Traditionally welded headed studs have been used to generate composite interaction between a steel beam and a (cast in-situ) concrete floor. This permanent connection impairs the demountability of the structural components and therefore demolition of the composite floor system is inevitable at the end of the functional service life. The demolition of functionally obsolete but technically sound building components is in contradiction with the globally prevailing ambition of more sustainable development of the built environment through reduced demand for primary resources and reduced emissions of harmful substances. This dissertation aims to overcome the need for demolition of composite floor systems by developing methods, tools and recommendations to enable easy demountability of the structural components. The recommendations are both based on practical experience obtained by full-scale laboratory experiments on a demountable composite floor system consisting of large prefabricated concrete floor elements (2.6 × 7.2 m), and on the (analytical) methods and tools developed to predict the response of the floor system during execution (e.g. instability) and service life (e.g. deflection and stresses). @en

Injection bolts are bolts in which the cavity produced by the clearance between the bolt and the wall of the hole is completely filled up with a two-component resin. Filling of the clearance is carried out through a small hole in the head of the bolt. After injection and complete curing, the connection is slip resistant. Recently the injection material, typically an epoxy resin, was modified at TU Delft by adding steel shots (spherical particles) to mitigate the effects of resin compliance in the shear connection of reusable composite (steel-concrete) structures. Experimental compressive material tests on unconfined/confined resin and steel-reinforced resin are evaluated in this chapter. The uniaxial model which combines damage mechanics and the Ramberg-Osgood relationship is proposed to describe the uniaxial compressive behavior of resin and steel-reinforced resin. First-order numerical homogenization is employed as a high-fidelity model, where a combined nonlinear isotropic/kinematic cyclic hardening model is employed to define the steel plasticity, the linear Drucker-Prager plastic criterion was used to simulate resin damage, and the cohesive surfaces reflecting the relationship between traction and displacement at the interface. The linear Drucker-Prager plastic model is used as a low-fidelity model.

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Demountable and reusable composite floor systems enable the decoupling between the use of construction materials and economic activity, and hereby contribute to the sustainability of the built environment. Efficient material use through optimised cross-section design reduces construction material demand. Demountable steel-concrete composite floor systems are perceived as competitive when consisting of steel beams and large prefabricated concrete floor elements, with composite interaction achieved by demountable shear connectors. Compared to traditional monolithic floor systems, the demountable composite floor systems have an increased sensitivity to lateral-torsional buckling during execution, mostly because of unsymmetrical loading and the absence of rotational constraints in the execution phase. This increased sensitivity implies that the cross-section of the steel beam should not only be designed based on the required in-plane resistance, but should also maximise the out-of-plane resistance. The Energy method and Rayleigh-Ritz methods are combined to develop a prediction model for the critical bending moment of monosymmetrical web-tapered steel beams. The key cross-sectional dimensions and parameters that affect the in-plane and out-of-plane resistance are identified. An overarching strategy for the concurrent optimisation of the in-plane and out-of-plane resistance of monosymmetrical cross-sections is presented without compromising on material efficiency. The beneficial effects of the proposed optimisation strategy are quantified through a case study example.@en

The design of sustainable structures is increasingly gaining attention in the construction sector as a societal and technological challenge. Demountability and reuse of structures contributes to the reduction of the environmental impact of the built environment. Welded headed studs used in traditional steel-concrete composite floor systems need to be replaced by demountable shear connectors to enable the transition of the construction sector to a circular business model. The demountable shear connectors are embedded in large prefabricated concrete floor elements and connected to steel beams by bolts. The holes in the beam flange are oversized to account for geometrical and dimensional deviations of all members and to facilitate rapid execution and easy demounting. The goal of this paper is to present a methodology that quantifies the required nominal hole clearance for reusable composite floor systems. Statistical characteristics of dimensional and geometrical deviations serve as input for Monte-Carlo simulations. The aggregated results of the Monte Carlo simulations are used to determine the required nominal hole clearance for a specified probability of successful installation of the demountable shear connectors. The proposed methodology is applied to the composite floor system of a demountable and reusable car park building. The contradicting requirement of oversized holes and composite interaction is solved by injecting the hole clearance with a (steel-reinforced) epoxy resin. The bearing resistance of the (steel-reinforced) epoxy resin is addressed based on preliminary results of creep experiments on resin-injected bolted connections.@en

Composite beams are commonly used in current design practice due to their efficient material use and competitive execution. The shear connection is mainly achieved by means of headed studs welded on the top flange. However, the welded connectors obstruct the possibility of a non‐destructive disassembly required to reuse the steel beams and concrete slabs. Raised concern regarding sustainability aspects drive the construction sector to introduce a shear connector which enables the demountability of the flooring. Composite action can be enabled by a bolted connection consisting of an embedded bolt and coupler connected by an external injection bolt through the top flange of the steel beam. This paper aims to assess the initial investment costs and economic viability of two demountable steel‐concrete composite beam solutions. The investigated systems comprise of two different concrete flanges: a prefabricated solid deck and an in‐situ casted profiled sheeting slab. The cost inputs of the analysis were defined by industry experts based on assumed labour and material requirements. The unit price of the novel connector is significantly higher (approx. 15 times) compared to the regular headed welded stud. This justifies the need to optimize the connector arrangement in order to keep the cost per square meter as low as possible. Non‐uniform connector arrangements can be used to reduce construction time and costs with minor decrease in beam stiffness. A tool was developed to generate a batch of 13500 composite beam designs which were later analysed in terms of costs.@en

Steel-concrete composite beams are widely used in practice because of their simple construction sequence and economic cross-section design. Reuse of traditional composite beams is not possible due to the permanent connection between the steel beam and concrete deck established by welded headed studs. To allow for fast construction, demountability and reuse of composite beams, various demountable shear connectors can be used. In this paper the results of experiments carried out on demountable and reusable tapered composite beams, consisting of a tapered steel beam and large-scale prefabricated concrete decks, are presented. The performance of various arrangements of resin-injected bolt-coupler shear connectors was considered to optimize the beneficial effect of composite action whilst minimizing the number of shear connectors. An advantage of resin-injected bolted shear connectors is that composite action is obtained instantaneously and simultaneously for all connectors. Demountability and reusability of the composite beam were successfully demonstrated experimentally. Experimental and numerical results indicated that the number of shear connectors necessary to fulfil deflection and end-slip limits can be reduced by concentrating them near the supports of a simply-supported beam. Results obtained using finite element models closely matched the experimental results in terms of deflection, stresses and curvature.

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In this paper, compressive material tests on unconfined/confined resin and steel reinforced resin were experimentally evaluated in order to validate the numerical results. The uniaxial model which combines damage mechanics and Ramberg-Osgood relationship is proposed in this paper to describe the uniaxial compressive behaviour of resin and steel reinforced resin. Numerical homogenization is conducted to predict the tensile and shear behaviour of steel reinforced resin after validated by compressive material test results. The friction angle β the ratio of the yield stress in triaxial tension to the yield stress in triaxial compression K, and the dilation angle ψ of the linear drucker-prager plastic model are obtained based on experiments and numerical homogenization simulation. The confinement effects on resin and steel reinforced resin could be effectively simulated by combing above parameters and uniaxial compressive model. Finite element simulations on unconfined/ confined resin and steel reinforced resin material tests were conducted to validate the material parameters proposed in this paper. A good agreement is observed, indicating the model and parameters proposed in this paper could be effectively used in the finite element simulation of injected bolts.

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Environmental concerns steerthe construction industry towards more sustainable developmentssuch asdemountable and reusablestructures. Composite structures are a frequent solution for multi-story buildings and bridges, however the use of welded shear connectors requires labour and energy intensive disassembly. Two bays of a demountable flooring systemfor a multi-storey car park building were erected in the laboratory. The flooring system consists of large prefabricated concrete decks connected to taperedsteelbeams. The feasibility of assembly and disassemblyof the flooring system was tested under laboratory condition. Shear interaction was achieved by an embedded bolt and coupler which areconnected to the top flange of the steel beam by an external injection bolt. Oversized holes are used in thetopflangeof the steel beamto accommodate fabricationand executiondeviationsandthedeformations occurringduring construction. Extensive imperfection measurements and finite element models were used to design the oversized hole diameter to 32 mm. Thehole clearance must be compensated either by pretensioning or injecting the bolt-to-hole clearance with an epoxy resinto enable instantaneous composite action underlive loads.Experimental injection of 150 injection bolts confirmsthat epoxyresin can reliably fill the hole clearance, and that the injectionprocess takes30 seconds per bolt.Various non-uniform shear connector arrangementswere considered to minimizeconstruction costs and maximize the speed of execution. The mechanical behaviour of the demountable composite beam was tested experimentally and numerically.@en

This paper illustrates the most recent developments in the field of injected bolted connections. A novel injection material, steel-reinforced resin, is used to enhance stiffness of resin-injected bolted shear connections. The main goal is to achieve the slip resistance connection in a clearance holes without pre-tensioning of bolts. Steel-reinforced resins consist of spherical steel particles embedded in an epoxy resin matrix. Steel-reinforced resins are characterized by a higher Young’s Modulus compared to the bare epoxy resin. Numerical and analytical prediction methods for the quasi-static mechanical behaviour of steel-reinforced resins are presented and validated based on small-scale compression tests. The design of a tailor-made test setup, the simple pin connection, is presented. This setup allows for investigation of a generic behaviour of steel-reinforced resins subject to cyclic loading in confined conditions. Preliminary results obtained with the simple pin connection specimens are shown and improvements of the setup, specimens and process are discussed. An overview of potential applications focusing on easy and fast execution, dissembling and reuse of steel and steel/concrete structures is presented.@en

Circular Economy refers to a move from linear business models, in which products are manufactured from raw materials, used and then discarded, to circular business models where products or parts are re-used, remanufactured or recycled. Structural steel is highly compatible with this concept; however, when steel-concrete composite structures are used, recycling becomes difficult and the potential for reuse is lost. In order to make steel-concrete composite structures reusable, bolted connections should replace the commonly used welded headed studs. Furthermore, the reusable parts should be designed to withstand repeated use.
This paper presents a desktop study and the corresponding laboratory experiments on demountable shear connectors that facilitate recyclability and even provide the potential for reusing complete structural elements. In the Laboratory of Steel and Composite Structures of the University of Luxembourg 15 push-out tests have been carried out using different bolted connection systems suitable for multiple use. The shear connectors have been evaluated based on their shear strength, stiffness, slip capacity, ductility and ability of demounting. The investigated systems included pre-stressed and epoxy resin injection bolts, solid slabs and solid slabs in combination with profiled steel sheeting. The results showed that the tested demountable shear connections could provide higher shear resistance than conventional shear connections. The critical failure mode was the shear failure of the bolts, which is a brittle failure. There was no visible damage observed on the connected members. The application of epoxy resin in the hole clearance resulted in lower slip capacity. The outcome provides an important basis for the justification of the forthcoming enhancement and validation of numerical models of the demountable shear connections. The failure behaviour, the observed damages and the resulting ability of the elements for re-use are discussed in detail.@en

Composite slab consisting of in‐situ casted reinforced concrete on profiled sheeting, which is connected to steel beams by shear connectors, is a common structural flooring system in office buildings and car parks. The headed welded studs are inexpensive and rather easy to use in‐situ because they can be welded to the steel beam through the metal sheeting. A permanent link is created between the composite slab and steel beams leading to rather time‐consuming and expensive deconstruction process. Various types of bolted shear connections, recently investigated by various researchers in Europe, Australia, USA, provide a demountable alternative for the flooring system. This paper describes the experimental study using a bolted shear connector consisting of an embedded bolt/coupler and external bolt, originally developed for a prefabricated concrete deck. A full‐scale composite beam was tested under working loads up to 6.25kN/m2 in a 4‐point bending. In addition to bolted shear connectors a timber joist is embedded in the composite slab over the web of the steel beam. After the first life cycle, the timber joist provides the cut edge of the slab. The experiment is used to model behaviour in the first life cycle. The composite slab was then cut, demounted, re‐assembled and tested again in the second life cycle. The load was applied up to 6.25kN/m2 and finally to the failure. Multiple arrangements of shear connectors were investigated to analyse performance of “a modified composite slab”. Experience gained on the experiments of testing the composite beam in the first and the second life cycle is accompanied by FE analysis.@en

Duurzaamheid wordt steeds belangrijker in de bouwsector. Demontabel en herbruikbaar bouwen vermindert het gebruik en verbruik van natuurlijke grondstoffen en minimaliseert afval en uitstoot van schadelijke stoffen. Binnen de sectie Steel and Composite Structures van de TU Delft is ontwikkeling van technische oplossingen voor duurzame staal-beton liggers één van de hoofdonderzoekslijnen. De crux zit – zoals praktisch altijd – in een ontkoppelbare, maar effectieve verbinding tussen vloer en constructie.@en

Steel-concrete composite beams are widely used in practice because of their economic cross-section design. As sustainability becomes more and more important in the construction industry, the design of composite beams must be adapted to meet the requirements of the circular economy. This calls for demountability and reusability of the structural components, as well as optimized use of materials, for example by using non-prismatic beams. Linear-elastic design and the (optimized) use of demountable shear connectors are key in the design of reusable composite structures. In this paper, analytical prediction models for the elastic behaviour and the first eigenfrequency of non-prismatic composite beams with non-uniform shear connector arrangements are derived. The approach is based on 6th and 2nd order differential equations used to define matrix equations for a finite number of linearized composite beam segments. The analytical models are validated using experimental and numerical results obtained with a simply supported tapered composite beam. The analytical models are suitable for comprehensive structural analysis of non-prismatic composite beams with non-uniform shear connection.@en

Composite floor systems are frequently used for high-rise buildings and multi-storey car park buildings, mainly because of the competitive combination of the steel beam and the concrete deck. Traditionally, composite beams are cast in-situ and shear interaction between the concrete and steel beam is provided by welded headed studs. The application of welded headed studs prevents the non-destructive separation of the composite beam, which leads to a very low scoring in the sustainable assessment in terms of the reuse of structural components. An alternative to welded headed studs are bolted shear connectors, which allow for demountability and reusability of a (prefabricated) composite floor system. A key challenge for demountable and reusable composite beams consisting of prefabricated elements is to provide sufficient tolerances to allow for easy execution and demounting, but also to achieve a stiff and strong shear connection under live loads. The required tolerances can, for instance, be obtained by using large bolt-to-hole clearances. The, at first glance, contradictory requirement of a large hole clearance in the execution phase and high stiffness under live loading conditions was solved by using injection bolts. The goal of this paper is to demonstrate how the demountable and composite structures fit in the circular economy framework, and to show that such a demountable and reusable structure was successfully erected and demounted under laboratory conditions. In addition, a cost assessment will be addressed using a simple methodology based on estimated service life (ESL) factors to estimate the annual environmental costs of a composite floor system.@en

SIROCO investigated the slip-resistant behaviour of carbon and stainless steel preloaded connections as well as the preloading behaviour of stainless steel bolting assemblies in principle. The slip factor test procedure according to Annex G of EN 1090-2 was investigated regarding the influence of the test speed, preload level, tightening method, criteria for the slip load and load level for extended creep tests, different bolting assemblies and surface conditions (grit blasted, hot-dip galvanized, alkali/ethyl zinc silicate coating, thermally sprayed with aluminium/zinc and combinations). Improvements regarding the slip factor test procedure have been formulated which have already partly been implemented in the revision of EN 1090-2. Enhanced slip factors allow more economic slip-resistant connections. The use of stainless steel bolting assemblies in preloaded bolted slip-resistant connections joining stainless steel plates was studied through investigations into the creep/relaxation behaviour with regard to potential preload losses, the tightening and slip resistance behaviour for austenitic, duplex, lean duplex and super duplex stainless steels. Preload losses due to the viscoplastic deformation behaviour in preloaded stainless steel bolting assemblies lie in the same range as those for carbon steel. Stainless steel bolting assemblies are in principle preloadable and galling can be avoided using suitable lubricants and tightening methods. Slip factors for stainless steel slip-resistant connections show high values for grit blasted surfaces whereas even 1D and shot blasted surfaces demonstrated slip factors for practical use. Recommendations for design and execution of slip-resistant connections and amendments to EN 1993 1-4, EN 1993-1-8 and EN 1090-2 are formulated.@en

Injected bolted connections have been used in the Netherlands since the 1970s, initially to replace riveted connections of steel railway bridges. More recently, structural components with different geometrical tolerances have also been connected using injection bolts and oversize holes. The natural confinement of a bolted connection provides support to the injected epoxy resin so that it can withstand bearing stresses that are significantly higher than its uniaxial compressive strength. A recent innovation in the field of injected bolted connections is the development of steel-reinforced resin, which consists of a skeleton of steel particles and a conventional epoxy resin (polymer). In previous research, the steel-reinforced resin has shown to increase the connection stiffness and decrease creep deformation significantly. In this paper, a hybrid analytical-numerical homogenization method, which can consider the plasticity of steel and resin and the interfacial damage, is proposed to determine the stress-strain relationship of reinforced resins. The results of the hybrid homogenization method are validated against experimental data of small-scale specimen, subjected to compression in unconfined and confined conditions. Proposed hybrid homogenization method is an alternative to complex multi-scaling methods and allows for quick but accurate determination of mechanical properties of steel-reinforced resins.@en

The deconstruction of steel-concrete composite structures in buildings and the later separation of the materials is a labour- and cost intensive work. The shear studs are welded on the steel beam and imbedded in the concrete deck and a large amount of cutting work becomes necessary. As a result, recycling is difficult and the potential for reusing entire elements is lost. The carbon footprint of composite structures could be decreased by application of the principles of “design for deconstruction and reuse”. This paper presents a desk top study and corresponding laboratory experiments on demountable shear connectors that facilitate recyclability and even provide the potential for reusing complete structural elements. In the Laboratory of Steel and Composite Structures of the University of Luxembourg 15 push-out tests have been carried out using different bolted connection systems suitable for multiple uses in order to verify their performance focusing on shear strength, stiffness, slip capacity, ductility and ability of demounting. The investigated systems included pre-stressed and epoxy resin injection bolts, solid slabs and composite slabs with profiled decking. The results showed that the tested demountable shear connections could provide higher shear resistance than conventional shear connections. The critical failure mode is shear failure of the bolts, while there was no visible damage observed on the connected members. Most of the tested connections could fulfil the ductility requirement according to by Eurocode 4. The application of epoxy resin in the hole clearance resulted in lower slip capacity. The outcome provides an important basis for the justification of the forthcoming enhancement and validation of numerical models of the demountable shear connections. The failure behaviour, the observed damages and the resulting ability of the elements for re-use are discussed in detail.@en

Composite beams are frequently used because of their competitive combination of a steel beam and a concrete deck. Further optimization of composite beams is possible through use of tapered steel beams. In terms of material reuse, composite structures generally underperform, because of the concrete casted in-situ. The most common shear connector is the welded headed stud embedded in the concrete. An alternative to welded headed studs is a bolted shear connector, which allows for demountability of the composite floor system and subsequent reuse of it. The goal of this paper is to propose a method to determine the deflection of tapered composite beams with flexible shear connectors. Starting point is the theory available in literature for straight (i.e. prismatic) composite beams with flexible shear connectors. The proposed method is used in a case study to optimize the design of a composite beam in a multistorey car park. Validation of the derived hand-calculation method is carried out through finite element analysis. An approximation is derived based on which the deflection of tapered composite beams can be estimated through hand calculation, with a deviation less than 5%.@en

Steel-concrete composite beams are widely used in practice because of the simple construction sequence and the economic cross-section design. The application of welded headed studs in composite beams prevents the non-destructive separation of the composite beam, which leads to a very low scoring in the sustainability assessment in terms of the reuse of structural components. A demountable connection between the steel beam and concrete deck must be made to allow for reusability and adaptability of the structure, which maximizes its functional lifetime and minimizes its environmental footprint.@en

One of the increasingly important parameters in the construction sector is the time required for the execution and easy demounting of a structure. The goal of this paper is to provide insight into an on-going research focusing on structural performance of large prefabricated concrete decks connected by a demountable shear connectors. A large bolt-to-hole clearance is used to accomplish both requirements. The holes are injected by an epoxy resin to ensure composite action. The demountability and reusability of the composite beam system was successfully tested. @en