High-strength concrete has been used in many lower story columns of high-rise buildings, as well as low-rise and mid-rise buildings, bridges, and foundation piles. This study tested 21 high-strength, fiber-reinforced concrete columns consisting of nine 155-mm square columns and twelve 200-mm square columns. The concrete mix contained 2% (by weight) of end-hooked steel fibers and with concrete strengths ranging from 67 MPa to 88 MPa. The columns were tested in either concentric or eccentric compression with varying initial loading eccentricities. The study showed that the introduction of steel fibers into the mix design arrested the early spalling of the cover and increased the load capacity as well as the ductility of the columns over that of comparable nonfiber-reinforced specimens.

Strength and ductility of fiber-reinforced high-strength concrete columns

The near fault ground motion (NFGM) is characterized by a single long period velocity pulse of large magnitude.(Somerville et. al 1997) Extensive research for the far fault ground motion (FFGM) have been carried out in strong seismic region, but limited research have been done for NFGM in low or moderate seismic regions because of very few records. For reinforced concrete (RC) bridge piers constructed before implementing the 1992 seismic design code in Korea, longitudinal reinforcing steels were practically lapspliced in the plastic hinge region between column and footing. This research aims at investigating the seismic behavior of RC bridge piers with lap-spliced longitudinal steels subjected to NFGM in low or moderate seismic region. Five RC pier specimens with a diameter of 400 mm and height of 1400 mm were tested on a shake table, and two identical specimens were tested under a quasi-static load and a pseudo-dynamic load. The effects of lap-spliced longitudinal reinforcing steels are investigated. Shaking test results are compared to those by Quasi-static test and Pseudo-dynamic test. It was concluded that: a) displacement ductility was significantly decreased in RC column specimens with lap-spliced longitudinal reinforcing steels; b) bond failure in the lapped starter bars and buckling of the longitudinal steel bars initiated failure in RC specimens with and without lap-spliced longitudinal steels, respectively; c) more transverse reinforcing steels induced better displacement ductility; and d) a decrease of displacement ductility and energy dissipation was observed in the specimens on a shake table excitation in comparison with the specimens by the quasi-static and the pseudo-dynamic test.

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The 14th World Conference on Earthquake Engineering

Beam-column connections have been identified as potentially one of the weaker components of reinforced concrete moment resisting frames subjected to seismic lateral loading. Well-established knowledge of RC joint shear behavior is necessary because severe damage within a joint panel may trigger deterioration of the overall performance of RC beam-column connections or frames. However, despite the importance of understanding RC joint shear behavior, a consensus on the ways in which some parameters affect joint shear strength has not been reached. In addition, there has generally been no accepted behavior model for RC joint shear stress vs. joint shear strain. Therefore, in this research a more systematic understanding of RC joint shear behavior has been achieved by completing the following tasks: construction of an extensive experimental database, characterization of RC joint shear behavior, and development of RC joint shear strength models and proposed joint shear behavior models. An extensive experimental RC beam-column connection database (of 341 subassemblies in total) was constructed and classified by governing failure mode sequence, in-plane geometry, outof-plane geometry, and joint eccentricity. All included subassemblies were made at a minimum of one-third scale, and all used conventional types of reinforcement anchorages. RC joint shear behavior was described as an envelope curve by connecting key points displaying the most distinctive stiffness changes. The first point indicates initiation of diagonal cracking within a joint panel, the second point results from yielding of reinforcement, and the third point corresponds to maximum response. An RC joint shear strength model was then developed using the experimental database in conjunction with the Bayesian parameter estimation method. A simple and unified joint shear deformation model (at maximum response) was also developed, following the same procedure used to develop the simple and unified joint shear strength model. Full RC joint shear behavior models were constructed by employing the Bayesian method at each key point and also by adjusting the simple and unified joint shear strength and deformation models for maximum response. Finally, the Parra-Montesinos and Wight model was modified to improve its reliability by updating the key relation between principal strain ratio and joint shear deformation.

Joint shear behavior of reinforced concrete beam-column connections subjected to seismic lateral loading

where α0 is the coefficient related to the location of the plastic hinge of beams (=1.0 to 1.25); αf is the coeffi- cient related to the direction of the beam reinforcing bars; (=0.85 to 1.0); αd is the coefficient related to the ductility of the plastic hinge of beams (=1.0 to 1.2); γ is the coeffi- cient related to inter-story drift when the yield strength of beam reinforcing bars is greater than 300 MPa (43.5 ksi) (γ = 1.53 - 0.29 δc ≤ 1.0); and δc is the inter-story drift ratio expressed as a percentage.

A. Ichikawa

Papers

Experimental Studies on Seismic Behavior of Reinforced Concrete Members of High-Strength Concrete

Behavior of Beam Column Joints Using High-Strength Materials