02 



Timehri 



According to Mr. Smith's article previously referred to :: providing 

 " proper adhesion takes place between the wood and the cement (and 

 " tests have shown this to be the case) the timber cannot fail by longi- 

 " tudinal shear, but can only break in pure tension.'" It will follow there- 

 fore that, other things being equal, preference will be given to that wood 

 ■which has the highest resistance to tension.'' According to Rivington, 

 Part IV. Table 1, the relative resistance to tension of the leading timbers 

 of the world are as follow : 



It will be at once apparent that with the exception of English Oak 

 and Beech, which are not available in large quantities, there will be only 

 teak to compete with our greenheart as the most suitable wood for ligno 

 concrete. And of the two, as will be seen from the above figures, green- 

 heart has the advantage in uniformity, a matter of great moment in 

 reinforcement. 



In connection with the bridging of the East Coast Road 

 de%'iation last year the writer experimented with burnt earth reinforced 

 concrete beams of equal section and span, substituting greenheart bars tor 

 iron in the ratio of their assumed safe resistance to tension. 



The results of the experiments are shown graphically in Figures 1 and 

 2. It will be seen that the ligno concrete beam failed with only r '„ less load 

 than its ferro concrete competitor. It had, however, the advantage of nine 

 days in age. A burnt earth ligno concrete pile was also cast as in Fig. 3 

 and successfully driven about 17 feet through clay as one of the abutment 

 piles of the iron bridge over Triumph west side-line trench. It may be 

 mentioned incidentally that this bridge is the first known to the writer, 

 in which burnt earth piles have been employed. It is also the firsl 

 instance known to him in which ligno concrete construction has figured in 

 a permanent structure. 



Taking the cost of small greenheart scantling at $100 per 1,000 ft. 

 B.M. = $1.20 per c. ft. and common iron bars at £15 per ton= $15.58 per 

 c. ft. (present prices) the ratio of cost is about rVi while the ratio of safe 



