THEORY AND PRACTICE OF CONCRETE-IRON CONSTRUCTIONS. 125 



were inserted near the top surface two at each support. 

 The weld of the main iron bars being situated at the centre 

 of the spans, four additional bars 5 feet long by f inch 

 diameter were inserted at these places to provide against 

 risk of bad welding. The arrangement of the main bars as 

 shown provides for the ends of the beams being partially 

 fixed. Three-eighth inches diameter iron stirrups or struts 

 were placed at varying distances along the length of each 

 beam in order to assist to take up the shearing stresses. 

 The plate which was 2\ inches thick and 4 feet 1\ inch 

 wide contained f inch diameter iron bars alternately near 

 the lower and the upper surface. 



After the piers were built the centreings for the beams 

 and plate were fixed, and the iron rods placed in the posit- 

 ions shown and described, and carefully held there during 

 the process of encasing them with the concrete. The con- 

 crete which consisted of 1 part " Union Brand" tested Port- 

 land cement, 1 part Nepean sand, 2 parts f inch Milestone 

 shivers, containing all the small screenings and dust from 

 the crusher, or subdivided 1 cask of cement, 4 cubic feet of 

 sand, 4*62 cubic feet of dust, 6*38 cubic feet of shivers, 

 bulked when mixed and wetted of one half of a cubic yard. 

 It was well worked into place in a plastic state. The iron 

 bars were of Lithgow manufacture and withstood a break- 

 ing strain of from 24 to 26 tons per square inch, with an 

 elastic limit of two-thirds the breaking strength. 



The test took place in July 1903, being seven weeks after 

 its construction. Levers were fixed at three points on each 

 beam, and also on the plate, viz., at \ centre, and f span, 

 in order to measure the deflections. The points of the 

 levers were steel shod and rested on cement pats attached 

 to the beams and plate, whilst the other ends moved against 

 graduated scales. Verniers were also attached to the side 

 of the beams to ascertain if any movements took place 

 sideways under the loading. 



