Konstantinos Daniel Tsavdaridis

Vierendeel Bending Study of Perforated Steel Beams with Various Novel Web Opening Shapes through Nonlinear Finite-Element Analyses

The Vierendeel mechanism is always critical in perforated steel beams with single large web openings, where global shear forces and Vierendeel moments co-exist. Thus far, the main parameters that are known to affect the structural behavior of such beams are the depth of the web opening, the critical opening length of the top tee-section and the web opening area. A comprehensive Finite Element (FE) study of four sizes of perforated steel sections with three different sizes of eleven standard and novel non-standard web opening shapes was undertaken, and their primary structural characteristics presented in detail in order to provide a simple design method for general practice. The different geometric parameters were isolated and studied in order to understand the significance of their effects and in turn advance the knowledge on the performance of perforated steel beams. An elaborate FE model was established, with both material and geometrical non-linearity, allowing load redistribution across the web openings and formation of the Vierendeel mechanism. The reduction of the global shear capacities, due to incorporation of the local Vierendeel moments acting on the top and bottom tee-sections, was obtained directly from the FE analysis. Following that, a comparison of the global shear-moment (V/M) interaction curves of the steel sections with various web opening shapes and sizes was established and empirical generalized V/M interaction curves developed. Moreover, the accurate position of the plastic hinges was determined together with the critical opening length and the Vierendeel parameter. This work has now shown that the shape of the web opening can also significantly affect the structural behavior of perforated beams, as opposed to the equivalent rectangular shape predominately used so far. In addition, the effect of the position of the web opening along the length of the perforated beam was revealed. The importance of the parameters that affect the structural performance of such beams is illustrated. The thorough examination of the computational results has led to useful conclusions and an elliptical form of a web opening is proposed for further study. The outcome of this study is considered as being relevant for practical applications.

Discrete Element Modelling of Masonry Infilled Steel Frames with Multiple Window Openings Subjected to Lateral Load Variations

Steel framed structures are routinely infilled with masonry or concrete walls. The infill offers in-plane shear re- sistance that adds to the one from the steel frame. However, the stiffness effect on the entire frames response is usually neglected. In recent years, researchers have recognised the lack of in-depth understanding on infilled steel frames; hence specialised computational tools have been developed to provide an easy way of assessing these interactive structural sys- tems and aid practising engineers in evaluating the overall behaviour. A computational model to study the behaviour of masonry infilled steel frames for the non-standard case of variable po- tential positions of openings and their interaction, when subjected to in-plane monotonic loading, is herein developed. Us- ing the Discrete Element Method (DEM) and the software UDEC, the masonry wall is modelled as an assemblage of dis- tinct deformable blocks while the mortar joints as zero thickness interfaces. The numerical model validated against full scale experimental tests found in the literature and a good agreement obtained. In addition, a series of parametric studies were performed to draw the significance of the size and location of the openings on the lateral load capacity, as well as the stiffness and failure mechanisms of the infilled steel frames.� From the results analyses, it was found that the inclusion of multiple openings significantly reduces the strength and stiffness of the system. In particular, placing an opening close to the point of application of the lateral load will result to further reduction of masonry infills stiffness.

Assessment of Perforated Steel Beam-to- Column Connections Subjected to Cyclic Loading

This article presents a study of fully fixed (welded) perforated beam-to-column connections, used as strengthening techniques to seismic-resistant design. The effect of using non-standard novel web opening configurations of variable depths and positions is investigated. The improvements on the structural behavior foreshadow the enhancements gained using these perforated members. It is concluded that using large isolated perforations is an effective way of improving the behavior of connections enhancing their ductility, rotational capacity and their energy dissipation capacity. Moreover, the connections with novel openings outperform the conventional ones; therefore, they can be suitably used in the aseismic design of steel frames.

Post-fire assessment and reinstatement of steel structures

Purpose This paper aims to present technical aspects of the assessment method and evaluation of fire damaged steel structures. The current work focuses on the behavior of structural normal steel (hot-rolled and cold-formed) and high-strength bolts after exposure to elevated temperatures. Information on stainless steel, cast iron and wrought iron is also presented. Design/methodology/approach Because of the complexity of the issue, an elaborate presentation of the mechanical properties influencing factors is followed. Subsequently, a wide range of experimental studies is extensively reviewed in the literature while simplified equations for determining the post-fire mechanical properties are proposed, following appropriate categorization. Moreover, the reinstatement survey is also comprehensively described. Findings Useful conclusions are drawn for the safe reuse of the structural elements and connection components. According to the parametric investigation of the aforementioned data, it can be safely concluded that the most common scenario of buildings after fire events, i.e. apart from excessively distorted structures, implies considerable remaining capacity of the structure, highlighting that subsequent demolition should not be the case, especially regarding critical infrastructure and buildings. Originality/value The stability of the structure as a whole is addressed, with aim to establish specific guidelines and code provisions for the correct appraisal and rehabilitation of fire damaged structures.

Deterioration of Basic Properties of the Materials in FRP-Strengthening RC Structures under Ultraviolet Exposure

This paper presents an experimental study of the basic properties of the main materials found in reinforced concrete (RC) structures strengthened by fibre reinforced polymer (FRP) sheets with scope to investigate the effect of ultraviolet (UV) exposure on the degradation of FRP, resin adhesive materials and concrete. The comparison studies focused on the physical change and mechanical properties of FRP sheet, and resin adhesive materials and concrete before and after UV exposure. However, the degradation mechanisms of the materials under UV exposure were not analyzed. The results show that the ultimate tensile strength and modulus of FRP sheets decrease with UV exposure time and the main degradation of FRP-strengthened RC structures is dependent on the degradation of resin adhesive materials. The increase in the number of FRP layers cannot help to reduce the effect of UV exposure on the performance of these materials. However, it was verified that carbon FRP materials have a relatively stable strength and elastic modulus, and the improvement of the compression strength of concrete was also observed after UV exposure.

Pushover Analysis of Steel Seismic Resistant Frames with Reduced Web Section and Reduced Beam Section Connections

The widespread brittle failure of welded beam-to-column connections caused by the 1994 Northridge and 1995 Kobe earthquakes highlighted the need for retrofitting measures effective in providing ductility to connections. Researchers presented the reduced beam section (RBS) as a viable option to prevent brittle failure at the connection weld. More recently, an alternative connection known as a reduced web section (RWS) has been developed as a potential replacement, and initial studies show ideal performance in terms of rotational capacity and ductility. This study performs a series of non-linear static pushover analyses using a modal load case on three steel moment-resisting frames (MRFs) of 4-storeys, 8-storeys and 16-storeys. The frames are studied with three different types of connections; fully-fixed moment connections, RBS connections and RWS connections, in order to compare the differences in capacity curves, inter-storey drifts and plastic hinge formation. The seismic-resistant connections have been modelled as non-linear hinges in ETABS, and their behaviour have been defined by moment-rotation curves presented in previous recent research studies. The frames are displacement controlled to the maximum displacement anticipated in a 2 in 50 earthquake. The study concludes that RWS connections perform satisfactorily when compared with frames with fully-fixed moment connections in terms of providing consistent inter-storey drifts in low to mid-rise frames, without significantly compromising the overall strength capacity of the frames. The use of RWSs in taller frames causes an increase in inter-storey drifts in the lower storeys, as well as causing a large reduction in strength capacity. Frames with RWS connections behave comparably to frames with RBS connections and are deemed a suitable replacement.

Novel Morphologies of Aluminium Cross-Sections through Structural Topology Optimization Techniques

In the last decades, the deployment of aluminium and its alloys in civil engineering fields has been increased significantly, due to the material’s special features accompanied by supportive technological and industrial development. However, the extent of aluminium structural applications in building activities is still rather limited and barriers related to strength and stability issues prevent its wider use. In the context of the extrusion characteristic, appropriate design in aluminium cross-sections can overcome inherent deficiencies, such as the material’s low elastic modulus.This paper investigates a new breed of cross-sectional design for aluminium members employing pioneering structural topology optimisation techniques. Topology optimisation problems utilise the firmest mathematical basis, to account for improved weight-to-stiffness ratio and perceived aesthetic appeal of specific structural forms. The current study investigates the application of structural topology optimisation to the design of aluminium beam and column cross-sections. Through a combination of 2D and 3D approaches, with a focus on post-processing and manufacturability, ten unique cross-sectional profiles are proposed. Additionally, the variation of cross-section along the member is also investigated in order to identify correlation between 2D and 3D topology optimisation results. Conclusions attempt to highlight the advantageous characteristics of aluminium use as well as the potential benefits to the more widespread implementation of topology optimization within the utilization of aluminium in civil/structural engineering.

Simplified Density Indexes of Walls and Tie-Columns for Confined Masonry Buildings in Seismic Zones

ABSTRACT This paper discusses and quantifies the minimum requirements of walls and tie-columns in confined masonry (CM) buildings located in earthquake-prone regions. A research database including 238 damaged CM buildings obtained from the 2008 Wenchuan earthquake survey is established and comprehensively examined. The requirements of masonry walls in CM buildings are discussed, and a simplified tie-column density index is proposed for evaluating the potential damage of the structures. Besides, the minimum requirements of reinforced concrete tie-columns and their maximum allowable spacing in CM buildings at different seismic intensity zones are discussed.

Novel Optimised Structural Aluminium Cross-Sections Towards 3D Printing

In the last decades, the deployment of aluminium and its alloys in engineering fields has been increased significantly, due to the material’s special features accompanied by supportive technological and industrial development such as the extrusion manufacturing method. However, the extent of aluminium structural applications in building activities is still rather limited, and barriers related to strength and stability issues prevent its wider use. In the context of topology optimisation, appropriate design in aluminium cross-sections can overcome inherent deficiencies, such as the material’s low elastic modulus.

Seismic resistant design of connections with the use of perforated beams

M buildings are developed as an alternative to conventional on-site construction because of more predictable costs and faster construction. While the use of modular buildings is increasing rapidly and this construction system is becoming more popular, research activities on structural components and materials used in modules, analysis and design methods and connection systems in the modular building are needed and are continuing. Modular construction aims to optimize the use of materials, while forming spaces comparable in size to conventional construction and to offer benefits of installation speed. The modules act as the primary structural system of the building, while another stabilization system such as stair or elevation core can be used as well. Modules transfer gravity loads and resist lateral loads through the module-tomodule connections. Therefore, the connections must be strong enough and have inherent ductility to transfer loads from one module to another and accommodate building deformation under gravity and lateral loads. The presentation will introduce commonly used connection systems in several types of modular construction. As modular systems are seldom used in highrise building construction and because of limitations of structural and module-to-module connection systems, they are rather used in shorter than 7-8 stories. The presentation will explore the nature of these limitations and offer suggestion for improved structural-connection systems that provide desirable levels of strength, stiffness and ductility. In particular, the presentation discusses the possibility of using distributed isolation system as one option in such solution schemes.In this study, a new beam model called sinusoidal beam is discussed based on experimental investigation. • The presentation exhibits the moment-rotation curves of fixed end-plate connection made from sinusoidal beams and evaluation the structural performance of sinusoidal beams.