Mid-term 2.pdf - UBC Mechanical Engineering

Question 2
A schematic diagram of the anchoring cable (steel) of a rigid/fixed sail post at Canada
Place in Vancouver is shown. The cable is firmly attached to the top of the sail post at
one end. The other end of the cable has a rigid end cap, the position of which may be
adjusted by means of a tensioning device. The tensioning device has an identical pair of
steel bolts with nuts, and is rigidly attached to a fixed support base. The bolts pass
through the two holes in the end cap of the cable. The tensioning is done by tightening
the two bolts by equal amounts.
Under unstrained conditions:
L = length of the cable
L/10 = length of each bolt (from the nut position to the head).
Also,
δ = screw pitch of a bolt/nut
E = Young’s modulus of cable = Young’s modulus of bolt.
Assume that the area of X-section of the cable = area of X-section of the bolt.
If both nuts are tightened through n turns each, in the same direction, determine an
expression for the:
(a) Tensile stress in the cable
(30 points)
(b) Tensile stress in each bolt
(15 points)
in terms of E, L, n and δ.
Figure: Sail-post anchoring cable system.
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