The AASHTO LRFD Specifications are written based on probabilistic limit state theory with several listed load combinations. Improved from the Standard Specifications for WSD or LFD, the AASHTO LRFD Bridge Design Specifications introduce a limit states design philosophy, based on structural reliability methods, to achieve a more uniform level of safety (reliability) in new bridge design. The chief advantages of a probability-based LRFD specification are:

• A more uniform level of safety throughout the system will result;
• Measure of safety will be a function of the variability of loads and resistance;
• Designers will have an estimate of the probability of meeting or exceeding the design criteria during the design life;
• The potential exists to place all structural materials and methods of construction on equal footing;
• A realistic rational framework for future development of the specification will be available;
• Proponents of future changes in materials and construction techniques will be asked to provide the same measure of reliability that all current materials and construction methods will be asked to meet;
• Designers will have a better understanding of where and how uncertainties of load and resistance models are accounted for, and will be able to relate past performance.

The disadvantages of basing a specification on this philosophy include an increased design effort, as it is realistic to expect that a greater number of load and resistance factors will be available. However, the designer will need little or no knowledge of reliability theory.

The purpose of this short course is to present the fundamentals and theory of LRFD for highway bridge design and how to design the bridges in computer. The course outlines are as follows:

1. INRODUCTION
   1.1 Limit State
   1.2. Load Combinations
   1.3. Design Vehicle Live Load
   1.4. Fatigue Load
   1.5. Impact (Dynamic Load Allowance = IM)
   1.6. Wind
   1.7. Distribution Factor
2. STEEL STRUCTURES
   2.1 Steel Material
   2.2 Fatigue and Fracture Limit State
   2.3 Resistance Factor
   2.4 Tension Members
   2.5 Compression Members
   2.6 Bending of a Straight I-Section
   2.7 Composite Sections
   2.8 Constructibility
   2.9 Non-Composite Sections
   2.10 Wind Effects
   2.11 Effective Section
   2.12 Strength Limit State Flexure Resistance
   2.13 Lateral-Torsional Buckling
   2.14 To Control the Permanents Deflection (Service II)
   2.15 Fatigue Requirements for Web (Fatigue)
   2.16 Shear
   2.17 Shear Connectors
   2.18 Transverse Intermediate Stiffeners
   2.19 Bearing Stiffeners
   2.20 Longitudinal Stiffeners
3. CONCRETE STRUCTURES
   3.1 Material Properties
   3.2 Fatigue Limit State
   3.3 Strength Limit State
   3.4 Flexure
   3.5 Flexure Design Example
   3.6 Flexural, Design Example of Negative Moment Region
   3.7 Shear
   3.8 Horizontal Interface Shear
4. HANDS-ON SESSION
   4.1 Overview of DASH program
   1. Analysis/design calculation by DASH
   2. Rating calculation by DASH
   3. Staging Analysis by DASH

   4.2 “Hands on” session

   1. Three 1-span, 2-span and 3-span continuous steel bridges based on AISI “Four LRFD Design Examples of Steel Highway Bridges”
   2. Three design examples from AASHTO-PCI BIII-48 single-span, Bulb-Tee BT-72, single-span and three-span continuous bridges with composite deck based on “PCI Bridge Design Manual”