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A new type of stiffening rib is proposed to improve the mechanical performance of T-shaped concrete-filled steel tubular (CFST) columns. A finite element model was established using the general-purpose commercial software ABAQUS 2022. After verification through comparison with experimental data, the developed finite element model was employed to numerically evaluate the performance of T-shaped CFST short columns with stiffening ribs under axial compression. The results indicated that the new stiffening ribs are capable of significantly reducing the buckling deformation of the steel tube, enhancing the confinement effect of the steel tube on the core concrete, and improving the combined performance of the steel tube and the concrete. The thickness and material strength of the stiffening ribs had a notable impact on the ultimate bearing capacity and ductility of the short column specimens. When the thickness of the stiffening ribs increased from 5 mm to 8 mm, the ultimate bearing capacity correspondingly increased by 10.51% to 31.77%, while the ductility coefficient improved by 6.48% to 17.20%. When the steel strength increased from 262.50 MPa to 345 MPa and 390 MPa, the ultimate bearing capacity correspondingly increased by 17.36%, 19.78%, and 30.50%, and the ductility coefficient improved by 12%, 13.87% and 23.92%. The changes in the specifications and arrangement of the stiffening ribs had no significant effect on the ultimate bearing capacity and ductility of the specimens. The change in angle steel specifications caused variations in ultimate bearing capacity within ±5% and variations in the ductility coefficient within ±10%. Changes in the arrangement caused variations in ultimate bearing capacity within ±1% and variations in the ductility coefficient within ±5%. [ABSTRACT FROM AUTHOR]

Buildings on hill slopes have suffered significant damage from past earthquakes due to poor design and construction practices. Therefore, Indian building code restricts the natural period of building on slopes based on their shortest height. Different building configurations located on hill slopes perform differently in the event of an earthquake, making it necessary to check the applicability of provisions using elastic and inelastic analyses. This study investigated a spectrum of two-dimensional (2D) RC moment frame building configurations (with or without including infill walls as an equivalent strut), including (1) type of building configuration; (2) angle of slope; (3) boundary conditions; and (4) varying height of buildings using modal analysis, equivalent static analysis, and response spectrum analysis. Mass participation (from 80% to 37%) and base shear decrease due to extreme short columns, which demand massive forces; interstory drift decreases for buildings on hill slopes, but increases drastically by varying the boundary conditions. The responses from nonlinear static and dynamic time-history analyses were studied based on the capacity curve, performance point, and level of damage toto structural elements under the maximum considered earthquake (MCE). The presence of struts increases lateral stiffness and lateral strength for building on slopes, resulting in less damage to structural elements than regular buildings (BC1). However, damage to beams and columns is more common in bare-frame buildings than in buildings with struts, because the struts sustain more damage. Although a few building configurations on slopes incurred less damage (e.g., step-back setback buildings, due to decreased stiffness along the height), more damage is evident in the struts of other buildings on slopes. Thus, strut failure may cause a building to behave like a bare-frame building under MCE demand, sustaining more damage; this also was demonstrated with a three-dimensional (3D) building on slope. Thus, designing buildings based on code-based natural periods by assuming the sloped region to be rigid may not be valid for all building configurations. It is necessary to account for other critical parameters while placing restrictions on the building code provisions. [ABSTRACT FROM AUTHOR]

Geogrids, first developed in the late 20th century, revolutionized soil reinforcement using polymer materials in grid-like structures to enhance soil stability, reduce erosion, and strengthen infrastructure, marking a pivotal advancement in geotechnical engineering. However, geogrids typically find limited application in structural engineering, especially reinforced concrete (RC) columns. The present research explores the feasibility of geogrids in concrete columns, thus optimizing construction practices by exploring innovative reinforcement methods beyond conventional steel, aiming to bolster durability and performance in diverse structural scenarios. The traditional method of using steel stirrups to confine circular columns was substituted with a new approach; i.e., geogrids were introduced partially as confining material alongside steel stirrups. Furthermore, the research examines the performance of concrete columns confined partially with geogrid, both with and without the inclusion of steel fibers, in comparison to traditional columns reinforced with steel. Columns, 16 in number, with different steel stirrup spacing, concrete types, and geogrid configurations, were cast and put under axial load. Load-deflection curves were obtained, and parameters including ultimate load, maximum axial displacement, ductility, secant stiffness, and energy dissipation were assessed and compared. The findings indicated that incorporating geogrids with greater tensile strength alongside steel fibers could uphold a peak load value 10.16% higher than the control column, improved stiffness, and enhanced energy dissipation, indicating a promising approach for reinforcing columns in conjunction with steel fibers. [ABSTRACT FROM AUTHOR]

The research aims to study the behaviour of concrete columns reinforced with fibreglass as bars exposed to seawater. Firstly, hardened concrete properties as the compressive strength and the tensile strength were investigated at ages 14, 28, and 56 days. Secondly, the experimental testing also involved casting 18 short concrete columns that have a length of 300 mm with the cross-sectional dimensions of 100 mm × 100 mm. Six samples were plain concrete, six were reinforced with a diameter of 6 mm longitudinal fibreglass bars, and six polypropylene fibre concrete columns were reinforced with a diameter of 6 mm fibreglass bars. The results added useful information using fibreglass bars (anti-corrosion materials) as reinforced longitudinal concrete columns, so the ultimate load of the reinforced concrete column with fibreglass rod exposed to seawater was 174.8 kN that it was higher than that of the plain concrete column at 104.9 kN. Thus, the fibreglass reinforcement technology enhances the capacity of the columns. So, it could be used in non-impacting structural parts. Meanwhile, the ultimate load of the fibre-reinforced concrete column with fibreglass rod exposed to seawater was 201.8 kN. It is 15.4% higher than that of the ultimate axial load of the reinforced concrete column with fibreglass rods only. Also, the results achieved of this research were encouraging, as the maximum failure load for short columns reinforced with fibreglass rods reached approximately 84 to 87% of failure load relative to polypropylene fibre concrete columns containing reinforcing fibreglass bars. As a result, the structural behaviour bars have been enhanced using fibreglass rod and polypropylene fibre.

A new type of stiffening rib is proposed to improve the mechanical performance of T-shaped concrete-filled steel tubular (CFST) columns. A finite element model was established using the general-purpose commercial software ABAQUS 2022. After verification through comparison with experimental data, the developed finite element model was employed to numerically evaluate the performance of T-shaped CFST short columns with stiffening ribs under axial compression. The results indicated that the new stiffening ribs are capable of significantly reducing the buckling deformation of the steel tube, enhancing the confinement effect of the steel tube on the core concrete, and improving the combined performance of the steel tube and the concrete. The thickness and material strength of the stiffening ribs had a notable impact on the ultimate bearing capacity and ductility of the short column specimens. When the thickness of the stiffening ribs increased from 5 mm to 8 mm, the ultimate bearing capacity correspondingly increased by 10.51% to 31.77%, while the ductility coefficient improved by 6.48% to 17.20%. When the steel strength increased from 262.50 MPa to 345 MPa and 390 MPa, the ultimate bearing capacity correspondingly increased by 17.36%, 19.78%, and 30.50%, and the ductility coefficient improved by 12%, 13.87% and 23.92%. The changes in the specifications and arrangement of the stiffening ribs had no significant effect on the ultimate bearing capacity and ductility of the specimens. The change in angle steel specifications caused variations in ultimate bearing capacity within ±5% and variations in the ductility coefficient within ±10%. Changes in the arrangement caused variations in ultimate bearing capacity within ±1% and variations in the ductility coefficient within ±5%.

Concrete confinement using fiber-reinforced polymers (FRPs) has been vastly used for strengthening of reinforced concrete (RC) columns. The strengthening of RC columns belongs to the realm of existing structures, which has been recognized as distinct from the design of new structures. Code development efforts for the strengthening of RC columns should follow a reliability-based framework similar to the one used in the code development for new structures. In this process, a number of additional issues arise: the mechanical model of FRP confinement representing existing RC columns, the statistical description of the design variables, and the target reliability to be attained. In this study, the reliability levels of 288 axially loaded, FRP-RC short columns of circular cross sections, strengthened according to ACI 440 guidelines, are assessed. Monte Carlo simulation is used in the probabilistic description of column strength and computation of the probability of failure. An FRP confinement model that explicitly accounts for the presence of transversal steel and attendant model errors associated to the estimation of ultimate stress and ultimate strain are used in the computation of the FRP-RC column capacity. The values of the reliability index are in the range of 3.92 to 4.61, satisfying the target reliability suggested for both new and existing structures. The research findings presented herein provide further support for the efforts of ACI Committee 440 in the development of standards related to the FRP strengthening of RC columns. [ABSTRACT FROM AUTHOR]

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Pitting corrosion is harmful during bridge construction, which will lead to uneven roughness of steel surfaces and reduce the thickness of steel. Hence, the effect of pitting corrosion on the mechanical properties of cold-formed thin-walled steel stub columns is studied, and the empirical formulas are established through regression fitting to predict the ultimate load of web and flange under pitting corrosion. In detail, the failure modes and load-displacement curves of specimens with different locations, area ratios, and depths are obtained through a large number of non-linear finite element analysis. As for the specimens with pitting corrosion on the web, all the specimens are subject to local buckling failure, and the failure mode will not change with pitting corrosion, but the failure location will change with pitting corrosion location; the size, location, and area ratio of pitting corrosion have little influence on the ultimate load of cold-formed thin-walled steel short columns, but the loss rate of pitting corrosion section area has a greater impact on the ultimate bearing capacity. As for the specimen with flange pitting corrosion, the location and area ratio of pitting corrosion have less influence on the ultimate load of cold-formed thin-walled steel short columns, and the section area loss rate has greater influence on the ultimate bearing capacity; the impact of web pitting corrosion on the ultimate load is greater than that of flange pitting corrosion under the same condition of pitting corrosion section area. The prediction formulas of limit load which are suitable for pitting corrosion of web and flange are established, which can provide a reference for performance evaluation of corroded cold-formed thin-walled steel. [ABSTRACT FROM AUTHOR]

The main objective of this research is to investigate the concrete cover thickness effect on the corrosion degree of the longitudinal reinforcing steel of short circular high-performance concrete columns. The practical program consists of casting and testing six circular columns with dimensions of (150 × 1000) mm tested under a central load. Three of them were reference columns, and three were corroded using an accelerated corrosion cell. The main variable adopted in the present research included the concrete cover thickness (10, 20, and 30) mm to compare results for weight and surface area loss of corroded steel and bearing capacity reduction among all samples. The results showed that increasing the concrete cover thickness from 10 to 20 and 30 mm decreased the loss percentage of the reinforcing steel weight by (12.47, 11.82, and 11.26) %, respectively. Also, the loss percentage of the cross-sectional area of the reinforcing steel decreased by (77.44, 64.00, and 57.75) %, respectively. While bearing capacity was reduced by (29.07, 25.25, and 32.23) % for 10, 20, and 30 mm clear covers, respectively, compared with the control columns of 10, 20, and 30 mm clear covers.

With rapid economic and social development, both concrete-filled steel tube (CFST) composite structures and basalt fiber (BF) have been widely applied in the field of civil engineering. To investigate the laws and characteristics of the influence of chopped BF on the mechanical properties of CFST columns and further promote the application of BF in CFST structures, the axial compressive bearing capacity test of 18 CFST short columns was carried out, and the influence of BF of different lengths on their structural mechanical properties was analyzed. The test results were compared with the theoretical calculation results and the finite element analysis results to verify the reasonableness of the test results. The results reveal that the axial compressive bearing capacity of the CFST short column after adding BF is significantly improved compared to the ordinary CFST short column, in which the bearing capacity and the ductility coefficient are increased by approximately 8.1% and 31.6%, respectively, on average. In addition, changing the length of BF has less effect on the bearing capacity of CFST short columns, the rate of increase in bearing capacity decreases with an increase in the steel ratio of CFST, and the coefficient of ductility increases with the increase in the steel ratio. [ABSTRACT FROM AUTHOR]

The effectiveness of textile-reinforced mortars (TRM) utilized as jacketing overlays that are applied to short, shear-critical reinforced concrete (RC) columns was investigated experimentally and verified analytically in this study. Moreover, the possibility of replacing the standard ordinary portland cement (OPC) matrix with an alternative alkali-activated material (AAM) in the TRM retrofitting technique was explored. Seven rectangular-shaped RC columns were constructed with a shear span-to-height ratio of 1.5. Four of the seven specimens were constructed to be more ductile with closely spaced shear reinforcement, and the rest had their stirrups positioned at larger spacings. Both series of columns were retrofitted with two and four layers of TRM jacket overlays, which were made from uncoated carbon textiles and AAM or OPC-based mortar. They were subjected to cyclic loading combined with a constant vertical load. The control (unretrofitted) specimens exhibited brittle failure, and the retrofitted specimens performed significantly better for deformation capacity, with a clear shift in the failure mode toward shear–flexure. The load capacity of the jacketed columns was governed by yielding in the longitudinal reinforcement. An important result is that AAM-based TRM jacketing is not inferior to its OPC-based counterpart. [ABSTRACT FROM AUTHOR]

Existing reinforced concrete structures designed according to previous generation seismic codes, often suffer from premature, abrupt and detrimental failures in cases of intense earthquakes. In this study the seismic response of an existing building is analytically investigated while taking into account the influence of different detailing of brick wall infills. The assessment is performed with 3D static inelastic (Pushover) or with incremental Dynamic time‐history analyses (IDA) with the SeismoStruct Software. Buildings with inadequate performance receive continuous transverse pre‐tensioned Basalt Fiber Ropes (BFR) as external shear and confining strengthening reinforcement. The inelastic analyses conclude that buildings with short columns suffer from early collapses at low top displacements due to detrimental local shear failure of the above‐mentioned members. Both shear and crush confined concrete related failures of the critical columns are eliminated and overall base shear strength is increased. BFR external wrapping increases the ultimate top building displacements as well. IDA are thoroughly elaborated to assess the collapse mechanism of the structures and conclude ultimate base shear and top displacement values for the critical cases of buildings under investigation. [ABSTRACT FROM AUTHOR]

Reinforced concrete columns play an important role in distributing loads from slabs and beams to foundations. As a result of time, fatigue, or other factors, the reinforced columns are exposed to deterioration, and it is required to strengthen or repair these columns. Ferrocement jacketing can be considered as an easy and cheap method which has a significant effect on strengthening members. The main objective of this research is to study the effect of strengthening short columns using ferrocement jackets. Fourteen short square columns having the same dimensions were tested under axial loading. One column was designed as a control specimen and the other thirteen specimens were strengthened with ferrocement while changing the type and number of layers. It was found that using ferrocement as strengthening method increased the strength of columns in average from 11 to 40 %. Following that, a finite element analysis was conducted using the tested column specimens to further assess the usage of ferrocement jackets for strengthening concrete columns. A modified equation was proposed to calculate the capacity of short square columns strengthened using ferrocement jackets. Comparison with experimental data showed that the proposed equation gives good correlation compared to the experimental data.

Deep members can exist in different forms in concrete structures, such as coupling beams, short columns, pile caps, and corbels. Because they are typically prone to shear failure, accurate calculation of the shear behavior in these members is vital. The existing analysis procedures for deep members are either computationally expensive or limited to the calculation of shear strength for design purposes. There is a great need for reliable macromodeling analysis tools that can evaluate safety and performance of structures at the system level while considering the nonlinear shear behavior of deep members in detail. This paper presents a shear plastic hinge model developed based on the beam-arch action mechanism for nonlinear analysis of deep RC members. The contribution of web concrete and transverse reinforcement (i.e., beam action) to the shear response is considered based on the modified compression field theory, while the contribution of the inclined concrete compression chord (i.e., arch action) is taken into account using the compatibility condition for shear deformations. The model is capable of calculating the shear force and shear deformation at different stages of the response while considering important nonlinear material effects in RC and interactions between internal force components. Through a comprehensive verification and parametric study, it is demonstrated that the model is able to accurately compute the shear behavior in deep RC beams and columns with various design variables. Last, the effectiveness of the proposed model for system-level analysis of structures is evaluated by modeling a multistory RC shear wall with coupling beams. The analysis results show that shear deformations can have a great influence on the performance of the structure as a whole in addition to the behavior at the component level. [ABSTRACT FROM AUTHOR]

The current experimental work investigates the structural behavior of steel tubular columns filled with concrete (STCFC) subjected to corrosion conditions as well as direct axial and uniaxial loading. To find out the ultimate capacity for bearing corroded columns, eight steel tubular square columns filled with normal strength concrete (NSC) having a cross-section of (100×100mm), a thickness of (1.5mm) and a length of (1000-1200mm) were tested under concentric and eccentric loads. The main variables that were adopted in this experiment are the column type (slender or short), the type of the applied loads (concentric or eccentric), and the thickness of the steel columns (before and after corrosion). The experimental results indicated that, after the steel columns were exposed to (5%) dilute sulfuric acid for (8 days), it was found that the thickness of the steel columns had decreased by about (55%), which led to a decrease in the bearing capacity of the tested corroded steel columns by about (48% and 43%) for slender columns subjected to concentric and eccentric loads respectively, and by about (47% and 44%) for short columns subjected to concentric and eccentric loads respectively.

One of the reasons that cause the collapse of buildings is deficient short columns, which need to be retrofitted to prevent the collapse of the building in a potential earthquake. External reinforced concrete (RC), steel plates, and fiber-reinforced polymer (FRP) jacketing are standard retrofitting methods to retrofit columns to increase their shear capacity. However, in compression shear failure, the effectiveness of steel and FRP jacketing is quite limited due to the premature buckling of the FRP and steel material. On the other hand, RC jacketing is not practical because it requires more labor and covers more architectural places. Thus, the main motivation of this study is to present the effectiveness of a new method to retrofit short columns, including those with dominated shear compression failure. For this purpose, HSPRCC (high-performance steel plate-reinforced cementitious composite) was adapted to retrofit such short columns. This method is a combination of high-performance concrete and perforated steel plates. Short-column specimens representing existing RC buildings were retrofitted using the HSPRCC and tested. Perforated steel plates anchored to the specimen by steel bolts and repair mortar are used as a matrix. The retrofitted specimens were found to exhibit much better performance both in terms of shear strength and deformation capacity. It was also observed that the retrofitting method is effective in contributing to increasing the compression shear capacity. [ABSTRACT FROM AUTHOR]

The hybrid double-skin tubular column (DSTC) is a unique composite column composed of an outer tube made of a fibre-reinforced polymer (FRP) and an inner tube made of steel, with concrete filling the space between the outer and inner tubes. The external and internal tubes provide excellent confinement to the concrete. The column is characterised by the outer FRP tube’s excellent corrosion resistance, improved ductility due to the composite effect, and low weight due to its hollow cross-section. Previous studies were limited to the wet-layup of glass fibre reinforced polymer oriented in the circumferential direction of a double-skin tubular column, both experimentally and analytically. A total of 36 specimens were tested for axial compression loading. The behaviour of the column was inferred from the following parameters: orientation of fibre angle (0°,0°/90°and ± 45°) with respect to the circumferential direction, thickness of the FRP tube (2.1 mm and 4.2 mm), concrete strength (NSC and HSC), and void ratio (0.5, 0.59 and 0.67) of the steel tube. The experimental results showed that the fibres oriented in the hoop direction provided higher ultimate load-carrying capacity in comparison with fibres oriented at 0°/90°and ± 45°. The fibres oriented at ± 45° showed an increase in the ultimate strain than the other orientations. It was also found that the normal-strength concrete (NSC) specimens display better strength and strain enhancement ratio than the high-strength concrete (HSC) specimens. An improvement in resisting compressive stress and strain was observed when an increase was made in the FRP tube thickness and steel tube diameter. The results obtained from the experiments were compared to the theoretical prediction model results. The predicted model was found to be accurate in estimating the ultimate stress and strain of concrete in hollow DSTCs.

An experimental investigation has been carried out to evaluate the effectiveness of Polyvinyl chloride (PVC) confinements in short plain circular concrete columns. The experimental part is conducted using different PVC tube diameters (110, 160, 220, and 250 mm) with two types of confinement strategies (fully and confined with the cut ends). The results are validated with unconfined samples (control samples). The test results showed that using external confinement of concrete columns by PVC tubes enhances the ultimate load capacity of the short columns. For fully confined samples, the enhancement ratio ranges between 5% and 8.3%, and from 4.16% to 15% for samples with cut ends. Furthermore, the confining of PVC pipes with the cut ends (C CC) has a more considerable effect on load capacity for all diameters except the ones with 250 mm, where the samples with full confinement ( C c ) carried a bigger load than those with cutting ends. Finally, a numerical simulation of samples is carried out by the finite element (FE) model using the ABAQUS software. For all scenarios, the results of the numerical analysis showed considerable similarity to the experimental results, with R 2 of 0.95 indicating the high linearity between the actual and simulated compressive strength values. Moreover, the FE induces fewer simulated errors with a relative error (RE) ranging from 0.16% to 6% for all scenarios. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive experimental programme and analysis of ultra-high-performance fibre-reinforced concrete (UHPFRC)-encased concrete-filled steel tube (CFST) columns subjected to axial and eccentric compression. Twelve short columns were tested, with six of them utilising UHPFRC encasement while the other six employing normal strength fibre-reinforced concrete (FRC) encasement for comparison purpose. The study focused on the effects of load eccentricity ratio, concrete encasement type, and steel tube configuration. Key findings from the test results including failure modes, load-deflection behaviour, moment-curvature relationships and curvature ductility were examined. The findings showed that UHPFRC-encased CFST columns exhibited significantly enhanced strength and bending capacity, while FRC-encased columns showed remarkable ductility. A notable shift in failure mode was observed with increasing load eccentricity ratio, transitioning from crushing of concrete to compression, and then to balanced failure. Furthermore, applicability of prevalent design codes such as EC4, AIJ, and ACI 318 in calculating the peak loads of UHPFRC- and FRC-encased CFST columns was assessed. The plastic stress distribution methods in EC4 and AIJ overestimated peak loads, while ACI 318's strain compatibility approach accurately predicted FRC-encased columns but not UHPFRC-encased columns. To address this, modifications of the parameters α and β were incorporated into the ACI design method to reflect the relative brittle nature of UHPFRC, resulting in accurate predictions. • Twelve short UHPFRC- and FRC-encased CFST columns were tested. • Test parameters were load eccentricity ratio, encasement type, and steel tube configuration. • Outer concrete encasement remained intact without spalling. • UHPFRC-encased CFST columns exhibited significantly enhanced strength and bending capacity. • FRC-encased columns showed remarkable ductility. [ABSTRACT FROM AUTHOR]

Recent earthquakes severely damaged short columns due to high lateral stiffness and low ductility. Some conditions, such as reductions in the heights of some columns compared to others on the same floor, deep beams, partially buried basements, and nonstructural walls, cause short column effects. The prominent characteristics of engineered cementitious composites (ECCs) reinforced with polyvinyl alcohol (PVA) fibers -- including their high tensile strength, micro and multiple cracks, energy dissipation, high ductility, and strain hardening -- lead to improved seismic performance and economic efficiency in structure elements. In this study, 11 ECC columns with different fiber fractions (0-1.5%) and aspect ratios (3-7), as well as one conventional concrete column, were tested and evaluated. The results showed that increasing fiber friction and shear aspect ratio increased the length of the plastic hinge zone and ductility by at least 50% and 100%, respectively. Furthermore, the failure mode changed from brittle shear to ductile shear. [ABSTRACT FROM AUTHOR]

To research the axial compression behavior of steel reinforced recycled concrete (SRRC) short columns confined by carbon fiber reinforced plastics (CFRP) strips, nine scaled specimens of SRRC short columns were fabricated and tested under axial compression loading. Subsequently, the failure process and failure modes were observed, and load-displacement curves as well as the strain of various materials were analyzed. The effects on the substitution percentage of recycled coarse aggregate (RCA), width of CFRP strips, spacing of CFRP strips and strength of recycled aggregate concrete (RAC) on the axial compression properties of columns were also analyzed in the experimental investigation. Furthermore, the finite element model of columns which can consider the adverse influence of RCA and the constraint effect of CFRP strips was founded by ABAQUS software and the nonlinear parameter analysis of columns was also implemented in this study. The results show that the first to reach the yield state was the profile steel in the columns, then the longitudinal rebars and stirrups yielded successively, and finally RAC was crushed as well as the CFRP strips was also broken. The replacement rate of RCA has little effect on the columns, and with the substitution rate of RCA from 0 to 100%, the bearing capacity of columns decreased by only 4.8%. Increasing the CFRP strips width or decreasing the CFRP strips spacing could enhance the axial bearing capacity of columns, the maximum increase was 10.5% or 11.4%, and the ductility of columns was significantly enhanced. Obviously, CFRP strips are conducive to enhance the axial bearing capacity and deformation capacity of columns. On this basis, considering the restraint effect of CFRP strips and the adverse effects of RCA, the revised formulas for calculating the axial bearing capacity of SRRC short columns confined by CFRP strips were proposed. [ABSTRACT FROM AUTHOR]

This study investigated the efficiency of strengthening low-strength RC short columns with fiber-reinforced cementitious matrix (FRCM). Twelve columns were cast with concrete with a compressive strength of 18 MPa. All columns had a reinforcement ratio of 1.5%. The investigated parameters were the column cross section (square or circular), the spacing between the ties (90 and 180 mm) selected based on the columns' dimensions, and the number of FRCM layers used in wrapping the columns [zero, two, and four layers of paraphenylene-ben-zobisoxazole (PBO) FRCM]. All columns had a clear height of 800 mm and were tested monotonically until failure. Results showed that for columns wrapped with two PBO-FRCM layers, using a tie spacing of 90 mm eliminated the effect of varying the cross section. However, circular columns showed a higher increase in capacity than square columns for a tie spacing of 180 mm, where the increase was 40%. For all columns wrapped with four PBO-FRCM layers, the cross-section shape was the sole influence on ultimate capacity, where circular columns noticeably showed a more improved capacity. Also, column load–strain relationships were only influenced by the tie spacing. All strengthened columns showed improved ductility with the increase in PBO-FRCM layers. Using existing design provisions, the theoretical capacity of the columns was calculated, and results showed that the code underestimates ultimate capacity, where the theoretical capacities were lower than the experimental ones by 5%–20%. [ABSTRACT FROM AUTHOR]

Short columns with deficiencies of low-strength concrete and large spacing of transverse reinforcement are quite common in construction practice in many developing countries in seismically active regions. Therefore, it is important to retrofit this type of column to avoid negative consequences in the case of severe damage. External fiber–reinforced polymer (FRP) jacketing is one of the most practical methods to retrofit reinforced concrete (RC) frame members against shear actions. However, knowledge of the seismic behavior of FRP-retrofitted RC short columns is still limited. Thus, the aim of this study was to investigate the seismic response of FRP-retrofitted low-strength RC short columns with and without predamage through the testing of 11 short column specimens representing old and deficient RC buildings. Accordingly, the results of a research program on the seismic behavior of such columns and on their repair and FRP retrofitting, covering experimental and analytical phases, are presented. In the experimental phase, test results obtained for short columns, FRP-retrofitted short columns, and repaired and retrofitted short columns are documented. Test results provide important knowledge about the effects of extremely low-strength concrete, and of different levels of predamage on the behavior of FRP-retrofitted substandard short columns. In the analytical phase, the performance of relevant design documents in predicting the shear strength of such columns retrofitted with FRP jacketing was tested through the comparison of predicted and experimental results. [ABSTRACT FROM AUTHOR]

This article investigates the axial compressive performance of concrete-filled double steel tubular (CFDST) short columns composed of circular section loaded concentrically. An experimental program comprised of compression tests on short columns is carried out to examine their structural performance. Axial compression tests on conventional concrete-filled steel tubular (CFST) columns and double-skin concrete-filled steel tubular (DCFST) columns are also performed for comparison purposes. The test parameters include the diameter-to-thickness of the outer and inner steel tubes, concrete strength, and diameter ratio. The test results exhibit that CFDST short columns composed of the circular section have improved structural performance compared to its CFST and DCFST counterparts. A theoretical model is also presented to simulate the test ultimate strengths and load-axial strain relationships of CFDST columns. The existing design models proposed including the codified design specifications are evaluated against the collected test data for predicting the axial compressive strengths of circular CFDST columns. It is seen that the existing codified design models cannot yield their ultimate axial compressive strengths accurately. A practical artificial neural network (ANN) model is proposed to estimate the ultimate load of such columns loaded concentrically. [ABSTRACT FROM AUTHOR]

One of the reasons that cause the collapse of buildings is deficient short columns, which need to be retrofitted to prevent the collapse of the building in a potential earthquake. External reinforced concrete (RC), steel plates, and fiber-reinforced polymer (FRP) jacketing are standard retrofitting methods to retrofit columns to increase their shear capacity. However, in compression shear failure, the effectiveness of steel and FRP jacketing is quite limited due to the premature buckling of the FRP and steel material. On the other hand, RC jacketing is not practical because it requires more labor and covers more architectural places. Thus, the main motivation of this study is to present the effectiveness of a new method to retrofit short columns, including those with dominated shear compression failure. For this purpose, HSPRCC (high-performance steel plate-reinforced cementitious composite) was adapted to retrofit such short columns. This method is a combination of high-performance concrete and perforated steel plates. Short-column specimens representing existing RC buildings were retrofitted using the HSPRCC and tested. Perforated steel plates anchored to the specimen by steel bolts and repair mortar are used as a matrix. The retrofitted specimens were found to exhibit much better performance both in terms of shear strength and deformation capacity. It was also observed that the retrofitting method is effective in contributing to increasing the compression shear capacity.

An experimental investigation has been carried out to evaluate the effectiveness of Polyvinyl chloride (PVC) confinements in short plain circular concrete columns. The experimental part is conducted using different PVC tube diameters (110, 160, 220, and 250 mm) with two types of confinement strategies (fully and confined with the cut ends). The results are validated with unconfined samples (control samples). The test results showed that using external confinement of concrete columns by PVC tubes enhances the ultimate load capacity of the short columns. For fully confined samples, the enhancement ratio ranges between 5% and 8.3%, and from 4.16% to 15% for samples with cut ends. Furthermore, the confining of PVC pipes with the cut ends (CCC) has a more considerable effect on load capacity for all diameters except the ones with 250 mm, where the samples with full confinement (Cc) carried a bigger load than those with cutting ends. Finally, a numerical simulation of samples is carried out by the finite element (FE) model using the ABAQUS software. For all scenarios, the results of the numerical analysis showed considerable similarity to the experimental results, with R2 of 0.95 indicating the high linearity between the actual and simulated compressive strength values. Moreover, the FE induces fewer simulated errors with a relative error (RE) ranging from 0.16% to 6% for all scenarios.

The study investigated the strengthening effect of glass fiber and polypropylene fiber-based engineered cementitious composites (GFPPECC) on fire-damaged reinforced concrete short exterior columns. Both moderate (500 °C) and high (900 °C) intensities of fire load corresponding to the ISO834 fire curve were adopted. A total of 15 columns (150 mm × 150 mm × 1000 mm) were cast. The columns were grouped as control column (CC), unstrengthened column-(C2, C3), and strengthened column-(C1, C4) with three columns in each group. The columns in group CC were subjected to axial compression up to failure and kept as the standard reference. The columns in the group (C2, C4) and (C1, C3) were fired up to 900 °C and 500 °C, respectively. Compressive loading on C2 and C3 was applied without any strengthening technique. C1 and C4 were repaired and strengthened using GFPPECC. A similar group of columns, namely unstrengthened-(A-C2, A-C3) and strengthened-(A-C1, A-C4) columns, were analyzed numerically using ANSYS. The parametric analysis was carried out from experimental and numerical results. Variations between experimental and numerical results were negligible. The strengthening has restored to about 68% of the stiffness of columns damaged due to moderate fire intensity. The energy absorption, ductility, and modulus of elasticity were also good, with only about less than 10% reduction compared to the control column. The performance of columns shows that the GFPPECC composite was utilized effectively without any debonding. Whereas for high fire intensity, the GFPPECC composite was not fully used, and premature failure has occurred due to the softening of concrete at high temperatures. [ABSTRACT FROM AUTHOR]

Steel fibers increase the strain capacity of normal and high-strength concrete columns. Availability of normal or high-strength concrete and conventional reinforcement is limited for low-rise concrete houses in rural areas. It is in the interest of society, of the thousands of people that live in those houses, that house performance be evaluated. This paper assesses the behavior of 18 short, square-section columns made of low-strength concrete reinforced with hybrid steel bars and micro-fibers under axial compressive loads. The investigated variables were the steel ratio (2.8% and 5.6%) and layout of transverse reinforcement and the fiber dosage (10 kg/m3 and 20 kg/m3). Response of the specimens was assessed in terms of crack patterns and failure modes, compressive stress–strain curves and the contribution of concrete, conventional steel reinforcement and steel fibers to the performance of the columns. Experimental stress–strain curves of the columns were compared with those computed using existing analytical models. The comparison of the measured and calculated stress–strain curves showed that it is required to calibrate a model for the columns with the key characteristics included in the experimental campaign. The study developed a behavioral model that is consistent with the trends of the results measured. The effectiveness of the proposed model was evaluated through statistical analysis. [ABSTRACT FROM AUTHOR]

Failure of short columns in concrete buildings has been extensively reported during past earthquakes. Assessing the behaviour of short columns is challenging and often requires using time-consuming advanced numerical modelling. This article presents a new and practical Short Column Macro Element (SCME) that predicts accurately the behaviour of concrete short columns. A 1/3-scale one-storey building with short columns is subjected to lateral loading tests until failure. The experimental results from the building are then used to calibrate a numerical model in Abaqus®. It is shown that the numerical model matches well the experimental results. The experimental crack patterns and stress distribution from Abaqus® are then used to determine the load path within the short column. Based on these data, a new strut-and-tie SCME is proposed and implemented in OpenSees software to simulate accurately (within 5% accuracy) the behaviour of the short columns of the tested building. Subsequently, the frame models calibrated in OpenSees and Abaqus® are modified to examine numerically the effectiveness of highly deformable FRP-confined rubberised concrete (FRP CRuC) at increasing the deformability of short columns with different levels of FRP confinement (1, 2 or 3 layers). The numerical results show that whilst the tested building failed at a small displacement of 5.4 mm (0.43% drift ratio), the use of FRP CRuC short columns with minimal confinement (1 layer of AFRP only) increased the building's displacement by almost seven times to 37 mm (3.0% drift ratio). This also enabled more redistribution of forces to other structural members of the building. This article contributes towards the development of practical design/analysis models for short columns made of conventional concrete and FRP CRuC, which are scarce in the existing literature. • Cyclic loading tested were performed on a 1/3-scale one-storey RC building with short columns. • A practical Short Column Macro Element (SCME) is proposed using the results of experimentally validated Abaqus® models. • The SCME is implemented in OpenSees and shown to be accurate to model the shear-flexural behaviour of RC short columns. • The SCME is modified to study numerically the use of FRP-confined rubberised concrete (FRP CRuC) in short columns. • Highly deformable FRP CRuC short columns with 1 layer of AFRP increased the drift capacity by almost seven times. [ABSTRACT FROM AUTHOR]

Concrete-filled steel tubes are widely applied in offshore structures, which often being exposed to aggressive ocean climate. This has recently led to the introduction of concrete-filled aluminum alloy tubular (CFAT) columns, of which aluminum alloy tube is used as a superior anti-corrosion metal material. However, limited research has led to the design of CFAT columns not being included in the current design specifications, limiting their engineering applications. Accordingly, in this paper, an experimental program including 9 CFAT specimens was launched to further investigate the compressive behavior of CFAT short columns and to clarify the confinement mechanism in such columns. The test results indicate that the ultimate capacity of CFAT short columns is improved with the increase of concrete strength or the decrease of tube diameter-to-wall thickness ratio. Based on the experimental results, the finite element model (FEM) was established, and then used to clarify the confinement mechanism of CFAT columns and investigate the effects of the salient parameters on the behavior of such columns. By comparing with the existing experimental results, the accuracy of current strength calculation formulas for CFAT columns was assessed, and the conclusion indicates that there is an unexpected deviation in the prediction results. To this end, a simplified strength prediction formula for CFAT columns was proposed, which successfully introduced a novel confinement factor that well reflects the confinement effect of the concrete core. This confinement factor considers the effects of proof stress, concrete strength, and tube diameter-to-wall thickness ratio. Finally, compared with other formulas, the proposed formula has better performance in predicting results. • An experimental program including 9 CFAT specimens is launched. • The FE model is established and validated against the experimental results. • A novel confinement factor considering salient variables is suggested. • A simplified strength prediction formula for CFAT columns is proposed. • The proposed formula exhibits good predictive performance. [ABSTRACT FROM AUTHOR]

series of earthquakes across the globe (1990 Luzon earthquake, 1992 Cairo earthquake, 1999 Izmit earthquake, 2001 Gujarat earthquake, 2008 Sichuan earthquake, 2009 L'Aquila earthquake etc.) have demonstrated real modalities of imposing a fragile seismic response to reinforced concrete frame systems with infilled masonry walls. The global structural effects and negative local effects of masonry infill walls proven to be crucial in the last phases of structure collapse. It is desired through this theoretical study to classify the consequences that cause a series of phenomena in this structural system and some practical methods that can help solve them. [ABSTRACT FROM AUTHOR]

Concrete-filled stainless-steel tube (CFSST) columns, which would be more durable than their mild-steel counterparts, are potentially a more economical method of using stainless-steel for structures. Spiral-welded stainless-steel tubes (SWSSTs) could further increase the cost-effectiveness of CFSST columns. SWSSTs are an alternate and advantageous form of welded tube fabricated by welding a helically bent steel plate. The behaviour of concrete-filled SWSST (CF-SWSST) columns can potentially be different to CFSSTs using other tube types, especially due to larger residual stresses present in SWSSTs. Given this background, twelve self-compacting CF-SWSST short columns with nominal diameter-to-thickness ratios (D/t) equal to 51, 76, 101.5 and 114.5 were tested under axial compression considering eccentricities of 0, 0.15D and 0.4D. The observed failure mode, consisting of flexural local buckling, was equivalent to that reported for non-SWT CFSST columns. The spiral weld did not act detrimentally to the strength. Concrete-filled mild-steel tube design standards provided satisfactory predictions of the experimental capacities for CF-SWSSTs under eccentric loading though they were less conservative when the loading was concentric. The need for separate calibration of design guidelines for CF-SWSST short columns was established since, on average, the actual to predicted capacity ratios were noticeably less than those of non-SWT CFSSTs. Fibre-based section analyses using a confined concrete material model gave better predictions of the eccentric axial capacities than codified methods suggesting greater confinement benefit than considered in the standards are applicable to eccentrically loaded CF-SWSST short columns. The study also confirmed equivalent strength behaviour of CF-SWSST short columns to their mild-steel counterparts though with greater ductility. • Concrete-filled spiral-welded stainless-steel tubes (SWSST) short columns under eccentric axial compression loading. • Assess the applicability of existing standards for eccentrically loaded CF-SWSST short columns. • Failure behaviour of eccentrically loaded CF-SWSST short columns. • Fibre-element based analyses to obtain the capacity of CF-SWST short columns. [ABSTRACT FROM AUTHOR]

In this paper, concrete filled steel tubes columns (CFT) are investigated by using finite element program ANSYS 15.0. Analysis are done for four different shapes of columns (circular, square,hexagonal andoctagonal). Results of analytical solution (for circular and square) were compared with existing experimental data provided by [Alwash et al., 2013].Comparative resultsof failure load give 4% difference between experimental and ANSYS 15.0. Also, parametric studies have been carried out to investigate the effect of concrete filled steel tubes columns shapes (for hexagonal and octagonal) on load carrying capacity.Finally, a newformulaefor predicting the ultimate strength of CFT is proposedbased on experimental data of 148 CFT columns of different cross sections with side length ranging between 200 and 4000 mm. To check the validity of the proposed equation, the loads calculated from the designmethods (American Concrete Institute (ACI 318M-14), Eurocode (EC4),New Zealand Standard of concrete structures(NZS) and American Institute of Steel Construction (AISC)) are used to compare with it. The comparison shows least convergence percentageof the proposed equation.

This research studies the behavior of reactive powder concrete (RPC) circular short columns with and without steel fibers of different types, as well as change of the reinforcement kinds of lateral (hoops and spiral) and the spacing between them. The experimental work consist study of fifteen short column specimens having an overall height of 1 m with circular cross-section of 150 mm diameter are loaded at ends with concentric loads. Six of the specimens are cast with the inclusion of steel fibers with aspect ratio of 75(group 1), and six of other specimens are cast with the inclusion of steel fibers with aspect ratio of 100 (group 2),and the other three specimens is without steel fibers, with hybrid steel fibers and high strength concrete. The concrete mix of fiber-reinforced samples contains 1% by volume of steel fibers of variable reinforcement longitudinal and lateral (hoops and spiral reinforcement). Experimental data for strength, failure mode, lateral, and the ductility were obtained for each test. The work concluded that the using of steel fibers in RPC was an effective way to prevent spalling of the concrete cover and increase the ductility and the using of high ratio of longitudinal reinforcement delays the pickling of the columns and increase strength. The ultimate load capacity of RPC columns of spiral lateral reinforcement is greater than the load of RPC columns of tied lateral reinforcement by about 1.25 to 1.35 times for the two groups.

In this paper, the axial behaviors of reactive powder concrete (RPC) short columns confined with carbon fiber reinforced polymer (CFRP) were investigated. All the specimens have square cross section of 100 mm × 100 mm and length of 400 mm with aspect ratio 4. The experimental work consists of three groups. The first group consists of six specimens of RPC with 2% micro steel fiber, without ordinary reinforcing steel and confining by zero, one and two layer of CFRP respectively. The second group consists of six specimens of RPC with 2% micro steel fiber and minimum ordinary reinforcing steel and confining by zero, one and two layers of CFRP respectively. The third group consists of four specimens of RPC without micro steel fiber and ordinary reinforcing steel and confining by one and two layers of CFRP respectively. Experimental data for strength, longitudinal and lateral displacement and failure mode were obtained for each test. The toughness (area under the curve) for each test was obtained by using numerical integration. The RPC columns confined with CFRP showed stiffer behavior compared with RPC columns without CFRP. The ultimate load of the RPC columns with 2% micro steel fiber + two layers of CFRP + minimum ordinary reinforcement were more than that of the RPC columns with 2% micro steel fiber + minimum ordinary reinforcement and without CFRP by about 1.333.

Abstract Spiral-welded steel tubes (SWTs) are fabricated by helically bending a steel plate and welding the resulting abutting edges. These tubes enable larger diameters, longer joint-less lengths, smaller dimensional tolerances, and more cost-effective construction compared to other types of steel tubes. Notwithstanding this, the use of SWTs for concrete-filled steel tubes (CFSTs) has been rather limited. Many international design standards contain guidelines on strength assessment of CFST columns. Even so, unlike for other tube types, there is a lack of experimental verification of the applicability of those guidelines for concrete-filled spiral welded steel tube (CF-SWST) columns. This has inhibited their widespread use, especially since the residual stresses in SWTs are generally larger than for other tubes. Given this context, twelve self-compactingCF-SWST short columns with nominal diameters (D)equal to 102, 152, 203 and 229 mm were tested under axial compression, considering load eccentricities of 0, 0.15D and 0.4D. The tube walls were nominally 2 mm thick while the effective length to diameter ratios were in the range 4.5–6.0. A ductile failure mode was observed for all the tests consisting of flexural local buckling in the maximum compression region, which was observed during post-peak deformation. The spiral weld seam was observed to neither provide a preferential location for failure nor be detrimental to the strength capacity. On average, the predicted capacities as per six commonly used international standards agreed well with the experimentally obtained values. The predicted capacities were observed to be more conservative for eccentric loading compared to concentric loading. For eccentric loading, fibre-element analyses using material models proposed for confined concrete provided better predictions of the actual capacity. This suggested that greater confinement benefit than considered in the codes is effective for eccentrically loaded CF-SWST short columns. The study provided evidence of equivalent behaviour of CF-SWST columns to other tested CFSTs and the applicability of existing guidelines for assessing their strength. Highlights • Concrete-filledmild-steel spiral welded tube short columns under eccentric axial compression loading. • Assess the applicability of existing standards for eccentrically loaded CF-SWST short columns. • Failure behaviour of eccentrically loaded CF-SWST short columns. • Fibre-element based analyses to obtain the capacity of CF-SWST short columns. [ABSTRACT FROM AUTHOR]

In the context of building protection against earthquakes, the strengthening technique by FRP (Fibre-Reinforced Polymers) plating and wrapping provides a relevant solution. The objective of this research is to evaluate the ultimate strength and failure mechanisms of externally FRP retrofitting on RC short columns. The analytical approach employs design equations proposed in construction guidelines for reproducing the concrete confinement provided by FRP wraps with fibres predominantly in the hoop direction. The strength and failure modes provided by the analytical approach are consistent with the experimental data. Then, a pushover analysis using a finite-element method is performed to investigate the efficiency for the FRP-retrofitted configurations of the short RC columns. The numerical assessment of the shear strength turns out to be more accurate than the one issued from analytical approach. In addition, the observed failure modes are well retrieved and are clearly illustrated through the display of consistent bending or shear cracking patterns. Finally, the ultimate displacements are assessed by the numerical procedure, highlighting the advantages of the partially FRP-strengthened configuration in comparison to the fully strengthened case in terms of ductility. [ABSTRACT FROM AUTHOR]

Elliptical concrete-filled steel tubular (CFST) columns have recently attracted significant attention because of their increased strength and stiffness compared with empty elliptical hollow sections (EHSs). As with any new cross-section, there are still many aspects to be investigated to allow for its inclusion in different design specifications. Based on literature survey, this paper investigates the elliptical CFST columns which are filled with high-strength concrete (HSC). Numerical investigations into the structural behaviour of the elliptical CFST columns subjected to pure axial compression and eccentric loading have been performed using the general purpose commercial finite element (FE) software, Abaqus. The validity of the current FE models is examined by comparing their outcomes with those test results in literature. Then, parametric studies are performed considering three main parameters, namely the slenderness of the EHS, the steel yield strength and the concrete compressive strength. This is followed by a discussion of the results, showing in detail the characteristics of their load-strain responses. A comparison of the ultimate strengths with the existing design models is then considered, from which it is found that improved design model could be suggested to save additional weight and reach an optimum design. Hence, a new design formula is presented at the end which considers the effective confined concrete strength. Overall, this investigation expands the available engineering knowledge and assists in utilising the HSC, currently used in a wide range of applications, with the elliptical CFST columns with their favourable aesthetical and structural characteristics. [ABSTRACT FROM AUTHOR]

Due to the increasing usage of concrete-filled steel tube (CFST) members in structural engineering, there will be more chances of fire hazards on these structures in the near future. Externally bonding carbon fiber reinforced polymer (CFRP) composites has emerged as a popular method for repairing damaged steel-reinforced concrete members. However, limited research is available to evaluate the behavior of CFRP strengthened CFST members. This paper presents the results of an experimental investigation on the compressive behavior of the post-heated circular CFST short columns externally strengthened with CFRP sheets. A total of twenty-one specimens are tested to investigate the influence of temperature and the number of CFRP layers on the mechanical behavior of repaired specimens. The ultimate strength is obtained from monotone static tests. The extensometer technique based on gauge strain is used to measure strains of electric gauges glued to the external surface of specimens. The results indicate that the increase in the number of CFRP layers leads to a significant change in the mechanical properties of post-heated CFST columns. Furthermore, it is shown that increases in the number of CFRP layers remarkably enhance the ultimate strength and initial stiffness of specimens subjected to the same heat treatments, while deteriorate the ductility. Based on extensive experimental analysis, simplified formulae are proposed to estimate the compressive ultimate strength of all specimens tested, providing reasonably good correlation with the experimental results. Besides, the proposed formulae are compared with some existing empirical models, and validity of the proposed formulae is evaluated. [ABSTRACT FROM PUBLISHER]