GENERAL INFORMATION: This section of the chapter establishes the practices and requirements necessary for the design and detailing of semi-integral abutments. For general requirements and guidelines on the use of semi-integral abutments, see File Nos. 0.01-1 thru -5. Sample design calculations are provided to assist the designer and are intended to correspond to the sample details shown in File Nos. 0.03- thru -10. Note that calculations are provided for the backwall and associated structural components only. Plan and elevation views and sections of the semi-integral abutment are provided in this chapter for information on the shape of the backwall in relation to the semi-integral backwall and to illustrate some additional details required on the abutment sheets. Back of stem is the reference line on the semi-integral abutment and substructure layout sheets. End of slab is the reference line on remaining sheets. Additional sample details are provided to assist the designer in the detailing of semi-integral abutments. These details are provided to show differences in details between steel/concrete stringers, bridges with/without skew and semi-integral abutment layout. Preferred practice on semi-integral abutment layout falls in the following order: 1. Wingwalls oriented transversely to traffic, elephant ears, with the terminal wall on the superstructure. See File Nos. 0.03-11 thru -14.. Wingwalls oriented parallel to traffic, u-back wings, with the terminal wall on the superstructure. Offset the inside face of wall 3 feet from the face of rail/parapet to allow for dynamic deflection of the attached guardrail. See File Nos. 0.03-15 thru -18. It is generally desirable to eliminate potential conflicts between superstructure and substructure components. As such, the second layout preference should only be used where right-of-way (R/W), maintenance of traffic (MOT) or design restrictions make the preferred layout not feasible. For design/detailing check list for semi-integral abutments, see File Nos. 0.03-19 and -0. SHEET 1 of 0 GENERAL INFORMATION FILE NO. 0.03-1 VOL. V - PART DATE: 11May007
Given and Assumptions: DESIGN OF SEMI-INTEGRAL BRIDGE The calculations provided below do not fully correspond to the details shown in File Nos. 0.03-11 thru -14 but are similar. γ 145 pcf K p 4 Unit weight of soil (select backfill material) (See Manual of S&B Division Vol. V - Part, file no. 17.10-) Assumes the use of EPS material behind backwall W 43.33 Total bridge width Bridge L 50.0 ft Bridge length Bridge L Thermal 15.0 ft Length of thermal expansion H 6.33 ft Backwall height Backwall T 1.58 ft Backwall thickness Backwall S 9.33 ft Beam spacing Beam Overhang 3.0 ft Cover 3.5 in Slab (and integral backwall) overhang Cover over reinforcing steel in backwall f c 4,000 psi Compressive strength of backwall concrete f 3,000 psi Compressive strength of wing concrete cwall f y 60,000 psi θ 30 deg -6 α 6.5 x 10 per deg F D AS 1.5 ft Yield strength of reinforcing steel Bridge skew angle Coefficient of thermal expansion Depth of approach slab at backwall H 3.0 in Height of bearing Bearing T 1 in Thickness of bottom flange bottomflange T 15.0 in Wing thickness wing n b E s 8 Modular ratio of concrete to steel for backwall 1.5 ' 33w fc n w E s 9 Modular ratio of concrete to steel for wing 1.5 ' 33w fcwall SHEET of 0 SAMPLE DESIGN CALCULATIONS FILE NO. 0.03- VOL. V - PART DATE: 11May007
SHEET 3 of 0 SAMPLE DESIGN CALCULATIONS FILE NO. 0.03-3 VOL. V - PART DATE: 11May007
Design of Backwall: Determine backwall moments and shears 1 w K (H p Backwall ) γ Earth pressure resultant per foot 1 w 145 pcf x 1k/1000 lbs)(4)(6.33 ft) ( 11.6 klf SBeam L Beam/girder spacing along skew cos θ 9.33 ft L 10.77 ft o cos 30 For simplicity, use the following equations to determine moments, shear, and reaction. M 0.08wl pos 0.08(11.6 klf)(10.77 ft) 107.6 ft-kip Maximum positive moment neg M 0.10wl 0.10(11.6 klf)(10.77 ft) 134.6 ft-kip Maximum negative moment V max 0.6wl 0.6(11.6 klf)(10.77 ft) 75.0 k Maximum shear R max 1.1wl 1.1(11.6 klf)(10.77 ft) 137.4 k Maximum reaction at girder Check to make sure overhang does not govern. M OH Overhang 0.5w cos θ 3.0 ft 0.5(11.6 klf) o cos 30 M OH 69.6 ft-kip < M Interior support governs neg V OH Overhang w 3.0 ft (11.6 klf) 40. k < V max Interior support governs o cos θ cos 30 SHEET 4 of 0 SAMPLE DESIGN CALCULATIONS FILE NO. 0.03-4 VOL. V - PART DATE: 11May007
Design Integral Backwall: Group IV load combination controls. Group IV allowable overstress is 15%. **For this example, Group IV loading controls the design. It shall be the responsibility of the designer to verify which load case controls, and design accordingly. fs 15%(0.4F y ) f s 30,000 psi Allowable stress of steel f c 15%(0.4f c ) f c,000 psi Allowable of stress of concrete ' v c.allowabl e 15%(0.95 fc ) v c.allowable 75 psi Allowable shear stress in concrete Flexure design using negative moment: n 8 Modular ratio of backwall concrete to steel h T Backwall h 19.0 in Height of section resisting flexure D 76.0 in 18.0 in 58.0 in Width of section resisting flexure b H Backwall AS d 1 h Cover 19.0 in 3.5 in 15.5 in d h 10.0 in 19.0 in 10 in 9.0 in Depth to first mat of reinforcing steel Depth to second mat of reinforcing steel d 3.5 in Depth to compression steel Try #6 bars at ~9 spacing. For this backwall height, there are 7 bars in each tension layer. A s1 3.08 in As 3.08 in A s1d1 + A sd d Depth to centroid of tension steel A s1 + A s 3.08 in (15.5 in) + 3.08 in (9.0 in) d 1.5 in 3.08 in 3.08 in + 3.08 in 7 bars in compression layer A sc Performing section analysis (including the compression steel) Y 3.75 in Distance from compression face to neutral axis NA F s1 9,800 psi < f s.allowable 30,000 psi OK In first layer of tension steel F c 1,00 psi < f c.allowable,000 psi OK SHEET 5 of 0 SAMPLE DESIGN CALCULATIONS FILE NO. 0.03-5 VOL. V - PART DATE: 11May007
Shear Design: V V max 75.0 k Vmax 75.0 k(1000 lbs/1k) v 106 psi Actual shear stress in concrete 58.0 in(1.5 in) ( bd) v > v c.allowable, Shear reinforcement required v c.allowable 75 psi Use #4 stirrups, with legs in the shear plane, A v 0.4 in. Equation (8-7) from AASHTO Sec. 8.15.5.3 ( A fs.allowable ) ( v v ) 0.4 in (30,000 psi) s v 6.7 in b (106 psi 75 psi)58.0 in Stirrup spacing c.allowable Check AASHTO Sec. 8.19.1. to see if spacing above is OK. A v.min ( 50bs) f y Rearranging the above equation, with A v 0.4 in : s ( A f ) v.min 50b s 6.7 in controls y 0.4 in (60,000 psi) 8.3 in 50(58.0 in) Shear Stud Design at Girder Ends: Z r 8.1 k For 7 / 8 φ AASHTO Sec. 10.38.5.1.1 Z r 15%(8.1 k) Z r 10.15 k Horizontal shear capacity per stud, with 5% overstress n R Z 137.4 k 10.15 k max studs r 13.5 Therefore, use 7, 7 / 8 φ studs on each side of beam web, for a total of 14 studs. SHEET 6 of 0 SAMPLE DESIGN CALCULATIONS FILE NO. 0.03-6 VOL. V - PART DATE: 11May007
Determine reaction at acute corner and wing buttress: See lateral force derivation in files nos. 0.07-4 thru -6. R ( w( W ) tan θ) W 1 + L Bridge Bridge [11.6 klf(43.33 ft)tan 30 43.33 ft o tan θ 1 + tan 30 50 ft Bridge o ] p 63.8 k Determine size of rub plates: Δ t 10 deg. L Thermal ΔL rub 15.0 ft L 3 Thermal αδ t 6 o ΔLrub [15 ft(1 in/1ft)](6.5 10 per deg. F)(10 F) 0.78 in 3 Estimated maximum movement in one direction at abutment. Assume that the temperature increase will only be two-thirds of the total range. h rp H Backwall - 3 in - in - H Bearing Tbottomflange Height of rub plates (See note 4 on File No. 0.03-19) h rp 6.33 ft(1 in/1 ft) 3 in in 3 in 1 in 67 in F g,000 psi Maximum galling stress for ASTM A76 Type 316 steel, of which the rub plates are constructed. f g 0.55 F 1,100 psi Allowable galling stress min g Rp w Minimum rub plate width ( h f ) rp g 63.8 k(1000 lbs/1 k) w min 3.58 in 67 in(1,100 psi) SHEET 7 of 0 SAMPLE DESIGN CALCULATIONS FILE NO. 0.03-7 VOL. V - PART DATE: 11May007
Ensure the minimum rub plate width is maintained during extremes of the temperature cycle. w wmin + ΔL rub 3.58 in + 0.78 in 4.36 in Use 5 in x 64 in x 0.5 in rub plate Design wing haunch to resist load transferred through the rub plates: Slope 1.5 Rate of slop of wing per ft w R H 63.8 k 6.33 ft p w Backwall ( w H ) 41.7 klf Assume that the resultant is uniformly distributed along the rub plate w Backwall Ms Moment about seat level 41.7 klf(6.33 ft) Ms 835.4 ft kip SHEET 8 of 0 SAMPLE DESIGN CALCULATIONS FILE NO. 0.03-8 VOL. V - PART DATE: 11May007
V R p 63.8 k Shear force L wing.0 ft + H Backwall (Slope) Length of shear plane that is resisting R p L wing.0 ft + 6.33 ft(1.5) 11.5 ft C 4.5 in Centroid of tension steel cg L C Distance from compression face to cg of d wing wing cg tension steel d wing 11.5 ft (4.5 in(1 ft/1 in) 11.1 ft v c allowable wing 15%(0.95 f ' cwall ) v c allowable wing T wing 15.0 in 65 psi Allowable shear stress for Group IV V 63.8 k(1000 lbs/1k) v 13 psi Actual shear stress T d 15.0 in[11.1ft(1 in/1ft)] wing wing v > v c allowable, Shear reinforcement required Use #4 stirrups, with legs in the shear plane, A v 0.4 in. Equation (8-7) from AASHTO Sec. 8.15.5.3 s A f v s allowable Stirrup spacing s ( v v c allowable wing ) Twing 0.4 in (30,000 psi) 11.9 in (15.0 in) ( 13 psi - 65 psi) Check AASHTO Sec. 8.19.1. to see if spacing above is OK. A v.min ( 50bs) f y Rearranging the above equation, with A v 0.4 in : A v.minf s 50T y wing 0.4 in (60,000 psi) 3 in 50(15.0 in) s 11.9 in controls SHEET 9 of 0 SAMPLE DESIGN CALCULATIONS FILE NO. 0.03-9 VOL. V - PART DATE: 11May007
Design Wing Reinforcement to resist moment due to R p : Try two rows of #5 bars, with 5 bars per row d 1 L wing Cover Depth to first mat of reinforcing steel d 1 11.5 ft(1 in/1 ft) 3.5 in 134.5 in d d 1 3 in 134.5 in 3 in 131.5 in Depth to second mat of reinforcing steel A s1 1.53 in A s 1.53 in Performing section analysis (including the compression steel) f s1 5,940 psi < f s allowable 30,000 psi OK in first layer of tension steel f c 350 psi < f c allowable,000 psi OK Thickness of the EPS layer: Thickness of EPS layer as per File No. 0.06-6: Δt 10 F Δ L (L thermal αδt) Δ L 15.0 ft(1in/1ft)(6.5x10-6 per deg. F )10 F 1.17 in Total range of movement at abutment due to temperature EPS t 10(0.01H Backwall + 0.67Δ L ) EPS t 10[(0.01)(76.0 in)+ (0.67)(1.17 in)] 15.4 in Therefore, use EPS t 16 in. NOTE: DESIGN FOR PRESTRESSED CONCRETE BEAMS IS SIMILAR. VOL. V - PART DATE: 11May007 SHEET 10 of 0 SAMPLE DESIGN CALCULATIONS FILE NO. 0.03-10
CHECK LIST FOR 1 Wing haunch at acute corner shall be designed to resist the moment and shear induced by the force resulting from the passive earth pressure and the skew. Rub plates and the additional backwall thickness are only required at the acute corners of skewed bridges. Rub plates to be centered vertically and horizontally over contact area. Minimum thickness of the preformed joint filler between the backwall and the wing at the obtuse corner shall be 1. This may be increased due to thermal expansion in the transverse direction. 3 Extend wing 6 above finished grade. Not required for bridges without skew or where terminal wall is on the substructure. 4 Top of rub plate to begin 3 below top of deck. Bottom of rub plate to maintain clear from top of bottom flange for steel superstructures; 3 clear from bottom of beam for concrete. Preformed joint filler to extend as shown. 5 Provide distance from back of stem to break in seat to allow for contraction and creep with 1 clear. 6 Delete this note if railings are used or slip forming of parapets is not allowed. 7 Bridge plans shall be arranged such that backwall details follow the Deck Plan. For general sheet order, see File No. 01.0-4. 8 Show plan and elevation view of integral backwall at a preferred scale of 3 / 8 1-0. The elevation view should be projected down from the plan view. When bridge is not on skew and where sufficient room is not available in elevation view, plan view is not required. 9 Label the location centerline/baseline as shown on the title sheet. 10 End of slab shall be used as the reference line for layout of integral backwalls. 11 Label skew angle (if applicable). 1 The minimum width of integral backwall shall be 1-7 for steel stringers and 1-10 for concrete stringers. Clipping flanges is preferable to increases in thickness where required due to skew. 13 All ST series and SV series bars shall be aligned parallel to the beam/girder centerline. The maximum spacing shall be 1. ST060 bars between the backwall and the approach slab (where applicable) are not required outside of the exterior beam/girder. 14 Thickness of backwall shall be increased by 10 at the acute corner of skewed bridges outside of the exterior stringers. The increase in thickness shall end at the top surface of the bottom flange for steel stringers or 1 above the bottom of beam for concrete stringers. 15 ST0501, ST060, SV040 and SV0504 shall be galvanized. All other backwall reinforcing steel shall be epoxy-coated. 16 Distance between face of integral backwall and back of stem shall be a minimum of 4. VOL. V - PART DATE: 11May007 SHEET 19 of 0 CHECK LIST FILE NO. 0.03-19
CHECK LIST FOR (Continued) 17 The approach slab seat (7 ) shall be provided on all integral backwalls regardless of whether the bridge will have an approach slab. 18 In case of single span semi-integral bridge, use the temporary blocking note shown. Otherwise, delete it. 19 Show sections taken through the integral backwall at a preferred scale of 3 / 4 1-0. Coordinate the sections to provide the necessary details with repetition only where required. 0 Location and details of holes in the web and the studs should be included with the beam/girder details. 1 For additional details concerning the use of EPS material and calculations for the required thickness, see File No. 0.06-6. To ensure adequate cover on ST060 bar, the designer must modify the approach slab standard. 3 Maximum spacing is 1. 4 Note not needed for PCBT-53 and larger. 5 The minimum embedment into the backwall is 6 for steel stringers and 9 for concrete stringers. 6 When approach slab is used with concrete superstructure, hook ST060 bar and embed as shown. 7 For instructions on completing the title block, see File No. 03.03. 8 For instructions on completing the project block, see File No. 03.0. 9 For instructions on developing the CADD sheet number, see File Nos. 01.01-7 and 01.14-4. VOL. V - PART DATE: 11May007 SHEET 0 of 0 CHECK LIST FILE NO. 0.03-0