1、Section 1 GENERAL PROVISIONS 1.1 DESIGN ANALYSIS AND GENERAL STRUCTURAL INTEGRITY FOR BRIDGES The intent of these Specifications is to produce in- tegrity of design in bridges. 1.1.1 Design Analysis When these Specifications provide for empirical for- mulae, alternate rational analyses, based on the
2、ories or tests and accepted by the authority having jurisdiction, will be considered as compliance with these Specifica- tions. 1.1.2 Structural Integrity Designs and details for new bridges should address structural integrity by considering the following: (a) The use of continuity and redundancy to
3、 provide one or more alternate load paths. (b) Structural members and bearing seat widths that are resistant to damage or instability. (c) External protection systems to minimize the ef- fects of reasonably conceived severe loads. 1.2 BRIDGE LOCATIONS The general location of a bridge is governed by
4、the route of the highway it carries, which, in the case of a new highway, could be one of several routes under considera- tion. The bridge location should be selected to suit the par- ticular obstacle being crossed. Stream crossings should be located with regard to initial capital cost of bridgework
5、s and the minimization of total cost including river channel training works and the maintenance measures necessary to reduce erosion. Highway and railroad crossings should provide for possible future works such as road widening. 1.3 WATERWAYS 1.3.1 General 1.3.1.1 Selecting favorable stream crossing
6、s should be considered in the preliminary route determination to minimize construction, maintenance, and replacement costs. Natural stream meanders should be studied and, if necessary, channel changes, river training works, and other construction that would reduce erosion problems and prevent possib
7、le loss of the structure should be con- sidered. The foundations of bridges constructed across channels that have been realigned should be designed for possible deepening and widening of the relocated channel due to natural causes. On wide flood plains, the lowering of approach embankments to provid
8、e overflow sections that would pass unusual floods over the highway is a means of preventing loss of structures. Where relief bridges are needed to maintain the natural flow distribu- tion and reduce backwater, caution must be exercised in proportioning the size and in locating such structures to av
9、oid undue scour or changes in the course of the main river channel. 1.3.1.2 Usually, bridge waterways are sized to pass a design flood of a magnitude and frequency consistent with the type or class of highway. In the selection of the waterway opening, consideration should be given to the amount of u
10、pstream ponding, the passage of ice and de- bris and possible scour of the bridge foundations. Where floods exceeding the design flood have occurred, or where superfloods would cause extensive damage to adjoining property or the loss of a costly structure, a larger water- way opening may be warrante
11、d. Due consideration should be given to any federal, state, and local requirements, 1.3.1.3 Relief openings, spur-dikes, debris deflectors and channel training works should be used where needed to minimize the effect of adverse flood flow conditions. Where scour is likely to occur, protection agains
12、t damage from scour should be provided in the design of bridge piers and abutments. Embankment slopes adjacent to structures subject to erosion should be adequately pro- 3 4 HIGHWAY BRIDGES 1.3.1.3 tected by rip-rap, flexible mattresses, retards, spur dikes or other appropriate construction. Clearin
13、g of brush and trees along embankments in the vicinity of bridge open- ings should be avoided to prevent high flow velocities and possible scour. Borrow pits should not be located in areas which would increase velocities and the possibility of scour at bridges. 1.4 CULVERT LOCATION, LENGTH, AND WATE
14、RWAY OPENINGS Culvert location, length, and waterway openings should be in accordance with the AASHTO Guide on the Hydraulic Design of Culverts in Highway Drainage Guidelines. 1.5 ROADWAY DRAINAGE 1.3.2 Hydraulic Studies Hydraulic studies of bridge sites are a necessary part of the preliminary desig
15、n of a bridge and reports of such studies should include applicable parts of the following outline: 1.3.2.1 Site Data (a) Maps, stream cross sections, aerial photographs. (b) Complete data on existing bridges, including dates of construction and performance during past floods. (c) Available high wat
16、er marks with dates of occur- rence. (d) Information on ice, debris, and channel stability. (e) Factors affecting water stages such as high water from other streams, reservoirs, flood control projects, and tides. (f) Geomorphic changes in channel flow. The transverse drainage of the roadway should b
17、e pro- vided by a suitable crown in the roadway surface and lon- gitudinal drainage by camber or gradient. Water flowing downgrade in a gutter section should be intercepted and not permitted to run onto the bridge. Short, continuous span bridges, particularly overpasses, may be built with- out inlet
18、s and the water from the bridge roadway carried downslope by open or closed chutes near the end of the bridge structure. Longitudinal drainage on long bridges should be provided by scuppers or inlets which should be of sufficient size and number to drain the gutters ade- quately. Downspouts, where r
19、equired, should be made of rigid corrosion-resistant material not less than 4 inches in least dimension and should be provided with cleanouts. The details of deck drains should be such as to prevent the discharge of drainage water against any portion of the structure or on moving traffic below, and
20、to prevent ero- sion at the outlet of the downspout. Deck drains may be connected to conduits leading to storm water outfalls at ground level. Overhanging portions of concrete decks should be provided with a drip bead or notch. 1.3.2.2 Hydrologic Analysis 1.6 RAILROAD OVERPASSES (a) Flood data appli
21、cable to estimating floods at site, including both historical floods and maximum floods of record. (b) Flood-frequency curve for site. (c) Distribution of flow and velocities at site for flood discharges to be considered in design of structure. (d) Stage-discharge curve for site. 1.3.2.3 Hydraulic A
22、nalysis (a) Backwater and mean velocities at bridge opening for various trial bridge lengths and selected discharges. (b) Estimated scour depth at piers and abutments of proposed structures. (c) Effect of natural geomorphic stream pattern changes on the proposed structure. (d) Consideration of geomo
23、rphic changes on nearby structures in the vicinity of the proposed structure. 1.6.1 Clearances Structures designed to overpass a railroad shall be in accordance with standards established and used by the af- fected railroad in its normal practice. These overpass structures shall comply with applicab
24、le Federal, State, and local laws. Regulations, codes, and standards should, as a mini- mum, meet the specifications and design standards of the American Railway Engineering Association, the Associa- tion of American Railroads, and AASHTO. 1.6.2 Blast Protection On bridges over railroads with steam
25、locomotives, metal likely to be damaged by locomotive gases, and all concrete surfaces less than 20 feet above the tracks, shall be protected by blast plates. The plates shall be placed to 1.6.2 DIVISION I-DESIGN 5 take account of the direction of blast when the locomotive is on level or superelevat
26、ed tracks by centering them on a line normal to the plane of the two rails at the centerline of the tracks. The plates shall be not less than 4 feet wide and shall be cast-iron, a corrosion and blast-resisting alloy, or asbestos-board shields, so supported that they may be readily replaced. The thic
27、kness of plates and other parts in direct contact with locomotive blast shall be not less than 3/4 inch for cast iron, VE inch for alloy, 92 inch for plain as- bestos-board, and 7/16 inch for corrugated asbestos-board. Bolts shall be not less than VE inch in diameter. Pockets which may hold locomoti
28、ve gases shall be avoided as far as practical. All fastenings shall be galvanized or made of corrosion-resistant material. 1.7 SUPERELEVATION The superelevation of the floor surface of a bridge on a horizontal curve shall be provided in accordance with the standard practice of the commission for the
29、 highway construction, except that the superelevation shall not ex- ceed O. 10 foot per foot width of roadway. 1.8 FLOOR SURFACES All bridge floors shall have skid-resistant charactens- tics. 1.9 UTILITIES Where required, provisions shall be made for trolley wire supports and poles, lighting pillars, electric conduits, telephone conduits, water pipes, gas pipes, sanitary sew- ers, and other utility appurtenances.
