Thermal Effects on Concrete Substructure Elements

Upcoming changes to the American Association of State Highway and Transportation Officials (AASHTO) Load And Resistance Factor Design (LRFD) Bridge Design Specification (BDS) include the modification of how thermal effects are calculated, specifically related to uniform temperature change. Historically load factors for uniform temperature change (γTU) were 0.5 for force effects and 1.2 for displacement effects for strength limit states, and 1.0 for force effects and 1.2 for displacement effects for service limit states. The reduced force effect (γTU = 0.5) was used to account for changes in cross-section and material properties over time, allowing the use of gross section properties in a simplified analysis. In the upcoming BDS these values will change to 1.0 for force effects and 1.2 for displacement effects, regardless of limit state being evaluated. The rationale for removal of the reduced force effect is that modern analysis software packages are capable of accounting for varying section and material properties over time, and the conflation of load factors and analysis procedures is unnecessary and confusing. Current Kansas Department of Transportation (KsDOT) policy allows for the application of γTU values equal to 0.33 and 1.20 for force and displacement effects, respectively. Policy states that one-third of the instantaneous modulus has been used in the past and is suggested for LRFD substructure design. Although no known issues have been caused by this design policy, there is no known justification for its noncompliance with current AASHTO LRFD specifications and the resulting force effects may be unconservative. Additionally, the conflation of analysis processes with load factors may be confusing to engineers, introducing the potential for design errors. With the upcoming changes to the LRFD BDS, KsDOT policy will be further out of compliance with no known justification. Information is needed to ensure that force effects are being appropriately determined and accounted for in the KsDOT bridge design process.

Language

• English

Project

• Status: Active
• Funding: $162,627.00
• Contract Numbers:

  K-TRAN: KU-26-1

  RE-0925-01

  C2257

• Sponsor Organizations:

  Kansas Department of Transportation

  Eisenhower State Office Building
  700 SW Harrison Street
  Topeka, KS  United States  66603-3754
• Performing Organizations:

  University of Kansas Center for Research, Incorporated

  2291 Irving Hill Drive, Campus West
  Lawrence, KS  United States  66045
• Principal Investigators:

  Collins, William

  Lequesne, Rémy D

• Start Date: 20250818
• Expected Completion Date: 20270817
• Actual Completion Date: 0

Subject/Index Terms

• TRT Terms: Bridge design; Bridge substructures; Concrete; Load and resistance factor design; Thermal conductivity
• Subject Areas: Bridges and other structures; Data and Information Technology; Design; Geotechnology; Materials;

Filing Info

• Accession Number: 01976225
• Record Type: Research project
• Source Agency: Kansas Department of Transportation
• Contract Numbers: K-TRAN: KU-26-1, RE-0925-01, C2257
• Files: RIP, STATEDOT
• Created Date: Jan 13 2026 2:58PM