Concrete Infill Research Articles

Cyclic behavior of autoclaved aerated concrete block infill walls strengthened by basalt and glass fiber composites

In this study, the effects of 10 mm bilaterally applied basalt and glass fiber reinforced (BRC and GRC) cementitious plasters with different fiber content (1.0%, 2.0% and 3.0%) on the behavior of the autoclaved aerated concrete (AAC) block infill walls were investigated. For this purpose, 8 infill walls with dimensions of 150 × 150 × 20 cm were produced to examine the behavior of the infill walls under reversed cyclic loading. The load carrying capacities, stiffness degradation and energy dissipation capacities of the infill walls placed in a steel frame with hinges on all four corners were determined by using hysteretic load–displacement curves to evaluate effects of fiber reinforced cementitious plaster. The test results show that BRC and GRC plaster applications considerably increase the load carrying and energy dissipation capacities of the infill walls. However, the experimental results illustrated that the usage of BRC plasters in strengthening of the AAC block infill walls needs more attention. Having similar results for different fiber ratios in the use of GRC reveals that it may be more rational to use 1.0% fiber content for the most economical solution for strengthening. Although the results obtained in this study are valid for infill walls, the experimental results show that GRC plasters can also be used in strengthening of masonry walls. It is recommended that this method can be used quickly and effectively in strengthening of masonry structures, which occupy an important place in the existing building stock.

Circular concrete filled thin-walled steel tubes under pure torsion: Experiments

This study experimentally explored the torsional behaviour of 33 specimens, which comprises of 18 concrete filled steel tube (CFST), 9 steel tube (ST) and 6 concrete (C) specimens. The length to diameter (L/D) ratio was 7.14 while the ratios of diameter to thickness (D/t) were 60.9, 46.7 and 40.0. The compressive strength of the infill concrete was 24.2 MPa (normal) and 33.3 MPa (relatively high). All specimens were tested to failure and the obtained data was analysed. The results indicated that buckling failure of CFST specimens was prevented due to the presence of concrete infill. Diagonal cracks of concrete infill observed on CFST specimens after cutting steel tubes are the evidence for the collaboration between steel tube and concrete. This evidence also reveals that the concrete infill contributes to increase the torsional moment capacity of CFST and helps steel tubes to work effectively. The superposition method fails to apply for CFST members under torsion because it does not take into account the mutually beneficial collaboration and interaction between steel tubes and concrete infill which resulted in the improvement on the failure mode, mechanical properties and behaviour of CFST specimens under torsion. Details of the test results and above-mentioned findings are reported in this paper.

Experimental Research on Reinforced Concrete Columns Strengthened with Steel Jacket and Concrete Infill

Experimental research on axially compressed columns made from reinforced concrete (RC) and RC columns strengthened with a steel jacket and additional fill concrete is presented in this paper. A premade squared cross-section RC column was placed inside a steel tube, and then the space between the column and the tube was filled with additional concrete. A total of fourteen stub axially compressed columns, including nine strengthened specimens and five plain reinforced concrete specimens, were experimentally tested. The main parameter that was varied in the experiment was the compressive strength of the filler concrete. Three different concrete compression strength classes were used. Test results showed that all three cross-section parts (the core column, the fill, and the steel jacket) worked together in the force-carrying process through all load levels, even if only the basic RC column was loaded. The strengthened columns exhibited pronounced ductile behavior compared to the plain RC columns. The influence of the test parameters on the axial compressive strength was investigated. In addition, the specimen failure modes, strain development, and load vs. deformation relations were registered. The applicability of three different design codes to predict the axial bearing capacity of the strengthened columns was also investigated.

Performance of concrete-filled stainless steel tubes subjected to concentric tension: Numerical investigation and parametric study

Concrete-filled stainless steel tube (CFSST) has great potential to be applied in the marine environment attributed to its excellent structural behavior and corrosion resistance. This paper presents numerical investigation and parametric study on the performance of CFSST members subjected to concentric tension. Firstly, a three-dimensional finite element analysis (FEA) model is established and validated against the experimental results reported in a companion paper. Secondly, the calibrated FEA model is used to investigate the tensile behavior of CFSST members, especially the composite action and stress distribution between the outer stainless steel tube and the concrete infill, which determines the load-carrying capacity of the steel–concrete composite member. Then, a wide-range parametric analysis is conducted by varying the parameters of both the stainless steel tube and concrete infill, and the influence of different parameters on the load-carrying capacity of CFSST tensile members is studied. Finally, a calculation model is proposed to be used to predict the ultimate strength of CFSST tensile members, and a good agreement is achieved between the model-predicted values and the FEA-computed ones.

Structural performance of concrete-filled cold-formed high-strength steel octagonal tubular stub columns

This paper presents a comprehensive experimental and numerical study on the structural performance of concrete-filled cold-formed high-strength steel octagonal tubular stub columns. Stub column specimens formed using high-strength steel and infilled concrete with grades C50 and C90, and with three different plate width-to-thickness ratios were tested. The ultimate loads, load-displacement responses and failure modes of the structures were observed and discussed. In addition to the experimental investigations, a finite element model validated using the stub column test results was developed. A series of parametric studies were subsequently conducted to obtain supplementary data for concrete-filled cold-formed high-strength steel octagonal tubular stub columns with a wide range of plate width-to-thickness ratios and different concrete compressive strengths. The applicability of existing design approaches in European and American standards and in literature provided for concrete-filled steel tubular structures with rectangular, circular or octagonal cross-sections were evaluated using the results obtained from the experimental and numerical study. The accuracy of design predictions for concrete-filled cold-formed high-strength steel octagonal tubular stub columns using different design approaches was discussed. A design approach that more accurately incorporates the strength contributions from steel tubes and concrete infill was also proposed for structural design.

Numerical Study Of Spun Pile To Pile Cap Connections In Soft Soil

Numerical study was conducted by SAP software to investigate behavior of two spun piles embedded in soft soil which were connected to pile cap based on Indonesia design code. Push over analysis were performed using SAP software with two different axial loads; 0.1 and 0.4 of fc.Ag and two different percentages of rebar on concrete infill. To ensure validity of numerical results, model validation was performed against experimental test conducted by other researcher. Horizontal spring was generated by LPILE software to represent soil. The results found that different axial force as 0.1 and 0.4 of fc.Ag affect the occurrence of moment crack of spun piles by 18% and 39%, respectively. Addition of rebar on concrete infill slightly improve moment crack of spun pile. Both parameters do not affect displacement ductility of pile which defines as ratio of maximum displacement to yield displacement.

Investigation of Tie Bars Axial Force Demands in Composite Plate Shear Walls—Concrete Filled

Tie bars axial force demands due to concrete dilation and prying action were investigated through numerical studies. In the first part of this study, the Karagozian and Case Concrete model, which proved to provide reasonable in-plane flexural cyclic inelastic wall response while accounting for concrete dilation effect, was used to investigate the variation of confinement inside the infill concrete, the distribution of passive confining pressures at the steel–concrete interface, and the resulting tie bar axial force demands. Finite element analyses involving C-PSW/CF having different tie spacings, wall depths, and wall thicknesses were performed. In the second part of this study, the influence of plate local buckling on tie bar axial force demand was investigated and explained by prying action. A separate finite element study was performed to investigate the significance of prying action and equations were developed from free-body diagrams. The results showed the significance of the passive confining pressures due to concrete dilation, and prying action due to local plate buckling, on imparting axial forces in tie bars. Neither of these behavior are currently considered as design parameters for tie bars. The numerical analyses and results presented here are intended to provide useful insights and direction for the design and instrumentation of future C-PSW/CF experiments by the broader research community.

Finite element modelling of concrete-filled spiral-welded mild-steel and stainless-steel tubes in flexure

This study investigated the capability of widely-used finite element modelling (FEM) methods, to predict the flexural capacity behaviour of concrete-filled spiral-welded mild-steel and stainless-steel tubes (CF-SWMSTs and CF-SWSSTs). For this purpose, twelve CF-SWMST and CF-SWSST flexural tests each were modelled using the ABAQUS software. The main parameters that had been varied in the respective tests were the outside diameter to thickness (D/t) ratio and infill concrete strength. The nominal D/t of the modelled specimens were in the range 51–114.5, while the infill concretes were of nominal grades 20 and 50 MPa. The moment capacities predicted by the FEM were observed to be, on average, conservative for the modelled CF-SWMSTs. The predicted flexural capacities were more closely in agreement with the corresponding experimental capacities for the CF-SWSSTs. The respective average actual to predicted moment capacity ratios were 1.07 and 1.00, respectively. The experimental and predicted deformation modes were also in qualitative agreement, with local buckling also being predicted by the finite element models. Though the experimentally obtained local buckling patterns were not exactly replicated, there was, nonetheless, good qualitative agreement. This study provided evidence of the capacity of commonly used FEM approaches, relating to CFSTs, to act as a predictive tool for CF-SWMSTs and CF-SWSSTs in flexure. Given the distinct difference in capacity prediction conservativeness, the study also indicated that separate material model formulations may be warranted for CF-SWSSTs compared to CF-SWMSTs. The predicted results were also found to be negligibly sensitive to explicitly modelling the spiral weld seam geometry, even though it was the default case adopted for the FEM in this study.

Experimental behavior of laser cut I-beam-to-CHS-column steel-concrete composite joints under vertical loads

This paper presents the results of an extensive experimental campaign on I beam to Circular Hollow Section column joints obtained cutting a dedicated slot on the column through precision laser technology and letting the beam or connection plates pass through the column itself. The application of this technology minimizes the welding necessary to complete the connection, the number and dimensions of the plates, and it assures the continuity of the beam within the column leading to a more favorable mechanical behavior of the joint under vertical loads. Even if the passing-through beam idea was already tested in the past, only recently the laser cutting technology made it really feasible and competitive from a technical and economic point of view. However, several issues about this structural solution needs further clarifications, especially when considering the interaction of the bare steel node with the reinforced concrete slab or the influence of the infill concrete in the column. For this reason, within this research, different joint configurations were designed extrapolating them from realistic case study buildings and testing them under monotonic vertical loads. To deeply understand their behavior, the specimens were designed and realized as four-way joint, differentiating the structural scheme of the joint connecting the main beams and the joints connecting the secondary beams, obtaining a representation of the most common solutions currently adopted in the real practice.

Effect of self‐compacting concrete infill on the flexural behavior of hollow channel sections: Experimental and numerical studies

AbstractUse of hollow cold‐formed steel (CFS) sections has gained popularity in the construction of light industrial and commercial structures. However, their overall load carrying capacity under flexure can be severely affected due to the possible buckling failure modes. Addition of concrete as an infill material for hollow CFS sections can significantly improve their overall performance by resisting their inward local buckling. In this paper, the effectiveness of self‐compacting concrete (SCC) as an infill material for hollow channel sections (HCS) is investigated under flexure. In total, nine full‐scale hollow channel sections with and without SCC infill are tested to understand the effect of different parameters namely (i) width to depth ratio, (ii) section thickness, and (iii) developed length. In addition, a detailed nonlinear finite element (FE) modeling was performed using the software ABAQUS. Moreover, an analytical investigation was performed to determine the ultimate moment capacity of SCC infilled sections using the strain compatibility procedure. Test results revealed that the addition of SCC infill helped in increasing the ultimate moment resistance by more than 100% when compared to the specimens with no infill. Moreover, the local buckling resistance of HCS is significantly improved due to the addition of SCC infill. The validated analytical and finite element models were used for performing an extensive parametric investigation.

Revisiting the composite action in axially loaded circular CFST columns through direct measurement of load components

The composite action in circular concrete-filled steel tube (CFST) columns under axial compression is one of the most fundamental problems in the research area of steel-concrete composite structures. However, it cannot be easily investigated through experiments as the load components of the steel tube and concrete infill cannot be measured in a conventional axial loading test. In this study, an innovative testing method was devised to directly measure the load components of circular CFST columns under axial compression. Six innovative specimens with varying concrete strength and diameter-to-thickness (D/t) ratio and their conventional counterparts were tested. Although some difference existed between the load-deformation responses of the innovative and corresponding conventional specimens, it was essentially insignificant. The development of hoop stresses in the steel tube tends to reduce the corresponding axial stresses, but this effect can be offset by the strain hardening of the steel tube. Strain hardening of the steel tube should be considered when evaluating the confinement effect at the ultimate load, especially for columns with low concrete strength and small D/t ratio. The average values of the coefficients related to the axial and hoop stresses of the steel tube at the ultimate load, computed using available tests results, are 0.92 and −0.14, respectively. The proposed axial load capacity formula with these two values can reasonably predict the ultimate loads of circular CFST columns under axial compression.

Seismic performance evaluation of a steel tubular bridge pier in a five-span continuous girder bridge system

The seismic performance of a steel tubular bridge pier in a five-span continuous girder bridge system was evaluated through dynamic non-linear time-history analysis under strong ground motions. The seismic performance of the hollow steel tubular (HST) and partially concrete-filled steel tubular (PCFST) bridge piers was assessed with different eccentricities of superstructure. Considering the variation of ground classification under rare earthquakes, six seismic waves were input. The analytical results indicate that the eccentricity of superstructure has little effect on the maximum displacement response of the HST bridge piers and the PCFST bridge piers under ground motion excitations in the longitudinal (LG) direction; however, under the ground motion excitations in the transverse (TR) direction, the maximum displacement response of the bridge piers increases when the eccentricity (e/H) increases from 0 to 0.2, which implies that eccentricity affects the seismic response of the two types of piers. Both in the LG direction and TR direction, the HST piers have reached their yield strengths; stress concentration and local buckling were observed around the plastic hinge zone and the load bearing capacity decreases. Although the PCFST piers entered the elasto-plastic range, the expansion of local buckling deformation of the steel tubular column has been restrained by the concrete in-fill. According to the simulated results, the PCFST pier exhibits high ductility and bearing capacity, which can improve the seismic performance of the bridge system.

Mechanical model of steel frames with reinforced concrete infill walls

This paper presents a mechanical model developed for the simulation of the monotonic behaviour of Steel frames with Reinforced Concrete infill Walls (SRCW). In particular, it deals with a specific typology of SRCW, obtained from the classical one through the interposition of dissipative elements in the columns and by stiffening and shaping the steel frame’s corners in a way to prevent the brittle failure of the concrete in compression. This system has demonstrated in past researches to be able to overcome the typical problems of SRCWs and to assure, through a capacity design approach, a global ductile behavior. The selection of the main components to be included in the model is carried out on the base of the analysis of the available experimental tests and of the results of accurate 3D Finite Element model analyses. The behaviour of each component is represented though consolidated models present in the current state-of-the-art and, where necessary, calibrated using the results of the experimental and numerical analyses. The capacity of the proposed mechanical model in representing the global behaviour of the SRCWs is finally demonstrated comparing the results in terms of force–displacement curves with the ones obtained through the refined 3D Finite Element models.

Experimental and numerical analysis of cold-formed steel floor trusses with concrete filled compression chord

Floor trusses fabricated from cold-formed steel (CFS) sections offer several advantages over more conventional floor systems. The current paper reports the findings of an integrated experimental and numerical study focusing on the behavior of CFS floor trusses made of lipped channel sections with the compression chord member filled with concrete. This type of configuration occurs when CFS trusses are used together with a cast-in-place concrete slab. The experimental part of the study included load testing of seven full-scale CFS floor trusses, while numerical investigation included three-dimensional finite element modeling of these trusses. An analytical procedure based on a simple linear-elastic mechanics approach was also developed in an attempt to predict the response of steel-concrete composite CFS trusses without the need of detailed FE analysis or physical testing. Test results indicate that presence of concrete infill inside the compression chord member prevented the initiation of chord local/distortional buckling. In these specimens the failure mode was tension yielding of the bottom chord member. With the introduction of concrete infill within compression chord, significant improvement in truss response in terms of increase in stiffness and load capacity was obtained. The increase in load capacity was 41% and 46% depending on the orientation of the compression chord member. Presence of a concrete slab resulted in an additional 27% increase in load capacity. Truss response predicted by nonlinear FE analyses agrees well with the measured response, both in terms of global load-deflection behavior and chord strains.

Flexural properties of concrete-filled, double-skin, square-hollow-section tubular beams

Concrete-filled double-skin tubular beams consist of two tubes, placed eccentrically or concentrically, with the hollow space between the two tubes filled with concrete. This type of construction can thus combine the properties of steel and concrete to provide the advantage of increased strength, ductility, stiffness and economy of the section. This paper reports on a study into the flexural properties of beams made of square hollow section steel for the both inner and outer tube, connected with steel strips. In total, 12 specimens were tested under monotonic and cyclic loading. The effects of the concrete infill, the eccentricity of the inner tube, the provision of minimum steel reinforcement and slip control due to the attachment of steel strips at the end of the beams were studied. Beams with an eccentric inner tube showed better flexural response and were also more economical due to the reduced concrete volume; their load-carrying capacity under cyclic loading was less than that under monotonic loading. Compared with beams without longitudinal reinforcement, the beams with longitudinal reinforcement showed improved flexural strength when subjected to cyclic loading.

The different effect of cyclic loading protocol on spun pile performance

Numerical study to investigate the effect of various loading protocol to seismic performance of spun pile connection has been performed using OpenSees. Six loading protocols adopted in FEMA P440 were applied to three specimens. The study started with validation of FE model, and the model can closely simulate the experiment conducted by another researcher. The loading was presented in the form of a drift ratio, a number of cycles, and the rate of loading. It is found that different types of loading protocols affect seismic performance in terms of stiffness and strength degradation. Among six loading protocols, TP-01, as adopted in ACI 437.1R-07, give moderate results. Significant stiffness degradation was observed on hollow spun pile compare to those with concrete infill. It is found that the presence of concrete infill improves the strength of the spun pile connection by 45%. Increase the strength of concrete infill slightly improve the performance of spun pile.

Building wall corner structures, its microclimate and seismic resistance

Widespread low-rise residential buildings with a seismically resistant concrete frame and brick infill walls have lower microclimate levels in cold seasons due to low temperatures on the inner wall corner surfaces.These temperatures are lower if there is a corner column. For Bishkek, this temperature is 4.6 °C lower than that for permissible microclimate, even when the external wall has the required 70 mm of mineral wool slab insulation. It is caused by the negative effect of the wall corner thermal bridge. This effect is determined by ArchiCAD 20 software packages by visualizing the temperature distribution in the cross-section of the corner, which needs an additional thermal insulation layer of 40 mm. Using the LiraSAPR 2013 software package, the authors reduced the square cross-section dimensions of the column by 40 mm to allow for that additional thermal insulation layer. The optimal width of this layer is determined for different options for the meeting angle of two external walls from 70° to 180°. For a typical 90° angle, an acceptable width is 860 mm. With this insulation, it is possible to achieve the required temperature at the corner. The authors eliminated the negative thermal effect of the corner by rounding it with cement-sand plaster. Using the isotherms, it was determined that the rounding radius of 300 mm allowed for equal temperatures on the corner and inner surface of the external walls. The achieved results show that the microclimate formed as in a room without external wall corners.

Cyclic Behavior of SCBFs with Through-Gusset Plate Connections and Concrete-Filled Tube Columns

ABSTRACT In Hollow Structural Section (HSS) column-beam-brace connections, offset between gusset plate and HSS column webs leads to large distortion and out-of-plane deformation in HSS column face. To alleviate such undesirable effect, this paper proposes a new connection which consists of concrete infill and gusset plate passing through HSS column, called Through-Gusset Plate (TGP).The results indicated that the proposed connection increases the lateral stiffness, lateral strength, and energy dissipation capacity of frame specimens by up to 74, 67, and 73%, respectively. Moreover, due to using this novel connection, the normal force component capacity of connection is enhanced by approximately 3.2 times.

Computational simulation of eccentrically loaded reinforced concrete walls formed with modular thin-walled permanent formwork system

Stay-in-place formwork (SIPF) systems represent a conventional formwork-free, corrosion-resistant substitute for construction of new reinforced concrete walls. The composite of infill concrete and thin-walled fibre cement board (FCB)/steel studs SIPF consists of a core concrete, filled between two FCBs that are connected to each other using steel studs, embedded to the concrete infill. Similarly, the concrete-filled Polyvinyl Chloride (PVC) hybrid system is comprised of extruded PVC interlocked encasements core-filled with concrete. These lightweight structural SIPFs are utilised in modular construction in which the system is prefabricated in the factory, transported to the site, erected and assembled for concrete casting. Further, the SIPF-encased wall is a composite system that facilitates taking advantage of mixed effects of reinforced concrete and SIPF. These are the major benefits of these systems compared to conventional formwork systems. However, there is a gap in knowledge regarding the strength and ductility measurement of SIPF-encased walls under eccentric axial loads that is presented in this paper. A series of tests was conducted to failure on both composite walls and compared with the reference specimens, i.e. standard walls (STWs). Substantial finite element (FE) studies considering material and geometric nonlinearities as well as contact behaviour are also performed. After a reasonable model verification against test results, a comprehensive parametric investigation accounting for the concrete compressive strength, the thickness of SIPF components (i.e. steel studs, FCB, and PVC), longitudinal bar reinforcement, and axial load ratio is performed. Further, the experimental and numerical results are used to assess the suitability of the theoretical formulation specified in the current Australian Standard (AS3600) for the axial-flexural interaction resistance of SIPF-encased walls. It is demonstrated that the predictions from the current design specifications are overall conservative. Further, it is found that FCB/steel studs SIPF effectively contributes to improve curvature ductility index and axial-flexural strength compared to STWs.

Behavior and modelling of FRP-concrete-steel hybrid double-skin tubular columns under repeated unloading/reloading cycles

Fiber-reinforced polymer (FRP)-concrete-steel hybrid double-skin tubular columns (hybrid DSTCs) consist of an outer FRP tube, an inner steel tube and a concrete infill between the two tubes. Extensive research has been conducted on the monotonic behavior of hybrid DSTCs, but only a limited number of studies have examined their behavior under cyclic axial compression. In particular, no systematic experimental study has been conducted on hybrid DSTCs under repeated unloading/reloading cycles. This paper first presents a systematic experimental study on hybrid DSTCs under two types of loading schemes: (a) a single unloading/reloading cycle to evaluate the relationship between the unloading strain and the plastic strain; (b) repeated unloading/reloading cycles to investigate the effect of loading history. In the present study, hybrid DSTCs were prepared using filament-wound FRP tubes of a relatively large scale (up to 300 mm in diameter), and the experimental program covered a wide range of concrete strengths (from 40.9 MPa to 104.4 MPa). The systematic experimental study with extensive instrumentation allowed the cyclic stress-strain behavior of the concrete in hybrid DSTCs to be examined in detail, clarifying the cumulative effect of the loading history on both the stress deterioration and the plastic strain of the concrete. This paper also presents a detailed comparison between the test results and the predictions of an existing cyclic stress-strain model for FRP-confined concrete in solid columns, in terms of the repeated unloading/reloading cycles. The cyclic stress-strain model is shown to provide reasonably accurate predictions, and thus can be used together with a monotonic stress-stress model for the concrete in hybrid DSTCs to predict the complete cyclic stress-strain curve of such concrete.