Figure 11。 (a) Column confinement and shear strength of exterior joints and (b) shear strength of column C6 and retrofitted structure  overview。

shear recorded on the retrofitted structure was slightly lower (7 and 2% in directions X and Y , respectively) than that achieved in the retrofitted structure at 0。20g。 In contrast, the maximum displacement of the structure was significantly enhanced, especially in direction X ; the maximum top displacement recorded was 0。2053 m, roughly twice that reached during the previous tests。 This confirms that the FRP retrofit is able to greatly increase the global deformation capacity of the structure, affecting its strength only slightly。 Further experimental evidence is obtained if the results in terms of absolutely inter-story drift are analyzed。 Table I shows a significant increase in absolute inter-story drifts at each floor if values recorded at the 0。3g and 0。20g PGA tests are compared。 In particular, an increase of about 85% was recorded at the second story in the weak direction X (0。1060 m vs 0。0570 m)。

The experimental behavior of the rehabilitated structure was very close to that expected according to the rehabilitation design: (1) very ductile behavior of the columns was observed and (2) no brittle mechanisms occurred (i。e。 shear failure or significant damage of joints)。

As-Built Structure (PGA = 0。20g) FRP retrofitted Structure (PGA = 0。30g)

Column view after the test

Column after damaged concrete removing

Column view after the test

Concrete core after FRP removing

Figure 12。 Damage on columns: comparison after the test on the ‘as-built’ and FRP-retrofitted configuration。

8。 CONCLUSIONS

The paper deals with full-scale tests on an under-designed RC structure in the ‘as-built’ and FRP retrofitted configurations。 The retrofit criteria and calculation procedures used to design the amount and layout of FRP required to improve the seismic performance of the structure are presented and discussed。

The experimental results provided by the structure in the ‘as-built’ and GFRP-retrofitted config- urations highlight the effectiveness of the FRP technique in improving the global performance of under-designed RC structures in terms of ductility and energy dissipation capacity。 In the present case study, this goal was achieved by confining the column ends and preventing brittle mechanisms (i。e。 exterior joints and rectangular column shear failure)。

The experimental results confirmed that this seismic upgrade approach, outlined by the Italian guideline CNR-DT 200/2004, could be effective。 The design equations used for shear strengthening of exterior beam–column joints and of the wall-type column were found effective to quantify the GFRP laminates needed to enable the structure to fully exploit its improved deformation capacity given by the increased ductility of the FRP-confined columns。

Pushover analysis provided results qualitatively close to the experimental outcome, confirming the effectiveness of the FRP retrofit in increasing the global deformation capacity of the ‘as-built’ structure by strongly improving its displacement capacity at a significant damage limit state。 The experimental results confirmed the theoretical predictions, showing that the FRP retrofit allowed the structure to withstand a level of excitation, in two directions, 1。5 times higher than that applied to the ‘as-built’ structure, without exhibiting significant damage or structural deterioration。

ACKNOWLEDGEMENTS

The SPEAR project was co-ordinated by Dr Paolo Negro from the Joint Research Centre with the administrative co-ordination of Prof。 Michael Fardis from the University of Patras。 Professor Fardis also provided the original design of the structure。 The cooperation of members of the EU Joint Research Centre at Ispra is gratefully acknowledged。 The SPEAR consortium for the preliminary numerical analyses and