As the “blood vessel” of the power plant, the coal transport trestle connects the coal yard, the transfer station, and the coal bunker of the main powerhouse to provide raw material guarantee for the steam turbine generator. The coal-conveying trestle is generally in the form of reinforced concrete columns or steel columns supporting the upper structure of the continuous truss of the steel structure. Coal conveying belt conveyors, maintenance channels, cable bridges, etc. The trestle is divided into the closed type and open type according to functional requirements; single or multiple coals conveying belt conveyors can be arranged according to the size of the coal conveying. Due to the limitation of belt conveyors, the inclination angle of the coal conveying trestle is usually 0°~16°. When the inclination angle is greater than 10°, the maintenance channel needs to be set with steps for maintenance.
2 Structural layout
2.1 Column layout
The arrangement of the pillars of the coal conveying trestle and the determination of the distance between the trestle should be combined with the general plan, and the roads, the foundations of surrounding buildings (structures), underground pipelines, zero-meter equipment, rainwater pipes and rainwater wells should be fully considered to avoid collisions. It is necessary to combine the position of the door of the surrounding buildings, pay attention to avoid it, and ensure that there is a clear distance of more than 1m between the trestle column and the door. Trestle bridges across roads and railways need to meet the clearance requirements of various dimensions. Generally speaking, the clearance between the bottom of the trestle truss and the road should be greater than 5m, and the clearance from the railway should be greater than 6.6m; the clearance between the trestle column and the road shoulder should be greater than 1m, and The clear distance of the railway centerline shall be greater than 4.5m.
2.2 Structure selection
First of all, it is necessary to determine whether to use an open-air trestle or a closed trestle according to the professional requirements of the craft. For a low coal conveying trestle with a small span, the trestle body and lower columns should be reinforced concrete columns; when the span exceeds 18m, the trestle body structure should be steel truss structures, and the lower columns may be cast-in-place reinforced concrete columns or reinforced concrete columns. Steel column.
The design of the coal transport trestle should take into account the aesthetics under the premise of satisfying structural safety, especially the coal transport trestle connecting the coal bunker, the height is usually relatively high, it is appropriate to use a long-span trestle and steel pipe columns or lattice steel columns.
2.3 Superstructure layout
Since the coal-conveying trestle of the reinforced concrete bridge body is usually used in the case of a small span, the superstructure here only discusses the structure of the steel truss bridge body. When the superstructure is arranged, the clearance height is mainly limited by factors such as the operation of the belt conveyor and the arrangement of the cable bridge; the height of the steel truss of the super-span trestle (usually refers to the span greater than 30m) is determined by the calculation of the span-to-height ratio. When reinforced concrete columns are used and the upper steel trusses are hinged to the columns, the distance between the expansion joints of the ground-closed trestle should not exceed 130m, and the distance of the expansion joints of the open-air trestle should not exceed 100m; when the coal conveying trestle adopts steel columns, the distance between the expansion joints of the ground closed trestle should not exceed If it exceeds 150m, the spacing of expansion joints of open-air trestle bridges should not exceed 120m; the spacing of expansion joints of underground coal transport corridors should not exceed 30m.
The steel truss of the trestle is provided with portal rigid frames at the supports at both ends along the longitudinal direction, and its beams and columns are designed according to rigid nodes. Rigid spans should be set along the longitudinal direction of the trestle, and the rigid span column spacing is generally set at 6-7m.
The roof of the trestle steel truss shall be provided with the upper chord horizontal support along the entire longitudinal length; for the reinforced concrete bridge deck using the profile as the bottom form, when the trestle span is less than 24m, the lower chord horizontal support may not be provided, and when the trestle span is ≥24m, it shall be provided at both ends of the truss. Set the bottom chord horizontal support. However, when the strength of the floor concrete is not reached, measures should be taken to ensure the lateral stability of the trestle floor structure.
The upper and lower chords of the steel truss of the coal conveying trestle should be made of hot-rolled H-beams, and the webs should be made of square steel pipes, round steel pipes or double-angle steels, so as to be light and beautiful, and easy to construct. The steel truss form of the open-air trestle should adopt the inverted triangular pipe truss. The height of the reinforced concrete column section of the coal conveying trestle can be taken as H/25～H/20 (H is the distance from the top surface of the foundation to the bottom of the trestle steel truss support); The height of the trestle column.
2.4 Other Notes
(1) Seismic joints shall be set up between the coal-conveying trestle and adjacent buildings in accordance with Article 11.8.1 of the Technical Regulations for the Design of Civil Structures of Thermal Power Plants (DL5022-2012).
(2) When the length of the coal conveying trestle exceeds 150m, safety evacuation stairs should be set up, and the safety evacuation stairs should be arranged at the rigid span position.
(3) The connection between the two ends of the coal transport trestle and the adjacent buildings can be completely separated from the adjacent buildings by a cantilever structure or set as a sliding bearing; the middle support of the coal transport trestle is set as a hinge bearing.
(4) In the selection of material types, Q355 steel should be used for strength-controlled components as much as possible, which can reduce the cross-section of the components; Q235 steel should be used for non-strength-controlled components such as horizontal supports.
(5) Water retaining edges shall be provided around all openings on the deck of the trestle bridge, and the deck of the steel truss trestle shall be provided with a 1m high waterproof edge along the longitudinal length of both sides.
(6) The fire hazard of the closed coal trestle is Class C, and the fire resistance level is Class II. When no automatic fire extinguishing system is installed, fire protection measures shall be taken for its steel structure.
The coal transport trestle is an important thermal power plant building. When arranging its columns, the arrangement of surrounding structures and pipelines must be considered. Rigid spans must be arranged in the trestle, and economical spans should be selected as far as possible. In the calculation of the trestle bridge, finite element software must be used to complete the modeling and calculation work. In the calculation, various loads borne by the trestle bridge must be considered, and the connection method between the trestle bridge members must be simplified, so as to obtain the correct internal force and deformation results, and guide the design and construction.