International Concrete Abstracts Portal

SP-185 Up until now there has been very little information on the use of high-performance fiber-reinforced concrete (HPFRC). But recent laboratory studies and field applications show that HPFRC improves performance of civil engineering infrastructure in a cost-effective manner. This publication includes 11 papers on the mechanical properties of HPFRC for infrastructural repair and retrofit.

This paper suggests design guidelines for seismic retrofit of non-seismically designed reinforced concrete frames using High Performance Fiber Reinforced Concretes (HPFRCs), I.e., Slurry Infiltrated Mat Concrete (SIMCON) and Slurry Infiltrated Fiber Concrete (SIFCON). The following retrofit schemes are addressed: (1) column retrofit with either discontinuous or continuous SIMCON jackets, and (2) joint retrofit by either "internal" retrofit with prestressing bars or "external" SIMCON jacketing. Validity of the suggested guidelines was experimentally verified by testing a series of seismically retrofitted non-ductile beam-column sub-assemblages. Experimental data indicate that the suggested design procedure was appropriate for the retrofit design of the specimens. Additional experimental and analytical investigations are suggested to confirm the validity of proposed design approach for different beam-column connections. The paper focuses on the design procedure. Key pieces of information on the experimental investigation are only reviewed here and are presented in detail elsewhere [1].

Three reinforced concrete columns with inadequate strength, non-contact, lap splices at their base were tested to failure under reversed cyclic loading. An investigation was then made a method for jacketing such damaged columns in order to reinstate and improve their seismic performance. The damaged columns were jacketed using a steel fiber mat infiltrated with slurry and then again tested to failure under reversed cyclic loading. The degree of restoration and improvement in the seismic performance of the columns was partially dependent on the degree of damage suffered by the column during the initial non-jacketed testing. However, in all cases the jacketed columns exhibited load-deflection hysteretic characteristics equal to, and ductility characteristics exceeding, those of the non-jacketed column. Details are provided of the seismic performance characteristics of the columns, and the repair techniques used.

Older reinforced concrete structures constructed in seismically active areas of the United States are usually non-ductile and are thus identified as hazardous. Extensive efforts have been devoted to the development of adequate retrofitting techniques for these buildings. While laboratory studies have shown that the use of "conventional" Fiber Reinforced Concretes (FRCs) and High Performance FRCs (HPFRCs) in new construction leads to substantially improved seismic response, seismic retrofit techniques have not yet taken advantage of these advanced composites. The advantages of conventional FRCs is a significant increase in ductility over that of reinforced concrete. The advantage of HPFRCs is that, when loaded beyond the elastic limit, they exhibit significant increases in structure to dissipate energy--a feature particularly desirable for earthquake resistant design. The goal of the presented research was to develop a novel seismic retrofit technique, using recently developed HPFRCs, to solve the following common problems of non-seismically designed reinforced concrete frames: 1) inadequate anchorage of the discontinuous bottom beam reinforcement, 2) inadequate confinement of the column lap splices, and 3) inadequate confinement of the joint. HPFRCs used in the presented research include Slurry Infiltrated Fiber Concrete (SIFCON) and Slurry Infiltrated Mat Concrete (SIMCON). The presented research was conducted in collaboration with a project Advisory Panel consisting of consulting structural engineer from Wiss, Janney, Elstner Associates, Inc.

A large variety of materials and techniques are available to increase strength of existing concrete structures in an effort to extend their service life. The way to make repaired and strengthened concrete structures durable is to ensure that the new composite system is "tailored" to serve the intended service life, and that the composite human system, the team involved with a project, is knowledgeable and experienced enough to recognize the complexity of their task. The paper reviewed traditional methods and also offers a review on the use of advanced composite materials for strenghening existing comcrete structures. The advantages and limitations of different techniques are presented. It is concluded that, in the futrue, advanced composite materials will be widely used for repair and strengthening. To achieve this, it is vital that research and engineering education in cement-based and advanced composite materials are improved.