Innovative Bridge Designs for Rapid Renewal Toolkit (2012)

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31 3 SAMPLE DESIGN CALCULATIONS AND SPECIFICATIONS FOR ABC INTRODUCTION The challenge to future deployment of ABC systems lies partly in the area of being able to codify the design and construction of these prefabricated modular systems so that they are not so unique from a design and construction perspective. The LRFD design philosophy should explicitly deal with the unique aspects of large-scale prefabrication, including issues such as element interconnection, system strength, and behavior of rapid deployment systems during construction. For rapid replacement, it is possible that the stages of construction may in fact provide the critical load combinations for some structural elements or entire systems. Ongoing developments in material technol- ogy and increasing steel and concrete strengths have allowed designers to extend the useful span lengths of bridges ever farther. In some cases, the most extreme load case these ever-longer and more-slender beams will experience is that which occurs during shipping and handling prior to fi nal erection. At the current time, under a design−bid−build delivery method, the engineering design services for the design of a large-scale prefabricated bridge system are per- formed by different entities. The engineer of record is responsible only for the bridge in its fi nal support condition. It is the contractor who typically proposes some innovative method of construction and thus carries the burden to hire a construction engineer- ing fi rm to provide the engineering services required to prove an innovative erection technique can be used. When design−build procurement is used, there is greater align- ment between design and construction that could facilitate greater innovation in rapid renewal projects. Closing some of these gaps or inconsistencies in the specifi cations as related to the engineering and construction of rapid replacement bridges will be a worthwhile goal for this project and other ongoing projects related to rapid renewal.

32 INNOVATIVE BRIDGE DESIGNS FOR RAPID RENEWAL: ABC TOOLKIT Guidance has been developed for engineers alerting them of an increased obligation for strength, stability, and adequate service performance prior to final construction. Maintaining individual module stability and limiting the erection stresses induced through the choice of pick points (crane lifting points) would be a critical consider- ation for modular construction. The location of the pick points should be calculated so that the unit is picked straight without roll or stability problems and with erection stresses within allowable limits. The plans should indicate the lifting locations based on the design of the element. The engineer is responsible for checking the handling stresses in the element for the lifting locations shown on the plans. The contractor may choose alternate lifting locations with approval from the engineer. In order to accom- plish this, the design community needs guidance or minimum analysis requirements for various erection methods for modular construction. RECOMMENDED LRFD DESIGN SPECIFICATIONS FOR ABC Design criteria proposed for the ABC standards are in accordance with the AASHTO LRFD Bridge Design Specifications. The “Design Life—Period of time on which the statistical derivation of transient loads is based—is 75 years for these Specifications.” Therefore the completed structure will need to satisfy the same design requirements as any conventionally built bridge. Any new bridge system should meet this minimum design life requirement for wide acceptance and implementation. However, it is not necessary or economically feasible for prefabricated systems during construction to be bound by the same criteria as the completed structure. The design of bridges using large- scale prefabrication is not specifically covered in the LRFD Bridge Design Specifications. The work in this project entailed the identification of any shortcomings in the cur- rent LRFD Bridge Design Specifications that may be limiting their use for ABC designs and making recommendations for addressing these limitations. The primary deliver- able was to develop recommended specification language for ABC systems, suitable for future inclusion in the AASHTO LRFD Bridge Design Specifications. Design issues specific to ABC include the following: • Construction loads. What kinds of loads are unique to rapid construction? Deter- mine which loads associated with support conditions during fabrication may differ from the permanent supports, loads associated with member orientation during prefabrication, loads associated with suggested lift points, loads associated with various erection methods, impact considerations for shipping and handling of components, loads associated with camber leveling, etc. • Limit states and load factors during construction. What are the applicable limit states and load factors during construction, including limit state for checking of construction vehicles and equipment? Check critical stability effects as the com- ponent is fabricated, moved, assembled, and erected. Depending on construction sequencing, abutments may be backfilled and subjected to the full earth pressure during construction prior to placement of the superstructure. Requirements for extreme events during construction. The design community needs guidance or minimum analysis requirements for various erection methods for modular construction.

33 INNOVATIVE BRIDGE DESIGNS FOR RAPID RENEWAL: ABC TOOLKIT • Constructability checks. Erection analysis to evaluate lifting and erection stresses in prefabricated components. To what extent is cracking allowed in a pre fabricated system during transportation and erection? What are the limiting stresses, deflec- tions, and distortion during construction for steel and concrete components? Requirements for SERVICE III checks in prestressed members. What are the brac- ing requirements for transportation and erection of elements and systems? Need for temporary supports during erection. • Cross frames and diaphragms. What are the requirements for modular construc- tion with regard to these bracing elements during construction? In modular construction the girder stability is greatly enhanced by the precast deck, which could allow opportunities to ease the requirements for intermediate cross frames and diaphragms and achieve savings in weight and cost. Additional bracings for temporary support points during construction. The designer should consider the impact on live load distribution from any reductions in the use of cross frames or diaphragms. • Analysis methods. What are the minimum recommended levels of analysis or stages of analysis required for bridges erected by various unique methods? Consid- eration of sequence of loading during construction. Are there any unique changes to structural load distribution that must be addressed for certain prefabricated bridge types and connection configurations? • Connections. What are the requirements for closure pour design for strength and durability? Development of reinforcing steel and lapped splices in closure pours. Requirements for grouted splice couplers. Provisions for UHPC joints. Implementing the recommended ABC design provisions into the existing sections of the LRFD Bridge Design Specifications would be difficult because the ABC design incorporates components from several sections of the code. As such, the specifications are written as if they were to be added as a new LRFD subsection (5.14.6) under Sec- tion 5, Concrete Structures, in the LRFD Bridge Design Specifications. See Appendix C for the Recommended LRFD Design Specifications for ABC. ABC SAMPLE DESIGN EXAMPLES The sample design calculations will be instructive in highlighting the differences between CIP construction and modular prefabricated construction and the advantages of modular systems. Currently, economical design using CIP construction requires sim- plified fabrication and minimizing girder lines, with less emphasis on weight reduction. However, for ABC, shipping weights have to be minimized for economy and construc- tability. Shop labor is then easier to control quality. Shop-fabricated modular elements also increase the speed of construction. Stability of the shape must be ensured for all stages of construction per LRFD. Unlike CIP construction, girder stability during con- struction is less of an issue for predecked modular construction. This will allow more efficient designs of steel modular systems to minimize material and fabrication expense while ensuring adequate strength, stiffness, and stability.

34 INNOVATIVE BRIDGE DESIGNS FOR RAPID RENEWAL: ABC TOOLKIT Prefabricated modular steel bridges compete favorably with other materials when considering the greater use of shop labor in comparison to field labor, the speed at which they can be installed, and the significant reduction in time required to close a given roadway to the public. The light weight of steel modular systems could reverse this trend in ABC designs. Often designers concentrate on optimizing individual spans by minimizing the number of lines of girders and in so doing will generally reduce superstructure weights by 5% to 10%. While important, in ABC design it is the careful determination of span arrangement and module dimensions for shipping and erection that can add significant savings. In fact, for CIP construction it is the cost of the substructure, particularly intermediate piers, for each design that usually determines the most economical span arrangement. Conventional rules of design used for economical span arrangement may not apply to modular systems, with cost of shipping and erection taking on additional significance in the overall economics of ABC projects. It may be more economical to reduce the shipping weight of pier components by adding more piers to reduce the superstructure dead loads on each pier. The sample design calculations developed in this project will serve as training tools to increase familiarity about ABC design issues and design criteria among engineers. Three sample design calculations are provided in Appendix B to illustrate the ABC design process for the following prefabricated modular systems: • Decked steel girder; • Decked precast prestressed concrete girder; and • Precast pier. The sample design calculations pertain to the same standard bridge configurations for steel and concrete used in the ABC standard concepts. The intent was to have sample design calculations that could be used in conjunction with the ABC standard concepts so that the practitioner will get a comprehensive view of how ABC designs are performed and translated into design drawings and details. The sample design calculations focus on the design checks for the modules for each stage of construc- tion and the design of the connection details. Additional features of the sample design calculations include demonstration of any special LRFD loadings during construction and in the final condition; load combinations for design; stress and strength checks; deformations; and lifting and handling stresses. The sample design calculations have extensive documentation describing the design criteria, the design steps executed, the design philosophy adopted, and the design specifications checks performed. All sam- ple design calculations are based on the LRFD Bridge Design Specifications, 5th ed. AASHTO specification references are presented in a dedicated column in the right margin of each page, immediately adjacent to the corresponding design procedure. Two separate designs are illustrated for the precast pier—one for a straddle bent and one for a conventional pier. The examples are organized in a logical sequence to make them easy to follow. Each example has a table of contents at the beginning (as given below) to guide the reader and allow easier navigation. The sample design calculations are contained in Appendix B. While important, in ABC design it is the careful determination of span arrangement and module dimensions for shipping and erection that can add significant savings.

35 INNOVATIVE BRIDGE DESIGNS FOR RAPID RENEWAL: ABC TOOLKIT Sample Design Calculation 1: Decked Steel Girder Design for ABC General: 1. Introduction 2. Design Philosophy 3. Design Criteria 4. Material Properties 5. Load Combinations Girder Design: 6. Beam Section Properties 7. Permanent Loads 8. Precast Lifting Weight 9. Live Load Distribution Factors 10. Load Results 11. Flexural Strength 12. Flexural Strength Checks 13. Flexural Service Checks 14. Shear Strength 15. Fatigue Limit States 16. Bearing Stiffeners 17. Shear Connectors Deck Design: 18. Slab Properties 19. Permanent Loads 20. Live Loads 21. Load Results 22. Flexural Strength Capacity Check 23. Longitudinal Deck Reinforcing Design 24. Design Checks 25. Deck Overhang Design Continuity Design: 26. Compression Splice 27. Closure Pour Design Sample Design Calculation 2: Decked Precast Prestressed Concrete Girder Design for ABC General: 1. Introduction 2. Design Philosophy 3. Design Criteria Girder Design: 4. Beam Section 5. Material Properties 6. Permanent Loads 7. Precast Lifting Weight

36 INNOVATIVE BRIDGE DESIGNS FOR RAPID RENEWAL: ABC TOOLKIT 8. Live Load 9. Prestress Properties 10. Prestress Losses 11. Concrete Stresses 12. Flexural Strength 13. Shear Strength 14. Splitting Resistance 15. Camber and Deflections 16. Negative Moment Flexural Strength Sample Design Calculation 3a: Precast Pier Design for ABC (70-ft Span Straddle Bent) 1. Bent Cap Loading 2. Bent Cap Flexural Design 3. Bent Cap Shear and Torsion Design 4. Column / Drilled Shaft Loading and Design 5. Precast Component Design Sample Design Calculation 3b: Precast Pier Design for ABC (70-ft Span Conventional Pier) 1. Bent Cap Loading 2. Bent Cap Flexural Design 3. Bent Cap Shear and Torsion Design 4. Column/Drilled Shaft Loading and Design 5. Precast Component Design RECOMMENDED ABC CONSTRUCTION SPECIFICATIONS FOR LRFD These ABC construction specifications pertain specifically to prefabricated elements and modular systems (Tier 2) and are intended to be used in conjunction with the stan- dards concepts for steel and concrete modular systems developed in SHRP 2 R04. As such, these specifications for rapid replacement focus heavily on means and methods requirements for rapid construction using prefabricated modular systems. The speci- fication also identifies responsibilities for design, construction, and inspection during an ABC project. It also identifies two phases of inspection—fabrication inspection and field inspection—that are the responsibility of the owner. Quality control and geometry control of components are identified as key parts of ABC construction. Adherence to prescribed tolerances and verification of fit-up in the yard are identified as the basis for successful field assembly within a tight ABC window. Requirements for various connection types commonly used in ABC, including UHPC joints, are defined so that they may be selected to fit the needs of specific projects and component types. Much of these provisions reflects a compilation of best practices for ABC construction that will need to be continually reviewed and updated as new information and lessons learned are accumulated from future ABC projects.

37 INNOVATIVE BRIDGE DESIGNS FOR RAPID RENEWAL: ABC TOOLKIT Implementing ABC concepts into the existing sections of the LRFD Bridge Con- struction Specifications would be difficult because these ABC concepts include ele- ments from several sections. As such, the following is written as if it were to be added as a stand-alone section in the LRFD Bridge Construction Specifications. A table of contents (as given below) is provided to guide the reader and allow easier navigation. See Appendix D for the Recommended LRFD Construction Specifications for ABC. A bridge owner using these specifications as a guide could develop its own special provisions for an ABC project. Table of Contents 1 General 1.1 Description 1.2 Benefits 2 Responsibilities 2.1 Design 2.2 Construction 2.3 Inspection 3 Materials 3.1 Description 3.2 Concrete 3.3 Steel 3.4 Closure Pours 3.5 Grout 3.6 Couplers 4 Fabrication 4.1 Qualifications of the Fabricator 4.2 Fabrication Plants 4.3 Fabrication Requirements 4.4 Fabrication Tolerances 4.5 Yard Assembly 5 Submittals 5.1 Shop Drawings 5.2 Assembly Plan 6 Quality Assurance 7 Handling, Storing, and Transportation 8 Geometry Control 8.1 General 8.2 Camber and Deflection 8.3 Equalizing Differential Camber 8.4 Finishing of Bridge Deck 8.4.1 Diamond Grind Bridge Deck 8.4.2 Saw Cut Groove Texture Finish

38 INNOVATIVE BRIDGE DESIGNS FOR RAPID RENEWAL: ABC TOOLKIT 9 Connections 9.1 Requirements for UHPC Joints in Decks 9.2 Requirements for Mechanical Grouted Splices 9.3 Requirements for Posttensioned Connections 9.4 Requirements for Bolted Connections 10 Erection Methods 11 Erection Procedures 11.1 General Requirements for Installation of Precast Elements and Systems 11.2 General Procedure for Superstructure Modules 11.3 General Procedure for Pier Columns and Caps 11.4 General Procedure for Abutment Stem and Wingwalls