APPENDIX B ABC STRUCTURES DESIGN GUIDE

Transcription

1 APPENDIX B ABC STRUCTURES DESIGN GUIDE The Cohos Evamy Partners

2 TABLE OF CONTENTS Page No. DISCLAIMER... I 1. STRUCTURAL DESIGN GUIDELINES GENERAL REQUIREMENTS (FIGURE B.2, STEP 1) GENERAL LAYOUT AND GEOMETRY (FIGURE B.2, STEP 2) LOADS (FIGURE B.2, STEP 3) MATERIALS (FIGURE B.2, STEP 4) EQUILIBRIUM OF ARCH-BEAM-CULVERT (FIGURE B.2, STEP 5) DEAD LOAD DESIGN ACTIONS (FIGURE B.2, STEP 6) LIVE LOAD DESIGN MOMENTS FOR ROOF SLAB (FIGURE B.2, STEP 7) LIVE LOAD DESIGN SHEARS FOR ROOF SLAB, MOMENTS AND SHEARS FOR HORIZONTAL ARM, AND AXIAL FORCE IN CULVERT WALL (FIGURE B.2, STEP 8) DESIGN ROOF SLAB AND ARMS FOR SHEAR AT ULTIMATE LIMIT STATE (FIGURE B.2, STEP 9) CULVERT TOP PLATE STRENGTH IN TENSION (FIGURE B.2, STEP 10) DESIGN ROOF SLAB AND ARMS FOR FLEXURE AND AXIAL LOADS AT ULTIMATE LIMIT STATE (FIGURE B.2, STEP 11) SHEAR CONNECTORS FOR ULTIMATE LIMIT STATE (FIGURE B.2, STEP 12) TRANSFER OF AXIAL FORCE FROM CULVERT TO SLAB (FIGURE B.2, STEP 13) SERVICE LOAD RESISTANCE OF BOLTED JOINTS (FIGURE B.2, STEP 14) FATIGUE LIMIT STATE STRESSES AND FORCES (FIGURE B.2, STEP 15) FATIGUE RESISTANCE (FIGURE B.2, STEPS 16, 17 AND 18) DISTRIBUTION REINFORCEMENT (FIGURE B.2, STEP 19) CULVERT PLATE AND SEAM STRENGTH IN COMPRESSION (FIGURE B.2, STEPS 20 AND 21) SOIL CAPACITY UNDER ARMS AND ADJACENT TO CULVERT SIDE WALLS (FIGURE B.2, STEP 22) HEADWALL BEAMS AND FOOTINGS (FIGURE B.2, STEP 23)... 9 The Cohos Evamy Partners

3 DISCLAIMER The material presented in these structural design guidelines has been prepared in accordance with generally recognized engineering principles and practices for Alberta Transportation. These guidelines should only be used by qualified consultants designing structures for Alberta Transportation. In using the guidelines, the principles of CAN/CSA- S6-00, Canadian Highway Bridge Design Code must be applied, and appropriate engineering judgment used. CONTACT Questions or further information on this guideline may be directed to Raymond Yu, P.Eng., Structural Standards Engineer, Alberta Transportation (780) The Cohos Evamy Partners i

4 1. STRUCTURAL DESIGN GUIDELINES Figure B.1 shows the Arch-Beam-Culvert system. The system consists of a structural plate corrugated steel pipe, surrounded by compacted granular backfill, with a reinforced concrete slab on top. Horizontal arms project transversely from the slab, beyond the steel pipe on either side of the structure. The slab acts compositely with the corrugated steel pipe to resist load from fill placed above and vehicular traffic passing over top of the structure. Arch-Beam-Culverts are normally used in installations where the depth of cover (Figure B.1) is small. Figure B.2 provides a flow chart that can be used to organize the structural design calculations for these structures. 2. GENERAL REQUIREMENTS (Figure B.2, Step 1) Arch-Beam-Culverts shall be designed to conform to the requirements of CAN/CSA-S6-00. Normally, the design life of these structures will be 75 years. For sites with highly corrosive environmental conditions, it may not be possible to achieve the design life of 75 years required by Clause As part of the normal evaluation process, the potential for early replacement should be considered and Arch-Beam-Culverts should be compared to other structural alternatives using life-cycle cost analysis. Prior to initiating structural design, geotechnical, hydraulic, and corrosion investigations for the site must be undertaken by qualified specialists. 3. GENERAL LAYOUT AND GEOMETRY (Figure B.2, Step 2) The general layout and cross-sectional geometry for the Arch-Beam-Culvert shall be selected to satisfy the requirements of the project. Roof slab span lengths, L, shall be limited to the range of 5 to 10 m. Rise-to-span ratios for the roof slab shall be no larger than 0.2. The lengths of the horizontal arms shall be not less than 0.15 L. The minimum roof slab span to culvert span ratio shall be The Cohos Evamy Partners 1

5 The minimum thicknesses of the culvert plates shall be not less than those required for a culvert of the same dimensions meeting the minimum cover requirements of CAN/CSA-S6-00, Clause In addition, the minimum thickness of the top and side plates shall be 5 mm to allow for the welding of studs and for durability considerations. The minimum thickness of the bottom plates shall be 4 mm. The minimum bottom width of the excavation and compacted granular backfill shall be (L + 2a). A 200 mm thick layer of uncompacted granular backfill shall be placed below the bottom plates. 4. LOADS (Figure B.2, Step 3) The load factors and load combinations used for the design of conventional bridge structures shall be used for the proportioning of Arch-Beam-Culverts. The design live load in Alberta is the CL800 Truck. For live load effects, the dynamic load allowance for arch type buried structures in accordance with Clause shall be used. It should be noted that where asphaltic wearing surface is placed directly in contact with the crown of the roof slab, it is not considered as earth cover and there will be no reduction in dynamic load allowance. Where appropriate, an allowance should be made for the dead load from an additional 100 mm thickness of wearing surface placed at some time in the future. Temporary supports are generally placed 30 mm below the top plates prior to pouring the roof slab concrete when the roof slab is cast. All loads including the weight of the slab, the soil and asphalt wearing surface within the slab span above the roof, and live loads shall be carried by the composite roof slab. 5. MATERIALS (Figure B.2, Step 4) Structural Plate Corrugated Steel Pipe shall be in accordance with the current edition of CSA G401. The designer may consider the increase in yield strength that occurs as a result of cold working of the corrugated plates during manufacturing when substantiated by the appropriate test results. High quality backfill is required around Arch-Beam-Culverts to ensure that the structural performance is satisfactory. Reinforcing bars shall be epoxy coated. The Cohos Evamy Partners 2

6 Class SF concrete shall be used for Class A Highways. Class C concrete is acceptable for Class B and lesser highways. 6. EQUILIBRIUM OF ARCH-BEAM-CULVERT (Figure B.2, Step 5) The analytical model shown in Figure B.3 may be used to determine the dead load design actions and live load bending moments in a one metre wide strip of the structure. Figure B.3(a) shows the free body diagram of the roof slab and the soil above. In this figure, W r is the weight of the roof slab, W s is the weight of the soil and W is the portion of truck wheel load distributed to the one metre wide strip. At node B, M D is the dead load moment, M L is the moment from wheel load, H D is the dead load axial force, and H L is the axial force from wheel load. At node A, M r, V r and H r are the roof slab moment, vertical force and horizontal force, respectively. Horizontal forces H S1 and H S2 are the resultant forces from horizontal soil pressures. In this figure K o is the at-rest horizontal earth pressure coefficient and γ is the unit weight of the backfill. Figure B.3(b) shows the free body diagram for node A. The moments, M, vertical forces, V, and horizontal forces, H, have subscripts r, a and c to represent the roof slab, horizontal arm and culvert wall below, respectively. Figure B.3(c) shows the free body diagram for the horizontal arm. The distance along the arm to the resultant vertical reaction from soil pressures below is assumed to be 0.5a. As a conservative simplification when using Figure B.3 for the design of the roof slab, it may be assumed that 75 percent of the vertical load on the roof slab is carried by the culvert sidewall and the remainder by the horizontal arm. For the design of the culvert side wall, it may be assumed that 100 percent of the vertical load on the roof slab is carried by the culvert wall below. If the depth of soil cover above the slab is small, the resultant forces from horizontal soil pressures may be ignored. In the design of the roof slab for shear and bending moment, it is generally conservative to neglect the horizontal forces H r, H D, and H L. 7. DEAD LOAD DESIGN ACTIONS (Figure B.2, Step 6) Once the dead loads are determined from the geometry, the analytical model in Figure B.3 may be used to calculate the dead load actions for the design of the Arch-Beam-Culvert. The Cohos Evamy Partners 3

7 8. LIVE LOAD DESIGN MOMENTS FOR ROOF SLAB (Figure B.2, Step 7) Once the portion of the wheel load distributed to the one metre wide strip in Figure B.3 is determined, the analytical model may be used to calculate the live load longitudinal bending moments for the design of the roof slab at the ultimate, serviceability and fatigue limit states. It may be assumed that the second two axles of the design truck are positioned symmetrically over the centre of the structure. The provisions of CAN/CSA-S6-00, Clause may be used to determine the truck wheel load distribution. The distribution for longitudinal bending at the ultimate and serviceability limit states may be determined from [Clause (b)] m 2F Wheel load distribution = nr m L = (1) Mwheel Be The distribution for bending at the fatigue limit state may be determined from [Clause (d)] m 2Fm Wheel load distribution = = (2) M B wheel e In these equations, m is the maximum longitudinal moment per metre width, M wheel is the maximum moment for a line of wheel loads, F m is an amplification factor to account for transverse variation in maximum longitudinal moment intensity compared to average longitudinal moment intensity, n is the number of design lanes and B e is the effective barrel length of the Arch-Beam-Culvert. These parameters are defined further in CAN/CSA-S6-00. The effective barrel length shall be taken as not more than the clear roadway width between guardrails plus 0.5 m on either side. In determining the wheel load distribution and design moments, the span should be taken as the roof slab span, L. The Cohos Evamy Partners 4

8 9. LIVE LOAD DESIGN SHEARS FOR ROOF SLAB, MOMENTS AND SHEARS FOR HORIZONTAL ARM, AND AXIAL FORCE IN CULVERT WALL (Figure B.2, Step 8) The provisions of CAN/CSA-S6-00, Clauses (b) and may be used to determine the live load longitudinal vertical shears near the mid-span of roof slabs. The span of the roof slab shall be taken as L. Near the ends of the slab, the live load longitudinal vertical reaction for all of the design lanes on the structure shall be distributed uniformly over an effective width equal to the sum of the lane widths plus the sum of the depth of fill and one-half of the slab thickness on either side of the lanes. The effective width calculated in this way must be less than the barrel length of the structure. In determining the live load longitudinal vertical reaction per metre width near the ends of the slab, the wheel loads may be distributed parallel to the span in accordance with Clause The live load reaction shall be multiplied by the appropriate modification factor for multilane loading. For design, the live load longitudinal vertical reaction per metre width near the ends of the roof slab may be resolved into a radial shear component and a tangential axial force component. In determining the resultant vertical reaction from soil pressures, V a, in Figure B.3(c), for the design of the horizontal arm at the ultimate and fatigue limit states, the live load reaction from wheel load may be taken as 50 percent of the uniformly distributed live load longitudinal vertical reaction per metre width at the ends of the roof slab. The culvert side wall immediately below the roof slab should be proportioned to resist 100 percent of the uniformly distributed live load longitudinal vertical reaction per metre width from the roof slab at the ultimate limit state. The live load axial force per metre width in the culvert wall is equal to the design live load reaction per metre width divided by the sine of the angle the wall makes with the horizontal. The potential for the settlement of the soil under the horizontal arms shall be taken into consideration in the design of the arms and the culvert wall below the arms. The Cohos Evamy Partners 5

9 10. DESIGN ROOF SLAB AND ARMS FOR SHEAR AT ULTIMATE LIMIT STATE (Figure B.2, Step 9) The requirements of CAN/CSA-S6-00, Clause for beam action should be used to proportion the roof slab and horizontal arms to resist the design shears. The requirements of Clause should be used to check the roof slab for two-way shear under the action of truck wheel loads. The critical location will be near the slab mid-span where the wheel loads are applied directly on the roof slab. Shear strength requirements will normally control the thickness of the roof slab. The slab thickness should be selected so that no shear reinforcement is required. 11. CULVERT TOP PLATE STRENGTH IN TENSION (Figure B.2, Step 10) The culvert top plate acts compositely with the roof slab to resist bending moments. The culvert wall strength in tension is needed to determine the flexural strength of the composite roof slab. The axial tensile resistance of the culvert top plate may be determined from Clause using a resistance factor for the culvert steel of The tension capacity of the culvert at longitudinal seams between adjacent structural plate corrugated steel pipe sections may be determined by calculating the shear resistance of the bolted connections. Clause may be used to check the bearing resistance of the culvert wall adjacent to bolts and the shear resistance of bolts using a resistance factor of Calculations should assume that bolt threads are intercepted by a shear plane. 12. DESIGN ROOF SLAB AND ARMS FOR FLEXURE AND AXIAL LOADS AT ULTIMATE LIMIT STATE (Figure B.2, Step 11) The requirements of CAN/CSA-S6-00, Clause 8.8 should be used to proportion the roof slab and horizontal arms to resist the design moments. In designing the roof slab for longitudinal bending moment, the culvert top plate and the circumferential reinforcing steel may be considered as the flexural reinforcement. The contribution of the culvert top plate is limited to the tensile capacity determined in Figure B.2, Step 10. The Cohos Evamy Partners 6

10 13. SHEAR CONNECTORS FOR ULTIMATE LIMIT STATE (Figure B.2, Step 12) The tensile force in the culvert wall at the ultimate limit state must be developed between the point of maximum moment in the composite roof slab and the location of minimum moment at the intersection of the horizontal arm and the culvert. CAN/CSA-S6-00, Clause may be used to determine the number of connectors required to transfer this force. 14. TRANSFER OF AXIAL FORCE FROM CULVERT TO SLAB (Figure B.2, Step 13) The shear connectors between the culvert wall and the roof slab must transfer the axial force in culvert below into the roof slab. CAN/CSA-S6-00, Clause may be used to determine the number of connectors required. These shear connectors are in addition to those determined in Figure B.2, Step SERVICE LOAD RESISTANCE OF BOLTED JOINTS (Figure B.2, Step 14) The service load tension in the longitudinal bolted joints between adjacent structural plate corrugated steel pipe sections may be determined by the cracked transformed section approach. When the factored tensile resistance calculated from Step 10 is limited to less than 55 percent of the unfactored seam strength in compression, service load deformations of the bolted splices should be acceptable and no further investigation will be required. 16. FATIGUE LIMIT STATE STRESSES AND FORCES (Figure B.2, Step 15) The stresses in the culvert top plate and circumferential reinforcing steel in the composite roof slab at the fatigue limit state may be determined by the cracked transformed section approach. The Cohos Evamy Partners 7

11 17. FATIGUE RESISTANCE (Figure B.2, Steps 16, 17 and 18) For the top plate portion of the culvert acting compositely with the roof slab, the longitudinal seams between adjacent plate sections shall be assessed for structural fatigue using Clause of CAN/CSA-S6-00. Stresses should be checked at the net section of the culvert wall for the fatigue stress range resistance determined from the average of the resistances for detail categories (C) and (D). CAN/CSA-S6-00, Clause should be used to determine the fatigue resistance of reinforcing steel in the composite slab. CAN/CSA-S6-00, Clause may be used to determine the fatigue resistance of the studs connecting the culvert wall to the concrete roof slab. 18. DISTRIBUTION REINFORCEMENT (Figure B.2, Step 19) Distribution reinforcement is required to resist the transverse moments in the roof slab. The transverse reinforcement should be sized to resist a transverse bending moment of 30 percent of the maximum longitudinal moment from truck loading at the ultimate limit state. The amount of transverse reinforcement shall be not less than that required by Clause CULVERT PLATE AND SEAM STRENGTH IN COMPRESSION (Figure B.2, Steps 20 and 21) For the portion of the culvert below the horizontal arms, the wall strength and seam strength in compression shall be reviewed for the factored axial forces using the procedures in Clause 7.6 of CAN/CSA-S6-00. In reviewing the culvert wall strength using Clause , the modified modulus of soil stiffness should be used, the factor λ should be taken as 1.22 and the reduction factor accounting for depth of cover, ρ, may be taken as 1.0. The continuous longitudinal seam between the side plates and the top plates near the end of the roof slab shall be detailed as shown in Figure B.4. The Cohos Evamy Partners 8

12 20. SOIL CAPACITY UNDER ARMS AND ADJACENT TO CULVERT SIDE WALLS (Figure B.2, Step 22) The soil capacity for vertical loads transferred by the horizontal arms to the backfill below and the horizontal soil pressure adjacent to the side walls of the culvert should be reviewed. The vertical soil pressures under the arms and the horizontal soil pressures adjacent to the culvert side walls shall not exceed 500 kpa and 650 kpa for the serviceability and ultimate limit states, respectively. 21. HEADWALL BEAMS AND FOOTINGS (Figure B.2, Step 23) Headwall beams are normally placed at the ends of the Arch-Beam-Culverts to stiffen the structure and retain soil. These beams shall be supported on spread footings. Unless a refined analysis is undertaken, the headwall beams shall be proportioned to support a single line of truck wheel loads applied in the vertical direction and soil pressures applied in the horizontal direction. The resultant vertical force acting on the soil below the spread footings supporting the ends of the headwall beams shall be taken as 100 percent of the vertical reactions from dead and live loads at the end of the beam. The Cohos Evamy Partners 9

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14 START 1 General Requirements Design Life Geotechnical Requirements Hydraulic Requirements Corrosion Requirements 2 Select General Layout and Cross-Sectional Geometry 3 Establish: Load Factors and Load Combinations [CAN/CSA-S6-00, Clause 3.5] Dead Loads [CAN/CSA-S6-00, Clause 3.6] Live Load [CAN/CSA-S6-00, Clause 3.8] Dynamic Load Allowance [CAN/CSA-S6-00, Clause ] FIGURE B.2: FLOW CHART FOR THE DESIGN OF ARCH-BEAM-CULVERTS The Cohos Evamy Partners

15 4 Select Materials: Structural Plate Corrugated Steel Pipe Compacted Granular Backfill Concrete Reinforcing Steel Shear Studs 5 Equilibrium of Arch-Beam-Culvert Figure B.3 6 Determine Dead Load Design Actions Figure B.3 7 Determine Live Load Moments For Roof Slab: Longitudinal Bending Moment for Ultimate and Serviceability Limit States [CAN/CSA-S6-00, Clause (b)] Longitudinal Bending Moment for Fatigue Limit States [CAN/CSA-S6-00, Clause (d)] Figure B.3 The Cohos Evamy Partners FIGURE B.2 (CONT D)

16 8 Determine Live Load Shears For Roof Slab, Moments and Shears For Horizontal Arm And Axial Force In Culvert Wall Longitudinal Vertical Shear for Ultimate and Serviceability Limit States [CAN/CSA-S6-00, Clause (b)] Longitudinal Vertical Shear for Fatigue Limit States [CAN/CSA-S6-00, Clause ] Distribute Wheel Loads Through Fill Near Ends of Slab [CAN/CSA-S6-00, Clause ] Figure B.3 9 Design Roof Slab And Arms For Shear At Ultimate Limit State [CAN/CSA-S6-00, Clauses and ] 10 Determine Culvert Top Plate Strength In Tension [CAN/CSA-S6-00, Clauses and ] 11 Design Roof Slab And Arms For Flexure and Axial Loads At Ultimate Limit State [CAN/CSA-S6-00, Clause 8.8] 12 Shear Connectors For Ultimate Limit State [CAN/CSA-S6-00, Clause ] The Cohos Evamy Partners FIGURE B.2 (CONT D)

17 13 Provide Additional Shear Connectors To Transfer Axial Force From The Culvert Wall Near The Ends Of The Span To The Roof Slab 14 Check The Service Load Resistance Of The Bolted Joints In The Connections Between Adjacent Plate Sections 15 Determine Fatigue Limit State Stresses and Forces 16 Check Fatigue Resistance of Culvert Wall [CAN/CSA-S6-00, Clauses and ] 17 Check Fatigue Resistance of Reinforcing Steel [CAN/CSA-S6-00, Clause ] The Cohos Evamy Partners FIGURE B.2 (CONT D)

18 18 Check Shear Connectors for Fatigue Resistance [CAN/CSA-S6-00, Clause ] 19 Provide Distribution Reinforcement [CAN/CSA-S6-00, Clause ] 20 Review Culvert Wall Strength, Check Side and Bottom Plate Thicknesses [CAN/CSA-S6-00, Clause ] 21 Review Culvert Seam Strength [CAN/CSA-S6-00, Clause ] The Cohos Evamy Partners

19 FIGURE B.2 (CONT D) 22 Soil Capacity Review Bearing Capacity of Soil Under Arms [CAN/CSA-S6-00, Clause 6.7.2] Check Horizontal Soil Pressure Adjacent To Side Walls 23 Design Headwall Beams and Footings: Select Geometry Determine Wheel Load Distribution [CAN/CSA-S6-00, Clause ] Determine Design Shear Forces and Bending Moments Design for Flexure At Ultimate Limit State [CAN/CSA-S6-00, Clause ] Design For Shear At Ultimate Limit State [CAN/CSA-S6-00, Clause ] Design Spread Footings Supporting Headwall Beams END The Cohos Evamy Partners FIGURE B.2 (CONT D)

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