My specific field of interest from the viewpoint of research is steel structures, hence, my research efforts have been targetted towards investigating problems on various topics of this interesting branch of structural engineering. I research efficient ways of designing metal structures (hot and cold formed steel, stainless steel, aluminum and high strength steel) with special emphasis on members and connections that these structures are composed of. My research has tackled problems regarding safe and economic design of these system components under the effects of static as well as dynamic earthquake effects. Utilizing advanced numerical modelling supported by physical experimental testing my research ultimately aims to fill the gap in existing structural design guidelines. On a system level I am interested in understanding the behavior of light gauge steel framed structures under the effects of static gravity and lateral seismic loads. One peculiar application for light gauge steel structures is steel storage racks used in warehouses. The design of these structures are challenging because they're built as lightly as possible but on the other hand they are very heavily loaded, and they can collapse for a range of reasons including the strong seismic effects.
Seismic Vulnerability and Risk Assessment of Industrial Storage Racking Systems
Industrial storage racking systems (ISRS) are extensively used in regions where seismic risk is high and hence the effective seismic resistant design of new systems and as well as the identification of seismic performance and risk assessment of existing systems is vital primarily for the ISRS users and also for the insurance companies. The current project is being proposed with reference to this important motivation and it will include detailed laboratory testing and numerical analysis studies based on experimentally validated models. As a result of the planned numerical studies seismic fragility curves for storage racking systems will be produced which will lead to the development of risk identification algorithms for loss estimation. Laboratory test program will be planned to carry out physical tests both on members and the system as a whole. The program will be comprised of tests to better understand the structural behavior on element and connection level, pushover tests to investigate the behavior of frames in lateral direction in linear and non-linear regions and finally full scale dynamic tests which would simulate the actual seismic behavior of 3-dimensional systems. Full scale dynamic tests will present the most realistic representation of the actual behavior of the ISRSs providing a thorough understanding of the cyclic behavior of the members and connections within the system as well as the dynamic friction behavior of the stored palletized products
Stability Criteria for Thin-Walled Box Columns of High Performance Steel (HPS) in Axial Compression
The goal of this project sponsored by British Steel plc. was to provide a rational basis for the development of refined rules for the design of thin-walled axially compressed fabricated box columns of HPS. A critical assessment of current design practice (Eurocode 3 provisions) with respect to welded box columns was carried out that revealed the implications of existing code formulations for High Performance Steel (HPS) columns (with a yield strength of 690 MPa, in particular). Numerical modelling of thin-walled welded box columns in mild steel and HPS were performed by using theoretically & experimentally validated finite element models. Design recommendations for the design of thin-walled welded HPS box columns were reviewed and suggestions were made for more efficient design of HPS in welded box columns comprising of plates with high width-to-thickness ratio.
Stainless steel circular hollow section members
The use of stainless steel structural members has grown rapidly in recent years. This is mainly due to the fact that stainless steel offers favorable strength, ductility, and fire/corrosion resistance properties and a pleasing appearance. Through efficient design, higher material costs for stainless steel would be offset by using less material. In that context, research studies on structural stainless steel have mostly covered issues that focus on more efficient design of structural stainless steel members.This research covered an experimental/numerical study on stainless steel CHS members under bending, which were then critically examined and compared with currently available design guidance, in terms of strength and cross section stability. The test specimens were provided by Avesta Sheffield.
Corrugated web steel beams research
Steel corrugated web beams are fabricated girders with a thin-walled, corrugated web and wide steel plate flanges. Owing to its profiled form, corrugated web exhibits an enhanced shear stability and hence eliminate the need for transverse stiffeners or thicker web plates. In this respect, it is an innovative design where the amount of web material is optimized through the inherent stability provided by profiling of the web. In this research project we have focused on the effect of web openings on the transverse load carrying capacity of steel beams with sinusoidally corrugated webs. Various cases were analyzed including the size of the openings and the corrugation density which is a function of the magnitude and length of the sine wave. Models without web holes were also analyzed and compared with other cases which were all together examined in terms of load deformation characteristics and ultimate web shear resistance.
Strength and ductility of stainless steel bolted connections
As part of the growing interest in exploting stainless steel in structural applications a research program was carried out to study the strength and ductility behaviour of stainless steel bolted plates under in-plane tension. An experimentally validated finite element (FE) program was used for this purpose. A numerical parametric study was organized which includes examining the behavior of stainless steel plate models with various proportions, bolt locations and in two different material grades. The models were designed to fail particularly in bolt tear-out and material piling-up modes. In the numerical simulation of the models, non-linear stress-strain material behavior of stainless steel was considered by using expressions which represent the full range of strains up to the ultimate tensile strain. Using the results of the parametric study, the effect of variations in bolt positions, such as end and edge distance and bolt pitch distance on bearing resistance of stainless steel bolted plates under in-plane tension has been investigated. The results obtained are critically examined using design estimations of the currently available international design guidance
Effect of web penetrations on the strength of cold formed steel sections
Cold-formed steel sections are increasingly used in residential and commercial construction as both primary and secondary framing members. For ease of installation of electrical or plumbing services one preferred method is to provide openings in the web of cold formed steel members. Therefore it is vital to understand fully the effect of such openings on the ultimate strength of such members. In this research project we have focused on the effect of circular form web openings within a wide range of member height-to-hole diameter ratio. We have extended the investigation well above the limits set by the current codes of practice. Experimentally validated numerical tools were extensively utilized.
Stainless steel tubular member welded end connections
Among the various alternatives to make a steel tubular member connection, making a slotted and gusset plate welded connection is one of the most frequently preferred alternatives. This type of connection is essentially an end connection that is made by slotting the tube longitudinally, inserting the gusset plate and then placing longitudinal fillet welds at the tube-to-plate interface. In this study we have performed an experimental study on the behaviour of such connections in stainless steel. 24 specimens were physically tested under concentrically applied axial tensile forces for varying tube-to-gusset plate weld lengths. Both circular and box section members were considered in the test program. Load-deformation curves were obtained and comparisons were made in terms of strength and ductility. The results obtained from the study were then critically examined and compared with currently available design guidance for slotted gusset plate welded tubular end connections. It is noted that no specific rules exist in international specifications on structural stainless steel which cover the design of such connections. Therefore, the results of this study are compared with the existing design rules for carbon steel.
Investigation of steel storage rack column behaviour under axial compression
The research project focused on the prediction of the load carrying capacity of perforated rack columns using the direct strength method (DSM). The procedure involves the prediction of the elastic buckling loads of members with perforations and the assessment of the accuracy of the DSM buckling curves when applied to storage rack columns with complex cross-sections and with multiple perforations along their length. Very promising results were obtained that would allow substituting the distortional buckling tests, that are currently carried out in the process of design of these columns, by a simple and easy to apply calculation procedure.
Investigations on the effect of joint fixity in braced cold formed steel upright frames
Shear stiffness of braced upright frames in steel storage racking systems is an important parameter in identifying the transverse stability and strength of the frames in the cross-aisle direction. It is also directly related to the fixity of the brace member connections to the main upright columns. In this research work, the behavior of steel rack column-to-brace member connections (as applied mostly in North America) was investigated by using Finite Element Analysis under the effects of axial tension and compression on the brace member. Finite Element Analysis models were produced, by using ABAQUS, for two different brace cross-sections and configurations (brace member horizontal or diagonal to the lipped C section column). The brace member cross sections are C sections without lips and for both configurations (horizontal and diagonal) they are welded to the lips of the column in two ways being “flush” and “extended” over the lips. Strength and stiffness of the connections were identified and results were related to the behavior of frames with such connections.
Cyclic behavior and design of steel boltless connections
Steel storage rack systems play a key role in the industrial supply chain by providing efficient storage spaces for industrial products. Safe storage of products is of vital importance to prevent both economic and possible human life losses. Among various possible reasons that could risk the safety of the systems, one important reason is the earthquake. The flexibility and low-redundancy characteristics of lightweight steel storage racking systems may complicate the behavior of rack frames under lateral seismic effects. In particular, the behavior of the hooked beam-to-column connections (boltless) plays an important role in the seismic behavior of these structures. From this viewpoint, in this resarch work we have focused on the cyclic behavior of the hooked beam-to-column connections and investigate possible practical ways to upgrade the strength and energy dissipation characteristics of existing hooked connections
Strength of complex cross-section cold formed steel columns with multiple perforations
Steel storage rack columns face difficulties for their design as different manufacturers apply different complex forms of cross-sections with various forms of perforations existing along their lengths. As a result, cold-formed steel storage rack columns cannot be designed based on a unified design method. The non-linear finite element analysis is considered to be the best alternative to experimental testing, but still it cannot be considered as a practical way for design. From this viewpoint, this research study strives to contribute to the determination and use of an analytical procedure for checking the strength and stability of light gauge steel rack columns. By producing additional experimental data regarding the strength of columns within a practical range of column slenderness values, the study provides strong evidence for the validty of a currently suggested analytical formulation for the design of such columns and eliminating the need for physical testing.
Effect of wall thickness on the behavior of steel plate wall frame systems
The purpose of this work is to identify the building response to variations in modeling thicknesses for the steel plate shear wall systems. Different frame models for this system were developed and nonlinear pushover analysis were carried out. The frames investigated involved nonlineer hinges for the beam and column ends and analysis parameters for the pushover analysis. Static pushover analysis was used to assess the performance of frames subjected to lateral forces. The global storey level and roof displacement demands, storey drift ratio demands, base shears and structural periods were obtained by subjecting the eleven frames to a set of lateral forces. The results are compared to evaluate the influence of plate thickness on the nonlinear response of the frames. According to the results obtained in the studies, it is concluded that varying the plate thickness has a significant effect on the linear and nonlinear response of the frames. It was found out that increasing the plate thickness results in higher elastic frame stiffness and a higher lateral load resisting capacity. However, frame ductility reduces in frames with plates of higher thickness.