1、2.1 GENERAL Section 2 GENERAL FEATURES OF DESIGN 2.2 STANDARD HIGHWAY CLEARANCES- GENERAL 2.1.1 Notations 2.2.1 Navigational Af = area of flanges (Article 2.7.4.3) b = flange width (Article 2.7.4.3) C = modification factor for concentrated load, P, used in D = clear unsupported distance between flan
2、ge compo- d = depth of W or I section (Article 2.7.4.3) Fa = allowable axial stress (Article 2.7.4.3) Fb = allowable bending stress (Article 2.7.4.2) F, = allowable shear stress (Article 2.7.4.2) F, = minimum yield stress (Article 2.7.4.2) fa = axial compression stress (Article 2.7.4.3) h = height o
3、f top rail above reference surface (Figure L = post spacing (Figure 2.7.4B) P = railing design loading = 10 kips (Article 2.7.1.3 P = railing design loading equal to P, P/2 or P/3 (Article t = flange or web thickness (Article 2.7.4.3) w = pedestrian or bicycle loading (Articles 2.7.2.2 and the desig
4、n of rail members (Article 2.7.1.3.1) nents (Article 2.7.4.3) 2.7.4B) and Figure 2.7.4B) 2.7.1.3.5) 2.7.3.2) 2.1.2 Width of Roadway and Sidewalk The width of roadway shall be the clear width mea- sured at right angles to the longitudinal center line of the bridge between the bottoms of curbs. If bru
5、sh curbs or curbs are not used, the clear width shall be the minimum width measured between the nearest faces of the bridge railing. The width of the sidewalk shall be the clear width, measured at right angles to the longitudinal center line of the bridge, from the extreme inside portion of the hand
6、rail to the bottom of the curb or guardtimber. If there is a truss, girder, or parapet wall adjacent to the roadway curb, the width shall be measured to the extreme walk side of these members. Permits for the construction of crossings over naviga- ble streams must be obtained from the U.S. Coast Gua
7、rd and other appropriate agencies. Requests for such permits from the U.S. Coast Guard should be addressed to the ap- propriate District Commander. Permit exemptions are al- lowed on nontidal waterways which are not used as a means to transport interstate or foreign commerce, and are not susceptible
8、 to such use in their natural condition or by reasonable improvement. 2.2.2 Roadway Width For recommendations on roadway widths for various volumes of traffic, see AASHTO A Policy on Geometric Design of Highways and Streets, or A Policy on Design Standards-Interstate System. 2.2.3 Vertical Clearance
9、 Vertical clearance on state trunk highways and inter- state systems in rural areas shall be at least 16 feet over the entire roadway width with an allowance for resurfac- ing. On state trunk highways and interstate routes through urban areas, a l6-foot clearance shall be provided except in highly d
10、eveloped areas. A l6-foot clearance should be provided in both rural and urban areas where such clear- ance is not unreasonably costly and where needed for de- fense requirements. Vertical clearance on all other high- ways shall be at least 14 feet over the entire roadway width with an allowance for
11、 resurfacing. 2.2.4 Other The channel openings and clearances shall be accept- able to agencies having jurisdiction over such matters. Channel openings and clearances shall conform in width, height, and location to all federal, state, and local requirements. 7 8 HIGHWAY BRIDGES 2.2.5 2.2.5 Curbs and
12、 Sidewalks The face of the curb is defined as the vertical or slop- ing surface on the roadway side of the curb. Horizontal measurements of roadway curbs are from the bottom of the face, or, in the case of stepped back curbs, from the bottom of the lower face. Maximum width of brush curbs, if used,
13、shall be 9 inches. Where curb and gutter sections are used on the road- way approach, at either or both ends of the bridge, the curb height on the bridge may equal or exceed the curb height on the roadway approach. Where no curbs are used on the roadway approaches, the height of the bridge curb abov
14、e the roadway shall be not less than 8 inches, and preferably not more than 10 inches. Where sidewalks are used for pedestrian traffic on urban expressways, they shall be separated from the bridge roadway by the use of a combination railing as shown in Figure 2.7.4B. In those cases where a New Jerse
15、y type parapet or a curb is constructed on a bridge, particularly in urban areas that have curbs and gutters leading to a bridge, the same widths between curbs on the approach roadways will be maintained across the bridge structure. A parapet or other railing installed at or near the curb line shall
16、 have its ends properly flared, sloped, or shielded. 2.3 HIGHWAY CLEARANCES FOR BRIDGES HORIZONTAL CLEARANCE o :L- 1 ROADWAY WIDTH O1 FIGURE 2.3.1 Clearance Diagram for Bridges limits of structure costs, type of structure, volume and de- sign speed of through traffic, span arrangement, skew, and ter
17、rain make the 30-foot offset impractical, the pier or wall may be placed closer than 30 feet and protected by the use of guardrail or other barrier devices. The guardrail or other device shall be independently supported with the roadway face at least 2 feet O inches from the face of pier or abutment
18、. The face of the guardrail or other device shall be at least 2 feet O inches outside the normal shoulder line. 2.3.1 Width 2.4.2 Vertical Clearance The horizontal clearance shall be the clear width and the vertical clearance the clear height for the passage of vehicular traffic as shown in Figure 2
19、.3.1. The roadway width shall generally equal the width of the approach roadway section including shoulders. Where curbed roadway sections approach a structure, the same section shall be carried across the structure. 2.3.2 Vertical Clearance The provisions of Article 2.2.3 shall be used. 2.4 HIGHWAY
20、 CLEARANCES FOR UNDERPASSES A vertical clearance of not less than 14 feet shall be provided between curbs, or if curbs are not used, over the entire width that is available for traffic. 2.4.3 Curbs Curbs, if used, shall match those of the approach road- way section. 2.5 HIGHWAY CLEARANCES FOR TUNNEL
21、S See Figure 2.5. 2.5.1 Roadway Width See Figure 2.4A. 2.4.1 Width The pier columns or walls for grade separation struc- tures shall generally be located a minimum of 30 feet from the edges of the through-traffic lanes. Where the practical The horizontal clearance shall be the clear width and the ve
22、rtical clearance the clear height for the passage of vehicular traffic as shown in Figure 2.5. Unless otherwise provided, the several parts of the structures shall be constructed to secure the following limiting dimensions or clearances for traffic. 2.5.1 DIVISION I-DESIGN 9 7 30-O MIN. PAVEMENT GEN
23、ERAL CONDITION FACE OF WALL Y FACE OF WALL OR PIER FACE OF GUARD RAIL Y$ 2-0 MIN. PAVEMENT SHOULDER SHOULDER LIMITED CONDITION *The barrier to facc of wall or pier distance should not be less than the dynamic defection of the barrier for impact by a full-sized automobile at impact conditions of appr
24、oximately 25 degrees and 60 miles per hour. For information on dynamic deflection of various harriers, see AASHTO Road- side Design Guide. FIGURE 2.4A Clearance Diagrams for Underpasses (See Article 2.4 for General Requirements.) NOT LESS THAN 30 FT. HORIZONTAL CLEARANCE It ROADWAY WIDTH AT LEAST 2
25、FT. GREATER THAN APPROACH TRAVELLED WAY BUT NOT LESS THAN 24FT. o FIGURE 2.5 Clearance Diagram for Iiinnels-Two-Lane Highway Traffic 10 HIGHWAY BRIDGES 2.5.1 The clearances and width of roadway for two-lane traf- fic shall be not less than those shown in Figure 2.5. The roadway width shall be increa
26、sed at least 10 feet and preferably 12 feet for each additional traffic lane. railing or barrier with a pedestrian railing along the edge of the structure. On urban expressways, the separation shall be made by a combination railing. 2.7.1 Vehicular Railing 2.5.2 Clearance between Walls 2.7.1.1 Gener
27、al The minimum width between walls of two-lane tunnels shall be 30 feet. 2.5.3 Vertical Clearance The vertical clearance between curbs shall be not less than 14 feet. 2.5.4 Curbs The width of curbs shall be not less than 18 inches. The height of curbs shall be as specified for bridges. For heavy tra
28、ffic roads, roadway widths greater than the above minima are recommended. If traffic lane widths exceed 12 feet the roadway width may be reduced 2 feet O inches from that calculated from Figure 2.5. 2.6 HIGHWAY CLEARANCES FOR DEPRESSED ROADWAYS 2.6.1 Roadway Width The clear width between curbs shall
29、 be not less than that specified for tunnels. 2.6.2 Clearance between Walls The minimum width between walls for depressed road- ways carrying two lanes of traffic shall be 30 feet. 2.6.3 Curbs The width of curbs shall be not less than 18 inches. The height of curbs shall be as specified for bridges.
30、 2.7.1.1.1 Although the primary purpose of traffic railing is to contain the average vehicle using the struc- ture, consideration should also be given to (a) protection of the occupants of a vehicle in collision with the railing, (b) protection of other vehicles near the collision, (c) pro- tection
31、of vehicles or pedestrians on roadways underneath the structure, and (d) appearance and freedom of view from passing vehicles. 2.7.1.1.2 Materials for traffic railings shall be con- crete, metal, timber, or a combination thereof. Metal ma- terials with less than 10-percent tested elongation shall no
32、t be used. 2.7.1.1.3 Traffic railings should provide a smooth, continuous face of rail on the traffic side with the posts set back from the face of rail. Structural continuity in the rail members, including anchorage of ends, is essential. The railing system shall be able to resist the applied loads
33、 at all locations. 2.7.1.1.4 Protrusions or depressions at rail joints shall be acceptable provided their thickness or depth is no greater than the wall thickness of the rail member or VE inch, whichever is less. 2.7.1. I .5 Careful attention shall be given to the treat- ment of railings at the brid
34、ge ends. Exposed rail ends, posts, and sharp changes in the geometry of the railing shall be avoided. A smooth transition by means of a con- tinuation of the bridge barrier, guardrail anchored to the bridge end, or other effective means shall be provided to protect the traffic from direct collision
35、with the bridge rail ends. 2.7.1.2 Geometry 2.7 RAILINGS Railings shall be provided along the edges of struc- tures for protection of traffic and pedestrians. Other suit- able applications may be warranted on bridge-length cul- verts as addressed in the AASHTO Roadside Design Guide. Except on urban
36、expressways, a pedestrian walkway may be separated from an adjacent roadway by a traffic 2.7.1.2.1 The heights of rails shall be measured rela- tive to the reference surface which shall be the top of the roadway, the top of the future overlay if resurfacing is an- ticipated, or the top of curb when
37、the curb projection is greater than 9 inches from the traffic face of the railing. 2.7.1.2.2 Traffic railings and traffic portions of combination railings shall not be less than 2 feet 3 inches 2.7.1.2.2 DIVISION I-DESIGN 11 from the top of the reference surface. Parapets designed with sloping traff
38、ic faces intended to allow vehicles to ride up them under low angle contacts shall be at least 2 feet 8 inches in height. 2.7.1.2.3 The lower element of a traffic or combina- tion railing should consist of either a parapet projecting at least 18 inches above the reference surface or a rail centered
39、between 15 and 20 inches above the reference surface. 2.7.1.2.4 For traffic railings, the maximum clear opening below the bottom rail shall not exceed 17 inches and the maximum opening between succeeding rails shall not exceed 15 inches. For combination railings, accom- modating pedestrian or bicycl
40、e traffic, the maximum opening between railing members shall be governed by Articles 2.7.2.2.2 and 2.7.3.2.1, respectively. 2.7.1.2.5 The traffic faces of all traffic rails must be within 1 inch of a vertical plane through the traffic face of the rail closest to traffic. 2.7.1.3 Loads 2.7.1.3.1 When
41、 the height of the top of the top traffic rail exceeds 2 feet 9 inches, the total transverse load dis- tributed to the traffic rails and posts shall be increased by the factor C. However, the maximum load applied to any one element need not exceed P, the transverse design load. 2.7.1.3.2 Rails whose
42、 traffic face is more than 1 inch behind a vertical plane through the face of the traffic rail closest to traffic or centered less than 15 inches above the reference surface shall not be considered to be traffic rails for the purpose of distributing P or CP, but may be con- sidered in determining th
43、e maximum clear vertical open- ing, provided they are designed for a transverse loading equal to that applied to an adjacent traffic rail or P/2, whichever is less. 2.7.1.3.3 Transverse loads on posts, equal to P, or CP, shall be distributed as shown in Figure 2.7.4B. A load equal to one-half the tr
44、ansverse load on a post shall si- multaneously be applied longitudinally, divided among not more than four posts in a continuous rail length. Each traffic post shall also be designed to resist an indepen- dently applied inward load equal to one-fourth the out- ward transverse load. 2.7.1.3.4 The att
45、achment of each rail required in a traffic or combination railing shall be designed to resist a vertical load equal to one-fourth of the transverse design load of the rail. The vertical load shall be applied alter- nately upward or downward. The attachment shall also be designed to resist an inward
46、transverse load equal to one- fourth the transverse rail design load. 2.7.1.3.5 Rail members shall be designed for a mo- ment, due to concentrated loads, at the center of the panel and at the posts of PL/6 where L is the post spacing and P is equal to P, P/2, or P/3, as modified by the factor C wher
47、e required. The handrail members of combination railings shall be designed for a moment at the, center of the panel and at the posts of O. 1 wL2. 2.7.1.3.6 The transverse force on concrete parapet and barrier walls shall be spread over a longitudinal length of 5 feet. 2.7.1.3.7 Railings other than t
48、hose shown in Figure 2.7.4B are permissible provided they meet the require- ments of this Article. Railing configurations that have been successfully tested by full-scale impact tests are ex- empt from the provisions of this Article. 2.7.2 Bicycle Railing 2.7.2.1 General 2.7.2.1.1 Bicycle railing sh
49、all be used on bridges specifically designed to carry bicycle traffic, and on bridges where specific protection of bicyclists is deemed necessary. 2.7.2.1.2 Railing components shall be designed with consideration to safety, appearance, and when the bridge carries mixed traffic freedom of view from passing vehicles. 2.7.2.2 Geometry and Loads 2.7.2.2.1 The minimum height of a railing used to protect a bicyclist shall be 54 inches, measured from the top of the surface on which the bicycle rides to the top of the top rail. 2.7.2.2.2 Within a band bordered by the bikeway surface and a lin
