Numerical assessment of slab-interaction effects on the behaviour of steel-concrete composite joints

• Published in: Journal of constructional steel research Vol. 139; pp. 397 - 410
• Main Authors: Amadio, Claudio, Bedon, Chiara, Fasan, Marco
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.12.2017
• Subjects: Design; Experimental validation; Finite element numerical modelling; Isolated slab; Resisting mechanisms; Seismic performance; Steel-concrete composite joints; Resisting mechanisms; Design; Finite element numerical modelling; Experimental validation; Isolated slab; Steel-concrete composite joints; Seismic performance
• ISSN: 0143-974X; 1873-5983
• DOI: 10.1016/j.jcsr.2017.10.003

In current design practice for seismic resistant steel braced frames, general rules and standard provisions are aimed to ensure a structural behaviour for beam-to-column joints of non-braced spans as close as possible to perfect hinges. This is done to prevent any kind of interaction with the bracing systems, in particular under horizontal loads. However, the global performance of composite joints is markedly affected by the structural interaction between the concrete slab and the steel components and - especially during seismic events - struts can occur in the slab at the beam-to-column intersection. In this paper, the possibility of realizing a composite joint that behaves as moment-resisting under gravitational loads and essentially as hinged under horizontal loads is investigated. Aiming to assess the actual slab-interaction effects on the overall response, a full 3D Finite Element (FE) model representative of a beam-to-column composite joint taking part of a braced frame is described in ABAQUS and validated towards past full-scale experiments. A parametric study is hence proposed, by accounting for three geometrical configurations, being characterized by (i) isolated slab with absence of rebar continuity (i.e. fully disconnected slab and steel joint only), (ii) presence of slab with partial column interaction (i.e. isolated slab and continuity of rebar), (iii) presence of fully interacting slab. It is shown that, if properly detailed, a joint with isolated slab and continuous rebars can be used in non-braced spans of composite braced frames without affecting the behaviour of the bracing system (i.e. as in presence of a hinge). Nonetheless, the composite beam can be designed as continuous on multiple supports under vertical loads, hence leading to a reduction of the steel cross-sectional size. •The structural performance of steel-concrete composite joints is investigated via full 3D numerical models•Preliminary validation of 3D models is carried out towards past full-scale experiments•Key aspects deriving from slab-to-column interaction are examined, under various loading conditions•Several resisting mechanisms are observed, by changing joint features and loads, in accordance with Eurocode provisions•Preliminary design recommendations for the activation of the so called ‘mechanism 4’ are given