The capacity spectrum approach (CSA) was also used for the seismic verification [13]。 Thus, both the elastic acceleration and displacement spectrum were scaled at PGA levels of 0。20g and 0。30g and plotted in acceleration–displacement (AD) format (see Figure 4)。 In Figure 5, the seismic

demand for the equivalent SDOF system is determined for the two levels of ground motion analyzed by using a CSA [13]; demand is computed for direction NX , where the maximum capacity–demand gap was recorded。 By using the same graph to plot the demand spectra and capacity, it is possible to determine the elastic acceleration and the corresponding elastic displacement demand (named Sae

and Sde, respectively) required in the case of elastic behavior。 They are computed by intersecting the radial line corresponding to the elastic period of the idealized bilinear system, T ∗, with the elastic demand spectrum。 Once the ductility demand, µ = Sd/D∗, is computed (depending on whether T ∗ is greater or less than TC), the inelastic demand in terms of accelerations and displacements is

provided by the intersection point of the capacity diagram with the demand spectrum corresponding to µ。 Figure 5 highlights that the ‘as-built’ structure in direction NX , hardly able to satisfy the

As Built Structure (Push NX)

Figure 5。 ‘As-built’ structure elastic and inelastic demand spectra vs capacity diagram。

demand due to the 0。20g PGA level, totally lacks the appropriate capacity to resist the 0。30g PGA level。 Indeed, the requested ductility is µ = 5。2 against the available structural ductility of µ = 3。5。 The displacement demands in Figure 5 refer to the equivalent SDOF system; thus, to obtain   the

displacement demands of the MDOF system (reported in Table III), it is necessary to multiply the SDOF system demand by the transformation factor F = 。 mi 0i / 。 mi 02 = 1。23 (where mi is

the mass in the i th story and 0i

are the normalized displacements)。

The results of theoretical analysis closely approximated those of the experiment, indicating the first attainment of the significant damage limit state (i。e。 0。758u in the plastic hinge) at the column ends of the second floor (i。e。 at columns C3 and C4 in directions PX and NX , respectively) where the most significant damage was found during the test。 Moreover, according to the damage detected on the structure after the test, it provided 0。20g as a limit acceleration value for the verification of the LSSD。

5。 DESIGN OF THE REHABILITATION WITH COMPOSITES

The selection of fiber texture and retrofit design criteria were based on deficiencies underlined by both the test on the ‘as-built’ structure and the theoretical results provided by the post-test assessment。 They indicated that a retrofit intervention was necessary in order to increase the structural seismic capacity; in particular, the theoretical results showed that the target design PGA level of 0。30g could have been sustained by the structure if its displacement capacity were increased by a factor of 48%。

In  order  to  pursue  this  objective,  the  retrofit  design  strategy  focused  on  two  main  aspects:

(1) increasing the global deformation capacity of the structure and thus its dissipating global performance and (2) fully exploiting the increased deformation capacity by avoiding brittle collapse modes。 Thus, the retrofit design was aimed at maximizing the benefits of the externally bonded FRP reinforcement along the direction of dominant stresses by increasing either the column confinement or the shear capacity of exterior beam–column joints and of the wall-type column, C6。 The design