TY - JOUR

T1 - Application of an iron-based shape memory alloy for post-tensioning glass elements

AU - Silvestru, Vlad Alexandru

AU - Deng, Zhikang

AU - Michels, Julien

AU - Li, Lingzhen

AU - Ghafoori, Elyas

AU - Taras, Andreas

N1 - Funding Information: The support of re-fer AG, Glas Trösch AG, Sika Schweiz AG and Huntsman Advanced Materials (Switzerland) GmbH in providing necessary materials for the test specimens is gratefully acknowledged. Furthermore, the authors would like to thank the laboratory staff of the Institute of Structural Engineering at ETH Zurich, the laboratory staff at the Structural Engineering Research Laboratory at Empa and re-fer AG for their support in performing the experiments. The commercial product names mentioned in this paper for the adhesives are provided only for the sake of factual accuracy, not as an endorsement of the products. Funding Information: Open access funding provided by Swiss Federal Institute of Technology Zurich. This research was funded by Innosuisse – Swiss Innovation Agency through the innovation cheque application number 51447.1 INNO-ENG and was supported by re-fer AG. Publisher Copyright: © 2022, The Author(s).

PY - 2022/8

Y1 - 2022/8

N2 - Previous research has evidenced that by adding a ductile reinforcement on the tension side of a glass beam, for instance by adhesive bonding, its post-cracking behaviour and redundancy were improved, while an additional pre-stressing of this reinforcement further helped to increase the initial cracking resistance. Past investigations used steel tendons or stainless steel strips, which required rather complex setups and procedures for mechanical pre-stressing. This study aims to introduce an easier-to-apply procedure with strips made of an iron-based shape memory alloy (Fe-SMA), which has the property of remembering its initial shape after a phase transformation from austenite to martensite. The Fe-SMA strips can be anchored to a parent structure as pre-strained strips, in case of a glass substrate by adhesive bonding. After activation of the Fe-SMA through a heating and cooling process, a tensile stress is generated in the strip, which applies a compressive stress field into the parent structure. This work discusses the results from first feasibility investigations dealing with the choice of adhesive and identifying a suitable activation procedure for Fe-SMA strips adhesively bonded to glass elements. The effective bond length, which needs to be considered when defining the anchorage length, was determined for two structural adhesives. While for the high-strength, brittle 2c-epoxy adhesive SikaPower®-1277, shorter bond lengths of a little more than 120 mm were sufficient, for the more ductile 2c-methacrylate adhesive Araldite® 2047-1, longer bond lengths were necessary for the same load level (more than 240 mm). Furthermore, an activation procedure by electrical resistive heating was applied, which (i) allowed sufficient heating of the Fe-SMA for activation, (ii) avoided too high instant temperature changes in the glass and (iii) did not affect the required anchorage bond length.

AB - Previous research has evidenced that by adding a ductile reinforcement on the tension side of a glass beam, for instance by adhesive bonding, its post-cracking behaviour and redundancy were improved, while an additional pre-stressing of this reinforcement further helped to increase the initial cracking resistance. Past investigations used steel tendons or stainless steel strips, which required rather complex setups and procedures for mechanical pre-stressing. This study aims to introduce an easier-to-apply procedure with strips made of an iron-based shape memory alloy (Fe-SMA), which has the property of remembering its initial shape after a phase transformation from austenite to martensite. The Fe-SMA strips can be anchored to a parent structure as pre-strained strips, in case of a glass substrate by adhesive bonding. After activation of the Fe-SMA through a heating and cooling process, a tensile stress is generated in the strip, which applies a compressive stress field into the parent structure. This work discusses the results from first feasibility investigations dealing with the choice of adhesive and identifying a suitable activation procedure for Fe-SMA strips adhesively bonded to glass elements. The effective bond length, which needs to be considered when defining the anchorage length, was determined for two structural adhesives. While for the high-strength, brittle 2c-epoxy adhesive SikaPower®-1277, shorter bond lengths of a little more than 120 mm were sufficient, for the more ductile 2c-methacrylate adhesive Araldite® 2047-1, longer bond lengths were necessary for the same load level (more than 240 mm). Furthermore, an activation procedure by electrical resistive heating was applied, which (i) allowed sufficient heating of the Fe-SMA for activation, (ii) avoided too high instant temperature changes in the glass and (iii) did not affect the required anchorage bond length.

KW - Activation procedure

KW - Iron-based shape memory alloy

KW - Lap-shear joint

KW - Post-tensioned glass element

KW - Shear strength

KW - Structural adhesive

UR - http://www.scopus.com/inward/record.url?scp=85134223914&partnerID=8YFLogxK

U2 - 10.1007/s40940-022-00183-z

DO - 10.1007/s40940-022-00183-z

M3 - Article

AN - SCOPUS:85134223914

VL - 7

SP - 187

EP - 210

JO - Glass Structures and Engineering

JF - Glass Structures and Engineering

SN - 2363-5142

IS - 2

ER -