Retrofit of Unreinforced Masonry Structures with FRP Overlays and Post-Tensioning

There is no more effective tool for transferring repair and retrofit technologies than a proof-of-concept test on a large model structure. Such tests can addresses concerns related to scale effects, 3D interaction (floor effects and force redistribution), and impact of non-structural elements and secondary (gravity) structural systems that are typically associated with small scale models and/or component tests. As part of an on-going project sponsored by the Mid-America Earthquake Center, a large two-story, full-scale unreinforced masonry building will be tested at Georgia Tech in the summer of 2001. The primary intent of the test is to investigate the effectiveness of two types of repair techniques that have been proposed for URM walls: FRP sheets and vertical prestressing. There will be multiple test conducted (i.e, initial cracking, first "yield" (i.e., rocking or sliding of some piers), initial repairs, damage into non-linear range, additional repair /strengthening, and tests to ultimate. The focus of the studies is to assess the effects of local repairs on overall building performance, i.e., to study the impact of a few, carefully selected repairs on the system response. In this paper the authors will report on: 1) the results of the extensive analytical studies conducted to date as part of the planning of this test, including expected failure sequences for the system, 2) the difficulties encountered in modeling even this relatively simple structure under dynamic loads, 3) assessment of current FEMA 273 and Eurocode provisions for evaluating the strength of existing and repaired walls, 4) studies on concrete specimens to assess the effects of environmental factors of the durability and reliability of FRP repairs, 5) comparisons with a companion, ½-scale test to be run on a shaking table at the US Army Corp of Engineers Civil Engineering Research Laboratory (CERL), and 6) preliminary studies conducted at the CERL laboratory on different FRP retrofit technologies, and at the University of Illinois on vertical prestressing. It is expected that all of these issues will be touched upon for the presentation, while the first three will constitute the bulk of the written contribution. As the testing is still in the planning phase and as URM construction is of great importance in Latin America, interaction at this workshop could offer an opportunity to both test some innovative ideas from Latin American researchers and to involve some of them directly in the testing and processing of the results.