Reinforced concrete columns play a very important role in structural performance. As such, it is essential to apply a suitable analytical tool to estimate their structural behaviour considering all failure mechanisms such as axial, shear, and flexural failures. This book highlights the development of a fiber beam-column element accounting for shear effects and the effect of tension stiffening through reinforcement-to-concrete bond, along with the employment of suitable constitutive material laws.

Inadequate flexural strength and ductility or shear strength of concrete bridge columns has resulted in collapse or severe damage of a number of California bridges in recent moderate earthquakes. In general, these bridges were designed prior to the new seismic design methods which were implemented in the mid-seventies. Bridges constructed in accordance with the new design methods have performed well in recent earthquakes. However, the large number of older bridges that are in service, particularly freeway overpasses designed and constructed in the 1950s and 1970s, are now recognized to have substandard design details and to constitute a cause for major concern. This paper reports the results of a theoretical and experimental program investigating retrofit techniques for circular columns by encasing the critical regions within a steel jacket. The jacket is bonded to the column using grout. Results from six large-scale column tests show that the casing acts efficiently as confinement reinforcement, enabling a displacement ductility factor of greater than 6 to be achieved. The casing also inhibits bond failures at the laps of longitudinal reinforcement in the critical regions of the column by restraining the dilation and spalling of the cover concrete which degenerates into bond failure. Comparisons of 'as-built' and retrofitted columns are presented, and experimental strengths and ductilities are compared with analytical predictions. For the covering abstract of the Conference see IRRD Abstract no. 807839.

Research on seismic retrofitting of Reinforced Concrete (RC) bridge columns in the United States (U.S.) was motivated by damage observed following the 1971 San Fernando, 1989 Loma Prieta, and 1994 Northridge earthquakes of California. The research resulted in a retrofitting procedure that consisted of installing steel jackets around RC bridge columns to enhance the lateral deformation capacity. Although the research focused on the development of this retrofit strategy for bridge columns in California, the Washington State Department of Transportation (WSDOT) implemented the program in 1991. Unlike the strike-slip faults in California, seismicity in western Washington is generally dominated by the Cascadia Subduction Zone fault. The 1964 Alaska, U.S., 2010 Maule, Chile and 2011 Tohoku, Japan are examples of mega-thrust long duration earthquakes emanating from a subduction zone fault and producing ground motions with longer durations of strong shaking than strike-slip faults. The research conducted in this study was motivated by the need to assess performance of the existing retrofit strategy when subjected to the expected demands of subduction zone earthquakes. The research conducted herein was an experimental study on the behavior of steel jacket retrofitted bridge columns subjected to demands from long duration earthquakes. Six reduced scale column specimens were designed, constructed, and tested as cantilevers. WSDOT's inventory was characterized to inform the values used for the column parameters, such that the six columns were intended to reasonably cover the range of values for critical parameters. Five of six tests utilized a modified fully reversed-cyclic lateral loading protocol to include additional cycles characteristic of long duration earthquakes. The sixth test used an earthquake protocol, obtained from the response of a single degree of freedom model to a synthetic Cascadia Subduction Zone ground motion in western Washington. Study results indicated stable drifts, including minimal pinching in the load-displacement response indicative of favorable hysteretic energy dissipation, at drifts in excess of the 4\\% expectation set forth in the steel jacket retrofit design guidelines. Total deformation was primarily a result of longitudinal reinforcement bond slip and elongation at the footing-column interface with strength degradation due to low-cycle fatigue fracture.

In most parts of the developed world, the building stock and the civil infrastructure are ageing and in constant need of maintenance, repair and upgrading. Moreover, in the light of our current knowledge and of modern codes, the majority of buildings stock and other types of structures in many parts of the world are substandard and deficient. This is especially so in earthquake-prone regions, as, even there, seismic design of structures is relatively recent. In those regions the major part of the seismic threat to human life and property comes from old buildings. Due to the infrastructure's increasing decay, frequently combined with the need for structural upgrading to meet more stringent design requirements (especially against seismic loads), structural retrofitting is becoming more and more important and receives today considerable emphasis throughout the world. In response to this need, a major part of the fib Model Code 2005, currently under development, is being devoted to structural conservation and maintenance. More importantly, in recognition of the importance of the seismic threat arising from existing substandard buildings, the first standards for structural upgrading to be promoted by the international engineering community and by regulatory authorities alike are for seismic rehabilitation of buildings. This is the case, for example, of Part 3: Strengthening and Repair of Buildings of Eurocode 8 (i. e. of the draft European Standard for earthquake-resistant design), and which is the only one among the current (2003) set of 58 Eurocodes attempting to address the problem of structural upgrading. It is also the case of the recent (2001) ASCE draft standard on Seismic evaluation of existing buildings and of the 1996 Law for promotion of seismic strengthening of existing reinforced concrete structures in Japan. As noted in Chapter 1 of this Bulletin, fib - as CEB and FIP did before - has placed considerable emphasis on assessment and rehabilitation of existing structures. The present Bulletin is a culmination of this effort in the special but very important field of seismic assessment and rehabilitation. It has been elaborated over a period of 4 years by Task Group 7.1 Assessment and retrofit of existing structures of fib Commission 7 Seismic design, a truly international team of experts, representing the expertise and experience of all the important seismic regions of the world. In the course of its work the team had six plenary two-day meetings: in January 1999 in Pavia, Italy; in August 1999 in Raleigh, North Carolina; in February 2000 in Queenstown, New Zealand; in July 2000 in Patras, Greece; in March 2001 in Lausanne, Switzerland; and in August 2001 in Seattle, Washington. In October 2002 the final draft of the Bulletin was presented to public during the 1st fib Congress in Osaka. It was also there that it was approved by fib Commission 7 Seismic Design. The contents is structured into main chapters as follows: 1 Introduction - 2 Performance objectives and system considerations - 3 Review of seismic assessment procedures - 4 Strength and deformation capacity of non-seismically detailed components - 5 Seismic retrofitting techniques - 6 Probabilistic concepts and methods - 7 Case studies