Military

The charts that follow will help give you an accurate estimation of the load-bearing capacity of a road with flexible pavement. Tables 5-3, 5-4, and 5-5 and Figure 5-34 will help determine the road's load-bearing capacity. The load-bearing capacity of a road for wheeled vehicles is made by measuring the thickness of the surface and base course and by determining the type of subgrade material.

The road-classification formula is a systematic way of describing the worst section of a road. Do not confuse it with the route-classification formula. Recorded information from the road-classification formula is included in the route-classification formula. The following paragraphs describe each portion of the formula shown below:

A sample Road Reconnaissance Report is shown in Figures 5-35 and 5-36. The following are examples of the road-classification formula:

• A 5.0/6.2k--road with no limiting characteristics or obstructions, a minimum traveled way of 5.0 meters, a combined width of traveled way and shoulders of 6.2 meters, and a concrete surface.
• B g s 4/5 1 (OB)--road with limiting characteristics of steep gradients and a rough surface, a minimum traveled way of 4 meters, a combined width of 5 meters, gravel or lightly metaled surfaces, and obstructions.
• B c (f?) 3.2/4.8 p (4.3km) (OB) (T)--road with limiting characteristics of sharp curves and unknown foundation, a minimum traveled way of 3.2 meters, a combined width of 4.8 meters, paving brick or stone surface, obstructions and that is 4.3 kilometers longsubject to snow blockage.

NOTES:

2. DA Form 1248 is primarily self-explanatory. However, ensure that a new classification formula is entered each time the road changes significantly, as depicted in Figure 5-36.

A bridge recon must take place to ensure that commanders know what bridge load-carrying capabilities are along a certain route or what material is needed to destroy a bridge. Engineers are responsible for reconning all bridges.

This manual reviews the basics of hasty bridge load-classification procedures and recon procedures for bridge destruction. Appendix B references hasty bridge classification. (Refer to FM 5-446 for a complete discussion of bridge-classification procedures.) The Sheffield Method for bridge destruction is discussed in FM 5-250.

The method of bridge load classification covered in Appendix B is adequate for most bridge recons. It allows vehicle operators to avoid bridge failure by determining what can cross the bridge without causing damage. Vehicle operators may cross without restrictions if their vehicle's load class (including the load) is less than or equal to the bridge's load class. The vehicle's load class can be found in the vehicle's TM.

Appendix B covers the most common bridges in existence today, including a--

• Timber or steel trestle bridge with timber deck.
• Steel-stringer bridge with concrete deck.
• Concrete steel-stringer bridge.
• Concrete T-beam bridge with asphalt surface.
• Masonry arch bridge.

To classify a bridge (see Appendix B), you must know the information concerning the bridge's basic components, including the following:

• Approaches (the portions of a route leading to a bridge). Approaches may be mined or booby trapped, requiring thorough investigation during a recon.
• Substructure (lower part of a bridge). The substructure consists of the abutments and intermediate supports that transfer the bridge's load to the ground. It is important to measure all aspects of an abutment, including its height, width, and length; the abutment wings; and the intermediate supports for bridge demolition missions. It may be more feasible to destroy the intermediate supports or abutments when compared to the rest of the bridge structure.
• Superstructure (the upper part of a bridge). The superstructure consists of the following components (see Figure 5-37):

It is essential to note the bridge's general condition, paying particular attention to evidence of damage from natural causes (rot, rust, and deterioration) or combat action. Classification procedures presume that a bridge is in good condition. If the bridge is in poor condition, the class obtained from mathematical computations must be reduced according to the classifier's judgment.

Table 5-8 lists width restrictions for bridges. If a one-lane bridge does not meet width requirements, post a rectangular warning sign under the classification sign showing the actual clear width (see Figure 5-38). If this is a route restriction, annotate it in the route-classification formula. For a two-lane bridge, downgrade the two-way classification to the highest class for which it does qualify (one-way class is not affected). Post a limited-clearance sign if the overhead clearance is less than 4.3 meters. These signs must be a minimum of 40 centimeters in height or width, with a yellow background, and the appropriate description in black letters. Separate rectangular signs are used if necessary to denote width limitations, height limitations, or other technical information. The same signs are used for tunnels, if applicable.

Posting standard bridge signs and other signs needed for proper and efficient traffic control across a bridge is an engineer's responsibility. Additional signs are used when it is necessary to warn vehicles that require special controls while crossing. When necessary, holding areas, turnouts for parking and unloading vehicles, and checkpoints are installed near bridges to provide the necessary control during crossings.

Bridge information is recorded on a map or overlay by using the full NATO bridge symbol (see Figure 5-39). It is different from an on-site bridge-classification sign; do not confuse the two. The information necessary for the full bridge symbol includes the--

• Bridge's serial number.
• Geographic location.
• Bridge's MLC.
• Overall length.
• Traveled-way width.
• Overhead clearance.
• Available bypasses.

A bridge serial number is assigned for future reference and is recorded in the symbol's lower portion (assign a number according to the unit's SOP). For proper identification, do not duplicate serial numbers within any one map sheet, overlay, or document. The unit's S2 can obtain special maps containing bridge information for developed areas of the world.

The bridge's geographic location is shown by an arrow extending from the symbol to the exact map location. The bridge's MLC number is shown in the symbol's top portion. This number indicates the bridge's carrying capacity; classifications for both single- and double-flow traffic are included. In those instances where dual classifications for wheeled and tracked vehicles exist, both classifications are shown.

The bridge's overall length is the distance between abutments, measured along the bridge's centerline. This figure is placed to the right of the circle and is expressed in meters.

The minimum lane width is the clear distance between curbs. Place this figure below the symbol and express it in meters. Bridges may be obstructions to traffic flow because the traveled-way width of the overall route may be reduced on the bridge to below the minimum standards prescribed in Table 5-1.

The overhead clearance is the minimum distance between the bridge's surface and any obstruction above it. This figure is shown (in meters) to the left of the symbol. Underline any overhead clearance less than the minimum required by the bridge class number (see Table 5-9). Unlimited overhead clearance is indicated by the symbol . Often a telltale (see Figure 5-40) or other warning device is placed before the bridge to indicate overhead-clearance limitations. Report any overhead clearance less than 4.3 meters as an obstruction in the route-classification formula. A question mark is used to indicate information that is unknown or undetermined and is included as part of the bridge recon symbol. See Appendix E for signs used to mark roads and bridges.

Railway bridges, which could be used by road vehicles in an emergency, are indicated as use easy or use difficult. Samples of the full NATO bridge symbol used to indicate a railway bridge can be found in the glossary.

NOTE: A railroad bridge is considered to be easy to adapt for use if it can be adapted in less than 4 hours with 35 soldiers and the appropriate resources.

A systematic bridge recon obtains valuable data. However, this data will not benefit anyone unless it is recorded in an organized manner. Use DA Form 1249 to report information concerning any reconned bridge, as follows:

• Column 1. Record the assigned serial number. This number matches the serial number used in the bridge symbol of the route-classification overlay.
• Column 2. Record the grid coordinates, with the map identifier, of the actual bridge site.
• Column 3. Record horizontal clearance information, in meters. Horizontal clearance is the clear distance between the inside edges of the bridge structure, measured at a height of 0.3 meter above the surface of the traveled way and upwards. However, horizontal clearance for truss bridges is measured 1.21 meters above the traveled way. Any horizontal clearance less than the minimum required for the bridge's roadway width (as shown in Table 5-8) is underlined. Unlimited clearance is indicated by the symbol .
• Column 4. Record under-bridge clearance, in meters. It is the clear distance between the underside of each span and the surface of the water. The height above the streambed and the height above the estimated normal water level (pertaining to the appropriate bridge type) are included in this column for each span.
• Column 5. Record the number of spans. Spans are listed in sequence starting from the west. If the bridge is oriented more north to south, start with the northern most span and work south. Place the letter N in column 5 before the span and list in sequence.
• Column 6. Record the type of span construction. Refer to the diagrams in Figure 5-41 and Table 5-9 for this information.
• Column 7. Record the type of construction material. Refer to Table 5-10 for this information.
• Column 8. Record span length, in meters. This is a center-to-center spacing between bearings. The sum of the span length may not equal the overall length. Spans that are not usable because of damage or destruction are indicated by the pound symbol (#), placed after the dimension of the span length. Spans that are over water are indicated by placing the letter W after the dimension of the span length (see Figure 5-42).

When an abbreviated bridge symbol is used or when a recon mission requires it, columns are added to give the MLC, overall length, roadway width, overhead clearance, and bypass possibilities (specify use easy, use difficult, or use impossible). Do not forget to indicate whether the bridge is simply supported or continuous (see Figure 5-43).

Show as much information as possible when sketching the bridge on the backside of DA Form 1249 (see Figure 5-44).

Bypasses are detours along a route allowing traffic to avoid an obstruction. Bypasses limited to specific vehicle types, such as those capable of swimming or deep-water fording, are noted on the recon report. Bypasses are classified as easy, difficult, or impossible. Each type of bypass is represented symbolically on the arrow extending from the tunnel, ford, bridge, or overpass symbol to the map location (see Table 5-11).

A bypass is considered easy when the obstacle can be crossed within the immediate vicinity by a 5-ton vehicle without work to improve the bypass. The bypass is considered difficult when the obstacle can be crossed within the immediate vicinity; however, some work is necessary to prepare the bypass (ensure that the estimation of time, troops, and equipment necessary to prepare the bypass is included on the recon report). The bypass is considered impossible when the obstacle can be crossed only by repairing the existing bridge or tunnel, building a new bridge or tunnel, or providing a detour.