Development of plastic design procedures for stainless steel indeterminate structures

Kokosis, Georgios (2019). Development of plastic design procedures for stainless steel indeterminate structures. University of Birmingham. Ph.D.

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Abstract

Given the significant environmental impact of the construction industry, drastic improvements in terms of innovation and sustainability of the construction sector are required. To this end, the use of highly sustainable materials and the exploitation of their full potential is of paramount importance and will lead to more efficient utilization of resources and reduced carbon footprint. Stainless steel is gaining increasing usage in the construction industry owing to its excellent corrosion resistance, aesthetic appeal and a combination of favourable structural properties. The high initial material cost warrants the development of novel design procedures, in line with the observed structural response, which fully utilizes its merits and improve cost-effectiveness and sustainability of structural stainless steel design. Due to lack of available experimental data plastic design of stainless steel indeterminate structures is currently not permitted by Eurocode 3: Part 1.4 despite the excellent material ductility and the existence of a Class 1 slenderness limit, thereby compromising design efficiency. This dissertation focuses on the structural behaviour and design of stainless steel continuous beams and portal frames.

A comprehensive experimental study on eight simply supported and four two-span continuous beams employing austenitic and duplex stainless steel rectangular hollow sections (RHS) is reported in this thesis. An FE model was developed and validated against the reported experimental tests. The validated FE models were used to conduct parametric studies, , in order to obtain structural performance data over a range of cross-sectional slendernesses,

The behaviour of stainless steel frames has been investigated based on a comprehensive FE study. As no experimental results on the behaviour of stainless steel frames have been reported to date, experimental tests on pin-ended frames employing cold-formed steel RHS are utilized to validate an FE mode. Upon successful replication of the failure modes and overall structural behaviour, parametric studies were conducted to study the effect of key parameters on the ultimate response of stainless steel frames. The parameters investigated involve the material grade used, the degree of static indeterminacy (i.e. whether pin-ended or fixed-ended frames), the cross-section slenderness and the member slenderness. The importance of material strain-hardening at cross-section level, moment redistribution at system level and sway sensitivity/2nd order effects were determined and quantified.

Based on the obtained results, it was concluded that the current Eurocode 3: Part 1.4 approach significantly underestimates the strength of continuous beams and portal frames. This is because the formation of successive plastic hinges and moment redistribution in indeterminate structures with adequate deformation capacity as well as the effect of strain-hardening at cross-sectional level are not accounted for. It is shown that accounting for both strain-hardening and moment redistribution is of paramount importance for design. To this the application of a strain-based design approach, which rationally accounts for local buckling at cross-section level, in conjunction with traditional plastic analysis concepts are extended to the design of stainless steel indeterminate structures.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):