1. By section form of main arch ring: Steel box arch, steel pipe arch, steel truss arch
2. By space posture of two arch ribs: Parallel arch ribs, basket arch ribs, butterfly arch ribs
3. By position of carriageway system: Upper bearing type, middle bearing type and lower bearing type arch bridge
4. By layout of boom: Parallel vertical boom, inclined boom, mesh boom

Steel arch bridges have both composite system arch bridges and simple system arch bridges.

• Simple system arch bridge: Only the arch ring is the main force component, and the simple system is a thrust arch structure, and the thrust of the arch is directly borne by the pier or foundation.
• Combined system arch bridge: Carriageway beam and arch combination, common force.

Steel arch can be designed into truss arch, box arch, plate arch. Many truss arch bridges are built in foreign countries, and more than ten steel box arch bridges are built in China. Truss arch bridge is an important form of rigid arch bridge with large span.

The main arch of truss arch bridge along the span direction: equal height, variable height.

The overall design parameters of long-span steel truss arch bridge are:

1. Layout of arch rib truss
2. Arch axis
3. Vector span ratio
4. The selection of the height of the vault and arch foot
5. Boundary conditions
6. Bar section form
7. Bar section area

Trussed arch rib can be divided into Pratt truss, Warren truss, K truss, sub-truss and other forms according to the main truss frame classification.

• Mechanical properties: K-type truss are the best
• Economical: W-type truss with the least amount of steel
• Construction and aesthetics: P-type truss has advantages

1. Arch rib

The main load-bearing members of the structure mainly bear axial pressure, but also bear part of the bending moment, and the eccentric compression members are mainly compressed.

According to the form of section is divided into: box, pipe, truss type. Trussed arch rib has light weight, greater span capacity and good economy.

2. Boom

It is a force transfer component, which transfer the deck load to the arch rib of the bearing member, the boom is mainly an axial tension member.

• The rigid boom is made of multi-purpose steel pipe or section steel and can withstand pressure
• The flexible boom is made of high-strength steel wire bundle or steel strand, which can only be stretched, convenient construction and beautiful appearance

Elevation arrangement of the boom:

Boom spacing is the span length of the longitudinal beam of the carriageway, and it usually takes equal spacing.

According to its layout in the arch plane, the boom is divided into: parallel vertical boom, inclined boom, mesh boom. According to the placement quantity the boom is also divided into single boom, double boom.

3. Tie bar (beam)

For the non-thrust arch, the thrust of the arch is borne by the tie rod, and the tie rod bears the larger axial tension. Divided into: rigid tie rod, flexible tie rod.

4. Cross brace

To ensure the transverse stiffness and stability of the two arch ribs and withstand the transverse horizontal forces acting on the arch ribs, bridge deck and boom, it is necessary to set the transverse supports.

The cross brace can greatly improve the out-of-plane stiffness and torsional stiffness of the whole bridge, but basically do not improve the in-plane stiffness.

Basic requirements:

• It is arranged on the arch section outside the scope of the clearance height of the bridge floor
• The width of the brace should not be less than 1/15 of the length

Structural forms of cross brace:

The common ones are "one-word brace", "K-shaped brace", "X-shaped brace", "meter-shaped brace".

5. Arch post

The stand column is used for the upper bearing part of the upper bearing arch bridge or the middle bearing arch bridge, and is the force transfer structure between the bridge floor system and the main arch rib.

The main design parameters of long-span steel truss arch bridge are as follows: beam span ratio, selection of arch axis, choice of vault and arch height.

Rise span ratio

Mainly according to the topography of the bridge site, geological conditions, bridge clearance requirements and other factors to determine.

The common range of arch rib span ratio is 1/4~1/7, the span ratio of steel truss arch bridge is usually 1/4~1/5.

The smaller the span ratio is, the greater the horizontal thrust of arch foot is. When geological conditions are poor, a larger vector to span ratio can be used to reduce horizontal thrust.

Axis of arch

The ideal arch axis is consistent with the pressure line on the arch, and the section only bears the pressure without bending moment, which can make full use of the material strength.

Common forms of arch axis: arc line, quadratic parabola, catenary.

Arch rib vault and arch foot height selection

According to the variation of arch rib height, it can be divided into equal height arch rib and variable height arch rib.

When the span is large, the variable height arch rib is used to adapt to the internal force distribution of arch rib and save the engineering amount.

Span Length: Steel arch bridges can be designed to span various lengths, ranging from short to long spans. The span length depends on factors such as the width of the obstacle being crossed, desired clearance beneath the bridge, and engineering requirements. Steel arch bridges have the advantage of spanning long distances without the need for intermediate supports, making them suitable for crossing wide rivers or deep valleys.

Rehabilitation and Adaptive Reuse: Steel arch bridges have the potential for rehabilitation and adaptive reuse. In some cases, existing steel arch bridges can be renovated, strengthened, or repurposed to meet modern load requirements or accommodate changes in traffic demands. This feature allows for the preservation and reuse of historic or significant bridge structures.

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