International Concrete Abstracts Portal

Editors: Gustavo J. Parra-Montesinos and Mary Beth D. Hueste

Professor James (Jim) K. Wight has been one of the most remarkable researchers and educators in the field of reinforced concrete structures in the past several decades. Jim’s engineering career started at Michigan State University, where he obtained his BS and MS in 1969 and 1970, respectively. After completing his MS studies, he went on to the University of Illinois at Urbana-Champaign to pursue doctoral studies under the supervision of Professor Mete A. Sozen, obtaining his PhD in 1973.

It was while a student at the University of Illinois that Jim Wight made his first major contributions to the field of behavior and design of reinforced concrete structures, particularly under earthquake excitations. He was likely the first to study the phenomenon of shear strength decay in reinforced concrete columns during large shear reversals. He also identified and explained the “disappearance” of the yield plateau in longitudinal reinforcing bars of flexural members subjected to moment gradient. Referring to this, Mete Sozen later said that had Jim been in the field of Physics, he would have won the Nobel Prize.

In 1973, Jim Wight joined the faculty at the University of Michigan. In a career that has spanned over 40 years as a Professor of Structural Engineering, Jim has exemplified excellence in teaching, research, and professional service. Jim has made enormous contributions to the field of behavior and design of reinforced concrete members, including beam-column and slab-column connections, structural walls, and deep beams. Much of his research has led to key advances in the safety and performance of reinforced concrete building structures during seismic events. Further, he has advised over 30 PhD students, several of whom are currently faculty members at major research universities. Jim has also contributed to the education of thousands of structural engineers as co-author (with Professor James MacGregor) of the widely used textbook Reinforced Concrete – Mechanics & Design. He has made significant contributions to the development of design guidelines and codes for reinforced concrete structures as Chair of ACI-ASCE Committee 352 in the early 1980s and of ACI Committee 318 during the 2002-2008 Code cycle. His dedication and involvement in the American Concrete Institute includes the distinction of serving as President in 2012-2013.

It was therefore with great joy that a group of researchers and practicing engineers who, over the years, had the opportunity to interact closely with Jim, decided to honor his illustrious career with a series of technical sessions and this Special Publication. Fifteen presentations, distributed in three sessions named “James K. Wight: A Tribute from his Students and Colleagues,” were given at the 2014 ACI Fall Convention in Washington, DC. All speakers consisted of students of Jim’s; colleagues in ACI technical committees; and his doctoral advisor, Professor Mete A. Sozen. The sessions were well attended by former students, academicians, researchers, and practitioners. A room-packed reception and a dinner were also offered in honor of Jim Wight. This Special Publication contains 12 papers related to the presentations made during the three technical sessions in Washington, DC. Also, Professor James O. Jirsa contributed with his personal perspective of Jim Wight’s contributions to the design of beam-column joints.

This Special Publication is but one small token of the appreciation and gratitude that all those involved have for Jim Wight. He has been a mentor, role model, and a source of inspiration to many, as well as an example of honesty, integrity, dedication, and unselfishness. Professor James K. Wight is, without a doubt, a true educator in the broadest sense of the word. We all feel very grateful to have had the opportunity to honor such an outstanding individual.

In this paper, an existing analytical approach for estimating joint shear behavior of reinforced concrete (RC) beam-column connections is critically examined and then modified in light of its limitations. The approach considers that joint shear strength is provided by an equivalent diagonal compression strut activated by force transfer to the joint through direct bearing from beam and column compression zones, and via bond between beam or column reinforcement and surrounding concrete. The model had first been developed for estimating joint shear behavior of composite RC column-to-steel beam connections, and then adjusted for application to certain RC beam-column connections (based on limited test results). This paper describes some shortcomings of that approach in light of a much broader experimental database of RC beam-column connection subassembly test data for developing joint shear resistance models. The research then uses probabilistic methods to derive a general relationship between joint shear deformation and the so-called principal strain ratio (including proper consideration of concrete compression softening and reasonable upper limits on joint shear deformation). This updated relationship can be used as a modification in the model for increased accuracy and broader applicability. The resulting modified model compares favorably to other approaches available in the literature for characterizing the joint shear behavior of RC beam-column connections.

Since the late 1980s, FRP products have seen increased use in repair and strengthening of concrete structures. The traditional technique is referred to as wet layup where carbon or glass fabric are saturated with epoxy in the field and applied to the structure. In this paper I present several new products that I have developed in recent years. One is very large pre-cured carbon or glass laminate sheets that can be used to repair columns, piles underwater, pipelines, etc. The other is a honeycomb-FRP combination that allows construction of lightweight stiff elements. This product can be used to build pipes that can serve as free-standing elements or in slip-lining repair of deteriorated culverts and pipes. These products can also be used as stay-in-place forms for repair of seawalls, large piers and the like. Examples of field applications are also presented.

This paper provides a brief overview of a project comprising several parts, carried out in collaboration with Jim Wight and a number of graduate students over a period of about fifteen years, starting in the mid 1980’s. The project focused on the effects the addition of fibers can have on the performance of reinforced concrete joints. Lessons learned from early “non-success” and subsequent successes achieved are described. Although details of the effects of fiber reinforcement on the joint behavior under monotonic and cyclic loading such as load carrying capacity, hysteretic moment-rotation response, strength and stiffness degradation, shear resisting mechanisms, and absorbed energy are left to the references cited, a key observation related to the hysteretic energy dissipated is emphasized. It is observed in particular that not all fibers provide equal benefits and the fiber reinforcing parameters must be carefully selected in order to achieve superior results. Two important factors are further stressed: the need to achieve a fiber reinforced concrete composite that is strain hardening in tension (thus likely in shear as well), and the need to develop a postcracking resistance that remains significant even when crack widths exceed the millimeter range.

This paper presents simulations of early-age concrete behavior, as observed during restrained ring tests. The steel and concrete rings are represented by an irregular lattice model. The evolution of concrete properties, including stiffness and strength, is based on simple models and experimental results. For simulating cases of steel fiber-reinforced concrete, each fiber is explicitly represented within the concrete ring. The simulation results compare well with the experimental data, including readings from strain gages attached to the steel rings. As expected, the addition of short fibers prolongs the time to cracking and reduces crack widths. Viability of the model, as a means for analyzing the early-age behavior of fiber-reinforced concrete, is discussed.