Utilization of Existing Bridges

To save time, material, and labor and to obtain quicker results, existing bridges should always be utilized as far as possible. Unless the bridge is a complete wreck, it will nearly always be easier to repair or strengthen it than to build a new structure. Existing bridges should be examined by an engineer who is familiar with bridge construction in the particular locality. Any bridge built on approved standard design, and the parts of which are in good condition, may be regarded as safe for its rated loading. Any bridge that exhibits a radical departure from standard design should, of course, be looked upon with suspicion. The horizontal and vertical alignments of the structure should be noted, after which all its parts should be examined for weakness or deterioration. The conduct of the bridge as loads pass over it should be carefully observed.

A weak bridge of any type may be strengthened by placing additional trestle bents between its supports, or by strutting its stringers. All bracing should be thoroughly reinforced. Even in the case of a demolished bridge, it will generally be possible to utilize at least its abutments and piers, or what remains of them. A fallen truss may often be raised to position and its undamaged portion made available by introducing a new pier. A few hours' work will often render a weak bridge sufficiently strong to carry military loads; whereas, if it be allowed to break down, extensive reconstruction or even a new bridge may be needed. It certainly is a very poor bridge indeed that cannot be strengthened sufficiently to carry the desired loads, with less labor than would be required to build a new structure; and, in the interests of economy, such strengthening should always be undertaken.

Utilization of Local Resources

To save transportation, to promote mobility, and to meet the frequent emergencies in which no standard materials will be available, the military engineer will often have occasion to build his bridges of any local materials that may be available. Structures built of such materials are generally known as hasty or improvised bridges. While the utilization of local resources may save transportation, it will not economize time in construction. A great deal of time and effort must usually be expended in finding and collecting the available material, and in transporting it to the site of the work; and when it is there, further difficulty will be encountered in adapting the heterogeneous collection to the standard designs, or indeed to any design.

In a wooded area, round timber will be available, and will prove to be very satisfactory for the construction of bridges, though by no means equal to sawed lumber of standard sizes. As before stated, the military engineer does not use round timber from choice, although it may be remarked that bridges constructed of such material have a characteristically military appearance, and sometimes a certain rustic beauty quite pleasing to the