PSI - Issue 44

Sabatino Di Benedetto et al. / Procedia Structural Integrity 44 (2023) 1901–1908 Di Benedetto et al. / Structural Integrity Procedia 00 (2022) 000 – 000

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Fig. 2. RBS connection (left), FREEDAM joint (centre), dissipative double split tee connection (right)

Unlike RBSs, the FREEDAM connections can be classified as low-damage joints; they are composed of friction shims placed at the bottom flange of the beam end and connected with two L-stubs and a haunch to the column and the beam, respectively (Fig. 2). Instead, the top flange of the beam is bolted to the column flange thanks to a T-stub. The friction pads are steel plates coated with a thermally sprayed thin layer of aluminium that provides a dynamic friction coefficient equal to 0.53. According to the first principle of the capacity design, the friction pad is the first element to be designed assuming a limitation of the sliding force to 60% of the maximum flexural resistance of the beam, as shown in Eq. (3): , = 0.6 , 270 = 234 (3) where , 270 = 171.82 is the plastic bending moment of the beam and = 440 is the vertical distance between the centre of rotation of the connection and the barycenter of the haunch. As a consequence, the sliding bending moment is equal to 0.6 ∙ , 270 = 103 . Similarly to the RBSs, after the design of the dissipative elements, the remaining components have been conceived to behave elastically when dissipative parts attain their ultimate resistance. Consistently with the design of the same structure with the previous connection typologies discussed by Di Benedetto et al. (2020, 2022a, 2022b), the dissipative double split tee joints have been designed with a bending resistance equal to 100 kNm, with T-stubs in tension collapsing according to a type-1 mechanism. Since the design requirements are the joint's stiffness and resistance, the damper width and length are assumed as design parameters, while the flange plate's thickness is assumed to equal 25 mm. Starting from the assumptions reported in Eqs. (4-5), all the geometrical details can be defined (Latour and Rizzano, 2011). , = 2 2 ( − ) = 100 (4) , = 0.25 3 3 = 324.74 / (5) In Eqs. (4-5), is the material yield strength, is the beam depth, is the thickness of the beam flange, is the thickness of the T-stub, is the modulus of elasticity, is the distance between the plastic hinges in the flange of the T-stub, is a parameter accounting for moment-shear interaction in the yielded part of the T-stub, is the effective width of the simplified X-shape, , is the design bending moment of the connection, while , is its stiffness. In particular, the geometrical detail of the designed X-shaped T-stub connection is reported in Fig. 2. From the previous sentences, it is clear that the flexural strength of the three connections has been set equal to 100 kNm to compare the global and local responses provided by the tested mock-up. 3. Experimental set-up and test procedure The tested structure has been built at the STRENGTH laboratory of the University of Salerno. It is characterized by splice connections located at the columns' mid-heights and beam ends so that an easy replacement of column