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2007 ABC Workshop Follow up
The following summarizes the discussion documented for each idea from the four breakout sessions. An abbreviated title with the idea number in parenthesis enables tracking back to the more detailed information contained in the appendices. The associated detailed forms used to spur discussion on each topic are included in the appendices (reference Appendix H). It is expected that the summary included herein serves as a starting point to guide future action planning discussions, as well as developing research needs.
Table 4 provides a quick overview of those ideas associated with the top two categories through voting of the workshop attendees at large. It is anticipated that these ideas will be advanced through syntheses or additional focused research as necessary. Clearly, connections issues rise to the forefront of the discussion in many of these ideas. The last column of the table provides tentative recommendations of needs for each tabulated idea; such as synthesis studies, or focused research. A variety of funding vehicles will be pursued to advance these as needed, including NCHRP, FHWA and pooled DOT fund sources.
|CAT/NO.||RAW SCORE||CAT.||RANK||IDEA DESCRIPTION||RESEARCH NEEDS SUMMARY|
|F1/F2||15||A||1||Footing/pile and cap/pile connection||Synthesis, rank, and develop promising ideas|
|C1b||8||A||2||Connections/tolerances||Synthesis, rank and study|
|B2||6||A||3(1)||Accelerated post-earthquake repair||Synthesis and developmental effort|
|H6||6||A||3(1)||SABC code recommendations||Research|
|B6||5||B||5(1)||Segmental columns with isolation bearings||Synthesis, investigate applicability of non-seismic ideas to seismic applications, testing|
|C3||5||B||5(1)||Hybrid connections from other industries||Synthesis, rank, research, trial implementations|
|C6||5||B||5(1)||Integral cap/precast column connection||Synthesis, rank, research|
|D2||5||B||5(1)||Demonstration projects||Synthesis, rank and study|
|F3||5||B||5(1)||Grouted voided connections||Not addressed in breakout group|
- Received the same score, so no preference assigned herein.
Post-earthquake accelerated column repair/replacement (B2)
Discussions of ABC have largely centered on rapidly constructing new or replacement structures; however, another benefit derived from developing ABC technologies is rapid repair of damaged structures. Rapid repair of columns is the focus of this idea, and certainly represents the quality "out-of-the-box" thinking envisioned when planning the workshop. The group discussion pointed to both temporary and permanent applications of column repair/replacement. Existing technologies such as steel casings and carbon fiber wrapping were considered as viable options, but more research was also suggested to develop new methods and associated specifications. The ability to match existing aesthetics was considered important, and input from the construction industry considered essential.
Investigation of column seismic connections for ABC (C6, C8, and C10)
The proposal herein was to develop new connection details adequate for seismic loading. Adequate connection between precast columns and superstructures is important so as to provide more viable options for designers. The outcome of such research would be thorough testing, documentation of connection performance capacities, design examples and details, as well as design specifications. Test protocols should consider various levels of performance demanded, as they vary from one region to another in terms of seismic demand. Initially, a review of existing research was necessary to develop promising new technologies or advance existing ones through testing and calibration. Subsequent research focusing on one or more similar connection concepts could then be managed, with new marketable products defining the expected outcome. Care must be taken in such research to preclude proprietary issues that often plague similar efforts and reduce novel ideas to unusable products in the public forum.
Response of segmental systems (C4a, b, c, and B5)
The use of segmented superstructures has seen rapid growth in the past decade (reference Figure 1). However, more research is necessary to understand the seismic response of segmented structures. In general, a better understanding of jointed structure response is necessary - currently designed as emulative system. Advantages of allowing joint opening in large design events can be leveraged towards energy dissipation. This leads to a redefinition of desired performance level goals. This idea is not unlike rocking columns in that areas of high stress concentrations must be carefully investigated and detailed according to desired damage threshold values. The group felt that a focused workshop addressing the fundamental behavioral issues of jointed systems and providing comparison to monolithic designs was warranted. Analytical and experimental testing to quantify hypotheses was proposed. Similar work is underway currently at UCSD.
Additionally, a synthesis to gather and assess the response of existing jointed and segmented bridges subjected to large earthquakes was viewed as a means of identifying further research direction in developing a solid understanding of related behavioral response. Cited areas of concern included corrosion protection, and post-event inspection procedures and tools.
Connections - Ductile, Constructible, Rapid (C1b, D2, and E13)
Tolerances led this discussion. Constructible connection details for precast elements such as bent caps, footings, and pile heads require flexibility to allow for field corrections. They also should be verifiable during construction and later while in service. Developed details for SABC must consider simplicity or the connection detail may not find a niche in the growing market for ABC applications. The group cited a number of examples from current standards to those under investigation. Since connections are important elements in the success of ABC in regions of moderate-to-high seismicity, it was felt that a list of viable ductile connections was needed, followed by an assessment of further research needs and prioritization based on simplicity. Industry participation in this effort was deemed essential to ensure successful transition to field application. Final guidance developed must be comprehensive and include design examples where applicable.
Figure 1. Segmental column idealization
Demonstration projects were suggested in high seismic regions to test the constructability of specific proposed connection details, with short- and long-term monitoring established to quantify service-life performance. Close collaboration with contractors and industry representatives was considered essential to meeting the goals of simple, constructible and reliable ductile connection details for SABC applications. Depending on the application and timing relative to implementation, legislation may be required. As an example, if industry participation is demanded in the planning and design phases of a project to develop and employ new connection details specific to the project needs, some states may require legislative approvals. This is akin to the "design sequencing" philosophy used in several states in the past decade, or perhaps product "sole source" desires.
Rocking columns (B6)
This energy dissipating mechanism holds promise to reduce demands on the precast column and its connections. It has been used in New Zealand and Japan on bridges and buildings. Furthermore, New Zealand is researching rocking energy dissipation for retaining walls. Done correctly, the precast column or segmental columns experience a degree of self-centering after a seismic event. A concern that requires more study relates to the stress concentrations at the corners of rocking elements. Consideration should be provided in design of rocking elements to address these high stress zones, and inspection procedures are necessary to confirm performance and damage states after an event. These are critical areas requiring research attention. A synthesis study to review existing knowledge, including the building industry and abroad, was considered a first step, with possible research stemming therein. Potential research should carefully model high stress concentrations and develop sound engineering solutions to protect vulnerable members.
Segmental post-tensioned columns (connections) (F6)
Segmented post-tensioned columns are currently the subjects of intense research nationally and internationally. This subject is quite similar to that on "Rocking Columns" above, yet the two were not combined in the breakout discussions. Variations of this idea include bonded versus unbonded tendons, and mild steel crossing joints. Bonded tendons tend to provide emulative response; that is, behavior similar to conventional cast-in-place concrete columns. A major advantage of unbonded post-tensioning is the inherent self-centering feature for large displacements (reference Figure 2). Additionally, unbonded systems may provide for energy dissipation through joint opening and closing where mild reinforcement is not employed. The University of California at San Diego, the University of Washington, the State University of New York in collaboration with researchers in Taiwan, the University of Nevada-Reno, the University of California at Berkeley, and others in Japan and elsewhere are all investigating variations of this concept. Test results completed to date indicate segmental column performance using bonded and unbonded prestressing tendons may be equal to or better in general than conventional cast-in-place columns. Issues requiring careful investigation include tendon corrosion for unbonded systems especially where joint opening is allowed, creep monitoring, and post-event inspection. Additional research targeting these areas was considered warranted.
Footing-to-Pile and Column-to-Foundation connections (F1 and F2)
This idea received the most votes. It was recognized that successful applications of many different footing-to-pile and column-to-foundation connections have been realized outside of seismic regions. Although some research is underway as evidenced in the morning session discussion, more studies are necessary. The group sought simple, robust, repeatable designs that are economical, constructible, and maintainable. These were the basic concepts Bill Duguay promoted as essential to the success of SABC connections from a contractor perspective in his morning presentation. The first step suggested by the group was a synthesis study to review related efforts by various states and agencies.
FIGURE 2. Bonded/unbonded tendon performance
Research efforts currently funded through NCHRP, State DOTs, or others are an integral component of this study. The outcomes of the synthesis were expected to guide future targeted research. Such research could be a redirection of on-going efforts, or entirely new, guided work.
Innovative materials (G1)
A synthesis study was recommended to identify innovative material applications, tabulate material properties, and define availability. Material availability was recognized as an important element in application viability, with concerns over the high manufacturing cost of some materials such as composites. It was further recommended that the synthesis be followed by targeted research as appropriate to develop promising technologies to the point that they are readily implemented. Finally, trial applications were considered important to showcase proposed technologies. As the title of this idea suggests, research herein is continuous. Recognizing this, and understanding that innovative material applications take time to develop, the group proposed emulative response for initial applications, followed by more innovative methods as the technology matured.
Segmental construction connection concepts (C3)
It was generally accepted that segmental construction techniques employed not only in bridge superstructure construction, but also in the building industry, could potentially be leveraged for advancing bridge construction. A synthesis study was suggested to identify promising techniques. The outcomes of this study should propose viable concepts and develop criteria for application. Additional research needs could stem from the synthesis study. This topic should be merged with ideas C4a, b, c, B5, and perhaps F6 for research advantage.
Long-term performance of SABC connections (G2)
The concerns listed herein related to the long-term performance of connections details for SABC. Certainly, accelerated environmental tests were deemed essential when qualifying new ideas or innovative applications of existing technologies. Additionally, the lack of reliable nondestructive test tools for many evolving technologies holding promise for ABC in moderate-to-high seismic regions was discussed. Maintainability and confirmation of in-situ performance were considered important to successful deployment of many technologies. Predictable performance of structures, an area receiving more attention recently as calibration adjustments are underway with the AASHTO LRFD Design Specifications, and as extended system and component durability is demanded, requires a solid understanding of long-term performance. Structural health monitoring concepts were considered an important element in quantifying long-term performance of innovative connection details for SABC applications, especially since oftentimes, designs employing special connection detailing to address seismic demands rely on a prescribed performance level during infrequent seismic design events.
Code recommendations for SABC
Rather than an opportunity for research, this concept is something that should be part of the implementation strategy for every idea considered. The group recognized this as the end result of well-managed research. Codification ensures standardization, and provides a measure of liability protection to the engineer of record. Standardization leads to repeatable, biddable and constructible details, which hopefully are robust in nature so as to minimize or create manageable maintenance concerns. The action plan for this topic provides a draft conclusion for every research project undertaken. The importance of this idea lies in the underlying message its author conveyed; that is, innovation will only succeed and realize widespread deployment when it is thoroughly developed and standardization is a reality.
Two meetings have been scheduled during the January 2008 TRB Annual Meeting, as shown below, to further develop next steps. The first meeting will provide an overview of the October 11 workshop outcomes, a review of the subsequent action plan, a discussion of current research, and further open discussions related to direction. The intent of discussions herein is to capture new ideas that might emerge from a slightly different audience, recognizing the dynamics involved in processes largely materializing from research as in this subject matter. The second meeting will be a working meeting to develop specific research problem statements. These will largely derive from the two top prioritization categories (A and B) developed at the workshop and shown in Table 4.
- Seismic ABC Collaboration Meeting, Part 1: Tuesday, January 15, 3:45-5:30 p.m., Marriott
- Seismic ABC Collaboration Meeting, Part 2: Tuesday, January 15, 7:30-9:30 p.m., Marriott
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