Ductility and strength demands for connecting plates and bolts in bearing type connections of normal and high-strength steels

Description:

The project addresses the ductility and strength requirements for eccentrically connected bolted gusset plates under compressive loading and for bolted lap connections made of normal and high strength steels (HSS) up to S1000. The main objective of the project is to develop simple analytical design methods for engineers and to implement the developed analytical models into an existing software tool using the Component Based Finite Element Modelling (CBFEM) method. This tool will assist practitioners in the efficient and safe design of these types of bearing connections. The first research topic of the project is gusset plates in compression, which are typically found in trusses or braces connecting individual structural members. Some analysis methods for the design of gusset plate connections have been developed, some of which are used in standards, mainly in Australia, New Zealand and Canada. In Europe, however, the Eurocodes do not yet provide design methods for gusset plate connections. Neither in EN 1993-1-8 (Design of joints) nor in the recently published revision of the standard, the final draft prEN 1993-1-8:2020, are there specific design rules for gusset plates. EN 1993-1-5 (Plated structural elements) provides only general rules. It is therefore clear that a more general description of the behaviour of gusset plate connections in compression, complemented by a simple and clear new design procedure that will fill a gap in the current European standards, is needed. Even in a time when most static solutions are performed with software based on numerical methods, simple analytical methods or software solutions based on these analytical methods are indispensable tools for the practical design of connections. To achieve the research objective, a test programme for gusset plate connections with circular hollow section member in compression is planned to achieve the research objective. Based on previous findings, full-size tests with wide gusset plates and different slenderness and shapes of the plates (perpendicular end and oblique end of gusset plates) will be prepared. Bolted gusset plates with cleat plates will be prepared for the tests. During the tests, the axial and lateral displacement of the specimens and the planar deformation of the plates will be measured using the 3D digital image correlation method. The second research topic of the project is bolted lap connections with steel grades up to S1000. The distribution of forces between bolts is associated with a high concentration of stresses and local ductility of steel plates. The design of lap connections is simple if the ductility of the steel plates and the strength of the bolts are sufficient. The problem, however, is that the ductility criteria are difficult to meet for HSS connections. If not met, the failure occurs in the bolts, which is considered as a brittle (undesirable) failure and the connection should be designed on actual distribution of forces between bolts, which is not appropriate for engineers. The working group on high strength steels CEN/TC 250/SC 3/WG12 has the mandate to develop a new standard for additional rules for steel grades up to S1000. The working group (the project leader is its member) has determined that research is needed to create new design rules or to extend the existing rules to bolted lap connections of steels up to S1000. For this reason, the experimental programme for lap connections in steel S1000 with several bolts is proposed to investigate two main issues: (i) the minimum strength requirements for bolts due to the fabrication tolerances and (ii) to provide the design criteria when the ductility rule i.e., the shear resistance of bolt is higher than the bearing resistance of the plate, is not satisfied, where the ductility rule being reviewed and revised as necessary.

Main Goals:

The goals are given in the project description.

Work Packages:

WP1 Designing and preparation
WP2 Full-size and material testing
WP3 Numerical modelling
WP4 Design recommendations