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Considerations regarding bond and development of reinforcement in high strength concrete (HSC) are presented from a North American perspective. The information contained in this paper is a compilation of information from various sources and represents a survey of the basis for North American approaches to bond of normal and high strength concrete under monotonic and cyclic loading. The paper was presented in part at the Second US-Japan-New Zealand-Canada Multilateral Meeting on the performance of HSC held in Honolulu November 29-December 1,1994.

In this paper, research on bond and anchorage of reinforcement in high strength concrete were reviewed. They were classified to three groups: research on bond capacity with splitting of surrounding concrete, bond deterioration of bars passing through beam-column joints and anchorage capacity of hooked bars in beam-column joints. A characteristic property of low tensile strength relative to the high compressive strength results in a small increase of bond and anchorage capacity if the failure mode is governed by concrete splitting. Transverse reinforcement is more important for high strength concrete. The effect of concrete strength is more for the bond which failed in concrete crushing or direct shearing at the interface, such as the bar passing through the joint. High compressive strength and high rigidity of stress-strain curve makes the local bond-slip curve stiffer. Low sedimentation and low bleeding effects make the top bar effect small. bBfyy By analyzing available research, bond and anchorage capacities were evaluated quantitatively for practical design use.

In May of 1993, approximately twenty researchers and five representatives from construction firms met in Kyoto, Japan, for the First Multilateral Meeting on Structural Performance of High-Strength Concrete in Seismic Regions. Four countries (United States, Japan, New Zealand, and Australia) were representated at the meeting. The 3-day meeting divided into eight sessions covering current research programs and applications of high-strength concrete in the respective countries. The objectives of the meeting were to exchange information and to develop a coordinated program for further information exchange, evaluation of information, and development of design guidelines for the use of high-strength concrete in seismic regions. The follow-up meeting was held in November 1994 in Honolulu, Hawaii, and was attended by twenty seven participants from the US, Japan, Canada, New Zealand and Hong Kong. The Second Multilateral Meeting on Structural Performance of High-Strength Concrete in Seismic Regions consisted of thirteen sessions. Six of the sessions concentrated on the following behavioral topics: bond and anchorage, confinement, flexural members, axially-loaded members (columns and walls), beam-column joints, and shear and torsion. An additional session was devoted to presentation and discussion of design concepts and applications of high-strength concrete (HSC) in seismic regions. The remaining six sessions consisted of large and small working group sessions. During the small group sessions, participants were divided into groups of five to ten members to discuss the results of the previous sessions. Summaries of the small working group were then presented to the entire group fro additional comments and conclusion during the large working group sessions. This ACI Symposium Publication comprises selected papers which were the outcome of the Second Multilateral Meeting on Structural Performance of High-Strength Concrete in Seismic Regions. The working group discussion summaries are also included in this special publication. The editors are appreciative of the eforts of the authors and reviewers of these papers. The cooperation of the authors in the careful revision of their papers in accordance with the reviewers' comments is greatly appreciated. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP176

High strength concrete with a specified compressive cylinder strength fi of up to 70 MPa for ductile elements in seismic design and of up to 100 MPa for other elements is now permitted by the recently revised New Zealand concrete design standard NZS 3101:1995. Also, longitudinal reinforcement with a characteristic yield strength of up to 500 MPa is allowed, and for transverse reinforcement in strength calculations a useable steel stress of up to 500 MPa for shear strength and 800 MPa for confinement is permitted. For concrete with f' f' c greater than 55 MPa the parameters for the equivalent rectangular compressive stress block have been modified to take into account the stress-strain characteristics of high strength concrete. Also, new design equations for confining reinforcement have been included to better account for the affect of the variation of axial load level. Simulated seismic load tests have been conducted in New Zealand to investigate the behaviour of high strength concrete columns confined with normal and very high strength transverse reinforcement. The tests demonstrated that the yield strength of very high strength confining reinforcement may not be attained at the stage when the column reaches the peak flexural strength and that the thickness of concrete cover has an important influence on the behaviour of the columns.

Use of high-strength reinforced concrete walls in regions of high seismic risk is evaluated using current U.S. code provisions, an example building, parametric studies, and experimental results. The format of current U.S. code provisions for structural walls promotes the use of high-strength concrete; however, the use of these provisions has not been evaluated for high-strength concrete. Analytical studies of building systems utilizing slender walls indicate that there is not a significant advantage associated with the use of high-strength concrete waUs and that this advantage tends to diminish with increasing concrete strength. Evaluation of test results conducted in Japan for low-aspect ratio walls indicates that ACI 318-95 requirements do not represent the observed shear strength well. Based on the limited database considered in this study, a value of 1.0 f' c MPa (126) was found to provide a good estimate of wall shear strength.