Type Of Stirrups Research Articles

Axial compression behavior of a prefabricated F4T-section thin concrete encased steel short columns with different stirrup types

A prefabricated F4T-section thin concrete encased steel (F4T-TCES) column with a low reinforcement ratio is proposed to address instability, corrosion resistance issues in pure steel columns, and column protrusion out of the wall. The F4T-section is a T-shaped column with internal steel featuring four flanges. Ten F4T-TCES short columns were tested under axial compression loads, examining five new stirrup types to facilitate construction and study their impact on load-carrying capacity. The effects of steel flange and web thicknesses, stirrup and longitudinal bar diameters, stirrup spacing and form, and concrete encasement thickness on axial compressive behavior were investigated through tests and finite element (FE) analysis. Results indicate that less reinforcement and thin concrete cover can restrain steel elastic buckling and fully utilize material properties. Using 8 mm diameter longitudinal bars and a 1.32 % stirrup ratio provides sufficient strength and adequate confinement. Reliable performance is achieved with a flange thickness of 12 mm, while increasing web thickness beyond 8 mm shows no significant improvement. Increasing concrete encasement thickness from 45 to 70 mm effectively reduces the cracking of the concrete cover. Specimen with stirrup type C exhibits the highest load-carrying capacity, delayed crack initiation, and narrower crack widths, with type D also performing well in crack control. All five stirrup types meet load-carrying requirements, with types C and D being easier to construct and thus preferable. Formulas for the axial compressive strength and a simplified load-axial deformation model for F4T-TCES columns are proposed and validated.

Shear behavior of circular concrete short columns reinforced with GFRP longitudinal bars and CFRP grid stirrups

Although fiber-reinforced polymer (FRP) reinforcements have become popular, the post-pultrusion bending leads to significant deficiency in bent portions of FRP hoops and spirals. This study adopts flexible carbon FRP (CFRP) grids as stirrups, and investigates the shear behavior of circular short columns reinforced with GFRP bars and CFRP grid stirrups. Six specimens with different shear reinforcement ratios, axial load ratios and types of stirrups (CFRP grids and steel hoops) were tested to shear failures. The failure modes, crack and strain developments, and shear load-horizontal displacement responses were presented for discussion. All specimens experienced shear-compression failures, and the critical diagonal crack widths increased approximately linearly with shear loads. The typical shear load-horizontal displacement curve consisted of three branches: a linear elastic branch, a cracking branch with progressive slope deteriorations, and an almost flat failure branch. Increasing CFRP grid stirrup ratio could not only enhance strength and ductility performance, but also alleviate the slope degradations, while increasing axial load ratios could enhance the initial cracking loads, restrain crack propagations, and reduce the lateral displacements. In terms of strength performance, steel hoops could be replaced by CFRP grid stirrups even with smaller stirrup ratio. Additionally, analytical investigations suggested that the effective stresses and strains of CFRP grid stirrups at failure may be lower than code limits.

A Comparative Study of the Structural Behavior of Concrete Beams Reinforced with Different Configurations of GFRP and Steel Bars

This study examined experimentally and numerically the performance of five concrete beams reinforced with longitudinal and transverse bars made of Glass Fiber Reinforced Polymer (GFRP) or steel. All beams had the same dimensions of 2700 mm in length, 180 mm in width, and 260 mm in depth. The beams were classified into two groups with different variables and compared with a reference beam reinforced with longitudinal and transverse steel bars. The first group consisted of two beams with longitudinal GFRP bars and no stirrups, varying the main reinforcement ratio. The second group comprised two beams with longitudinal GFRP bars and transverse GFRP or steel stirrups, varying the stirrup type. The results indicated that the beams with GFRP bars improved their flexural strength for different ratios but had limited shear resistance when using GFRP stirrups because increased deflection causes the number and width of cracks to grow, reducing the shear strength. All the tested beams exhibited linear elastic behavior until failure, with GFRP being more brittle than steel due to no yield point or plastic behavior in GFRP. The numerical simulation of the five beams using ABAQUS software showed good agreement with the experimental data obtained in the laboratory.

Analytic Investigation of Hooked Stirrups on Seismic Behavior of Reinforced Concrete 3D Frame Buildings

Ensuring the safety and stability of buildings during earthquakes is of utmost importance. This can be achieved by assessing the seismic performance of reinforced concrete structures with consideration of design details. This study focused on the seismic behavior of reinforced concrete buildings by comparing the effects of two different types of stirrups, namely those with a 135° angled end-hook shape and straight hooks, with variation of concrete strength. Pushover analysis of a sample building was performed to determine the effect of hook shape on stirrup reinforcement with a constant volumetric ratio for various concrete strength classes. The results of the analysis indicated significant differences in concrete strength and seismic behavior between the two stirrup configurations. The hooked stirrups demonstrated superior energy dissipation capability and ductility, which led to better seismic performance compared to unhooked stirrups across varying levels of concrete strength. To extend the investigation, the study compared the Mander et al., Kent–Scott–Park, and Kappos–Konstantinidis concrete models with different concrete classes (C50-C25-C20-C16-C10). The findings emphasized the importance of stirrup configuration in the design of earthquake-resistant structures. The study concluded that RC structural performance with the 135-degree hooked concrete members exhibited much better behavior of the 90-degree members for the various concrete strength. In this way, it has been revealed the arrangement and detailing of reinforcement in the construction beams and columns improves the governing effect on seismic structural performance.

Shear performance of partially encased composite beams with high-strength steel and UHPC

Various countries across the globe have implemented strategic policies that encourage the development and use of high-performance materials in engineering structures. This study focused on the shear performance of partially encased composite beams with high-strength steel and UHPC (PEHC beams). Seven PEHC beams under simply supported three-point loading conditions were tested to investigate the effect of main parameters such as the shear span-depth ratio, thickness of steel web, types of steel web, and types of stirrups on shear failure modes, crack patterns, load-deflection behavior, and the response of strains. Two failure modes were observed in PEHC beams, involving diagonal compression failure and shear compression failure. As the shear span-depth ratio decreased from 2.0 to 1.5 and 1.0, the shear strength increased significantly by 13.3% and 70.8%, respectively. Test results demonstrated that the increase in the thickness of steel web and the use of steel solid web positively affect the shear strength of PEHC beams, whereas the impact of normal-strength stirrups types proved insignificant. Finally, a theoretical method was proposed to predict the shear strength of PEHC beams by considering the coworking of four mechanisms: the composite truss, the steel web, the stirrups, and the steel fibres. Then the method was validated by the good agreement between the predicted and tested shear strength results, highlighting its applicability in providing accuracy.

Experimental Investigation on the Seismic Behavior of Precast Concrete Beam-Column Joints with Five-Spiral Stirrups

Precast concrete structure is a low-carbon building system that has been attracting extensive attention in recent decades. Beam–column joints are the weak links in precast concrete structures. Past studies showed that the five-spiral stirrups had excellent confinement effects and had the potential to enhance the seismic performance of concrete structures. This study proposed the reinforcement of precast concrete beam–column joints by using five-spiral stirrups and investigated their seismic performance. Considering the influences of the joint failure mode, joint type, construction method, and stirrup type, low-cycle loading tests were conducted on six full-scale precast concrete beam–column joint specimens. Various seismic behavior indicators, such as failure modes, hysteresis curves, skeleton curves, ductility, and energy dissipation, were obtained. The results indicated that the deformation capacity of the precast joints with five-spiral stirrups was comparable to that of cast-in-place joints. Under different failure design criteria, the seismic performance of the precast joints was superior to that of cast-in-place joints. Furthermore, the experimental capacities of the precast joints, using five-spiral stirrups, were higher than the calculated values according to the design code, demonstrating an adequate safety margin. This research contributes to the development of low-carbon and sustainable construction practices in the field of precast concrete structures.

Effectiveness of flange plates on torsional behaviors of ultra-high-performance fiber-reinforced concrete hollow beams

This study investigates the effectiveness of flanges with various types of stirrup and cross-sectional dimensions on the torsional behaviors of ultra-high-performance fiber-reinforced concrete (UHPFRC) hollow beams. A finite element model was developed and validated for simulating the torsional behavior. The impact of the essential parameters of flanges was investigated through experimental and numerical methodologies. The results showed that the inclusion of flanges substantially influenced the torsional strength of UHPFRC hollow beams, attributed to the section torsional plastic resistance moment and UHPFRC tensile capacity in flanges. The effectiveness of flange plates was considerably influenced by the web wall thickness. The stirrup type and the increase in flange reinforcement ratio, flange width, and thickness had a favorable effect on the torsional behaviors of thick-walled UHPFRC beams but minimal effect on thin-walled UHPFRC beams. The failure of thin-walled beams was determined by the web thickness and web reinforcements.

Estimation of lateral stress of stirrups at peak stress and residual stress of confined concrete at stirrups fractured in confined concrete under axial compression

The lateral stress of stirrups at the peak stress of confined concrete was closely related to the load-bearing capacity and deformability of concrete columns, while the fracture of stirrups affected the axial deformability of concrete columns after the peak stress of confined concrete. In this paper, 156 circular concrete columns confined with spiral stirrups and 141 square concrete columns confined with mesh stirrups were tested under axial compression. The effects of the compressive strength of unconfined concrete, the volumetric ratio and the yield strength of stirrups on the lateral stress of stirrups at peak stress and the residual stress of confined concrete at stirrups fractured were analyzed. Furthermore, the prediction models for evaluating the lateral strain of stirrups at the peak stress of confined concrete were established by considering the effects of the volumetric ratio and type of stirrups and the compressive strength of concrete, which had high prediction performance. In addition, the method for judging whether stirrups fractured or not was developed, which was suitable for evaluating the stirrups with and without yield platform. The prediction model for evaluating the residual stress of confined concrete at stirrups fractured was proposed.

Structural Behavior of Hollow Beam Reinforced with Different types of GFRP stirrups

The structure could be impacted by concrete's steel reinforcement corroding. When exceptional corrosion resistance capabilities are required, fiber-reinforced polymer (FRP) reinforcements offer a practical choice for constructions exposed to hostile environments. However, only a small number of the building's most important structural components are currently permitted to use FRP bars as interior concrete reinforcement, leaving the rest of the building unprotected. This is due to the lack of available curved or shaped reinforcing FRP pieces, which have subpar structural performance.
 Eighteen concrete beams with dimensions (1200×225×150) mm were divided into three groups and each group had five beams with three References and five different types of stirrups in each group and tested them up to failure. The first group included longitudinal reinforcing steel bars 6Ø10mm, the second group longitudinal reinforcing GFRP bars 6Ø10mm, and the third group longitudinal reinforced with hybrid (3steel+ 3GFRP) bars 6Ø10mm. All beams are self-compacting concrete with a longitudinal hollow with dimensions (50×100) mm.
 The results showed that the ultimate load of a hollow beam reinforced with steel reinforcement is less than a solid beam reinforced with steel (reference 1) by (15%) and a hollow beam reinforcing with GFRP reinforcement is less than a solid beam reinforced with GFRP (reference 2) by (5%), and a hollow beam hybrid reinforced with (Steel+ GFRP) reinforcement is less than a solid beam reinforced with GFRP (reference 3) by (4%).

Study on Shear Behaviors and Damage Assessment of Circular Concrete Short Columns Reinforced with GFRP Bars and Spiral Stirrups.

This study investigated the shear resistance and damage evolution of glass fiber-reinforced polymer (GFRP)-reinforced concrete short columns. Five circular concrete short columns reinforced with GFRP bars and spiral stirrups were fabricated and tested under lateral thrust in the laboratory. The test variables involved the stirrup reinforcement ratio, the longitudinal reinforcement ratio and the type of stirrups. The failure modes, load-displacement curves, strain responses and crack characteristics of these columns were documented and discussed. The accuracy of shear design equations in predicting shear capacity of such columns was evaluated. In addition, the digital image correlation (DIC) instrument was used to identify the full-field strain and damage zones of circular concrete short columns. Several smart aggregate (SA) transducers coupled to the surface of these columns were used to monitor its damage status. The energy ratio index (ERI) and the damage index based on smart aggregate were established to characterize damage level of such columns. The test results indicate that the shear capacity is improved 5.6% and 31.1% and the lateral ultimate displacement is increased 67.7% and 400% as the stirrup reinforcement ratio of the concrete short column is increased from 0 to 0.19% and 0.47%, respectively. The shear capacity equation proposed by Ali and his co-workers, considering a strain limit of 0.004Efv, gives accurate predictions of the shear capacity of circular concrete short columns reinforced with GFRP bars and spiral stirrups. The variation in ERI values is explained by the development of damage zones of the column obtained with DIC technology and with the proposed damage index based on the smart aggregate it is feasible to evaluate the damage level of circular short concrete columns.

Experimental and theoretical analysis on shear behavior of RC beams reinforced with GFRP stirrups

The objective of this paper is to experimentally study the shear behavior of reinforced concrete (RC) beams reinforced with glass fiber reinforced polymer (GFRP) stirrups. Six specimens including five RC beams reinforced with GFRP stirrups (GFRP-S-RC beams) and one beam strengthened with steel stirrups (RC beam) are fabricated. The effects of several parameters (i.e., stirrup type, the shear span ratio, and stirrup spacing) on the failure modes, shear crack width, shear capacity, strain variation of stirrup and longitudinal rebar, and the mid-span deflection are investigated. Similar to the conventional RC beam, three different types of shear failure modes including the shear compression failure, the diagonal compression failure, and the diagonal tension failure are observed on the GFRP-S-RC beams. The shear capacity of GFRP-S-RC beams decreases as the shear span ratio or stirrup spacing increases. GFRP stirrups exhibit a slight opposite effect on the shear capacity. The average and maximum strain of the stirrup both increase as the shear span ratio increases. The increase in the shear span ratio and the stirrup spacing adversely affects the ultimate deflection and longitudinal steel strain. A modified formula for the allowable strain of FRP stirrup is proposed. Considering the effect of uneven stress of stirrups, a model for predicting the shear capacity of GFRP-S-RC beams is proposed, and it shows good agreement with various test data.

Performance of stirrup-confined concrete-filled steel tubular stub columns under axial loading: A further investigation

To investigate the effects of stirrup ratio and connection type of stirrups on axial compression performance of stirrup-confined concrete-filled steel tubular (CFST) stub column, experiments were conducted on 16 CFST stub columns. The axial compressive bearing capacity and ductility of square and circular CFST stub columns with welded and non-welded stirrups were studied. Besides, numerical models of the stirrup-confined CFST stub columns were established to validate whether the numerical modeling method for welded stirrup-confined CFST column is suitable for the non-welded counterparts. Then, the applicability of the formulas for the axial compressive bearing capacity of the large stirrup ratio CFST stub column was investigated. The results indicated that the stirrups have a significant constraint effect on the steel tube and improve the axial compressive bearing capacity and ductility of the CFST stub column obviously. The effects of the stirrups on the square composite column are more significant than the circular composite column. The welded stirrups are more effective on the bearing capacity and ductility. The numerical modeling method and formulas are suitable for the non-welded stirrup-confined and large stirrup ratio CFST stub columns.

Effect of Stirrups on the Behavior of Semi-Precast Concrete Slabs

A semi-slab of precast concrete (or half-slab) is a structural system that consists of concrete at the bottom half of a slab and concrete cast in situ at the top. To avoid traditional formwork and minimize the bottom half of the slab, this section can function as formwork and reduce the thickness of precast slabs, which makes their transportation easy. The interface between precast and overtopping concrete is effective for the slab system's performance. To improve the half-slab floor system, it is needed to have a shear connector (stirrups). Therefore, to better understand the behavior of this slab system, six full-scale slab specimens (2×7.5 m) with different shapes of the stirrups and spacing between them were constructed for this study. One specimen was produced with no connections and served as a reference specimen, while the other employed stirrups to connect slab units. The tests found that the distribution and type of stirrups affect the structural performance of the semi-precast concrete slab. The maximum load capacity of slabs with rectangular or triangular connections was nearly more significant than reference slabs, reaching 136.11 and 86.11%, respectively. The maximum load increased by 81.4 % for rectangular connections and 54.9% for triangular connections when the distance between the connectors was reduced from 600 to 300 mm. Furthermore, stirrups in semi-precast slabs could improve the cracking behavior, stiffness, and ductility. Doi: 10.28991/CEJ-2022-08-08-09 Full Text: PDF

Experimental Study on the Influence of Type of Stirrup of Prestressed Concrete Beams with Corroded Rebars

Corrosion of longitudinal reinforcement and stirrup in reinforced and prestressed concrete beams is very common for structures and infrastructures, which is one of the main reasons for the decrease in stiffness and durability of structure. In order to evaluate the influence of corrosion of different types of stirrups on the bearing capacity of the prestressed concrete beam, the method of using electricity to accelerate corrosion was adopted. Load experiment on 4 corroded prestressed concrete beams with different corrosion rates and different stirrup types was carried out. In this paper, reduced scale model beams were designed based on the 5 × 50 m simple‐continuous box girder of the Donghai Bridge. The results show that for prestressed concrete beams with different corrosion rates and stirrup types, the load‐deflection curve can be divided into an elastic stage and a plastic stage. The corrosion of longitudinal bars and stirrups will reduce the flexural capacity, but the overall decline is not obvious. When the corrosion rate is 10%, the bearing capacity of the ordinary stirrup specimen decreases by 6.1%; epoxy‐coated stirrup specimen decreases by 4.9%; stainless stirrup specimen has nearly no change. The influence of different types of stirrups on cracking load, deflection, and bond‐slip behavior is discussed.

Punching shear resistance of flat slabs with different types of stirrup anchorages such as shear reinforcement

Concrete codes demand that the stirrup type shear reinforcements must be adequately anchored in the longitudinal reinforcements. However, this requirement hinders the executive process and makes the use of some reinforcements unfeasible. The goal of the present study was to assess the influence of different types of anchoring of shear reinforcements with closed stirrups on the punching resistance of flat slabs that do not meet the code's standards. An experimental program was conducted assessing nine flat square slabs, a reference slab, and four different types of detailings concerning anchoring. Only one of those details met the normative prescriptions. As a result, it was found that the variation in the anchorage of the stirrups had not influenced the behavior of the slabs. All types of connections had similar punching shear resistance increases.

Analysis and Modification of Methods for Calculating Axial Load Capacity of High-Strength Steel-Reinforced Concrete Composite Columns.

To investigate the applicability of the methods for calculating the bearing capacity of high-strength steel-reinforced concrete (SRC) composite columns according to specifications and the effect of confinement of stirrups and steel on the bearing capacity of SRC columns. The axial compression tests were conducted on 10 high-strength SRC columns and 4 ordinary SRC columns. The influences of the steel strength grade, the steel ratio, the types of stirrups and slenderness ratio on the bearing capacity of such members were examined. The analysis results indicate that using high-strength steel and improving the steel ratio can significantly enhance the bearing capacity of the SRC columns. When the slenderness ratio increases dramatically, the bearing capacity of the SRC columns plummets. As the confinement effect of the stirrups on the concrete improves, the utilization ratio of the high-strength steel in the SRC columns increases. Furthermore, the results calculated by AISC360-19(U.S.), EN1994-1-1-2004 (Europe), and JGJ138-2016(China) are too conservative compared with test results. Finally, a modified formula for calculating the bearing capacity of the SRC columns is proposed based on the confinement effect of the stirrups and steel on concrete. The results calculated by the modified formula and the finite element modeling results based on the confinement effect agree well with the test results.

Axial compressive behavior of concrete-encased CFST stub columns with open composite stirrups

The existing method to improve the coordination performance of the inner and outer parts of concrete-encased concrete-filled steel tube (CFST) composite columns by increasing the volume-stirrup ratio causes difficulties in construction due to over-dense stirrups. Thus, this paper proposes an open polygonal composite stirrup with high strength and high ductility CRB600H reinforced rebar, and seventeen specimens were constructed, and their axial compressive performance was tested. The main parameters considered were the volume-stirrup ratio, the steel tube size, the stirrup type and the stirrup strength. The test results indicated: For the specimens restrained by open octagonal composite stirrups, compared with the specimen of 0.5% volume-stirrup ratio, the compressive bearing capacity increased by 14.6%, 15.7% and 21.5% for volume-stirrup ratio of 0.73%, 1.07% and 1.61%, respectively. For the specimens restrained by open composite rectangle stirrups, compared with the specimen of 0.79% volume-stirrup ratio, the compressive bearing capacity increased by 7.5%, 6.1%, and -1.4% for volume-stirrup ratio of 1.12%, 1.58% and 2.24%, respectively. The restraint ability and the bearing capacity of the octagonal composite stirrup are better than other stirrup types. The specimens equipped with open polygonal composite stirrup not only had a higher ductility than those with the traditional closed-loop stirrup, but they also had a higher axial bearing capacity than those with an HPB300 strength grades stirrup. Therefore, the open composite stirrup can be used in practical engineering. A new calculation method was proposed based on the stress-strain models for confined concrete under different restrain conditions, and the predicted value was close to the experimental value.

Seismic Damage Model of High-Strength Reinforced Concrete Frame Columns

In this paper, several existing seismic damage models as well as their characteristics were discussed first of all. And then it was figured out that variational history of incremental dissipated hysteretic energy of tentative frame columns under different loading cycle levels; the influence of axial compression ratio, type of stirrups, stirrup ratio, reinforcement ratio, strength grade of concrete and shear span ration on the incremental dissipated hysteretic energy was discussed and analysed. The damage index of tentative frame columns was compared and analysed according to the existing seismic damage models, and the seismic damage models adapt to high-strength concrete columns and ordinary-strength concrete columns were offered. The influence of shear span ration, axial compression ratio and stirrup ratio on the damage was discussed and analysed according to the variational history of the damage index under different loading cycle levels. Lastly through analysing all sorts of seismic damage models comparatively, the seismic damage model of high strength concrete frame columns is put forward, which offers good basement for further damage analysis.

Comparative studies on passivation and corrosion behaviors of two types of steel bars in simulated concrete pore solution

The corrosion behavior of two types of stirrups, a plain steel bar and a ribbed steel bar, were studied in this work. The results demonstrated that a better passive state was achieved on B500, which was due to a relatively higher concentration of Fe2+ oxides at the first 2 nm depths of the film, even though B500 film had relatively less FeOx contents, because Fe2+ oxides had a better protective property than Fe3+ oxides. Furthermore, the slightly lower donor density of B500 film in the M-S analysis results presented the much less point defect in the film, showing an increase in the anti-corrosion property of passive film. These contributed to a higher chloride threshold value of B500, 4 times higher than that of S275. Therefore, compared with S275, B500 stirrups could be more suitable for the application in the severe service environment.

The Effect of Stirrup Iron Style on Normal Forces and Rider Position

The stirrup iron has the potential to modify the forces experienced by a horse and rider during ridden exercise. A range of stirrup designs are available, but no previous studies have investigated if these modifications influence riders’ position and interaction with the horse. Novel flexible (F) or flexible and rotatable (FR) irons versus traditional (T) stirrups may positively impact the welfare and performance of the horse and rider. Four riders rode using the three stirrup types (T, F, and FR). Hip, knee, and ankle angles and toe position from film, and the normal force exerted bilaterally on force sensors on the stirrups tread were evaluated at the highest (HP) and lowest point (LP) of the posting trot (n = 4) and canter (n = 2). Statistics included Shapiro-Wilk’s test, Friedman’s test, and Wilcoxon signed rank test (significant at P < .05). No significant difference was seen between joint angles, toe position, or forces between the types of stirrups. At the HP, mean hip, knee, and ankle angles were 169.4° ± 10°, 150.7° ± 9.7°, and 94.5° ± 9.6°, and 139.1° ± 9.6°, 123.9° ± 10.9°, and 92.7° ± 9.5° at the LP. Riders had an 8.74° ± 6.66° difference of right versus left joints. Right toes rotated more laterally (P = .02) regardless of stirrup type. The mean trot and canter forces applied (N)/body weight (N) were 0.72 ± 0.15 (HP), 0.19 ± 0.15 (LP), and 0.18 ± 0.05 (canter). Riders shortened the stirrup leathers with F or FR. Stirrup style minimally impacted rider position or the forces experienced; however, forces differed by gait. Future studies regarding how a rider’s experience and painful joints may contribute to asymmetries are warranted.