1、STD-AC1 SP-L4-ENGL 1799 I 0bb2949 054b480 30b DEVELOPMENT OF SEISMIC STEEL REINFORCEMENT PRODUCTS AND SYSTEMS SP-184 international- STD-AC1 SP-L4-ENGL 1999 W Obb2949 054b481 242 Development of Seismic Steel Reinforcement Products and Systems international SP- 184 STD-AC1 SP-LB4-ENGL 1999 Obb2949 054
2、b482 L89 = DISCUSSION of individual papers in this symposium may be submitted in accordance with general requirements of the AC1 Publication Policy to AC1 headquarters at the address given below. Closing date for submission of discus- sion is May 1, 2000. All discussion approved by the Technical Act
3、ivities Com- mittee along with closing remarks by the authors will be published in the September/October 2000 issue of either AC1 Structural Journal or AC1 Materials Journal depending on the subject emphasis of the individual paper. The Institute is not responsible for the statements or opinions exp
4、ressed in its publications. Institute publications are not able to, nor intended to, supplant indi- vidual training, responsibility, or judgment of the user, or the supplier, of the information presented. The papers in this volume have been reviewed under Institute publication proce- dures by indivi
5、duals expert in the subject areas of the papers. Copyright O 1999 AMERICAN CONCRETE INSTITUTE P.O. Box 9094 Farmington Hills, Michigan 48333-9094 Ail rights reserved including rights of reproduction and use in any form or by any means, including the making of copies by any photo process, or by any e
6、lectronic or mechanical device, printed or written or oral, or recording for sound or visual reproduction or for use in any knowledge or retrieval system or device, unless permission in writing is obtained from the copyright proprietors. Printed in the United States of America Editorial production:
7、Jane D. Carroll Library of Congress catalog card number: 99-64291 STDmACI SP-184-ENGL 1999 Obb2949 054b483 O15 E PREFACE Over the past decade there have been many changes to the traditional range of reinforcing systems available for engineers and contractors. These changes have included development
8、of new types and styles of welded wire reinforcement. With new steel-making technology and the latest practices of cold-working rod to wire, the industry is producing higher strength and higher ductility wire and welded wire for more structural uses. New headed reinforcing bar criteria is discussed
9、that promises mechanical anchorage of reinforcing to eliminate or reduce development lengths and ease construction over conventional hooks. There is new guidance criteria to qualify mechanical reinforcement splices for designs requiring high-strain energy capacity. At the AC1 1997 Spring convention
10、in Seattle, Wash., AC1 Committee 439, Steel Reinforcement, sponsored a full day technical session comprised of two parts. Both parts were a mix of various reinforcement products and systems. The presentations provided state-of-the-art coverage of important developments in reinforcing systems that ha
11、ve occurred in recent years. Seven papers were submitted for this symposium volume that cover welded wire reinforcement applications and design approaches, headed reinforcing bar applications and mechanical reinforcement splice system design, and performance standards. These papers will provide engi
12、neers and contractors with up-to-date information on new technologies that are available now to improve the performance of reinforced concrete structures, especially in zones of high seismicity and to make design and construction more cost effective. The manuscripts in this publication were assemble
13、d by R. H. Reiterman, who also ensured that each was reviewed according to Institute publication policies. . 111 CONTENTS INTERRELATIONSHIPS BETWEEN REINFORCING BAR PHYSICAL PROPERTIES AND SEISMIC DEMANDS by J. McDermoti . i DESIGN AND PERFORMANCE OF BRIDGE CAP BEAMCOLUMN JOINTS USING HEADED REINFOR
14、CEMENT AND MECHANICAL COUPLERS by S. Sritharan, J. Ingham, M. Priestley, and F. Seible 7 DESIGN AND DETAILING WITH HEADED REINFORCEMENT FOR SEISMICALLY RESISTANT CONCRETE BRIDGE STRUCTURES by D. Berner, T. Dahlgren, and K. Dahl 23 EFFECTS OF CYCLIC BEHAVIOR OF REINFORCING STEEL ON SEISMIC PERFORMANC
15、E OF REINFORCED CONCRETE MEMBERS by M. Rodriguez . 45 NEW DEVELOPMENTS WITH STRUCTURAL WELDED WIRE REINFORCEMENT (WWR) IN ZONES OF HIGH SEISMICITY by R. C. Richardson . 65 AN UPDATE-HIGH-STRENGTH CONCRETE REINFORCEMENT IN CURRENT CODES by R. H. Reiterman . 79 V Previous page is blank STD-AC1 SP-LB4-
16、ENGL 1999 0662949 05Yb485 498 SP 184- 1 Interrelationships between Reinforcing Bar Physical Properties and Seismic Demands by J. McDermott This paper (Title no. S-17) was published in the March-Apd 1998 AC1 StructirralJourPial, p. 175-182. Therefor, the following is a summary of the paper, plus a po
17、stscript included in the convention presentation. Reinforcing bar physical properties are main determinants for reinforc modulus of elasticity; reinforcing bar 1 STD-AC1 SP-LBY-ENGL 1999 0662749 054b48b 824 9 2 McDermott The analysis strategy included (1) relating Sd to e/L. where L is the beam elas
18、tic length and e is the depth from the reinforcing bar centroid to the neutral axis, (2) stating a reasonable denition for tensile stress along the beam, in temu of the unknown length of plastic hingui column; footing; reinforcement 7 H Obb2949 054b492 028 W 8 Sritharan et al. INTRODUCTION The 1989
19、Loma Prieta earthquake caused significant damage to bridge stock in the San Francisco Bay area 4. This damage, combined with post-earthquake analysis, identified several design shortcomings in existing bridge structures 8, emphasizing the need for a critical review of California bridge seismic desig
20、n procedures. Consequently, comprehensive research programs were initiated at several institutions in California investigating possible retrofit techniques for existing structural deficiencies and establishing seismic design guidelines for modem bridges. One of the design deficiencies identified in
21、existing bridges was inadequate detailing of cap bedcolumn connections, whose performance is critical at the survival limit state. Collapse of, or damage to a number of bridges in the Loma Prieta earthquake, including the double-deck Cypress viaduct, was attributed to poor detailing of the beardcolu
22、mn joints 4. As outlined in the following section, when joints are detailed in accordance with the conventional design philosophy based directly on shear forces, considerable reinforcement congestion is likely. In this paper, testing conducted at the University of California at San Diego (UCSD) is u
23、sed to demonstrate that simplified reinforcement details can be obtained for structural members when utilizing new reinforcement products such as headed rebars and mechanical couplers in conjunction with joint force transfer models. This significantly reduces congestion problems, particularly in cap
24、 beamcolumn connections, while providing satisfactory overall seismic performance for the structure. SEISMIC DESIGN PROCEDURE The capacity design philosophy, which now forms the basis for bridge design in most seismically active countries of the world, emphasizes ductile structural performance under
25、 severe seismic loading. In concrete bridges, ductile response is typically developed by forming plastic hinges at the top and/or bottom of bridge columns. The reinforcement located in these hinge regions is carefully detailed to accommodate large inelastic reinforcement strains and local member rot
26、ations, allowing seismic energy to be dissipated in the form of hysteretic damping. The remaining elements of the structure are protected from significant inelastic action by providing a strength hierarchy sufficient to cope with potential strain hardening and uncertainties in material strengths. 06
27、62949 0546493 Tb4 Seismic Steel Reinforcement Products and Systems 9 The elastic design of non-critical structural members (typically the bridge cap beam) is generally well established. However, the design of joints which the bridge members frame into is in comparison poorly understood and is not sp
28、ecifically addressed in bridge design codes such as AASHTO i and Caltrans specifications 3. Two alternative methods may be considered for detailing bridge joints to ensure satisfactory performance complying with capacity design criteria. I. Building Code Approach In building codes that require speci
29、fic design ofjoints, such as NZS 3101: 1995 2 and AC1 318-95 12, the design of beamcolumn connections is based upon the maximum joint shear force which is expected at the ultimate limit state. If a similar approach is considered for the design of bridge joints, robust joint performance is ensured. H
30、owever, this design procedure, when applied to bridge joints, has been found to require an unnecessarily conservative amount of reinforcement, resulting in major congestion within the joint 6,9,1 i. 2. Rational Force-Transfer Method In research studies at UCSD the design of bridge joints has been in
31、vestigated 5 - 111 using force transfer mechanisms which ensure a satisfactory pathway for forces through the joint. It has been shown experimentally that good seismic bridge joint response can be obtained using significantly less than the code-recommended quantity of joint reinforcement when the de
32、sign is based on force transfer mechanisms. In a well-designed bridge joint, the flexural capacity of the column, which frames into the joint, dictates the shear demand within the joint. Consequently, when a concrete bridge bent is designed with high longitudinal reinforcement content in the columns
33、 (pi 2 2.5%), the required reinforcement in the joint region based on force transfer models can also create congestion problems. In such circumstances, joint reinforcement congestion can be alleviated using altemative reinforcement products as demonstrated in the two large-scale tests presented in t
34、his paper. Headed Reinforcement Corp., 11200 Condor Ave., Fountain Valley, CA 92708. M Obb294 0546494 TO 1 O Sritharan et al. RECENTLY-DEVELOPED REINFORCEMENT PRODUCTS In recent years a large number of products have become available in the United States to simplie the anchorage and lap splicing of c
35、onventional reinforcement. Two such products, namely headed reinforcement and mechanical couplers (or bar extenders) were used in large-scale experiments on bridge structural systems at UCSD. These reinforcement products were designed and manufactured by Headed Reinforcement Corporation. When new re
36、inforcement products are used in seismic design, it is not always sufficient to assess these products based upon monotonic stress-strain response. Depending upon the design, it may be necessary to ensure that the product can withstand cyclic inelastic strains to produce a satisfactory structural res
37、ponse when subjected to earthquake loading. In all cases, it is required that the ultimate capacity of the reinforcement product be not less than the ultimate capacity of the parent reinforcing bar. Description and relevant laboratory tests performed on the headed reinforcement and bar extender prod
38、ucts are as follows. 1. Headed Reinforcement Headed reinforcement provided in the knee joint unit was manufactured by friction welding forged circular heads to conventional ASTM A706/A706M-90 grade 60 (414 MPa) weldable reinforcement (see Fig. la). In the process of quality-assurance tests performed
39、 by the manufacturer, the headed reinforcement exhibited cyclic behavior identical to that of the parent reinforcing bar with ultimate failure consistently occurring in the reinforcement, not at the friction weld. To veri that the full capacity would be developed in the parent reinforcing bar, a tot
40、al of eight headed bars were randomly selected during construction of the knee joint unit at the UCSD facilities, and tested in uniaxial tension. In all cases, fracture of these randomly selected samples occurred in the reinforcing bar, away from the fiction weld. 2. Mechanical Coupler (or Bur Exten
41、der) System The mechanical coupler system used in the second test unit incorporated two fixtures which coupled two headed reinforcing bars using standard threads (see Fig. lb and lc). The reinforcement heads were formed using a technique E Obb2949 S4bY95 837 E Seismic Steel Reinforcement Products an
42、d Systems 11 suitable for field implementation by heating the bar ends and forging them with a hand-held hydraulic device. Quality-assurance testing conducted by the manufacturer consisted of uniaxial tension tests on the mechanical coupler system, ensuring that full reinforcement capacity could be
43、developed when using the coupler. Several couplers were also tested at UCSD with failure occurring in a similar fashion. This reinforcement product was used exclusively in the cap beam design of the test unit. Consistent with the capacity design philosophy, the beam reinforcement connected by the co
44、upler was not expected to undergo any significant inelastic strains. EXPERIMENTAL INVESTIGATION 1. Bridge Knee Joint A sequence of four 1/3d scale units having a geometry (see Fig. 2) based upon the pin-based two-column 1-980 Bent #38 in Oakland, California, were tested under simulated seismic condi
45、tions 5. These units represented the as-built joint and its prototype repair, together with a retrofit and redesign of the as- built joint based upon rational force transfer models. The reinforcement details of the redesigned joint are shown in Fig. 3, clearly indicating that there was major congest
46、ion of reinforcement in the joint region of this unit despite the use of rational design models. Strain data confirmed that an appropriate quantity of joint reinforcement had been provided in the redesigned unit, enabling a column plastic hinge to form at the joint interface for both directions of l
47、oading without major damage to the cap beam or joint region. A further unit was then designed using headed reinforcement throughout, eliminating the need for hooks with horizontal tails to the embedded longitudinal column reinforcement and vertical tails for the embedded longitudinal cap beam reinfo
48、rcement 7. Combining the use of rational procedures for assessing realistic joint force levels with careful attention to detailing of the headed reinforcement in the joint region ensured that flexural forces acting at the joint boundaries could be effectively transmitted through the joint via a sing
49、le diagonal strut for each direction of loading, as shown in Fig. 4. The resulting design required no conventional joint reinforcement other than joint cross-links, which were provided to prevent excessive out-of-plane joint dilation and assist in confinement of the joint core. Details of the joint reinforcement for this unit are shown in Fig. 5, and footing reinforcement details for the test unit are depicted in Fig 6. Clearly the elimination of joint hoops or stirrups greatly reduced congestion of reinforcement in the joint zone, as did elimination of 90“
