Building Materials, Third Edition

‡2—2‡2€

™ IIW

specified gauge length of 150 mm at regular intervals of torque such that 8 to 10 readings are
available upto the limit of proportionality. Readings are continued well beyond the proportional
limit and final reading of torque at failure are recorded. The torque-twist curve is drawn. The
torque and angular twist at proportional reading limit is read from the curve. The various
characteristics are determined by the following formulae:

p



2R

IW „2€

™22„



S. No. Characteristic Unit Formula

1. Torsion shear stress at proportional N/mm^2

2

3

M

limit πr

2. Torsion shear stress at maximum N/mm^2

2

3

M′

torque πr

3. Torsion modulus of rigidity N/mm^2

2

4

ML

πr

where M = torque at the limit of proportionality
r = radius of the portion of the specimen under gauge
M = maximum torque
L = gauge length
= the angular twist of one end relative to other end at a distance of L

w2g2„

The moisture content of timber and products made of it can be determined by any of the
following methods.

y&E) w is most reliable, except where certain timber species containing volatile
oils (like deodar) are involved. The method is, however, time consuming and requires cutting
of the timber to be tested. Test specimens consisting of a cross-section, 15 to 20 mm long in the
direction of the grain, free from all defects, are cut from each sample.
Immediately after each test specimen is cut and loose splinters and saw dust are removed by
brushing or scraping, it is weighed. The weighed test specimens are completely ovendried at
103  2°C for 12–18 hours. The oven-dry mass of all the test specimens, is now determined
directly after removing from the oven, or after cooling them in desiccators to near room