What is a beret piece?

The Bailey bridge comes in two main types: the 321 and the 200. The 321 model has a theoretical weight of 270 kilograms, while the 200 model weighs 292 kilograms. It was invented in 1938 by British engineer Donald West Bailey. This type of bridge is constructed from high-strength steel and consists of lightweight, standardized truss units, along with cross beams, longitudinal girders, decking, abutments, and connecting components. With the aid of specialized installation equipment, it can be rapidly assembled on-site into truss-beam bridges suitable for various spans and load capacities. During World War II, the Bailey bridge was widely used across European and Asian battlefields—either to repair damaged bridges or as temporary structures. After the war, the design was further refined and adapted for civilian applications. In the U.S., an improved version became known as the Acrow Bridge. Meanwhile, China’s highway authorities adopted a design using 16Mn steel and named it the Prefabricated Highway Steel Bridge. A single set of equipment can be used to construct single-lane bridges spanning 9 meters, 12 meters, 15.60 meters, and even up to 63 meters, capable of supporting vehicle loads ranging from Class 10 to Class 80—including cars, trucks, and heavy-duty trailers. Additionally, these bridge components are also extensively utilized as scaffolding or tower structures during construction projects.

The Composition of Beret Pieces

The Bailey panel consists of top chords, bottom chords, main posts, and diagonal braces. The ends of the top and bottom chords feature male-and-female tenons, each equipped with pin holes for connecting to the post frames. The chord members are constructed from two No. 10 channel steels placed back-to-back. The bottom chord is welded to multiple steel plates that have circular holes. Both the top and bottom chords are fitted with bolt holes, enabling connections to reinforcing bars and double-layer trusses. Additionally, the top chord includes four bolt holes specifically designed for attaching support brackets—two of these holes accommodate connections between double or multiple rows of trusses within the same cross-section, while the other two holes facilitate cross-sectional interconnections. When using multiple shell panels as beams or columns, it’s essential to secure the upper and lower sections of the panels together via dedicated support brackets. On the bottom chord, there are four transverse beam bearing blocks with tenon features, which help precisely position the beams in the horizontal plane. At the ends of the bottom chord, the steel web also features two oval-shaped holes, intended for connecting wind-resistant tension rods. Finally, the vertical posts of the Bailey panel are made from No. 8 I-beams, with square holes drilled on one side of the bottom chord member for specific functional purposes.
The beam fixing device is used for assembling beams. The material of the Bailey panels is 16Mn, with each panel weighing 270 kg. The "321" national highway bridge is a prefabricated steel highway bridge characterized by its lightweight structure, convenient disassembly and assembly, and high adaptability—allowing it to be quickly erected using simple tools and manual labor. It is suitable for five types of load classifications: Class 10, Class 15, Class 20 vehicles, Class 50 trucks, and Class 80 trailers. The bridge deck has a clear width of 3.7 meters, enabling the construction of simply supported bridges with spans ranging from 9 to 63 meters. Additionally, this system can also be utilized to build continuous girder bridges.

Bellee Sheet Specifications

The standard specification for Bailey panels is 3 feet by 1.5 meters, and non-standard Bailey panels are also available for customization. Currently, Bailey beams come in two specifications: imported and domestically produced. For domestically produced Bailey beams, the truss nodes are made from 16Mn steel, while the pin shafts are crafted from manganese-titanium steel, and the cotter pins are made of spring steel. The bridge deck and wheel stops are constructed using either pine or cedar wood. The allowable stress for these materials should be increased by 30% based on their basic stress values. If a single steel component exceeds these specified limits, its stress must not surpass 85% of the material's yield strength. In design, the following allowable stresses are applied: - Bending stress, compressive stress, and stress parallel to the wood grain: 16.2 MPa; - Shear stress parallel to the wood grain under bending: 2.7 MPa. The elastic modulus is E = 98.5 × 10⁵ MPa. For the steel used—16Mn steel—the tensile, compressive, and bending stresses are 1.3 × 210 = 273 MPa, while the shear stress is 1.3 × 160 = 208 MPa. For the more complex manganese-titanium alloy, the tensile, compressive, and bending stresses are 0.85 × 1300 = 1105 MPa, with a shear stress of 0.45 × 1300 = 585 MPa. Most of the imported Bailey beams currently available date back to the 1940s. These older models feature a material yield strength of 351 MPa, with an allowable stress of 0.7 × 35 = 245 MPa. Notably, the allowable stress for the pin shafts in these imported beams can be considered equivalent to that of domestically produced pin shafts.