Special Issue on AASHTO-LRFD Bridge Design and Guide Specifications: Recent, Ongoing, and Future Refinements

The AASHTO Load and Resistance Factor Design Bridge Design Specifications (LRFD Code) were introduced in the early to mid1990s as an eventual replacement for the AASHTO Standard Specifications for Highway Bridges (Standard Specifications). The LRFD Code is effectively modernizing bridge design practice in the United States as an ever-increasing number of engineers and state departments of transportation become familiar with and use its provisions. The LRFD Code is also structured in such a way that updating it is more straightforward than the Standard Specifications had become over time. Since introduction of the LRFD Code, the document has undergone numerous significant revisions. Making it much more userfriendly was one reason for this. However, incorporating the results from recently completed research projects also played a very significant role in a number of the revisions. Research is still being conducted, has recently been completed, or may be proposed in the near future that could further refine the LRFD Code in the coming years. This special issue of the Journal provides highlights of some of these efforts over a broad range of bridge engineering topics. The first paper offers several perspectives on the LRFD Code by an author (Tobias) from a state department of transportation. It provides an overview of the Code’s history, the mechanisms associated with revision, and current and future research topics that could or should be addressed. Other reliability-based AASHTO manuals and guide specifications are also discussed in the paper, along with the processes by which researchers and practitioners can effect future refinements for most AASHTO structural publications. The other papers contained in this issue are sequentially grouped into general categories that include extreme events, foundations, bridge decks, loads and load distribution, prestressed and posttensioned concrete members, effective flange width, bridge piers, and bridge rating. Several of the subjects briefly discussed in the first paper are also discussed in more and varied detail in subsequent papers of this special issue. These include, but are not limited to, papers entitled “Evaluation of Combination Rules for Orthogonal Seismic Demands in Nonlinear Time History Analysis of Bridges” by Bisadi and Head, “Calibration of Live Load Factor in LRFD Bridge Design Specifications Based on State-Specific Traffic Environments” by Kwon et al., “Framework for Simplified Live-Load Distribution Factor Computations” by Puckett et al., and “Full-Scale Testing of Pretensioned HighStrength Concrete Girders with Debonded Strands” by Kim et al. The research described in several of the included papers has already had recent significant impacts on the LRFD Code and/or other AASHTO manuals and guide specifications. These include the papers entitled “Performance of Bridge Columns Subjected to Blast Loads. I: Experimental Program” by Williamson et al., “Performance of Bridge Columns Subjected to Blast Loads. II: Results and Recommendations” by Williamson et al., “Proposed Revisions to AASHTO-LRFD Bridge Design Specifications for Orthotropic Steel Deck Bridges” by Kozy et al., “Bridge Rating Using System Reliability Assessment. I: Assessment and Verification by Load Testing” by Wang et al., and “Bridge Rating Using System Reliability Assessment. II: Improvements to Bridge Rating Practices” by Wang et al. Other papers in this special issue not cited above may have a future influence on the LRFD Code and/or other AASHTO structural publications by functioning as a contribution to the marketplace of ideas. As described in the first paper, it is very common for research published in archived journals, conference papers, and project reports to provide “shape, substance, and a coalescing of concepts and methods in particular subject areas over time, which commonly affects how AASHTO ballots (proposed revisions) are formulated.” Some of these papers include “Evaluation of AASHTO-LRFD Design Methods for Thermal Loads in FixedFlexible Twin-Walled R/C Bridge Piers” by Schultz et al., “Proposed Modification of AASHTO-LRFD for Computing Stress in Unbonded Tendons at Ultimate” by Harajli, and “Unified Approach for LRFD Live Load Moments in Bridge Decks” by Higgins et al. The contributing authors, guest editors (Dennis Mertz and John Kulicki), reviewers, and chief editor of the Journal (Anil Agrawal) all deserve acknowledgment with regard to their contributions to this special issue of the Journal.