PSI - Issue 44

4

Domenico Magisano et al. / Procedia Structural Integrity 44 (2023) 456–463 Magisano et al. / Structural Integrity Procedia 00 (2022) 000–000

459

2a

2e

Fig. 2: Mildly irregular frame: geometric and structural features. 2a: Axes dimension in meters. Control node highlighted in red; 2b:building plan and structural element sections. (a) Column section 0 . 30 × 0 . 60 m, 20mm steel bars. (b) Beam section 0 . 30 × 0 . 50 m, 16 mm steel bars; 2c: Front view, XZ plane; 2d:Front view, YZ plane.

The method presented is tested on a mildly irregular frame (Fig. 2). It is a five-story reinforced concrete frame with 3 spans in X directions (with width of 4, 6 and 5 m) and 4 spans in Y direction (5, 6, 4 and 4 m respectively). Its total height H is 15.9 m. The vertical load on the one-way ribbed slabs along the X direction is distributed 90% on the supporting beams and 10% on the parallel ones. The ROM is made using three linear modes (Fig. 3), the corresponding plastic mechanism (Fig.4) and single story plastic mechanisms (Fig.5). The test is dedicated also to show the need of both linear and plastic modes for describing the dynamic structural behavior for significant excursions in the plastic range. The building is subjected to vertical dead loads and seismic action in horizontal direction only. Dead loads are kept constant all over the analyses. The seismic action is obtained from a spectrum compatible accelerogram built using a dedicated code based on Simqke algorithm Gasparini and Vanmarcke (1976). The acceleration time history represented in Fig.1 is used as seismic load in all the tests, except when comparing the random frequency content of the seismic action. The target spectrum is obtained from EC8 guidelines Eurocode (1996) with parameters reported in Tab.1. The bi-linear elasto-plastic material model is characterized by the following properties for all the tests:

v 1

v 2

v 3

Fig. 3: Mildly irregular frame: linear elastic mode shapes in XZ plane.

concrete with compressive strength f c = 20 MPa zero tensile strength and E = 28607 MPa; steel rebars with strength f y = 450 MPa and E = 210000 MPa. A fiber model is adopted for obtaining the section response. Due to the zero tensile strength of the concrete, inelastic deformations occur for every amplitude of the ground motion, except for fully compressed members. ROM results are compared to those of the FULL model, in order to examine accuracy. Test outputs are illustrated by displacement time history and maximum profile deformation along the height of the building. A control node is taken on the top of the building (Fig. 2) and its displacement projected onto the seismic direction, named u , is monitored. Profile deformation is obtained plotting analogous displacements at the same control node of the lower stories, at the time when the maximum value of u is reached in the full model. Total analysis interval ∆ T covers the whole duration of seismic action time history, that is 20 seconds.