The rigid beam is supported by a pin at C and an A992 steel guy wire AB of length 6 ft. If the wire has a diameter of 0.2 in., determine how much it stretches when a distributed load of w=200lb/ft acts on the beam. The wire remains elastic

Respuesta :

Answer:

change in length = 0.0913 in

Explanation:

given data

length = 6 ft

diameter = 0.2 in

load of w = 200 lb/ft

solution

we apply here first equilibrium moment about C that is express as

∑M(c)  = 0    .............1

so it can express as to get force in AB

10× 200 × ( 5) - (T cos(30)) × 10  =  0

solve it we get

Tension is wire T(AB)  = 1154.7 lb

and we know modulus of elasticity will be here for A992

E = 29000 ksi

and area will be

Area = [tex]\frac{\pi }{4}\times 0.2^2[/tex]  

so change in length will be express as

change in length = [tex]\frac{PL}{AE}[/tex]      ................2

put here value and we get

change in length = [tex]\frac{1154.7 \times 6 \times 12}{\frac{\pi }{4}\times 0.2^2 \times 29000 \times 1000}[/tex]

change in length = 0.0913 in

The length by which the guy wire stretches is; δ = 0.091 in

Elastic Modulus of Steel

We are given;

Length of guy wire AB = 6ft = 72 in

Diameter of wire = 0.2 in

UDL = 200 lb/ft

From the free body diagram of the rigid beam system and the guy wire attached, we can say that;

Taking moments about point C gives;

∑Mc = 0; -(2000 * 5) + (F_BA * cos 30 * 10) = 0

-10000 + 8.66F_BA = 0

8.66F_BA = 10000

F_BA = 10000/8.66

F_BA = 1154.73 lb

Now, the length which it stretches is gotten from the formula;

δ = PL/AE

Where;

δ is change in length

P is Force

L is length of wire

A is area

E is modulus of elasticity of wire(steel) = 29000 ksi = 29000000 psi

A = πd²/4

A = π * 0.2²/4

A = 0.0314 in²

Thus;

δ = (1154.73 * 72)/(0.0314 * 29000000)

δ = 0.091 in

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