. Ontario Sessional Papers, 1907, . abridge are only 1-4 and 5-16 of an inch thick, it is evident that rust, actingon both sides, can greatly weaken the structure. Connections, too, requirespecial care, to see that they are fully protected. Bridge companies rarelyexercise sufficient care, when erecting a bridge, to see that the scale is fullyremoved and the bridge properly painted. The materials commonly used in painting bridges are red lead mixedwith linseed oil, and oxide of iron, with linseed oil. The former is much themore desirable paint. These are subject to much adulteration an
. Ontario Sessional Papers, 1907, . abridge are only 1-4 and 5-16 of an inch thick, it is evident that rust, actingon both sides, can greatly weaken the structure. Connections, too, requirespecial care, to see that they are fully protected. Bridge companies rarelyexercise sufficient care, when erecting a bridge, to see that the scale is fullyremoved and the bridge properly painted. The materials commonly used in painting bridges are red lead mixedwith linseed oil, and oxide of iron, with linseed oil. The former is much themore desirable paint. These are subject to much adulteration and care hasto be exercised to procure reliable materials. Lamp-black added to red leadwill change the color to a rich chocolate, and will not injure the paint. Concrete Flooring. All steel bridges now being built should have concrete floors, or shouldat least be made strong enough to carry them. When erecting a bridge itis cheaper and more satisfactory to provide for this additional strength ofbridge, than to reinforce the bridge WAUiiEN TiiUfcitt Bridge i.\ ^NIiudle^ to carry a coiuretc floor. Bridge floors of plank usually wear out in from two to four years, andare a constant matter of expense for renewal or repair. With the increasingprice of lumber, and the inferior quality now obtainable, it is only a matter■ of time until all bridge floors must be made of concrete. Concrete adds a considerable load to the dead weight of the bridge, butthis is largely compensated by the extent to which it distributes the live a plank floor, the weight of every vehicle passing over it is transmittedto the individual members of the bridge, causing a constant jarring and dis-tortion that is very destructive to the joints. With concrete, on the otherhand, the weight of a passing vehicle is spread over a greater area of thebridge structure, the floor being a monolith and distributing the live loadover a much greater bearing than can each plank. In this way the
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