Advanced Precast Concrete Dual-Shell Steel Columns

Project # NCTRJR

Research Team

  • José I. Restrepo, Professor, UC San Diego (PI)
  • Gabriele Guerrini, Graduate Student Researcher, UC San Diego

Research Abstract

An innovative bridge column technology for application in seismic regions is being developed, designed, and tested at UC San Diego Structural Engineering Department. This element combines a precast concrete hollow-core column with on-site post-tensioning and added energy dissipation.

The column consists of two steel shells running for the full-height of the column, with concrete sandwiched in between. The outer shell acts as permanent formwork and substitutes longitudinal and transverse reinforcement. The inner shell also behaves as permanent formwork, and prevents concrete implosion under large compressive strains. Constructability is enhanced by the use of a precast element of reduced weight (hollow-core section) without a reinforcing cage.

Large plastic rotations can be attained with minimal structural damage: column-cap and column-foundation joints are allowed to open in tension under severe earthquake excitation, and to close subsequently upon load reversal. Re-centering behavior is ensured by post-tensioned longitudinal bars, designed to respond elastically. A special connection between column, bent-cap, foundation, and PT bars allows for eventual bar replacement, and protects bars from yielding. Energy dissipation is provided by internal or external steel devices, yielding axially or in flexure.

Research Outcomes

Analytical and experimental work is currently in progress:

  • Parametric nonlinear analysis and guidelines for design of hysteretic energy dissipators
  • Nonlinear dynamic analysis of prototype bridge structure
  • Experimental test of PT-bar-to-bent-cap connection materials (polyurethane)
  • Experimental characterization of hysteretic energy dissipators
  • Quasi-static, cyclic test of column units with internal and external dissipators

Research Impact

Replacement of existing infrastructure or construction of new facilities in congested and economically or environmentally sensitive areas is an issue faced by many communities worldwide. Constructability enhancement, an intrinsic objective of this project, will allow for reduction of on-site construction time, traffic impact, environmental disruption, and life-cycle costs. In fact, this project responds to the Accelerated Bridge Construction (ABC) initiative promoted the Federal Highway Administration (FHWA).

While the notion of structural damage is accepted in design, resilient communities expect bridges to survive a moderately strong earthquake with little or no disturbance to traffic. This implies that partial or total bridge closures are tolerated with uneasiness, particularly in heavily congested urban areas. This project represents a resilient, economically viable technology, where residual damage to the main structural elements is reduced, and self-centering properties allow the structural system to return to its original position after an earthquake.

As an example the State of California, as well as many other countries, is currently planning a new high-speed railway infrastructure, which will connect the largest urban and industrial areas of the State. The size of the required investment, together with the social and economic impact caused by an eventual service interruption, makes accelerated construction and seismic resilience one of the main concerns for the design of bridges along this transportation facility.

Moreover, the combination of these rocking/hybrid columns with seismic isolation of the bridge deck will provide bridge structures with a backup system to accommodate larger-than-expected seismic demands. Under seismic events up to the design earthquake, deck isolation would provide lateral displacement capacity without rotation of the superstructure. Under events exceeding the isolator displacement capacity the rocking mechanism would be engaged, allowing additional, recoverable displacement capacity.

The research outcomes will provide the tools necessary for Caltrans, precast concrete manufacturers, and contractors to successfully implement Advanced Precast Concrete Dual-Shell Steel Columns and, thus, achieve cost-effective, durable bridge columns that provide good constructability, rapid onsite construction, and seismic resilience, satisfying the philosophy of “Get in, Get out, and Stay out.” The research efforts will be focused on delivering practical results for direct implementation into current practice.