General Features of Design
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BRIDGE DESIGN AIDS DECEMBER 1987 1 0-1 General Features of Design Determination of Waterway Area. Restricted Waterways. Channel Openings All information needed by the designer relative to the above three subject wills b e set forth in the Preliminary Report. Size o f Culvert Openings See "Culvert Design," Highway Design Manual. Length o f Culverts See "Physical Standards for Culverts," Highway Design Manual. Structural Design of Culverts The Office o f Structure Design shall be responsible for the Structural adequacy of all drainage structures. Standard Box Culver t sheet s are available for a large range. 4' to span14' , o f single and multiple box culverts. A standard Arch Culvert sheet is available for arches ranging in size from 6' to 22' span . Structura l fil l height tables are also available for corrugated metal pipe, structural plate pipe and reinforced concrete pipe. Special designs o f any drainage structure are to be prepared or reviewed by the Office o f Structure Design toassure structural adequacy. All information needed for the structural design of special culvert s (i.e. , those outside the range of size and load capacity available in standard corrugated metal pipe and reinforced concrete not covered by the Standard Box or Arch Culvert sheets wil) l b e furnished by the Districts. Bridge Roadbed 1 . Width The width of bridge roadbed shall be measured normal to the centerline between the bottoms of curbs or if curbs are nousedt , the clear width shall be the minimum measured between the nearest faces of the bridge railing or barrier. The width of bridges shall be as outlined by page 10-8 of this manual, Memo t o Designers 14-2, and Topic 208 of the Highway Design Manual and in agreement with the geometric plan approved by the District Reviewer. BRIDGE DESIGN AIDS DECEMBER 1987 10-2 2 . Medians on Bridges Medians on multilane divided highways shall be decked over where the bridge median is 36 feet wide orless, o r where prior approval of a wider deck median i s given b y Headquarters. Where the median width exceeds 36 feet and prior approval is not given, a n economic analysis should be made. In general, the most economical structure wit, h either a closed or open median, shall be used. A median slab that might be used as a roadway at some later date shall b e designed for the full live load. A median slab or open grating to be constructed above the general deck level may be designed for a allowable overstress of 50% | See Chapter 7 of the Traffic Manual for requirements of median barriers. 3. Bridge Sidewalks Bridge sidewalks shall be provided where justified by pedestrian traffic. See page 10-16 of this manual or Inde 208.x 4 o f the Highway Design Manual. 4 . Pedestrian Overcrossings - Undercrossings - Bicycle Paths The minimum clear width of deck for pedestrian and bicycle overcrossings shall b e 8 feet. For bikeway bridges, the actual clear width shall be the paved width of the approach bikeway. The width of pedestrian undercrossings requires individual analysis and requires approval of Headquarter s Office o f Planning and Design. (See Index 105.2 of the Highway Desig n Manual.) The details of pedestrian ramps are governed to a large extent by the requirements for the handicapped as issued b y th e Office o r the State Architect and are included i n the Memo to Designers. 5. Equestrian Undercrossings Such structures shall normally provide a clear opening 10 feet high and 10 feet wide in cross section. Bridge Design Aid s - Apri l 1993 Clearance A t Structures A. Bridge Columns, Abutments, Retainin gWalls and Barriers 1 . Horizonta l Clearance: The horizontal clearance to bridge columns, abutments, retaining walls and barriers for freeways and expressways shall be determined upon thbasie s o f engineering judgment with the objective of eliminating fixed objects from near th eedge o f shoulder wherever economi cally feasible. A horizontal clearance of 30 feel or mor efrom the edge o f the traveled way i s desirable. Lesse r clearance s may be used where span length, median width or other controls make the desired clearance unreasonable. The followin g are minimum horizontal clearance standard sfor bridge columns, abutments, retaining walls and barriers which, in th ecase o f freeways and expressways, may be used only under very restricted conditions, upon individual analysis anwitd h Headquarters' approval. Additional horizontal clearance shall be provided wher enecessary t o meet sight distance requirements. Clearances are measure d from th eedge o f the traveled way. a ) Two-lane State Highways- 10 feel minimum o n each side. b ) Multi-lane Divided Highways- For the through roadbed on divided highways and for freeway facilities including the through roadbed, auxiliary lanes, ramps and collector roads, the minimum clearance to th e left o f traffic shall be 9 feet. On the right side, the minimum clearance shall be 11 feet. In th case e o f extensive walls, 10 feet may be used o n the right and 8 feet may be used on thlefet o f traffic. c ) Other Roads and Frontage Roads - O n all other roads, including frontage roads, the minimum clearances t o the face of the bridge columns, abutments, retaining walls and other obstructions shall be as follows: • Two-way traffic: 6 feet minimum o n each side. • One-way traffic : 4 1/2 feel minimum o n th lefe t and 6 feet minimum o n the right i n the direction o f traffic. The elevation i n Figure 10-3 on page 10-11 illustrates the required distance sfrom edge o f traveled way to face of columns, abutments, walls, and other obstructions. Barrier- mounted walls shall meet the clearance requirement for bridge barriers. Clearance a t Structures Page 10-3 Bridge Design Aids - Apri l 1993 2 . Vertica l Clearance: Freeway and Expressway - The minimum vertical clearance shall be 1/2 fee16 t over the entire width o f traveled way and shoulders on the through facility, speed change lanes, ramps and collector roads on all parts of the freeway and expressway system. Exceptions to this may apply when standard or existing routes having loweclearancer s make the higher standard impractical or where due to unusual conditions the cost of the higher standard becomes excessive. In such cases the minimum vertical clearance shall be 15 feet over the ultimate traveled way and 14 feet above the ultimate shoulders. Non-Freeway o r Expressway- The minimum vertical clearance at all other structures shall b e 15 feet over the ultimate traveled way and 14 feel above the ultimate shoulders. Pedestrian Overcossings -The vertical clearance for pedestrian overcrossings shall be 2 feel greater than the vertical clearance provided for major structures on the portion o f highway involved. I f a pedestrian overcrossing is protected by a major structure, a clearance greater than that of the major structure need not be provided. Sign Structures- Al l sign structures shall have a vertical clearance of 18 feet. B. Highwa y Clearance i n Tunnels Tunnel construction is so infrequent and costly that the width should be considered on a n individual basis. Normally, the minimum horizontal clearance on high volume freeways in urba arean s shall include the ful l roadbed width o f th e approaches. I n one-way tunnels on low volume freeways, freeways in rura areasl , and on conventional highways, the minimum side clearance from the edge o f the traveled way shall b e 4 1/4 feel o n the left and 6 feet on the right. For two-way tunnels, this clearance shall be 6 feet on each side. The minimum vertical clearance shall be 15 feel measured at any point over the traveled way and 1 4 feel above the lip of the gutter. The vertical clearance shall be 16 1/2 feel on those routes selected for this clearance. C. Clearanc e for Railroads 1 . Railroa d Tracks: Minimum clearances, bolh horizontal and vertical, for structures over or adjacent to railroad tracks are established by the Publi Utilitiec s Commission o f the Slate o f California and are Page 10-4 Clearance a t Structures Bridge Design Aids - Apri l 1993 scl forth i n their General Order No. 26-D, effective February 1, 1948, an d subsequenin t orders. This minimum vertical clearance over railroad tracks, as required by General Order No. 26-D and subsequent orders, for all new construction shall be 22 feet 6 inches except for electric railways carrying passengers only, and unless otherwise specifically directed. The Office o f Structure Design is to increase this minimum vertical clearance by 6 inches t o provide for future minor changes i n track grades. The minimum vertical clearance shown o n the plans shall he 23 feet 0 inches. Horizontal clearances shall be as outlined o n thi spage and as shown in Memo to Designers 17-105 and 17-115. All curbs, including median curbs, shall be designe d with 1 0 feet minimum clearanc e from the track centerline measured normal thereto. I t should be noted that collision walls may be required for th clearancee s given o n page 2 o f Memo t o Designers 17-105. Usually n o collisionwall s are required i f the clearance is 10 feet o r more on tangent track and 11 feet or more on curved track. 2 . Off-Trac k Maintenance Equipment: Eighteen foot horizontal clearance from centerline o f track is required for sections o f railroad where the railroad company is using or definitely plans to use off-track maintenance equipment.