1、Section 12 SOIL-CORRUGATED METAL STRUCTURE INTERACTION SYSTEMS 12.1 GENERAL 12.1.1 Scope The specifications of this Section are intended for the structural design of corrugated metal structures. It must be recognized that a buried flexible structure is a composite structure made up of the metal ring
2、 and the soil envelope, and that both materials play a vital part in the structural design of flexible metal structures. Only Article 12.7 is applicable to structural plate box culverts. 12.1.2 Notations A A AL = total axle load on single axle or tandem axles (Ar- C, = number of axles coefficient (A
3、rticle 12.8.4.3.2) C2 = number of wheels per axle coefficient (Article cdl = dead load adjustment coefficient (Article Cet = live load adjustment coefficient (Article D = straight leg of haunch (Article 12.8.2) E, = modulus of elasticity of metal (Articles 12.2.2 and E, = modulus of elasticity of pi
4、pe material (Articles FF = flexibility factor (Articles 12.2.4 and 12.3.4) fa = allowable stress-specified minimum yield point fCr = critical buckling stress (Articles 12.2.2 and 12.3.2) f, = specified minimum tensile strength (Articles fy H I = required wall area (Article 12.2.1) = area of pipe wal
5、l (Article 12.3.1) ticles 12.8.4.3.2 and 12.8.4.4) 12.8.4.3.2) 12.8.4.3.2) 12.8.4.3.2) 12.3.2) 12.2.4 and 12.3.4) divided by safety factor (Article 12.2.1) 12.2.2 and 12.3.2) = specified minimum yield point (Article 12.3.1) = height of cover above crown (Article 12.8.4.4) = moment of inertia, per un
6、it length, of cross section of the pipe wall (Articles 12.2.4 and 12.3.4) k = soil stiffness factor (Articles 12.2.2 and 12.3.2) Mdl = dead load factored moment (Article 12.8.4.3.3) Mu = live load factored moment (Article 12.8.4.3.3) M, = crown plastic moment capacity (Article Mph = haunch plastic m
7、oment capacity (Article P P 12.8.4.3.3) 12.8.4.3.3) = design load (Article 12.1.4) = proportion of total moment carried by the crown. Limits for P are given in Table 12.7.4D (Article 12.8.4.3.3) = radius of gyration of corrugation (Articles 12.2.2 and 12.3.2) = radius of crown (Table 12.8.2A) = radi
8、us of haunch (Table 12.8.2A) = rise of box culvert (Articles 12.7.2 and 12.8.4.4) r r, rh R Rh = haunch moment reduction factor (Article S = diameter of span (Articles 12.1.4, 12.2.2, 12.8.2, s = pipe diameter or span (Articles 12.2.4, 12.3.2, and SF = safety factor (Article 12.2.3) SS = required se
9、am strength (Articles 12.2.3 and T = thrust (Article 12.1.4) TL = thrust, load factor (Articles 12.3.1 and 12.3.3) T, = thrust, service load (Articles 12.2.1 and 12.2.3) t = length of stiffening rib on leg (Article 12.8.2) V = reaction acting in leg direction (Article 12.8.4.4) A = haunch radius inc
10、luded angle (Table 12.8.2A) y = unit weight of backfill (Articles 12.8.4.3.2 and + = capacity modification factor (Articles 12.3.1 and 12.8.4.3.3) and 12.8.4.4) 12.3.4) 12.3.3) 12.8.4.4) 12.3.3) 12.1.3 Loads Design load, P, shall be the pressure acting on the struc- ture. For earth pressures, see Ar
11、ticle 3.20. For live load, see Articles 3.4 to 3.7,3.11, 3.12, and 6.4, except that the 339 340 HIGHWAY BRIDGES 12.1.3 words “When the depth of fill is 2 feet or more” in Article 6.4.1 need not be considered. For loading combinations, see Article 3.22. 12.1.4 Design 12.1.4.1 The thrust in the wall s
12、hall be checked by three criteria. Each considers the mutual function of the metal wall and the soil envelope surrounding it. The cri- teria are: (a) Wall area; (b) Buckling stress; (c) Seam strength (structures with longitudinal seams). 12.1.4.2 The thrust in the wall is: (12 - 1) S T=Px- 2 where:
13、P = design load, in pounds per square foot; S = diameter or span, in feet; T = thrust, in pounds per foot. 12.1.4.3 Handling and installation strength shall be sufficient to withstand impact forces when shipping and placing the pipe. 12.1.5 Materials The materials shall conform to the AASHTO specifi
14、- cations referenced herein. 12.1.6 Soil Design 12.1.6.1 Soil Parameters The performance of a flexible culvert is dependent on soil structure interaction and soil stiffness. The following must be considered: (a) Soils: (1) The type and anticipated behavior of the foun- dation soil must be considered
15、; i.e., stability for bedding and settlement under load. (2) The type, compacted density, and strength properties of the soil envelope immediately adjacent to the pipe must be established. Good side fill is ob- tained from a granular material with little or no plas- ticity and free of organic materi
16、al, i.e., AASHTO classification groups A- 1, A-2, and A-3, compacted to a minimum 90% of standard density based on AASHTO Specification T 99 (ASTM D 698). (3) The density of the embankment material above the pipe must be determined. See Article 6.2. (b) Dimensions of soil envelope. The general recom
17、mended criteria for lateral limits of the culvert soil envelope are as follows: (1) Trench installations-2-feet minimum each side of culvert. This recommended limit should be modified as necessary to account for variables such as poor in situ soils. (2) Embankment installations-one diameter or span
18、each side of culvert. (3) The minimum upper limit of the soil envelope is 1 foot above the culvert. 12.1.6.2 Pipe Arch Design The design of the corner backfill shall account for comer pressure which shall be considered to be approxi- mately equal to thrust divided by the radius of the pipe arch corn
19、er. The soil envelope around the corners of pipe arches shall be capable of supporting this pressure. 12.1.6.3 Arch Design 12.1.6.3.1 Special design considerations may be ap- plicable; a buried flexible structure may raise two impor- tant considerations. The first is that it is undesirable to make t
20、he metal arch relatively unyielding or fixed com- pared with the adjacent sidefill. The use of massive foot- ings or piles to prevent any settlement of the arch is gen- erally not recommended. Where poor materials are encountered, consideration should be given to removing some or ali of this poor ma
21、- terial and replacing it with acceptable material. The footing should be designed to provide uniform longitudinal settlement, of acceptable magnitude from a functional aspect. Providing for the arch to settle will pro- tect it from possible drag down forces caused by the con- solidation of the adja
22、cent sidefill. The second consideration is bearing pressure of soils under footings. Recognition must be given to the effect of depth of the base of footing and the direction of the foot- ing reaction from the arch. Footing reactions for the metal arch are considered to act tangential to the metal p
23、late at its point of connection to the footing. The value of the reaction is the thrust in the metal arch plate at the footing. 12.1.6.3.2 Invert slabs and other appropriate mea- sures shall be provided to anticipate scour. 12.1.7 DIVISION I-DESIGN 341 12.1.7 Abrasive or Corrosive Conditions Extra m
24、etal thickness, or coatings, may be required for resistance to corrosion and abrasion. For highly abrasive conditions, a special design may be required. 12.1.8 Minimum Spacing When multiple lines of pipes or pipe arches greater than 48 inches in diameter or span are used, they shall be spaced so tha
25、t the sides of the pipe shall be no closer than one-half diameter or 3 feet, whichever is less, to permit adequate compaction of backfill material. For diameters up to and including 48 inches, the minimum clear spacing shall not be less than 2 feet. 12.1.9 End Treatment Protection of end slopes may
26、require special consid- eration where backwater conditions may occur, or where erosion and uplift could be a problem. Culvert ends con- stitute a major run-off-the-road hazard if not properly de- signed. Safety treatment, such as structurally adequate grating that conforms to the embankment slope, e
27、xten- sion of culvert length beyond the point of hazard, or pro- vision of guardrail, are among the alternatives to be con- sidered. End walls on skewed alignment require a special design. 12.1.10 Construction and Installation The construction and installation shall conform to Sec- tion 23-Division
28、II. 12.2 SERVICE LOAD DESIGN Service Load Design is a working stress method, as tra- ditionally used for culvert design. 12.2.1 Wall Area A = T,lf, (12-2) where: A = required wall area in square inches per foot; T, = thrust, service load in pounds per foot; fa = allowable stress-specified minimum yi
29、eld point, pounds per square inch, divided by safety factor, f,/SF. 12.2.2 Buckling Corrugations with the required wall area, A, shall be checked for possible buckling. If the allowable buckling stress, f,JSF, is less than fa, the required area must be re- calculated using f,JSF in lieu of f,. Formu
30、lae for buckling are: (12 - 4) 12E, If S LJF then f, = - (12 - 9) k (ks/ r)2 where: f, = specified minimum metal strength in pounds per fcr = critical buckling stress in pounds per square inch; k = soil stiffness factor = 0.22; s = pipe diameter or span in inches; r = radius of gyration of corrugati
31、on in inches; E, = modulus of elasticity of metal in pounds per square inch; square inch. 12.3.3 Seam Strength For pipe fabricated with longitudinal seams (riveted, spot-welded, bolted), the seam strength shall be sufficient to develop the thrust in the pipe wall. The required seam strength shall be
32、: SS = TL/+ (12-10) where: SS = required seam strength in pounds per foot; TL = thrust multiplied by applicable factor, in pounds + = capacity modification factor. per linear foot; 12.3.4 Handling and Installation Strength Handling rigidity is measured by a flexibility factor, FF, determined by the
33、formula: FF = s2/E,I (12-1 1) where: FF = flexibility factor in inches per pound; s E, = modulus of elasticity of the pipe material in pounds per square inch; I = moment of inertia per unit length of cross section of the pipe wall in inches to the 4th power per inch. . , = pipe diameter or maximum s
34、pan in inches; 12.4 CORRUGATED METAL PIPE 12.4.1 General 12.4.1.1 Corrugated metal pipe and pipe-arches may be of riveted, welded, or lock seam fabrication with annular or helical corrugations. The specifications are: Aluminum Steel AASHTO M 36, M 190, M 245 AASHTO M 190, M 196 12.4.1.2 Service Load
35、 Design-safety factor, SF Seam strength = 3.0 Wall area = 2.0 Buckling = 2.0 12.4.1.3 Load Factor Design-capacity modification factor, + For Helical pipe with lock seam or fully welded seam: Wall area and buckling + = 1.0 For Annular pipe with spot welded, riveted or bolted seam: Wall area and buckl
36、ing + = 1.0 Seam strength 4 = 0.67 12.4.1.4 DIVISION I-DESIGN 343 12.4.1.4 Flexibility Factor (a) For steel conduits, FF should generally not exceed the following values: %-in. and Yi-in. depth corrugation, FF = 4.3 x 10-2 1-in. depth corrugation, FF = 3.3 X (b) For aluminum conduits, FF should gene
37、rally not exceed the following values: %-in. and %-in. depth corrugations, FF = 3.1 X FF = 6.1 X FF = 9.2 X 1-in. depth corrugation, FF = 6 X lo-* for 0.060 in. material thickness for 0.075 in. material thickness for all other material thicknesses 12.4.1.5 Minimum Cover The minimum cover for design
38、loads shall be Span/8 but not less than 12 inches. (The minimum cover shall be measured from the top of a rigid pavement or the bottom of a flexible pavement.) For construction requirements, see Article 23.10-Division II. 12.4.2 Seam Strength Minimum Longitudinal Seam Strength 2 X ln and 2-23 X 112
39、Corrugated Steel Pipe-Riveted or Spot Welded 3 X 1 Corrugated Steel Pipe- Riveted or Spot Welded Single Double Double Thickness Rivet Size Rivets Rivets Thickness Rivet Size Rivets (in.) (in.) (kipdft) (kipslft) (in.) (in.) (kipslft) 0.064 5/16 16.7 21.6 0.064 318 28.7 0.079 5/16 18.2 29.8 0.079 318
40、 35.7 o. 109 318 23.4 46.8 o. 109 7/16 53.0 0.138 318 24.5 49.0 O. 138 7/16 63.7 0.168 318 25.6 51.3 o. 168 7/16 70.7 2 X 112 and 2-23 X 112 Corrugated Aluminum Pipe-Riveted Rivet Single Double Thickness Size Rivets Rivets (in.) (in.) (kipslft) (kipslft) 0.060 5/16 9.0 14.0 0.075 5/16 9.0 18.0 o. 10
41、5 318 15.6 31.5 0.135 318 16.2 33.0 o. 164 318 16.8 34.0 344 HIGHWAY BRIDGES 12.4.2 3 x 1 Corrugated Aluminum 6 x 1 Corrugated Aluminum Pipe-Riveted Pipe-Riveted Double Double Thickness Rivet Size Rivets Thickness Rivet Size Rivets (in.) (in.) (kips/ft) (in.) (in.) (kips/ft) 0.060 3/8 16.5 0.060 112
42、 16.0 0.075 3/8 20.5 0.075 112 19.9 O. 105 112 28.0 O. 105 112 27.9 O. 135 112 42.0 O. 135 112 35.9 o. 164 1/2 54.5 O. 167 112 43.5 * 12.4.3 Section Properties 12.4.3.1 Steel Conduits Thickness (in.) 0.028 0.034 0.040 0.052 0.064 0.079 0.109 0.138 O. 168 A, (sq in./ft) 0;304 0.380 0.456 0.608 0.761
43、0.950 1.331 1.712 2.098 r (in.) 0.0816 0.0824 0.0832 0.0846 0.0879 0.0919 0.0967 I x 10-3 (in.4/in.) 0.253 0.344 0.439 0.567 0.857 1.205 1.635 As r I x 10-3 (sqin./ft) (in.) (in./in.) 0.465 0.1702 1.121 0.619 0.1707 1 SOO 0.775 0.1712 1.892 0.968 0.1721 2.392 3.425 O. 1741 1.356 1.744 O. 1766 4.533
44、2.133 o. 1795 5.725 3 x 1 Corrugation 5 X 1 Corrugation Thickness A, r I x 10-3 As r I x 10-3 (in.) (sqin./ft) (in.) (in.4/in.) (sq in./ft) (in.) (in.4/in.) 0.064 0.890 0.3417 8.659 0.794 0.3657 8.850 0.079 1.113 0.3427 10.883 0.992 0.3663 11.092 o. 109 1.560 0.3448 15.459 1.390 0.3677 15.650 O. 138
45、 2.008 0.3472 20. 183 1.788 0.3693 20.317 0.168 2.458 0.3499 25.091 2.186 0.3711 25.092 12.4.3.2 Aluminum Conduits 1-112 X 1/4 Corrugation 2-U3 X 112 Corrugation Thickness A, r I x 10-3 A, r I x 10-3 (in.) (sq in./ft) (in.) (in.4/in.) (sq in./ft (in.) (in.4/in.) 0.048 0.608 0.0824 0.344 0.060 0.761
46、0.0832 0.349 0.775 0.1712 1.892 0.075 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.1721 2.392 0.105 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.1741 3.425 0.135 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.1766 4.533 0.164 . . . . .
47、 . . . 2.130 0.1795 5.725 0.968 1.356 1.745 3 x 1 Corrugation 6x 1 Effective Thickness A, r I x 10-3 A, Area r I x 10-3 (in.) (sq in./ft) (in.) (in3in.I (sq in./ft) (sq in./ft) (in.) (in.4/in.) 0.060 0.890 0.3417 8.659 0.775 0.387 0.3629 8.505 0.075 1.118 0.3427 10.883 0.968 0.484 0.3630 10.631 O. 1
48、05 1.560 0.3448 15.459 1.356 0.678 0.3636 14.340 0.135 2.088 0.3472 20.183 1.744 0.872 0.3646 19.319 o. 164 2.458 0.3499 25.091 2.133 1 .o66 0.3656 23.760 12.4.4 DIVISION I-DESIGN - 345 12.4.4 Chemical and Mechanical Requirements 12.4.4.1 Aluminum-corrugated metal pipe and pipe- arch material requir
49、ements-AASHTO M 197 Mechanical Properties for Design Minimum Minimum Material Tensile Yield Mod. of Grade Strength Point Elast. (psi) (psi) (psi) 3004-H34 3 1 .O00 24.000 10 x 106 3004-H32 27;OOO 20;ooo 10 x 106 H34 temper must be used with riveted pipes to acheive seam strength. Both H32 and H34 temper material may be used with helical pipe. 12.4.4.2 Steel-corrugated metal pipe and pipe-arch material requirements-AASHTO M 218 M 246: Mechanical ProDerties for Desien Minimum Minimum Tensile Yield Mod. of Strength Point Elast. (psi) (psi) (psi) 45,000 33,000 29 X lo6 12.4.5 Smooth-Lined
