A bridge is a structure that is erected over obstacles such as a river or other watercourse, a chasm, or a railroad to make a passageway from one bank to the other. A bridge is usually constructed of wood, stone, brick, concrete, steel, or iron. This book identifies methods and procedures for performing bridge reconnaissance, vehicle and bridge classification, and analytical design of superstructures and substructures; constructing bridge connections; and repairing or reinforcing existing bridges.
Reconnaissance is critical to any military operation and for analyzing existing and potential bridge sites. Information must be gathered for bridge use and construction that might normally be overlooked. The engineer and reconnaissance elements must be knowledgeable and prepared for the mission. Proper vehicle and bridge classification is also an important engineer responsibility that helps keep lines of communication (LOC) through the preservation of existing bridges in the TOs.
The purpose of bridge reconnaissance is to collect data that is necessary to support operational planning and movement. Existing bridges are inspected to determine their load-carrying capacity and the requirement for repair and reinforcement. The alternatives might revolve around the erection of a new semi permanent bridge or the repair of a damaged permanent structure. When a demolished bridge is to be replaced, reconnaissance should include a report of the serviceability of structural members and accessories, which might be useful for the contemplated construction.
|This chapter implements STANAGs 2010 (Edition 5)
and 2021 (Edition 5) and QSTAG 180 (Edition 4).
Rapid movement on the battlefield requires existing road networks or natural high-speed avenues that cross an assortment of wet and dry gaps. Many existing bridges in the TOs will adequately support military loads and only need to be classified for safe use. Gap crossings might be needed where none currently exist. Reinforcing or repairing a bridge can serve tactical purposes; however, mobility of the force is the key issue.
1-1. To maintain a high momentum, the forces must use bridges in the order discussed below. Each method has specific benefits.
EXISTING BRIDGES, INTACT
1-2. Engineers should first consider the bridges in the TO that do not need repair. Engineers must classify them for military use before using. The classification depends on the type of construction ( concrete, steel, timber, or suspension) and the bridge's intended use. The bridge and vehicle classification systems established by STANAGs 2010 and 2021 and QSTAG 180 permit the use of bridges at their maximum safe military capacities. The classification systems relate bridge capacity to the overall loading effect a vehicle might impose on a bridge. The classification systems-
- Protect existing bridges from overload and subsequent damage or failure.
- Prevent loss or damage of equipment and costly time-consuming delays due to bridge failure.
DETOURS AND BYPASSES
1-3. Engineers should consider detours and bypasses after analyzing the existing bridges. The assumption is that finding and using detours and bypasses is quicker than reinforcing or repairing existing bridges. The engineer commander will determine the best alternative. Road and approach conditions (along with detours and bypasses) are important considerations. The work necessary to make the roads usable might outweigh the advantages of a detour or bypass. Traffic-supporting properties, grade and alignment, and sharp curves or corners involving clearances are also important considerations. Usually, detours and bypasses are-
- Alternate routes over undamaged bridges.
- Alternate routes over minimally damaged bridges.
- Alternate highway routes over railroad bridges.
- A grade crossing around an overpass.
- Local ferries, rafts, or barges.
- Ice bridges.
EXISTING BRIDGES, REINFORCED OR REPAIRED
1-4. The third consideration is to reinforce or repair existing bridges. Frequently, military load-carrying requirements will necessitate this action.
1-5. The fourth consideration is tactical bridges, which are generally used in an assault and provide a rapid means of crossing gaps. The bridges' assets are temporary, and advancing forces should remove and carry the bridges forward as they advance. Sustained mobility of forces and logistical support depend on the tactical bridges, which support existing permanent bridges. Stan dard, tactical bridges are discussed below.
Armored Vehicle-Launched Bridge
1-6. The armored vehicle-launched bridge (AVLB) can carry military-load-classification (MLC) 70 traffic over a 48-foot-wide gap and MLC 60 traffic over a 60-foot-wide gap. The AVLB's eight main sections come with the necessary bracing, diaphragms, and pins. The AVLB-
- Is crew-served and highly mobile.
- Can be rapidly launched or retrieved from either end with minimum personnel exposure to enemy fire.
- Can be emplaced with little or no site preparation.
1-7. Prior reconnaissance of potential launch sites is often limited to preliminary studies of maps, aerial photos, and intelligence reports. Consider the weight of the AVLB (57 tons with the M60 chassis launcher) when selecting a launch site. See Technical Manual (TM) 5-5420-203-14 for more information on the AVLB.
1-8. The medium-girder bridge (MGB) is a lightweight, hand-built, easily transportable bridge that can be erected in various configurations to cover a full range of military and emergency bridging requirements. The deck units are fitted between two longitudinal girders to provide a 13-foot-wide roadway. A bridge set has sufficient components to construct one 102-foot bridge in a double-story configuration or three 31-foot bridges in a single-story configuration. The MGB is constructed on rollers and launched using a detachable launching nose. It is transported on 5-ton trucks with trailers.
1-9. The ribbon bridge is a floating modular asset with an integral superstructure and floating supports. Individual bays are joined to form rafts or bridges for river-crossing operations. Ribbon bridges and rafts provide a reliable and responsive means of crossing wet gaps.
1-10. Expedient bridges, built with locally procured materials, might be substituted for tactical military bridges if tactical bridging assets are not available.
1-11. Semipermanent, fixed, or float LOC bridges replace tactical assets until permanent bridges are constructed. The Army currently uses the Bailey bridge, Army Facilities Components System (AFCS) preengineered bridges, and nonstandard fixed bridges. See FM 5-277 for more information on the Bailey bridge. For information on in-depth design methods for permanent bridges, see the latest edition of the Standard Specifications for Highway Bridges (published by the American Association for State Highway and Transportation Officials [ AASHTO]). See TM 5-304 for more information on AFCS bridges.
1-12. Engineers design nonstandard fixed bridges to match specific conditions of a particular site when standard fixed bridges are not available or are needed forward of the proposed bridge site. Available structural materials, site details, proposed traffic, and time will influence the design. While constructing nonstandard fixed bridges is usually limited to rear areas, the tactical situation might require reinforcing or repairing a damaged bridge or constructing a new bridge in the combat zone (CZ).
1-13. The design of military nonstandard fixed bridges is similar to that of civilian fixed bridges. Military methods, however, include several simplifications and assumptions about the loads to be carried, the type of construction, and the material types available. Therefore, use the methods in this manual for temporary (3 to 5 years) military construction. Use the analytical method whenever possible. The design chapters in Part Three of this manual outline the specific assumptions made for military design.
ARMY FACILITIES COMPONENTS SYSTEM
1-14. The Theater Construction Management System (TCMS) is an automated personal computer (PC) based construction planning, design, management, and reporting system that is used by military engineers for contingency construction activities. Its primary purpose is to support outside continental US (OCONUS) requirements. It combines state-of-the-art computer hardware and software with AFCS design information to support and enhance the accomplishment of engineer mission activities in the TO or other mission arenas.
1-15. The TCMS is the approved method for distributing AFCS designs and related information according to Army Regulation (AR) 415-16. TM 5-304 is the AFCS user's manual. The TCMS is updated and distributed annually.
1-16. The TCMS provides the automation tools necessary to use the AFCS information. This enhances the accomplishment of TO engineering and construction activities and supports mission requirements.
1-17. The AFCS does not include bridge installations (sets of material). The TCMS includes bills of materials with material cost data, construction drawings, and labor and equipment estimates (LEEs) for 84 bridging facilities. The US Army Corps of Engineers (USACE), Engineer Support Center, Huntsville, Attention: CEHNC-ED-SY-F, 4820 University Square, Huntsville, Alabama 35816-1822, maintains current data for facilities and installations in the AFCS.
1-18. A physical plant (such as real estate and improvements [including a separate building, a bridge, or a piece of equipment]) that serves a function is referred to as a facility. A facility is any piece of equipment that, as an operating entity, contributes or can contribute by providing some specific type of physical support. Facilities are uniquely identified in the AFCS by a seven-character alphanumeric code (five numeric and two alpha characters) (for example, 85120NA: BRIDGE, TIMBER FRAME TRUSS, FOR 30-FOOT SPAN, DOUBLE LANE, CLASS 60). AFCS numbers are based on the facility class and construction category codes listed in AR 415-28. Each facility has an associated facility number, description, unit of issue, shipping volume, shipping weight, and cost. Several facility numbers might be required to complete a functional facility.
LABOR AND EQUIPMENT ESTIMATES
1-19. The LEEs within the TCMS are divided into three categories-vertical, horizontal, and general. This information can be exported to project management software and presented in any desired format.
1-20. Vertical data is an estimate of the number of hours (by skill) required to construct a particular facility. A military occupational specialty (MOS) represents each skill (such as carpenters or electricians).
1-21. Horizontal data is an estimate of the number of hours of equipment needed to construct a facility. For example, bulldozers and backhoes.
1-22. General data is an estimate of the unskilled labor required in each area (horizontal and vertical). The general data consists of two figures-the vertical workhours and the horizontal workhours.
1-23. Local Army engineer units research bridges and maintain files on the bridges in their areas of operation (AOs). This information is passed to engineers at a higher level for consolidation and dissemination to all interested parties. As-built plans for military bridges are also available. Foreign countries maintain engineer intelligence studies that can provide classification information.
1-24. Local civilian authorities are the most important source of bridge-classification information. In most jurisdictions, as-built plans and information on material properties are available. Local and state officials in the US and most foreign countries will impose maximum load limits or permissible stresses on bridges. Consult with these officials to determine the maximum MLC of bridges for peacetime or military purposes.
1-25. Engineer units are responsible for classifying bridges of military significance (using the analytical method if possible). If a nonengineer unit classifies a bridge, a responsible engineer officer should verify the classification as soon as possible. If the temporary class is accurate, it may be used as the permanent class. The engineer determining the actual bridge class will post the permanent markings.
1-26. Engineer units will maintain records for bridges in its AOs. As a minimum, the file should contain a copy of DA Form 1249 and other sketches, plans, calculations, and assumptions that were used to determine the bridges' classification. The unit should also maintain files of as-built plans of military nonstandard fixed bridges, along with the classification calculations. In many cases, the actual classification is higher than the design classification due to rounding in the design process.
1-27. Appendixes A through H contain the following additional information:
- Appendix A contains an English-to-metric measurement conversion chart.
- Appendix B contains information on vehicle classification.
- Appendix C contains information on timber properties.
- Appendix D contains information on steel properties.
- Appendix E contains information on structural mechanics.
- Appendix F contains classification examples.
- Appendix G contains information on concrete properties.
- Appendix H contains information on soil properties.
- Appendix I contains superstructure design examples.
|Join the GlobalSecurity.org mailing list|