C2 154 090 2。44 3。67 4。81 5。72

C7 91 520 2。11 3。53 4。72 5。43

2nd story C5 28 010 1。71 3。25 4。43 5。27

C8 20 060 1。65 3。16 4。39 5。37

C2 72 740 2。00 3。41 4。56 5。38

C7 43 360 1。81 3。39 4。52 5。44

3rd story C5 23 590 1。68 3。23 4。41 5。26

C8 15 650 1。62 3。14 4。37 5。35

C2 68 320 1。97 3。42 4。60 5。44

C7 38 940 1。78 3。37 4。50 5。42

Shear Stress (MPa)

4 5 6

Figure 7。 Principal tensile stress inclination vs shear stress relationship for different amounts of external GFRP reinforcement (corner joint C8—third  story)。

2。44 MPa for exterior joint at columns C8 and C2 on the first floor, respectively), as confirmed by shear cracks observed on joints after the tests, it was decided to preserve the corner joints by installing FRP laminates。 The shear improvement provided by FRP laminates was assessed according to the approach proposed by Antonopoulos and Triantafillou [15] which, on the basis of equilibrium considerations, allows following the possible states of joint behavior up to failure。 Once geometric, bond and material properties are given and the acting axial forces are evaluated,

the equations provide the inclination of the principal tensile stress, 8, and the shear stress, v, corresponding to any given state of joint strains。 Failure of the FRP strengthened joint occurs when either the concrete crushes (i。e。 the principal compressive stress attains the crushing strength of concrete) or the FRP fails (i。e。 the ultimate stress is attained or debonding occurs)。 In order to take account of the fact that by increasing the joint strains, the inclination of principal tensile stresses, 8, changes considerably, it was decided to upgrade the exterior joints by using quadriaxial laminates; according to the column retrofit, glass fibers were chosen。 As the Antonopoulos and Triantafillou

[15] model referred to uniaxial laminates, only fibers placed along the axial direction of columns and beams and those with a component on them were taken into account for calculations。 The