu mber of rivet/bolt holes is known as net sectional area.
In case of chain riveting,
anet= (b - nd) t
10. What is Lug angle?
A larger length of the tension member and the gusset plat e may be required
sometimes to accom modate the required number of connection rivets. But this may not
be feasible and economical. To overcome this difficulty lug angles are used in
conjunction with ma in tension members at the ends. It provides extra gauge lines
for accommodating the rivets and thus enables to reduce the length of the
connection. They are generally used when the members are of s ingle angle, double
angle or channel sec tions.
11. What are the main objectives of the lug angles?
They produce eccen tric connections, due to rivets placed along lug angle. The centroid of the rivet s ystem of the connection shifts, causing eccentric connection and bending moments.stress distribution in the rivets connecting lug ang les is not uniform. It is preferred to put a lug angle at the beginning of the connection where they are more effective and not at th e middle or at the end of the connection.Rivets on the lug angles are not as efficient as those on the main member.The out-standing le g of the lug angle usually gets deformed and so the load shared by the rivets on the lug angles is proportionately less.
12.What is meant byTen sionsplice?
Splicing of tension members is necessary when the required length of the
member is more than the length available or when the member has different cross-
sections for different parts of its length. If actual member is to be of greater length, two or more lengths shall have to be spliced at the joints.
13. What is the net effective area of a pair of angles placed back to back connected by one leg of each angle subjected to tension?
Anet = A1 + A2 K
A1 - effective cross - section area of connected legs A2 - Gross area of outstanding legs
K = 5A1 5A1 + A 2
14. What is the permissible stress in axial tension?
As per IS: 800 - 1984, the permissible stress in axial tension
?at = 0.6 fy N/mm2
fy = minimum yield stress in steel in N /mm2.
15. How will you join the member of different thickness in a tension member?
When tension member of different thickness are to be jointed, filler plates may be used to bring the member in level.
16. What happens when a single angle with one leg is connected to a gusset plate, which is subjected to an eccentric load?
The rivets connecting the angle to the gusset plate does not lie on the line of action of load. This gives rise to an eccentric connection due to which the stress distribution becomes non-uniform. The net cross-sectional area of such a section is reduced to account for this non- uniform stress distribution resulting from eccentricity.
17. What is the allowable stress in axial tension for channel section?
The allowable stress in axial tension for channel section is depends upon the diameter of the section
18. What are tacking rivets? Why are they essential in compression members?
Rivets used to connect long length of members to reduce the effective length of individual part
19. What will be the maximum pitch when the angles are placed back to back?
The maximum pitch when the angles are placed back to back is 1mm.