Figs. 992, 993, 994, 995, 996. This is designed as for a light road bridge for use in country districts, and is for a live load consisting of a 12-ton roller. Figs. 997, 998, and 999. A road bridge, capable of carrying a 15-ton traction engine, or road roller about similar weight.

Figs. 1000, 1001, 1002, and 1003. Road bridge, capable of carrying a 15-ton traction engine hauling a trolley when fully loaded weighing 20 tons.

The span for this type of flooring should not be more than about 36 ft., and although the flooring in this instance consists of E troughing, viz. made up of troughs and flats, for smaller spans ordinary sections of troughing such as C and D might be used.

Figs. 1004 and 1005. Road bridge suitable for ordinary road traffic, designed to carry a 15-ton traction engine hauling a trolley weighing 20 tons when fully loaded.

Figs. 1006 and 1007. Road bridge in two spans suitable for carrying ordinary road traffic over a wide shallow stream, where it is possible to obtain a good foundation in the bed of the stream for the central pier. Designed to carry a 15-ton traction engine hauling a trolley 20 tons in weight.

Figs. 1008 and 1009. Road bridge designed to carry a 10-ton road roller. By increasing size of girders at sides of bridges a stone or brick parapet may be used in place of steel hand-railing.

Figs. 1010, 1011, and 1012. Long span road bridge designed to carry a live load consisting of a 14-ton traction engine hauling a trolley when fully loaded weighing 20 tons. Also sufficiently strong to support a uniformly distributed load of 75 lbs. per sq. ft., thus providing for bridge being crowded with people.

Finally, owing to the courtesy of H. C. S. Ree, Esq., M.I.C.E., engineer to the Cardiff Railway Co., and Messrs Andrew Handyside & Sons of Derby, I am able to illustrate in figs. 1013 to 1017 a swing bridge, with the following particulars:

Total weight of superstructure 254 tons, approximate total swinging weight 325 tons.

The bridge turns on a central hydraulic pivot with a balance roller at the rear end, this end being supported on wedge bearings, withdrawn by means of hydraulic lifting and lowering presses, so as to tilt nose end of girder clear of bearings before swinging. Hydraulic power supplied by horizontal rams on shore through a wire rope which turns a drum on the under side of the bridge. The hydraulic power plant was made by Messrs W. G. Armstrong, Whitworth & Co., Newcastle-on-Tyne.

In bridges which have straight bottom booms and curved top ones the stress diagrams, when drawn in accordance with the principles set forth in Chapter XII., become rather complicated and unsuitable.

The matter, which is of course of importance to the bridge designer, is greatly simplified by a method introduced by an engineer, Mr Rinquist, whereby, by means of a few simple lines, all the stresses can be readily got at. The procedure is fully dealt with in Professor Jamieson's Applied Mechanics, to which the reader is referred, because, for obvious reasons, we do not discuss the matter here. It is also equally applicable to girders having both booms curved.

Previous mention has been made of the use of turnbuckles for tightening up tie-rods, provided that the design is properly carried out, and that the rods are thickened if necessary for plus threads; their efficiency is good. An alternative method of connecting tie-rods is by means of a sleeve and cotters,

=

=

Let f safe tensile strength of material employed, and f, safe shear ='75ft.

as shown by figs. 1018 and 1019, which are subject to the following calculations: