The ways of designing and building steel girder bridges with a composite concrete deck vary much between different parts of the world. A bridge system with twin steel I-girders or a concept with multiple (more than two) girders can be used. The design and use of details and secondary systems also vary a lot. In order to give horizontal stabilization and distribute horizontal loads, bracing between the I-girders bracings are often used. Although not so common, the bracing can also be used to distribute vertical loads between the main girders. To describe and to analyze the possible impact from using a lateral bracing, this paper describes the design of a curved bridge in Guatemala City and its challenges. The new Bridge over the Pinula River is designed as a steel-concrete composite bridge with multiple steel girders with a concrete deck on top and has lateral bracing between the girders. The bridge is used as a case study to analyze the impact from a lateral bracing system on the vertical load distribution between the longitudinal girders. The bridge was designed with lateral bracing between the top flanges along the whole bridge and with bracing between the lower flanges near the supports. The case study shows that the distribution of eccentric vertical loads between the longitudinal girders can be improved by using lateral bracing between the lower flanges for multiple girders. In some cases, it may not be beneficial to use lateral bracings along the whole bridge length, like for example this bridge. In this case due to the governing design cases in the construction stages where these bracings influenced the torsional stiffness of the bridge in such way that an unfavorable distribution of the support reactions between the six girders at some supports was achieved.

This paper describes a study of the S650 high strength steel material properties including the effect of cold-formed angle. Coupon specimens with different cold-formed angles (90°, 100°, 120°, 140°, 160° and 180°) and different thicknesses (4 mm and 6 mm) were examined. Relationships between cold-formed angle and yield stress as well as tensile stress of the material were determined, based on the tensile coupon test results. Yield and tensile stresses assessed by considering the influence of the cold-formed angles were compared with those without considering this influence. Analyses revealed that both yield and tensile stresses decreased with increasing cold-formed angle. Ductile-damage material models available in the finite element analysis software ABAQUS were used to simulate tensile coupon tests. The experimental and numerical results showed good agreements.

This paper describes a study of the behaviour of cold-formed high strength steel angles. Thirty-six specimens with different cold-formed angles (90°, 100°, 120°, 140°, 160°, and 170°) and different thicknesses (4 mm and 6 mm) were considered. The initial geometric imperfections of the specimens were determined using the 3D laser scanning method. The magnitudes of these geometric imperfections for torsional and torsional-flexural buckling and flexural buckling analyses were proposed. The commercial finite element analysis (FEA) programme ABAQUS with shell elements S4R was used for finite element analyses. Different material strengths in corner and flat parts along with different proof stresses (0.2%, 0.01%, and 0.006%) were considered in the numerical models. The experimental and FEA results showed good agreement. Influence of cold-formed angle on non-dimensional slenderness and reduction factor curves of the 4 mm thick columns with 90° and 120° cold-formed angles was analysed.

Development of the wind energy industry continues to push the need for innovative solutions in terms of structural requirements. High-performance materials are thus needed to improve the efficiency of the structures and to ease the erection costs. The materials used for the towers have not improved significantly in the past years mainly because the design guidelines do not allow the efficient use of the high-strength steels. Lattice wind turbine towers could benefit from cost reductions if cold-formed high-strength steels would be used. Currently high-strength steel members have the same reductions factors for the relevant flexural buckling curve for cold-formed members regardless of the strength of steels. The paper discusses the approach towards the current European buckling curves and draws attention to potential limitations. The residual stresses present in rectangular hollow sections are discussed based on the method of fabrication. Different patterns of residual stresses are investigated by means of finite element simulations. The results indicate that the design codes slightly underestimate the flexural buckling resistance of high-strength steel members in the medium slenderness range.

This paper reports on the results from extensive finite element study of single storey industrial halls subjected to the action of localized fires. The results show offer structural resistance in fire situations that are much higher than would be expected from a prescriptive approach. It has been shown that actual resistance of these structural members in fire situations can exceed their primary resistance mechanism through flexural action only. Alternative load transfer mechanism through catenary action offers the added resistance at much higher temperatures than the conventional critical temperatures from prescriptive design. The paper also presents simplified calculation procedures that can be used to reasonably predict the structural resistance at elevated temperatures considering the catenary action

Friction connections with long open slotted holes have been proven to be a competitive alternative to the conventional flange connections in steel tubular towers for wind energy converters. As full-scale tests are not available, results of Finite Element Analysis (FEA) of the real-scale tower geometry are used in this paper to investigate the influence of tower cross section shape, execution tolerance (gap between the shells) and length of the connection on the bending resistance. Buckling behaviour of the shell in the vicinity of the friction connection in circular and polygonal towers is compared. The friction connection is thoroughly examined and recommendations for execution tolerances are given. The influence of two types of the execution tolerances on the connection strength is considered: inward bended "fingers", leading to inclined gaps, and a parallel gap created by different tower diameters.

The design, laboratory investigation and main results of an experimental programme on the joints of an innovative 3D truss made of high strength steel (HSS) is presented. An entire truss of triangular cross-section was fabricated (two compression chords and a single tension chord) to provide realistic loading conditions. Both compression and tension chords were fabricated by cold forming hot-rolled HSS plates by means of press braking. The chords were as follows:

• — an open angle-type profile with 45° contained angle as tension chord (U-chord),
• — a semi-closed octagonal profile made of 3 sectors bolted along their length every 1.2 diameters as compression chords (P-chord).

The focus of this study is on the tension chords joints where a pair of tension and a pair of compression diagonals converge. Joints were tested to ultimate load by introducing shear to one bay of the truss at a time. Two design approaches for the joints were tested resulting in four individual tests.

Ultimate load levels, stiffness and failure modes varied between the considered joint configurations. Stiffening increased the ultimate load by as much as 170% of that of the unstiffened version achieving higher utilisation of the tension chord, thus making more efficient use of HSS. The stiffness loss at loads close to failure varied between 60% – 80%. Two distinctive failure modes were observed, one caused by cracking of the welds connecting the diagonal's gusset plates to the tension chord while the second by cross-section tensile fracture of the circular hollow section (CHS) diagonal.

This paper introduces a novel joint based on a friction connection designed for column-splices. The jointwas developed within the scope of modular construction to improve the fast assembly of prefabricatedframes and to accommodate eventual misalignments. Gaps at the connection are considered on the jointhorizontal and vertical axis to accommodate misalignments whether they are rotations and/ordisplacements and so to allow for the easy fit of the columns. The efficiency of the joint resistance basedon different connection gaps subjected to uniform compression is assessed.

Structural fire design is exceedingly adopting the performance based approach. There are evidentadvantages of this approach compared to the prescriptive methods from codes. An analytical procedure, based on thereal performance, must accurately predict the beam behaviour in fire. The study presented here proposes one suchsimplified analytical procedure aim to predict the real behaviour of a restrained steel beam. The proposed analyticalprocedure is validated through FE Analysis using FE models validated through test results. The study also attempts toestablish the importance of using semi-rigid connection strength with respect to accurately predicting the behaviorof the restrained beam at catenary stage.

Structural fire design is exceedingly adopting the performance based approach. There are evident advantages of this approach compared to the prescriptive methods from codes. An analytical procedure, based on the real performance, must accurately predict the beam behaviour in fire. The study presented here proposes one such simplified analytical procedure aim to predict the real behaviour of a restrained steel beam. The proposed analytical procedure is validated through FE Analysis using FE models validated through test results. The study also attempts to establish the importance of using semi-rigid connection strength with respect to accurately predicting the behaviour of the restrained beam at catenary stage.

Wind turbine design today has the ability to operate at different rotational speed. Together with the pitch control system of the turbine, its maximum rotational speed is where it is required for safety reason and limit the system’s electrical and mechanical load. A study of structural response under different wind speed using numerical analysis software in order to assess fatigue performance of the steel tower. To understand the relationship between wind speed and tower structural response, structural stress are obtained with different constant wind speed. Analyses are carried out to assess the sensitivity of structural response to wind speed and gain understanding and relevancies of certain inputs in relation to variation of output. Second analysis is done by varying the time step and third analysis is to compare performance between the different software versions.

Prefabricated steel and concrete composite decks are an interesting option to improve competitiveness and sustainability of the composite structures. Longitudinal shear connection is usually established by grouped headed studs, but possible alternative solution is to use bolted shear connectors. Welded headed studs and bolts (grade 8.8) are experimentally examined in the push-out tests (four tests on each). The same arrangement and dimensions of shear connectors (16 mm diameter and 100 mm height above flange) are considered and their resistances and behaviour are compared. Experimental results showed that headed studs and bolted shear connectors have similar shear resistance, while headed studs are more ductile. FEA is performed by ABAQUS/Explicit solver with damage material models to get more insight into behaviour of the specimens. FEA shows rather good agreement with experimental results. Influence of the bolt to hole clearance on the behaviour of specimens with bolted shear connectors is analysed and discussed

The constant increase in the wind power production leads to the need of higher wind towers, which brings up some questions regarding the effectiveness of tubular towers and respective foundations. This work focuses on the comparative structural design, life cycle behaviour and costs of onshore concrete shallow foundations for tubular wind towers (WT) when steel micropiles are used to improve resistance of the soil–structure interface (hybrid foundation). Typical wind loading for Turbine Class II and moderate seismicity (.25 g peak ground acceleration) is used to design and analyse 18 WT foundation case studies. This allows the comparison between shallow and hybrid foundations designed for three different hub heights and respective turbine rated power (80 m/2 MW, 100 m/3.6 MW and 150 m/5 MW) and for three different tubular tower solutions (steel, concrete and hybrid steel–concrete). The possible benefits of the solution using steel grouted micropiles are discussed in terms of potential environmental and economic impacts using life cycle analysis. The use of micropiles reveals to be an interesting solution to improve common shallow WT foundations since it allows the reduction of the dimensions of the foundation leading to significant environmental and cost benefits.

Sweden has a strong demand on the construction of student accommodations and consequently significant efforts have been taken to increase and streamline construction methods. In addition, the fluctuation on the number of students admitted at each year, in each university, lead to periods of house shortage or, in opposition to that, to eventual surplus on the housing market. For these reasons urges finding a fast execution process in construction to fulfil the market needs, together with a housing mechanism of control which balances the students’ needs with the housing availability. In this sense, the Frameup system arises as a solution to solve both problems by combining a modular construction with an innovative execution process.

The FRAMEUP buildings uses a steel frame in combination with prefabricated 3D modules - fully equipped and suitable for student accommodations – which are assembled by starting from the roof to the 1^st floor. The existence of the lifting system permits the erection of the building, promoting each time the building is lifted, a clearance of one-floor-height, at ground level, for the assembly of a new floor. The procedure is repeated several times, according to the number of floors, until the 1^st floor of the building, the last floor of the execution sequence, is assembled.

Alongside with its advantage on the fast execution, the Frameup system allows to efficiently increase or decrease the number of the floors and consequently its exchangeability with other buildings of same nature. Thus, assuming a net of FRAMEUP buildings at each university, its exchangeability system would create the necessary conditions so that the number of floors at each campus would follow the fluctuations of the students’ population among the different universities on different periods of time, so to suppress the needs for housing or to avoid the surplus on construction.

The methods proposed by the design codes for single member design in fire situation assume that these members are isolated in their response. The real response of structural members such as beams is, however, more complex due to thermal expansion and the presence of restraints against this expansion by the surrounding structure. It is therefore imperative to study the response of structure at high temperature in a way which includes its interaction with its surroundings such as in a full-scale fire test and in numerical analysis. This paper focuses on the numerical investigation of steel beams, with a concrete slab and connected to concrete filled tubular (CFT) columns through reverse channel connections. The finite element software ABAQUS has been used in this study. The aim of the investigation is to study the behaviour of the composite steel-concrete beam exposed to increasing temperature in fire.

This paper presents results from experiments performed on cold-formed high strength steel circular and polygonal sections. The test specimens were conceived to provide necessary information for development of tubular towers for wind turbines. A total of 32 high strength steel specimens were tested under uniaxial compression. Various thicknesses, openings and geometric imperfections were studied. Sixteen specimens without opening and sixteen specimens with opening were tested under axial compression in order to investigate influences of opening on the resistances. Tensile tests of coupon specimens taken from flat part, circular part and corner part were used to investigate basic properties of high strength steel material S650 and to evaluate influence of corner on the material strength and ductility. Initial geometric imperfections of the specimens were determined by using a 3D laser scanning method. The coupon test results were used to calibrate the ductile damage material models for modelling of fracture. Results from the experiments are fully described in this paper

This paper is the second part of the study on the cold-formed high strength steel circular and polygonal sections intended to be used in tubular wind towers. Results from 32 numerical finite element analysis (FEA) models were compared with and calibrated against results of the tests on 32 corresponding specimens. The FEA results agreed well with the experimental results in terms of resistances and load-displacement curves. Further investigations on the numerical models were performed. Yield stress used in the FEA significantly affected the resistances of the numerical models. Using 0.2% proof stress leaded to higher resistance than the experimental results. Corners significantly influenced buckling behaviour in the polygonal section models. Analyses of an oval opening in the tubular specimens showed that peak stresses around the opening were considerably higher in the polygonal section models than in the circular section models. Finally, investigation of sensitivity to geometrical imperfections indicated that failure modes of numerical models with geometrical imperfections according to EC3 significantly differed from those of tested specimens and numerical models with geometrical imperfections obtained from the 3D scans.

The present paper addresses how the commonly used Hertz formulas for contact stresses underestimate the actual stresses seen in practice due to temperature differentials, misalignments and other contruction-related defects. First, two failure cases of Swedish bridge roller bearings are analyzed and discussed; then, a detailed finite element (FE) model is used to investigate the accuracy of the traditional roller bearing design rules in view of issues such as abutment and girder deformability, misalignment imperfections and material nonlinearity. The bearing capacity of the studied rollers as provided by the manufacturer is used as reference. A rigorous FE model that accurately models girder, roller assembly and abutment provides the necessary information for the assessment of the related contact stresses, which were traditionally calculated by means of the Hertz analytical formulas. Numerical results first establish that roller bearings develop contact stress concentrations at the outer edges of the cylindrical drums. Second, it is established that the contact stresses are very sensitive to misalignment imperfections between the bridge girder and the abutment. Last, it is shown that the roller bearings develop inelastic deformation at relatively low loads in relation to the design load. These reasons, combined with the unlikelihood for roller bearings to shake-down, constitute the basis of the observed roller bearing failures.

The problem considered in this thesis concerns how the thermal expansion of steel beams in the ceiling of industrial halls affects the building and the fire protection. The subject has been up for discussion in Sweden for a while because of the difficulty in classifying the buildings correctly according to existing construction rules. In the thesis several dimensions of a fairly generic industrial hall with two compartments are analysed. One compartment exposed to fire consisting of three fourths of the building and the other sectioned off with a firewall class R30 and thus able to withstand fire for the full duration of the simulation. First the temperatures attained in the ceiling beams of the structures are simulated using Fluid Dynamic Simulator (FDS). After that these are used to calculate the strain caused by the thermal expansion on the firewall with the help of a worksheet developed during the course of the thesis.Using these beam calculations and computer programmes the problem has been reviewed and the following conclusion is drawn: Thermal expansion of the beams on its own is not enough to cause a collapse of the adjacent firewall in the cases studied in the thesis. Under simulated conditions the worst strain was nowhere near what was required to cause a collapse and temperatures would need to be a couple hundred degrees higher. The interactions between the bending and compression of the beams was not enough to cause a buckling either, further insuring the integrity of the firewalls protection.The thesis lends further support to the state of art regarding the construction of buildings sectioned with differing levels of fire protection.

The on-going RUOSTE project aims to improve understanding of HSS by means of tests and FEA, addressing issues of ductility and stability of structures made of HSS. Various material models used in FEA are verified by tests. This paper presents calibration and verifica-tion of ductile damage material model in Abaqus FE software package referring to series of tensile test experiments on coupons and plate specimens with a single circular hole. Nominal steel grade S700MC and S960Q are used. Damage initiation criterion and evolution law are derived analysing localization of plasticity by FEA. Quasi-static analysis using explicit dy-namic solver is chosen in order to create the most realistic FEA of the specimens.

The cost of a tubular steel tower supporting a wind converter becomes increasingly important in a competitive energy market. In-situ connection between tower segments is an important factor of the design. The tower segments are usually connected by welded ring flanges. An alternative solution based on a novel single lap friction connection is analysed. The purpose of the research presented in this paper is to thoroughly analyse the behaviour of both connections by an experimental testing programme and advanced finite element analysis (FEA). Down-scaled experiments of ring flange and friction connection in circular towers were performed using a 4-point bending test set-up. Altogether eight connections joining cylindrical shell, 1 m diameter, plate thickness 8 mm and total span of about 7 m were tested. A friction connection with long open slotted holes and two different cases of the ring flange connection are considered: with perfectly flat flanges and flanges with geometric imperfection. Results of advanced quasi-static FEA, using explicit dynamic solver and ductile damage material model for bolts, are compared to experiments. Failure modes, bolt forces and distribution of meridional membrane stresses in the shell in the vicinity of connections are analysed. Existing hand-calculation models, for the bolt force and normal stress distribution in the shell are validated by experiments and FEA.

A novel friction connection consisting of a single lap joint with long open slotted holes is proposed for use in tubular towers for wind converters for in-situ connections. This is a competitive alternative to the common ring flange connection as it has been shown in the European Project “HISTWIN”. Two sets of experiments are analysed: the down-scaled tubular steel tower 4-point bending experiments using high-strength bolts M20 and a single lap joint using plate thickness 25 mm and tension control bolts M30.The main motivation for this paper is a much higher bending resistance obtained in the 4-point bending experiments compared to predictions based on hand-calculation models.Results of experiments are used to validate finite element analysis (FEA). Explicit solver and the most realistic geometry of the bolts are the main characteristics of the FEA performed. Very good agreement between the experiments and FEA results is obtained, which provides credibility of the computational approach used to thoroughly examine experimental results. New evidences of the friction connection behaviour are provided: a short-term loss of preloading force due to external loading, transfer of shear force in the single lap joint and influence of the slotted hole on the joint resistance.Results obtained from hand-calculation models are used to predict the loss of preloading, the bending resistance of the connection and meridional stresses in the tower shell in the vicinity of the connection, which are compared to the experiments and the FEA. Recommendations related to use of the hand-calculation models in the design are provided.

An increase in the height of new generation of wind towers is foreseen in order to improve their performance. This will imply larger shallow foundations, which represent a substantial percentage of the overall budget. Consequently, it is of interest to develop alternative foundation solutions, with a smaller environmental impact, in particular in terms of the required volume of excavation and reinforced concrete. The proposed improvement consists in the use of micropiles placed along the foundation perimeter as a way to increase the overturning resistance of the system as well as the foundation behavior. The main focus of this paper is the characterization of the behavior of single and groups of micropiles, tested under controlled conditions. An extensive set of experimental tests were conducted on single and 2x2 groups of micropiles under monotonic or cyclic loading installed in loose sand. The effect of the cyclic loading on the behavior of the micropiles was assessed as well as the effect of the grouting on the improvement of the micropile resistance and stiffness and also on the improvement of the soil mechanical properties. The assembly and procedure of the tests are described and the corresponding resistance and stiffness are presented and compared

Tubular steel towers are the most commonly used structures to support wind converters. Towers are fabricated in welded segments, complying with the traffic requirements for transportation, and in-situ assembled. Ring flange connections are used to connect two segments. Fatigue endurance of the ring flange to the shell weld, class 71, is often the design criterion and imposes a limit on the shell thickness. Recently studied friction connections with long opened slotted holes, in HISTWIN and HISTWIN2 projects, provides a remedy for this limitation. The main purpose of this paper is to compare performance of the ring flange connection and the novel friction considering connection of a real tubular tower segment 3.37 m in diameter and 24 mm shell thickness. This cross-section is designed for the ultimate load MEd = 45.8 MNm and the steel grade S355. Finite Element Method is used to investigate possible failure modes of the connection. Advanced FEA comprise the realistic geometry of the connection, ductile damage material model and element removal using explicit dynamic solver. This allows sophisticated analysis of the behaviour and direct comparison of the results for both connection alternatives. The FEA is validated by down-scaled experiments performed previously within the HISTWIN project. The friction connection is thoroughly examined: geometry of the connection, influence of the shell imperfection in the vicinity of the connection and possible use of higher resistance steel grades. By focusing on key issues of the friction connection recommendations for the design are provided together with a numerical example.

The so-called Reverse Channel connection has been conceived for the purpose of accommodating the thermal expansion of beams so that premature failure due to thermal buckling is avoided. The connection is made of a channel-shaped element, welded along the tips of its flanges onto the face of a hollow section column; an endplate welded on the beam is bolted onto the web of the channel. In a fire situation, the thermal expansion of a reverse-channel supported beam causes extensive bending deformation of the connection, therefore preventing the development of significant axial stress in the beam. Furthermore, this connection offers a high rotational capacity, if designed properly, which is beneficial in a fire situation where excessive deflections of beams can be expected. This paper aims to provide analytical stiffness assessment tools for reverse channel connections in compression and tension under uniform temperatures. The proposed analytical models are compared to results of Finite Element simulations, which in turn have been benchmarked with experiments. In addition, a comprehensive parametric study is conducted in order to identify all influencing factors on the initial stiffness response: reverse channel geometry and thickness, plate thickness, bolt position, and bolt diameter. Correction factors that account for 3D effects and bolt size are presented and discussed. The obtained expressions for the reverse channel stiffness are found to provide an accuracy that is acceptable for structural applications and can, therefore, be used as a design tool.

Sweden has a strong demand on the construction of student accommodations and therefore significant efforts have been taken towards an affordable and easy solution of the problem. A concept combining these requirements may be based on the use of structural steel frames in combination with prefabricated 3D modules fully equipped and suitable for student accommodations. Therefore, the need to investigate and develop a system suitable for an effective assembly of student residences is considered in this paper, as part of an international project, Optimization of the frames for effective assembling - FRAMEUP. The Fig. 1 reveals an overview of the system within the execution process.The Frameup system introduces a new approach in terms of execution technique which consists of the execution of a building starting from the roof to the 1st floor. The existence of a lifting system constituted of a horizontal rigid frame - grid - in combination with lifting towers - pylons - permits the erection of the building, promoting each time the building is lifted, a clearance of one-floor-height plus tolerances at the ground level. This creates room enough for the assembly of the lower floor from below the previously assembled floor. The procedure is repeated several times according to the number of floors until the 1st floor of the building, the last floor of the execution sequence, is assembled. Moreover the Frameup system introduces an innovation, the Frameup conveyor system, which streamlines the assembly process so to move/slide the elements, as they come, directly from the lorry to their final position in the building.The development of the Frameup system benefits from a stepwise detailed 3D modeling and structural analysis and design tools. However, when it comes to attest the reliability and efficiency of the system, a full scale feasibility test is essential and it is performed on the majority of the sequences of construction.

The design methods currently proposed by the codes prescribe the strength assessment of structures to be based on their strength limit state. These design methods can be applied to isolated steel members to determine their design strengthin fire. The real response of a structural member is, however, more complex due to the thermal expansion and the presence of restraints against this expansion by the surrounding structure. It is therefore imperative to study the response of a structural member at high temperature in a way which includes its interaction with its surroundings. This paper focus on the numerical investigation of steel beams in structural frames connected to concrete filled tubular (CFT) columns through reverse channel connections and comparison to hand calculation procedures. Finite element models (FEM) of the sub-frames were validated against fire tests conducted on sub-frames and then their results were compared to the proposed simplified hand calculation procedures (HCM).

A novel type of connection, referred to as the “crocodile nose” (CN) connection for circular hollow sections (CHS) is investigated in the framework High Strength Long Span Structures (HILONG) project. This connection provides an aesthetically improved alternative to the commonly used slotted-end CHS connection. The end of the CHS member is doubly bevelled and a pair of inflected plates, welded on the edges of the cuts, undertakes the load transfer. This investigation focuses on two parameters, the bevelling angle and the influence of a stiffener connecting the inflected plates. The program is completed through FE calcula-tions and laboratory tests. The design of the test specimens, preliminary FEM and test results are presented in this paper.

The methodology developed under the project FRAMEUP includes the construction of residential buildings from the top to the base, whose compartments are prefabricated modules. The construction begins with the execution of the roof, on the ground level, which is later on lifted, allowing from beneath the construction of the lower floors, while it protects them from the weather. The construction ends with the execution of the ground floor. It is adopted a framed structure with tubular sections for which the beam-to-column connections are developed and the columns-splices designed to facilitate and the use of this constructive methodology.

The novel joint presented in this paper is a friction connection used for column-splice connections of modular buildings as part of the innovative construction method introduced in the research project Optimization of frames for effective assembling - FRAMEUP. This type of joint provides a quick assembly and can deal with misalignments by introducing a connection gap. A filler and finger plate are welded to the upper part of the column to this end.The gap between finger plates and lower column faces is closed during tightening of the bolts and, thus, establishes a slip-resistant connection. The efficiency of the joint resistance based on different connection gaps subjected to uniform compression is assessed.The column-splice is composed of four slip-resistant connections, one at each side of the tube. Each finger plate consists of three long slotted holes and is welded to the upper column face. Long slotted holes are used to accommodate vertical misalignments and, therefore, allow fitting the bolts which are pre-installed in the lower column. Filler plates with different thicknesses (4, 6 and 8 mm) welded between the finger plate and upper column face are used to create a connection gap which allows balancing horizontal misalignments. The lower column faces consist of each nine holes with no clearance in order to pre-fit the bolts in a workshop. Thus, the assembling process on the construction site can be speeded up as once the lowercolumns are in place all bolts can be tightened immediately.

This paper presents the experimental results of the investigation on the coupled joint-structure behaviour of the composite sub-frame, using the reverse channel connections between an I-beam and the concrete filled tube (CFT) columns. This experimental programme includes seven full-scale tests: three tests at ambient temperature and four tests under heating-cooling curves. The parametric study was dedicated to: temperature-time curve and channel wall thickness (8, 10 and 12 mm). The main objective of these tests is to provide experimental information on the behaviour of the reverse channel joints and its influence on the structure under a heating-cooling fire. The restraining effects from the unaffected part of surrounding structure induce highly variable loading histories on the joints during fire; therefore the investigation on coupled joint-structure behaviour should lead to a realistic prediction of progressive collapse of the structure.

Seit 2005 werden in den europäischen Forschungsprojekten HISTWIN (High-Strength Steel Tower for Wind Turbines, 2006–2009) und HISTWIN 2 (High steel tubular towers for wind turbines, 2010–2013) Untersuchungen zur Optimierung von konventionellen sowie polygonalen Stahltürmen von Windenergieanlagen durchgeführt. Die maximale Nabenhöhe von Windenergieanlagen mit Stahlrohrtürmen ist aufgrund der über das Straßennetz transportfähigen Dimensionen und der daraus resultierenden Durchmesserrestriktionen auf ca. 100 bis 120 m begrenzt. Im Rahmen dieser europäischen Forschungsprojekte wurde ein Beitrag zur Lösung dieses Problems durch die Entwicklung einer innovativen Reibverbindung geleistet, welche eine vertikale Segmentierung des Turms ermöglichen sollen. Kommt das Verbindungskonzept überdies anstelle konventioneller Ringflansche zum Einsatz, so ist nicht mehr die Ermüdung im Bereich der Ringflanschverbindung das kritische Bemessungsdetail, vielmehr verschiebt sich die bemessungsrelevante Größe hin zur Stabilität der Turmschale. In diesem Artikel liegt der Schwerpunkt auf den theoretischen Untersuchungen zur möglichen Erhöhung des Stabilitätswiderstandes und gleichzeitig möglicher Materialeinsparung durch die Verwendung eines polygonalen Querschnitts anstelle eines kreisförmigen Querschnitts. Im Rahmen dieser materialbasierten Wirtschaftlichkeitsstudie wurden die Untersuchungen auf Längsspannungen (keine Schubspannungen) und lokales Stabilitätsversagen (Beulen, kein Knicken) beschränkt. Darüber hinaus wurde eine Ovalisierung des Querschnittes nicht berücksichtigt und die Beulfeldkanten als fest unterstellt.Economic feasibility studies on polygonal and circular towers for wind turbines. Since 2005 numerous studies regarding functional and cost optimisation of circular and polygonal steel wind towers are conducted within the scope of the European research projects HISTWIN (High-Strength Steel Tower for Wind Turbines, 2006–2009) and HISTWIN 2 (High steel tubular towers for wind turbines, 2010–2013). The maximum hub height of wind turbines built with tubular steel towers is limited to approximately 100 to 120 m. This is due to restrictions regarding the maximum tower foot diameter to allow for road transportation logistics. Within the framework of the European research projects a contribution to solving that problem was made by introducing an innovative friction connection, allowing for a vertical segmentation of the tower. By use of this friction connection instead of a conventional ring flange connection, the critical design detail changes from fatigue of the ring flange connection to stability of the tower shell. The main focus of this article lies on the investigations of the possible increase of stability resistance and potential material savings by using polygonal cross sections instead of circular cross sections.

Nowadays, sustainability is one of the most interesting topics for research due to the economic and environmental aspects which is constantly improving [1]. Furthermore, constructions were and will be under development because of the big number of social and economic needs, a perspective which is long sought in the EU [2]. It’s clearly seen that research involving those two topics can be at least very creative.Although the use of high strength steel (HSS) is not so popular in constructions yet, in this thesis, optimized HSS members are investigated [3] for the design of industrial building and compared to an equivalent hall made of typical S355 in terms of sustainability.It is noted that the Eurocodes [4]–[6] provisioning the designing of steel structures involves steel grade from S235 to S460. Currently there are no specific details for designing members with strength higher than 460 MPa. EN1993-1-12 [7] came up to specify that for the most of cases of designing S700 steel elements can be calculated with the same procedure as followed for S460.Herein the focus is on the design and the environmental assessment of industrial buildings, considering the production phase. From the environmental perspective, a big impact is dedicated to the use of phase while a considerable part comes from the production and erection phases. The energy consumption during the use phase is commented in [8].A 3-hinged frame with tapered beams and columns is chosen for the structural system, leading to a portal-frame design, ideal 20 m to 60 m spans [9]. Beam elements are preferred against trusses, as the later require big welding length. Especially for HSS, full strength requirement lead to extreme welding demands, indication of a structure with low environmental efficiency. Moreover, the tapered beams allow for an even better utilization of the material.The first part of thesis will cover the designing procedure for the industrial building using HSS and the second part will cover the calculation of the same building designed using mild steel. Throughout the thesis, S700 is considered for the HSS case and S355 for the mild steel case.The above decisions will lead to a comparative sustainability assessment. To what extend can the efficiency be improved, resulting to a more economic and environmentally friendlier construction? In the third part, such questions will be answered through a side-by-side comparison, aiming to conclude on the overall benefits achieved with the use of HSS.

The use of tubular towers made of steel, concrete or hybrid steel–concrete has become standard in the wind energy industry. However, more powerful wind energy generators are leading to the need for increasing the towers height. This implies rethinking of existing solutions for the support onshore structure composed of tower and foundation, including design concept, life cycle and environmental repercussion. The need for transportation of larger prefabricated elements and more complex processes of assembling on site become important issues. This paper addresses the comparative study concerning the influence of increasing height on the structural design and outcome of different structural solutions. Steel, concrete and hybrid steel–concrete wind towers with heights of 80, 100 and 150 m supporting multi-megawatt turbines of 2, 3.6 and 5 MW power respectively are addressed. The design of the towers is made in accordance with the structural Eurocodes. Two different scenarios are addressed, the first considering common lifetime of 20 years and the second considering increased lifetime of 40 years with reuse of tower parts. In-situ erection of steel tubular parts is achieved using flange connections or newly developed friction connections. Conclusions point out that, for towers up to 80 m, the use of steel tubular sections and flange connections are the most suitable. Friction connections are suitable for higher towers, leading to less material consumption. The use of concrete towers, particularly for heights above 100 m, is penalized when seismic risk is considered in special in the dimensions of the slab foundations

In the first part of the paper the design of tubular towers and respective onshore foundations was addressed. The considered solutions were based on steel, concrete and hybrid steel-concrete tubular towers supporting multi-megawatt turbines of 2, 3.6 and 5 MW power with hub heights of 80, 100 and 150 m respectively. In this second part of the paper, the life cycle analysis of the designed case studies is performed and conclusions about their environmental impact are drawn. Two different scenarios concerning the lifetime of the towers were established. The first scenario considers 20 years lifetime and two different construction methods for the connection of the steel segments, the first based in current technology using flange connections and the second using newly developed friction connections. Assuming equal importance for all environmental categories in this scenario, it may be concluded that for heights up to 100 m hybrid towers with friction connections are the most efficient solution. For higher heights, the concrete tower becomes more efficient. The second scenario considers an increased total lifetime of 40 years, assuming the reuse of the tower after 20 years of operation. In this case, the use of friction connections in steel towers enhances the possibility of dismantling and reusing the tower potentiating much better performance in relation to the environmental category of global warming.

During recent years pre-fabricated lightweight elements, here used as 3D room modules, have become popular. There has also been an increased interest to place the fire protection outside of the room, in order to keep the production process simpler. Therefore, the only way to check the fire resistance is by using performance-based design. The combination of these two constrains creates the background for this work. A case study has been performed for lightweight 3D room modules constructed of steel cassettes, which are externally insulated. The modules will serve as student accommodations and have been analysed with respect to temperature development and bearing resistance. Following are the research questions raised at the beginning:1. How does external insulation affect the fire- and steel temperature in the room and is it necessary to take this into account?2. What is the modules’ resistance at elevated temperatures and how realistic can 3D effects be predicted by calculation? 3. Can the connections between wall and roof for self-supporting steel cassettes, be considered satisfactory at elevated temperature?4. How well does simple calculation methods compare to advanced computer programs for these types of self-supporting lightweight modules?Externally insulation of steel modules contributes to higher gas temperature in the room and therefore higher steel temperatures, which should be considered in performance-based design. Influence of a low degree of utilization on the bearing resistance, will be investigated by using two different types of methods for structural resistance (a simpler method and an advance method). The standard fire curve ISO-834 and other fire scenarios are used to predict temperature development in the room.

Extensive research is conducted on the improvement of renewable energies. One field is the use of wind energy, where the tower construction is one of the main issues. This paper deals with new ideas and ongoing research in this area. To raise the height of steel tubular towers, fatigue as the design limit and constraints due to transportation issues have to be overcome. Changes in the cross-section are considered as one of possible solutions. This work presents an extensive finite element study dealing with different ways to improve shell stability, which become the limiting criteria if a friction connection substitutes the common flange connection between two tower segments. The use of circular and polygonal cross-sections is briefly described and will be investigated in an experimental program.

Towers for wind turbines are very sensitive to geometrical imperfections. Pattern and amplitude of imperfections significantly influence the strength of the towers. Rather limited number of experiments exists on a tubular tower like structure and no experiments are available considering door opening in towers with cylindrical or polygonal cross-section. One of the objectives of the RFCS research project “HIGH STEEL TUBULAR TOWERS FOR WIND TURBINES, HISTIWIN2” was to investigate current practice for design of door openings and propose a competitive solution, possibly using higher strength steel grades. A comprehensive experimental program was conceived to gain experimental evidence for the design of stiffening of the door openings.The following compression tests were evaluated in the paper:•4 static down-scaled compression tests of components of circular tubes •4 static down-scaled compression tests of components of polygonal tubes•4 static down-scaled compression tests of components of circular tubes with opening•4 static down-scaled compression tests of components of polygonal tubes with openingPlate thickness is down-scaled to 4 mm thick plate made of S650 steel grade.Most of FE nonlinear analyses of thin walled shell structures were performed using geometrical imperfections according to Eurocode 3. In this approach, geometrical imperfections are based on the pattern that coincides with the critical buckling mode. A comprehensive numerical investigation was made to conclude whether there is need to use a real geometrical imperfection pattern. The real geometry of the imperfections was obtained by laser scan measurements. Both, the measured geometrical imperfections and the geometrical imperfections according to Eurocode 3 were considered. Furthermore, results obtained from polygonal specimens were compared with specimens with circular cross sections.

The robustness of a structure in a fire situation greatly depends on the rotational capacity of the connection region. High rotational capacity is required at elevated temperatures since the steel beams lose their bending stiffness and exhibit increasingly large deflections under constant load. Beam deflections result in increasing rotations at the supports and may lead to collapse due to connection failure. The reverse channel has been proposed as a practical alternative to assemble beams to tubular columns. In a simple implementation, the bending moment generated in the joint due to rotation of the beam may be neglected; however, research efforts are being attempted to quantify the level of constraint. The typical arrangement of the connection type consists of a reverse channel with its flanges welded onto the face of concrete-filled tubular columns and the web bolted to the endplate of a beam. Thicknesses and depths of the reverse channel determine the level of rotational restraint at high temperature. The reverse channel has the ability to undergo catenary deformation in the tensile zone due to the applied rotation at the support and similarly it is relatively ductile in the compression zone. Overall, the reverse channel connection response is rather ductile in terms of its ability to undergo large rotational deformation as long as bolt failure is avoided through proper design.Various tests have been performed to study the behaviour of this type of connection such as full scale buildings, sub-frames, isolated joints and individual sections. The aim of these tests was to capture the connection behaviour in relation to other structural components in fire. This paper, however, focuses on the derivation and verification of analytical models to assess the initial stiffness of reverse channel/partial-depth endplate connections. The results from finite element analyses have been utilized to validate analytical models that describe the behaviour of this type of connection at ambient and elevated temperature. Insight into the analytical models provides proper background to a structural designer to estimate the initial stiffness and understand the behaviour of the reverse channel in the connection.

A localized fire is a fire which in a compartment is unlikely to reach flash-over and uniform temperature distribution. Designing for localized fires is generally more difficult than for flash-over compartment fires because of the complexity of the problem. There is also a lack of experimental data. We report here on a full scale test series on a steel column exposed to localized fires. The setup is a 6 meters tall hollow circular column, ϕ = 200 mm with a steel thickness of 10 mm. The unloaded column was hanging centrally above different pool fires. Temperatures of gas and steel were measured by thermocouples, and adiabatic surface temperatures at the steel surface were measured by plate thermometers of various designs. The results are compared with estimates based on Eurocode 1991-1-2 which in all cases studied overestimate the thermal impact for this setup. The input from plate thermometers was used to compute the steel temperatures using finite element methods. Excellent agreement was found if the radiation exchange within the column due to asymmetry of the exposure was taken into account.