Steel Structures

Stability

The research on stability contributes to a better understanding of the stability behavior of steel structures. On the basis of this stability behavior new and better design rules are developed. Steel structures are known for their lightness and long column free spans inducing stability phenomena to be predominant necessitating the research into flexural, torsional and flexural-torsional buckling of columns, lateral torsional buckling of beams and buckling of plates. Examples of research projects are:

  • Inelastic spatial stability of circular wide flange steel arches;
  • Structural properties and out-of-plane stability of roller bent steel arches;
  • In-plane stability of pitched-roof frames in line with Eurocode 3;
  • In-plane stability of non-orthogonal asymmetric steel frames;
  • The ultimate load of stacked steel propping systems;
  • Buckling length factors of hollow section members in lattice girders;
  • Comparison of global analysis methods and design rules for steel frames according to Eurocode 3;
  • Stability of laterally supported steel sway frames;
  • Design rule for lateral torsional buckling of channel sections;
  • Lateral torsional buckling of laterally restrained steel beams;
  • The influence of semi-rigid joint representation on the force distribution and stability of steel frames.

Connections

The research on connections focuses on the mechanical behavior of bolted and welded connections. Design rules for simple connections have to be available to the practicing engineer in order to make cost effective steel structures.  Application of simpler connections induces connection strength and connection stiffness to have more influence on strength, stiffness and stability of buildings. The research aims at investigating the structural behavior and at developing design methods for including this influence. Examples of research projects are:

  • Partial strength and flexible connections in steel frames;
  • Method to calculate horizontal deflection of high-rise buildings with flexible connections;
  • Requirements for column splices with respect to stability;
  • Numerical research on steel flange tip connections.

Cold-formed sections

The research on cold-formed sections concentrates on the development and improvement of design techniques to contribute to a broader application of cold-formed thin-walled plate products and sections. Examples of research projects are:

  • Elastic web crippling stiffness of thin-walled plate products under concentrated load;
  • Combined Web Crippling and Bending Moment Failure of Second-Generation Trapezoidal Steel Sheeting;
  • Web-crippling under concentrated loads and bending moments of steel sheeting.

Structural systems

Combinations of steel with other structural materials in load-carrying structures form a separate research area. Attention is focused on the way the different materials interact. Examples are research into the behavior of pre-stressed steel structures, stay-cable structures in buildings, stability structures in high-rise steel buildings. Materials should be used in an optimal way and this leads to combining materials: steel with e.g. concrete, timber, glass or FRP. Very well-known are composite steel concrete structures and with the introduction of high-strength materials there are new challenges requiring additional research. But also combinations of (high-strength) steel with other materials like glass in hybrid structures - where the glass suppresses buckling of steel parts - yields promising new structural solutions. Steel in combination with FRP is another interesting relatively new area of research. FRP is relatively light and has good fatigue properties and can be used to e.g. strengthen or even replace fatigue prone structures. Examples of research projects are:

  • Lateral behaviour of steel frames with discretely connected precast concrete infill panels;
  • Glass panes stabilizing an in-plane loaded steel frame;
  • Lateral Stiffness of Hexagrid Structures;
  • Parametric design and calculation of circular and elliptical tensegrity domes;
  • The sustainable motorway – a structural optimization;
  • Effect of tuned mass dampers in footbridge design.

High-strength steel

A trend can be observed towards the development and application of high-strength steel. High-strength steel is not very common yet in the building practice, but society’s need for sustainable solutions using less material will push its use. Design rules in codes are available for high-strength steel grades but for many rules the research back-up is missing. The steel research necessary for higher strength steels concerns bolted and welded connections, buckling stability aspects, (brittle) fracture and fatigue. High-strength steels have usually a lower toughness and a lower tensile to yield stress ratio and it has to be checked through research if current design rules are still appropriate. Scientific research is also necessary if other failure criteria than strength become decisive for the design. Fatigue may become decisive due to increased loading frequencies and if the solutions for mild steel are copied to high-strength steel. Fatigue of high-strength steel needs research, especially in case of undermatched welding. Also deformations under service conditions may become decisive and therefore other structural forms are to be used in design: trusses and triangulated structures rather than frames. This requires design research enabling full utilisation of the higher strength properties. Research projects related to high-strength steel are in preparation.  Currently a research project is underway for ArcelorMittal to investigate the residual stress levels in their Histar 460 and S460 Jumbo sections for the American high-rise building market and to determine the appropriate buckling curves to be used for these huge sections.