PSI - Issue 44

Marco Gaetani d’Aragona et al. / Procedia Structural Integrity 44 (2023) 1052–1059 Author name / Structural Integrity Procedia 00 (2022) 000–000

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reinforcement can be calculated according to a “simply supported beam” or to a “continuous” scheme; in case of seismic design, horizontal design forces can be distributed according to a “shear-type” or “plane frames” scheme and transformed in internal actions by using “approximate” or “refined” methods depending on the construction age (Polese et al., 2009; Verderame et al., 2009) Once that geometric and structural model are generated, the response of structural members composing the frames (i.e., beams, columns, beam-column joints) and non-structural members contributing to building behavior (i.e., infill panels) is properly characterized (2). Existing buildings constructed and designed prior to the introduction of modern capacity design principles are often characterized by poor reinforcement details. This can lead to limited ductility, brittle failures, and inadequate performances during earthquakes. Brittle failures can be activated at the member level (e.g., shear failure, rebar buckling, bar-slip) or at the sub-assembly level (e.g., beam-column joint panels). The activation of latter failure mechanisms can also result in the development of local collapse mechanisms characterized by low energy dissipation capacity (i.e., soft-story mechanism) with respect to global collapse mechanisms.

BUILDING INFORMATION DATA (INPUT) NUMBER OF STORIES IN-PLAN SHAPE/DIMENSIONS CONSTRUCTION AGE LOCATION

SIMULATED DESIGN (1)

GEOMETRIC CONFIGURATION (1.1)

STRUCTURAL CONFIGURATION (1.2)

ELEMENT DESIGN (1.4) ELEMENT DIMENSIONING (1.3)

ELEMENT CHARACTERIZATION (2)

DESIGN OF RETROFIT INTERVENTIONS (3)

RC COLUMNS (2.1)

FRP/SRP JACKETING (3.1)

BEAM-COLUMN JOINTS (2.2)

RC JACKETING (3.2)

BAR-SLIP (2.3)

INFILL PANELS (2.4)

GENERATION OF INSTERSTORY BACKBONE (4)

LOCAL INFILL-FRAME INTERACTION EFFECTS (4.1)

COMPOSITION OF THE INTERSTORY BACKBONE (4.2)

DEFINITION OF STORY-LEVEL COLLAPSE (4.3)

Fig. 1. Methodology outline

To capture the most likely failure mechanism in RC members, reliable capacity models need to be employed to simulate the most probable failure modes of structural members. In Gaetani d’Aragona et al. (2022b) the envelope adopted to simulate the behavior of ductile RC columns is a multilinear backbone depending on the reinforcement bar type (i.e., deformed, or smooth bars) (2.1). Depending on the member geometry and material properties, brittle failure mechanisms may occur limiting the exploitation of the full flexural deformation. In this case, the element envelopes are modified depending on the comparison between shear demand and capacity curves, and possible failure mode is identified: (i) flexure, (ii) flexure-shear and (iii) pure shear failure. Beam-column joint (2.2) shear failure also may significantly affect the building performance possibly leading to the collapse of the beam-column sub-assembly before significant damage occurs in either beam or column members, facilitating the formation of soft-story collapse (Pampanin et al., 2002). According to several literature proposals, joint damage can be conveniently represented in terms of principal stresses in the joint panel (e.g., Pampanin et al., 2002; Tasligedik et al., 2016): existing unreinforced beam-column joints generally fail in tension, while joint failure may be potentially governed by principal compressive stress when adequately reinforced beam-column joints are considered. For beam-column joints, the model adopted (Gaetani d’Aragona et al., 2022b) depends on the position of the joint panel in the frame (i.e., exterior, interior, knee-joint), on the presence of transverse confining beams, and details of