High-strength Transverse Reinforcement Research Articles

Behavior of UHPC columns confined by high-strength transverse reinforcement under eccentric compression

This paper presents the experimental and analytical studies on the compressive behavior of ultra-high performance concrete (UHPC) columns confined by high-strength transverse reinforcement under eccentric compression. Nine columns including test variables of spacing, strength and arrangement type of transverse reinforcements, steel fiber content and eccentricity were tested to analyze the load-lateral deflection behavior, failure modes and carrying capacity. The experiment results showed that the deformation capacity, peak load and residual carrying capacity of UHPC columns confined by high-strength transverse reinforcement under eccentric loading were significantly better than those of ordinary-strength transverse reinforcement. Reducing the spacing of transverse reinforcement and increasing the volume fraction of steel fiber could also improve the ductility and carrying capacity of UHPC columns. Then, a mesoscale model was proposed to characterize the tensile behavior of UHPC which considered the fiber inclination, fiber-matrix interface bonding and fiber embedded length. Based on the proposed tensile model, a simplified method for calculating the carrying capacity of UHPC columns under large eccentric compression was developed, where the tensile behavior of UHPC and the confinement effect of transverse reinforcements were considered. The errors between the theoretical and test values were within 10%, indicating that this method can be used to guide the design of UHPC columns.

Axial compressive behavior of ultra-high performance concrete confined by high-strength transverse reinforcements

The axial compressive performance of the confined system composed of the high-strength transverse reinforcements and ultra-high performance concrete (UHPC) was studied in this paper. The axial compression tests were carried out on 24 UHPC columns to investigate the effect of strength, spacing and configuration of the transverse reinforcements and steel fibers content on the ductility, toughness and maximum load of UHPC columns. The failure modes, axial load-axial strain behavior and strain of steel bars were also analyzed and discussed. The test results showed that high-strength transverse reinforcement could significantly increase the post-peak ductility of UHPC columns, compared with the ordinary-strength transverse reinforcements. In addition, the ductility, maximum load and toughness of the UHPC columns could be improved by reducing the transverse reinforcements spacing and using the L-type multiple hoops. Then, simulated axial load-axial strain curves and failure modes of UHPC columns were obtained by finite element analysis. Three performance indexes, i.e., the maximum axial load, strain corresponding to the maximum load and strain corresponding to 85% drop of the maximum load of UHPC columns were evaluated in the numerical model. The error between test value and simulated value of the three performance indexes was mostly within 15%. The results demonstrated that the three-dimensional numerical model of UHPC columns could effectively simulate the axial compressive performance and failure modes of the specimens.

Experimental investigation of full-scale concrete columns confined by high-strength transverse reinforcement subjected to lateral cyclic loading

The use of high-strength longitudinal and transverse reinforcements in confined concrete columns can improve bearing capacity and deformability. Besides, experiments on confined concrete columns with side length of 400 mm can better reflect the behaviour of confined concrete columns in engineering project. Thus, the purpose of this study is to investigate the seismic behaviour of full-scale confined concrete columns with high-strength longitudinal and transverse reinforcements. Based on 15 confined concrete columns subjected to lateral cyclic loading, the effects of axial compression ratio, shear span ratio and volumetric ratio on the seismic behaviour of confined concrete columns were studied. The results showed that the ultimate drift ratios of the 15 confined concrete columns ranged from 1/43 to 1/20, i.e. 1.2–2.5 times as much as the specified limit (1/50) of rate earthquake, indicating excellent ductility. Additionally, the high-strength transverse reinforcements could not yield at peak load but could yield at the ultimate displacement. The high-strength transverse reinforcement stresses at the peak lateral load were 430–690 MPa, approximately 56–91% of the transverse reinforcement yield strength. Finally, an empirical formula was proposed to predict the ductility factor that was then evaluated by comparing the predicted values with the experimental results of 37 confined concrete columns.

Structural state of stress analysis of confined concrete based on the normalized generalized strain energy density

This paper investigates the behavior of 32 high-strength concrete square columns confined by high-strength transverse reinforcement under concentric compression, by applying structural state of stress theory. First, the sum of generalized strain energy density values (Eij) of columns at every load value (Fj) is normalized as Ej,norm to describe the structural state of stress. Then, the Ej,norm-Fj curves reveal the characteristics of the state of stress and failure mechanism of confined concrete columns under load-bearing condition. The Ej,norm-Fj curves also reveal an updated failure load definition and failure criterion. Furthermore, the effects of unconfined concrete compressive strength, volumetric ratio, and transverse reinforcement yield strength on the state of stress are studied. Finally, a formula is proposed to predict the updated failure loads of confined concrete columns. In summary, a novel method to identify some working characteristics of structures is explored.

Structural behaviour of prestressed concrete beams with high-strength stirrups

Many studies related to high-strength concrete material have been conducted, but relatively few studies have considered high-strength steel reinforcement. Four current design codes – ACI 318-14, Eurocode 2, CSA A23.3-04, and JSCE-07 – limit the yield strength of transverse reinforcement to control diagonal crack width, and to ensure yielding of transverse reinforcement prior to brittle failure mode. ACI, Eurocode 2 and CSA A23.3-04 limit the yield strength of transverse reinforcement to 420, 600, and 500 MPa, respectively; while JSCE-07 limits the yield strength to 800 MPa, when the compressive strength of concrete is higher than 60 MPa. The implementation of high-strength transverse reinforcement in prestressed concrete (PSC) and reinforced concrete (RC) beams has been determined in this study. A total of 16 beams were strengthened using higher yield strength stirrups than the code limitations, and were monotonically loaded to failure. All the beams were designed to experience shear failure prior to flexural failure. Most of the test results showed yielding of the stirrups, and narrower crack width than the code limitations even though the specimens were strengthened with higher than 420 MPa stirrups. The test results imply the feasibility of using high-strength stirrups for PSC beams with regard to serviceability.

Enhancing the confinement of ultra-high-strength concrete columns using headed crossties

This study investigates the influence of headed crossties on the confinement of 200MPa ultra-high-strength concrete (UHSC) columns. A Total of six UHSC columns confined by headed crossties (deformed reinforcing bars with heads welded on both ends) and seismic crossties, detailed with 90° bend anchorages alternated end to end, were constructed and tested under pure axial load. The amount and yield strength of transverse reinforcement were varied to determine the efficiency of headed crossties on the confinement of the UHSC columns. The columns with seismic crossties exhibited some loss in confinement due to the loss of anchorage of the 90° hooks that opened up before significant yielding of the crossties could occur. The relatively small heads used are capable of developing the yield force of high-strength transverse reinforcement in the UHSC columns. The use of high-strength headed crossties resulted in improved confinement compared to columns with high-strength seismic crossties resulting in improved post-peak performance of UHSC columns. A prediction model that accounts for the additional confinement pressure due to the bearing of the heads, brittle cover spalling and the stress-strain relationship of UHSC was used to predict the axial load-strain behavior of the UHSC columns.

High Strength Concrete Columns under Axial Compression Load: Hybrid Confinement Efficiency of High Strength Transverse Reinforcement and Steel Fibers.

Addition of steel fibers to high strength concrete (HSC) improves its post-peak behavior and energy absorbing capability, which can be described well in term of toughness. This paper attempts to obtain both analytically and experimentally the efficiency of steel fibers in HSC columns with hybrid confinement of transverse reinforcement and steel fibers. Toughness ratio (TR) to quantify the confinement efficiency of HSC columns with hybrid confinement is proposed through a regression analysis by involving sixty-nine TRs of HSC without steel fibers and twenty-seven TRs of HSC with hybrid of transverse reinforcement and steel fibers. The proposed TR equation was further verified by compression tests of seventeen HSC columns conducted in this study, where twelve specimens were reinforced by high strength rebars in longitudinal and transverse directions. The results show that the efficiency of steel fibers in concrete depends on transverse reinforcement spacing, where the steel fibers are more effective if the spacing transverse reinforcement becomes larger in the range of 0.25–1 effective depth of the section column. Furthermore, the axial load–strain curves were developed by employing finite element software (OpenSees) for simulating the response of the structural system. Comparisons between numerical and experimental axial load–strain curves were carried out.

Numerical Test Research on High-Strength Concrete Square Columns with High-Strength Aseismic Transverse Reinforcement under Concentric Compression

This paper focuses on the the relationship between strength and ductility of high-strength concrete (HSC) columns with high-strength aseismic transverse reinforcement under concentric compression and its influencing factors. Some confining models for HSC with high-strength aseismic transverse reinforcement are introduced. Based on 10 groups of high-strength aseismic stirrup confined high-strength concrete square columns are tested under concentric compression, the influence of stirrup in binding strength and the ductility of concrete columns on different stirrup strength, different volume ratio of reinforcement, different stirrups type and different stirrup spacing form is studied by using finite element software ABAQUS. The results indicate that a good agreement is obtained between calculated results and experimental ones. The high-strength stirrup confined concrete columns can improve the bearing capacity and deformation performance of components effectively, laying the foundation of the applications of high-strength stirrups in concrete structures.

Seismic Design for Bridges with Short Piers in High Earthquake Intensity Zones

AbstractAimed at short bridge piers that are vulnerable to brittle shear failure in high earthquake intensity zones, seismic design countermeasures for bridges with short piers were put forward in combination with the Guidelines for Seismic Design of Highway Bridges (JTG/T B02-01-2008). Based on a designed simple two-span pre-stressed concrete T-beam bridge located in a high earthquake intensity zone, specific schemes and suggestions, including seismic isolation technology, multi-column pier design, composite short column (Fiber Reinforced Plastic (FRP) or steel tube), or high-strength transverse reinforcement, were proposed, respectively. By using the numerical analysis model for seismic isolation and the multi-column pier design scheme established by the special finite element software MIDAS, the maximum longitudinal and lateral loads of bridge piers and the pile foundations of different designs under E2 earthquake excitation were compared. It is found that the seismic demand of short piers and foundati...

Study of High-Strength Lateral Ties Stress of High-Strength Confined Concrete

This paper presented a concentric loading test of 10 high-strength concrete columns confined by normal-and high-strength lateral ties. It was confirmed that high-strength transverse reinforcement did not yield at peak strength of confined concrete．On the basis of test date，new equation was proposed to compute the stress in the transverse reinforcement at peak and ultimate strength of confined concrete, which shows good accordance with experimental results. These equations are suitable in the analysis of lateral ties confined concrete.

Structural Behavior of RC Cylinders Confined with High Strength Transverse Reinforcement

The number of high-rise reinforced concrete (RC) buildings is steadily increasing since 1980’s. The use of high strength concrete is indispensible for high-rise RC construction to ensure sufficient strength of the structure. The effect of high strength concrete can be significantly improved by the use of high strength and large size reinforcing bars. The yield strength of transverse reinforcement is limited in the current design codes to prevent possible sudden concrete failure due to over reinforcement. This paper presents the effects of the yield strength of transverse reinforcement and compressive strength of concrete on the structural behavior of reinforced concrete cylinders. Two parameters were considered in this investigation: compressive strength of concrete and the yield strength of transverse reinforcement (472MPa, 880MPa, and 1,430 MPa). Analytical and experimental results indicated that the structural behavior of RC cylinders confined with high strength transverse reinforcement is strongly influenced by compressive strength of concrete.

Ductility of High-Performance Concrete Beams with High-Strength Lateral Reinforcement

The aim of this study was to investigate the flexural behavior of high workability, high-performance concrete (HPC) beams with high-strength transverse reinforcement under static load. A total of 21 beam specimens were fabricated in this study: 7 were normal concrete beams, and the remainder were HPC beams. The parameters included concrete strength, amount of tension reinforcement, amount of compression reinforcement, amount of transverse reinforcement, and strength of transverse reinforcement. Results show that HPC beams have slightly higher strengths than normal concrete beams. In addition, an increase in tension reinforcement will increase the strength but decrease the ductility of the beams. An increase of compression steel and concrete strength will increase the ductility of the beams effectively. HPC beams show better ductility than normal concrete beams. HPC beams also have better crack control than normal concrete beams. Beams with high-strength shear reinforcement exhibit the same crack control ability as beams with normal strength shear reinforcement.

軸部を細くした場所打ちコンクリート杭の耐震性能

The cast-in-place-concrete piles can be slimmed by the construction method of the under-reamed pile. However, the seismic shear stress increases because the area of the pile head decreases. In this paper, first, the specification of such piles and the result of frame analysis which consists of building and foundation are shown as the background data. Secondly, the earthquake-resistant properties of reinforced concrete piles with the normal-strength transverse reinforcement(350MPa) or the high-strength transverse reinforcement(1300MPa) are experimentally considered. Six-teen specimens were tested; two with the diameter of 450mm, twelve with the diameter of 350mm, and two with the diameter of 300mm. The specimens with the diameter of 450mm are models of standard cast-in-place-conerete piles, and the specimens with the diameter of 350mm or 300mm are models of under-reamed piles. Experimental results show that, when properly reinforced with the transverse reinforcement, slim reinforced concrete piles can exhibit stable hysteretic behavior and significant ductility.

STRENGTH AND DEFORMABILITY ESTIMATION OF CENTRIFUGED CONCRETE/ОЦЕНКА ПРОЧНОСТО И ДЕФОРМАТИВНОСТИ ЦЕНТРИФУГИРОВАННОГО БЕТОНА

Influence of several factors, namely high strength longitudinal reinforcement, transverse (spiral) reinforcement, precompression level and concrete age, on mechanical properties of centrifuged concrete is investigated. It has been established by tests that longitudinal and transverse (spiral) reinforcement make worse compaction, casting and hardening conditions of centrifuged concrete. But the spiral reinforcement reduces transverse deformations of compressed centrifuged members of ring cross-section and hence increases concrete strength. During the experiments for central compression, centrifuged concrete members of a ring cross-section were investigated. The parameters of these members: diameter 260 and 500 mm, height 400 and 800 mm, web thickness 35…80 mm. The specimens were reinforced by longitudinal bars of 10, 12, 14 mm diameter and 4 or 5 mm cross-section spirals. Coefficient of longitudinal reinforcement μ s , varied from 1,5 to 6%, coefficient of transverse reinforcement μ cir —from 0,25 to 1,25%, lead of spirals—from 40 to 100 mm. During testing the ring concrete compressive strength Rb was 30…60 MPa. The results of the above-mentioned experiments are presented in Tables 1, 2 and 3. It is recommended to evaluate the reinforcement influence on mechanical properties of such concrete in members of real constructions by formulas (5) and (6). Relationships of concrete strength, initial modulus of deformation and intensity of precompression (9) and (10) are discussed in this article. The latest test results on relationship between concrete compression, tension strength and concrete age are presented. It is established, that hydration of cement takes quite a long time and compression and tension strength of centrifuged concrete increases. This increase in strength is given in Table 4. The strength of centrifuged concrete of 14, 120, 240 and 360 days was determined by direct compression and tension of concrete rings (Table 4). After 9,600 days (26 years) due to a limited number of specimens (concrete rings) the compressive strength was determined by testing prisms cut from the rings. The tensile strength was determined indirectly—by cutting these prisms, as it is recommended by a standard [11] according to formula (12). The results of these tests are presented in Tables 5 and 6. Theoretical connection between tensile and compressive strength may be described by Ferret formula (13), which we propose to use in a slightly changed form, i. e. as (14). Comparative calculations showed that the centrifuged concrete strength calculated according formula (14) corresponds to the results of direct testing (Table 7).

超高強度コンクリートを用いたRC柱の曲げ強度と靭性

Four test columns were constructed using concrete with compressive strength of 130 MPa, transverse reinforcement with yield strength of 408 or 873 MPa and ordinary longitudinal reinforcement. Those columns tested under reversed cyclic lateral loads with constant axial compressive load levels of 0.343 or 0.473. Test results indicated that even for such high strength concrete columns adequate ductility was secured by using high strength transverse reinforcement. Based on the. test results, the stress-strain model on confined concrete previously proposed by the authors was modified so as to be applicable not only to ordinary strength concrete but also to high strength concrete. It was also found that the flexural strength of such high strength concrete columns can be predicted by using ACI 318-89 stress block equation.