OECD/NEA/CSNI Project ASCET on Numerical Simulations of Squat Shear Walls with Alkali-Silica Reaction

Abstract of the technical paper presented at:
SMiRT 25 Conference
Charlotte, North Carolina, USA
August 4-9, 2019

Prepared by:
Nebojsa Orbovic¹, Olli Nevander² and Thambiayah Nitheanandan^1
1Canadian Nuclear Safety Commission
²OECD/ Nuclear Energy Agency

Abstract

The alkali–silica reaction (ASR), a type of alkali–aggregate reaction, is observed in some concrete structures in eastern North America, Europe and Japan. The Nuclear Energy Agency has put in place a three-phase international research program titled Assessment of Structures Subject to Concrete Pathologies (ASCET). Phase I of the project was related to the general recommendations for aging of concrete structures with concrete degradations, while Phases II and III were related to the numerical simulations of squat shear walls with the same geometry and reinforcement: three with ASR concrete and two with regular concrete. All shear walls were manufactured and cured under accelerated aging at the University of Toronto, under a CNSC research program. This paper addresses the numerical simulation benchmark performed in ASCET Phases II and III.

Nine teams from Canada, France, Japan, Sweden, and the United States participated in the ASCET benchmark. Most of the participants used commercially available software and modelled the ASR concrete degradation using different approaches. The ASCET Phase II benchmark (2017) consisted of blind simulations of shear walls tests with ASR and regular concrete after 995 and 975 days of accelerated aging. To calibrate the numerical models, the organizing committee provided the participants with the tests results of the ASR and the regular concrete after 260 and 240 days of accelerated aging. In Phase III, the organizing committee provided the participants with all available information on these four walls and, in addition, the test results of one ASR concrete wall tested after 610 days of accelerated aging. All the walls were loaded using the same protocol. The amplitude of the cycling loading was incrementally increased up to the failure of the wall. Maximum shear (ultimate) capacity, failure modes, crack patterns, structural ductility and energy dissipation were considered for this benchmark.

The findings of the testing program were: 1) ultimate wall capacity was not affected by ASR and 2) structural ductility and energy absorption (hysteretic damping) were significantly reduced. All participants successfully simulated the ultimate wall capacity. However, the simulations of failure modes, crack patterns, structural ductility and energy dissipation were less successful. The paper provides conclusions of the numerical simulations and recommendations for conducting this type of structural analysis.

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