Behavior Of Square Research Articles

Seismic behavior of strengthened square reinforced concrete columns under combined loadings

This paper presents an experimental study examining the seismic behavior of square reinforced concrete (RC) columns subjected to combined loadings. In this study, nine full-scale square RC columns were made with the same structural properties. Five of them were strengthened with high-performance ferrocement laminate and bonded steel plates in order to investigate the effects of strengthening on the seismic behavior of RC columns under combined loadings. Finally, the failure mode, hysteretic load-displacement response, bearing capacity, energy dissipation, ductility and plastic hinge characteristics were recorded and analyzed. The results show that combined loadings reduced the bearing capacity and changed the failure modes and deformation characteristics. Strengthened RC columns had significantly improved bearing capacity and different failure modes under the same combined loadings in contrast to the non-strengthened RC columns. The vertical eccentricity had little effect on the mechanical properties of columns, while the horizontal eccentricity significantly weakened the mechanical properties of columns. The mechanical properties of uniaxial compression-bending-shear-torsion columns were the worst. The tri-linear model calculation parameters under different failure modes and combined loadings were fixed and validated by experimental results.

Experimental Investigation of the Effectiveness of Hybrid FRP–Strengthened RC Columns on Axial Compression–Bending Interaction Behavior

AbstractThis research work presents the interaction behavior of square reinforced concrete (RC) columns strengthened with different fiber-reinforced polymer (FRP) techniques, namely, near-surface m...

Cyclic and Monotonic Behavior of Strengthened and Unstrengthened Square Reinforced Concrete Columns

The use of composite materials is an effective technique to enhance the capacity of reinforced concrete columns subjected to the seismic loading due to their high tensile strength. In this paper, numerical models are developed in order to predict the experimental behavior of square reinforced concrete columns strengthened by glass fiber reinforced polymer and steel bars and unstrengthened column under cyclic and monotonic loadings, respectively. Two columns are modeled in the present work. The first one corresponds to the column without strengthening subjected to lateral monotonic loading, and the second one corresponds to the column strengthened by glass fiber reinforced polymer and steel bars subjected to lateral cyclic loading. Comparison of the numerical modeling and the experimental laboratory test results are performed and discussed. A good agreement between the numerical and experimental force-displacement responses is obtained. Moreover, improvements in the strength of the reinforced concrete column subjected to the cyclic loading along with the comparison of the behavior of the strengthened column with the unstrengthened reference column are discussed. The results show a good improvement in the load carrying capacity and ductility of the column. The main objectives of this numerical modeling are to contribute the comprehension of the monotonic and cyclic behavior of the square reinforced concrete columns and to compare the numerical results with the experimental ones.

Behaviour of concrete filled glass fibre-reinforced polymer tubes under static and flexural fatigue loading

Abstract Concrete-filled glass fibre-reinforced polymer tubes (CFFTs) have reportedly been considered for industrial applications such as fender piling for marine structures and bridge girders. Even though previous investigations of the flexural fatigue behaviour of circular sectioned CFFTs have been reported in the literature, no such study has been carried out for square or rectangular sectioned tubes. In order to address this research gap, an experimental programme was carried out to investigate the flexural fatigue behaviour of square sectioned CFFTs, considering fatigue deformation cycles equal to 75%, 80%, 85% and 90% of the deformation corresponding to the static flexural failure of the tested CFFTs. The used glass fibre-reinforced polymer (GFRP) tubes contained reinforcements at the longitudinal direction and ±45° to the longitudinal axis of tubes. They were also specified to have much larger longitudinal tensile and compressive strength compared to typical rectangular GFRP tubes. Self-compacting concrete was used for the core-infill of the tested CFFTs. In total, eight static flexural tests and sixteen flexural fatigue tests were conducted under displacement-control fatigue loading using two loading arrangements, namely three-point and four-point bending. All CFFTs beams subjected to the fatigue loading failed due to buckling of the compression flange of CFFT. It was observed that the number of cycles to failure for the employed fatigue deformation ranges were quite low and decreased with increasing the amplitude of fatigue deformation. The bending stiffness of the tested specimens was observed to decrease as the fatigue loading progressed. It was also found that the amount of dissipated energy in a given cycle and the rate of stiffness degradation increases with an increase in the amplitude of fatigue deformation, especially for specimens tested under four-point bending. Furthermore, the bending stiffness at failure for the specimens tested under four-point bending was found to be approximately 80–90% of its initial value.

Experimental study on seismic performance of square RC columns subjected to combined loadings

This study presents an experimental investigation on the behavior of square reinforced concrete (RC) columns subjected to combined cyclic bending–shear–torsion loadings. Four full–scale square RC columns with exactly similar structural properties were tested under four types of loading conditions. The effects of combined loadings on the failure mode, hysteretic load–displacement response, bearing capacity, energy consumption, ductility and plastic hinge characteristics are discussed. Based on the results, it is concluded that combined loadings reduced the bearing capacity and changed the failure modes and deformation characteristics.

Behavior of The RC Slab-Beam System Using Self Compacting Concrete

The present study includes an experimental investigation of the behavior of square reinforced concrete slabs. These slabs are with and without edge beams under uniformly distributed load with corner supports using two types of self compacting concrete (SCC), the first type of SCC incorporated limestone filler and the other was without filler, the results obtained are compared with those obtained from conventional concrete (CC).The experimental program consists of testing nine square slab samples. Three of these slab samples are flat in shape with panel dimensions of 1050×1050×50 mm depth. The others three slab samples are of the same outer dimensions with surrounding edge beams of depth to slab thickness equal 100/50 and 100 mm width. The last three slab samples are similar to the former slab-beam systems but with increasing the depth of edge beams by 50%.In general, for a specified flat plate panel, the ultimate load carrying capacity can be increased, if the panel is restricted by four surrounding beams. The slab-beam samples with surrounding beams of depth to slab thickness equal to 3 showed greater ultimate load capacity by about 79.37%, 52% and 97.82% when compared with the corresponding flat slabs samples produced using CC, SCC with and without filler, respectively.

Investigation on the behaviour of partial wrapping in comparison with full wrapping of square RC columns under different loading conditions

This study investigates the behaviour of square reinforced concrete (RC) columns partially and fully wrapped with CFRP under different loading conditions. The experimental results of twelve specimens with 150 mm × 150 mm cross-section and 800 mm height tested under concentric axial load, eccentric axial loads and four-point bending are presented in this study. The experimental results showed that partial and full wrapping increased the strength and ductility of square RC column specimens. The increase in the strength and ductility of fully wrapped square RC column specimens was higher than the increase in the strength and ductility of partially wrapped square RC column specimens under all loading conditions. However, the increase in the axial load eccentricity (concentric, 25 mm eccentric and 50 mm eccentric axial loads) resulted in a significant decrease in the maximum axial load with the largest reduction observed for fully wrapped specimens compared to partially wrapped specimens. The experimental axial load-bending moment interaction diagrams showed the better performance of partially and fully CFRP wrapped square RC specimens compared to non-wrapped square RC specimens.

Experimental Behavior of Square Tubed-Reinforced-Concrete Column to RC Beam Joints with Internal Diaphragms under Cyclic Loading

This paper describes experimental investigation on three square tubed-reinforced-concrete (TRC) column to reinforced concrete (RC) beam joints with internal diaphragms subjected to cyclic loading, where width-to-thickness ratios of the steel tube in the panel zone and levels of axial load were selected as test parameters. Two failure modes, namely, joint shear failure and beam failure + bond failure were observed in the current test. Test results showed that the proposed composite joints exhibited favorable seismic performance.

Experimental Study and Numerical Assessment of the Flexural Behaviour of Square and Rectangular CFST Members under Monotonic and Cyclic Loading

This paper focuses on the characterization of the behaviour of Concrete Filled Steel Tubular (CFST) columns made with Rubberized Concrete (RuC), and on the development of an accurate numerical model for the simulation of CFST columns under monotonic and cyclic bending. The test campaign involves 18 CFST specimens with different configurations, namely the cross-section slenderness, the concrete strength, the axial load level and the lateral loading type. All CFST members tested exhibited good ductility under monotonic loading. The Eurocode 4 design provisions was verified against the test results and the design capacities of the CFST members were validated to be conservative. A comprehensive 3D Finite Element (FE) model was developed and calibrated based on test results. The FE model proved to be reliable in predicting the bending behaviour of CFST member, in terms of local buckling deformation modes, ultimate capacity and ductility of the CFST columns.

Eccentrical behavior of square and circular footings resting on geogrid-reinforced sand

A simple approach to describe the centrically and eccentrically ultimate bearing capacity of circular and square footings resting on geogrid-reinforced sand is developed in this paper. To establish and evaluate this approach, a series experimental test for circular footing and square footing were considered as shallow foundation models. The proposed approach for eccentrical loading in unreinforced and reinforced conditions has been validated with Meyerhof’s Effective Width Concept, laboratory model tests, numerical analyses data and field tests on actual full scale reported in the literature review. It was revealed that the new method provides reasonable agreement of the ultimate bearing capacity. Also, the results show ultimate bearing capacity of circular footing decreases less with increment of load eccentricity in comparison of square footing in reinforced condition. Improvement Index investigated that reinforcement layers increased the ultimate bearing capacity in both loadings and their contributions increased with increasing the load eccentricity.

Performance of Multi-Edge Skirted Footings Resting on Sand

In the present study the improvement in pressure-settlement behaviour of square and multi-edge (H plan shaped) footing with and without structural skirts resting on sand and subjected to a vertical load is evaluated by conducting series of laboratory plate load tests. For square footing the width of footing was kept 8 cm whereas for H plan shape footing the flange width and overall depth both were kept 8 cm. The depth of skirt was varied from 0.25 B to 1.5 B whereas the relative density of sand was kept between 30 and 60%. The results of present study reveal that, the use of structural skirt improves the bearing capacity and reduce settlement of footing significantly. At given relative density, the bearing capacity of H plan shaped footing was observed slightly higher than that of bearing capacity of square footing. The skirted footings were found more effective for sand with low relative density i.e. relative density of 30 and 40% as compared to relative density of 50 and 60%. The obtained results from the study for footing with and without skirts were comparable with available solutions from literature.

10.33: Flexural buckling behaviour of high strength steel columns under fire conditions

ABSTRACTIn this paper, a numerical modelling study using the finite element (FE) analysis package ABAQUS [1] has been carried out to study the flexural behaviour of square and rectangular hollow section columns made from high strength steel (HSS) grades S690QL and S700MC at temperatures up to 800°C. The FE model was validated using existing experimental data and then parametric studies were performed on columns with varying length and cross‐sectional properties. The results have been compared with recommendations given in Eurocode 3 Part 1–2 [2]. The analyses showed that the Eurocode is generally conservative with respect to the buckling coefficients derived and safely predicts the buckling behaviour resistance of columns made from S700MC and suggest a lower buckling curve may be needed for S690QL. It was also shown that the 0.2% proof stress rather than the stress at 2% total strain is a better parameter for deriving buckling curves in fire.

Behaviour of square footing on sand reinforced with coir geocell

The use of geosynthetics as a ground improvement technique offers the advantages such as space saving, environmental sensitivity, material availability, technical superiority, higher cost savings and less construction time. Coir geotextiles can be considered as an efficient replacement to its synthetic counterparts due to its economy and excellent engineering properties. The present study aims at exploring the possibilities of utilising coir geocells as a potential reinforcement material for shallow foundations and thereby increasing the load carrying capacity of soil. Geocells were fabricated from coir geotextiles with the aim of providing an additional confinement to the soil. An enumerated parametric study was conducted by varying the relative density, depth of the first layer, width and height of coir geocell. The surface displacement profiles of the non-reinforced and coir geocell-reinforced soil indicate that the footing rotation and heave are considerably reduced with the provision of geocell. The results of the relative density study indicate that bearing capacity characteristics increase with denseness of the soil sample. It was also observed that geocell arrangement and configuration play a pivotal role in the performance characteristics of reinforced soil.

FE modelling of the flexural behaviour of square and rectangular steel tubes filled with normal and high strength concrete

In this research, numerical investigations were carried out to study the behaviour of concrete filled steel tubes having square or rectangular cross-sections. Separate models were used for both normal strength concrete and high strength concrete. More than 50 experimental results were used to verify the FE model and it was found that the FE model accurately predicts the load-deflection curve and ultimate moment capacity of the Concrete filled steel tube (CFST) beams. Thereafter, a parametric study was carried out to evaluate the effect of depth-to-thickness ratio (20−200), compressive strength of infilled concrete (2–100MPa), shear span-to-depth ratio (1–8), depth-to-width ratio (0.6–2), and yield strength of steel tube (380–490MPa) on the flexural behaviour of square and rectangular CFST members. It was found that the depth-to-thickness ratio, yield strength of steel and height-to-width ratio has significant effect on the ultimate capacity of CFST beams. The effect of shear span-to-depth ratio and strength of infilled concrete was found to be marginal. Finally, the results of parametric study and experimental data available in literature were used to check the accuracy of the existing design methods presented in EC4 (2004), CIDECT, AISC (2010) and GB50936 (2014). From comparison, it was found that GB50936 (2014) was more accurate but unsafe for low strength infilled concrete. For all cases, EC 4 (2004) was found to be safe and hence is recommended.

Simulation of seismic behavior of square recycled aggregate concrete – filled steel tubular columns

Concrete-filled steel tubes can improve the mechanical behavior in terms of strength, stiffness, ductility and energy dissipation for the initial deficiencies of recycled aggregate concrete compared with natural aggregate concrete. The firsthand seismic performance indices on recycled aggregate concrete-filled steel tubular (RACFST) structural members are very limited due to the rare experimental results reported in the literature. To this end, a computer-assisted program for the nonlinear analysis of square RACFST columns was developed by employing SeismoStruct Software, to emphasize the effect of recycled coarse aggregate (RCA) content on the behavior of recycled aggregate concrete and the confinement effect provided by outer tubes on core concrete. Concerning the hysteretic curves, load carrying capacity and ductility, comparisons between simulation results and existing experimental ones were made to examine the rationality of numerical square RACFST model. The analysis results show that the numerical model can well simulate and predict the seismic behavior of square RACFST columns. To obtain more structural performance indices, the parametric study was performed to investigate the effects of RCA content and pre-wetting, steel yield strength, length-diameter ratio, diameter-thickness ratio, axial load ratio and structural size ratio on the hysteretic characteristic, initial lateral stiffness, ultimate lateral load and ductility of cyclic bended square RACFST columns. Both the measurement and simulation results demonstrate that concrete-filled steel tubular columns employing recycled coarse aggregates have laudable seismic behavior, and it is feasible to apply and promote the recycled aggregate concrete into concrete-filled steel tube structures in anti-seismic regions.

Pressure-settlement behavior of square and rectangular skirted footings resting on sand

The present study deals with the Pressure-settlement behavior of square and rectangular skirted footing resting on sand and subjected to a vertical load through a laboratory experimental study. A series of load tests were conducted in the model test tank to evaluate the improvement in pressure-settlement behavior and bearing capacity of square and rectangular model footings with and without structural skirt. The footing of width 5 cm and 6 cm and length/width ratio of 1 and 2 was used. The relative density of sand was maintained at 30%, 50%, 70%, and 87% respectively. The depth of skirt was varied from 0.25 B to 1.0 B. All the tests were carried out using a strain controlled loading frame of 50 kN capacity. The strain rate for all test was kept 0.24 mm/min. The results of present study reveal that, the use of structural skirt improves the bearing capacity of footing significantly. The improvement in bearing capacity was observed almost linearly proportional to the depth of skirt. The improvement in bearing capacity of skirted footings over footing without skirt was observed in the range of 33.3% to 68.5%, 68.9% to 127% and 146.7% to 262% for a skirt depth of 0.25 B, 0.50 B and 1.0 B respectively. The skirted footings were found more effective for sand at relative density of 30% and 50% than at relative density of 70% and 87%. The bearing capacity was found to increase linearly with footing width for footings with and without skirts. This observation was found to be consistent for footings with different skirt depths and for relative density of sand i.e., 30%, 50%, 70%, and 87%. The obtained results from the study for footing with and without skirts were comparable with available solutions from literature.

Finite Element Modeling of Axial Compressive Behaviour of Ultra High Strength Concrete Filled Square and Rectangular GFRP Tubes

Objective: An exploratory research on developing finite element model for studying the axial compressive behaviour of square and rectangular UHSC filled GFRP tubes was conducted. Methods/Statistical Analysis: The well-known fact of deviation in uniformity of confinement in square and rectangular concrete filled GFRP tubes was focused in the nonlinear finite element model. A square and rectangular cross section having same thickness 3mm was chosen keeping two different corner radii 30, and 40mm. The unconfined concrete strength was limited to 120 MPa. The simulation of UHSC filled GFRP tubes were done using ANSYS using elements SOLID 65 for concrete and MEMBRANE 41 for GFRP tube. Findings: The research findings from this investigation on verification by ACI code (ACI committee 440, 2002) revealed that the square CFFTs offer better confinement when compared with rectangular CFFTs and the corner radii significantly affected the ultimate load capacity of the square and rectangular CFFTs. Applications/Improvements: The study has come up with newer method of simulation of GFRP tubes using shell elements assuming perfect bonding between concrete and the tubes. This is the first kind of study in existing FEA database using shell elements. The results agreed with those predicted by the code.

Axial compressive behavior of square reinforced concrete columns confined using two layers of stirrups

Reinforced concrete column confined using two layers of stirrups is a new kind of column form recently proposed by the authors. The concrete of the column is under three different levels of confinement, namely unconfined concrete cover, singly confined, and doubly confined concrete core. This column form provides a simple but effective solution for reinforced concrete columns located in seismic hazard zones and/or reinforced concrete columns with large axial load ratio, where large amount of transverse reinforcement is necessary to achieve a ductile response. This study aims to investigate the axial compressive behavior of square reinforced concrete columns confined using two layers of stirrups. In total, 15 columns were prepared and tested under axial compression. Two different stirrup configurations were investigated. The axial responses and the failure modes of the columns were examined in detail, and the average stress–strain curve of the singly confined and doubly confined concrete core was derived. A stress–strain model with satisfactory accuracy was proposed based on the interpretation of test results.

Numerical analysis of recycled aggregate concrete-filled steel tube stub columns

This article presents a numerical analysis on the behavior of square recycled aggregate concrete-filled steel tube stub columns with the cold-formed hollow structural steel tube being used. A nonlinear finite element model for the square recycled aggregate concrete-filled steel tube stub column under axial compression has been developed using the general-purpose finite element program. An equivalent stress-strain model is proposed to simulate the behavior of the recycled aggregate concrete confined by a steel tube. The results obtained from the finite element model are compared with the experimental data. The comparison indicates that the finite element model is capable of predicting the mechanical behavior of the square recycled aggregate concrete-filled steel tube stub columns. After the validation of the numerical model, the effects of the recycled aggregate replacement ratio on the behavior of the square recycled aggregate concrete-filled steel tube stub columns are investigated. Furthermore, the applicability of the current design specifications and the proposed empirical formulas by various researchers to predict the ultimate compressive strengths of the recycled aggregate concrete-filled steel tube stub columns are examined. The comparative study shows that the specification Eurocode 4 gives closer prediction of the ultimate compressive strength than the other methods.

Square [5]molecular necklace formed from cucurbit[8]uril and carbazole derivative

The formation of square 5-member molecular necklace ([5]MN) is presented by utilizing the host–guest recognition-driven self-assembly between CB[8] and carbazole derivative 1·2Cl−, which bears two 4,4′-bipyridin-1-ium (BP) arms with a orthogonal geometry. The self-assembly and stimuli-responsive behaviors of square [5]MN are comprehensively investigated by NMR (1H, COSY, NOSEY, and DOSY), UV–vis, DLS, and SEM methods.