Influencing factors on creep displacement assessment of bonded fasteners in concrete

摘要

The long-term sustained load behaviour of bonded fasteners in concrete is tested and assessed in accordance with European Assessment Documents (EADs) 330087 and 330499. In these EADs, the measured displacements during sustained loading are projected to a 50-year working life using a power-law regression and extrapolation combining an initial displacement delta 0 and a time-dependent creep term a center dot tb. The projection of sustained load displacement data is sensitive to methods for determining and employing the initial displacement, data sampling choices for regression, and the length of testing. To illustrate these sensitivities, six sustained load tests with an extended test duration of 300 days and high displacement measurement frequency were conducted and numerically investigated. The aim of this paper is to address and verify the influence of various parameters on the displacement projection. In particular, the determination of the initial displacement, sampling window, and their proper use in the application of the Findley power-law method for creep displacement extrapolations are evaluated. To that end, different scenarios are assessed varying the time step between the displacement measurements, the size of the time window of measured displacements used for the regression analysis and use of the initial displacement in regression. A final check on the appropriateness and conservatism of the use of a powerlaw regression is proposed. Based on this analysis, proposals for the assessment of long-term displacement of bonded fasteners in concrete under sustained load are made.