Interactive Panel Proceedings from the First International Interactive Symposium on Ultra-High Performance Concrete

Transcription

1 Interactive Panel Proceedings from the First International Interactive Symposium on Ultra-High Performance Concrete July 18-20, 2016 Des Moines, Iowa, USA INTERACTIVE PANEL 2 UHPC for Bridges, Part 2: The Future of UHPC in Bridges Panel Chair: Benjamin Graybeal, Ph.D., P.E., Federal Highway Administration Expert Panel Members: Byung-Suk Kim, Ph.D., Korea Institute of Civil Engineering & Building Technology Francois Toutlemonde, Ph.D., P.E., the French Institute of Science and Technology for Transport, Development and Networks Dean Bierwagen, P.E., Iowa Department of Transportation J.P. Binard, P.E., Bayshore Concrete Products William Nickas, P.E., Precast/Prestressed Concrete Institute Panel Interactivity Administrator: Zachary Haber, Ph.D., GENEX Systems Interactive Panel Synopsis Report Authored by: Zachary Haber Benjamin Graybeal

2 Interactive Panel 2: UHPC for Bridges, Part 2 The Future of UHPC in Bridges Chaired by Benjamin Graybeal from the Federal Highway Administration (FHWA), this interactive panel on the use of ultra-high performance concrete (UHPC) for bridges was comprised of experts from the FHWA, the Korea Institute of Civil Engineering & Building Technology (KICT), the French Institute of Science & Technology for Transport, Development and Networks (IFSTTAR), the Iowa Department of Transportation (Iowa DOT) and the Precast/Prestressed Concrete Institute (PCI). This session provided an international perspective on the current state and future of ultra-high performance concrete (UHPC) in bridges. The main goals were: to educate participants on the global implementation of UHPC applications in bridge construction and; present ideas about how future opportunities are related to UHPC in bridge construction. Panel 2, Part 1 of "UHPC for Bridges" addressed "UHPC for ABC Connections". Panel 2, Part 2 addressed "The Future of UHPC in Bridges", and began with the following introductory presentation by Dr. Graybeal. First International Interactive Symposium on Ultra-High Performance Concrete, July 18-20,

3 Prior to opening the interactive portion of this session, short presentations were delivered by each panel member to provide background and motivate audience questions. Panel member names, affiliations, and presentation titles are listed below: 1. Benjamin Graybeal, FHWA: Overview of the Status and Direction - pg Byung-Suk Kim, KICT: Innovative UHPC Solutions from Korea and Asia - pg François Toutlemonde, IFSTTAR: Experience from French Applications - pg Dean Bierwagen, Iowa DOT: Iowa DOT Perspective - pg J.P. Binard, Bayshore Concrete Products: Fabrication Opportunities - pg William Nickas, PCI: Industry Perspective - pg. 9 This State-of-the-Art Report provides copies of each presentation, along with brief summaries. The transcribed questions from the interactive session are provided in Appendix A. 1. Presentation by Benjamin Graybeal: Overview of the Status and Direction First International Interactive Symposium on Ultra-High Performance Concrete, July 18-20,

4 Dr. Graybeal s presentation began with an interesting analogy, explaining how the development of UHPC is very similar to the development of modern structural steel. In the beginning, steel structures were actually composed of iron, whether it be wrought or cast. Although a suitable building material for the time, iron structures were not durable, nor did they possess ductility. As metallurgical science advanced, it was found that raw iron could be doped with other elements such as carbon or chromium to improve the mechanical and durability properties. Similar advancements in concrete science have led to the development of improved admixtures, highstrength steel fibers and applications of the particle packing theory, all used to transform conventional concrete into UHPC. This subsequently improved the durability and mechanical properties of the material and led to what is now referenced as UHPC. In conclusion, Dr. Graybeal presented the mechanical and durability properties of UHPC and explained how they differ from properties found in conventional concrete materials. 2. Presentation by Byung-Suk Kim: Innovative UHPC Solutions from Korea and Asia First International Interactive Symposium on Ultra-High Performance Concrete, July 18-20,

5 Dr. Kim s presentation began with an overview of UHPC bridges in East Asia, providing about 24 examples of highway and pedestrian bridges constructed with UHPC in Japan, South Korea, China, Malaysia, and Myanmar. Dr. Kim then detailed some recent UHPC bridge projects completed in the aforementioned nations. He noted that a variety of UHPC bridge types have been constructed in East Asia, including: prestress girder; segmental box girder; arch-type; and long-span, cable-stayed. Two examples are shown in Figure 1. In conclusion, Dr. Kim described current design guidelines available in East Asia for the design of structures using UHPC. These guidelines have been published in South Korea, Japan, and China. (a) (b) Figure 1. Examples of UHPC bridge construction in East Asia: (a) Perak River UHPC Bridge, Malaysia (2015); (b) Chuncheon LEGO Land Cable-Stayed Bridge (planned 2017) First International Interactive Symposium on Ultra-High Performance Concrete, July 18-20,

6 3. Presentation by François Toutlemonde: Experience from French Applications Dr. Toutlemonde s presentation provided insight regarding some recent UHPC bridge engineering applications in France. He initially explained that UHPC has been used in elements that are subject to high compressive stresses, such as arches and columns. The high compressive strength of UHPC means that these elements can be slender, cross longer spans, and aesthetically pleasing. An example is provided in Figure 2-a. Dr. Toutlemonde then discussed how UHPC has become a popular material choice for pedestrian bridges that are lightweight, with long spans, and produced in a wide range of architectural features. He then presented the use of UHPC in bridge decks and bridge repairs. Some applications include bridge deck overlays (Figure 2-b), waffle slabs, and strengthening of bridge girders. In conclusion, Dr. Toutlemonde presented the durability, efficiency, and economics of UHPC in bridge construction. (a) Pont de la République, Montpellier, France (b) UHPC bridge deck overlay on the Chillon Viaduct, France Figure 2. Examples of UHPC in bridge construction in France First International Interactive Symposium on Ultra-High Performance Concrete, July 18-20,

7 4. Presentation by Dean Bierwagen: Iowa DOT Perspective Mr. Bierwagen s presentation highlighted a few completed UHPC bridge projects in Iowa, USA. The first project used UHPC in prefabricated waffle slab bridge deck elements, in conjunction with field-cast UHPC connections. Due to the advanced properties of UHPC, the deck was designed to be much lighter than a conventional reinforced concrete bridge deck. (See Figure 3-a.) The second project used UHPC for precast, prestressed H-shaped piles, designed to have similar weight and stiffness comparable to a standard steel high performance (HP) pile section. The use of UHPC allowed for reduced pile tip damage (during pile driving) and good resistance to aggressive soils. Finally, Mr. Bierwagen explained how UHPC was used as a bridge deck overlay material. For this project, a special thixotropic UHPC formulation was developed by the UHPC supplier, specifically for overlay projects. (See Figure 3-b.) Mr. Bierwagen then highlighted some potential, future UHPC projects in Iowa, including: waffle slabs; deck overlays; repair applications; and UHPC piles. The presentation concluded with a discussion of some of the challenges that may occur when deploying UHPC solutions in bridge construction. First International Interactive Symposium on Ultra-High Performance Concrete, July 18-20,

8 (a) UHPC waffle slab bridge deck, Wapello County, IA (b) UHPC overlay - Mud Creek Bridge, Buchanan County, IA Figure 3. Examples of UHPC in bridge construction in Iowa, USA 5. Presentation by J.P. Binard: Fabrication Opportunities Mr. Binard s presentation focused on how UHPC could be used to improve precast concrete fabrication processes and serviceability. First, he explained how reinforcement congestion in precast girder elements delays and complicates fabrication. Significant amounts of reinforcement are required in locations subject to high stresses. See Figure 4-a, depicting the end region of a prestressed bulb tee girder. First International Interactive Symposium on Ultra-High Performance Concrete, July 18-20,

9 Mr. Binard then explained how UHPC could be used in high-stress regions in order to significantly reduce the amount of reinforcing bars. This would, in turn, expedite fabrication and reduce costs associated with fabrication delays. He also discussed that, when UHPC is used in bridge girder elements, their section geometries can be optimized, thereby significantly reducing required material volumes. Furthermore, UHPC can reduce the potential for end region cracking. In conclusion, Mr. Binard discussed hybrid applications where UHPC could be used in conjunction with conventional concrete materials. Examples included: composite bridge deck panels; pier diaphragm segments (Figure 4-b); and deck bulb tees with UHPC barriers. In hybrid elements, UHPC would be used strategically, to reduce element self-weight and improve resistance to high stresses. Conventional Segment Segment using UHPC (a) Reinforcement congestion at the end of prestressed bulb tee girder (b) Comparison between conventional diaphragm segments and those employing UHPC Figure 4. Example of how UHPC could reduce material volume, element self-weight and reinforcement congestion in precast concrete construction. 6. Presentation by William Nickas: Industry Perspective First International Interactive Symposium on Ultra-High Performance Concrete, July 18-20,

10 Mr. Nickas s presentation provided insight on how the precast concrete industry views UHPC as an emerging solution, and how the industry can overcome some challenges related to the institutionalization of UHPC. First, Mr. Nickas highlighted some current UHPC applications in bridge construction, including: field-cast connections; precast piles; waffle slabs; columns, pier caps; and girders. He then discussed how a Malaysian precast company, over the course of 10 years, built a business producing UHPC components. Their factory, mixers, and formworks were specially designed to accommodate UHPC, resulting in the economical fabrication of UHPC elements; a feat that many U.S. precasters are finding difficult. The company produced its first UHPC bridge elements in 2010 and will have over 41 UHPC bridge projects in service by the end of Figure 5 shows the trends and locations of UHPC bridge construction in Malaysia. Mr. Nickas concluded by posing the question; Can this Malaysian approach work in the US? If so, the industry must consider the economics of using UHPC from a holistic perspective; not just the up-front material cost, but also the costs related to transportation/freight, construction and life cycle. (a) Number of UHPC bridges in Malaysia (b) UHPC bridge locations in Malaysia Figure 5. UHPC bridges in Malaysia First International Interactive Symposium on Ultra-High Performance Concrete, July 18-20,

11 Summary of Panel-Audience Interaction During the one-hour interactive panel discussion, 18 questions were submitted by the audience using the app-based interactive platform. Thirteen questions were then passed to the moderator and, in some cases, modified or edited to combine multiple, similar questions related. In general, the questions could be categorized into 1 of 6 categories (related to the use of UHPC in bridge construction): challenges and obstacles; the precast concrete industry; specific questions related to structural systems and detailing; design guidance, cost and economics; and other. Figure 6 shows the percentage of questions asked within each category. Although a high percentage were asked about specific structural systems and detailing, the majority of time was spent discussing the challenges, economics, and precast concrete industry. (See Appendix A for a complete list of questions.) Other 22.2% 11.1% Challenges & Obstacles Precast Construction Industry 11.1% Cost & Economics 16.7% Structural Systems & Detailing 27.8% Design Guidance 11.1% Figure 6. Summary of the types of questions asked by the audience in Part 2 Upon completion of the interactive session, two poll questions were directed to the audience. The first question was related to current obstacles that are preventing the deployment of UHPC solutions. The audience was instructed to respond with a statement or phrase. The responses were then reviewed and categorized into 1 of 4 groups: lack of design guidance; industry resistance to change/lack of understanding; cost; and other. A summary/chart is provided in Figure 7. A total of 13 responses were collected, provided in Table 1. The second question asked the audience what (they believed) was the biggest opportunity for UHPC in the next 10 years: prefabricated infrastructure elements; field-cast connections; repair solutions; consumer goods; building facades; and security applications. A total of 15 responses were collected, provided in Figure 8. First International Interactive Symposium on Ultra-High Performance Concrete, July 18-20,

12 Other 7.7% Cost 15.4% Lack of Design Guidence 38.5% Industry Resistance to Change / Lack of Understanding 38.5% Figure 7. Summary of 13 responses to the question: What is the biggest challenge that you face as you work toward integrating UHPC into your toolbox? Table 1. Individual audience responses to the question: What is the biggest challenge that you face as you work toward integrating UHPC into your toolbox? Response Design specifications & ASTM tension material qualification test Lack of understanding Design standards Resistance to change Design standards Design specifications for building structures We need to develop as industry - all of us together Resistance to the unknown Conservative mind set Specifications. Research on structural behavior Risk aversion to paradigm shifts Perception of high cost Cost First International Interactive Symposium on Ultra-High Performance Concrete, July 18-20,

13 Percentage of Response 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Figure 8. Summary of 15 responses to the question: Based on what you ve seen, what is the biggest opportunity for UHPC in the next 10 years? First International Interactive Symposium on Ultra-High Performance Concrete, July 18-20,

14 APPENDIX A - Interactive session Below is a list of questions, as addressed by the following panel experts. Byung-Suk Kim, Korea Institute of Civil Engineering & Building Technology Francois Toutlemonde, the French Institute of Science and Technology for Transport, Development and Networks Dean Bierwagen, Iowa Department of Transportation J.P. Binard, Bayshore Concrete Products William Nickas, Precast/Prestressed Concrete Institute Chair: Dr. Benjamin Graybeal, FHWA Question Likes Passed to Moderator In the U.S., how can we begin using UHPC for primary structural elements when we don t yet have a design specification? 7 YES For each panel member; what do you see as the primary impediment to adoption of UHPC in the U.S.? Are there documents or guides for developing or producing non-proprietary UHPC materials? What would it take to get precast plants geared up to use UHPC as a standard material for precast beams and other PBES? Are any heavy precasters ready to invest in a plant optimized for UHPC component production? For sentimental construction, can UHPC be effectively used on form travelers? With the desirable durability and surface bonding characteristics of UHPC, what applications have there been with UHPC as an overlay? 4 YES 4 YES 3 YES 3 YES 2 YES 2 YES What is the status of the ACI 239 UHPC document? 2 YES How many cables did you save by using UHPC in the superstructure? 1 YES Is UHPC still applicable when used in a run-of-the-mill project (that does not involve an architect)? What are the differences between conventional and UHPC prestressed girders? Reinforcement, web thickness, etc. What is FHWA's role with respect to encouraging the use of UHPC in new bridges and structural repair? Can lateral post tensioning in box girder bridges be eliminated with UHPC connections? 1 YES 0 YES 0 YES 0 YES What is the general unit price comparison of UHPC vs regular concrete? 0 NO When Korean UHPC was used in the Iowa bridge, what was shipped from Korea and; what local material was used? What is the cost of Korean UHPC versus Ductal UHPC? 0 NO If we can reduce sections and materials by using UHPC, will the cost savings outweigh the high unit cost of UHPC? Has an economic study been done? Is UHPC only applicable to horizontal structures like bridges? Is the application of UHPC for high rise buildings under consideration? 0 NO 0 NO Where are UHPC s properties most advantageous in bridges? 0 NO First International Interactive Symposium on Ultra-High Performance Concrete, July 18-20,