Description
This paper presents an experimental investigation on reinforced concrete beams with different slenderness strengthened with unbonded Fe-SMA strips. The retrofitting system acts as an external prestressed tendon with a mechanical anchorage. In a first step, the strips are positioned against the concrete bottom surface and fixed against the concrete substrate with a direct fastening system. Activation and hence prestressing of the strips is performed with a gas torch and a subsequent temperature control. The concrete elements are afterwards subjected to 4-point bending up to failure. The aim of the investigation is to assess the structural behavior of the retrofitted members as well the additional strain and stress development in the Fe-SMA strips under additional loading after prestressing. Stress increase in the external strip resulting from the flexural loading has a direct influence on the failure mechanism in a sense that the ultimate stress is governed by the anchorage resistance. It is for instance shown that failure in bending with slender beams and plates is governed by concrete crushing in the upper compression zone, whereas beams with a reduced span exhibit premature failure by steel bar failure in tension or by ultimate anchorage resistance. The experimental results are compared with numerical simulations from an advanced cross section analysis tool established for unbonded strengthening systems.
