Shape memory alloy and UHPFRC for ageing bridges: design notes for engineers
Reviewed by Tom Sullivan

First reported on New Civil Engineer
30 Second Briefing
Swiss researchers have strengthened ageing bridge decks by embedding heat‑activated iron‑based shape memory alloy (Fe‑SMA) bars within an ultra‑high‑performance fibre‑reinforced concrete (UHPFRC) overlay, creating active prestress when the bars are heated. The Fe‑SMA bars contract on activation and lock in compressive stresses as the UHPFRC hardens, improving fatigue performance and crack control without adding significant self‑weight. This approach offers a thin, bonded strengthening layer that can be installed on existing decks with minimal clearance loss and limited traffic disruption.
Technical Brief
- Fe‑SMA bars are heated electrically after casting, then cooled to lock in recovery stress.
- UHPFRC overlay behaves compositely with the existing RC deck through full-surface bonding preparation.
- Laboratory fatigue tests on scaled bridge deck specimens validated crack width reduction and stiffness recovery.
- Researchers monitored strain in Fe‑SMA bars and concrete using embedded gauges during activation and loading.
- Cyclic loading protocols simulated heavy traffic, with millions of load cycles applied to assess long‑term behaviour.
- Method targets decks with limited remaining reinforcement capacity but adequate global load‑bearing capacity.
- Application to real bridges is envisaged mainly during resurfacing campaigns to combine waterproofing and strengthening.
- Scope is currently limited to deck slabs; girders, diaphragms and support regions were not investigated.
Prepared by collating external sources, AI-assisted tools, and Geomechanics.io’s proprietary mining database, then reviewed for technical accuracy & edited by our geotechnical team.
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