The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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The Axial Load-Displacement Behavior of Steel Strands Used in Rock Reinforcement
Ilkka Satola
Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Civil and Environmental Engineering for public examination and debate in Auditorium V1 at Helsinki University of Technology (Espoo, Finland) on the 22nd of October, 2007, at 12 noon.
Dissertation in PDF format (ISBN 978-951-22-8973-8) [3894 KB]
Dissertation is also available in print (ISBN 978-951-22-8972-1)
Abstract
The aim of this thesis was to test and evaluate the load-displacement behavior of different types of grouted steel strands and rebar applicable to rock reinforcement. The main interest was focused on the effect of the epoxy and zinc coatings on the axial load-displacement behavior of the strand.
The bolt types tested were standard steel strand, galvanized steel strand, epoxy-coated steel strand, bulbed strand and rebar. New equipment for the axial laboratory pull test was designed and constructed for this study. The test apparatus enabled testing of different bolt types with embedment lengths from 250 mm up to 2000 mm. The loading rate used in the tests was 10 kN/min. The test apparatus worked as desired and was easy to operate.
The results showed that untwisting mechanism dominates the axial behavior of the steel strands. The roughness of the surface of the steel strands had a remarkable effect on the untwisting of the steel strands and thus on the axial behavior as well.
Rebar had a significantly higher bond strength, breaking load and maximum load, allowing shorter displacement values corresponding to the loads than any of the tested strands. The strands allowed larger displacement than rebar, especially the plain steel strand. The axial behavior of the bulbed strand was very close to that of the rebar, however.
On the basis of the results, corrosion protection on the surface of the steel strand significantly increased the bond strength and the stiffness of the grouted steel strand and decreased the displacement in proportion to the load under axial loading. The results showed that the maximum load-carrying capacity of galvanized steel strand and epoxy-coated steel strand increased linearly as the embedment length increased from 250 mm to 1000 mm. The critical embedment length of these bolt types was between 750 and 1000 mm.
The effect of the debonding material was found to be based both on the thickness of the debonding layer and the ability to decrease the friction between the strand and the grout. By thickening the layer, the pull-out resistance is decreasing leading lower pull-out loads for the strand.
Keywords: rock reinforcement, steel strand, rebar, epoxy-coated steel strand, galvanized steel strand, pull-out tests
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© 2007 Helsinki University of Technology
Last update 2011-05-26