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:
- 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
- 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
- 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
- HANDS-ON SESSION
4.1 Overview of DASH program
- Analysis/design calculation by DASH
- Rating calculation by DASH
- Staging Analysis by DASH
4.2 "Hands on" session
- Three 1-span, 2-span and 3-span continuous steel bridges based on AISI
"Four LRFD Design Examples of Steel Highway Bridges"
- 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"
