Shape modification and reinforcement of columns confined with FRP composites

Abstract

Strengthening reinforced concrete columns by using Fiber Reinforced Polymer (FRP) composites can be an effective method of retrofitting existing columns. FRP composites have a number of advantages over steel, including their high strength-to-weight ratio and excellent durability. The confinement effectiveness of FRP materials for rectangular sections can be improved by performing shape modification such that a rectangular column section is modified into a shape that does not have 90 degree comers such as an elliptical, oval or circular column. An expansive concrete can be advantageously used between the FRP material and the existing concrete in order to post-tension the FRP material circumferentially and improve confinement of the concrete. A finite element analytical model is also disclosed which model describes the stress-strain relationship for the FRP-confined columns after shape modification.

Description

RELATED APPLICATIONS [0001] This application claims benefit of U.S. Provisional Patent Application No. 60 / 610,265 filed on Sep. 15, 2004, and U.S. Provisional Patent Application No. 60 / 640,545 filed on Dec. 30, 2004, each of which are incorporated herein by reference.BACKGROUND OF THE INVENTION [0002] In recent years, fiber reinforced polymer (FRP) composites have emerged as an alternative to traditional materials for strengthening and rehabilitation of structures. The light weight of FRP, high-strength to weight ratio, corrosion resistance, and high efficiency of construction are among many of the advantages which encourage civil engineers to use this material. FRP composites have been used in the retrofit of bridge columns due to insufficient capacity or displacement ductility. FRP jackets can provide lateral confinement to the concrete columns that can substantially enhance their compressive strength and ultimate axial strain. One of the most significant problems which concerns c...

AI Technical Summary

Benefits of technology

[0008] It has been recognized that development of improved materials and methods for strengthening structural columns which avoid many of the above deficiencies would be a significant advancement in the industry. Accordingly, the present invention provides fiber reinforced polymer (FRP) composite structures which include a core and a fiber reinforced polymer material at least partially surrounding the core. The core includes an inner cement structure at least partially surrounded by an outer cement structure. The outer cement structure comprises or consists essentially of expansive cement or non-shrink cement. Typically, this is the result of applying the principles of the present invention to reinforce existing structures. Frequently, the inner cement structure of non-expansive cement can include steel reinforcements. However, the materials and methods of the present invention can significantly reduce or even eliminate the need for steel reinforcement in cement structures.

[0010] In accordance with an embodiment of the present invention, the FRP jacket can be post-tensioned and have a hoop stress along the FRP material. In one aspect, post-tensioning of the FRP jacket can be readily accomplished by using expansive concrete. The post-tensioning induced in the present invention can be in the form of tensile stress along the FRP fibers, i.e. circumferential rather than axial.

Problems solved by technology

This results in a composite structure having a non-uniform gap thickness or non-uniform thickness of the non-shrink or expansive portion of the core.

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