Composite Construction in Steel and Concrete VI

Where a composite floor slab is supported on a composite beam of steel and concrete, shear connection is provided by studs in troughs of the sheeting. The resistance of these studs to longitudinal shear depends on over 20 parameters, of which 15 appear in the mechanical models for shear resistance of Johnson and Yuan [1998]. These models have been revised. The mean of over 200 ratios of test/predicted shear resistance is now 1.03. Their mean is higher and their variation is much less than for ratios predicted using the design method of ANSI/AISC 360-05 (2005). Ratios of test to predicted shear resistances to the relevant British standard and the Eurocode have been studied elsewhere. Summaries of these results are given. All the comparisons show that methods that are both accurate and simple will not be found unless the number of variables is reduced by further standardization.

In current national and international standards for composite structures of steel and concrete the determination of the ultimate load capacity and the fatigue life of headed shear studs takes place with separate and independent verifications at the ultimate limit state, serviceability limit state and fatigue limit state. The fatigue resistance is verified in accordance with the design concepts for steel structures, based on nominal stress ranges and linear damage accumulation according to Palmgren and Miner. The effect of pre-damage due to fatigue loading on both the ultimate and the serviceability limit state is not considered. Because cyclic loading of headed shear studs leads to a decrease of static strength of stud connectors, the assumptions for independent limit states are not given and the reliability index of steel-concrete composite structures subjected to fatigue loading may fall below the target values in codes. This paper is dealing with the results of a comprehensive programme of experimental work with more than 90 standard EC4-push-out test specimens and two full scale-beam tests which consider the crack propagation through the stud foot and the local damage of concrete surrounding the studs resulting from high cycle loading. Based on the results of the push-out tests, new design concepts were developed to predict the fatigue life and the residual strength of headed shear studs after high cycle loading. Considering the interaction between the local damage and the behaviour of the global structure, these research results were taken as the basis to simulate the cyclic behaviour of composite beams by means of a new damage accumulation rule.

Headed studs arranged close to the concrete edge, especially loaded in direction to the free edge, show a lower static resistance and partly a different behaviour than studs further away from the concrete edge. Whereas the static resistance for both load directions and the fatigue strength for a loading parallel to the free edge are well investigated in earlier research works, there is no design rule for the fatigue strength for the load direction orthogonal to the free edge. Based on push-out tests this paper gives information about the fatigue strength for a loading orthogonal to the concrete edge subjected to the edge distance. Another focus is the residual static resistance after a cyclic preloading. An interesting development is the application of corrugated steel webs in composite girders. Omitting the steel flange and welding the headed studs close to the surface as shear connectors leads to a favourable application. Due to the corrugation there are tension stresses in the studs limiting the resistance on one hand, however, the corrugation itself acts as connector in the concrete increasing thus the overall connection strength on the other hand.

The paper deals with the fatigue behavior of headed studs and continuous shear connectors in high strength concrete. For both types of shear connectors cyclic push-out tests as well as large-scale beam tests under cyclic loading were carried out. The headed studs failed after a mean lifetime of 2.3-10⁶ applying 40% to 50% of the static resistance as a maximum amplitude and R = 0.45 and 0.65, respectively. The residual strength after 1.0-10⁶ load cycles was reduced by about 25% in comparison to the static push-out strength. The continuous shear connector, which is called "puzzle strip", did not fail in the fatigue tests with up to 2.0-10⁶ load cycles, and there was no reduction in residual strength at all. The cyclic beam tests with headed studs show that the prediction of the fatigue failure according to the current standards is not satisfactory. A good prediction of the crack propagation (thus fatigue) can rather be accomplished by using an approach based on the crack-slip relationship. For the continuous puzzle strip the fatigue behavior depends on the state of the cutting-induced heat treatment of the surface material and on the surface roughness. For these connectors a threshold value for the crack propagation could be determined.

Natural cyclic loads such as strong winds and earthquakes can cause changes in bending moment signs in composite structural elements. Consequently, the connectors will be subjected to alternate shear forces. For this reason, the cyclic behavior of shear connectors is particularly important in these loading conditions. The research described in this paper refers to a set of 10 experimental tests on five different types of connectors (angle profiles, φ16mm and φ22mm shear connectors, perfobond connectors and reinforcement hooks), subjected to cyclic and monotonic loading, through push-out and respectively push-pull tests. The experimental results are discussed in terms of resistance, ductility and stiffness, and compared to analytical formulae used for strength determination.

This paper presents experimental and analytical research that was conducted on new connections "by adherence" for steel-concrete composite bridges. Their resistance is achieved by the frictional shear resistance of different interfaces positioned in a judicious manner. These connections make it possible to erect the structure quickly with full-depth precast concrete slabs, while the concreting works on site are limited as much as possible. Experimental results show that these connections exhibit a high resistance to horizontal shear forces and are very rigid compared to traditional connectors (headed studs). However, their ductility is limited. Based on the experimental results, a calculation model was developed and was used in a parametric study. Some results of the parametric study are presented and discussed in this paper. A simplified method for determining the resistance of these connections, design rules and recommendations for construction are proposed.

Continuous shear connectors offer an upcoming solution for composite beams. They are characterized by a high initial stiffness, bearing capacity and ductility. With their use new and economic construction methods have been invented, e.g. the PreCoBeams (Prefabricated Composite Beam). PreCoBeams are composite beams associating T-sections acting as tension member with a concrete top chord acting as compression member. Steel parts are generally obtained from rolled steel profiles that are longitudinally cut, with a special shape, in two T-sections. The shape of the cut allows for shear transmission between steel and reinforced concrete, which is continuous regarding the steel. In general, prefabricated composite bridge elements are produced, consisting of the steel T-section with a precast first phase concrete flange. The second phase concrete layer is then completed in-situ after placing of the bridge elements on the abutments. These PreCoBeam bridges are very economic in design and construction, though the main market drawback for PreCoBeams is the missing design approach for the shear connection. This paper introduces the static and fatigue design of continuous shear connections used for PreCoBeams derived from recent research activities; however the focus is on the steel design.

For the design of shear connection for region of highly concentrated shear force in steel-concrete composite bridges, connection details are the most important design issues. Failure modes of the shear connection govern the ultimate strength for the design and governing design parameters can be changed. Instead of rigid shear connectors, this paper deals with the group stud shear connection for the precast decks. Shear pockets for stud connectors arise difficulty in the details of precast decks. Push-out tests were conducted to evaluate the ultimate strength according to the expected failure modes. Main parameters of the test were stud spacing, reinforcement details and stud diameter. Test results showed that current design provisions for the stud connectors can be used for the design of group stud shear connection when the design requirements on the minimum spacing of studs are satisfied and the splitting failure of concrete slab is prevented. An empirical equation was proposed to consider the effect of stud spacing when the spacing is less than the minimum requirement. Fatigue tests showed that the group stud connectors with spacing of more than three times of diameter has similar fatigue life with current design codes. Based on the test results, design recommendations for shear connection in a precast deck bridge were derived.

In modern buildings various installation systems for HVACR, electricity and communication have to be installed. An innovative approach to this requirement is to include the necessary space in the slab construction. Using this approach a new composite slab system has been developed. It consists of two concrete slab layers on top and bottom side of the construction that are connected with vertical steel webs. Precast slab elements with pre-assembled HVACR equipment are installed at site. For improvement of performance in SLS and ULS the system is prestressed without bonding. To optimize the economics the shear connection between concrete and steel shall be realized with concrete dowels. Due to the installation of pipes and ducts various web openings have to be incorporated in the design of the slab system. Secondary bending moments cause considerable additional loads to the steel web and especially to the concrete dowels connecting steel and concrete. Therefore new types of dowels shall be developed to improve load capacity and ductility both for vertical and horizontal shear forces. Results of the new development on concrete dowel's geometry will be presented. Also a short overview of the first application of this slab system in a multi-story building will be given.

The paper presents a new composite floor system using cellular beams. A major benefit of the novel system is the integrated installation floor, adding additional value to the floor without extra costs. The system is based on half cellular beams made of existing hot-rolled sections. The openings in the cellular beams allow placing all kind of installations in all directions, thus providing excellent flexibility to the user when changing installations. First the paper presents the general design and details of the construction of the novel floor system. Then the paper experimentally analyses the load-carrying and dynamic behaviour of two floor elements with a span of 7.2 m. The results are compared to common calculation models for composite slabs.

The paper deals with composite slabs using steel fibre reinforced concrete as topping. The aim of a research project of the Kaiserslautern University of Technology is the evaluation of design recommendations for steel fibre reinforced composite slabs. The constructive as well as the structural conventional reinforcement are substituted completely by the use of steel fibres. The main focus of a first test series was to research the load-bearing behaviour and the possible rotation capacity of steel fibre reinforced composite slabs in the region of negative bending. In a second test series, four full scale tests on continuous composite slabs were accomplished.

This paper discusses a new experimental bending test and shear bond modeling of steel deck reinforced concrete (composite) slabs. The objective of experimental work is to develop a new elemental bending test method for evaluating the performance and behavior of composite slabs, and also for determining the shear interaction property for use in numerical analysis. The analytical study is conducted to determine whether data from the small scale tests can be used in the present shear bond (m-k) and Partial Shear Connection (PSC) methods, to predict the strength of the actual slabs, to use the same test data for input in numerical analysis, and to improve the existing PSC design procedure. The results of the study demonstrate that the elemental bending test of composite slab using trapezoidal shape steel deck is feasible as a replacement for the full-size test utilizing the same steel deck. Data from the elemental bending test can be used not only in the existing analytical methods but also in the numerical analysis, thus eliminating the need for separate push off type tests. The improved PSC design procedure is found to be comparable with the m-k method.

Deep trapezoidal slabs supported compositely on steel I-beams by headed mechanical stud shear connectors provide a popular and economical structural solution for flooring in steel building frames, and they are used widely. When the ribs in the sheeting are oriented orthogonal to the steel beams so that longitudinal stresses traverse the voids, predicting their structural response is difficult, and full-scale testing is very costly. Because of this, an inexpensive and accurate means of analysis that incorporates the non-linear response of the shear connection is much needed. This paper presents such a finite element technique, which incorporates non-linearity in the concrete, steel joist, reinforcement and the shear connection; the latter being derived from specialised push test data embodying the complex interactions in the trough region of the slab. The procedure is used to analyse two full-scale beams for which relevant push test data is available, and the agreement is shown to be very good.

In composite steel-concrete construction applications, the behavior of the shear connectors is paramount to the overall system performance. The most common method for evaluating shear connector strength and its behavior is through the use of a push test. Push tests have been used as early as the 1960's to predict the strength and behavior of shear studs in solid slabs. The performance of steel-concrete composite structures is greatly dependent on the load-slip characteristics of shear connectors. Significant research work has been performed on composite beams in regard to their stiffness and ductility of the shear connectors for both solid and profiled slabs. This paper describes the strength and ductility of the shear connectors in composite beams with both the solid and profiled steel sheeting slabs when different strain regimes were implemented in the concrete element. An accurate non-linear finite element model using ABAQUS is developed herein to study the behavior of shear connectors for both solid and profiled steel sheeting slabs. The reason for employing different strain regimes in push tests is to properly simulate the behavior of shear connectors in composite beams where trapezoidal slabs are used. The pertinent results obtained from the finite element analysis were verified against experimental results from other researchers. Based on the finite element analysis and experimental results, it has been determined that the strength and the load-slip behavior of composite steel-concrete beams is greatly influenced by the strain regimes existent in the concrete element.

Continuous composite beams can be designed according to the plastic hinge theory. In that case in a statically indeterminate system plastic hinges are formed one after the other until a kinematic mechanism is generated (ultimate limit state). In the case of continuous beams with web openings, areas of plastic deformation can be generated in the area near the opening itself. This means that under certain circumstances local plastic moment hinges are formed in the corners of the opening. All these local hinges together result in a global plastic hinge for shear forces. Up to now the structural and deformation behaviour of such a hinge was not clarified if it acts as a global mechanism with one degree of freedom. The necessary conditions to generate such a plastic hinge for shear forces were also not clear. At Kaiserslautern a research project, that examined such beams, has been completed. Its results and a design model are described in this paper.

Composite slim-floor girders form an attractive alternative to usual reinforced concrete beams. However, their effective design suffers from assumptions concerning the effective width of the concrete chord that are not reflecting the real deflection behaviour. This paper reports on the investigations already executed concerning the deformation of single span slim-floor girders as well as analytical and numerical evaluations of the effective width. Ongoing research work now deals with the effective width at the support area of multi span girders. Considering the restraint moment at support the calculated deflection that often limits the utilization of slim-floor girders may be reduced. First analytical conclusions are shown. Aside of the bending restraint at support the limited shear capacity of the slim-floor girders may be decisive. Usually, the contribution of the concrete chord of a composite girder is not considered for the shear force capacity. Only the steel web is adopted to verify sufficient shear capacity. However, tests with slim-floor girders showed that the shear capacity of the concrete chord was up to 80% of the total shear force, underlining the importance of the concrete chord for the shear capacity.

From 2000 till 2007 a complete new fairground was developed nearby the Stuttgart-Airport. Within this project arose 7 exhibition halls with 75.000 m², one high hall with 25.000 m², one convention centre and a multi-storey car park with 4.000 lots. Additional planning of the traffic flow was necessary. At that time it was the biggest construction site in Germany with an investment volume of 800 million Euros. More than 65.000 to of steel structure were erected. 13.500 to for the multi-storey car park across the highway A8. The car park is an eye-catching landmark for the new fairground in Stuttgart. This paper concentrates on the planning and the erection of the multi-storey car park.

This paper presents the results of the laboratory testing conducted at serviceability and ultimate limit-states on two full size composite underspanned beams and comparisons with the previous in situ measurements, as well as with finite element calculations. The comparisons have shown very good correlations in terms of static behavior under point loads (simulation of an heavy forklift truck), of the composite behavior (embedment of the steel beam in the concrete slim-floor, introduction of the tensile force of the tie bar in the top chord, relative slippage between steel and concrete) and of the dynamic behavior (natural frequencies, damping rates). These results confirm the very good structural behavior of the floor under service loads as well as the capability of the underspanned system to withstand asymmetrical loads

Concrete filled steel tubes (CFTs) are efficient members in structural applications including bridges, buildings and piled foundations and their use in the building industry is increasing. To date their primary use has been in axial applications, with the design methodology based on theory and tests of columns under loads applied axially or at relatively small eccentricities. Limited in to research into the behaviour of CFTs subjected to large eccentricities or loading in pure flexure have been conducted, with preliminary experimental investigation suggesting that stiffness of composite members tending towards that of the tube at relative low loads. An ongoing research program on the flexural behaviour of CFTs is being undertaken at the University of Western Sydney with a particular emphasis on thin-walled steel tubes that can provide an economical form of construction. In this paper, the results from additional experimental work will be presented with a particular emphasis on the stiffness of the members when subjected to flexural loading. The experimental work to date has demonstrated that even in composite specimens where there is negligible end slip; the stiffness of the specimens under pure flexure tends to the stiffness of the bare steel tube. A numerical model will also be presented that can accurately generate the bond/slip relationship of the concrete within the steel tubes and consequently the behaviour of the specimens modelled. From the experimental results and the numerical model some guidelines for the design of concrete filled tubes subjected to primarily flexural loading will be presented.

The results obtained from nonlinear fiber element analyses for concrete filled tubes (CFT) are discussed. The studies were aimed at assessing primarily the overall behavior and stability effects on these structural elements as a prelude to a large full-scale testing program. The study focuses on ultimate strength analyses for CFT composite columns with different stress-strain models for both concrete and steel. Fiber analyses using OpenSees are used to assess the impact on the ultimate strength based on the assumed stress-strain material curves, member slenderness, initial imperfections, and both material and geometric nonlinearities. Fiber analysis results are also compared with those obtained from AISC (2005). Fiber-based results show a compatible correlation with the expected element behavior, which is also captured in the current AISC (2005) Specifications.

This paper presents the behaviour and design of axially loaded elliptical steel hollow sections filled with normal and high strength concrete. The experimental investigation was conducted with three nominal wall thickness (4mm, 5mm and 6.3mm) and different infill concrete cube strengths varied from 30 to 100 MPa. The effect of steel tube thickness, concrete strength, and confinement were discussed together with column strengths and load-axial shortening curves were evaluated. The study is limited to cross-section capacity and has not been validated at member level. Comparisons of the tests results together with other available results from the literature have been made with current design method used for the design of composite circular steel sections in Eurocode 4 and AISC codes. It was found that existing design guidance for concrete filled circular hollow sections may generally be safely applied to concrete filled elliptical steel tubes.

This paper presents the results of experimental and analytical studies on Engineering Wood Encased Concrete-Steel (EWECS) composite columns. A total of four specimens with the scale of about two-fifth were tested under combined constant axial load and lateral load reversals. Variables investigated include the type of woody shell connection between column and loading stub and the presence of shear studs. The test results indicated that EWECS columns had excellent hysteretic behavior without severe damage even at large story drift of 0.04 radian. The results also showed that EWECS columns with the type of column-stub connection consisting of woody shell and wood panel attached to stub showed high performance in both capacity and damage limit. In addition, the presence of shear studs on EWECS columns improved the deformation capacity of the column and reduced the damage of woody shell. An analytical study was also performed using fiber section analysis to simulate the behavior of the composite columns.

Composite columns are a combination of two traditional structural forms: structural steel and structural concrete. As composite columns were generally developed after steel columns and reinforced concrete columns, their design approach could have been based on either steel or concrete design methods. However, steel column design methods have differed from concrete design methods in a number of fundamental ways. Despite this, either design approach can be used as the basis for developing a design method for composite columns and this can be seen in the different methods currently used in Europe and the USA for composite columns. While the design approaches appear fundamentally different, the end results can be surprisingly similar. By understanding the design philosophies, designers can take full advantage of each approach for the effective use and economy of composite columns.

A Split Hopkinson Pressure Bar (SHPB) equipment was used to perform the high-strain rate compressive tests on concrete filled steel tubes (CFT) under both room and elevated temperatures. This paper reports the results of load-deformation relationships, the dynamic compressive strength corresponding to different strain rates and temperatures. The results reveal the existence of a steel tube and concrete core interaction mechanism. Although the dynamic yielding strength of CFT specimens under elevated temperatures decreases somewhat with the increasing of temperature, the dynamic ultimate strength decreases little with the elevated temperature. A calculation of the dynamic compression strength for CFT columns under both room and elevated temperatures using the simple additive equations without considering confinement was attempted and shown to yield reasonable underestimation to the test results.

Cast-iron columns were used in many industrial and public buildings erected from about 1800 until the early 1900s. During renovation of these old buildings the load carrying capacity has to be checked again and if it fails following the higher load it's obvious to fill the mainly hollow columns with concrete to increase the ultimate load capacity. Because of the special material properties of structural cast-iron it is not possible to determine the capacity of these columns with simple design rules based on present design codes for composite structures e.g. DIN EN 1994-1-1 or the German code DIN 18800-5. As part of a general investigation on historic cast-iron columns a number of tests and numerical calculations have been carried out to clarify the special behaviour of concrete-filled cast-iron columns. Additionally, the bond strength between concrete and the inner surface of the columns was determined by push-out tests.

This paper summarises the data from 1819 tests on concrete-filled steel tube columns and compares their failure load with the prediction of Eurocode 4. The full data is given on the website http://web.ukonline.co.uk/asccs2 . The comparison with Eurocode 4 is discussed and shows that Eurocode 4 can be used with confidence and generally gives good agreement with test results, the average Test/EC4 ratio for all tests being 1.11. The Eurocode 4 limitations on concrete strength could be safely extended to concrete with a cylinder strength of 75 N/mm² for circular sections and 60 N/mm² for rectangular sections.

This paper deals with the design of composite columns made of concrete filled tubes with inner massive core profiles as well as high strength steel and high strength concrete. New research work regarding the effect of residual stresses in inner core profiles resulting from the cooling process during fabrication is presented. Based on Finite Element studies new models are presented for the determination of the distribution of residual stresses in solid round steel bars, taking into account the steel grade, the dimensions of the core profiles and the cooling conditions during fabrication. Additional theoretical investigations are presented to estimate the effects of creep and shrinkage under long term loading. Finally recommendations are given for the design of this type of composite column based on the methods given in Eurocode 4-1-1 [1].

Steel or composite joints can be designed and optimised by the component method according to Eurocodes [EN 1993-1-8:2005] and [EN 1994-1-1:2004]. The structural behaviour (strength, stiffness, ductility) of these joints is defined by assembled components. Their individual behaviour is described by a mechanical spring model. For the extension of the component method to anchor plates, which are used to transfer loads between steel and concrete structures, a mechanical model has been developed. The model is based on several test series with anchor plates carried out by the Institute of Structural Design (Universität Stuttgart) and describes the load-carrying capacity of anchor plates. In some tests supplementary reinforcement has been taken into account influencing the load capacity and ductility of these steel-to-concrete joints. Additional tests have been performed to study the influence of a flexible anchor plate on the structural behaviour of the joint. Altogether, the component model shows transparency of load distribution and may easily be transferred to alternative situations.

Concrete filled steel tubes (CFT) are economical and result in rapid construction. The steel tube serves as formwork and reinforcement to the concrete fill, and the fill increases the compressive strength and stiffness of the tube. The fill delays and restrains local buckling, and enhances ductility and resistance if composite action is achieved. Circular CFT provides better performance because the circular tube provides greater confinement of the concrete and composite interaction between the two materials. However, circular CFT is more difficult to connect to other structural elements, and recent research has provided a simple and economical connection to connect circular CFT piers or columns to reinforced concrete foundations, beams and pier caps. The connection does not require any reinforcement or dowels connecting the tube to the footing. A second variation of this connection permits sequencing of steel and concrete construction trades and connecting to precast concrete elements. A series of experiments have been completed to evaluate the inelastic seismic performance and establish design criteria for the connection. This work shows that the connection can develop the full capacity of the composite column, and provide great ductility and inelastic deformation capacity under seismic loading.

Exposed column bases in Japan are commonly covered with lightly reinforced concrete (RC) slab, whose effect is neglected in seismic design so far. However, many experimental investigations showed that the strength, stiffness and energy dissipation are increased by the contribution of the RC slab. In this study, steel fiber reinforced cementitious composites (SFRCC) is employed for the covered slab to further improve the behavior of exposed column base. Here, 0.4 mm x 12.0 mm and 6% volume fraction straight steel fibers were adopted for SFRCC. Eight specimens, one exposed, three concrete and four SFRCC specimens, are tested. The test parameters included slab material and reinforcement ratio (size and strength of steel bars).

Starting in the early 1950s the use of composite members in buildings increased significantly in Germany. High-rise office buildings and since the 1980s multi-storey industrial buildings were built with composite decks, beams, and columns. Basic research and the development of design procedures on fire-resistant composite members supported this development. The paper presents some of the most important composite buildings that were built in Germany recently.

The Eurocodes for the design of steel, concrete and composite bridges have been introduced in Germany since 2003. The development and the implementation of the new generation of design codes in combination with the construction of several new freeways in the eastern part of Germany after the German Reunification initiated new types of composite bridges. This paper gives an overview about new developments in composite bridge design and about the experience and the consequences resulting from the new generation of European design codes.

Traditionally "steel structures" and "concrete structures" formed more or less two different worlds in structural engineering. Fortunately this situation is changing rapidly. It is now recognised that each of the two materials have advantages and disadvantages and that often an optimal solution is found by combining both materials. This may be a combination of steel and concrete in an element as is the case in "Composite steel-concrete construction" or the combined use of concrete elements and steel elements in "Mixed construction". For the design of composite steel-concrete elements specific design standards have been developed. However for "Mixed construction" a combined use of steel design standards and concrete design standards is necessary. It is important that the design rules for the two materials are consistent, especially for those components connecting both materials. However, in the past the design standards and recommendations for concrete and steel have been developed separately. So evidently, at this moment there are considerable differences in design assumptions and treatment of various aspects. In the paper design methods for connections between structural steel and concrete will be discussed. The methods will be illustrated for column bases, being the most frequently used type of connection between steel and concrete, though the information can also be used for related types of connections.

In the last decades the Eurocodes have been developed in order to harmonize the technical rules for the structural design in Europe. Since the beginning in 1975 the aim was the elimination of technical obstacles in trades throughout Europe. Today most of the Eurocodes are published. The ECs are no rigid technical rules; they keep room for national differences. The National Annex which is valid in conjunction with the relevant Eurocode contains information on those parameters which are left open for national choice. Due to the fact that the Eurocodes are still not mandatory in Europe and not even used by some of the European Countries, it is necessary to make the engineers sensitive to the Eurocodes and to train the use. The European Union launched in 1995 the Leonardo Da Vinci Programme with the objective of improving the provision of vocational education and training across Europe. The paper will describe the current Leonardo Project named "Eur-Ing" and show some results.

While there is a wealth of literature regarding strength models used to determine the capacities of encased composite columns, there is little information devoted to the equally important topic of detailing provisions with respect to these columns. The goal of this paper is to fill this gap by summarizing and comparing detailing provisions within three different model standards. Several areas where broad differences exist between the standards reviewed are highlighted, and recommendations for harmonizing these provisions are made.

Recent events such as natural catastrophes or terrorism attacks have highlighted the necessity to ensure the structural integrity of buildings under exceptional actions. Accordingly, a European RFCS project entitled "Robust structures by joint ductility" has been set up in 2004, for three years, with the aim to provide requirements and practical guidelines for the design of steel and composite structures under exceptional actions. In this project, the importance of the structural joints has been shown; as a particular case, these ones experience additional high tying forces after the loss of a column, as a result of the development of membrane forces in the beams located just above the damaged column. Moreover a reversal of moments occurs in some joints. In this paper design models for the evaluation of the mechanical properties of joints in such extreme situations are presented. References are made to recent tests on joints in isolation and joints in frames recently achieved at Stuttgart and at Liège University in the framework of the above-mentioned RFCS project.

New composite structural systems consisting of only steel and concrete, the concrete encased steel (CES) structures, have been proposed by the author in order to realize simplification and cost reduction in construction works for SRC structures. Experimental studies on CES columns using fiber reinforced concrete (FRC) have been carried out to investigate the seismic performance, in which the main test parameters were the section shape of encased steels, the type and content of fibers used for FRC and the applied axial load levels. The experimental results showed that CES columns had excellent seismic performance with a stable spindle-shape hysteresis characteristic and less damage. This paper introduces the summary of the experimental studies carried out in past about eight years with the advantage of CES structure.

A new hysteretic damper system utilizing slit steel shear plates and out-of-plane restraining wood panels is proposed. In this system, the upper half of the damper is a slit shear plate, whereas the lower half is a base wall. The slit shear plate and the wooden restraining panels are attached through bolts designed to prevent shear force transfer to the wood panels. Cyclic loading tests were performed to investigate seismic performance of the proposed system. The restrained specimens mostly behaved in stable manner. While the local out of plane deformation around the slit ends were not restrained, the wood panels were effective to restrain global out-of-plane deformation of shear plates.

The paper presents an ongoing investigation of the cyclic performance of steel coupling beams in hybrid coupled core wall systems. Coupled core wall systems offer remarkable lateral strength and stiffness, and taking advantage of the favorable cyclic behavior of steel coupling beams makes the best use of all materials employed. Moreover, the inherent characteristics of the systems considered are ideal for an application of performance-based design approaches. Preliminary results are discussed from the standpoint of seismic performance, demonstrating the advantages of steel coupling beams and innovative details of coupling beams, conceived with reparability in mind, are presented. The design of a prototype structure is discussed, and a two-phase experimental campaign is described. It is anticipated that a hybrid, pseudo-dynamic analysis of the coupled core wall systems considered will show that the use of steel coupling beams in a performance-based design framework can deliver economical and safe structures with remarkable strength, stiffness, and ductility.

In this paper, a multi-objective advanced design methodology is proposed for steel-concrete composite moment-resisting frames. The research activity mainly focused on the design of beam-to-column joints under seismic-induced fire loading together with the definition of adequate structural details for composite columns. Thermal analyses of cross sections were performed in order to obtain internal temperature distribution; structural analyses were then carried out on the whole frame to assess the global behavior under the combined action of static and fire loadings. Furthermore, results of numerical analyses were used in order to derive information about the mechanical and numerical behavior of joints. In this paper the experimental program carried out on four beam-to-column joint specimens under seismic loading is described and results are presented and discussed together with the outcomes of numerical simulations owing to seismic and fire actions. Experimental tests demonstrated the adequacy of the seismic design. Numerical simulations showed a satisfactory performance of joints under seismic-induced fire loading.

A multi-objective design methodology dealing with seismic-induced fire on steel-concrete composite moment resisting frames endowed with concrete filled tubes (CFT) full strength joints is presented in this paper. In order to achieve these goals analytical and FE simulations including thermal analyses were carried out to design the proposed joints: this was followed by experimental tests under monotonic and cyclic loadings. Preliminary, seismic and fire analyses provided valuable information on the performance of moment resisting frames endowed with the chosen joint typology. A total of six specimens was designed and subjected to lateral loads. The specimens were subassemblages of interior beam-to-column joints connected by means of welded connections. Relevant experimental results are presented and commented. Furthermore, since the scope of the project was to promote joint typologies able to survive a seismic-induced fire, specimens were damaged by imposing monotonic loads equivalent to damage induced by seismic excitations, before being subjected to fire loadings. Thus, valuable information was obtained about the endurance of the proposed joint typology.

To make full use of the excellent mechanical performance of gangue light-weight concrete, half-size models of joints between steel beams and gangue concrete-filled steel tube columns with ring stiffeners were tested under reversed low cyclic loads. Data collected included extensive strain measurements in key areas of the connection. The data indicates that the behavior of the connection can be adequately predicted by simple mechanical models except in the vicinity of the ring stiffeners. The joints exhibited very robust behavior, with loads increasing until failure was reached due to weld fracture. The cumulative plastic strain resisted by the welds was large, and the gangue lightweight aggregate concrete demonstrated equal or better performance than conventional LW concretes.

This paper deals with the strengthening of beam-to-column end-plate bolted joints. Two strengthening dispositions have been developed and studied. The first one consists in adding a haunch welded on the beam bottom flange in the vicinity of the column. The second one consists in strengthening the column web panel (in presence or not of haunches) with double steel plates. This strengthening arrangement is studied in this paper from both experimental and numerical approaches. Based on these studies, two new static design models are proposed. The first model deals with the composite haunched joints. The second model provides a design method for the column panel zone strengthened by double steel plates.

This paper deals with a numerical F.E. modelling investigation of new joint typology to connect continuously composite beams in bridges. Different types of joint have been selected, designed and tested under fatigue and monotonic loading. For an accurate interpretation of the test results and a better understanding of some specific behaviours (not accessible to measurement) with complex geometries and with the objective to generalize the study, numerical models have been developed using several Finite Element programs including specific programs for composite beams and 3D models based on standard FEM codes. The main numerical results are presented and compared against experimental ones.

In modern composite structures, higher steel grades are used for structural steel profiles in order to increase span capacity without an unnecessary increase in the composite floor depth. This tendency results in beams that are more vulnerable to the failure modes that involve either web LSB (local shear buckling) and/or compression flange RDB (restrained distortional buckling). The effects of shear stresses as well as web buckling and post-buckling behavior on the overall beam performance have been investigated both experimentally and numerically in order to resolve the most important behavioral issues of plain-webbed composite beams. Less attention has been paid to investigations of instability effects on the ultimate strength of steel profiles in continuous castellated composite beam systems. In this paper, different finite element techniques are used to investigate the in-plane behavior with use of geometrically linear analysis and the out-of-plane distortional behavior with use of geometrically nonlinear analysis, with both techniques applied to trace the performance of continuous composite beams.

In this paper, we investigate the performance of three finite element formulations for continuous composite beam analysis. These formulations include displacement-based, force-based and mixed models. Specific attention is devoted on how to take into account discrete connection which seems, in some cases, to be more representative of the actual behavior. The nonlinear behavior of concrete is modeled using a softening plasticity model. The parameters of the models are obtained by matching the uniaxial stress-strain relationship provided by the CEB-FIP 90 model. Tension-stiffening is taken into account as well. A consistent time-integration is performed using the Euler backward scheme. The predictions of the FE models are compared and the study shows good performance of the mixed formulation.

To get good results in the prediction of deflections of composite girders a good mechanical model is needed. For research 3-dimensional finite elements with nonlinear geometry and material laws are a very good tool. Unfortunately they generate very much effort in the modeling of the structure which reduces their applicability to special problems that have to be solved by specially trained engineers. In our paper we will show how very good results can be obtained by using a combination of simple beam and shell elements. Special emphasis is laid on the modeling of the effective width, shear lag effects in the beam and the slab, creep and shrinkage, and the non-linear behavior of the steel element due to the cambering process. First results show very well the influence of shear lag effects for short beams with thick concrete slab as they are mainly used in experimental evaluations. Comparisons with the test results of [Rieg 2006] prove the necessity of calculating deflections with a "deflection based effective width" in contrast to the current practice of using the same width for stress and deflection analyses.

A comprehensive computational model to simulate the nonlinear seismic response of composite frames with rectangular concrete-filled steel tube (RCFT) beam-columns and steel girders and braces is presented in this work. A three-dimensional fiber-based distributed plasticity mixed finite element formulation is introduced. The finite element formulation of RCFT beam-columns was derived with separate translational degrees-of-freedoms (DOFs) defined for the concrete core and the steel tube to simulate the slip deformation that is typical for composite members. Cyclic constitutive relations were derived accounting for the interactions taking place between the steel tube and the concrete core including slip, confinement, and local buckling. A representative composite frame structure was analyzed under a suite of ground motion records and the demand imposed on the RCFT columns was quantified. A methodology based on the use of the damage function equations was proposed to evaluate the performance of RCFT members under seismic loads.

The behavior of macro-elements can be described by a set of orthogonal boundary states, each consisting of displacements and forces associated by a one-dimensional constitutive relationship. Combinations thereof are described by surface models in the force space with flow rules. Local models describing the mechanics inside the element are not restricted in detail and are needed only once to develop the constitutive relationships, surfaces models and flow rules: The problem is scaled in a mechanically consistent manner without loosing information or accuracy. A macro-element for a plane beam-column connection has five orthogonal states: Two bending, two normal and one shear state, if linear boundary displacements are assumed. These "beam-type" boundaries enable the connection to any beam element. Thus, it can be included in regular frame analysis greatly improving its accuracy. To demonstrate this powerful scaling technique, typical component models for beam-column connections are used to develop a "beam-type" macro element.

A generic finite element model for composite beam-column joints with welded connections has been developed using current state-of-the-art local modeling. Using mechanically consistent scaling, it provides the constitutive relationship for a plane rectangular macro element with beam-type boundaries that can be used in high-accuracy frame analysis. Global geometric variables allow the generation of specific FE models for each instance of a joint. Using assumptions typical for most composite frames, the constitutive relationship of the macro element can be represented by bilinear laws for the macro bending and shear states which are then coupled by a two-surface law with yield and failure surfaces. This is demonstrated in an example.

The formulation for partial shear interaction in composite beams was developed over 50 years ago in closed form. This formulation is suitable for many cases encountered in practice, but it does not account for the geometric non-linearity produced by the "P-delta" effect. This effect is important in a compartment in a steel or composite framed building in a fire, where the initially large compressive forces which develop because of restraint against thermal expansion interact non-linearly with the large deflections of the composite floor slab, and a geometrically non-linear formulation must necessarily be invoked to capture the partial interaction behaviour of the composite floor system during a fire. This paper provides an elastic analysis of partial interaction at moderately low levels of temperature, so as to shed light on the significance of the parameters that affect the structural behaviour as well as to provide a precursor for an inelastic analysis to treat catenary action. The differential equations which quantify the problem are derived and solved numerically, and an illustrative example is worked.

Fire resistance is one of the main arguments for using Composite Structures. Therefore it is important that reliable and accepted methods are available for the determination of the fire resistance. In the recently completed series of the Eurocodes each material dependent code has a separate part on structural fire design. For Composite Structures this is EN1994-1-2. This Eurocode part includes rules for structural fire design of composite beams, composite columns and composite slabs. Also rules are given for constructional details. The design rules are on three different levels of sophistication e.g.: (1) Tabulated data; (2) Simple calculation models; (3) Advanced calculation models; In the paper a review is given of these methods and the opinion of a practitioner is presented on the possibilities for use of the different methods in present practice. The presentation of the code rules is illustrated by examples of the structural fire design as used fora building in the Netherlands. Emphasis in the paper is on practical application rather than theoretical background.

This paper presents the development and verification of an analytical approach based on the finite element method for modeling and predicting the standard fire behavior of composite steel beams. This approach consists of two sequentially coupled numerical analysis steps. The first step conducts nonlinear heat transfer analysis of the composite beam for the thermal loading applied using the gas furnace. The analysis was conducted using a detailed 3D finite element model of the composite beam inside the furnace. The results included the complete thermal response (nodal temperature histories) of the beam. The second step conducts nonlinear stress analysis of the composite beam for the applied structural loading and the thermal response from the first step. This analysis was conducted using two types of models: (i) detailed models using solid and shell elements, and (ii) simplified models using shell and beam elements for the concrete slab and steel beam, respectively. This two-step analytical approach was used to model and predict the standard fire behavior (thermal and structural) of ten composite beam specimens tested by other researchers. The comparisons of the experimental and analytical results are presented in this paper. These comparisons indicate that the analytical approach (using either SS or SB models) predicts the standard fire behavior of composite steel beam with reasonable accuracy. The verified approach is recommended for conducting parametric studies, and for evaluating the realistic fire behavior of composite beams with restraints.

Aim of the project was to measure deflections of standard steel concrete composite beams, used in office and industrial buildings assess and analyze the reasons for those deformations and develop simple design aids for a realistic calculation of the deflections. This research was necessary, since experience has shown that results do frequently not match the deflections measured on site. This can reduce the serviceability of a structure and lead to high rectification costs. The focus was on the differences between calculations and in-situ behavior by analyzing the measured deflections of beams in structures under construction. During the measurements it appeared that cambered beams deform more than straight beams. This effect was analyzed in tests and it was found that the reason for this behavior lies in the Bauschinger Effect, rather than in residual stresses. It will be shown when and how this effect should be considered.

At present adhesive bonding as an alternative to mechanical connectors does not belong to the standard practice in structural applications of the building and construction industry. Therefore the scope of this study is to experimentally investigate the behaviour of adhesively bonded joints between steel and concrete. The main attention was focused on shear stressed; tension stressed and combined stressed connections. To study the typical characteristics of adhesives in combination with steel and concrete different high-strength polyaddition curing adhesives, one polyurethane and two epoxy adhesives, were examined in this study. All tests were conducted at room temperatures. Also different aggregates for concrete such as crushed stone and round edged gravel were used. To promote a good adhesive bond cleaning and pre-treatment of the surface prior to bonding is of outmost importance. Therefore different pre-treatments for steel and concrete surfaces and their effect on the load behaviour and deformation capacity were considered. The concrete surfaces were used as grit-blasted and cut with a diamond saw. The steel adherents were grit-blasted and coated with primer prior to bonding.

HSB600 is a high performance steel which is currently developed by a Korean steel company. HSB600 does not have an obvious yield point and yet undergoes large strains after proportional limit. Its 0.2% offset yield strength and tensile strength are over 450 MPa and 600 MPa respectively. Modern standards such as AASHTO LRFD and Eurocode 4 provide rules for determining the flexural strength of composite girders. These rules are based on the presence of a yield point in the stress-strain diagrams of steel materials. This paper presents experimental works conducted for the purpose of verifying the ultimate flexural strength of hybrid composite girders using the tension flange made of HSB600. Totally five composite girder specimens (one hybrid and a conventional composite girders (Series I), three hybrid composite girders (Series II)) have been tested. The results of the test are compared with the flexural strengths obtained by nonlinear moment-curvature analysis based on the stress-strain curves of each material and the code predictions. The test results show that, if the plastic moment is calculated with using 0.2% offset yield strength, the ultimate flexural strength is underestimated. Finally, based on the test results, some design recommendations regarding the flexural strength and the ductility requirement for hybrid composite girders with HSB600 are suggested.

The present paper summarizes the results of a research program involving the testing of push-out specimens and composite beams with innovative continuous shear connectors in ultra-high performance concrete. In the push-out tests the load-slip behavior of the shear connectors was evaluated and compared for various parameters. The parameters included the steel fiber content and the transverse reinforcement ratio. The test results indicate that the steel fiber reinforcement ratio has only a minor influence on the load carrying capacity whereas the transverse reinforcement ratio is more vital. The beam tests are focused on the moment carrying capacity and the transition of the shear forces across the joint between steel and concrete. Two beam tests are presented and discussed.

Most extant fiber reinforced polymer (FRP) applications in the structural engineering field involve concrete-FRP composite systems, where FRP components are attached to or embedded into concrete structures to improve their structural performance. A relatively small and innovative body of work focusing on steel-FRP composite structural systems is beginning to develop. A state-of-the-art review of progress in this emerging and rapidly developing area is presented. The review is divided into applications: strengthening steel structures with FRP, stabilizing (or bracing) buckling-critical steel elements with FRP and relieving fatigue or fracture-critical conditions. Discussions of concerns pertaining to joining FRP and steel as well as the potential and future of this technology are also presented.

One of the issues that has not been completely resolved in bridges built without expansion joints is the influence of seasonal temperature variations and soil characteristics on the maximum bridge length. To study this problem, a 40 meter long road composite bridge over the river Leduân in the north of Sweden was built in 2005. The bridge superstructure was cast integrally with the substructure. One row of piles on each side of the bridge was constructed to support the abutment. The bridge was continuously monitored for 18 months in order to provide information on the strain level at the top of the pile as a function of the air temperature variations. The results from the measurements were compared to results obtained from 2D Finite Element Analysis. Soil characteristics were varied in the FEA to investigate its influence on the overall bridge behaviour as well as on the level of strain variations at the top of the piles. The bridge monitoring was a part of a research project, INTAB, Economic and Durable Design of Composite Bridges with Integral Abutments, 2005–2008. The main objective of the project was to propose recommendations for rational analysis and design of bridges with integral abutments. The total environmental impact and the life cycle costs of the integral abutment bridge were compared with a concrete bridge alternative for the same crossing.

This paper describes the results of a study investigating methods to strengthen existing non-composite steel bridge girders using post-installed shear connectors. Four non-composite steel-concrete beams representing existing non-composite bridge girders were strengthened using three types of post-installed shear connectors. The full-scale, retrofitted partially composite beams were tested under static loading to evaluate their strength, stiffness, and ductility. One non-composite beam was also tested as a baseline specimen. Results of the study indicate that the addition of a relatively small number of post-installed shear connectors can increase the load-carrying capacity of non-composite girders by more than 50 percent. Based on the results of this study, a design approach based on partial composite action was developed for strengthening existing steel bridge girders by using post-installed shear connectors.

Three innovative solutions of joint to restore the continuity between beams in composite bridges have been selected. Experimental specimens, representative of each innovative solution, have been designed, erected and tested under fatigue and monotonic loadings. This paper presents the moment-rotation curves: initial stiffness, maximum moment and rotation capacity obtained for each tested joint and more particularly slip measurements at the slab - steel girder interface, insofar as one joint collapse occurred by shear failure of studs connecting the slab to the steel flange of the girders. In addition, two approaches to evaluate the fatigue damage of the shear connection are compared. In conclusion, this paper gives useful data for a better understanding of the behaviour of shear connections between the slab and the steel girder and to propose new design methods.

A representative horizontally curved composite I-girder bridge system was designed near the limits of the 2007 AASHTO bridge design specifications and tested at the Federal Highway Administration (FHWA) laboratories for its ultimate loading capacity. A synthesis of the experimental and full nonlinear FEA responses of the test bridge indicates that the component and system behavior was predominantly linear up to the AASHTO M_p-based 1/3 rule load level on the critical outside girder. Similar observations were also made for other parametric simply-supported bridges. These results indicate that simply-supported horizontally-curved composite I-girder bridges may be designed elastically using the AASHTO equation M_u + S_xf_l /3 ≤ φ_fM_n, where φ_fM_n can be as large as φ_fM_p. This is a substantial gain in strength for curved I-girder bridges relative to the current curved bridge provisions, which limit φ_fM_n to a maximum of φ_fM_y. Since the test bridge was simply-supported, a logical and natural extension is the consideration of continuous-span bridges. A convenient and simple way of achieving this extension is to use the base test bridge configuration but to assume that the girder ends are fully restrained. This paper presents a synthesis of the full nonlinear FEA results for this hypothetical fixed-end case.

In this study, in order to erect a cantilever deck without supports and formwork, the use of a steel-concrete composite cantilever deck system was explored. The cantilever deck system consists of steel plate, perfobond ribs that have been welded onto the steel plates, concrete, and reinforcing bars. In order to form a cantilever deck, the steel forms consisting of steel plate and ribs must be fabricated then, the ribs of steel form were bolted to the girder to prevent large rotation and deflection under erection loads and finally, the concrete must be cast-in-place. A total of four specimens were built and tested under erection loads. As a result of the tests, it is found that, under erection loads, the weight of the laborers, and wet concrete, the connection of the ribs to the girders has enough stiffness to satisfy in-erection deflection and the bolt connections supply sufficient force to prevent rotation. The proposed cantilever deck erection method should improve the efficiency and economy of bridge construction.