Epoxy Anchors in URM Elements with Mechanical Enhancements to Achieve Higher Tension and Shear Capacities

摘要

Tension and shear capacities of epoxy anchors in unreinforced masonry (URM) elements are published in various International Code Council-Evaluation Services (ICC-ES) reports jointly developed by the anchor manufacturers and ICC-ES. These reports were developed based on the testing procedures found in the Acceptance Criteria for Adhesive Anchors in Concrete and Masonry Elements (AC58) and Acceptance Criteria for Anchors in Unreinforced Masonry Elements (AC60) published by ICC-ES. Mandatory upper bound limits on allowable shear and tension values for all epoxy anchors in URM elements are imposed in AC60 regardless if higher values are achieved through testing. A recent project involving the authors' required higher tension and shear capacities for epoxy anchors than what could be achieved under the AC60 criteria. The project consisted of replacement of a fire escape that is directly attached to a historic URM building located within the Seattle Pioneer Square Historic Preservation District (SPSHPD). To maintain the appearance and historical value of the existing building, the size, number, and location of anchors for the replacement fire escape had to match the original as closely as possible. This resulted in higher tension and shear demands on the anchors than what were allowed under the current code. In order to achieve higher anchor capacities mechanical enhancements were made to the epoxy anchors using direct bearing mechanisms and an on-site project-specific test program was carried out following the AC58 and AC60 testing protocols. Higher tension and shear capacities were achieved and test results were accepted by the city building department for the building permit application. The replacement of the fire escape is currently underway. This paper discusses the specifics of the epoxy anchor mechanical enhancements developed by the authors, the project specific anchor testing program, and the fire escape replacement.