Bailey piece has the characteristics of simple structure, convenient transportation,

quick erection, large load capacity, good interchangeability and strong adaptability.

The "321" steel bridge is a fast assembled bridge developed on the basis of the original British beret truss bridge 

and combined with the national conditions and actual situation of our country, which was finalized and produced in 1965, 

and has been greatly developed in our country.

Bailey piece  widely used in national defense, war preparation, traffic engineering, municipal water conservancy projects, 

and is the most widely used and the best assembled bridge in our country. 

It has the features of simple structure, convenient transportation, quick erection, large load capacity, 

good interchangeability and strong adaptability.

" HD200" assembled highway steel bridge increases the height of truss, improves the bearing capacity, 

enhances the stability, increases the fatigue life and improves the reliability.

Compared with Type 321 steel bridge, the strength is increased by 33% 

and the stiffness is increased by 2.3 times under the same combination.

Scope of application: single lane bridge deck net width 4.2M, combined span 9.14-76.2M, 

two lane bridge deck net width 7.4M, combined span 9.14-57.91M.

Beret pieces can be used for highway bridges, assembling gantry cranes, guide girders, bridge erectors, cradles and so on. 

Bailey truss combination gantry crane, using assembled highway steel bridge components assembled gantry, 

and its span and column height adjustable to adapt to different work sites, widely used in highways, railroads, municipal, 

construction, water conservancy and other construction projects, bridge construction prefabrication yard lifting 

and moving prefabricated components, piers next to the transport and loading of large girders .

Bailey piece by the upper and lower chord, vertical rod and oblique rod welded together, the upper 

and lower chord end of the yin and yang joints, joints with mortar and pestle frame connecting pin holes. 

The stringers of the beret piece are combined by two No.10 channel steel (back to back), on the lower stringers,

 there are several steel plates with round holes welded, 

there are bolt holes in the upper and lower stringers for connecting with the reinforced stringers and double trusses. 

There are also four bolt holes for connecting with the support frames in the upper stringers, 

in which two holes in the middle are for the connection of the double-row or multiple rows of trusses between the same sections. 

The two holes in the middle are for double or multi-row trusses to be connected with the same section. 

The two holes at the two ends are for connection between sections. 

When the multi-row berries are used as beams or columns, the joints of the upper and lower berries must be reinforced with braces.

In the lower chord bar, there are four crossbeam pads with raised tenons on top to fix the position of the crossbeam in the plane, 

and two elliptical holes are provided in the grooved steel web at the end of the lower chord bar for connecting the wind-resistant tie rods. 

The vertical bars of the beret sheet are made of 8# I-beam, 

and there is a square hole on the side of the vertical bar against the lower chord bar, 

which is used for fixing the crossbeam by the crossbeam jig. 

The material of the beribboned piece is 16Mn, and the weight of each piece is 270kg.

"321" steel bridge is assembled highway steel bridge, its biggest feature is: 

lightweight components, easy disassembly and assembly, adaptability, with simple tools and manpower can be quickly built. 

It is suitable for 5 kinds of loads, such as automobile-10 grade,  automobile-20 grade, crawler-50 grade, and trailer-80 grade. 

The net width of the bridge travelway is 3.7m, 

and it can be combined into a variety of spans of simply-supported sorghum bridges within the range of 9m to 63m, 

and it can be constructed as a continuous girder bridge.

There are two kinds of specifications for berber girders: imported and domestic ones, 

domestic berber girders are made of 16 manganese steel for truss joints, chromium-manganese-titanium steel for pins, 

spring steel for pins, T505X for welding rods, and pine or cedar for deck boards and wheel guards. 

The allowable stress of the material is increased by 30% according to the basic stress, 

and the individual steel rods shall not exceed 85% of their yield point when exceeding the above provisions,

And the allowable stresses used in the design are as follows: 

Wood - 16.2 MPa for bending stress, compressive stress and compressive stress along the grain; 

2.7 MPa for shear stress along the grain in the case of bending, and the modulus of elasticity E=98.5×105MPa. 

Steel - 16manganese steel tensile stress, compressive stress and bending stress; 

2.7 MPa for shear stress along the grain in the case of bending, and E = 98.5×105MPa for elasticity. 

The tensile stress, compressive stress and bending stress is 1.3×210=273 MPa; 

shear stress is 1.3×160=208 MPa. 30CrMnTi tensile stress, compressive stress and bending stress is 0.85×1300=1105 MPa;

 shear stress is 0.45×1300=585 MPa. 

The existing imports of beribboned beams more than the 1940's products, the material yield strength of 351 MPa, 

and its allowable strength is 2.7 MPa. 351 MPa, its allowable stress according to 0.7 × 351 = 245 MPa considerations, 

pin allowable stress can be considered with the same domestic pin.