Engineering Mechanics

Chapter 35 : Hydrostatics „„„„„ 739

Resultant pressure on bulkhead

Fig. 35.24.
The pressure diagram or both sides of bulkhead is shown in Fig. 35.24. We know that the
pressure BO = w 1 H 1 = (9.8 × 0.78) × 1.8 = 13.76 kN/m^2

Similarly, pressure OE =w 2 H 2 = (9.8 × 0.88) × 0.9 = 7.76 kN/m^2

∴Pressure per metre length of the bulkhead

P= Area of triangle ABO – Area of triangle DOE

=

11

(13.76 1.8) – (7.76 0.9) 8.89 kN

22

××=

and resultant pressure on 3 m long bulkhead

= 3 × 8.89 = 26.67 kN^ Ans.

Position of the resultant pressure

Let h = Height of the point of the resultant pressure from O.

Taking moments of all the pressures about O, and equating the same,

Ph× = [Pressure ABO × (1.8 ×

1

3

)] – [Pressure DOE × (0.9 ×

1

3

)]

8.89h =[(

1

2

× 13.76 × 1.8) 0.6] – [(

1

2

× 7.76 × 0.9) 0.3]

= 7.43 – 1.05 = 6.38

h =

6.38

0.72 m

8.89

=^ Ans.

EXERCISE 35.4

1. A masonry dam 15 m long contains 6 m deep water. Find the total pressure on the dam
   and the point where it acts. [Ans. 2646 kN; 2 m from the water bottom]


2. A rectangular container 2.5 m wide has a vertical partition wall in the middle. It is filled
   with water to a height of 1.5 m on one side, and oil of specific gravity 0.9 to a height of
   1.2 m on the other.
   Find the resultant thrust on the partition wall and its point of application.
   [Ans. 11.7 kN; 0.63 m from the bottom of the partition wall]