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# Shear Strength Test (IS: 1121 (Part IV)), Using Jhonson Shear Tool

Posted On :  14.07.2016 07:08 pm

The test is carried out either in Jhonson shear tool (Fig. 3) or Dutton punching shear device (Fig. 4). Three test pieces are used for conducting the test in each of the saturated and dry condition.

Shear Strength Test (IS: 1121 (Part IV))

The test is carried out either in Jhonson shear tool (Fig. 3) or Dutton punching shear device (Fig. 4). Three test pieces are used for conducting the test in each of the saturated and dry condition.

Test piece for use in Jhonson shear tool should be bars 50 � 50 mm in section and not less than 100 mm in length and that for use with the Dutton punching shear device should be slabs 30 mm in thickness, 100 mm in width and not less than 100 mm in length.

Using Jhonson Shear Tool

The test piece is carefully centred in the shear tool and the bolts drawn up tightly. The tool is then centred in the testing machine with the centre of the spherical block in contact with the centre of the top portion of the plunger of the shear tool. The speed of the moving head of the testing machine during load application should not be more than 1 mm/min. During the test, the beam of the testing machine should be kept constantly in floating position. The shear strength of test piece is calculated by

S=W/2A

where

S = Shear strength (N/mm2) W = total maximum load (N)

A = area of the centre cross-section of test piece (mm2)

The average of all the three results separately for each condition is calculated and taken as the shear strength of the test piece.

Using Dutton Punching Shear Device

Centre lines are laid over one surface of the slab. Thickness of the slab is measured at three points approximately equidistant around the circumference of a 50 mm circle centred on the intersection of the two center lines. The test piece is centred in the punching device keeping it under the plunger. The punching device is then centred in the testing machine with the centre of the spherical bearing block in contact with the centre of the top portion of the plunger of the shear device. The speed of the moving head of the testing machine during load application should not be more than 1 mm/min. During the test, the beam of the testing machine should be kept constantly in floating position. The shear strength of the test piece is calculated by

S= WtWi SDT

where

S = Shear strength (N/mm2) Wt = total maximum load (N)

Wi = initial load (N) required to bring the plunger in contact with the surface of specimen D = diameter (mm) of the plunger

T= thickness (mm) of the specimen

The average of all the three results separately for each condition is calculated and taken as shear strength of the test piece.

Tags : Civil - Construction Materials: Stones, Bricks,Concrete Blocks
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