Behavior of Post-Installed Anchors Tested by Stepwise Increasing Cyclic Load Protocols

Abstract

Cyclic loads are a characteristic feature of actions acting on structures and anchorages during earthquakes. For this reason, seismic qualification of post-installed concrete anchors according to the internationally recognized American Concrete Institute (ACI) standard ACI 355 is based on cyclic load tests. The protocols for these tests, however, have limited scientific basis. Therefore, in the present paper newly-developed test protocols with stepwise-increasing load amplitudes are utilized to more realistically evaluate anchor seismic performance. The study focuses on the load-displacement behavior of common anchor types installed in cracked concrete and subjected to both cyclic tension and cyclic shear actions. The results confirmed robust behavior for anchors loaded in cyclic tension even in the presence of crack widths in the anchorage material larger than currently required by ACI 355. In addition, the critical influence of low cycle fatigue on the performance of anchors loaded in cyclic shear is demonstrated.

Development and validation of European guidelines for seismic qualification of post-installed anchors

“…Nevertheless, Silva argues that a stepwise-increasing load is preferable because it provides additional information about the anchor stiffness throughout the entire anticipated loading range. Silva’s results were subsequently extended to other anchor types and failure modes for tension and shear load cycling [[33], [34]] and for crack cycling [[35], [36]]. The results of these studies corroborate using stepwise-increasing protocol for seismic anchor qualification.…”

“…Furthermore, the number of crack cycles in a crack movement test (cumulative cyclic damage), and not just the crack width amplitude, must be accurately represented. Results from these tests are reported in [34] and [36]. …”

“…The crack width of 0.5 mm corresponds to the maximum crack width for anchor qualification currently used for the simulated seismic tests according to ACI 355 and 0.8 mm is the maximum crack width considered for seismic anchorage (see Section 3.3). Due to the small influence of crack width on anchor shear test results, the crack width was chosen conservatively as 0.8 mm throughout the shear cyclic load test [34]. …”

“…Reversed cyclic shear loading typically results in anchor steel failure. The coefficient of variation for anchor steel failure is generally less than 10 % [34], so the characteristic shear load was calculated as V max = (1−1.645·10 %) V u,m,cr = 0.85· V u,m,cr . The values 0.75· N u,m,cr and 0.85· V u,m,cr were selected as the maximum considered loads at the suitability level demand.…”

“…For the cyclic crack tests, the concrete specimen was loaded axially by a 630 kN actuator (Figure 5c), while a 250 kN servo-hydraulic actuator was used to load the anchor axially (Figure 5c,d). Additional details can be found in [34] and [36]. …”