ALDOT Structural Design Manual - ALDOT - Home
Structural DesignManualALDOT Bridge BureauJanuary 2021
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ALDOT Structural Design ManualREVISIONS since May 2020 Edition Revised Preface, I. ALDOT Policy statement Revised Preface, III. Design Method/Specification, updated AASHTO LRFDto 9th Edition Revised Preface, V. Approval, updated Chief Engineer Revised Section 2.1 to include criteria for bridge widths Deleted paragraph 13 in Section 5.2 Added Section 5.5, minimum deck requirements Added Section 5.6, mass concrete Added Section 6.6, minimum deck requirements Revised Section 9.1, deleted requirement for bridge decks to be designedusing bridge deck chart (old Figure 9.1). Added requirements for standardbridge decks for ALDOT projects. Revised Figure 9.1. Revised Section 16, deleted Figure 16.1March 2021 Revisions Revised Section 5.2: Revised first sentence of section; added paragraph 10,renumbered remaining paragraphs.January 2021R-1
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ALDOT Structural Design ManualTABLE OF CONTENTSPREFACE ------------------------------------------------- iiiI. ALDOT Policy Statement -------- iiiII. Purpose and Scope --------------- iiiIII. Design Method/Specifications - ivIV. Related ALDOT Manuals/Documents ----------------------------------------- ivV. Approval ----------------------------- vSECTION 1. INTRODUCTION -------------------- 1-11.1 Limit States ---------------------- 1-1SECTION 2. GENERAL DESIGN AND LOCATION FEATURES ------------------------ 2-12.1 Clearances ---------------------- 2-12.2 Deformations ------------------- 2-22.3 Drainage ------------------------- 2-2SECTION 3. LOADS AND LOAD FACTORS - 3-13.1 Permanent Loads -------------- 3-13.2 Water and Wind Loads ------- 3-13.3 Temperature Force Effects - 3-1SECTION 4. STRUCTURAL ANALYSIS AND EVALUATION ---------------------------- 4-1SECTION 5. CONCRETE STRUCTURES ---- 5-15.15.25.35.45.55.6Concrete Compressive Strengths ------------------------------------------- 5-1Prestressed Concrete Girder Design Policy ------------------------------ 5-2Intermediate Diaphragms --- 5-4Steel Reinforcement ---------- 5-4Decks ---------------------------- 5-5Mass Concrete ---------------- 5-5SECTION 6. STEEL STRUCTURES ------------ 6-16.16.26.36.46.56.6Materials ------------------------- 6-1Girder Design Policy ---------- 6-1Shear Connectors ------------- 6-3Shop Connections ------------- 6-3Field Connections ------------- 6-4Decks ---------------------------- 6-4SECTION 7. ALUMINUM STRUCTURES ----- 7-1January 2021i
ALDOT Structural Design ManualSECTION 8. WOOD STRUCTURES ------------ 8-1SECTION 9. DECKS AND DECK SYSTEMS -------------------------------------------------- 9-19.1 Reinforced Concrete Decks -------------------------------------------------- 9-19.2 Incremental Deck Finish Grade Elevations ------------------------------- 9-1SECTION 10. FOUNDATIONS ----------------- 10-110.1 Scour -------------------------- 10-110.2 Piling -------------------------- 10-110.3 Geotechnical Coordination ------------------------------------------------ 10-3SECTION 11. ABUTMENTS, PIERS, AND WALLS ---------------------------------------- 11-111.1 Abutments ------------------- 11-111.2 Bents/Piers ------------------ 11-111.3 Retaining Walls ------------- 11-2SECTION 12. BURIED STRUCTURES AND TUNNEL LINERS ------------------------ 12-112.1 Reinforced Concrete Box Culverts -------------------------------------- 12-1SECTION 13. RAILINGS ------------------------- 13-113.1 Bridge Railings ------------- 13-1SECTION 14. JOINTS AND BEARINGS ---- 14-114.1 Expansion Joints ----------- 14-114.2 Bearing Devices ------------ 14-114.3 Anchor Bolts ----------------- 14-1SECTION 15. DESIGN OF SOUND BARRIERS -------------------------------------------- 15-1SECTION 16. BRIDGE RATING --------------- 16-1SECTION 17. STRUCTURES FOR TRAFFIC CONTROLDEVICES AND HIGHWAY LIGHTING -------------------------------------- 17-117.1 Overhead Highway Sign Structures ------------------------------------ 17-1SECTION 18. PRECAST BRIDGES ---------- 18-1END OF DOCUMENTJanuary 2021ii
ALDOT Structural Design ManualPREFACEI. ALDOT POLICY STATEMENTAll bridge and miscellaneous transportation structures in Alabama shall bedesigned in accordance with the ALDOT Structural Design Manual. Allproposed exceptions shall have the prior written approval of the State BridgeEngineer prior to proceeding with design.II. PURPOSE AND SCOPEThis manual contains specific design criteria policies mandated by the ALDOTBridge Bureau applying equally to ALDOT as well as consultants completingstructural designs. The primary purpose of this manual is: To provide interpretation and consistency in the application of the AASHTOLRFD Bridge Design Specifications. To encourage the uniform preparation of plans and specifications. To provide direction to be followed on projects under the authority oroversight of the Bridge Bureau. Exceptions, based on sound engineeringprinciples & judgement, are anticipated. Exceptions requiring prior approvalof the State Bridge Engineer shall be documented per the procedures notedin the Bridge Plan Development Quality Control and Quality AssurancePlan and Checklist.Structural plans and specifications must clearly communicate the design intentand construction requirements of each project. This manual is targeted forinternal Bridge Bureau use; however, consultants preparing designs for projectsto be let through ALDOT are expected to follow the directives noted herein.The contents of this manual generally follow the section headings of theAASHTO LRFD Bridge Design Specifications. ALDOT exceptions to specificrequirements of the AASHTO LRFD Bridge Design Specifications areindicated as follows:ALDOT exception to AASHTO:A description of the ALDOT exception is given here.January 2021iii
ALDOT Structural Design ManualThis manual will be continually updated as revisions and improvements arewarranted.Any questions, comments, concerns, and/or suggestions arewelcomed and should be submitted to:William T. Colquett, PEState Bridge EngineerAlabama Department of Transportation1409 Coliseum Blvd., Rm. U201Montgomery, AL 36130-3050colquettw@dot.state.al.usIII. DESIGN METHOD/SPECIFICATIONSAll bridge and miscellaneous transportation structures in Alabama shall bedesigned using Load & Resistance Factor Design (LRFD), unless otherwisedirected by the State Bridge Engineer. The governing design specification for allbridges and miscellaneous transportation structures in Alabama shall be theAASHTO LRFD Bridge Design Specifications, 9th Edition and applicableinterims, along with any notations and exceptions indicated herein. Within thismanual, the AASHTO LRFD Bridge Design Specifications is referred to asAASHTO LRFD. Other AASHTO specifications & guides, as well as the relatedALDOT manuals & documents listed below, shall also apply as appropriate.Consultant prepared designs, whether prepared directly for the Bridge Bureau orany other office in the Department, shall be submitted according to therequirements given in the Alabama State Board of Registration forProfessional Engineers and Land Surveyors Administrative Code, Chapter330-X-11-.03.IV. RELATED ALDOT MANUALS/DOCUMENTSOther documents maintained and/or used by the ALDOT Bridge Bureau includethe following: ALDOT Guide for Developing Construction Plans ALDOT Guidelines for Operation ALDOT Special and Standard Highway Drawings ALDOT Standard Specifications for Highway Construction Bridge Plan Development Quality Control and QualityAssurance Plan and Checklist Bridge Special Project Drawings Quality Control Manual for Bridge Plan DetailingJanuary 2021iv
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ALDOT Structural Design ManualSECTION 1. INTRODUCTIONThe provisions of AASHTO LRFD, Section 1 shall apply to this section unlessnoted and/or excepted below.1.1 LIMIT STATESThe value of the load modifier, ηi (see AASHTO LRFD, Article 1.3.2.1) and itsfactors, ηD, ηR, and ηI, shall all be set equal to 1.00, unless otherwise directed bythe State Bridge Engineer.January 20211-1
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ALDOT Structural Design ManualSECTION 2. GENERAL DESIGN AND LOCATION FEATURESThe provisions of AASHTO LRFD, Section 2 shall apply to this section unlessnoted and/or excepted below.2.1 CLEARANCESCriteria for highway vertical and horizontal clearances is presented in AASHTOLRFD, Articles 2.3.3.2 and 2.3.3.3 respectively.ALDOT exception to AASHTO:Horizontal and vertical clearances for grade separation structures shall conformto ALDOT Guidelines for Operation, Section 3-25: Bridges VerticalClearance for Highway Grade Separations New Construction and Criteriafor Raising Existing Bridges and Section 3-76: Bent or Pier PlacementCriteria for Proposed Bridges Overpassing Multilane Roadways.Criteria for bridge width is presented in AASHTO LRFD, Article 2.3.3.3.ALDOT exception to AASHTO:Minimum clear roadway width (face of barrier to face of barrier) for new andreconstructed bridges should follow current AASHTO Policy (A Policy onGeometric Design of Highways and Streets; A Policy on Design StandardsInterstate System) as noted below:Interstate: Bridges less than or equal to 200 feet: Full paved width of the approachroadway including shoulders. Bridges greater than 200 feet: Width may be based on reduced left and rightshoulder width of not less than 4 feet.Local roads and streets: With curbed approaches: Match curb to curb width With shoulders and no curb:Design volume: 400, traveled way 2 ft. each side400 to 2000, traveled way 3 ft. each side 2000, approach roadway widthaCollector roads and streets: With curbed approaches: Match curb to curb width With shoulders and no curb:Design volume: 400, traveled way 2 ft. each side400 to 2000, traveled way 4 ft. each sidea 2000, approach roadway widthaa forbridges over 100 feet, traveled way 3 ft. each side is acceptableJanuary 20212-1
ALDOT Structural Design ManualArterial roads and streets: Full width of approach roadway including shoulders and space allocated forbicycles/pedestrians. Bridges over 200 feet, width may be based on 4 ft. min. shoulder each side.NOTE: Prior to proceeding with final design, consult with the Region Engineerand/or Design Bureau for concurrence on bridge width.2.2 DEFORMATIONSCriteria for deflection is presented in AASHTO LRFD, Article 2.5.2.6.2.ALDOT exception to AASHTO:Live load deflection shall be checked for both loading options as given inAASHTO LRFD, Article 3.6.1.3.22.3 DRAINAGECriteria for the design storm is presented in AASHTO LRFD, Article 2.6.6.2.ALDOT exception to AASHTO:The design storm shall be the 10-year recurrence except where the low point of asag vertical curve exists on the bridge wherein the 50-year recurrence shall beused. Exceptions to this policy shall have the prior approval of the State BridgeEngineer.Criteria for deck drains is presented in AASHTO LRFD, Articles 2.6.6.3 and2.6.6.4.ALDOT exception to AASHTO:Bridge deck drainage shall be allowed to fall freely to the ground through deckscuppers unless otherwise directed by the State Bridge Engineer. Typically, 4” Øscuppers spaced on 5’ centers (max.) shall be provided in normal crown sectionsup to 44’ gutter to gutter. In wider sections, and superelevated sections greaterthan 28’, reduce scupper spacing to 4’ centers (max.).Scuppers shall be omitted over roadway lanes and railroad right-of-way’s, 10’from bridge ends, and 5’ from interior bents.Hydraulic calculations may require the use of larger diameter scuppers, reducedspacings, deck drain inlets, or a closed system if the above parameters are notadequate.January 20212-2
ALDOT Structural Design ManualSECTION 3. LOADS AND LOAD FACTORSThe provisions of AASHTO LRFD, Section 3 shall apply to this section unlessnoted and/or excepted below.3.1 PERMANENT LOADSThe following loads shall be used: Metal stay-in-place forms for bridge decks (as applicable) – Allow 15 psf deadload (this includes the dead weight of concrete in the forms). Barrier rails – The barrier rail dead load shall be considered equallydistributed across all girders. However, the dead load for girder design shallnot be less than 25% of a single barrier rail weight.ALDOT exception to AASHTO:Dead loads from wearing surfaces and future overlays as specified inAASHTO LRFD, Section 3.5.1, shall not be included without the priorapproval of the State Bridge Engineer.3.2 WATER AND WIND LOADS Bridges exposed to coastal influences shall be designed in accordance withthe latest AASHTO Guide Specifications for Bridges Vulnerable toCoastal Storms, 2008.3.3 TEMPERATURE FORCE EFFECTS Thermal baseline shall be set at 70º F.January 20213-1
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ALDOT Structural Design ManualSECTION 4. STRUCTURAL ANALYSIS AND EVALUATIONThe provisions of AASHTO LRFD, Section 4 shall apply to this section unlessnoted and/or excepted below.ALDOT has no analysis and evaluation considerations beyond those covered inthe AASHTO LRFD Bridge Design Specifications.January 20214-1
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ALDOT Structural Design ManualSECTION 5. CONCRETE STRUCTURESThe provisions of AASHTO LRFD, Section 5 shall apply to this section unlessnoted and/or excepted below.5.1 CONCRETE COMPRESSIVE STRENGTHSReinforced Concrete:Designers shall refer to the current edition of the ALDOT StandardSpecifications for Highway Construction for strengths to be used in differentstructures. Individual plan sheets for various structural members shall indicatethe required concrete strength of that member. Superstructure (including barrier rails and deck) and substructure (includingfootings [except as noted below] and drilled shafts) concrete strength (ƒ’c)shall be 4.0 ksi Retaining wall and cast-in-place box culvert concrete strength (ƒ’c) shall be4.0 ksi Seal footing and miscellaneous drainage structure concrete strength (ƒ’c)shall be 3.0 ksiGreater concrete strengths may be utilized when required by design (subject tothe prior approval of the State Bridge Engineer) and shall be noted accordinglyon the contract drawings.Prestressed Concrete:The following values of ƒ’c @ 28 days shall be used for these structures:Bridge Componentƒ’c (ksi)Girders5.0 to 8.0*Piles5.0 to 6.0Table 5-1* Higher strengths shall require the priorapproval of the State Bridge EngineerFor prestressed concrete members, compressive strength of concrete used fordesign (ƒ’c) and at time of prestressing (strand release) (ƒ’ci) shall be specified onthe contract drawings.January 20215-1
ALDOT Structural Design Manual5.2 PRESTRESSED CONCRETE GIRDER DESIGN POLICYThe following policies shall be used for typical prestressed concrete girderdesigns using a composite concrete deck:1. The following standard shape AASHTO-PCI type girders are preferred:Type I, Type II, Type III, BT-54, BT-63, and BT-72, as well as solid andvoided slab beams. Modifications of these girders or other girder types maybe proposed for use in special circumstances and shall have the priorapproval of the State Bridge Engineer prior to implementation.2. Girders shall be designed as simple spans for all dead and live loads. Spansshall not be made continuous for live load. To eliminate joints, decks may bemade continuous (link slabs).3. Girders shall be designed so that no tension occurs in the bottom of the girderafter losses under the Service III load combination limit state. In no case shalltension in Service III conditions exceed 0.0948 ƒ’c (ksi). Exceptions to thispolicy shall have the prior approval of the State Bridge Engineer.4. Prestressing strands shall be 0.5 or 0.6 inch in diameter, Low Relaxation, 270ksi Ultimate Tensile Strength. Use strand areas as follows: For 0.5” Ø strands, use A 0.153 sq. in. For 0.5” Ø Special strands, use A 0.167 sq. in. For 0.6” Ø strands, use A 0.217 sq. in.5. Shear steel reinforcement shall be spaced so that no additional reinforcementis necessary to address horizontal shear forces at the top of the girder andshall not be spaced greater than 18” o.c. Shear steel reinforcement in thegirder ends shall be spaced 4” o.c. and shall extend from the end of the girderfor a distance equal to the girder depth. Shear steel reinforcement shall beno smaller than #5’s and shall extend above the top of the girder to engagethe slab at the approximate mid-depth with standard 90º hooks.6. Confinement steel reinforcement shall be #3’s spaced at 4” o.c. and shallextend from the end of the girder for a distance equal to the beam depth.7. Use K1 1.16 (based on regional dolomitic limestone aggregate) in AASHTOLRFD, Equation 5.4.2.4-1 for Ec, Modulus of Elasticity. Adjust the value of K1as appropriate for other aggregates if known. Unit weight of concrete shall beassumed to be 0.150 k/ft3 unless known otherwise.January 20215-2
ALDOT Structural Design Manual8. In AASHTO LRFD, Equation 5.9.3.1-1 for total prestress loss in pretensioned members, the value of ΔƒpLT shall be calculated using AASHTOLRFD, Article 5.9.3.3, Approximate Estimate of Time-Dependent Losses.The value for H, relative humidity, shall be taken as 75%.9. The following shall apply for purposes of computing expected camber anddeflection values to be presented in the contract plans only. A second girderanalysis run separate from the design run will be required to determine thesevalues. Use AASHTO LRFD, Article 5.9.3.4, Refined Estimate of TimeDependent Losses. Time at strand release: 0.75 days. Time from release of strands to pouring of the bridge deck: 120 days. Relative humidity: 75%. Final age: 27,500 days. Concrete strengths: Use expected concrete strengths computed asfollows:o At pre
January 2021 2-2 . ALDOT Structural Design Manual Arterial roads and streets: Full width of approach roadway including shoulders and space allocated for bicycles/pedestrians. Bridges over 200 feet, width may be based on 4 ft. min. shoulder each side. NOTE: Prior to proceeding with final design, consult with the Region Engineer
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ALDOT Foundation Design Review (cont'd) 3. Contractor submits the pole designs to ALDOT Construction Bureau and ALDOT sends a plan set, boring logs/passive pressures, and pole design calculations and design sheets to an outside consultant for review in accordance with DOT specifications (Contractor will assume certain soil parameters) 4.
AASHTO T 23 AASHTO T 24 AASHTO T 97 AASHTO T 119 . Alabama Dept. of Transportation ALDOT Procedures Bureau of Materials and Tests ALDOT-405 Testing Manual Revision Date: 08/08/19 Page 5 of 8 AASHTO T 121 AASHTO T 141 AASHTO T 152 AASHTO T 23
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wood property response at elevated temperature; and (3) further effort in reliability-based design procedures so that the safety of fire-exposed members and assemblies may be determined. Keywords: Structural design, structural members, timber/structural, wood, wood laminates, fire resistance, fire protection, structural analysis, connections .
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Tank 6 API-653 In-Service, Internal Inspection Report less severe corrosion than the west perimeter. The average thickness of the sketch plates away from the west perimeter was 0.281”. Other than the perimeter corrosion noted, the remainder of the tank bottom showed no signs of significant metal loss and the thickness readings appeared consistent with the readings from the 2004 robotic .
