Micro and Macro Structural Investigations on Welded Joints of Composite Truss Steel Concrete Beams

Silvia Caprili,Walter Salvatore,Renzo Valentini

doi:10.1155/2021/6183178

Abstract

The results of an experimental test campaign including micro and macro investigations on welded joints typically used in Composite Truss Steel-Concrete beams are presented. The research was carried out with the aim of assessing the relevance of welding effects on the mechanical performance of different typologies of steel grades that can be used to realize the internal truss steel system, connected to the bottom steel plate used with the double structural and formwork function. Two different steel typologies were adopted for the steel truss: the “traditional” structural micro-alloyed steel, normally used for composite steel-concrete elements, and the typical reinforcing steel with TempCore® structure, achieved through the application of two-phase thermomechanical treatment of quenching and tempering. The interest in the possibility of adopting reinforcing steel for the internal truss arises from its potential economic benefit, finding its justification in the intermediate condition in which this structural typology lies, between composite steel-concrete and ordinary reinforced concrete buildings. Welding has a strong impact on such reinforcing steel material, resulting in relevant drops of ductility and brittle failure usually taking place in correspondence of the heat-affected zone. So, it is advisable to refrain from using such steel grade, especially in constructions in seismic-prone areas, where ductility is a major influencing and design factor.

Highlights

Modern design standards for buildings in seismic areas foresee the application of specific requirements and details concerning sections’ dimensions, reinforcements’ layout, and material properties
Difficulties still exist related to how to realize connections, or which design and detailing rules to adopt; it is quite usual that each single producer of CTSC system employs its own approach to realize connections between beams and vertical supports provided by adequate ductility levels and that, frequently, despite the structural typology, to all effects, a composite steel-concrete system reference for detailing joints is made to reinforced concrete (RC) ones, since the satisfaction of consolidated design criteria is easier and more reliable
For welding between steel reinforcing bars, prescriptions provided by EN17760-1:2007 [16] were adopted; both in the case of Lap and Double-sided joints (Dub) joints, the minimum welding length needs to be equal to 4 times the diameter of the connected component; no specific indications are otherwise provided for structural steels, required only to follow EN1090 : 2012 [7]. e effective welding length of the specimens was designed based on design rules normally adopted for CTSC beams with the aim of representing what is realized in the common practice

Summary

Introduction

Modern design standards for buildings in seismic areas foresee the application of specific requirements and details concerning sections’ dimensions, reinforcements’ layout, and material properties. Difficulties still exist related to how to realize connections, or which design and detailing rules to adopt; it is quite usual that each single producer of CTSC system employs its own approach to realize connections between beams and vertical supports provided by adequate ductility levels and that, frequently, despite the structural typology, to all effects, a composite steel-concrete system reference for detailing joints is made to RC ones, since the satisfaction of consolidated design criteria is easier and more reliable. With the main aim of evaluating the reliability of adopting different steel typologies for the realization of the steel truss of CTSC systems, including both structural and reinforcing steels, the mechanical performance of welding to join the different components was evaluated by adopting the different possible schemes realized in practical applications. (2) Double-sided lap joints (in the following identified with the tag Dub) with double welding was used to connect a structural steel plate made up of microalloyed steel (S355J0) and a steel bars was used both

Example of dub joint

Used for specimens

Steel type

Conclusions