Bridge Design Manual-Texas Department of transportation

Bridge Design Manual-Texas Department of transportation Load and Resistance Factor Design (LRFD) is a design methodology that makes use of load and resistance factors based on the known variability of applied loads and material properties. In 1994, the American Association of State Highway and Transportation Officials (AASHTO) published the first AASHTO Load and Resistance Factor Bridge Design Specifications. The Federal Highway Administration (FHWA) mandated the use of LRFD for all bridges for which the Texas Department of Transportation (TxDOT) initiated preliminary engineering after October 2007.

Bridge Design Manual December 2001 © by Texas Department of Transportation (512) 416-2055 all rights reserved Manual Notice 2001-1 To: Districts, Divisions and Offices From: Steven E Simmons, P.E Deputy Executive Director Manual: Bridge Design Manual Effective Date: December 1, 2001 Purpose This manual provides policies and guidelines set forth by TxDOT regarding the design of bridges It has been developed to help bridge designers working on TxDOT projects Instructions This is a new manual containing new and significantly reorganized material It supersedes the 1990 Bridge Design Guide and the 1990 Bridge Design Examples, both first editions Contents The manual contains ten chapters – Organizational Overview, TxDOT and Bridge Design, Design Specifications, Geometric Restraints, Preliminary Considerations, General Design Controls, Superstructure Design, Substructure Design, Special Designs, and Foundation Design The manual also has four appendices Contact For more information regarding any chapter or section in this manual, please contact the Design Section of the Bridge Division Chapter Organizational Overview Contents: Section — This Manual .1-2 Section — Evolution of the TxDOT Bridge Division .1-4 Bridge Design Manual 1-1 TxDOT 12/2001 Chapter — Organizational Overview Section — This Manual Section This Manual Overview This manual was developed to provide bridge designers working on Texas Department of Transportation (TxDOT) projects with the policies and guidelines set forth by TxDOT regarding the design of bridges Its purpose is to improve the bridge design and detailing process by promoting uniformity among bridge designers working on TxDOT projects This manual is subject to revision as conditions, experience, or research data warrant Changes will be issued by Manual Notice Changes may be in the form of new sheets to be added, revised sheets to replace superceded ones, or sheets to be deleted The manual is not intended to be a complete substitute for engineering experience, knowledge, or judgment Special situations may arise that appear to call for variation from the policy requirements herein Such variation will be subject to approval of the administration of the TxDOT Bridge Division Direct any questions or comments on the content of the manual to the Director of the Design Section of the Bridge Division, Texas Department of Transportation Bridge Design Manual Format The manual begins with this overview of the manual and a description of the evolution of the TxDOT Bridge Division The chapters that follow include information on TxDOT Divisions/Sections, design specifications, geometric restraints, preliminary considerations, general design controls, superstructure design, substructure design, special designs, and foundation design The following paragraphs briefly discuss these chapters: Chapter presents a description of the TxDOT Divisions/Sections primarily involved in bridge design, planning, construction, and maintenance and provides descriptions of the responsibilities of the TxDOT Bridge Division’s Bridge Design Section Chapter lists and briefly describes the governing design specifications, or “Rule Books,” involved in bridge design The chapter includes information on mandatory specifications, guide specifications, and industry recommendations Chapter discusses the common roadway geometric restraints inherent in bridge design Bridge widths, span lengths, clearances, and alignment are discussed A section on the constraints involved during stage construction is also included Chapter presents some common aspects a designer/planner must consider during the preliminary planning and design process These aspects include materials, structure type, Bridge Design Manual 1-2 TxDOT 12/2001 Chapter — Organizational Overview Section — This Manual economics, and aesthetics A discussion on bridge railing and use of corrosion protection is also included Chapter discusses in greater detail some of the more common design specifications involved during the design of a bridge, giving the designer additional information on the application and usage of common design specifications and criteria Chapter presents design criteria and design guidance for the most commonly used superstructure types, including cast-in-place, precast, and steel superstructures Background information on the development of each superstructure type is also included Chapter presents design criteria and design guidance for the most commonly used substructure items, including caps, columns, and foundations Background information on the development of some of these items is also included Chapter presents design criteria and design guidance for designs that inherently involve unique aspects, culverts and drainage, bridge appurtenances, sign bridges, and some common bridge items Background information on the development of some of these designs is also included Chapter 10 discusses in greater detail the relationship between structural design and geotechnical design Some guidance on bridge foundation designs and retaining wall designs is included, as well as background information on the development of some of these items Bridge Design Manual 1-3 TxDOT 12/2001 Section — Evolution of the TxDOT Bridge Division Chapter — Organizational Overview Section Evolution of the TxDOT Bridge Division Origin of the TxDOT Bridge Division The Texas Highway Department was established in 1917 and is responsible to the Governor of Texas to design, construct, and maintain an adequate system of highways in the state In 1918, a Bridge Office was created with the primary responsibility of preparing standard designs and drawings in an attempt to bring some uniformity to the bridges being constructed by the counties The Bridge Division appeared in 1928, retaining bridge design as a big part of its mission The Bridge Division continued to maintain standards and design non-standard bridges In time, advance planning, railroad negotiations, and plan review capabilities were developed Construction management was provided for some of the more complicated structures 1940s and 1950s Activities were curtailed during the war years, but in the late 1940s and 1950s increased demand for improved infrastructure produced a large volume of expressways, for which special design offices were established in the affected cities Some of the groups adopted their own design and detailing standards When welding began to replace rivets for field splices in steel beams and girders in the early 1950s, the Bridge Division sent qualified welders to the larger projects to help with quality assurance and quality control In the middle 1950s the Bridge Division, with the cooperation of precast manufacturers, developed a group of standard pretensioned concrete beams, which quickly proved to be the most economical way to construct medium-span length bridges When the Interstate Highway System was inaugurated in the middle 1950s, the design workload increased dramatically and has remained generally good to date Between the expressway offices, district design groups, and the Bridge Division, plan preparation was handled for several years with a minimum of help from consulting engineers Recent Years In the early 1980s, consulting engineers began to a significant portion of the highway plans and a somewhat smaller portion of the bridge plans After a period of reduced activity, consulting engineers are now preparing a significant portion of highway and bridge plans Meanwhile, the use of TxDOT “bridge standards” has become more uniform, as many district design groups have abandoned their own plan preparation activities Currently, the Bridge Design Manual 1-4 TxDOT 12/2001 Section — Evolution of the TxDOT Bridge Division Chapter — Organizational Overview Bridge Division continues to prepare its share of structure plans while attending to a growing number of non-engineering responsibilities Bridge Design Manual 1-5 TxDOT 12/2001 Chapter TxDOT and Bridge Design Contents: Section — Coordinating with TxDOT Divisions and Sections 2-2 Section — Primary Responsibilities of the Bridge Design Section 2-3 Section — Coordination Responsibilities of the Bridge Design Section 2-7 Section — Contractive Responsibilities of the Bridge Design Section 2-10 Bridge Design Manual 2-1 TxDOT 12/2001 Section — Coordinating with TxDOT Divisions and Sections Chapter — TxDOT and Bridge Design Section Coordinating with TxDOT Divisions and Sections Overview Before a bridge is designed, critical preliminary functions described in the Bridge Project Development Manual must be completed The planning and design of a bridge project involves several divisions and sections within the Texas Department of Transportation (TxDOT) Some of the contributing entities are: ♦ Bridge Division ♦ Design Division, Field Coordination Section ♦ Transportation Planning and Programming Division ♦ Traffic Operations Division, Railroad Section ♦ Environmental Affairs Division ♦ Construction Division, Materials Section ♦ Maintenance Division, Maintenance Operations Section Within the Bridge Division, the Bridge Design Section is responsible for functions that include engineering and non-engineering aspects of bridge design These responsibilities are discussed in this chapter Bridge Design Manual 2-2 TxDOT 12/2001 Section — Primary Responsibilities of the Bridge Design Section Chapter — TxDOT and Bridge Design Section Primary Responsibilities of the Bridge Design Section Overview The primary responsibilities of the Bridge Design Section are structural design and the preparation of working drawings or plans These primary responsibilities involve a procedure that begins with a concept to construct a highway facility and concludes with the submission of finalized plans, specifications, and estimates (PS&E) The procedure includes many steps and it is important to know these steps to fully grasp the responsibilities of the Bridge Design Section Generally, the procedure for preparation of plans by the Bridge Design Section is as follows Consultation Consultation between the Bridge Design Section, bridge project development manager, and the district design engineer, district bridge engineer, and/or area engineer should precede determination of structure type and scheduling of the letting Note: This is a good time to make a preliminary decision about who will prepare the bridge plans Preliminary Bridge Layouts The area engineer or the project’s designated consulting engineer prepare preliminary bridge layouts These layouts are usually complete with geometric controls, type, size, length of spans, hydraulic data, required clearances, soil test boring data, classification of highway, and projected traffic At this time, type of foundation should be proposed and conveyance of water through stream crossings and scour analysis should be addressed and coordinated with the Hydraulics Section Note: Area engineers and consulting engineers are encouraged to contact the Geotechnical Branch for advice if there is any question regarding the proper foundation The layouts are sent to the bridge project development manager who will forward them to the Design Division, the Federal Highway Administration (FHWA) on federal oversight projects, or other agencies that may exercise review authority Bridge Plan Preparation When approval has been secured from all the appropriate agencies, timing for the plan work is re-negotiated with the district and the job of bridge plan preparation is given to the bridge design engineer or to the consultant The following steps apply to the Bridge Design Section, but the routine for consultants will be similar Note: If consultants are unsure about the current design or detailing standards for an item, they are encouraged to contact the director of the Bridge Design Section ♦ The director of the Bridge Design Section assigns the work to a Design Group according to its particular expertise in that type of design, and primarily on its ability to complete the plans in the required length of time Bridge Design Manual 2-3 TxDOT 12/2001 Appendix B Design Formulas for Inverted Tee Bents Ledge Reinforcing Figure B-3 Ledge Reinforcing Online users can click here to view this illustration in PDF format Shear Friction Requirement: φ = 85 Avf = Pu φ × 1.4fy Distribution width equals the lesser of: Interior Beam: (B + 4a) or S Exterior Beam: 2C , (C + 5S ), or (B + 4a) Flexure Requirement: φ = Asf = 04f ′c × dsf Pu × a , but not less than × dist width φ × fy × 0.8dsf fy Distribution width equals the lesser of: Interior Beam: (B + 5a) or S Exterior Beam: 2C , (C + 5S ), or (B + 5a) Bridge Design Manual B-4 12/2001 Appendix B Design Formulas for Inverted Tee Bents Tension Requirement: φ = An = Nu , where Nu = 2Pu φ × fy Distribution width equals the lesser of: Interior Beam: (B + 5a) or S Exterior Beam: 2C , (C + 5S ), or (B + 5a) Top Layer: 667 Avf An Asf + An A ≥ + , or s distr width distr width distr width Second Layer: 333Avf A ≥ s distr width Bridge Design Manual B-5 12/2001 Appendix B Design Formulas for Inverted Tee Bents Web Reinforcing Hanger Reinforcement: φ = 85 Design for the largest value of Bridge Design Manual Av from the following equations s B-6 12/2001 Appendix B Design Formulas for Inverted Tee Bents 2Pu − f ′c × bf × dpv Av φ = s fy (B + 2dpv ) S Av 2Pu Av 2Pu = for interior beams or = for exterior beams, if C < s φfyS s φfy × 2C B + 3a Av 3Ps Av 3Ps = for interior beams or = for exterior beams, if C < s fy (B + 3a) s fy (2C ) Where: Pu = The largest factored single beam reaction on one side of the cap Ps = The largest service load single beam reaction on one side of the cap Av = Area of both/all stirrup legs s = stirrup spacing Note: It is recommended that the distance from centerline of exterior beam at centerline of bearing to the end of cap (C) should not be less than 24 inches This allows for a reasonable size and spacing of hanger reinforcement and limits cracking between the flange and stem Also, additional hangers with anchorage hooks at their ends should be arbitrarily placed along the end face of inverted-T caps These end hangers should be sized to match the stirrups and spaced at inches max Shear: φ = 85 φVn = φ (2 f ′c × bwdw + Av fydw ) s Note: Take Vu at face of column, not depth of cap from column face Stirrup requirements for shear are normally not added to the hanger requirements (See Appendix A reference 56) Torsion: φ = 85 Figure B-4 Torsion Elements Online users can click here to view this illustration in PDF format ù é f ′c x y Av æ φTn = φ ê fy (α t x1 y ) , but 18 f c ỗ + ỗ 2s ờở è Bridge Design Manual B-7 x 2y ö 12/2001 Appendix B Design Formulas for Inverted Tee Bents Where α t = 66 + 33 y1 ≤ 1.5 x1 ổ Vu ổ Tu ỗỗ ữữ + çç ≤ è φVn è φTn If >1.0 add additional stirrups A′v s and additional longitudinal steel A = A′v s (x1 + y ) Note: A should be distributed to the four corners of the web, the four corners of the beam ledges, and added to the flexural reinforcing “Design of Reinforced and Prestressed Concrete Inverted T-Beams for Bridge Structures,” Furlong and Mirza, PCI Journal, July – August 1985 Bridge Design Manual B-8 12/2001 Appendix C Load vs Moment Interaction Diagrams Introduction The following Load vs Moment interaction diagrams were developed for 24- through 72inch diameter, round columns with common reinforcing patterns used on TxDOT projects Diagrams for 3000 psi and 3600 psi concrete represent commonly used drilled shaft and column concrete strengths Note that the reinforcing is grade 40 This is because grade 40 is commonly used in the design of interior bent columns even though grade 60 will be required by the specifications Column design is normally not a strength issue The AASHTO minimum reinforcement ratio of one percent is normally the controlling design feature Using grade 40 allows for considerably shorter lap and embedment requirements, reducing congestion and improving constructibility Bridge Design Manual C-1 TxDOT 12/2001 Appendix C Load vs Moment Interaction Diagrams Figure C-1 Diagrams for 24-Inch Diameter Columns Online users can click here to view this illustration in PDF format Bridge Design Manual C-2 TxDOT 12/2001 Appendix C Load vs Moment Interaction Diagrams Figure C-2 Diagrams for 30-Inch Diameter Columns Online users can click here to view this illustration in PDF format Bridge Design Manual C-3 TxDOT 12/2001 Appendix C Load vs Moment Interaction Diagrams Figure C-3 Diagrams for 36-Inch Diameter Columns Online users can click here to view this illustration in PDF format Bridge Design Manual C-4 TxDOT 12/2001 Appendix C Load vs Moment Interaction Diagrams Figure C-4 Diagrams for 42-Inch Diameter Columns Online users can click here to view this illustration in PDF format Bridge Design Manual C-5 TxDOT 12/2001 Appendix C Load vs Moment Interaction Diagrams Figure C-5 Diagrams for 48-Inch Diameter Columns Online users can click here to view this illustration in PDF format Bridge Design Manual C-6 TxDOT 12/2001 Appendix C Load vs Moment Interaction Diagrams Figure C-6 Diagrams for 54-Inch Diameter Columns Online users can click here to view this illustration in PDF format Bridge Design Manual C-7 TxDOT 12/2001 Appendix C Load vs Moment Interaction Diagrams Figure C-7 Diagrams for 60-Inch Diameter Columns Online users can click here to view this illustration in PDF format Bridge Design Manual C-8 TxDOT 12/2001 Appendix C Load vs Moment Interaction Diagrams Figure C-8 Diagrams for 66-Inch Diameter Columns Online users can click here to view this illustration in PDF format Bridge Design Manual C-9 TxDOT 12/2001 Appendix C Load vs Moment Interaction Diagrams Figure C-9 Diagrams for 72-Inch Diameter Columns Online users can click here to view this illustration in PDF format Bridge Design Manual C-10 TxDOT 12/2001 ... Responsibilities of the Bridge Design Section Chapter — TxDOT and Bridge Design Section Coordination Responsibilities of the Bridge Design Section Overview All responsibilities of the Bridge Design Section... Responsibilities of the Bridge Design Section Chapter — TxDOT and Bridge Design Section Contractive Responsibilities of the Bridge Design Section Overview The Bridge Design Section manages a pool of consultants... chapter Bridge Design Manual 2-2 TxDOT 12/2001 Section — Primary Responsibilities of the Bridge Design Section Chapter — TxDOT and Bridge Design Section Primary Responsibilities of the Bridge Design