A three-hinged symmetrical arch is loaded as shown in the figure below. Which one of the following is the magnitude of the correct horizontal thrust?

This question was previously asked in
UKPSC AE Civil 2013 Official Paper I
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  1. 2.66 P
  2. 2 P
  3. 1.5 P
  4. 0.75 P

Answer (Detailed Solution Below)

Option 2 : 2 P
Free
ST 1: Theory of Structures - UKPSC AE Civil
20 Qs. 40 Marks 20 Mins

Detailed Solution

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Concept:

A three-hinged arch is a statically determinate structure and its reactions are calculated using equilibrium equations only. It is mounted on two hinged support and contains one hinge anywhere in the arch rib, generally at the crown which makes the structure determinate.

Let the reactions be as shown below.

∵ ΣFY = 0

⇒ RA + RB = 2P

∵ ΣFX = 0

⇒ HA = HB

∵ ΣMA = 0

⇒ 2P × 5 - RB × 8 = 0

Again,

∵ ΣMC = 0 (Because it is an internal hinge)

⇒ RA × 4 - HA × 1.5 = 0

HA = 2P and HB = 2P

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