Cyclic response of hollow and concrete-filled circular hollow section braces

yesThe behaviour of seismic-resistant buildings relies heavily upon the inclusion of energy dissipating devices. For concentrically-braced frames, this function is accomplished by diagonal bracing members whose performance depends upon both cross-sectional properties and global slenderness. Traditionally preferred rectangular hollow sections are susceptible to local buckling, particularly in cold-formed tubes, owing to the residual stresses from manufacture. This paper explores the response of hollow and concrete-filled circular tubes under cyclic axial loading. The uniformity of the circular cross-section provides superior structural efficiency over rectangular sections and can be further optimised by the inclusion of concrete infill. A series of experiments was conducted on filled and hollow specimens to assess the merit of the composite section. Comparisons were drawn between hot-finished and cold-formed sections to establish the influence of fabrication on member performance. Two specimen lengths were utilised to assess the influence of non-dimensional slenderness. Parameters such as ductility, energy dissipation, tensile strength and compressive resistance are presented and compared with design codes and empirically derived predictions

Finite element analysis on the capacity of circular concrete-filled double-skin steel tubular (CFDST) stub columns

YesThis paper presents the behaviour of circular concrete-filled double-skin steel tubular (CFDST) stub columns compressed under concentric axial loads. To predict the performance of such columns, a finite element analysis is conducted. Herein, for the accurate modelling of the double-skin specimens, the identification of suitable material properties for both the concrete infill and steel tubes is crucial. The applied methodology is validated through comparisons of the results obtained from the finite element analysis with those from past experiments. Aiming to examine the effect of various diameter-to-thickness (D/t) ratios, concrete cube strengths and steel yield strengths on the overall behaviour and ultimate resistance of the double-skin columns, a total of twenty-five models are created to conduct the parametric study. In addition, four circular concrete-filled steel tubes (CFST) are included to check the dissimilarities, in terms of their behaviour and weight, when compared with identical double-skin tubes. A new formula based on Eurocode 4 is proposed to evaluate the strength of the double-skin specimens. Based on the comparison between the results derived from the analysis, the proposed formulae for the concrete filled double-skin would appear to be satisfactory

Structural behaviour of beam to concrete-filled elliptical steel tubular column connections

YesElliptical Hollow Sections (EHSs) have been utilized in construction recently because of their visual appearance as well as the potential structural efficiency owing to the presence of the two principle axes. However, little information currently exists for the design of beam to elliptical column connections, which is an essential part of a building structure. Thus, to ensure the safe and economic application of EHSs, a new research project has been initiated. Rotation behaviour of simply bolted beam to concrete-filled elliptical steel column connections was investigated experimentally. Various joint types were considered and the benefits of adopting core concrete and stiffeners were highlighted. This paper covers the experimental studies and simulation of the connections using the ABAQUS standard solver. Comparisons of failure modes and moment vs. rotation relationships of the connections between numerical and experimental results were given. Good agreement has been obtained and the developed finite element model was therefore adopted to conduct a preliminary parametric study to explore the effect of critical parameters on the structural behaviour of beam to concrete-filled elliptical column connections

Experimental study of beam to concrete-filled elliptical steel tubular column connections

YesThis paper investigated the rotation behaviour of simply bolted I-beam to concrete-filled elliptical steel tubular (CFEST) column connections experimentally. Ten different joint assemblies were tested to failure, with a constant axial compressive load applied to the column and upwards concentrated loads at the beam ends. All of the steel tubes were hot-finished and had a cross-sectional aspect ratio of 2. The orientation of the column and the arrangement of the stiffening plates were taken into consideration. Moment versus rotation relationships and failure modes were compared for each joint, highlighting the benefits of using core concrete and stiffeners in these connections

Long-term drying shrinkage of self-compacting concrete: experimental and analytical investigations

YesThe present study investigated long-term drying shrinkage strains of self-compacting concrete (SCCs). For all SCCs mixes, Portland cement was replaced with 0–60% of fly ash (FA), fine and course aggregates were kept constant with 890 kg/m3 and 780 kg/m3, respectively. Two different water binder ratios of 0.44 and 0.33 were examined for both SCCs and normal concrete (NCs). Fresh properties of SCCs such as filling ability, passing ability, viscosity and resistance to segregation and hardened properties such as compressive and flexural strengths, water absorption and density of SCCs and NCs were also determined. Experimental results of drying shrinkage were compared to five existing models, namely the ACI 209R-92 model, BSEN-92 model, ACI 209R-92 (Huo) model, B3 model, and GL2000. To assess the quality of predictive models, the influence of various parameters (compressive strength, cement content, water content and relative humidity) effecting on the drying shrinkage strain as considered by the models are studied. The results showed that, using up to 60% of FA as cement replacement can produce SCC with a compressive strength as high as 30 MPa and low drying shrinkage strain. SCCs long-term drying shrinkage from 356 to 1000 days was higher than NCs. ACI 209R-92 model provided a better prediction of drying shrinkage compared with the other models.Financial support of Higher Education of Libya (469/2009)

Experimental study on demountable shear connectors in profiled composite slabs

[EN] This paper presents an experimental study on demountable shear connectors in profiled composite slabs. Overall, three groups of push-off tests were conducted to assess the shear capacity, stiffness and ductility of the shear connectors. In all the specimens, a pair of shear studs were used per trough and were bolted to each side of the flange of a loading beam. Different concrete strength, embedment height of the shear studs and reinforcement cage were considered. Particularly, a joint was made between the pair studs in two groups of specimens when casting and formed two completely separate slabs per half specimen, to evaluate the load transfer between the pair studs. The experimental results showed that the shear capacity and behavior of the demountable connectors in separate slabs and continuous slab were both similar to the welded connectors and could fulfill the 6mm minimum ductility requirement stated in Eurocode 4 if proper embedment height of connector was used. The shear capacities of the tested specimens were compared against the calculated results obtained from the equations used for welded shear connectors in Eurocode 4 and bolted connections in Eurocode 3. Generally, the Eurocodes prediction underestimated the shear capacities of the push-off specimens.The research leading to these results is part of a joint project of the University of Bradford and University of Manchester and it has received funding from Engineering and Physical Sciences Research Council (EPSRC, EP/N011201/1).Yang, J.; Lam, D.; Dai, X.; Sheehan, T. (2018). Experimental study on demountable shear connectors in profiled composite slabs. En Proceedings of the 12th International Conference on Advances in Steel-Concrete Composite Structures. ASCCS 2018. Editorial Universitat Politècnica de València. 115-121. https://doi.org/10.4995/ASCCS2018.2018.6959OCS11512

Cyclic behaviour of hollow and concrete-filled circular hollow section braces

Presented in this thesis is an investigation on the response of hot-finished and cold formed, hollow and concrete-filled circular hollow section braces in earthquake resisting concentrically braced frames. The role of these braces is to act as structural ‘fuses’ in the frame, dissipating the seismic energy by undergoing plastic deformations. Circular hollow sections offer aesthetic and structural advantages over conventional rectangular hollow sections owing to the uniformity of the section geometry. Distinct behaviour is observed between cold formed and hot-finished tubes, since the cold formed sections retain a higher degree of residual stresses from manufacturing. Braces subjected to cyclic loading fail after the occurrences of global and local buckling, but the performance can be enhanced by employing concrete infill. The concrete-filled steel tube is an optimum combination of the two materials, resulting in an efficient, economic and practical structural member. Experiments were performed in which cyclic axial loading was applied to hollow and composite braces of each section type. Hot-finished specimens exhibited superior ductility to cold formed members. Concrete infill enhanced the tensile resistance for members of all lengths, the compressive resistance of shorter members and the number of cycles to failure. Finite element models were subsequently developed with ABAQUS® software, using the inbuilt nonlinear isotropic/kinematic hardening model and the damaged plasticity model to define the steel and concrete characteristics. Reliable simulations were achieved for the hollow braces but further work is required for the composite braces. Both local and global slenderness values influenced the specimen response. Expressions were proposed to predict the displacement ductility and energy dissipation capability of hollow braces in terms of these parameters. The findings suggest that distinct guidelines could be developed for introduction into Eurocode 8 for each steel section type, and that the benefits of concrete infill could be taken into account in dissipative design

Experimental investigation of bond behaviour of two common GFRP bar types in high-strength concrete

YesAlthough several research studies have been conducted on investigating the bond stress – slip behaviour of Glass-Fibre Reinforced Polymer (GFRP) bars embedded in high strength concrete (HSC) using a pull-out method, there is no published work on the bond behaviour of GFRP bars embedded in high strength concrete using a hinged beam. This paper presents the experimental work consisted of testing 28 hinged beams prepared according to RILEM specifications. The investigation of bond performance of GFRP bars in HSC was carried out by analysing the effect of the following parameters: bar diameter (9.5, 12.7 and 15.9 mm), embedment length (5 and 10 times bar diameter), surface configuration (helical wrapping with slight sand coating (HW-SC) and sand coating (SC)) and bar location (top and bottom). Four hinged beams reinforced with 16 mm steel bar were also tested for comparison purposes. The majority of beam specimens failed by pull-out. Visual inspection of the test specimens showed that the bond failure of GFRP (HW-SC) bars usually occurred owing to the bar surface damage, while the bond failure of GFRP (SC) bars was caused due to the detachment of sand coating. The GFRP bars with helical wrapping and sand coated surface configurations showed different bond behaviour and it was found that the bond performance of the sand coated surface was better than that of the helically wrapped surface. Bond strength reduced as the embedment length and bar diameter increased. It was also observed that the bond strength for the bottom bars was higher than that of the top bars. The bond strength was compared against the prediction methods given in ACI-440.1R, CSA-S806 and CSA-S6 codes. All design guidelines underestimated the bond strength of both GFRP re-bars embedded in high strength concrete.Ministry of Higher Education in Libya for funding

Use of bolted shear connectors in composite construction

[EN] Composite beam incorporated steel profiled decking has been extensively used for multi-storey buildings and is now one of the most efficient and economic form of flooring systems. However, the current composite flooring system is not demountable and would require extensive cutting on site during demolition, and the opportunity to reuse the steel components is lost even though these components could be salvaged and recycled. This paper presents the use of high strength bolts as shear connectors in composite construction, the shear behaviour and failure modes were observed and analysed through a series of push-off tests and numerical simulation. The results highlighted the structural behaviour of three different demountable shear connection forms in which continuous slabs or un-continuous slabs were used. Numerical models were validated against experimental observation. Both experimental and numerical results support the high strength bolts used as demountable shear connectors and lead to a better understanding to the behaviour of this form of shear connectors.The research leading to these results is part of a joint project of the Steel Construction Institute, the University of Luxembourg, the University of Bradford, the Lindab SA, the Tata Steel Ijmuiden BV, the Stichting Bouwen Met Staal, the Technical University of Delft and the AEC3 Ltd. The funding was received from the European Commission: Research Fund for Coal and Steel (RFCS-2015, RPJ, 710040).Dai, X.; Lam, D.; Sheehan, T.; Yang, J.; Zhou, K. (2018). Use of bolted shear connectors in composite construction. En Proceedings of the 12th International Conference on Advances in Steel-Concrete Composite Structures. ASCCS 2018. Editorial Universitat Politècnica de València. 475-482. https://doi.org/10.4995/ASCCS2018.2018.7039OCS47548

Flexural behaviour of composite slim floor beams

[EN] Composite slim floor beams comprise a steel section embedded in a concrete slab, offering the advantages of a steel-concrete composite structure combined with a reduced floor depth. Several mechanisms contribute to the shear connection in this type of beam, such as headed studs, friction and clamping effects and the using of reinforcement bars passing through holes in the steel beam web. However, to date, nobody has systematically identified these mechanisms and Eurocode 4 does not provide specific design guidance for slim floor beams. Hence, a series of shear beam tests and flexural beam tests were carried out in order to assess the degree of shear connection and connector capacity in these beams. The test set-up is described including different arrangements of shear connectors for each specimen. The paper presents the findings from the flexural beam tests. The results are compared with those from the previous shear beam tests. Numerical models will be developed in future to extend the data and include a wider range of parameters. The data will also be used to improve understanding of this type of beam and will lead to the provision of specific design guidelines for slim floor beams.The authors gratefully acknowledge the funding received from the European Community Research Fund for Coal and Steel under grant agreement number RFSR-CT-2015-00020.Sheehan, T.; Dai, X.; Yang, J.; Zhou, K.; Lam, D. (2018). Flexural behaviour of composite slim floor beams. En Proceedings of the 12th International Conference on Advances in Steel-Concrete Composite Structures. ASCCS 2018. Editorial Universitat Politècnica de València. 137-144. https://doi.org/10.4995/ASCCS2018.2018.6963OCS13714