HOW TO PERFORM STATIC BENDING STRENGTH TEST OF TIMBER ?

STATIC BENDING STRENGTH TEST

BY ONE POINT LOAD TEST : 

OBJECTIVE

To determine the bending strength of timber by one point load test under static load.

EQUIPMENT

• Static bending test equipment.

SAMPLE/SPECIMEN

The specimen may be 50 × 50 × 750 mm or 20 × 20 × 300 mm prepared for test.

PROCEDURE

• The test specimen is supported on the rig. The load is applied continuously at a constant rate of 2.5 mm per minute in case of 50 × 50 × 750 mm and 1.0 mm per minute in case of 20 × 20 × 300 mm. 

• Deflections of the neutral plane at the centre of the length are measured with respect to the points in the neutral plane above the supports. Deflections of the neutral axis are measured at the centre of the beam. 

• Deflection is measured at suitable load intervals such that about 8–10 readings are available up to limit of proportionality. 

• Beyond the limit of proportionality up to maximum load or beyond maximum load the test is continued until a deflection of 150 mm for 750 mm and 60 mm for 300 mm specimens is reached. or the specimen fails to support 1000 N for 50 × 50 × 750 mm or 200 N for 20 × 20 × 300 mm specimens, whichever is earlier.

• The failure of the specimen is recorded according to its appearance and development. 

• The readings of deflections and the load recorded and a load deflection curve is drawn.

CALCULATION

The various characteristics are determined by the following formula and from the load-deflection curve. 

where

P = load at the limit of proportionality, the point in load-deflection curve at which the graph deviates from the straight line.

l = length of specimen

b = width of specimen 

h =  height of the specimen 

P = maximum load

delta = deflection at the limit of proportionality

C = area constant

A = area of load-deflection curve up to limit of proportionality

A = area up to maximum load

A = area up to the final reading when total work is required