LIGNO CONCRETE. 



A LARGE FIELD FOR THE UTILIZATION OF. COLONY 

 HARDWOOD. 



By L. P. Hodge, Assoc. M. Inst. O.E. 



In these scientific days most of us are sufficiently acquainted with 

 Physics to be aware that when a beam is loaded the upper portion is com- 

 pressed and the lower portion is extended. The bending of a piece of 

 indian rubber will make this quite clear. Consequently the strength of 

 any beam depends upon the ability of the upper portion to resist crushing 

 (or "compression " as it is more usually termed by the Engineer) and 

 that of the lower portion to resist elongation (or " tension "). 



Concrete, being composed of small pieces of stone or some other hard 

 material, has naturally a high resistance to compression. It has, however, 

 so poor a resistance to tension that it is practically negligible. This 

 defect has been overcome of late years by inserting iron or mild steel 

 rods in the lower or tension part of the beam to take the whole of the 

 tensile stross. This enables the beam to be made much smaller than 

 would otherwise be necessary at a considerable saving in cost. Such 

 concrete is termed " reinforced " because the rods reinforce the resistance 

 of the concrete to tension, and when iron or mild steel rods are employed 

 the conjunction is termed " ferro " concrete (L. ferrum, iron). 



Iron or mild steel was selected for reinforcement on account of its 

 high resistance to tension, but there seems no reason why other materials 

 should not be substituted, the area in tension being increased as the 

 resistance diminishes. 



Experiments with concrete beams reinforced with wood by methods 

 suggested by Mr. G. O. Case were carried out before the war and the 

 results tabulated in an article by C. A. M. Smith, M. Sc. in " The 

 Engineer " of December 16th, 1910, who termed the combination "ligno 

 concrete." (L. lignum, wood) The woods experimented with were teak, 

 deal, oak. ash, mahogany, Jarrah, tallow wood, and stringy bark, and to 

 quote from the article "the results seem to show that equal strength 

 " can be gained either with wood or iron reinforcement, although, of 

 "course, the section of the wooden bars must of necessity be considerably 

 " larger than is required with steel bars. On the other hand this larger 

 " section is more than counterbalanced by the fact that wood is so much 

 " cheaper." 



One result of the present War has been to considerably increase the 

 cost of iron or mild steel reinforcement, and as present prices are likely 

 to be maintained, if not increased, for many years to come, owing to a 

 large anticipated demand for structural steel after Peace has been declared, 

 the use of " ligno concrete," if better known, is likely to become extensive. 



