Project Title/ID Number Influence of Design Ground Motion Level on Highway Bridge Costs—Lifelines 6D01
Start/End Dates 10/1/02—9/30/03
Project Leader Mark Ketchum (OPAC/Industrial Collaborator)
Team Members Vivian Chang (OPAC/Industrial Collaborator), James Scheld (OPAC/Industrial Collaborator), Kwong Cheng (OPAC/Industrial Collaborator), Francis Drouillard (OPAC/Industrial Collaborator), Tom Shantz (Caltrans/Industrial Collaborator), Fadel Alemeddine (Caltrans/Industrial Collaborator)
Project goals and objectives

The project proposes to quantify, in percentage terms, the cost impact of raising or lowering levels of design ground motion for new highway bridges. The nature of the cost curve may be influenced by many variables, including site-specific issues as well as bridge-type-specific issues. Its basic features, the nature of design constraints that define the cusps, and the relative economy of various bridge types at differing levels of design ground motions are immediately achievable objectives of this project. The project focuses on bridge types used for ramps, interchanges, and grade separations, which account for the majority of bridge construction costs in California.
Role of this project in supporting PEER’s vision
The project will have direct benefit to bridge designers by allowing rapid approximation of costs associated with seismic resistance. The cost functions developed here will supersede rules of thumb that have not been updated to match current performance requirements, design technology, or construction technology.
Methodology employed

The key to successful completion of the research is in adopting an efficient approach for evaluating data points on the cost vs. ground motions curve.

In a typical design project, the site’s ground motions are identified as response spectra (ARS curve), and the structure is designed and detailed to meet the demands of those motions. This process typically involves design iterations to meet economy as well as capacity requirements. To avoid the iterative process, the researchers turn this process inside out.

The researchers, therefore, are preparing preliminary designs of each selected structure with a balanced set of seismic capacities, and then performing seismic demand and capacity analyses to determine what factor of the base spectra the structure can resist. Experience will guide the selection of which components will be strengthened to provide the next data point (blanket increase of all capacities is generally not required to provide resistance to incrementally greater motions); little or no design iteration will be required per data point on the cost vs. design ground motion curve.

The bent or column sizes are selected to cover critical points (cusps) on the cost vs. motions curve. The sizes will include minimum dimensions and reinforcement required to meet non-seismic and/or minimum-seismic conditions, as well as larger dimensions and reinforcement that define potential break-points in the cost curve. These break-points include (for example) the column with maximum plastic moment that can be resisted without enlarging the girder, bent cap, pile cap, or foundation; as well as intermediate sizes that meet limitations on vertical or confinement reinforcing.

  


Figure 1: Typical Cost Curve
Larger View

 


Figure 2: Typical Bridge Design
Larger View

  
Brief description of past year’s accomplishments and more detail on expected Year 6 accomplishments
  • Adoption of Bridge Type Matrix (structures to be studied).
  • Adoption of bridge evaluation methodology.
  • Evaluation of foundation cost/performance issues.
  • Initial evaluation of cost curve for test-case bridge type.
Other similar work being conducted within and outside PEER and how this project differs
This is to our knowledge a first-of-its-kind effort, in application of research efforts to assessing influences of ground motion on cost, both within and outside PEER.
Plans for Year 7 if this project is expected to be continued
Continuation to additional bridge types, incorporating more rigorous evaluations of foundation influence.
Describe any instances where you are aware that your results have been used in industry
None to date.
Expected milestones
  • Notice to Proceed 10/2002
  • Draft Final Report 9/2003
  • Final Report 10/2003
Deliverables
  • Draft Final Report
  • Final Report