This paper presents the experimental results of six scaled high-strength concrete columns with concrete compressive strengths of 76-86 MP& Primary experimental parameters include axial loads ranging from 10 to 20% of column axial load-carrying capacity based on concrete gross section; longitudinal steel ratios of 2.46 to 3.53% of the gross sectional area; and volumetric ratios of transverse reinforcement ranging from 1.63 to 3.67%. Model columns with transverse reinforcement designed following the seismic provisions of current code developed sufficient ductility, with displacement ductility factors equal to or exceeding 6.0. The model columns designed with 50% of the transverse reinforcement required by current code also developed sufficient ductility when the axial load was 10% of its axial load-carrying capacity. Lateral load-carrying capacities of all the columns exceeded the flexural capacities calculated based on the equivalent concrete stress block used in current design code. Seismic shear strength of high-strength concrete columns was also examined, based on the test results and analytical approaches.

回顾了套管钢筋混凝土柱的发展过程。在套管钢筋混凝土柱中，套管用作柱中的横向增强，主要起约束和抗剪作用。Thomii和作者等人在1985年首次提出套管柱的概念，并验证了套管柱能够有效防止柱的剪切破坏并显著提高柱的延性。随后，这一概念被推广到利用焊接钢管和纤维增强塑料外包壳加固既存钢筋混凝土柱。本文还展望了使用纤维增强塑料套管进行新建柱设计的研究。

The effectiveness of prefabricated composite jacketing to retrofit existing circular reinforced concrete (RC) bridge columns for enhanced seismic shear strength is described in this paper. The jackets consist of multilayer prefabricated glass fiber reinforced composite shells adhered together. Three half-scale circular columns were tested under cyclic shear in double curvature and constant axial load. One column was tested in the "as built" condition to investigate the shear failure mode of columns designed based on pre-1971 codes. Two other columns were tested after being retrofitted using prefabricated composite jackets. The as built column suffered shear failure at low displacement ductility. The retrofitted columns developed significantly improved hysteretic responses with stable hysteresis loops even at displacement ductility levels as high as 10.0 corresponding to drift ratios exceeding 5.2%. Method for retrofit design using prefabricated composite jacketing is also provided and validated by the test results.

This paper describes experimental and theoretical studies on seismic retrofit of reinforced concrete circular columns with poor lap-splice details using prefabricated composite jacketing. Three 1:2 scale model columns have been tested. One column was tested under the condition of "as built" and two others were tested after being retrofitted using prefabricated composite jacketing. The as-built column suffered brittle failure due to the deterioration of lap-spliced longitudinal reinforcement without developing its flexural capacity or any ductility. The retrofitted columns showed significant improvement in seismic performance. The failed as-built column was retested after being repaired. The repaired column also demonstrated significant improvement in ductility. An analytical model, which takes into consideration the bond-slip deterioration of lap-spliced longitudinal bars, has been developed for seismic assessment and retrofit design.