Parametric study for wall-to-wall connection in mixed Steel Concrete Structures

The objective of this thesis work is to study the connection between two steel Concrete Structures (SCS) wall modules using embedded connection bars. The SCSs under investigation consist of two steel faceplates held together by tie bars, concrete is cast inside, and stress transmission between the concrete and the steel plates is provided by shear connectors as headed studs. The working principle is similar to that of Reinforced Concrete (RC), where the faceplates provide the tensile strength, replacing the rebars in RC, and the concrete the compressive strength. One of the main differences, which makes the use of SCS advantageous, is that the concrete is confined and thus improves its compressive performance by 4-5 times compared to normal RC. Further, the confinement due to the plates ensures insulation of the concrete from external agents, improving its durability. The use of prefabricated modules to be placed on site and the concrete cast inside reduces the working time and costs. For all these reasons, and especially for its higher performance compared to RC, this construction strategy is perfectly suited to the needs of large constructions such as nuclear reactors. However, one of the main disadvantages is the lack of codes, there are only two international codes JEAG 4618 (Architectural Institute of Japan, 2005) and ANSI/AISC N690-18 (American Institute of Steel Construction, 2018), a disadvantage that AFCEN is trying to solve by creating a European nuclear code to be included in the RCC-CW. AFCEN instructed EDF that in turn entrusted EGIS to compile a PTAN report as a technical justification for the chapters related to SCS in the nuclear application. The topic of this thesis is one of the PTAN technical specifications to be solved and is related to a second main drawback of the SCS system arising from the way the modules are connected. Currently, the most commonly used connection systems are welding, while the alternative proposed in this thesis project is the use of embedded connection bars. The use of welding to connect modules increases the working time and costs, creating potential problems, especially for thicker faceplates, when internal welding is not possible and can only be performed from the outside. The analysed solution consists of using longitudinal bars positioned between two modules to ensure the connection, leaving a gap of 2 cm or more between the faceplates of two adjacent modules and solving the problems of single-sided welding and reducing the working time. The analysis of this connection strategy is carried out in a parametric study in which 29 different configurations are tested in bending and tension to obtain general rules for the design. In almost all the models the failure occurs in the studs with reductions in the connection strength compared to the ultimate SCS capacity from 22% to 60% in bending and from 74% to 88% in tension, respectively for M48 and M30 as bar diameters. The conclusion of the analysis showed that the design of the shear-headed stud capacity is poor, due to the combined effect of shear and tension reducing the pure shear capacity by 60%. In fact, more studs are needed than estimated to reach the ultimate capacity of the bar or plate, which should be the two preferred failure modes of the connection.