Behavior Of Square Research Articles

Experimental research and finite element analysis on seismic behavior of square reinforced concrete columns with four interlocking spirals

The seismic performance of square reinforced concrete columns confined by an innovative transverse reinforcement configuration composed of four interlocking spirals and outer square stirrups were investigated experimentally and numerically. Five composite specimens were tested under quasi-static reverse cyclic loading. The experimental results indicated that compared with conventional single spiral reinforced square composite column (SSRSCC) the newly developed interlocking multi-spiral reinforced square composite column (IMSRSCC) even with a slightly lower volumetric confinement ratio exhibited superior seismic performance in ultimate bearing capacity, energy dissipation and delaying the degradation of strength and stiffness. Moreover, a detailed three-dimensional finite element model considering the bond-slip behavior between concrete and steel reinforcement was developed and validated through a comparison with experimental results. The stress development and confining mechanism of transverse reinforcement of IMSRSCC was explored and the effects of the main design parameters on the seismic performance of IMSRSCC were also discussed through parametric studies.

Behaviour of Square and Rectangular Tunnels Using an Improved Finite Element Method

Due to its advantages (fast and accurate calculations), the Hyperstatic Reaction Method (HRM) was used to calculate the internal forces of circular tunnel linings in former works. This paper presents an improved HRM method that is developed to estimate the internal forces induced in square and rectangular tunnel linings. Based on the comparison of the internal forces induced in these linings obtained from the HRM method and the finite element method (FEM), the improved HRM method was validated. An extensive parametric analysis of the tunnel lining and ground parameters was then carried out using both the HRM and FEM. The results indicated a great influence of the lateral earth pressure coefficient K0, and the tunnel lining flexibility ratio F on the internal forces induced. Accordingly, the bending moments M, normal forces N, and shear forces T, induced in the tunnel lining decrease when the flexibility ratio of tunnel lining F increases. The maximum bending moment is observed at the tunnel sides that are perpendicular with the larger principal stress direction.

Experimental and numerical studies of axially loaded square concrete‐encased concrete‐filled large‐diameter steel tubular short columns

AbstractThis article presents experimental and numerical studies on the axial compressive behavior of square concrete‐encased concrete‐filled steel tubular (CECFST) short columns composed of a circular inner steel tube. Tests on six full‐scale short CECFST columns with the inner circular tube diameter varying from 320 to 500 mm were carried out to study the influences of sectional diameter and the tube thickness of circular CFST columns on their axial performance. A theoretical model is developed using fiber analysis method and validated against a large test database. The accuracy of various codified design models is evaluated and a simple model is proposed to calculate their ultimate strengths. Test results show that CECFST columns have improved load carrying capacity and can sustain large axial loads without significant strength degradation. In addition, increasing the thickness of the steel tube significantly improves the composite action of the steel and concrete of the inner CFST column, which increases the compressive strength of CECFST columns by 27.3%. However, the rate of increase in the compressive strength of the core concrete of the CFST column has been found to be higher for the column with a smaller local slenderness ratio. The ductility of CECFST columns is influenced by the concrete strength and the spacing of the stirrups. Furthermore, the design model suggested in this study can provide a better estimation than the codified design models.

Experimental analysis of RC rectangular and square columns confined using carbon fiber composites

Most of the places around the world are associated with the deterioration of major components such as columns in the reinforced concrete buildings or structures. The inventive strengthening and rehabilitation techniques for reinforced concrete structures and components, specifically with fiber composites, have occupied a huge part of the investigation work in the arena of restoration and repair of structural components. The technique of strengthening RC columns by means of carbon fiber composite is widely used due to its excellent properties compared to other FRP sheets. Many research works were directed in the field of strengthening reinforced concrete circular columns. However, other cross-section shapes like rectangular or square columns did not take the same attention which is mostly preferred in actual constructions. The main focus of this present work is to study the comparative axial behavior of square and rectangular columns after strengthening with carbon fiber composite through experimental investigations. The experimental analysis comprised twelve reinforced concrete (RC) columns consisted of unwrapped and carbon fiber composite wrapped. The axial response of rectangular and square was recognized through the evaluation of outcomes in the form of axial strengths, ductility and failure patterns. The experimental outcomes exhibited that the effect of confinement on square columns significantly improves the strength-ductility behavior compare with confined rectangular columns. The comparative study exposes the variations in cracking patterns at failure loads on rectangular and square RC columns confined with carbon fiber composite. It is also observed that the axial behaviors of unwrapped and wrapped RC columns are significantly affected by the change in shape.

Effect of sheet pile wall on the load-settlement behaviour of square footing nearby excavation

ABSTRACT Due to the shortage of urban land, new buildings are constructed adjacent to old buildings. In this regard, there is limited information about the behaviour of the shallow foundations adjacent to the excavation. In this research, a series of experimental and numerical studies are conducted on reinforced and unreinforced granular soils adjacent to excavation loaded with square footings. The experimental results are in good agreement with the numerical study. Numerical investigations were carried out on sandy excavation by varying the footing distance from the edge of the different granular excavations. It was found that by using three reinforcing layers, the ultimate bearing capacity would increase. Additionally, excavation has no significant effect in the vicinity of 4B, in which B is the footing width. Furthermore, the need to build new large buildings in the vicinity of each other has reduced the distances between square footings and, as a result, has created the phenomenon of interference in the footings and excavation. This occurs through the interference of wedges and rupture surfaces. Since this phenomenon bears a substantial result on the bearing capacity of shallow footings, this work investigates the effect of interference of ruptured wedges on the carriage capacity, settlement, and deformation of square footings. The optimum interference factor is defined at spacings of 2B and 3B for dense and loose reinforced sands, respectively. Furthermore, by including three continuous geogrid layers underneath two square footing interferences, their behaviour will be improved.

FINITE ELEMENT BEHAVIOR OF AA7075 UNDER SQUARE SHAPE OF STRIKER OF SPLIT HOPKINSON PRESSURE BAR WITH VARYING LOADS

To know the high strain rate behavior of aluminum alloy 7075 (AA7075) is very significant due to its vital uses in aviation, buildings, and automobile industries. Taylor impact test, projectile tests and split Hopkinson pressure bar are usually utilized to know the behavior of materials under high strain rate conditions. But due to lack of availabilities and very costly setups, various types of changes can’t be done easily. However, numerical simulation gives opportunity to observe the phenomena of materials under different conditions without much cost. This paper investigated the behavior of square shaped specimens of AA7075 under varying impact velocities of impact velocities of 20m/s-50m/s of square striker bar of SHPB using Abaqus. To understand the importance of shape, striker bar and specimen shape are varying from square to circular under dynamic conditions. Results obtained under varying conditions indicated that the material behavior strongly dependent to the strain rates, striker shapes and specimen shapes.

Experimental investigation of axial compressive behavior of square and rectangular confined concrete-masonry structural wall boundary elements

Reinforced masonry boundary elements (RMBEs) are critical components in determining the lateral response of reinforced masonry structural walls with boundary elements. Fundamental interpretation of the effect of various influential parameters on the RMBEs′ behavior is essential to enhance their stress–strain response. This study investigates, experimentally, the influence of various design parameters and construction procedures on the axial compressive behavior of fully grouted RMBEs built with C-shaped concrete-masonry blocks. Thirty-eight unreinforced and RMBEs were constructed and tested under concentric axial loading till failure. The effect of five parameters, namely, the vertical reinforcement ratio, the volumetric ratio of confinement reinforcement, cross-section configuration, stack pattern and running-bond, and pre-wetting of dry masonry shell before grouting, was investigated. The test results showed that increasing the vertical reinforcement ratio of the RMBEs resulted in a significant increase in the peak compressive stress and a considerable reduction in the corresponding strain ductility. Moreover, as the RMBEs volumetric ratio of transverse reinforcement doubled, the strain ductility witnessed a remarkable enhancement, whereas the peak compressive stress experienced an inconsistent trend. RMBEs built with rectangular C-shaped cross-sections exhibited comparable peak stress, smaller drop following the face shell spalling, and better strain ductility than square RMBEs. The running-bond pattern had a negative effect on both the peak stress and the strain ductility of dry RMBEs, although it exhibited comparable or even enhanced response in wet RMBEs compared to those built in the stack pattern. Pre-wetting of dry masonry shell before grouting was found to boost the peak compressive stress of unreinforced and RMBEs significantly. However, it adversely affected their strain ductility. Wet RMBEs showed a steeper post-peak descending branch compared to their dry counterparts. Indeed, the vertical reinforcement ratio and pre-wetting of dry masonry shell were the most critical parameters affecting the RMBEs peak compressive stress, whereas the confinement ratio mostly influenced the strain ductility. This study sheds light on the most critical parameters influencing the stress–strain components (i.e., strength and ductility) of RMBEs.

Behavior of Square Footing Resting on Gypseous Soil and Surrounded by a Sheet Pile Wall

Abstract Laboratory model is used in this study to investigate the behavior of centrally loaded square footing resting on gypseous soil, and surrounded by a sheet pile wall at a distance of 2B from the footing edge and extend in depth to 2B as well. During this study the soil were subjected to ten cycles of saturation and drainage at one-week interval to simulate heavy rainfalls or floods. It should be noted that the soaking water were added only outside the area surrounded by the sheet pile. Four points were chosen to detect gypsum solubility, three of them below the footing edge at different depths and one outside the sheet pile wall for comparison. It has been found that the dissolved gypsum below the footing is significantly less than the one outside the sheet pile wall. For each cycle of saturation-drainage the gypsum content is found to be reduced by 3 % and 0.8 % for the outsider point and for average of the three points respectively. Settlement during first cycle of saturation – drainage was twice as the second cycle and about four times of the third cycle. However, this first cycle settlement is about 25 % of the settlement of footing where no sheet pile wall is used. To sum up, the sheet pile wall found to be an effective protection to reduce the collapsibility of gypsum soil and to reduce footing settlement.

Structural behaviour and design of end-restrained square tubed-reinforced-concrete columns exposed to fire

Tubed-reinforced-concrete columns are gaining increasing usage in engineering practices, whereas research on their fire behaviour is still limited and mainly concentrated on unrestrained columns. Since end-restrained columns might behave differently in fire as compared to the unrestrained columns, the fire behaviour of square tubed-reinforced-concrete columns with end restraints was investigated via numerical modelling in this study. The axial and rotational restraints were modelled using linear springs and then validated against fire test results. The effects of end restraints on the failure mode, axial force and buckling length at failure and fire resistance, and on the evolution of deformations, internal force and bending moment during heating, of end-restrained columns were systematically analysed through parametric studies. The axially-restrained columns mostly undergo axial contraction only in fire; their typical failure mode is uncontrolled overall axial deformation, except for those columns of relatively high axial restraints. An increase in axial restraint leads to a nearly linear decrease of axial force at failure and a linear increase of fire resistance. For rotationally-restrained columns, the typical failure mode is also uncontrolled overall axial deformation. As the rotational restraint increases, the bucking length at failure decreases and the fire resistance increases, which is particularly significant when the rotational restraint is relatively low. A practical design method is proposed for the fire resistance design of square tubed-reinforced-concrete columns with either axial, or rotational, or combined axial and rotational restraints. Both constant and temperature-dependent end restraints have been adopted and the outcome is that they provide very similar results.

Statistical and Numerical Study on the Performance of Skirted Foundations in Clayey Soil

Skirted foundation is considered as an alternative approach required for improving the bearing capacity of shallow foundations, by using structural skirts fixed to the edges of the foundation. The presence of vertical skirts at the base of footing generates a soil resistance on skirt side beneath the footing, which helps to resist sliding. For this purpose, a numerical analysis has been performed in order to explore the behavior of square and strip model footings with one and two sided skirts for different embedded ratio in soft clay. In this study, a vertical skirt depth (Ds) has been considered as the main parameter that significantly affects the bearing capacity. Finite element analysis using plaxis 3D Foundation has been performed to model the skirted foundation. This work indicated that, using structural skirts in one and two sides of footing has a paramount effect in improving the bearing capacity for both strip and square footings and a marginal precedence has been noticed for the strip once. Therefore, the results have demonstrated that the average improvement in bearing capacity in soft clay for the one and two sided skirts at skirted ratio of Ds/B=2 is 170 and 220% respectively. A derived equation has been proposed to calculate bearing capacity of skirted foundation and a feasible agreement has been obtained between the observed and there predicted test results where the coefficient of regression (R2) is found to be 90%.

Simulation of uniaxially compressed square ultra-high-strength concrete-filled steel tubular slender beam-columns

The application of ultra-high-strength concrete in a concrete-filled steel tubular (CFST) column is an emerging topic recognizing the greater member capacities and stiffness of high strength concrete. The current designing codes for composite structures have restricted the use of ultra-high-strength concrete. This is because very little research has been conducted on the structural response of eccentrically loaded square ultra-high-strength CFST slender beam-columns. Set against this limited research, a numerical model implementing the fiber element formulation has been developed in this paper to fill the knowledge gap on the behavior of square ultra-high-strength CFST slender beam-columns under combined compression-bending conditions. The fiber-based model accounts for important features including local and global interaction buckling, triaxial confinement mechanism, member imperfection, and geometric and material nonlinearities. The stress–strain relationships for normal- and high-strength concrete do not reflect completely the brittleness of ultra-high-strength concrete in the post-peak branch. The existing material model is modified for simulating the material response of ultra-high-strength concrete. A comparison is made between the experimental data and the numerical simulation to assess the accuracy of the fiber-based model. The model has shown to provide a good agreement between the test data and the simulation. The parametric investigation indicates that the ultra-high-strength concrete may be effectively and hence more economically used in short and intermediate steel–concrete composite columns subjected to the compression load with a small eccentricity. It is also noted that the steel section with yield stress up to 550 MPa can be utilized with the ultra-high-strength concrete. The design code, Eurocode 4, accurately predicts the bending strength of ultra-high-strength square CFST slender beam-columns subjected to uniaxial bending.

3D Finite Element Pseudodynamic Analysis of Deficient RC Rectangular Columns Confined with Fiber Reinforced Polymers under Axial Compression.

This paper utilizes the advanced potential of pseudodynamic three-dimensional finite-element modeling to study the axial mechanical behavior of square and rectangular reinforced concrete columns, confined with fiber reinforced polymer (FRP) jackets and continuous composite ropes in seismic applications. The rigorous and versatile Riedel-Hiermaier-Thoma (RHT) material model for concrete is suitably calibrated/modified to reproduce the variable behavior of characteristic retrofitted columns with deficient internal steel reinforcement detailing, suffering nonuniform local concrete cracking and crushing or bulging and bar buckling. Similarly, the 3D FRP jacket or rope confinement models may account for damage distribution, local fracture initiation and different interfacial bonding conditions. The satisfactory accuracy of the reproduced experimental stress-strain envelope behavior enables the analytical investigation of several critical design parameters that are difficult to measure reliably during experiments. Additional parametric analyses are conducted to assess the effects of steel quality. The significant variation of the field of developed strains on the FRP jacket at the ultimate and of the developed strains and deformations on steel cages among different columns are thoroughly investigated. This advanced analytical insight may be directly utilized to address missing critical parameters and allow for more reliable FRP retrofit design of seismic resistant reinforced concrete (RC) columns. Further, it allows for arbitrary 3D seismic analysis of columns (loading, unloading, cyclic or loading rate effects or preloading) or addresses predamages.

Axial behaviour of FRP-confined rubberised concrete: An experimental investigation

This paper investigates the axial behaviour of square and circular concrete specimens confined by externally bonded Fibre Reinforced Polymer (FRP) jackets. Axial compression tests were performed on 96 regular and rubberised concrete specimens. The parameters considered were rubber content (0% and 60%), section shape (circular and square), FRP type (Carbon or Aramid) and the number of FRP layer (1, 2 and 3). The behaviour of the specimens in both axial and lateral directions, as well as their dilation characteristics, were investigated. The test results indicate that the confinement effectiveness of Aramid-FRP is better than that of Carbon-FRP. It is also shown that the detrimental effect of sharp corner on confinement effectiveness is less critical when using high rubber content as the element can develop large lateral expansion at unprecedented axial deformation. Large axial deformations can enable the development of highly ductile concrete elements. Existing design-oriented models fail to predict the behaviour of confined rubberised concrete with rectangular cross-section, indicating the need for developing more refined confinement models.

Behavior of square concrete‐filled steel tubular beam‐columns subjected to lateral loads with constant cyclic displacement

AbstractThe objective of this study was to clarify the cyclic behavior of square concrete‐filled steel tube (CFT) beam‐columns subjected to lateral loads with constant cyclic displacement under constant axial load. The test parameters included the effective length‐section depth ratio, axial compression ratio, and rotation angle amplitude. The relationship between the lateral load and the rotation angle are indicated along with the axial strain and load deterioration behavior in this paper. Furthermore, the relationship between the axial strain and load deterioration behaviors is discussed. Moreover, the experimental load is compared with the cross‐section strength, ultimate strength, and allowable strength, as presented in the Architectural Institute of Japan's recommendations for the design and construction of CFT structures; and the relationship between the experimental load and load deterioration behavior is examined.

Using grooving and corner strip‐batten techniques for seismic strengthening of square reinforced concrete columns with fiber‐reinforced polymer composites

AbstractThis study represents the results of an empirical program investigating the behavior of square reinforced concrete (RC) columns retrofitted using longitudinal carbon fiber‐reinforced polymer (CFRP) composites under simulated seismic loading. The main challenges to tackle are the premature buckling and the debonding of the longitudinal FRP composites on the tension and compression sides of the columns, respectively. To postpone both, the two versions of the grooving methods (GM), that is, the externally bonded reinforcement on grooves (EBROG) and the externally bonded reinforcement in grooves (EBRIG), were employed and the results were compared with those obtained under the traditional externally bonded reinforcement (EBR) procedure. Another aspect of the study involves investigating the influence of the recently developed corner strip‐batten (CSB) method on confining column specimens. For these purposes, seven half‐scale RC columns strengthened using FRP sheets were subjected to reversal cyclic loading. Experimental results exhibited that using the EBRIG and EBROG methods simultaneously with CSB technique could prevent altogether the debonding and buckling of longitudinal CFRP sheets. It was also found that the application of FRP strips utilizing the GM and CSB methods could produce an important increment in the performance of the RC columns in different terms such as ductility and lateral strength.

FE modeling of concrete beams and columns reinforced with FRP composites

Compression and flexure members such as columns and beams are critical in a structure as its failure could lead to the collapse of the structure. In the present work, numerical analysis of square and circle short columns, and reinforced concrete (RC) beams reinforced with fiber reinforced polymer composites are carried out. This work is divided into two parts. In the first part, numerical study of axial behavior of square and circular concrete columns reinforced with Glass Fiber Reinforced Polymer (GFRP) and Basalt Fiber Reinforced Polymer (BFRP)bars and spiral, and Carbon Fiber Reinforced Polymer (CFRP) wraps is conducted. The results of the first part showed that the axial capacity of the circular RC columns reinforced with GFRP increases with the increase of the longitudinal reinforcement ratio. In addition, the results of the numerical analysis showed good correlation with the experimental ones. An interaction diagram for BFRP RC columns is also developed with considering various eccentricities. The results of numerical modeling of RC columns strengthened with CFRP wraps revealed that the number and the spacing between the CFRP wraps provide different levels of ductility enhancement to the column. For the cases considered in this study, column with two middle closely spaced CFRP wraps demonstrated the best performance. In the second part of this research, flexural behavior of RC beams reinforced with BFRP, GFRP and CFRP bars is investigated along with validation of the numerical model with the experimental tests. The results resembled the experimental observations that indicate significant effect of the FRP bar diameter and type ont he flexural capacity of the RC beams. It was also shown that Increasing the number of bars while keeping the same reinforcement ratio enhanced the stiffness of the RC beam.

Extending the elastic and plastic design space of metamaterials through load-specific, multiscale inner material architectures

In the current work we investigate the extension of the elastic and plastic design space of metamaterials by means of multiscale, load-specific inner material architectures. In particular, we analyse the use of a second scale of material architecturing at the level of the elements of the primal lattice structure. To that scope, we consider a wide range of inner element designs, from mere hollow shapes to double-curved architectures that allow for reduced relative density values. Thereupon, we evaluate both analytically and numerically the effective elastic and plastic behaviour of square, two-scale metamaterial lattice structures, as a function of their second level of inner material architecturing. We observe that hollow inner element designs allow for a substantially enhanced shear response performance both in the elastic and plastic analysis range, retaining invariant their specific axial loading behaviour. The performance improvement depends on the inner element design parameters and can be up to eighty per cent with respect to the reference, single-scale lattice design within the elastic analysis range. Accordingly, the results suggest that double-curved inner element architectures allow for a shear response improvement that can outperform the one of hollow element designs at the cost of a reduced axial loading performance.

Flexural behavior of concrete-filled SHS and RHS aluminum alloy tubes strengthened with CFRP

Conventional concrete-filled aluminum alloy tube (CFAT) can effectively delay the inward local buckling of aluminum alloy tube (AA). This paper experimentally and numerically investigates the suitability of strengthening square and rectangular hollow section (SHS and RHS) CFAT beams with a layer of carbon-fiber reinforcement polymer (CFRP) under four-point bending. Among 40 beams, 30 square and rectangular CFAT beams were strengthened with CFRP comprising three arrangement schemes of CFRP and 10 conventional square and rectangular CFAT beams were treated as reference beams. Flexural stiffness of square and rectangular CFAT beams are remarkably enhanced by external bonded CFRP, while the ductility is decreased. The bottom flange-bonded CFRP scheme is less effective in enhancing ultimate strength of CFAT beams than that of four sides-bonded CFRP scheme. New design approaches for evaluating both initial and post-yield flexural stiffness of square and rectangular CFAT beams strengthened with CFRP are proposed. FE models are correctly simulated to analyze the flexural behavior of square and rectangular CFAT beams strengthened with CFRP. CFRP strengthening technique using in this study can remarkably enhance the ultimate strength of square and rectangular CFAT beams and effectively delay the outward local buckling of AA tubes.

An Analytical Scalable Lumped-Element Model for GaN on Si Inductors

In this paper, a wide-band distributed model that can approximate the behaviour of square and octagonal inductors, both with and without tapering, is presented. This paper also presents a novel way of accurately modelling the lateral coupling in the substrate. The presented model can be applied to any foundry process, and its validity has been demonstrated using a novel technology, the D01GH GaN process developed by OMMIC, which has a high resistivity substrate. To do so, seventeen inductors have been designed and manufactured. The proposed model has been verified against EM simulations and measurements of the designed inductors. Comparisons show that the model can correctly estimate the behaviour of the inductor, improving the results of the EM simulations for most cases. The root mean square (RMS) error calculated across the samples when estimating the inductance is 0.0565. The RMS error for the quality factor results (2.2727) is also adequate, although there is more deviation when comparing the results with the measurements.

Seismic Behavior of Square and Circular Concrete Columns with GFRP Reinforcement

This paper presents results from tests on seven reinforced concrete square columns under simulated seismic loading and demonstrates their satisfactory behavior even when axial load is high. All seven specimens were confined by glass fiber–reinforced polymer reinforcement (GFRP) rectilinear ties, while five specimens were reinforced with steel longitudinal bars and two with GFRP longitudinal bars. The results showed that irrespective of the longitudinal bar type, GFRP confinement effectively improved the seismic resistance of columns. The difference in the type of the longitudinal bars resulted in significant changes in column behavior. A comparison was made between these test specimens and earlier circular columns from literature, and the confinement effectiveness of the GFRP rectilinear ties and circular spirals was evaluated. Lateral GFRP was found to have a greater influence on the flexural strength enhancement of columns with GFRP longitudinal bars versus steel longitudinal bars. Results indicate that available methods for predicting flexural strength enhancement due to confinement invariably miscalculated the true strength enhancement by a substantial margin, particularly when GFRP longitudinal bars are used. A new model for predicting the flexural strength enhancement of square and circular columns confined by lateral GFRP is proposed.