The structure is regular in elevation with a story height of 3 m and 2。5 m clear height of columns between the beams; it is nonsymmetric in both directions, with 2-bay frames spanning from 3 to 6 m。 The plan layout and the 3D view of the structure after the construction are shown in Figure 1。 The concrete floor slabs are 150 mm thick, with a bi-directional mesh of 8 mm smooth steel rebars, spaced at 200 mm in the short span, 400 mm in the long span and 100 mm into

the short span of the cantilever。 Beam cross-sections are 250 mm wide and 500 mm deep。 Eight out of the nine columns have a square 250 × 250 mm cross-section; the ninth (column C6)  has a rectangular cross-section of 250 × 750 mm, which makes it much stiffer and stronger than the others along direction Y (i。e。 the strong direction for the whole structure)。 The joints of the structure

are one of its weakest points: neither beam nor column stirrups continue into them, so that no confinement at all is provided。 Moreover, some of the beams directly intersect with other beams (see joints close to columns C3 and C4 in Figure 1) resulting in beam-to-beam joints without the

support of the column。 Details about the beam reinforcement for flexure and shear can be found in Negro et al。 [1]。

The materials used for the structure were characterized by experimental tests: the average strength of smooth steel bars was equal to fym = 320 MPa [2]; tests performed on samples extracted during concrete casting of each floor showed an average concrete compressive strength of fcm = 25。5 MPa。 Two types of FRP laminates were used: (1) uniaxial GFRP laminates at both ends of each square column (unit weight of 900 g/m2, thickness of dry fibers of 0。48 mm/ply, modulus of elasticity of

65。7 GPa, tensile strength of 1314 MPa and ultimate strain of 0。02); (2) quadriaxial GFRP laminates for exterior beam–column joints along with the large column C6 (wrapped for its entire height) at

3 m 5 m 1 m 0。70 m

C5 C1 C2

B1 B2

Figure 1。 (a) Plan view and (b) 3D view of the SPEAR structure。

Figure 2。 Location and direction of  actuators。

all stories (unit weight of 1140 g/m2, thickness of dry fibers of 0。1096 mm/ply direction, modulus of elasticity of 65。7 GPa, tensile strength of 986 MPa and ultimate strain of 0。015)。 It is noted that GFRP laminate properties were provided by experimental tests。

A bi-directional PsD technique was used both in the ‘as-built’ and in the FRP-retrofitted full-scale structure。 The bi-directional PsD test consisted in the simultaneous application of the longitudinal and the transverse earthquake components to the structure; a more detailed description of both the method and the mathematical approach can be found in Molina et al。 [3, 4]。 Four actuators per story with four associated control displacement transducers were connected to the structure; a plan view showing the positions of the actuators is depicted in Figure 2。 Details about records, measurements and instrumentation can be found in Negro et al。 [1]。

3。 EXPERIMENTAL BEHAVIOR OF THE ‘AS-BUILT’ STRUCTURE: 0。20g PGA LEVEL

Identifying the most appropriate ground motions to be used for experimental tests is not an easy task; a procedure specifically targeted at such an objective has been recently reported in [5]。 In the case of the full-scale SPEAR structure, accelerograms obtained from the Montenegro 1979 Herceg Novi ground motion record were used as the input signal for the PsD tests。 After extensive