PSI - Issue 44

Maria Zucconi et al. / Procedia Structural Integrity 44 (2023) 315–322 Maria Zucconi et al. / Structural Integrity Procedia 00 (2022) 000–000

316 2

1. Introduction The current worldwide seismic design philosophy establishes that a structure, to overcome an earthquake without collapsing, can face the seismic event by reaching a high deformation level, typically in the inelastic field, and exhibiting ductile damage mechanisms, like the formation of the plastic hinge. So, part of the incoming earthquake energy is dissipated in hysteretic energy that can also be associated with severe damage to both structural and non structural elements [1]. The capacity-design method, developed some years ago in an academic context for the seismic design of buildings but included nowadays in many international codes, furnishes criteria for calculating structural elements and constructive details for the design of the new seismic-resistant building generation [2]. The current building codes have a prescriptive nature and have the main aim to establish a design process providing buildings with a certain failure probability at a specific ultimate limit state for a particular design-level event or intensity. While building codes allow obtaining structures that meet a life-safety performance level for a specified seismic intensity level, they usually do not request the respect of other performance levels. On the other hand, earthquakes continue to highlight the thorny dilemma of the destiny of structures that report extensive structural and non-structural damage resulting out of service for a long period and requesting high disbursement for their restoration interventions [3–5]. Therefore, increasing attention has recently been devoted to defining criteria for designing more resilient structures. So, the new design criteria have started to include the minimization of disruption and costs associated with the post-earthquake retrofitting, as well as safety and financial aspects [6–10]. In this regard, this work aims to assess the economic losses of a non-ductile reinforced concrete framed building using the methodology proposed by FEMA-P58, according to the Performance-Based Earthquake Engineering method [3], evaluating the influence of bi-directional ground motion on loss estimates. The analyzed model is a three dimensional nonlinear framed building characterized by one weak and one strong seismic directions [11]. The model of the structures also considers the joint deformability and the flexural and shear damaging behavior of beams and columns [12,13]. Sixthy time-history analyses were performed considering bi-directional ground motions applied in the two main directions of the building and applying the higher spectral acceleration firstly in the weaker direction and then in the stronger one. Eight increasing hazard levels were selected for the nonlinear time-history analyses, and the corresponding structural analysis results, in terms of interstory drift ratio and peak floor acceleration, were implemented for the loss assessment. 2. The case study building The case study building is a typical non-ductile structure designed before the seismic codes. These structures are built without the capacity design criteria. They are characterized by strong-beam and weak-column and from the presence of vertical loads resisting frames in only one direction of the building, associated with low concrete and steel strength [14,15]. Then, the lack of confinement effects in the joint panel leads to relevant deformability of this region that influences the global behavior of the buildings, causing a possible brittle early failure of the panel nodes, especially on the lower floors [16,17]. All these features strongly influence the vulnerability of these buildings conditioning both the seismic performance and the resulting economic losses evaluated in the following in terms of the entire life cycle assessment [13,18,19]. The case study building, analyzed in this paper, represents structures built before the 1970s, characterized by the structural deficiencies described above, typical of Italian and the Mediterranean area. Figure 1 shows the plan and the lateral views of the selected case study building. The structure is an RC-frame building designed according to the 1939 Italian building code provisions [20]. The structure is characterized by three-story above ground with interstorey heights equal to 3.0 m, three bays in the X-direction of 6.0 m each, and two bays in the Y-direction of 5.0 m each. The beam cross-sections are equal to 600 × 300 mm in X direction and 240 × 300 mm in Y direction; the column cross section is equal to 30x40 mm. The case study is located in Messina, Southern Italy, on class soil B [21]. The assumed concrete and steel class are C20/25 and FeB32k, defined according to the 1939 Italian building code.