Table of Contents
Preface.
1. Introduction and General Principles.
Bridge Engineering and Aesthetics. Pier Types. Abutment Types. Abutment Walls. Foundation Types. Subsurface Exploration and Foundation Investigations. Specifications and Standards. Cost Correlation, Superstructure versus Substructure. Design Example 1-1. References.
2. Loads and Loading Groups. General Considerations. Permanent Loads. Transient Loads. Force Effects from Superimposed Deformations. Forces on Substructure. Earthquake Effects. Transfer of Loads from Superstructure to Substructure. Distribution of Longitudinal Forces to Fixed and Expansion Piers. Numerical Examples. Load Combinations and Load Factors. Case Study, Ice Load on Bridges. References.
3. Methods Of Analysis and Design. General Principles. Service Load Design Method (Allowable Stress Design, ASD). Reliability and Uncertainty in Design. Alternate Approach to Limit States. AASHTO Strength Design Method, Reinforced Concrete Structures. LRFD Principles of Strength Design (AASHTO, 1994 Specifications). Design for Thermal Effects. Shrinkage and Creep (LRFD Specifications). Design for Vessel Collision. Basic Philosophy of Seismic Design. Requirements of Reinforced Concrete in Seismic Design. Tolerable Differential Movement and Settlement of Bridges. Design Example 3-1, Settlement. Case Study, Forces Induced by Settlement. Design Requirements for Bridges in Waterways. References.
4. Piers For Conventional Bridges. Pier Types. Criteria for Pier Selection. Loads and Moments on Piers: End Conditions. Effect of Temperature Change and Shrinkage. Seismic Design Considerations for Piers and Columns. Structural Capacity under Combined Axial Compression and Bending. Section Analysis. Structural Capacity of Composite Columns. Design Example 4-1: Single Shaft Pier (Load Factor Design). Design Example 4-2: Hammerhead Pier. Design Example 4-3: Steel Bent Cap. Design Example 4-4: Steel Bent Cap for Torsional Loading. General Principles of Pier Frame Analysis. Design Example 4-5: Multiple Column Pier. Design Example 4-6: Pier Integral with Superstructure. Pier Trestles. Pier Protection Design Provisions in Navigable Waterways. Design Example 4-7: Bridge Protection in Waterways. Design Example 4-8: Pier Stability Under Stream Flow. References.
5. Piers For Special Bridges. Structural Interaction of Elastic Piers in Multi-Span Arch Bridges. Towers for Suspension Bridges. Towers and Pylons for Cable-Stayed Bridges. Piers for Segmental Concrete Bridges. Piers for Movable Bridges. Supports Integral with Superstructure. References.
6. Wall Systems. Diaphragm Walls in Traffic Underpasses. Gravity and Semi-Gravity Walls. Mechanically Stabilized Earth Walls and Prefabricated Modular Walls. Ground Movement in Excavations. Design Principles of Diaphragm Walls. Design Principles of Gravity and Semi-Gravity Walls. Commentary on Mechanically Stabilized Earth Walls. Commentary on Prefabricated Modular Walls. Design Example 6-1, Traffic Underpass. Design Example 6-2, Anchored Diaphragm Wall. Design Example 6-3, Stability of Ground-Anchored Wall System. Design Example 6-4, Posttensioned Diaphragm Wall. Seismic Design Requirements of Wall Systems. References.
7. Abutments. Top of Abutment Details and Treatment. Pile Bent (Stub) Abutments, Design Considerations. Closed (Full) Abutments, Design Considerations. Gravity and Semi-Gravity Abutments, Design Considerations. Abutments on Mechanically Stabilized Earth Walls. Abutments on Modular Systems. Wing Walls. Abutments for Segmental Bridges. Seismic Design of Abutments. Design Example 7-1, Pile Bent Abutments, ASD Method. Design Example 7-2, Full Abutment. Design Example 7-3, Spill-Through Abutment. Design Example 7-4, Abutment of a Simple Span. Deck Truss Bridge. Abutments for Arch Bridges. Abutments for Suspension Bridges. Integral Abutments. Prefabricated Concrete Sections. References.
8. Footings. Factors Affecting Selection of Foundation Type. Footing Types. Bearing Capacity Theories. Presumptive Bearing Pressures. Bearing Pressures from Tests. Bearing Resistance of Rock. Failure by Sliding. AASHTO and LRFD Requirements. Settlement of Footings in Soil, Methods of Analysis. Settlement of Footings in Rock. Structural Action of Footings. Flexural Strength of Modified Square Footing, Case Study. Strut-and-Tie Model (LRFD Specifications). Design Example 8-1, Bearing Capacity by ASD. Design Example 8-2, Settlement of Footings. Design Example 8-3, Footing in Rock. Design Example 8-4, Bearing Capacity by Strength Design. Design Example 8-5, Load Factor Design. Design Example 8-6, Strip Footing. Seismic Design Requirements. References.
9. Driver Piles. Soil-Pile Interaction. Pile Types and Selection Criteria. Design Considerations. Design Approach. Movement and Bearing Resistance at the Service Limit State. Design of Piles for Axial Load, Structural Capacity. Design of Piles for Axial Load, Geotechnical Capacity of Single Pile. Bearing Capacity of Pile Groups. Uplift Considerations. Negative Skin Friction. Pile Foundations Under Lateral Loads. Structural Capacity of Piles Subjected to Axial Load and Bending. Design Examples. Bridge Foundations Without Piles. References.
10. Drilled Shaft Foundations. Assessment of Construction Methods. Practical Considerations. Usual Defects and Repairs. AASHTO Requirements. Design Requirements. Generalized Design Approach. Structural Capacity for Axial Load. Geotechnical Strength (Bearing Capacity), Axially Loaded Shafts. Bearing Capacity from Load Tests. Axial Resistance in Rock. Group Action. Safety Factors for ASD. Settlement Considerations. Negative Skin Resistance (Downdrag). Uplift Resistance. Drilled Shafts under Lateral Load. Flexural Analysis, Laterally Loaded Shafts. Design Examples. References.
11. Prismatic and Linear Foundations. Shapes and Configurations. Construction Considerations. The Transfer of Axial Load: Basic Concepts. Data from Load Tests. Guidelines for the Design of Load Bearing Linear and Prismatic Elements. Structural Capacity for Axial Load. Geotechnical Capacity: Axial Load in Cohesive Soils. Geotechnical Capacity: Axial Load in Cohesionless Soils. Axial Resistance in Rock. Group Action. Settlement Considerations. Downdrag and Uplift. Effects of Lateral Load. Structural Capacity Under Bending and Axial Load. Design Example 11-1. References.
12. Strengthening and Rehabilitation. Design Options to Reduce Maintenance and Repair. Procedures for Detecting Defects and Deterioration. Assessment of Deficiencies of Substructures Below the Water Line. Repair of Scour Damage. Methods for Strengthening Substructures. Replacement and Repair Methods. Repair and Methods to Arrest Concrete Deterioration Below the Water Line. Example of Inspection Guidelines: Assessment of Underwater Concrete. Example of Structural Capacity Analysis. Example of Bridge Rehabilitation. References. Index.
Preface
Substructures and foundations constitute formidable components of bridges, and often represent more than half of the total bridge cost. The methods of analysis, design, and detailing are therefore important, and can influence the structural performance and project budget. The current extensive body of knowledge documents the concerted efforts made to advance the theory and practice of bridge engineering. This progress has encompassed the design of piers, abutments, walls and foundations, and is also evident in our present understanding of soil- structure interaction. Notable improvements are reflected in the use of materials with better physical and structural characteristics, and in the rational and more explicit analysis of structural behavior. In the present synthesis of the new and old concepts, traditional approaches have been integrated with recently evolved design philosophies, producing design options that enhance the field of structural analysis. Thus, the deterministic methodology represented in the past by the allowable stress design can now be supplemented or completely replaced by load factor design, a statistically-based probabilistic approach. Although many engineers believe that in this merge certain discernible gaps and inconsistencies are bound to remain for some time, the concensus of opinion is that in the field of bridge design there are now more workable alternatives that can be successfully applied to the entire structure and its foundation. The introduction of load factor design is now a key feature of structural analysis in most areas of structural engineering and in most parts of the world. Whereas it draws from completed research as well as from judgment, it also signifies new provisions and major areas of change. It addresses load and force models, load factors, nominal resistance and resistance factors, limit states, and the soil-structure system on a global basis. A logical extension is the consideration of the variability in the characteristics of structural elements, which is treated as the variability in the loads. Thus, the underlying philosophy moves bridge design toward a more rational and probability-based procedure, although the application of the working stress method is not excluded as an independent option. The text is developed to achieve the following objectives: (a) present a systems study of substructure and foundation elements; (b) introduce an independent design methodology demonstrating compliance with AASHTO and other relevant specifications; (c) cover both the allowable stress method and the LRFD approach; and (d) include a sufficient number of design examples and case studies that show how to obtain credible solutions. Chapter 1 provides a general review of pier types, abutments, wall systems, and foundation elements. Structure appearance and esthetics are discussed in conjunction with economic aspects. It appears that the process of selecting the visual characteristics of bridges and substructures represents largely an effort to create forms pleasing to the public in a format described in national terms, although bridge esthetics should also be examined in the context of structural requirements and budget con straints. Chapter 1 is completed with a discussion of subsurface explorations and foundation investigations, review of specifications and standards, and the fundamentals of cost relationship between superstructure and substructure. Loads and loading groups are reviewed in Chapter 2. A comparison of design loads used in the United States and in other countries shows a broad variability in load models and magnitudes. However, the present AASHTO loads and forces have been expanded by the load models of the LRFD specifications, and these are intended to enhance the live load representation. As a logical exercise of resourceful judgment, the new loads could be scaled by appropriate load factors to be compatible with other load spectra. Chapter 3 deals with methods of analysis and design, and articulates allowable stress and strength design procedures. A main concern is the reliability and uncertainty in the structural analysis. In routine practice, safety in working stress design is ensured by the application of a single factor of safety, usually taken as the ratio of design resistance to the design load. With the LRFD approach, reliability is ensured by treating both loads and resistances as random variables. Safety in the case is defined in terms of the probability of survival or the probability of failure. Conventional piers are discussed in Chapter 4. This category includes piers for all-concrete slab bridges, concrete deck bridges on multi-beam systems, two-girder systems with floor beams and stringers, truss bridges, and bridges across waterways and rivers. Although the great variety of functional, structural and geometric requirements implies a corresponding variety of pier forms and configurations, this seeming multiplicity is reduced and consolidated to a discussion of pier selection criteria, load effects, column analysis, seismic considerations, structural capacity under combined axial compression and bending, section analysis, pier frame analysis, and piers integral with the superstructure. This chapter includes also a review of pier protection design provisions in navigable waterways.