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.

Early research on the behavior of frame members subjected to reversed cyclic displacements has been reviewed, with an emphasis on the phenomenon of shear strength decay. Information is provided about variables that affect shear strength decay and measures that can be taken to mitigate this phenomenon, which should be of interest to students and structural engineers learning or involved in earthquake resistant design of reinforced concrete structures. Starting in the 1950s, the effect of reversing the loading direction on the flexural response of beams was investigated experimentally. Among other findings, tests showed that single and repeated reversals of load had little influence on flexural strength, but that loading history does influence the deformation capacity and stiffness of members. Although several researchers emphasized the importance of providing adequate transverse reinforcement confining the member core, the role of shear stresses on the response of frame members was not well understood until the early 1970s. Tests by Brown and Jirsa, Wight and Sozen, and Popov, Bertero and Krawinkler, showed that member strength can decay under reversals of load if shear stress demands are large or if inadequate transverse reinforcement is provided. In particular, it was shown by Wight and Sozen that maintaining the integrity of the concrete core through use of closely spaced transverse reinforcement with enough area to resist the entire shear demand without yielding is essential, although not necessarily sufficient. Changes to the ACI Building Code aimed at minimizing shear strength decay were first adopted in 1983 and have remained in subsequent editions of the Code with relatively minor changes.

A wall panel zone is a region in which forces from connecting wall segments are resolved. Four different types of wall panel zones are described. Among these, the case of a wall panel located under an aligned stack of openings in a coupled wall is examined closely. Instances in which such panel zones failed during past earthquakes are presented. Laboratory tests and analytical studies are used to define wall panel zone force demands and capacities. It is shown that simple mechanics and existing design expressions can be used to design wall panel zones against shear failure.

On October 12, 2013, a 27-story building collapsed in Medellín, Colombia, with no apparent evidence of vertical or horizontal overload. The building was shaped in plan as a circular arc whose gravity load resisting structure can be described as a three-dimensional structural concrete moment resisting frame consisting of columns and a grid of beams running in both radial and tangential directions that meet at the vertical structural member locations. The building structure was designed using the Colombian NSR-98 Code1, which is based on the ACI 318-95 Code3. An assessment of the structure, as built, was performed by the Universidad de los Andes, Bogotá, Colombia. Material samples of concrete and reinforcing bars were secured and tested for compliance with the materials properties specified in the construction documents. An evaluation of the strength of the structural members as built was performed and a comparison with the gravity load demands was performed. This evaluation identified a strength deficiency of the vertical supporting elements of the structure. The driving reason for the collapse of the structure was that the selfweight of the structure resulted in axial loads that were comparable to the nominal axial capacities of the columns. This was considered the root cause of the sudden collapse of the building with no apparent external factors.

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.