Ultimate Load Behaviour Research Articles

Investigation on behavior of concrete-filled double steel tubular columns infilled with nanomaterial-based concrete subjected to axial compression

Nanotechnology has been applied in construction to enhance the mechanical properties of concrete by using nanomaterials. A new stiffening scheme called catty-cornered propped concrete-filled steel tube (CFDST) column was proposed and analyzed under axial compression. The steel tube of CFDST specimens was filled with normal and nano material-based concrete, including nano-silica (NS), carbon nanotubes (CNT), and nano-titanium dioxide (NT). The study collected data on ultimate capacity, load vs strain behavior, and load vs deformation response, as well as ductility index (DI), secant stiffness, composite interaction, and confining effect variation. The results showed that the proposed stiffening scheme increased the ultimate capacity of unstiffened CFDST by approximately 14%, and the use of nanomaterials in CFDST infill concrete resulted in an approximately 7% increase in load capacity. Increasing the number of stiffening bars improved the ductility and stiffness of the column section, while the inclusion of nanomaterials decreased the ductility index and improved the stiffness of the section. The proposed stiffening scheme resulted in better composite interaction and increased confinement. The study concluded that the utilization of nanomaterial-based concrete as an infill in the stiffened CFDST column could enhance its performance under axial compression loading.

Optimization of non-bearing splice connection in GFRP short columns by manual testing and finite element analysis

Connection designs are established to ensure the stability of joined cut sections, the joints so designed should be based on the optimal performance as per the requirements. The connection joints so established should not be based on just strength but reliability and durability as well. This study focuses on tackling one of the major issues faced when using Glass Fibre Reinforced Polymers (GFRPs) as construction materials, which is based on the abrupt failure of the material under critical or maximum loading. Connection designs are established in GFRP short column H-sections based on Bolted Splicing connections by Eurocode 3 for steel splicing connections. A total of seven Connection designs are established using bearing and non-bearing splicing connections. A total of five models for each connection is established for manual testing and Finite Element Analysis (FEA) is used to simulate and analyze these connection designs. Parameters such as ultimate load, displacement at ultimate load, stiffness, compressive strength, failure mode, load versus displacement behavior graph, and percentage compressive strength compared to the un-cut section are provided in this study. The strongest specimen in this study displaced 128% and 127.7% compressive strength compared to an un-cut GFRP H-section when tested using manual testing and FEA accordingly.

Behavior of Smart Beams Reinforced with Superelastic Shape Memory Alloy Rebar (SMA)Subjected to Repeated Loading

A reinforced concrete beam with shape memory alloy rebar (SMA) is a novel form of smart beam used in smart seismic structural systems to reduce the effects of earthquakes while keeping nearly the same load-carrying capability as conventional concrete beams. The experimental research investigation is carried out to study beams' flexural behavior by replacing some steel rebars with shape memory alloy rebars (SMAs) in the longitudinal reinforcement zone. The experimental program included testing three beams to investigate the effects of the replacement of longitudinal steel rebar by shape memory alloy rebar on the flexure behaviour of beams. The beams were tested by the repeated load. The study was focused on determining ultimate load, maximum deflection, and load-deflection behaviour. Experimentally, the flexure behaviour beams are significantly affected by changing the number of reinforcing bars with shape memory alloys (SMA) longitudinal direction. However, for using one rebar of shape memory alloy as a longitudinal reinforcement, the replacement of one bar and two bars of shape memory alloy SMA beams have less yield load than the control beam by about (12.5%) and (37.5%) respectively. The replacement of one bar and two bars of shape memory alloy SMA beams having less ultimate load compared with reference beam by about (9.82%) and (21.94%) respectively. Because of its superelasticity quality, the introduction of superelastic SMA bars to the beam shows excellent recentering ability.

Ultimate Load Behaviour of Castellated Beams with Stiffened Octagonal Openings

ctagonal castellated beam is fabricated by adding spacer plates between the web joints of the hexagonal castellated beam to further increase the beam depth. The resulted deep beam is advantageous to enhance the shear carrying capacity and moment resistance. However, large web openings are prone to Vierendeel mechanism in the deformation that lowers the overall beam performance due to formation of plastic hinges. The present paper is concerned with non-linear analysis to predict the ultimate load behaviour of octagonal castellated beams. Finite element models were developed by using a commercial programme LUSAS. The numerical models were first validated against the experimental results reported by other researchers. This study aims to propose the ideal configuration of web opening stiffeners and evaluate the effectiveness of the additional stiffening material for different beam span lengths. Provision of ring stiffeners is effective in short span beams in respect of resistance to Vierendeel failure. The stiffeners have increased the ultimate load to the extent of 73% in which the strength restoration is considerably near to the capacity of its parent universal beam. In long span beams, however, the stiffeners can only improve the performance up to 26.61% with larger additional steel materialthan that of shorter span. In all cases, the stiffener thickness is found to be the governing factor to restoring the loss of shear strength due to large web openings. The number of stiffeners contributes no appreciable variation of ultimate load particularly in long span beams where bending is prominent

Behavior of stiffened concrete-filled steel tube columns infilled with nanomaterial-based concrete subjected to axial compression

The use of nanotechnology in the field of construction emerged as the utilization of nanomaterials to improve the mechanical properties of concrete. In this study, a novel form of stiffening scheme was suggested, named a catty-cornered propped concrete-filled steel tube (CFST) column. The performance of the suggested stiffened CFST column was analyzed under axial compression. The steel tube of CFST specimens was filled with normal and nanomaterial-based concrete. The three kinds of nanomaterials were utilized viz., nano-silica (NS), carbon nanotubes (CNT), and nano-titanium dioxide (NT). The results of the investigation were collected in terms of ultimate capacity, load vs strain behavior, and load vs deformation response. The ductility index (DI), secant stiffness, composite interaction, and confining effect variation were also discussed further. It was observed that the suggested stiffening scheme was able to increase the ultimate capacity of unstiffened CFST by approximately 14%. The use of nanomaterials in CFST infill concrete also resulted in an approximately 7% increase in load capacity. Further increasing the number of stiffening bars improved the ductility and stiffness of the column section. On the other hand, the inclusion of nanomaterials resulted in a decrease in the ductility index and improved the stiffness of the section. The proposed stiffening scheme resulted in better composite interaction and increased confinement. It was also concluded that the utilization of nanomaterial-based concrete as an infill in the stiffened CFST column could enhance its performance under axial compression loading.

Shear strengthening of continuous RC T-beams with deep embedded CFRP and steel bars: A numerical study

This paper presents a non-linear finite element parametric study of continuous RC T-beams shear retrofitted with deep embedded (DE) carbon fibre reinforced polymer (CFRP) bars and steel bars. Two-dimensional nonlinear finite element (NLFE) models for these shear-retrofitted beams have been developed and validated with the published literature based on the ultimate shear strength, load versus displacement behaviour, failure mode and strain developed in the longitudinal steel at mid-span. NLFE models of five RC T-beams are developed, out of which one model is for the un-strengthened beam, two are for the shear retrofitted beams with vertical DE bars and the leftover two are for the shear retrofitted with inclined 45° DE bars. Parametric investigations have been conducted to evaluate the impacts of shear span to depth ratio (a/d), compressive strength of concrete, effective beam depth and DE bar reinforcement to the existing shear links ratio on the shear strength, load versus deflection behaviour and strain developed in the shear links of these continuous beams. It is found that the above considered parameters of the continuous RC-T beams influence the shear capacity, load–displacement behaviour and strain in the shear link significantly. Moreover, the present work will provide sufficient knowledge to the designers for designing the shear retrofitted RC beams with DE bars.

Experimental–numerical studies of failure behavior of PLC optical splitters under uniaxial tensile loading

This work presents an experimental and numerical study of the failure behavior of planar lightwave circuit (PLC) optical splitters under uniaxial tensile loading. Based on the experimental results, the specific fracture position, ultimate failure load (Pm), failure mode and load-displacement behavior of the PLC optical splitter under uniaxial tensile loading were determined. In order to numerically simulate the real fracture behavior and stress distribution of adhesively bonded joints, a three-dimensional (3-D) explicit finite element analysis method based on material constitutive and tiebreak contact algorithm was proposed, which treats cohesive failure and adhesive/interfacial failure separately. The Pm predicted by the numerical simulation agrees well with the experimentally obtained Pm with a relative error of ∼4.3%, and the predicted failure mode is also similar to the experimentally observed mixed failure mode, which proves the accuracy and rationality of the adopted finite element method and model. This study can provide useful references for the reliability design and optimization of PLC optical splitters.

Numerical Investigation on the Axial Load Behaviour of Polygonal Steel Tube Columns

Hollow steel tubes members with different properties are being increasingly used for structural applications, such as columns in frame structures, roof structures, truss columns, and other applications. These structural members are primarily subjected to compressive and flexural loading. Due to the insufficient studies regarding the influence of the cross-section’s shapes on the axial load behaviour of hollow steel columns, this study has presented eight different cross-sections shapes and has indicated their effect on the axial load behaviour of the polygonal hollow steel columns. Eighty different FE models have been designed and analysed to find the effect of the cross-section shape, thickness, length, and materials on the axial load behaviour of the polygonal hollow steel columns. The FE results have proved that the cross-sectional shapes affect the ultimate axial load behaviour of the hollow steel tubes by 14%. The highest ultimate axial load resistance recorded by Rec. model has been followed by Squ. unlike Cir. model, which has presented the lowest ultimate axial load resistance followed by Ova. model. This study also demonstrates that when the cross-sectional shape of the hollow steel tubes is near to a rectangular shape, the ultimate axial load resistance will be higher, while, if it is near to a circular shape then low ultimate axial load has been registered. Moreover, there is a small effect of the steel tube thickness, length and material on the axial load behaviour of the hollow steel tubes with different cross-sectional shapes, with almost -2% to -14%.

Flexural Behaviour of SFRC Curved Deep Beams

Abstract: As per IS 456:2000, deep beams can be defined as the structures that having span to depth ratio less than 2 for a simply supported beam and 2.5 for a continuous beam. Also these members are loaded on one face and supported on the opposite face. Uses of curved deep beams are increasing in structures like rounded corners of buildings, circular balconies, water tanks etc. Steel Fiber Reinforced Concrete (SFRC) is a concrete with short, discrete lengths of steel fibers which are randomly dispersed. The load deformation behavior of curved deep beam of different curvatures gives an idea about the effect of curvature on the performance of curved deep beam. The structure that generates comparatively small deformation within the applied load can be considered as relatively safe. This paper illustrates the effect of curvature or central angle on the ultimate load behavior of SFRC curved deep beam and analyzing its flexural behaviour. Steel Fiber Reinforced Concrete with 1% steel fiber is used in the current study. The central subtended angles adopted for the study are 00 , 450 , 600 , 900 , 1200 , and 1800 . As the central subtended angle increases, curvature also increases. The analysis of the structure has been carried out using ANSYS Software

Parametric study of trapezoidally corrugated web beam

In this paper, the behaviour of cold-formed steel beam having trapezoidal corrugation profile of web has been studied by finite element method using ANSYS APDL V12.0. In this investigation, the considered parameters are corrugation angle, and the thickness of web plate. The corrugation angle has been varied from 30˚, 33˚, 36˚ 39˚, 42˚ and 45˚. The thickness of the web is taken as 3 mm. From the study, it is concluded that a rise in corrugation angle leads to an increase in the strength capacity of beams. The average increase in strength capacity of a corrugated web beam is 22% over a plain web beam. The 45˚ angle of web corrugation is found to be excellent amongst all angles of web corrugation. The height to thickness (h/tw) ratio is the main variable responsible for the buckling of the beam. As the ultimate load behaviour of trapezoidal corrugated web beams with stiffeners was found to be better than beams without stiffeners, therefore its importance cannot be neglected in the analysis and design.

Punching shear behaviour of interior slab-column connections strengthened by steel angle plates

The present paper is concerned with a series of tests on reinforced concrete flat slabs to examine the behaviour of interior slab-column connections employing steel angle plates and high strength bolts as strengthening elements. The angle plates were bolted to the column faces and slab at both tension and compression sides. The shorter leg of the angle plate attached to the column face acts as a column capital of an equivalent concrete width whilst the longer leg is treated as a drop panel of an equivalent concrete depth. Four flat slabs of practical size were constructed and tested to failure under shear load applied through the column. The strengthening technique has effectively turned the final mode of failure from punching shear to flexure-induced punching outside the strengthened zone. Such slab system has shown appreciable increases in the deformation capacity, stiffness, energy absorption and particularly load-carrying capacity with 20%, 24%, 209% and 51% in average, respectively over that of the unstrengthened slab. Non-linear finite element models were developed, analysed and validated against the test results, only to find that both findings were found to be in a good agreement. A parametric study was performed to investigate the effects of bolts strength, bolts spacing and dimensions of angle plates on the ultimate load behaviour of the slab. A simple theoretical method based on yield line theory to predict the flexural capacity of the strengthened slab is also outlined. In addition, the tests and numerical results are compared with the values predicted using the ACI design code.

Albemarle reports 4Q and full year 2020 results: Catalysts

The present paper is concerned with a series of tests on reinforced concrete flat slabs to examine the behaviour of interior slab-column connections employing steel angle plates and high strength bolts as strengthening elements. The angle plates were bolted to the column faces and slab at both tension and compression sides. The shorter leg of the angle plate attached to the column face acts as a column capital of an equivalent concrete width whilst the longer leg is treated as a drop panel of an equivalent concrete depth. Four flat slabs of practical size were constructed and tested to failure under shear load applied through the column. The strengthening technique has effectively turned the final mode of failure from punching shear to flexure-induced punching outside the strengthened zone. Such slab system has shown appreciable increases in the deformation capacity, stiffness, energy absorption and particularly load-carrying capacity with 20%, 24%, 209% and 51% in average, respectively over that of the unstrengthened slab. Non-linear finite element models were developed, analysed and validated against the test results, only to find that both findings were found to be in a good agreement. A parametric study was performed to investigate the effects of bolts strength, bolts spacing and dimensions of angle plates on the ultimate load behaviour of the slab. A simple theoretical method based on yield line theory to predict the flexural capacity of the strengthened slab is also outlined. In addition, the tests and numerical results are compared with the values predicted using the ACI design code.

Experimental and numerical studies on the flexural behavior of fibre reinforced concrete beams with innovative hybrid FRP-wrapped steel bars

ABSTRACT The durability and lifespan of concrete structures are significantly affected by the corrosion of steel reinforcement. Though epoxy-coated steel reinforcement is being used for practical applications, slight damage in the coating during the construction process is enough to initiate the corrosion process. The shortcomings in the current practices to prevent corrosion of steel reinforcement have led the researchers to look for alternatives. Innovative hybrid reinforcing elements with solid steel core and fibre-reinforced polymer (FRP) wrapping (called steel–FRP composite bars (SFCB)) can be considered as a suitable alternative to conventional steel reinforcement. In this research paper, experimental and numerical studies that investigated the flexural behaviour of concrete beam specimens reinforced with SFCB produced using glass fibres or carbon fibres are presented and discussed. Experimental study consisted of flexural testing of six concrete beam specimens with conventional steel reinforcement or SFCB with glass fibres or SFCB with carbon fibres. Two different spacings of shear stirrups were considered. Failure mode, first crack load, ultimate flexural load and load-deflection behaviour were recorded during the experiment. The test results showed that beam specimens with SFCB reinforced achieved less ultimate flexural load as compared to beam specimens with conventional steel reinforcement. The failure mode was found to be influenced by the spacing of the shear stirrups. The results of the numerical analysis were close to the experimental results. .

Behaviour of thin-walled castellated beams strengthened using CFRP

This paper presents the behavior of Carbon Fibre Reinforced Polymer (CFRP) strengthened Thin-Walled Castellated Beams (TCBs). A detailed experimental study was carried out in two phases viz, 1. Study on effective bonding between steel substrate and CFRP under varying surface preparation scales, 2. Ultimate load behavior of TCBs provided with and without CFRP strengthening. While studying the effect of bonding between steel substrate and CFRP under various surface preparation, the bond strength of specimens prepared with copper-slag blasting was potentially stronger due to the maximum ultimate direct tensile stress of 2.54 N/mm2 in pull-off test. The investigation on ultimate load behavior of TCBs provided with and without CFRP strengthening was carried out experimentally on ten beams under the domination of Shear (SDB), Moment (MDB) and Moment & Shear (MSDB). This strengthening process was more effective in MDBs. Especially the load carrying capacity was increased by 35.38% in plastic section and 42.53% in semi-compact section and significant ductility enhancement observed in MDBs. Simultaneous interaction between shear and bending mode of failure of TCBs were studied.

Modeling the Flexural Performance of Reinforced Concrete Built-up Beams

Finite element modeling is used for tracking the flexural response of built-up reinforced concrete beams under the influence of dominant flexural loading. ABAQUS finite element analysis program was used toward this goal, due to its superior capability to represent the mechanical properties of concrete including compressive and tensile strength in strain hardening and softening behaviors; and the features related to steel reinforcement rebar. This study is based on the comparison between the theoretical analysis by the finite element method and the experimental results. The experimental program consists of casting and testing six rectangular cross-sections of simply supported reinforced concrete beams. Two beams are cast as a reference which fully Conventional Concrete (CC) and Reactive Powder Concrete (RPC), the rest four were built-up beams made by the combination of two types of concrete in one element. The study deals with, the load which caused a first crack, ultimate carrying capacity, load and deflection behavior at mid-span of beams, cracks patterns, and damage index of the examined beams. Good agreement was gained with the available experimental results that show the effectiveness of the finite element method for simulating the flexural performance of beams.

Analysis of carbon fibre reinforced polymer wrapped square steel tubular sections under compression

This paper presents the Finite Element (FE) analysis of Square Hollow Steel (SHS) tubular sections externally wrapped with Carbon Fibre Reinforced Polymer (CFRP) strips under axial compressive load. CFRP sheets are used as strip form and the width of the strip is 50 mm. The spacing between the strips is considered as a constant of 20 mm and the numbers of layers are one, two and three in the horizontal direction. All the samples are subjected by axial compressive load till reached their ultimate failure load. From the test results, the failure style, axial load and displacement, Ultimate load and stress strain behaviour were compared with the control and each other. Finally a numerical analysis were designed for failure style, stress strain, ultimate load and axial displacement using ANSYS package and validated with the test results. FE modelling provided a suitable wrapping scheme for SHS tubular members.

Compression Splices of Reinforcing Bars in Reactive Powder Concrete

Compression splices are widely used in compression members such as columns in multi- story buildings. There are efficient design equations for compression splice of reinforcement embedded in conventional concrete proposed by design codes of practice. However, there is no design equation for compression splice in compression members made of reactive powder concrete (RPC). So, it is required to introduce a design equation to calculate the steel bars lap splice length of RPC compression members. In this study, an experimental work was conducted to investigate the effect of different variables on compression splices strength. These variables were compressive strength of concrete, transverse reinforcement amount, splice length, yield stress of reinforcement and spliced rebar diameter. The experimental results showed that; Increase in the yield stress of reinforcing bars, length of spliced bars and compressive strength of concrete result in increasing in splice strength. Meanwhile, increase in diameter of reinforcing bars result in decreasing in compression splice strength. The increase in the amount of transverse reinforcement has insignificant effect on compression spliced strength of rebar. Finite element analysis was used to analyze the tested specimens and compared between numerical and experimental result was carried out. The numerical and experimental ultimate load and load-deflection behavior is very close to each other. Finite element method was used to investigate a wide range of experimental variables values through a parametric analysis. A new proposing equation for compression splicing of rebar in RPC column is presented in this research.

Uni-axial behaviour of externally confined UHSCFST columns

Thanks to the larger and more continuous confining stress provided by hollow steel tube, ultra-high-strength concrete-filled-steel-tube (UHSCFST) columns are advocated rather than conventional transverse steel confined ultra-high-strength concrete. However, during elastic stage, de-bonding occurs as the Poisson's ratio of steel is larger than that of concrete, whereas in post-elastic stage, confining stress, strength and ductility of concrete decrease since the steel tube would buckle. Thus, the composite action cannot be fully developed. To overcome these problems, external confinement in the form of tie bars, steel rings and steel spirals are proposed in this paper to increase the confinement effect of UHSCFST columns. A series of uni-axial compression test has been conducted to study the behaviour of externally confined UHSCFST columns. Results showed that the proposed confining schemes can effectively improve the strength, elastic stiffness and ductility of UHSCFST columns. Moreover, rings and spirals are more effective than tie bars. Lastly, a modified theoretical model based on that developed previously by the authors was used to predict the ultimate load and axial load-strain behaviour of the tested columns, in which excellent agreement between the theoretical and experimental results has been obtained.

A Review of Previous Studies on the Reinforced Concrete Corbels

Corbels are short-hunched cantilevers that project from inner face of columns to support heavy concentrated loads or beam reactions. They are very important structural elements for supporting precast beams, girders and any other form of precast structure systems. ACI 318-14 provisions allow the structural design of shear-controlled corbels through either an empirical design method such as the shear-friction method or the strut-and-tie modeling (STM). This paper reviews some previous research studies on reinforced concrete corbels. From this literature; it was concluded that the STM method provides a more accurate estimation of ultimate load capacity and behavior than the shear-friction method. The ultimate shear strength increases with increasing main reinforcement, compressive strength (f’c), the presence of fibers, while it decreases with the increase of shear span-to-effective depth ratio (a/d) and horizontal to vertical load ratio (Nu/Vu).

Ultimate load behaviour of steel beams with web openings

ABSTRACTA detailed study on the ultimate load behaviour of steel beams with openings in the web is presented in the paper. Hot rolled steel beams ISMB 100 with openings in the web were tested to failure. The beams were simply supported at the ends and subjected to a concentrated load at the mid span. The behaviour of such special type of beams was closely studied in order to obtain a complete picture of the failure, to get the optimumspacing to diameter ratio for openings. All the beams were examined by the elasto–plastic finite-element method by using general finite-element analysis software ANSYS and the results were compared with those obtained experimentally. The test results indicate that the load-carrying capacity decreases with the increase in the openings area as well as positions of openings. The finite-element results show good agreement with that of the experiments. From the parametric study, it is observed that best location for web opening is middle 2/3 of the span.