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KEYWORDS: beam-column connection; mild steel reinforcement; moment-resisting frame; post-tensioned hybrid connection; seismic design; unbonded tendon. ABSTRACT: This paper presents the results of tests performed on post-tensioned, precast concrete moment-resisting, beamcolumn connections containing different mild steel reinforcement contents. In the experimental program, five hybrid connections were tested under displacement controlled reversed cyclic loading. The main variable was the mild steel's percentage of contribution to the flexural capacity of the connection, ranging from 0% to 65% of the connection's moment capacity. Each hybrid connection was compared with the test result of the reference monolithic subassembly in terms of connection strength, stiffness degradation, energy dissipation, and permanent displacement. The objective of this study was to determine the effect of mild steel reinforcement content on the behavior and performance of post-tensioned, precast concrete hybrid connections. The response of post-tensioned, precast concrete hybrid connections approached that of the monolithic subassembly as the mild steel reinforcement content increased. Connection capacities were well predicted by the joint gap opening approach. The design assumptions of hybrid connections are best satisfied with a 30% mild steel reinforcement contribution to the connection's flexural capacity. REFERENCE: Ozden, Sevket, and Ertas, Onur, "Behavior of Unbonded, Post-Tensioned, Precast Concrete Connections with Different Percentages of Mild Steel Reinforcement," PCI Journal, V. 52, No. 2, March­April 2007, pp. 32­44.

KEYWORDS: bridge; continuity diaphragm; continuous span; prestressed girder; skew angle. ABSTRACT: Continuity diaphragms have caused difficulties in detailing and construction when used in bridges composed of prestressed concrete girders supported on skewed bents. This study investigates the effect of full-depth continuity diaphragms on the deflection of, and stress in, skewed precast, prestressed concrete girders. Bridge models used in this study had the following parameters: girder type and spacing, bridge skew angle, span length, and diaphragm type. As either the skew angle increases or the girder spacing decreases in these types of bridges, construction becomes more difficult and the effectiveness of the diaphragms becomes questionable. If diaphragms are determined to be unnecessary as an outcome of this research, the construction and maintenance costs of these types of bridges could possibly be reduced. The objectives of this research were to determine the need for continuity diaphragms in skewed, precast, prestressed concrete girder bridges; study the load transfer mechanism through full-depth continuity diaphragms; and determine the minimum skew angle at which a diaphragm becomes ineffective in performing its function. REFERENCE: Saber, Aziz; Roberts, Freddy; Alaywan, Walid; and Toups, Joseph, "Effectiveness of Continuity Diaphragm for Skewed Continuous Prestressed Concrete Girder Bridges," PCI Journal, V. 52, No. 2, March­April 2007, pp. 108­114.

KEYWORDS: bridge; creep; long-term prestress loss; prestressed concrete; relaxation; serviceability; shrinkage. ABSTRACT: Creep and shrinkage of concrete and relaxation of prestressing steel cause gradual stress reductions in concrete when subjected to compression and in prestressing steel when subjected to tension. Inaccurate estimates of long-term prestress losses can cause serviceability problems, including concrete cracking and excessive deflection or camber. In this paper, the authors present an analytical method to predict the long-term prestress losses in precast, pretensioned or post-tensioned concrete members. Design aids are presented for cast-in-place, post-tensioned concrete bridges. The proposed method is based on equilibrium and compatibility principles of solid mechanics and can be used for multistage loading and prestressing. In deriving some of the equations, however, it is assumed that prestressing and dead loads are applied simultaneously and that the longterm effects of concrete creep and shrinkage and relaxation of prestressing steel occur gradually thereafter. Empirical equations in current bridge codes either underestimate or overestimate long-term prestress losses in concrete members, depending on the concrete creep and shrinkage properties and on the non-prestressed steel ratios. Examples show that the presence of non-prestressed steel has significant effects on the long-term deformation and long-term change in compressive stress remaining in the concrete after prestress losses. REFERENCE: Youakim, Samer A.; Karbhari, Vistasp M.; Ghali, Amin; and Hida, Susan E., "Prediction of Long-Term Prestress Losses," PCI Journal, V. 52, No. 2, March­April 2007, pp. 116­130.

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KEYWORDS: anchorage; beam-column connection; post-tension; prestress; seismic performance; shear capacity. ABSTRACT: This paper reports the results of cyclic load tests on seven precast, prestressed concrete beam-to-column joint assemblages conducted at Kyoto University. The experimental parameters are location of tendon anchorage, prestressing steel content in the beam section, and concrete compressive strength. To the authors' knowledge, there are no other experimental data available on the effect of post-tensioning anchor location on the seismic performance of external beam-to-column joints in precast, prestressed concrete assemblies. Based on the experimental results, the authors recommend a shear capacity evaluation method and design considerations for optimizing the location of post-tensioning anchors in precast, prestressed concrete beam-to-column joint assemblages. REFERENCE: Nishiyama, Minehiro, and Wei, Yue, "Effect of Post-Tensioning Steel Anchorage Location on Seismic Performance of Exterior Beam-to-Column Joints for Precast, Prestressed Concrete Members," PCI Journal, V. 52, No. 2, March­ April 2007, pp. 18­30.

KEYWORDS: finite element; L-beam; L-shaped spandrel; open web reinforcement; prestressed; spandrel; torsion. ABSTRACT: This paper presents the results of nonlinear finite element analyses conducted to model the behavior of L-shaped, precast, prestressed concrete spandrels constructed with open web reinforcement. The finite element model was calibrated using experimental results from recent tests of slender, L-shaped, precast, prestressed concrete spandrels. Detailed correlative studies between analytical and experimental results are presented, demonstrating the capability of the finite element program to describe the observed experimental behavior. The feasibility of using open web reinforcement in compact, L-shaped, precast, prestressed concrete spandrels to achieve a more construction-friendly reinforcement scheme is also examined. Five different web reinforcement configurations for the compact spandrels were studied in order to evaluate the contribution of closed stirrups to the spandrels' shear-torsion behavior. The behavior, ultimate load-carrying capacity, and mode of failure of both the slender and compact L-shaped precast, prestressed concrete spandrels are presented. When loading values near the ultimate, the out-of-plane bending behavior of compact, L-shaped, precast, prestressed concrete spandrels is strongly influenced by the web-reinforcement configuration. Results from the analysis show that for long-span, compact spandrels, open web reinforcement can be used effectively to resist torsional forces throughout the member. REFERENCE: Hassan, Tarek; Lucier, Gregory; Rizkalla, Sami; and Zia, Paul, "Modeling of L-Shaped, Precast, Prestressed Concrete Spandrels," PCI Journal, V. 52, No. 2, March­April 2007, pp. 62­76.

KEYWORDS: closed ties; L-beam; L-shaped spandrel; prestressed; skew bending; slender spandrel; spandrel; torsion; welded wire reinforcement. ABSTRACT: This paper presents the results from full-scale testing conducted at North Carolina State University on four precast, prestressed concrete L-shaped spandrels. The four L-shaped spandrels were each loaded through 12-ft-long (3.7 m), prestressed double tees that rested on the spandrel ledge at one end and on an independent support at the other. None of the beams were constructed with closed stirrups of mild-steel reinforcement. Rather, different arrangements of transverse L-shaped bars, welded-wire reinforcement, and longitudinal bars were provided to resist the shear and torsion induced in the spandrels. Shear and torsion forces were created by the double-tee reaction forces that were loaded eccentrically to the spandrels. The transverse and longitudinal reinforcement resisted the combined effects of vertical shear and out-of-plane bending of the web and satisfied the minimum vertical hanger reinforcement requirement for ledge-to-web attachment. All beams sustained loads well in excess of their factored design loads. Eliminating the need for closed reinforcement in slender spandrels would be of significant benefit to the precast concrete industry. This design approach would enhance the constructability of slender members, which could increase plant productivity and reduce overall costs. The paper presents the behavior of all four spandrels at various limit states, including their crack patterns and modes of failure. Researchers used these test results to better understand the fundamental mechanism developed in the L-shaped spandrels to resist shear and torsion. REFERENCE: Lucier, Gregory; Rizkalla, Sami; Zia, Paul; and Klein, Gary, "Precast Concrete, L-Shaped Spandrels Revisited: Full-Scale Tests," PCI Journal, V. 52, No. 2, March­April 2007, pp. 78­92.

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KEYWORDS: curved bridge; curved concrete girder; high-strength concrete; post-tensioned concrete girder; precast concrete deck panel; time-dependent analysis; value engineering. ABSTRACT: Arbor Road Bridge is an Interstate 80 overpass consisting of two spans that are about 142 ft (43.3 m) and 136 ft (41.5 m) long. It is a horizontally curved bridge with a skew of 31 degrees. The original design used Grade 50 (50 ksi [345 MPa]) weathering steel plate girders and haunched segments spliced over the pier. Due to the high cost of steel girders at the time the project was bid, a value engineering proposal using a precast concrete alternative was approved by the owner. This paper describes a number of innovative designs in this project, including the use of curved precast concrete girders and precast concrete deck panels. Also presented are the girder analysis and design procedures, a description of the production of the precast concrete girders and deck panels, the construction sequence, and a cost comparison between the concrete and steel alternatives. Empirical equations in current bridge codes either underestimate or overestimate long-term prestress losses in concrete members, depending on the concrete creep and shrinkage properties and on the non-prestressed steel ratios. Examples show that the presence of non-prestressed steel has significant effects on the long-term deformation and long-term change in compressive stress remaining in the concrete after prestress losses. REFERENCE: Sun, Chuanbing; Hennessey, Shane A.; Ahlman, Mark S.; Tadros, Maher K., "Value Engineering Arbor Road Bridge with Curved Precast Concrete Girders," PCI Journal, V. 52, No. 2, March­April 2007, pp. 94­106.

KEYWORDS: code; failure; L-beam; L-shaped spandrel; reinforcement; spandrel; torsion. ABSTRACT: Current code-required design procedures for eccentrically loaded L-spandrels assume that torsional distress is the mode of failure at ultimate shear-torsion capacity and prescribe appropriate reinforcement to accommodate such distress. The more commonly accepted design procedures vary in complexity, but all result in the need for heavy reinforcement and complex detailing that are expensive with regard to both material and fabrication labor costs. Based on observation of the failure mode of an L-beam in a full-scale torsion test conducted by the author in 1961, and particularly on his diagnosis of the failure modes of L-spandrels in tests conducted in the mid-1980s by Wiss, Janney, Elstner Associates Inc., the author concludes that the face shell spalling and severe spiral cracking associated with torsional distress is not induced in L-spandrels at ultimate failure by eccentric vertical loading. Thus, the current complex design procedures and the complexity and expense of reinforcement resulting from these procedures are not justified. Instead, the ultimate capacity in the end region of L-spandrels is satisfied by the reinforcement required in their inside face to resist out-of-plane bending. Concrete shear capacity is checked by the Vcw equation and seldom requires additional reinforcement in deep L-spandrels. REFERENCE: Logan, Donald R., "L-Spandrels: Can Torsional Distress Be Induced by Eccentric Vertical Loading?" PCI Journal, V. 52, No. 2, March­April 2007, pp. 46­61.

DISCUSSION NOTE

The editors welcome discussion of reports, papers, and problems and solutions published in the PCI Journal. Comments must be confined to the scope of the article under discussion. Reader comments and letters may be sent to: Emily Lorenz, P.E. Editor-in-Chief PCI Journal 209 W. Jackson Blvd., Suite 500 Chicago, IL 60606 Email: [email protected] All discussion of articles appearing in this issue of the PCI Journal must be received at PCI headquarters by June 1, 2007.

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PCI JOURNAL

abstracts of technical Publications

Analysis of Revisions to the 2006 IBC Structural Provisions

S. K. Ghosh, Susan Dowty, and P. Dasgupta This publication provides an analysis of the changes to the 2006 International Building Code (IBC) structural provisions (Chapters 16 through 23), which were approved by the International Code Council membership at the annual conferences in 2004 and 2005. The 2006 IBC is most different from the 2003 IBC in that referenced standards have been updated to reflect the most current standards and there is an almost exclusive reliance on the 2005 edition of the American Society of Civil Engineers (ASCE) standard Minimum Design Load for Buildings and Other Structures (ASCE 7-05) for prescribing structural loading requirements. This publication provides explanations and guidance on how to use the ASCE 7-05 standard in conjunction with the 2006 IBC, as well as a thorough discussion of the changes in the updated material standards referenced (for example, the American Concrete Institute's ACI 318-05, the 2005 edition of Masonry Standards Joint Committee code, the American Institute of Steel Construction's AISC 360-05, the AISC 341-05, and the American Forest and Paper Association's NDS-05). Structures and Codes Institute (SCI); 2006; Palatine, Ill.; 254 pp.; $40. tion, it is necessary to pay attention to the structural detailing of the columns and particularly to the connection of the individual precast elements. In this article, further suggestions based on Eurocode 8 are given. Concrete Plant + Precast Technology, V. 76, No. 11, November 2006, pp. 22­32.

Prevention of Progressive Collapse in Multistory Concrete Buildings

Francis K. Humay, Steven M. Baldridge, and S. K. Ghosh Recent world events have heightened public awareness of building safety and security issues. Engineers are now often faced with considering the prevention of progressive collapse in multistory building design. The most prevalent design guidance currently available on this topic is provided by two federal agencies: the General Services Administration (GSA) and the Department of Defense (DOD). Prevention of Progressive Collapse in Multistory Concrete Buildings provides a comprehensive discussion of the GSA and DOD requirements along with several complete evaluation ex-

Corrosion in Reinforced Concrete Structures

H. Böhni, Editor Reinforced concrete has the potential to be very durable and capable of withstanding a variety of adverse environmental conditions. However, failures in the structures do still occur as a result of premature reinforcement corrosion. In this book, the fundamental aspects of this complex process are analyzed, focusing on corrosion of the reinforcing steel and looking particularly at new scientific and technological developments. Monitoring techniques, including the newly developed online monitoring, are examined, as well as the numerical methods used to simulate corrosion and perform parameter studies. The influence of composition and microstructure of concrete on corrosion behavior is explored. The second half of the book, which deals with corrosion prevention methods, starts with a discussion on stainless steels as reinforcement materials. There are comprehensive reviews of the use of surface treatments and coatings, of the application of corrosion inhibitors, and of the application of electrochemical techniques. In each case the necessary scientific fundamentals are explained and practical instances of use are looked at. This will be an invaluable guide for engineers, materials scientists, and researchers in the field of structural concrete. Key features of the report include the fundamental aspects of corrosion in concrete and minimizing the effects of corrosion in concrete. Woodhead Publishing Ltd., 2005, 264 pp., 211 euros.

Read Any Good Books Lately?

Have you recently read a book on the concrete/ construction/engineering industry? Would you like to share a review of it with PCI members? The new PCI newsletter is currently soliciting reviews of industry-related books that touch on a wide range of topics, including biography, theory, history, and even fiction. Please contact Keith Ulrich, PCI manuscript editor, for additional information at [email protected] org or phone (312) 360-3209.

Earthquake Resistant Construction of Precast Concrete Halls

Martin Empelmann and Gunnar Heumann Halls made from precast concrete components are standard in the area of reinforced concrete construction. They are, therefore, inevitably erected also in earthquake regions. It is necessary to follow the main principles of the socalled modern earthquake capacity design method in order to come up with an earthquake-resistant design. In addiMarch­April 2007

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abstract of Pci technical Publication

Manual for the Evaluation and Repair of Precast, Prestressed Concrete Bridge Products

Third Edition, MNL-137-06 This manual is a resource document to guide owners, designers, inspectors, and fabricators in reaching informed decisions regarding repair options for precast, prestressed concrete bridge products. To this end, the engineering considerations related to individual defect types are provided. The ultimate value of this guide lies with the sound engineering judgment of the qualified individuals who use this document. In addition to the main topic of the manual's title, the document also includes discussion of imperfections or damage occurring during production, handling, transportation, and erection. This manual was prepared by a subcommittee (Edward P. Wasserman, chair) under the direction of the PCI Bridge Committee. Plant-cast prestressed concrete bridge beams and similar products produced in PCI-Certified plants are manufactured in a quality-controlled environment. These facilities meet the minimum standards for processes and equipment. They have trained supervisory and certified quality control staff operating within published procedures that will consistently result in high-quality products that meet project and customer requirements. As with any manufactured product, damage or defects can occur in the manufacturing precast concrete bridge products. Examples include voids and cracks in concrete and improperly placed or damaged reinforcement and hardware. These fall into one of three categories: · Productsthatcanbeaccepted without repair; · Productsthatcanbeaccepted with repair; and · Productsthatmustberejected.

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amples. A variety of reinforced concrete multistory structural systems are evaluated for resistance to progressive collapse, including moment frames, flat-plate construction, and bearing wall systems. While this manual is intended primarily for practicing engineers, it will also be an aid to students, educators, regulators, and those involved in the design, construction, and approval of buildings. SCI; 2006; Palatine, Ill.; 304 pp.; $65.

Reinforced Concrete Design, Seventh Edition

Chu-Kia Wang, Charles G. Salmon, and José A. Pincheira The manual contains six chapters: Introduction; Troubleshooting Guide; Standard Repair Procedures; Methods of Patching; Epoxy Injection; and Selected References. Discussion of the essential issues to be considered in the engineering evaluation of cracks and the methods of repair are included in the manual. One of the most useful topics in the manual is the chapter on epoxy injection in which the following questions are posed and answered: · Whoshouldperformtherepairs? · Whichcracksshouldbeinjected? · Howarecracksprepared? · Whatpressureshouldbeused in the injection process? · Howlongistheinjectionduration? · Whatproceduresareusedto fill honeycombs? This manual is an essential reference for any bridge engineer involved in the design, construction, inspection, and maintenance of bridge structures. The publication is in an 81/2 in. × 11 in. softcover format and is 70 pages long. It is well illustrated with numerous diagrams and some photographs. The price of the manual is $25.00 for PCI members; $50.00 for non-members. To purchase a copy, visit www.pci.org/publications/store/ or call (312) 786-0300. The seventh edition of Reinforced Concrete Design incorporates the changes in design rules arising from the publication of the 2005 Building Code Requirements for Structural Concrete (ACI 318-05). This new edition follows the same philosophical approach that has gained wide acceptance of users since the first edition was published in 1965. Herein, as previously, strength and behavior of concrete elements are treated with the primary objective of explaining and justifying the ACI code rules and formulas. Then, numerous examples are presented illustrating the general approach to design and analysis. Considering the limited scope of most examples, attempts to reach practical results are made insofar as possible. Considerable emphasis is placed on presenting for the student, as well as the practicing engineer, the basic concepts deemed essential to understand and properly apply the ACI code rules and formulas. The treatment is incorporated into the chapters in such a way that the reader may either study in detail the concepts in logical sequence or merely accept a qualitative explanation and proceed directly to the design process using the ACI code. This text is suitable for the undergraduate-level course. However, sufficient information is included for an additional course at the senior or graduate level. John Wiley & Sons Inc.; 2007; Hoboken, N.J.; 960 pp.; $134.95.

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