New Strategies for Maintaining Post-Seismic Operations of Lifeline Corridors

Abstract

This project furthered the development of three strategies that could positively impact maintaining post-seismic operations of lifeline corridors. In Year 1, most of the focus was on the development of the three individual strategies. In Year 2, a follow-up project will include more formal assessments of the situation in which each strategy might be preferred. The first part of the investigation, performed at Oregon State University, assessed the use of high strength reinforcement (HSS) for use in reinforced concrete (RC) columns. HSS is not currently allowed in RC due to lack of information on the material characteristics and lack of performance information when used in columns. But potential benefits in construction, performance, and economics justify the need for research, especially for critical corridors. Results indicate that a column constructed with Grade 80 HSS reinforcement performs similar to column constructed with conventional Grade 60 reinforcement. The second part of the investigation, performed at the University of Washington, focused on a new type of connection between a precast concrete column and a cast-in-place drilled shaft. The column is precast with a roughened outer surface at the bottom of the column which will be embedded in the cast-in-place shaft. The connection can be built rapidly and allows generous construction tolerances. Building on two previous tests, a third quasi-static scaled connection test between a precast bridge column and a drilled shaft was performed to investigate the seismic performance of the new connection. The geometry of the test specimen was based on the minimum practical difference between the diameters of the shaft and the column, and so represented the most critical cases. The performance of the system was investigated up to a drift ratio of 10%. The experimental results showed that, if adequate confining steel is included in the splice zone, the plastic hinging mechanism forms in the column, without incurring damage in the splice zone or shaft. If the confinement is insufficient, the strength of the splice zone deteriorates rapidly with cyclic loading. Recommendations for transverse reinforcement in the transition area are provided to ensure desirable performance. The third part of the investigation, also performed at the University of Washington, focused on the performance of concrete filled steel tubes (CFST), with specific focus on connections to precast concrete piers and piles caps. CFSTs have the potential to improve performance in seismic events and decrease overall costs. CFSTs may be used for bridge piers, shafts, caissons, and columns, but their use is limited because AASHTO design specifications for CFSTs are dated and few validated, constructible connections exist. Part 3 of this report (Part 3) compares current CFST design provisions to experimental results, noting limitations and deficiencies. Improved provisions proposed for the AASHTO specifications and partly based on the AISC provisions are summarized. CFST connections are also addressed. A foundation connection capable of developing the full composite capacity of a CFST was evaluated experimentally and initial study of CFST column-to-cap beam connections was conducted using numerical simulation. Both are effective in developing and transferring the full capacity of the CFST and are summarized.