The aim of “HSS-SERF” project was to investigate and evaluate the seismic performance of dual-steel building frames, realised from two different steel grades: Mild Carbon Steel (MCS) and High Strength Steel (HSS). The main objectives can be summarized as follows:

  • To find reliable structural typologies (e.g. moment-resisting frames, concentrically braced frames, eccentrically braced frames) and connection detailing for dual-steel building frames, and to validate them by tests and advanced numerical simulations;
  • To develop design criteria and performance based design methodology for dual-steel structures using HSS;
  • To recommend relevant design parameters (i.e. behaviour factor q, over-strength factor Ω) to be implemented in further versions of the seismic design code (EN 1998-1) in order to apply capacity design approach for dual-steel framing typologies;
  • To evaluate technical and economic benefit of dual-steel approach involving HSS.

Project implemented by

The Research Center for Mechanics of Materials and Structural Safety – CEMSIG, Politehnica University of Timişoara.

Implementation period:

01.07.2009 – 30.06.2013.

Research team

  • UPT Politehnica University of Timișoara, Romania (project coordinator)
  • RIVA RIVA Acciaio S.p.A, Italy
  • VTT Technical Research Centre of Finland
  • ULG University of Liege, Belgium
  • USTUTT University of Stuttgart, Germany
  • UNINA University of Naples "Federico II", Italy
  • UL University of Ljubljana, Slovenia
  • GIPAC Gabinete de Informática e Projecto Assistido por Computador Lda., Portugal
  • RUUKKI Ruukki Construction Oy, Finland
  • UPI University of Pisa, Italy

Main research activities

The aim and objectives of “HSS-SERF” project were accomplished through several research activities, which are briefly described in the following part.

1. Design of dual-steel multi-storey frames

An initial set of 18 dual-steel frame configurations were selected and designed, considering MRF’s, D-CBF’s and D-EBF’s, realised with composite columns: fully encased wide flange sections (FE-WF), partially encased wide flange sections (PE-WF), concrete filled rectangular hollow sections (CF-RHS). The design of the frames allowed the identification of realistic member sizes for both mild carbon steel beams and high strength steel composite columns. Several practical solutions for bolted and welded beam-to-column joints were identified and designed. Based on the joint solutions, new T-stub configurations whose design is not covered by Eurocode rules, were identified and considered in the experimental program.

Design of dual-steel multi-storey frames (MRF, D-EBF, D-CBF), choice of members (beams, columns) and design of beam-to-column joint specimens


Bolted beam-to-column joint configurations


Welded beam-to-column joint configurations


2. Seismic performance of dual-steel multi-storey frames

A comprehensive parametric study was defined by selecting and designing a set of 120 frames representative for the design practice. An extensive numerical program was carried out for the seismic performance evaluation of the 120 frames. In addition, the ductility and over-strength demands, and evaluation of q-factors associated with different performance levels were performed.

Analysis cases for the seismic performance evaluation


3. Experimental investigation of joint assemblies and components

An extensive experimental program was carried out for the investigation of joint components (weld details and T-stubs), and respectively bolted and welded beam-to-column joint assemblies.

isometry_milled.jpg series 100.jpg series 200.jpg series 300.jpg series 400_v1.jpg
Experimental investigation of welded details and T-stubs


Experimental investigationof beam-to-column joint assemblies


In the case of the partially encased and/or fully encased wide-flange columns, the load introduction is accomplished through shear studs. In contrast, for the case of rectangular hollow section columns, the connection solution between steel and concrete is more complex and can be realised in two methods which were studied within the project. Particularly, experimental tests were performed on the steel-concrete connection realised through the use of long bolts, and respectively shot fired nails.

Experimental investigation of steel-concrete connection through the use of long bolts, and respectively shot fired nails


In addition to the experimental program, extensive numerical investigations were carried out for the beam-to-column joint assemblies. The numerical simulation program helped to achieve a better understanding of the joint behaviour, and allowed the development and validation of simple design procedures for the studied joint configurations, as well as the extension of the experimental program with additional testing cases (parametric study).

Advanced numerical investigations of beam-to-column joint assemblies subjected to monotonic and cyclic loading conditions (calibration of numerical models)


4. Recommendations for seismic design and performance based evaluation of dual-steel structures

Based on the outcomes from the design of frames and joints, numerical investigation of the 120 frames, and experimental investigation of joint assemblies and components – Guidelines were developed for the conceptual design and performance based design of dual-steel building frames under seismic actions. The main outline of the guidelines was related to the design and detailing rules for connections and joints, and design methodology and criteria for MRF’s, CBF’s and EBF’s. In addition, several worked examples have been prepared covering the beam-to-column joint typologies investigated within the project.

5. Technical and economic efficiency

Last but not least, the evaluation of the technical and economic efficiency of dual-steel structures vs. conventional ones was performed. Consequently, a number of 15 frame configurations were selected and designed on a more detailed level.

Analysis cases for the evaluation of technical and economic efficiency, and the designed beam-to-column joints for the moment resisting bays


Main contributions of the project

  • Principles and design recommendations for dual-steel frames (guidelines);
  • The investigated frame typologies based on the dual-steel approach with composite columns, are solutions with a high innovative character in the European context; the dual-steel structures are not yet covered by the current code provisions (EN 1998-1, EN 1993-1-8, EN 1994-1); these configurations are to be taken into account within the further versions of the relevant Eurocodes;
  • Characterisation in terms of global ductility and over-strength demands of dual-steel frames realised in simple and dual configuration;
  • Modelling approach of members, such as braces, for non-linear analyses;
  • Proposal of a series of innovative beam-to-column joint typologies with composite steel-concrete columns (i.e. PE-WF, FE-WF and CFT) for which the structural performance was confirmed by experimental and numerical investigations;
  • Recommendations for weld details and appropriate component method design approaches.

Furthermore, the evaluation of the technical and economic efficiency of dual-steel structures vs. conventional ones showed that the use of high strength steel in non-dissipative members (columns of CBF & D-CBF, columns and braces of EBF & D-EBF) and connections represented an effective solution from the technical and economical point of view, leading therefore to cost reduction.

Financed by

Research Fund for Coal and Steel

Grant Agreement No: RFSR-CT-2009-00024

Contact information

Prof.dr.ing Dr.H.C. Dan Dubină

Corresponding Member of Romanian Academy         

Department of Steel Structures and Structural Mechanics, Faculty of Civil Engineering         

Politehnica University of Timișoara

e-mail: dan.dubina@upt.ro

tel: 0256 403 920