Structural Steel Sections Research Articles

Axial compressive behavior of square composite columns confined by multiple spirals

This study elucidates experimentally and analytically the axial compressive load-carrying capacity and behavior of square composite steel and concrete columns confined by multiple interlocking spirals. The variables of the specimens included type of the lateral reinforcement (rectilinear hoops and multiple spirals), spacing of the lateral reinforcement, and shape of the structural steel section (cruciform and box-shaped). Specimens were tested under monotonically increased axial load. The test results demonstrated that the composite columns with multiple spirals achieved great axial load-carrying capacity and deformability because of the excellent concrete confinement attributed to the multiple interlocking spirals and the structural steel section. Smaller spacing of the spirals and larger area of the highly confined concrete in the composite columns resulted in the better strength and ductility of the columns. An analytical model was proposed to calculate the load–displacement relations of the specimens, and the model predicted well the behavior of the specimens. The effectiveness of the multiple interlocking spirals in the square composite columns was evident via this study.

Development of design rules in the AISC Design Guide for structural stainless steel

This paper describes the development of an AISC (American Institute of Steel Construction) Design Guide for hot rolled and welded structural stainless steel sections. Where stainless steel behaves in a similar way to carbon steel, the Design Guide simply refers to the relevant section in ANSI/AISC 360-10 Specification for Structural Steel Buildings. Where the guidance in the AISC Specification would be unconservative when applied to stainless steel, specific rules for stainless steel were derived and presented in a format as close as possible to the equivalent expressions in AISC 360. The stainless steel design rules were calibrated against an extensive database of test results on members and connections. A full reliability analysis was carried out to calculate the LRFD resistance factors; in most cases, the carbon steel resistance factors were shown to be applicable to stainless steel also.

Are Reinforced Concrete Girder Bridges More Economical Than Structural Steel Girder Bridges ? A South African Perspective

This study investigated the cost-effectiveness of steel girders compared with conventional reinforced concrete girders used in bridge construction in South Africa. The investigation considered an existing bridge which required widening as a result of increased traffic flow. The consulting engineers chose two 10 m reinforced concrete girders for the end spans, while two 22 m post-tensioned reinforced concrete girders were used for the central spans. To determine the cost-effectiveness of the consulting engineer’s choice, steel girders were designed for the 10 m and 22 m beams based on the relevant South African design codes of practice. The analysis was conducted for both non-composite and composite action between the steel girders and the reinforced concrete bridge deck. Based on the design calculations, a cost comparison was performed. The investigation revealed that steel girders are an economically viable option when off-the-shelf steel sections up to 10 m in length are considered. For the 10 m girders, a significant cost saving was achieved for both noncomposite and composite construction compared with reinforced concrete. However, for the 22 m spans, the post-tensioned reinforced concrete girders are significantly more cost-effective compared with steel plate girders. Thus, bridge design engineers should consider steel girders as an option during the conceptual design stage for end spans. A survey was also conducted among senior engineering professionals to determine the reason(s) for the apathy towards using structural steel sections as girders in bridge construction in South Africa.

Analysis of modern three-span suspension bridges with stiff in bending cables

Suspension bridges are one of the most effective bridge structures used for large spans to overlap. Recently, not only the single-span bridges but also multi-span suspension bridges have been used. The main issue of design and analysis shall consider the excessive deformability induced by the interaction of flexible and kinematic displacement. Stabilization of suspension bridges could be ensured by various means. The most effective and up-to-date measure applied to reduce displacements of suspension bridges is the application of the so-called “rigid” cables with appropriate bending stiffness instead of conventional flexible cables. These retaining elements demonstrate high corrosion stability; their cross-sections are designed using conventional structural steel sections, factory and fabricated connections are simple and firm. The main advanced feature of these cables is that these elements along with the suspended stiffening girder stabilize the initial shape of the bridge effectively. It shall be noted that analysis methods applied for these innovative three-span suspension bridges with “rigid” cables are still under development. There are only few individual publications describing the behaviour of a single-span suspension bridge. The article describes the modern suspension three-span bridge and provides analytic expressions of internal forces and displacements calculated considering the erection sequence.

Analysis of CFT, RCC and Steel Building Subjected to Lateral Loading

Abstract Steel–concrete composite columns are used extensively in modern buildings. Extensive research on composite columns in which structural steel section are encased in concrete have been carried out. In-filled composite columns, however have received limited attention compared to encased columns. In this paper a comparative study of 10, 20 and 30 storey Concrete Filled Steel Tube (CFT), R.C.C. and Steel building is done. Comparison of parameters like time period, displacement, base shear and load carrying capacity is done with steel and R.C.C structures. Result shows CFT building is good in load carrying capacity with small cross section of column.

Applications, Behaviour and Design of Composite Steel-Concrete Structures

The behaviour of composite steel-concrete beams subjected to pure flexure and the presence of flexure and shear is fairly well understood and provisions do exist in international codes of practice for their design, however in most instances the influence of the concrete slab is not included in the strength design of the composite beam in shear. Combined internal actions including the presence of torsion and flexure have also been considered of late. These actions combine to occur in edge beams and curved composite beams and thus are of significant practical interest. Of increasing interest has become the presence of axial force and flexure in composite beams. These internal actions need to be considered in the design of raking beams of stadia, elevated approach spans for bridges and interchanges and in the design of integral abutment bridges and cable stayed bridges. Furthermore, composite beams in floor systems for braced multi-storey buildings are often required to resist axial force, flexure and shear force. This paper considers the effects of the presence of axial force in conventional composite beams. The effects of different forms of axial force and flexure combinations are considered in this paper. An analytical treatment, experiments and design approaches are given in this paper which is useful for structural engineers. Furthermore research in this area is also discussed. This paper will also present the results of an extensive experimental series to study the behaviour of high performance steel sections subjected to transverse impact loads which are able to simulate either a collision or blast. The experimental program has considered both mild structural steel and stainless steel hollow sections both filled and unfilled being tested. The purpose of the tests was to identify the potential advantages of using concrete infill to increase the energy absorption capability of steel hollow sections.

Test Data on Intumescent Fire Protection for Structural Steel Sections in Thailand

Current fire safety regulations in Thailand require that primary structural steel components of buildings be protected to achieve a minimum of 3-hour fire-resistance rating. For steel roof structures, 1-hour or 2-hour fire-resistance ratings may be specified depending on the number of stories. The verification methods of fire-resistance ratings set forth in the regulations are ISO 834 and ASTM E119 standards. The current trend of fire protection system for steel structures is intumescent paint due to aesthetical reasons. However, the fire-resistance ratings attained by proprietary intumescent systems currently available in the market are inconclusive. It is therefore the aim of this paper to provide an insight of the fire-resistance ratings of different intumescent products based on the data collected from the fire tests conducted by the Fire Safety Research Center of Chulalongkorn University during the period of 2009 - 2011. A statistical analysis was also conducted to compare the test data with the fire-resistance ratings specified in the current fire safety regulations.

Behaviour of Concrete Filled Rectangular Steel Tube Column

The Concrete Filled Steel Tube (CFST) member has many advantages compared with the conventional concrete structural member made of steel reinforcement. CFSTs are frequently used for columns, caissons and for piers, deep foundations because of their large compressive stiffness. The FEA modeling using ANSYS software is adopted to investigate the load versus lateral deflection behavior of the composite sections. The effects of steel tube thickness and strength of in-filled concrete tubes are examined. The size of the column is 140 x 160 x 1500 mm and the grades of concrete infill are M20, M30 and M40. The thickness of the tube is taken as 2 mm, 3 mm, 4 mm, 5 mm and 6 mm and, the D/t ratio varies from 26.67 to 80.00. Since past few decades, composite steel-concrete construction of column and girder is being used in the construction industry. These composite sections have the rigidity and formability of reinforced concrete with the strength and speed of construction associated with structure, thereby making them economical. The steel and the concrete element in a composite member complement each other ideally. Composite members consisting of rectangular steel tubes filled with concrete are extensively used in structures involving very large applied moments, particularly in zones of high seismic risk. Concrete Filled Tubes (CFTs) have been used as girder, beam and columns in frame structures. A steel hollow section in-filled with concrete has higher strength and larger stiffness than the conventional structural steel section and reinforced concrete. Composite column are structural members, which are mainly subjected to forces and end moments. The steel tube serves as a formwork for casting the concrete, which reduces the construction cost. No other reinforcement is needed since the tube itself act as a longitudinal and lateral reinforcements for the concrete core. The continuous provided to the concrete core by the steel tube enhances the core's strength and ductility. The concrete core delays bending and buckling of the steel tube, while steel tube prevents the concrete from spalling. Also concrete filled tube (CFT) columns are suitable for tall buildings in high seismic regions since concrete delays the local buckling of steel hollow sections and increases the ductility of the section significantly. While there is a large number of studies on the behaviour of CFT columns and beam-columns; there is relatively little research reported on the flexural behaviour of concrete-filled hollow structural steel column. The structural behavior of a CFT is governed by the member strength, reflecting the fact that the load resistance is dependent not only on the material properties but also on the geometric properties of the entire member. Tests on CFTs by Bridge showed that the concrete core only provides approximately 7.5% of the capacity in members under pure bending. Lu and Kennedy studied strength on twelve beams of concrete-filled Steel Square and Rectangular Hollow Sections for examining the effects of different depth to width ratios and different values of shear span to depth. The tests showed that the ultimate flexural strengths of the composite beams are increased by about 10% - 30% over that of bare steel sections, depending on the relative proportions of steel and concrete. Although composite columns of concrete and steel were rarely used from the end of World War II until the early 1970s (Viest et al. 1997, 1.13), research had started a long time before, at the beginning of the 20th century. Combining of these materials had a number of motivations; steel columns were often encased in concrete to protect them from fire, while concrete columns were combined with structural steel as reinforcement. The model is created for different width-to-wall thickness ratios (from 26.67 to 80.00) and different concrete cube strengths (27.8, 42, 51 MPa). It is found that in general, concrete filling of the steel tube enhances strength, ductility and energy absorption especially for thinner sections. Han proposed a mechanics model that can predict the behaviour of concrete-filled hollow structural sections. In this paper, CFTs with three different wall thicknesses (Table 1) are selected (D/t = 26.67 - 80.00). Three different grades of concrete in-fills are considered. An effort is made to find the relative contributions of the steel tube and the confined concrete core to the moment capacity and deformation of CFTs under flexure.

Advanced analysis of hybrid steel and concrete frames: Part 1: Cross-section analysis technique and second-order analysis

Hybrid frames composed of steel, concrete and composite members are widely used to-date due to their structural efficiency and economy as alternatives to traditional bare steel system, especially in high-rise buildings. However, the present design of this structural form is both inconvenient and inconsistent as it needs several separated design codes for bare steel (BS), reinforced concrete (RC) and steel-concrete composite (SCC) elements. This paper proposes a second-order design method which requires only section capacity check without the need of using prescriptive formulae in different codes for various structural forms. The member-based design using linear analysis and the effective length assumption is replaced by the iterative second-order analysis. Using the Pointwise-Equilibrium-Polynomial (PEP) element, which allows for member P-δ effects and initial imperfections in conjunction with a robust nonlinear incremental-iterative procedure, the nonlinear response of individual members and the structural system is captured directly and used for structure resistance checks. The sectional failure surface method is introduced for member strength checking. In the generation of failure surfaces of the arbitrarily shaped cross sections, the stress distribution along the concrete component is considered by an equivalent stress block or a number of segments and the entire structural steel section will be meshed into fibres for determination of section capacity. Verifications of the proposed integrated analysis and design method based on section capacity check are conducted using several examples with accuracy of the method demonstrated.

Nonlinear behaviour of unprotected composite slim floor steel beams exposed to different fire conditions

An efficient nonlinear 3D finite element model has been developed to investigate the structural performance of composite slim floor steel beams with deep profiled steel decking under fire conditions. The composite steel beams were unprotected simply supported with different cross-sectional dimensions, structural steel sections, load ratios during fire and were subjected to different fire scenarios. The nonlinear material properties of steel, composite slim concrete floor and reinforcement bars were incorporated in the model at ambient and elevated temperatures. The interface between the structural steel section and composite slim concrete floor was also considered, allowing the bond behaviour to be modelled and the different components to retain its profile during the deformation of the composite beam. Furthermore the thermal properties of the interface were included in the finite element analysis. The finite element model has been validated against published fire tests on unprotected composite slim floor steel beams. The time–temperature relationships, deformed shapes at failure, time–vertical displacement relationships, failure modes and fire resistances of the composite steel beams were evaluated by the finite element model. Comparisons between predicted behaviour and that recorded in fire tests have shown that the finite element model can accurately predict the behaviour of the composite steel beams under fire conditions. Furthermore, the variables that influence the fire resistance and behaviour of the unprotected composite slim floor steel beams, comprising different load ratios during fire, cross-section geometries, beam length and fire scenarios, were investigated in parametric studies. It is shown that the failure of the composite beams under fire conditions occurred for the standard fire curve, but did not occur for the natural fires. The use of high strength structural steel considerably limited the vertical displacements after fire exposure. It is also shown that presence of additional top reinforcement mesh is necessary for composite beams exposed to short hot natural fires. The fire resistances of the composite beams obtained from the finite element analyses were compared with the design values obtained from the Eurocode 4 for composite beams at elevated temperatures. It is shown that the EC4 predictions are generally conservative for the design of composite slim floor steel beams heated using different fire scenarios.

Proposed residual stress model for roller bent steel wide flange sections

The manufacturing process of structural wide flange steel sections introduces residual stresses in the material. These stresses due to hot-rolling or welding influence the inelastic buckling response of structural steel members and need to be taken into account in the design. Based on experimental data standardized residual stress models have been proposed for inclusion in inelastic buckling analyses. By incorporating these residual stress models their effect on the resistance of beams and columns can be obtained. Residual stress models for roller bent steel sections are currently not available. Roller bent wide flange sections are manufactured by curving straight members at ambient temperature. This manufacturing technique, which is also known as roller bending, stresses the material beyond its yield stress, thereby overriding the initial residual stresses prior to bending and generating an entirely new pattern. This paper proposes a residual stress model for roller bent wide flange sections, based on earlier conducted numerical investigations which were validated by experimental research performed at Eindhoven University of Technology. The proposed residual stress model can serve as an initial state of a roller bent steel section in fully non-linear finite element analyses to accurately predict its influence on the inelastic buckling response.

Finite element simulations of residual stresses in roller bent wide flange sections

Curved structural wide flange steel sections are frequently used in buildings or bridges. These sections are usually curved at ambient temperatures with a roller bending machine. This process alters the residual stress distribution, which may affect the elasto-plastic buckling behavior of arches. This paper presents a numerical modeling technique to estimate residual stresses in curved wide flange sections manufactured by the pyramid roller bending process. The technique incorporates material non-linearity, geometrical non-linearity and contact modeling. Numerically obtained residual stresses are compared to experimental results and good agreement was found for the top flange. Only moderate agreement was observed for the web but very good coherence was realized for the bottom flange. It is concluded that a finite element analysis can be used to estimate residual stresses in roller bent wide flange sections.

Behavior of T-shaped reinforced concrete beams partially confined by structural steel

External confinement of reinforced concrete (R/C) members with structural steel sections or fiber reinforcing wraps is commonly used to improve the flexural behavior of structural members. Flexural strengthening of R/C beams by external steel members is among the most effective and convenient techniques. A study is presented in this paper investigating the flexural behavior of R/C beams having T cross-sections partially confined (P/C) by a combination of various steel members connected together by intermittent batten plates. Four R/C specimens, representing dropped beams in solid slabs, were tested. One control beam had no confinement whereas the three other beams had four steel angles simply wrapped and tied around the stem by batten plates, two angles at the bottom corners of the stem and the other two angles at the stem-flange junctions. Two plates were placed on the top surface of the flange and connected by studs to the two angles at the bottom of the flange. The resulting P/C beams are categorized as partial composite beams because no shear connectors were used between the R/C beam and the jacketing bottom-tension steel angles as in the case of conventional composite beams. All specimens were tested in positive bending under two points loading. Test results revealed an enhancement in the flexural behavior, particularly in the post-yield range of loading, and ductility due to the proposed strengthening and partial composite effect. The number and spacing of the intermittent battens played a significant role in the behavior of the strengthened specimens. Analytical values of loads and deformations at yield and ultimate loading showed good agreement with the measured values.

Investigation of concrete encased steel composite columns at elevated temperatures

This paper presents a nonlinear 3-D finite element model investigating the behaviour of concrete encased steel composite columns at elevated temperatures. The composite columns were pin-ended axially loaded columns having different cross-sectional dimensions, different structural steel sections, different coarse aggregates and different load ratios during fire. The nonlinear material properties of steel, concrete, longitudinal and transverse reinforcement bars as well as the effect of concrete confinement at ambient and elevated temperatures were considered in the finite element models. The interface between the steel section and concrete, the longitudinal and transverse reinforcement bars, and the reinforcement bars and concrete were also considered allowing the bond behaviour to be modelled and the different components to retain its profile during the deformation of the column. The initial overall (out-of-straightness) geometric imperfection was carefully included in the model. The finite element model has been validated against published tests conducted at elevated temperatures. The time–temperature relationships, deformed shapes at failure, time–axial displacement relationships, failure modes and fire resistances of the columns were evaluated by the finite element model. It has been shown that the finite element model can accurately predict the behaviour of the columns at elevated temperatures. Furthermore, the variables that influence the fire resistance and behaviour of the composite columns comprising different load ratios during fire, different coarse aggregates and different slenderness ratios were investigated in parametric studies. It is shown that the fire resistance of the columns generally increases with the decrease in the column slenderness ratio as well as the increase in the structural steel ratio. It is also shown that the time–axial displacement relationship is considerably affected by the coarse aggregate. The fire resistances of the composite columns obtained from the finite element analyses were compared with the design values obtained from the Eurocode 4 for composite columns at elevated temperatures. It is shown that the EC4 is conservative for all the concrete encased steel composite columns, except for the columns having a load ratio of 0.5 as well as the columns having a slenderness ratio of 0.69 and a load ratio of 0.4.

Modeling of Residual Stresses in Structural Stainless Steel Sections

The influence of residual stresses on structural members is to cause premature yielding and loss of stiffness, often leading to deterioration of load carrying capacity. Knowledge of their magnitude and distribution is therefore important for both structural design and finite-element simulations, and hence extensive studies have been performed on structural carbon steel components. With greater emphasis now being placed on durability and reducing consumption of resources, the use of stainless steel in construction is growing, heralding the need for a more precise understanding of its structural response. Stainless steel exhibits differing physical and thermal properties from carbon steel, both of which influence the formation of residual stresses, and it cannot simply be assumed that residual stress models for carbon steel are also appropriate for stainless steel. This paper examines all existing data on residual stresses in stainless steel sections, including data generated from a recent experimental program carried out at Imperial College, London and summarized herein. The collated residual stress data have been used to develop models for predicting the magnitude and distribution of residual stresses in press braked, cold rolled, hot rolled, and fabricated stainless steel structural sections.

Residual stresses in cold-rolled stainless steel hollow sections

Stainless steel exhibits a pronounced response to cold-work and heat input. As a result, the behaviour of structural stainless steel sections, as influenced by strength, ductility and residual stress presence, is sensitive to the precise means by which the sections are produced. This paper explores the presence and influence of residual stresses in cold-rolled stainless steel box sections using experimental and numerical techniques. In previous studies, residual stress magnitudes have been inferred from surface strain measurements and an assumed through-thickness stress distribution. In the present study, through-thickness residual stresses in cold-rolled stainless steel box sections have been measured directly by means of X-ray diffraction and their effect on structural behaviour has been carefully assessed through detailed non-linear numerical modelling. Geometric imperfections, flat and corner material properties and the average compressive response of stainless steel box sections were also examined experimentally and the results have been fully reported. From the X-ray diffraction measurements, it was concluded that the influence of through-thickness (bending) residual stresses in cold-rolled stainless steel box sections could be effectively represented by a rectangular stress block distribution. The developed ABAQUS numerical models included features such as non-linear material stress–strain characteristics, initial geometric imperfections, residual stresses (membrane and bending) and enhanced strength corner properties. The residual stresses, together with the corresponding plastic strains, were included in the FE models by means of the SIGINI and HARDINI Fortran subroutines. Of the two residual stress components, the bending residual stresses were found to be larger in magnitude and of greater (often positive) influence on the structural behaviour of thin-walled cold-formed stainless steel sections.

A Performance-Based Design Approach for Coupled Core Wall Systems with Diagonally Reinforced Concrete Coupling Beams

Coupled core wall systems (CCWs) are lateral force resisting systems that can provide remarkable lateral stiffness for mid- to high-rise buildings, exceeding the lateral stiffness of isolated walls while providing the redundancy and force redistribution capabilities of framed systems. The lateral stiffness provided by CCWs largely depends on the type of coupling beams used to transfer forces between wall piers. Diagonally-reinforced concrete coupling beams are one of the more common details although composite alternatives (e.g., those using structural steel W-shapes, hollow structural steel sections, or embedded steel plates) or beams with rhombic reinforcement are increasingly being selected as viable alternatives. Despite the favorable behavior exhibited by diagonally-reinforced coupling beams in experimental studies, designing and constructing diagonally-reinforced coupling beams having practical span-to-depth ratios presents significant difficulties, impacting the use of CCWs as a viable lateral force resisting system. This paper presents a performance-based design (PBD) approach that allows the designer to successfully proportion a code-compliant CCW system that addresses the shortcomings related to the traditional strength-based design approach. A prototype building is designed following both approaches, and is analyzed both statically and dynamically. Results show that the PBD approach produces a code-compliant structure that satisfies the most pressing constructability constraints.

Behavior of Integrated Crosstie Trackwork System

Light rail systems are an important transportation mode in urban centers. An advanced rail transit system has been developed that utilizes linear induction motors (LIM) for propulsion and braking of the vehicles. Due to the tight motor-to-rail air gap tolerances required for the efficient operation of the LIM system, the trackwork requires special consideration. An innovative crosstie trackwork system has been developed to address competing requirements for high stiffness to ensure efficient operation of the LIM, and low track stiffness for acceptable ride quality. The crosstie incorporates a hollow structural steel section welded at each end to formed steel base plates which are supported by elastomeric pads. The crosstie supports steel running rails. This paper describes a finite-element model developed to predict the response of a crosstie to loads that simulate the passage of a steel wheeled transit vehicle. The model uses tetrahedral elements for the hollow structural steel section and the base plates. The elastomeric pads are modeled using elastic foundation elements. The model predicts stresses and deflections in the crosstie. An experimental program that was carried out on the crosstie to investigate its fatigue performance and to obtain data to verify the finite-element model is also described. The model conservatively predicts crosstie deflections and stresses. The hot spot stress approach is used to provide a conservative fatigue life prediction of the crosstie.

Minimizing Cutting Wastes of Reinforcement Steel Bars Using Genetic Algorithms and Integer Programming Models

Materials that are in the form of one-dimensional stocks such as steel rebars, structural steel sections, and dimensional lumber generate a major fraction of the generated construction waste. Cutting one-dimensional stocks to suit the construction project requirements result in trim or cutting losses, which is the major cause of the one-dimensional construction waste. The optimization problem of minimizing the trim losses is known as the cutting stock problem (CSP). In this paper, three approaches for solving the one-dimensional cutting stock problem are presented. A genetic algorithm (GA) model, a linear programming (LP) model, and an integer programming (IP) model were developed to solve the one-dimensional CSP. Three real life case studies from a steel workshop have been studied. The generated cutting schedules using the GA, LP, and IP approaches are presented and compared to the actual workshop's cutting schedules. The comparison shows a high potential of savings that could be achieved using such techniques. Additionally, a user friendly Visual Basic computer program that utilizes genetic algorithms for solving the one-dimensional CSP is presented.

Residual stress analysis of structural stainless steel sections

The magnitude and distribution of residual stresses in structural carbon steel sections have been thoroughly investigated. However, few residual stress measurements have been made on structural stainless steel sections. Stainless steel has differing material stress–strain characteristics and thermal properties to carbon steel, both of which influence the formation of residual stresses. This suggests that established carbon steel residual stress models may not be appropriate for stainless steel. With increased use of stainless steel in load bearing applications, it is important to establish the residual stresses that exist within structural members. An experimental program to quantify the residual stresses in stainless steel sections from three different production routes has therefore been carried out. Comprehensive residual stress distributions have been obtained for three hot rolled angles, eight press braked angles and seven cold rolled box sections, with a total of over 800 readings taken. This paper presents the experimental techniques implemented and the residual stress distributions obtained as well as discussing the assumptions commonly made regarding through thickness residual stress variations. In the hot rolled and press braked sections, residual stresses were typically found to be below 20% of the material 0.2% proof stress, though for the cold rolled box sections, whilst membrane residual stresses were relatively low, bending residual stresses were found to be between 40% and 70% of the material 0.2% proof stress.