Zlatko Marković

Composite steel and concrete structures are widely used in modern civil engineering due to their structural efficiency and economic performance. However, conventional composite systems limit the possibility of full structural disassembly and reuse of steel structure elements and composite slabs, which is increasingly important in sustainable construction. Ultra-High-Performance Fiber Reinforced Cementitious Composites (UHPFRC) provide very high strength, improved tensile behavior and enhanced durability, enabling thinner slabs and reduced structural weight, as well as reduced CO2 consumtion. This paper reviews the most important mechanical and rheological characteristics of UHPFRCC and discusses its potential application in composite structures from a sustainability circular economy perspective.

The aim of this study was evaluation of atmospheric corrosion of structural steel S235JR in an industrial environment. General corrosion testing was carried out for six months in the field, at selected atmospheric corrosion stations, near the Sulphuric acid plant, in the Electrolytic refining plant and next to the automatic air quality monitoring station in the city of Bor, Serbia. The results were compared with the standard specimens stored in the laboratory. The steel S235JR specimens were characterized regarding mechanical characteristics by tensile testing. With the aim of assessing the mutual effect of corrosion and polluted industrial environment meteorological parameters were also determined, as well as pollutants in the atmosphere (mainly SO2). The X-ray diffraction method was used to identify the composition of corrosion products. Research within this work enabled a better understanding of the behavior of structural steel S235JR in which there was a reduction in load capacity due to corrosion. The corrosion rates obtained under each tested exposure condition showed noticeable differences. It was found that depending on the content of pollutants in the atmosphere and the location of the steel specimen, the corrosion products represented different compounds and solid phases.

Although various atmospheric corrosion simulation models have been developed that give good results, industrial environments are still challenging. This paper aims to investigate the effect industrial atmospheres in Bor on the mechanical properties of structural steel S235JR and to create a constitutive model and also laboratory experimental conditions that will give the best results as an accelerated corrosion test. Atmospheric corrosion tests lasted six months, using sites close to the Electrolytic Refining Plant and Sulphuric Acid Plant, as well as air quality monitoring stations at a remote location in the city of Bor. The laboratory experiments included a salt chamber test lasting 120 h and 240 h and immersing the specimen in the electrolyte from the Electrolytic Refining Plant for 30 days. The results were compared with the standard specimens stored in the laboratory. The X-ray diffraction (XRD) method was used to identify the composition of corrosion products. The scanning electron microscopy (SEM) analysis was applied to analyze the fracture surfaces of the specimens. The use of the Complete Gurson Model (CGM) described the tensile characteristics of the corroded specimens. The study has shown that an enhanced acceleration model and conditions could be developed using numerical analysis of the test results.

Multi-storey car park buildings with steel–concrete composite floor structures are widespread in construction due to the distinct benefits of the implemented structural system. Although there are various possibilities for accomplishing composite action between a steel beam and a concrete slab, some solutions, such as friction-grip bolts commonly applied in the 1970s, did not show good durability. An example is the multi-storey car park building “Obilićev venac” in Belgrade. This case study presents two methods for life extension of the car park building structure. Both approaches focus on applying welded headed studs with the primary intention of providing a durable shear connection. While the first method has been applied during the structure’s reconstruction, the second method is proposed as a novel solution for implementation in steel–concrete composite floors. The application of the proposed connection is discussed and the results of the experimental and numerical research conducted are presented.

This paper aims to develop design recommendations for closely spaced built-up stainless steel columns, based on findings gained in performed research at the University of Belgrade. The research focuses on pin-ended built-up columns formed from two press-braked channel chords oriented back-to-back and addresses their flexural buckling capacity about the minor axis. The impact of overall and local chord slenderness, interconnection stiffness, geometric imperfections and material nonlinearity is evaluated. In order to fully exploit their structural performance, two separate approaches for the design of built-up columns with welded or bolted interconnections are defined that include different formulas for shear stiffness.

The design rules for centrically compressed stainless steel equal-leg angle members are not explicitly stated in the current European standard SRPS EN 1993-1-4. This paper summarizes the results of extensive research conducted on this type of structural elements aiming to define recommendations for their design. Based on a systematic experimental investigation, a detailed numerical analysis was performed, and a database of columns' resistances were defined. Material and geometric nonlinear analysis included three key stainless steel alloys, austenitic, ferritic and duplex. The design curves for flexural and flexural-torsional buckling check have been proposed in accordance with European codified procedures.

Human perception of floor vibrations and uncompromised serviceability of equipment are two most important acceptability criteria considering floor vibrations. While verification of deflection is a simple and well-known procedure in structures' design for serviceability limit state, the fulfilment of floor vibrations acceptability criteria are presented in different standards in the form of various calculation procedures. Results achieved through those calculation procedures are presented in the form of various classification of floor structures. Classification of composite floor structures due to vibrations is inconsistent considering different calculation procedures. Comparison of various calculation procedures for the definition of composite floor vibrations is presented in this paper. In addition, a parametric analysis is performed on the wide range of steel-concrete composite floor structures, through analysis of various composite floor layouts and a wide range of imposed loads values. The analysis of the relation between deflection, vertical vibrations and accelerations of steel-concrete composite floor beams is presented in this paper. The results of the parametric analysis are given through direct relation between deflections of composite beams and achieved floor class for the fulfilment of vibrations acceptability criteria due to the pedestrian walking.

One of the most important acceptance issues regarding the implementation of small-scale wind turbines in urban environments is related to human comfort. Turbine-induced vibrations can have a large influence on small-scale turbine implementation for urban wind harvesting. A typical five-storey steel-framed office building with a roof-mounted, horizontal-axis wind turbine was numerically analysed. The aim of the work was to investigate the increase in vibration after the installation of the turbine. A comparison was made between floor vibrations caused by wind action on the building only and by wind action on the building and turbine combined. The results were then compared with requirements given in various design codes. The main outcome of the analysis is that the installation of the turbine did not compromise the building's serviceability.

Even though structural elements of the elliptical hollow section (EHS) have been introduced to the construction market in the past years, the rules for their design were only partially introduced into the suitable codified procedures. The aim of this paper is to present a comparative numerical analysis of behaviour of coldformed and hot-finished EHS columns exposed to flexural buckling under pure axial compression. Pinended columns of a various slenderness without lateral restrains and with incorporated geometrical imperfections are analysed. Material nonlinear behaviour is included through published experimental tensile test results, conducted in previous researches. In addition, numerical simulations of stub column behaviour are performed in order to obtain a cross-section compressive resistance. Results of the finite element analysis are compared to the design criteria defined in the draft version of Eurocode EN 1993-1-1:2015 and in North American specification for cold-formed member design AISI-S100. It is observed that North American standard provides more accurate predictions of both a crosssection resistance and a buckling column resistance. Equivalent diameter method described in Eurocode 3 led to more conservative results. According to the obtained numerical results, similar buckling behaviour is observed for both hot-finished and cold-formed columns of higher slenderness, while in the lower slenderness region, coldformed compressed members tend to lower buckling curves. Underestimation of a column buckling resistance according to Eurocode regulations is noticed for coldformed members of a higher slenderness.