UNITED STATES / NEW ZEALAND / JAPAN / CHINA COLLABORATIVE RESEARCH PROJECT ON THE SEISMIC DESIGN OF REINFORCED CONCRETE BEAM-COLUMN-SLAB JOINTS General Report on the Project

A United States/New Zealand/Japan/China collaborative research project on the "Seismic Design of Reinforced Beam-ColumnSlab Joints" has been in progress during the last five years. This collaborative research project was initiated because there are currently a number of differences between the approaches used for the seismic design of reinforced concrete beam-columnslab joints in building frames in earthquake regions of the world. For example, New Zealand design procedures are more conservative than United States procedures for some joint configurations and are less conservative than United States procedures for other joint configurations. Japan and China have written new building codes for the seismic design of multistorey reinforced concrete moment resisting frames and are continuing to review the possible approaches. The major differences between the current design procedures of the various countries are in the quantities of transverse reinforcement required in joint cores for shear and confinement, and in the maximum allowable bar diameters permitted for longitudinal reinforcement passing through joint cores to satisfy bond requirements. Other significant differences in the design procedures also exist.


INTRODUCTION A United
States/New Zealand/Japan/China collaborative research project on the "Seismic Design of Reinforced Beam-Column-Slab Joints" has been in progress during the last five years.
This collaborative research project was initiated because there are currently a number of differences between the approaches used for the seismic design of reinforced concrete beam-columnslab joints in building frames in earthquake regions of the world.For example, New Zealand design procedures are more conservative than United States procedures for some joint configurations and are less conservative than United States procedures for other joint configurations.
Japan and China have written new building codes for the seismic design of multistorey reinforced concrete moment resisting frames and are continuing to review the possible approaches.The major differences between the current design procedures of the various countries are in the quantities of transverse reinforcement required in joint cores for shear and confinement, and in the maximum allowable bar diameters permitted for longitudinal reinforcement passing through joint cores to satisfy bond requirements.Other significant differences in the design procedures also exist.
In the early 1980s the Applied Technology Council of the United states set up a project to review the test data and design approaches for reinforced concrete beamcolumn joints of various countries (ATC-08).The members of the review committee were mainly consulting engineers.In 1983 Mr. J.L. Stratta, chairman of the ATC review committee, suggested to Professor R. Park of the University of Canterbury and to Professor J.O.The collaborative research project was set up in 1984 with the aims of (1) to achieve agreement on the mechanisms of behaviour of beam-column-slab joints of reinforced concrete building frames during earthquake loading and (2) to develop more unified design procedures for reinforced concrete buildings frames for earthquake resistance.These aims were to be achieved by carefully coordinated experimental testing and by discussion at meetings.
The principal investigators were to be from the University of Canterbury, the University of Texas at Austin and the University of Tokyo.

THE FIRST AND SECOND MEETINGS AND THE AGREED TEST PROGRAMME
Meetings of principal investigators of the United States, New Zealand and Japan, and other participants, were held in California in July 1984 and in Tokyo in May 1985.The meetings were to review design codes and research in the United states, New Zealand and Japan and to coordinate the design, instrumentation and simulated seismic loading history of beam-column-slab specimens which would be tested to investigate the differences between the design approaches of the three countries.
As a result of the two meetings it was agreed that the structural testing laboratories at the University of Canterbury, the University of Texas at Austin, and the University of Tokyo would each construct three reinforced concrete beam-column-slab assemblies, designed according to the code procedure of their country, for testing under the same simulated seismic loading.
The assemblies would be of the following types: Specimen 1 Specimen 2 Specimen 3 One-way interior beamcolumn-slab assembly Two-way interior beamcolumn-slab assembly Two-way exterior beamcolumn-slab assembly.
Each assembly represents a particular portion of a building structure in the region of the junction of beams, columns, and slab floor.
The three assemblies tested at the University of Canterbury and at the University of Texas at Austin are full-scale, and at the University of Tokyo the three assemblies are one-half scale.The overall dimensions of the full-scale assemblies are in the order of 3.5 m high and a maximum of 3.5 m x 3.5 min the The results of the tests will be of particular interest since the specimens are all designed for the same seismic loading and only differ in that the reinforcement is detailed according to the code of the country where the tests are being conducted.The specimens are subjected to the same simulated seismic loading history in the tests.This enables the performance of structures designed according to the codes of the countries to be compared on a rational basis.
Some additional specimens are also being tested in some countries.
In 1985 the China Academy of Building Research in Beijing and Tongji University in Shanghai requested that China be included in the project and will test reinforced concrete beam-column-slab assemblies designed according to the new Chinese code.
Hence the project now formally involves four countries, which represents significant international collaboration.
The principal investigators for New Zealand are Professors T. Paulay and R. Park of the University of Canterbury.
A PhD student, Mr. Cheung P.C., has been conducting the tests.Testing of the three specimens at the University of Canterbury began in mid-_1986 and was completed in 1988.
Financial support for the tests at the University of Canterbury has been provided by the Building Research Association of New Zealand ($33,900), the Ministry of Works and Development ($33,500) requirements for shear and bond in beamcolumn joint cores could be permitted.The current provisions of NZS 3101 were written a decade ago and the significant additional testing which has been conducted since that time indicates that those requirements could be made less severe.
In particular the large amount of testing which has been conducted in Japan during the last 5 years, and the associated well coordinated committee work, is extremely impressive.
A wealth of data is now available from Japan which can be used to assess the effects of the main variables in beam-column joint design.
The seminar was extremely valuable in providing a large amount of information from the three countries involved.
The opportunity to exchange views and to evaluate the test results of the three countries will result in a narrowing of the gaps between the design procedures of the three countries.The project has given the participants a much better insight into the design philosophies underlying the three national codes.
In working together in a cooperative effort much over 30 short papers were presented during the three days, covering research, design and construction aspects.The small number attending allowed a free exchange of ideas between parties.
Although the main focus of the Meeting was beam-column joints, the presentations and discussion spilt over into design philosophies and future research needs.
Highlights from the writer's point of view were: 1.The presence of top researchers from all three countries, representatives of the five major construction companies in Japan, and leading designers from the US.
2. Clear evidence that Japan has carried out an enormous amount of research in earthquake engineering in the last few years, each construction company having large research departments.
3. The differences in underlying philosophy and approach between all countries.
This forum showed very clearly that each country conducts its research and approaches design in the framework of its own historical approach.
Although there is much in common, the differences may be summarised as follows: NZ uses low forces requiring lJ.tgJl ductility demands and rigor(:rqi;i analysis.
.USA uses low forces, implying high ductility demands but a more pragmatic approach is taken ln formulating design requirements.4. In the case of beam-column joints, these differences are evident in the various criteria for acceptable performance.
New Zealand relates performance to subframe ductility demands, thus automatically accounting for varying beam and column stiffness.US researchers relate results to drift which makes direct comparison with NZ results difficult.
Japan relates results to drift but generally 1% drift corresponds to a displacement ductility of approximately 1.5. 5. Mechanisms of force transfer within the joint are generally agreed, although the relative contributions of strut action and truss action vary.Close attention was paid to the effectiveness of bond on the tension steel through the joint, including the effects of axial load.Generally axial load had a relatively small effect.
6.The influence of confining steel and beams at right angles was debated strongly.Here again comparisons were difficult because of the different approaches.
It seemed possible that the more demand placed on the joint, the more important confining steel may become.The same may apply to joint shear reinforcement.
Japan's larger design forces produce wider columns which eases bond problems in the joints.
7. The influence of slabs and slab steel on the performance of the joint was considered by a number of researchers using both theory and tests.This is a complex subject involving the development of forces by beam torsiqn and horizontal bending.Opinions differed as to the reliability of available extra strength and local damage.
While simple effective width formulae may not identify all the various mechanisms and complexities, they will suffice for allll.OSt an situations, especially in NZ where lightly reinforced toppings are conuion.a. Bi-axial Effects 9.

10.
Testing was done in all three countries on sub-assemblies with orthogonal beams intersecting at the joint.Performance was generally good and the influence of one beam upon the joint behaviour in the orthogonal direction was not significantly detrimental. • The behaviour of eccentric beam-column joints was explored, even though it is 125 BULLETIN OF THE NEW ZEALAND NATIONAL SOCIETY FOR EARTHQUAKE ENGINEERING, Vol.22 No.2 June 1989

Report on the Fourth Meeting held in Honolulu, May 24-26, 1989 D.C. Hopkins*
Oh the Loaders and the Jointers should be friends Yes the Loaders and the Jointers should be friends One group thinks about forces at points The other is obsessed with beam-column joints But that's no reason why they can't be friends.The Jointers' life is full of moments and shear They are all extremely fond Of struts confinement and of bond ... But their relation to the Loader's not too clear.Oh the Loaders and the Jointers should be friends Yes the Loaders and the Jointers should be friends One group thinks about forces at points The other is obsessed with beam-column joints But that's no reason why they can't be friends.Oh, the Loaders and Jointers should be friends Yes the Loaders and Jointers should be friends Loaders specify loads of course Jointers are left to deal with the force Surely now it's time to join the ends.Earthquake engineers should stick together Earthquake engineers should all be mates Conferences should continue between New Zealand China, Japan and United States.