High-strength Longitudinal Reinforcement Research Articles

Cyclic behaviors of reinforced concrete beam-column joints with debonded reinforcements and beam failure: experiment and analysis

It was experimentally validated that partially debonded high-strength longitudinal reinforcement can provide strong self-centering capacity to minimize residual deformation, and greatly mitigate seismic damage of column. To continuously investigate the influence of partially debonded longitudinal rebars (PDLR) of column and beam on seismic behaviors of beam-column joint assembly, three interior and three exterior joint specimens were fabricated to subject to cyclic lateral loading. It was showed experimentally that joint specimens with PDLRs in both beams and columns had slighter seismic damages, smaller stiffness and energy dissipating ratios, better ductility compared with joint specimens without PDLRs in the beams. Furthermore, the lateral load of joint specimens without PDLRs in the beams decreased from lateral drift of about 4.0%–5.0% due to much crushing and spalling of concrete in the compressive zones of the beams. Whereas, joint specimens with PDLRs in the beams had continuously increased lateral load until lateral drift up of 10.0%. An analytical approach was derived to evaluate the lateral behavior of beam-column joint assembly which can considering joint deformation and steel bond slip. The proposed approach can reasonably predict the lateral behaviors of joint specimens with or without PDLRs. Analytical results indicate that approximately 70% of total deformation of joint specimens with PDLRs in both beams and columns is contributed by slippage deformation of the beams, whereas, that contribution ratio of the other joint assembly specimens is only 30%.

Seismic behavior of high-strength concrete columns reinforced with high-strength steel bars

To investigate the influence of longitudinal reinforcement strength grade, stirrup spacing, concrete strength and axial load ratio (ALR) on seismic behavior of high-strength concrete (HSC) columns, seven full-scale square HSC columns reinforced with high-strength steel bars (HSSB) with nominal yield strength of 600 MPa or conventional steel bars were tested under constant axial load and cyclic lateral load. Furthermore, corresponding nonlinear finite element analysis was conducted in ABAQUS. The column top deformation and lateral load at different service states, stiffness degradation, bearing capacity degradation and strain of longitudinal and transverse reinforcement were discussed. The test result shows that using steel bars with nominal yield strength of 400 MPa as stirrup is a better choice for HSC columns and ALR is an important factor which determines whether the high-strength longitudinal reinforcement can reach its compressive or tensile yield strain before maximum point. Taking HSSB as longitudinal reinforcement (equivalent volume replacement) greatly improves the seismic behavior of HSC columns. After taking the influence of strain gradient on stress-strain relationship of compressive concrete into consideration, a confined strain gradient model (CSGM) which was suitable for finite element analysis (FEA) was established based on the model established by Razvi and Saatcioglu. Specific verification of finite element model (FEM) on deformation and lateral load at different service states were presented for further parameter analysis. The trend of displacement ductility factor were investigated in detail in numerical analysis part. With proper ALR and stirrup characteristic value, HSC columns reinforced with HSSB is able to present a displacement ductility of higher than 4, which is capable to meet the ductility demand of most codes.

Stress-deformation state of compound reinforced concrete bars with high-strength reinforcement prone to long-term compression

Introduction. Considering that reinforced concrete is the most common material in construction and reconstruction of buildings and facilities, research of work of high-strength reinforcement in reinforced concrete elements, including compressed columns, are still relevant at present. Analysis of compound-section columns with high-strength longitudinal reinforcement is of particular interest since the method of sectional build-up is widespread enough in the reconstruction of buildings and facilities. However, no information on the work of this kind of reinforced concrete structures under long-term compression was found either in foreign or domestic literature; this fact provides relevance and academic novelty of the study.
 Materials and methods. The article provides the research of parameters of the strain-stress state of compound reinforced concrete bars with high-tensile reinforcement under long time compression employing the modern methods of mathematical simulation.
 Results. The developed calculation method allows determining additional parameters of the strain-stress state of the compressed compound-section reinforced concrete bars considering the concrete creep deformations forming in time of the long-term compression. When comparing the analytical study results with authors’ experimental data and previous results of other researchers, an adequate degree of reliability of the developed calculation method was confirmed.
 Conclusions. When applying the developed calculation method of stress-deformation state parameters for the compressed compound-section columns with high-strength longitudinal reinforcement, the study discovered that significant effort redistribution from concrete to high-strength reinforcement occurs under long-term compression. This fact was confirmed with the results of an experimental investigation on the resistance of the compound reinforced concrete bars with high-tensile reinforcement to the longtime compression.

Research on Concrete Columns Reinforced with New Developed High-Strength Steel under Eccentric Loading.

The use of new developed high-strength steel in concrete members can reduce steel bar congestion and construction costs. This research aims to study the behavior of concrete columns reinforced with new developed high-strength steel under eccentric loading. Ten reinforced concrete columns were fabricated and tested. The test variables were the transverse reinforcement amount and yield strength, eccentricity, and longitudinal reinforcement yield strength. The failure patterns were compression and tensile failure for columns subjected to small eccentricity and large eccentricity, respectively. The same level of post-peak deformability and ductility could only be obtained with a lower amount of transverse reinforcement when high-strength transverse reinforcements were used in columns subjected to small eccentricity. The high-strength longitudinal reinforcement improved the bearing capacity and post-peak deformability of the concrete columns. Furthermore, three different equivalent rectangular stress block (ERSB) parameters for predicting the bearing capacity of columns with high-strength steel are discussed based on test and simulated results. It is concluded that the China Code GB 50010-2010 overestimates the bearing capacity of columns with high-strength steel, whereas the bearing capacities computed using the America Code ACI 318-14 and Canada Code CSA A23.3-04 agree well with the test results.

Strength of Short Concrete Filled Steel Tube Columns with Spiral Reinforcement

To further increase the bearing capacity and survivability of reinforced concrete filled steel tube (RCFT) columns, it is offered to supply their concrete core with additional spiral reinforcement. Such reinforcement also has a positive effect on the fire resistance of the columns. The practical use of compressed RCFT elements is restrained by the absence of procedures for determining their bearing capacity. A calculation procedure for determining the strength of short centrally compressed RCFT columns is offered. It is rather easy in terms of application and it allows one to take into account the main features of power resistance of such columns. The results of comparison of the calculated strength with experimental data are presented. The analysis of these results testifies that the accuracy of calculation of RCFT columns strength is sufficient for practice. The offered calculation procedure allows to provide the wider use of RCFT columns in construction practice as heavy loaded bearing elements of buildings and structures. It is recommended to use high-strength longitudinal reinforcement for further increase of the efficiency of these columns.

Behavior of Deep Beams Containing High-Strength Longitudinal Reinforcement

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Proportion of High-Strength Steel Bars in Reinforced Concrete Ductile Piers

This paper mainly focuses on the affect factors of ductility of reinforced concrete pier with the high-strength longitudinal reinforcement and stirrups. By finite element software ANSYS, changed the amount of longitudinal reinforcement and high-strength stirrups in the piers, the ductility performance of concrete piers was studied. The results show that under certain conditions, the ductility coefficient of concrete piers with high-strength reinforcement can increase with the amount of stirrups. In addition, high-strength longitudinal reinforcement can improve the ductility performance of the concrete piers, but it should be controlled in a reasonable range. If there are too much high-strength longitudinal reinforcement in the concrete piers, the ductility performance will be lower, and structural seismic performance will also be affected.

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).