Marios Theofanous

• Doctor of Engineering
• Associate Professor at University of Birmingham

Design automation addresses the problem of manual and time-consuming design processes by streamlining and optimizing the creation of products, systems, or solutions using automated tools and workflows. The insufficient implementation of design automation technologies in the building and structural design industry has significant implications for pr...

High-strength steel is increasingly popular in construction for its strength-to-weight ratio, which lowers the self-weight of structures and reduces transportation, erection, and foundation costs. Induction hardening (IH) process which involves rapid heating and cooling of the material leads to microstructural changes which enhance the hardness and...

The steel industry's substantial role in climate change is evident, contributing 6.5% of greenhouse gas emissions, half of which originate from the construction sector. Prioritizing steel reuse over energy-intensive recycling has shown the potential to meet the increasing steel demand and urges a shift towards sustainable practices. Recent data ind...

Purpose: This paper examines the effect of shear span-to-effective depth (a/d) ratio on the structural behaviour of reinforced concrete (RC) T-beams strengthened in shear with deep embedment (DE) carbon fibre reinforced polymer (CFRP) bars. Study design/methodology/approach: Two series of RC T-beams with an a/d ratio of either 1.9 or 3 were tested....

This paper reports the development and validation of an advanced FE model that can predict the overall behaviour and failure modes of blind bolted T‐stub to unfilled tube (UT), concrete‐filled tube (CFT) and foam‐filled tube (FFT) joints in tension. The joints investigated were made of S355 Square Hollow Sections (SHS) either empty or with concrete...

In the last two decades blind‐bolted connections have been developed to allow bolting of open section beams (e.g, I‐beam) to steel hollow section (SHS) columns where access from all sides of the column is not possible. Filling the tubular column with concrete in the vicinity of the beam‐to‐column connection has been shown to improve the anchoring m...

Aluminum is gaining more popularity in the construction industry due to its light weight, mechanical resistance and corrosion properties. Although several studies covering extruded and cold‐rolled aluminium members exist, research into the structural performance of 3D printed aluminium remains scarce. With the increasing importance of digital engin...

Fracture at net areas of steel sections often leads to premature failures of steel members, especially in the region of joints (bolted connections). This study develops a fracture model for hot rolled S355 steel for enabling a better understanding of the ultimate behaviour of steel sections through numerical simulations using the general‐purpose fi...

Bolt fracture often limits the ultimate strength and deformation capacity of bolted connections and leads to overall joint failure. Therefore, the prediction of structural collapse under extreme loads necessitates the incorporation of a reliable fracture model that reflects the observed structural response of bolts. This paper reports a comprehensi...

Following the experimental study on EN 1.4003 ferritic stainless steel T-stubs in tension discussed in the companion paper, this study reports the development and validation of an advanced FE model that can predict the overall behaviour and failure modes of ferritic stainless steel bolted T-stubs subjected to tension. Key simulation strategies rega...

The shear performances of simply supported (SS) and continuous (CN) reinforced concrete T-beams strengthened with deep embedded (DE) steel or carbon fibre-reinforced polymer bars are compared in this investigation. A nonlinear finite element (NLFE) analysis is performed for this purpose by modelling these beams with the FEM software by validating w...

The structural performance of stainless steel beam-to-column joints with double extended end-plate connections is numerically studied in this paper. Finite element (FE) models were developed and validated against previously reported experimental results including static and cyclic loading tests on stainless steel double extended end-plate beam-to-c...

Recently, a series of experimental tests and accompanying numerical studies has been conducted on austenitic and duplex stainless steel moment resisting connections which highlighted both the excellent ductility and significant overstrength exhibited by such connections as well as the severe conservatism of current design rules specified in EN 1993...

After yielding, steel structures progressively exhibit an asymmetrical hysteretic behaviour under earthquakes biased in one direction (ratcheting effect). This response may be favourable to structural components because of the absence of symmetrical cyclic loading reversals. To evaluate the inelastic behaviour of components to asymmetrical cyclic l...

This paper presents experimental and numerical investigations on the behaviour of reinforced concrete (RC) T-beams strengthened in shear with deep embedment (DE) fibre reinforced polymer (FRP) bars. The tests were carried out on an unstrengthened beam as well as two beams strengthened in shear with embedded glass FRP (GFRP) or carbon FRP (CFRP) bar...

Research on stainless steel structures has primarily focused on the structural response and design of individual members, whilst the response of joints has received far less attention to date. Recently, a series of experimental tests has been conducted on austenitic and duplex stainless steel moment resisting connections which highlighted both the...

Following the experimental study on EN 1.4003 ferritic stainless steel T-stubs in tension discussed in the companion paper, this study reports the development and validation of an advanced FE model that can predict the overall behaviour and failure modes of ferritic stainless steel bolted T-stubs subjected to tension. Key simulation strategies rega...

This paper reports a numerical study on the optimization of the lip size of Z-sections under gravity loads. Numerical models simulating the structural response of cold-formed steel Z purlins partially restrained by cladding and angle struts and subjected to sagging moment were developed and validated against a total of nine previously reported expe...

Due to their thin‐walled nature and complex geometry, cold‐formed steel purlins are prone to a variety of instabilities. In most applications, purlins rely on the attached sheeting to restrain member buckling and hence their cross‐section is optimized to maximize their cross‐sectional resistance to local and distortional buckling caused by sagging...

A comprehensive experimental study on the structural behaviour of stainless steel T-stubs in Grade EN 1.4003 ferritic stainless steel and employing A4–80 stainless steel bolts is reported in this paper. A total of 17 ferritic stainless steel T-stubs of various geometric configurations including both single and double bolt rows were tested under mon...

The aim of this paper is to investigate the hysteretic behaviour of stainless steel bolted T-stub connections. A total of 22 bolted T-stubs in austenitic grade EN 1.4301 were tested under monotonic loading and cyclic loading under both variable and constant amplitudes. The tested T-stubs were carefully designed with two different bolt configuration...

This paper focuses on the hysteretic performance of stainless steel beam-to-column joints with double extended end-plate connections under cyclic loading. Six full-scale joint specimens were fabricated, including three interior column joints and three exterior column joints. Two stainless steel grades — austenitic grade EN 1.4301 and duplex grade E...

A significant amount of research has been reported on stainless steel tubular sections, while studies on I- and C-sections remain relatively limited. This paper presents a comprehensive numerical study on the response of stainless steel I- and C-sections subjected to minor axis bending, with outstand flanges subjected to stress gradients. Numerical...

This paper reports 8 experimental tests on simply supported purlins with lipped Z-sections under gravity loads. The adopted test details are representative of the support conditions typically employed in practice with each specimen comprising two purlins connected to each other at regular intervals with angle struts used in lieu of anti-sag bars an...

This paper reports a numerical study on the optimisation of the lip size of Z-sections under gravity loads. Numerical models of cold-formed steel Z purlins restrained by cladding and angle struts and subjected to sagging moment were developed and validated against a total of 8 experimental results on Z-sections that failed in local or/and distortio...

Seven reinforced concrete (RC) T-beams, comprising two unstrengthened (control) beams and five beams strengthened in shear with embedded FRP bars, were tested to failure. The test parameters were steel-to-FRP shear reinforcement ratio and tension reinforcement ratio. A nonlinear finite element (FE) model was developed, validated and used to conduct...

Traditionally, experimental research on structural members has focused on the isolated fundamental cases of pure compression/tension, major axis bending or minor axis bending, whilst beam columns under compression and uniaxial bending have also been tested. Biaxial bending has received less experimental attention and it has always been assumed that...

This paper presents the results of psychical tests on reinforced concrete (RC) T-beams under static or cyclic loading. An unstrengthened (control) beam was tested under static loading whereas two RC T-beams strengthened in shear with deep embedment (DE) glass fibre reinforced polymer (GFRP) bars were tested under static or cyclic loading. The load...

Building upon a previous investigation, this study reports a total of 13 experimental tests on austenitic and duplex stainless steel T-stubs subject to monotonic loading. The structural behaviour of the tested T-stub specimens, including load versus displacement (F-Δ) curves and corresponding failure modes, was obtained and is reported herein. The...

The use of grout-filled double-skin tubular (GFDST) sections in civil, bridge and offshore engineering applications is rapidly increasing. The design of such composite members is not directly covered by design codes, despite recent research studies investigating their performance, proposing design equations or modifying existing codified methods. A...

The structural behaviour of beam-to-column joints with double extended end-plate connections is experimentally and numerically investigated in this paper. Two stainless steel grades representing austenitic and duplex stainless steel (i.e. EN 1.4301 and EN 1.4462 respectively) have been considered, whilst a joint made of the carbon steel grade Q345B...

This paper reports the results of a numerical investigation into the response of axially restrained austenitic stainless steel beams in fire, where in addition to the degradation of strength and stiffness at elevated temperatures, the influence of thermally induced stresses, are also included. The finite element (FE) programme ABAQUS has been used...

This paper presents a two-dimensional nonlinear finite element (FE) model for reinforced concrete (RC) beams strengthened in shear with embedded steel bars. A rotating crack model, where the crack direction changes with the change in the direction of the principal tensile stress, was used for the concrete. The steel reinforcement was modelled as a...

This paper examines the behaviour of reinforced concrete (RC) T-beams strengthened in shear with deep embedment (DE) glass fibre reinforced polymer (GFRP) bars. Tests were conducted on a control beam as well as two DE GFRP-strengthened beams with existing steel-to-FRP shear reinforcement ratios of 0.44 and 0.88. The shear strength enhancement decre...

The structural behavior of prestressed high strength steel (HSS) tubular members is investigated through the execution of advanced finite element modeling. Numerical models are developed and validated against published experimental data on HSS tubular members subjected to different levels of initial prestress and loaded either in tension or compres...

Size effect in shear-deficient reinforced concrete (RC) beams instigates a reduction in shear stress at failure with the increase in beam size. However, size effect in RC beams shear-strengthened with deep embedment (DE), also known as embedded through section (ETS), fibre reinforced polymer (FRP) bars is yet to be fully understood. This paper inve...

Structures used for temporary works are lightweight so that they are easy to transport, erect and dismantle. Particular care should be taken in their design as local instabilities could arise due to their thin-walled nature. This article presents 12 tests on proprietary soldier beams subjected to two concentrate opposing loads applied simultaneousl...

The structural behaviour of prestressed high strength steel arched trusses is studied in this paper through experimentation and numerical modelling. Four 11 m span prestressed arched trusses fabricated from S460 hot finished square hollow section members were loaded vertically to failure. Three of the tested trusses were prestressed to different le...

The shear behaviour of stainless steel plate girders investigated in this study is related to the introduction of diagonal stiffeners. Four plate girders with or without diagonal stiffeners were fabricated by welding hot-rolled stainless steel plates of different thicknesses. All the plate girders were tested to failure subject to shear loading. Th...

A comprehensive experimental study on structural behaviour of stainless steel bolted T-stub connections is presented in this paper. A total of 27 stainless steel bolted T-stubs with various geometric configurations were fabricated from hot-rolled stainless steel plates and assembled with stainless steel bolts. Two stainless steel grades - austeniti...

Several techniques for improving performance of reinforced concrete (RC) beam-column (BC) connections have been developed in last two decades, but these techniques have been criticized for being labourintensive and susceptible to premature de-bonding. To overcome these shortcomings, a novel technique utilising embedded steel bars has been developed...

High strength steels (HSS) are increasingly used in structural engineering applications owing to their high strength to weight ratio. Due to the inferior ductility and strain-hardening characteristics of HSS and the lack of relevant structural performance data, plastic design is currently not permitted for HSS indeterminate structures. To this end,...

Shear-deficient RC beam-column joints (BCJs) represent one of the main factors behind the seismic damage suffered by existing concrete infrastructure, as well as the associated loss of life. This study presents a novel technique for strengthening shear-deficient RC BCJs. The technique involves embedding carbon fiber–reinforced polymer (CFRP) or ste...

Structures used for temporary works are lightweight so that they are easy to transport, erect and dismantle. Design of such structures shall account for the various construction stages and hence various actions that may be applied to ensure that the structure remains stable and safe. Particular care should be taken in their design as local instabil...

In this paper an 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 parallel with the tests, finite element models were developed. Upon validation against the experimental results, parametric studies were conducted to expan...

This paper reports a detailed numerical (FE) study on planar stainless steel beam-to-column joints. A nonlinear FE model is developed and validated against the first set on full-scale tests on stainless steel beam-to-column joints reported in the companion paper. The FE model is shown to accurately replicate the experimentally determined, initial s...

In modern days, railway transportation comprising freight transport and passenger transport is the lifeblood of social economy of a country, especially for developing countries. Railway transportation can adapt more natural conditions compared by air transportation and shipping, therefore the punctuality rate of railway transportation is the highes...

Research on stainless steel structures has primarily focused on the structural response of individual members, whilst the response of joints has received far less attention to date. This paper reports for the first time full-scale tests on stainless steel beam-to-column joints, subjected to static monotonic loads, whilst the companion paper reports...

Abstract The application of high strength steels (HSS) in the construction industry can allow for lighter structures, more economic design and profound sustainability benefits. Even though most international structural design codes have included HSS within their contents, many of the recommended rules are widely based on assumed analogies with mild...

The benefits of high strength steel (HSS) as a structural material and its potential to lead to smaller sections and thus lighter structures has increased its use in the construction industry. Current design specifications for HSS are widely based on assumed analogies with normal strength steel, since they are based on a limited number of test data...

Due to lack of available experimental data, plastic design of stainless steel (SS) 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. The high initial material cost warrants the development of...

The recent increase in the use of high-strength steels (HSSs) in modern engineering practice necessitates a deeper understanding of their structural response. Given that HSS design specifications are largely based on a limited number of test data and assumed analogies with mild steel, their applicability to HSS sections needs to be assessed. In the...

The behaviour of hot-rolled high-strength steel (HSS) tubular sections under combined compression and uniaxial bending was investigated both experimentally and numerically. The experimental programme encompassed a series of material coupon tests, initial geometric imperfection measurements, residual stress measurements and 12 tests on stub columns...

The current paper discusses the simulation of the structural behaviour of prestressed tubular members in steel grade S460 and S690, through the execution of advanced numerical modelling. Numerical models are validated against published experimental data [1], in which different initial prestress levels and the presence of grouting has been examined...

An experimental investigation into the structural performance of compressed high strength steel (HSS) square and rectangular hollow sections is described in this paper. Both hot-rolled and cold-formed HSS sections were examined. In total six S460NH and five S690QH hot-rolled section sizes and three S500MC, two S700MC and four S960QC cold-formed sec...

Laser-welding is a high precision fabrication process suitable for joining a wide range of steels and stainless steels. Laser-welded structural stainless steel members, for which there are currently little experimental data owing to their recent introduction to the construction industry, are the focus of the present study. To address the lack of te...

High strength steels, considered in the context of the structural Eurocodes, as steels with a yield strength over 460 MPa, are gaining increasing attention from structural engineers and researchers owing to their potential to enable lighter and more economic structures. This paper focuses on the bending strength of hot-finished high strength steel...

The present paper discusses the simulation of the structural response of high strength steel prestressed trusses by means of advanced numerical modelling. In particular, detailed finite element models were developed in the general purpose FE software ABAQUS and validated against the experimental results of four vertically loaded S460 prestressed tr...

When subjected to elevated temperatures, steel displays a reduction in both strength and stiffness, its yield plateau vanishes and its response becomes increasingly nonlinear with pronounced strain hardening. For steel sections subjected to compressive stresses, the extent to which strain hardening can be exploited (i.e. the strain at which failure...

Substantial research has been conducted in recent years into the structural response of stainless steel components, with the focus being primarily on doubly symmetric cross-sections. Limited experimental data exist on non-doubly symmetric stainless steel sections in compression, while there is an absence of such data in bending, despite these secti...

Push-out tests have been conducted on 18 rectangular concrete-filled steel tubular (CFST) columns with the aim of studying the bond behaviour between the steel tube and the concrete infill. The obtained load-slip response and the distribution of the interface bond stress along the member length and around the cross-section for various load levels,...

The present study investigates the optimal structural configuration for steel planar tubular trusses and examines the effect of applying prestress via cables embedded to the bottom chord of the trusses on the response of the structure. At the first stage, topology optimisation of steel planar trusses subjected to vertical loads is performed with th...

The successful validation of a numerical model is presented that can realistically approximate the shear behavior of reinforced concrete (RC) T-section beams strengthened against shear with externally applied open hoop steel fiber reinforcing polymer (SFRP) strips. For this purpose, the measured load-deformation response of three (3) full-scale R/C...

An experimental study of stainless steel continuous beams not susceptible to lateral torsional buckling is reported in this paper and the applicability of plastic design methods to such structures is considered. A total of 18 two-span continuous beams were tested. Three cross-section types – cold-formed square hollow sections (SHS), cold-formed rec...

In this paper, material tests on tensile and corner coupons and a series of stub column tests on high strength steel hollow sections are reported. The steel grades considered vary between S460 and S960. Complementary measurements of local geometric imperfection shapes and magnitudes of the specimens are also reported. The stub column specimens were...

Load-reversed push-out tests have been carried out on 6 rectangular concrete-filled steel tubular (CFST) columns with the aim of investigating the nature of the bond between the concrete infill and the steel tube, the contribution of each bond stress component (i.e. chemical adhesion, microlocking and macrolocking) and the development of macrolocki...

To maintain consistency with carbon steel design guidance, the current European design code for stainless steel structures EN 1993-1-4 employs many of the relevant design expressions from the equivalent carbon steel design code EN 1993-1-1. While this is generally satisfactory, there are a number of instances in which overly conservative designs re...

The effect of element interaction and material nonlinearity on the ultimate capacity of stainless steel plated cross-sections is investigated in this paper. The focus of the research lies in cross-sections failing by local buckling; member instabilities, distortional buckling and interactions thereof with local buckling are not considered. The cros...

Stainless steel is well suited to a range of engineering applications owing to its durability and favourable mechanical properties. The most widely used grades of stainless steel are from the austenitic family and typically contain around 18% chromium and 8%–11% nickel — these grades have a relatively high initial material cost, due, in part, to th...

Analytical models with geometric non-linearities accounting for interactions between local and global instability modes leading to localized buckling in sandwich struts are formulated. For the core material response, two increasingly sophisticated bending models are compared against each other: Timoshenko beam theory (TBT) and Reddy–Bickford beam t...

Stainless steels are employed in a wide range of structural applications. The austenitic grades, particularly EN 1.4301 and EN 1.4401, and their low-carbon variants EN 1.4307 and EN 1.4404, are the most commonly used within construction, and these typically contain around 8%–11% nickel. The nickel represents a large portion of the total material co...

Structural hollow sections are predominantly square, rectangular or circular in profile. While square and circular hollow sections are often the most effective in resisting axial loads, rectangular hollow sections, with greater stiffness about one principal axis than the other, are generally more suitable in bending. Oval or elliptical hollow secti...

Cold-formed stainless steel oval hollow sections (OHS) offer the combined aesthetic appeal of circular hollow sections and stainless steel, together with the structural efficiency associated with cross-sections of differing geometric properties about their two principal axes. To date, no structural design guidance exists for these cross-sections, p...

Cross-section classification is an important concept in the design of metallic structures, as it addresses the susceptibility of a cross-section to local buckling and defines its appropriate design resistance. For structural stainless steel, test data on cross-section capacity have previously been relatively scarce. Existing design guidance has bee...