Search

The capacity of key structural members, particularly columns, to absorb and dissipate energy without severe strength degradation dictates the survival of structures during a major earthquake. Reinforced concrete columns with inadequate confinement do not possess the necessary ductility to dissipate sufficient seismic energy. This research evaluates the effectiveness of glass fiber-reinforced polymer (GFRP) wraps in strengthening deficient and repairing damaged square concrete columns. Each of the eight specimens tested, representing columns of buildings and bridges constructed before 1971, consisted of a 305 x 305 x 1473 mm column connected to a 508 x 762 x 813 mm stub. Specimens were tested under constant axial compression and cyclic lateral displacement excursions simulating earthquake loads. Test results reveal that retrofitting with GFRP wraps significantly enhanced ductility, energy dissipation ability, and shear and moment capacities of deficient columns. Cyclic behavior progressively improved as the number of GFRP layers increased, causing both stiffness degradation and strength reduction rates to decrease. Improvements observed following GFRP repair of damaged columns depended mainly on the extent of damage stained. GFRP-confined columns exceeded the performance of similar columns that contained transverse steel reinforcement in accordance with the seismic provisions of the current North American codes.

This paper investigates the prospect of strengthening deficient and repairing damaged square reinforced concrete columns with carbon fiber-reinforced polymer (CFRP) jackets. 8 specimens representative of structural members in bridges constructed prior to 1971 consisted of a 305 x 305 x 1473 mm column connected to a 508 x 762 x 813 mm stub. Each 900 kg specimen was tested under lateral cyclic displacement excursions and simultaneous constant axial load to simulate seismic forces. Results indicate that added confinement with CFRP at critical locations enhanced ductility, energy dissipation capacity, and strength of all substandard members. A positive relationship prevailed between favorable behavior and increasing reinforcement layers while improvements realized through CFRP repair declined as damage level prior to retrofit increased. Appropriately strengthened specimens also exceeded the performance of comparable columns with adequate seismic lateral reinforcement.

A softened strut-and-tie model has previously been developed for determining the shear strengths of exterior beam-column joints for seismic resistance. This existing model originates from the strut-andtie concept and satisfies equilibrium, compatibility, and the constitutive laws of cracked reinforced concrete. This paper examines the applicability of the previously proposed model to interior beamcolumn joints. The calculated shear capacities of 56 interior joints were compared with the experimental results, and good agreement was obtained.

The seismic performance of a reinforced concrete (RC) building designed primarily for gravity loads was presented in the first part of this investigative study. Since the source of most of the structural damage is attributed to nonseismic details in the beam-column joint area, it was decided to examine the effects of improving these details in a marginal way, so that the seismic performance could be enhanced without resorting to a full seismic design. An extensive parametric study of the original buildings with refined detailing characteristics is carried out to ascertain effectiveness of the techniques to improve seismic resistance of gravity load-designed buildings. The important feature of the study is that the buildings are not redesigned for lateral forces, but only that detailing in critical regions is altered to achieve improved performance. This study may also be viewed indirectly as an inquiry into the effectiveness of retrofit strategies, should they be considered in real practice. The investigation also includes a cost evaluation of the various detailing schemes.

An experimental investigation of the behavior of external beam-column joints with inclined reinforcing bars under seismic conditions is presented. A simple technique to prevent these elements from falling in premature, explosive cleavage shear fracture was implemented for the first time. Twenty full-scale reinforced concrete exterior beam-column subassemblies were tested. The primary variables were the amount of inclined bars, the ratio of the column-to-beam flexural capacity, and the joint shear stress. Test results showed that use of crossed inclined bars in the joint region is one of the most effective ways to improve the seismic resistance of exterior reinforced concrete beam-column joints.