Analytical Bond-Slip Model of Steel Bar to Concrete Under Confinement

The hysteretic capacity of reinforced concrete (RC) structures depends to a large extent on the hysteretic behavior of steel bar to sustain many cycles of high plastic deformations without obvious degradation of strength and stiffness. It is important to develop an accurate and computationally efficient model of steel bar in the nonlinear response analysis of RC structures subjected to cyclic loads. The high strength and ultra-high-strength (UHS, yield strength above 1000 MPa) steel bars are becoming more and more popular in concrete construction, which is beneficial for materials saving and reduction of steel bar congestion. In order to investigate the cyclic behaviors of UHS steel bars and to propose a hysteretic model for this kind of steel bars including buckling, a total of 54 specimens with nine slenderness ratios were carried out under compressive and cyclic loadings. The modified stress–strain curve model of UHS steel bars with different slenderness ratio was developed based on the experimental data, which can take buckling and fatigue-induced reduction of stress into account. This study offers a solid database for researches on the mechanical properties of UHS steel bars. And the proposed empirical model can easily be implemented in the finite element analysis of RC elements with UHS steel bars under cyclic loadings.

Study on bonding properties and constitutive model of steel bar and nano-SiO2 reinforced recycled aggregate concrete

Bond performance and constitutive model of steel bar in G-UHPC under cyclic loading

In this study, the bond stress distribution and bond–slip model of steel bars and iron tailing sand recycled aggregate concrete (ITRAC) were investigated using central pullout tests on 33 steel bars and ITRAC bonded specimens. The results show three failure modes for the bonded specimens: splitting, pullout, and splitting–pullout. Compared with the maximum bond strength of nature sand concrete (NAC), the maximum bond strength of the iron tailing concrete and ITRAC specimens increased by 23.12% and 6.08–23.96%, respectively. After adding 1% steel fiber, the maximum and residual bond strengths of ITRAC increased by 40.82% and 129.10%, respectively, compared with those of NAC. The maximum bond strength of ITRAC decreased after the configuration of the stirrups. The bond stress distribution characteristics of the ITRAC specimens resembled those of recycled aggregate concrete (RAC). Generally, two bond stress peaks emerged, and the uniformity of the bond stress distribution improved after adding RAC to the iron tailing sand (ITS). The results of the proposed ITRAC bond–slip constitutive model agreed with the test results.

Analysis of bond performance of steel bar in steel-polypropylene hybrid fiber reinforced concrete with partially recycled coarse aggregates

Monotonic and cyclic bond responses of steel bar with steel-polypropylene hybrid fiber reinforced recycled aggregate concrete

Probabilistic structural performance of RC frames with corroded smooth bars subjected to near- and far-field ground motions

The stress-strain properties of reinforcing steel for reinforced concrete are related to the design of reinforced concrete structures. In China Codes, steel bars for the prestressing of concrete (PCB) and hot-rolled ribbed bars in grade 600 (HRB600) were introduced to design concrete structures. However, the stress-strain properties of high-strength steel bars are not defined by the standard. In this paper, reinforcing steel for reinforced concrete in a China Code included hot-rolled plain bars (HPB), HRB, cold-rolled ribbed steel bars (CRB), PCB, hot-rolled wire rod for prestressed steel (PSW), and screw-thread steel bars for the prestressing of concrete (PSB), which were tested under axial tension. Results showed that the reinforcing steel was divided into two types: HPB, HRB, and CRB600H with yield plateau and PCB, PSW, PSB, and CRB550 without. Based on the experimental results, the tensile mechanical indicators of reinforcing steel were determined and the stress-strain curves prediction models of reinforcing steel were developed. The stress-strain curves prediction models of steel bars can predict the tensile properties of steel bars accurately, which can be used in finite element software to simulate the tensile properties of steel bars and explore the stress development of steel bars in concrete structures.

Glass-fiber-reinforced polymer (GFRP)–steel composite bar, a novel building material, is a promising longitudinal reinforcement for marine engineering in harsh environments. Previous research has primarily focused on altering individual parameters to assess their influence on the performance of composite bars, lacking a systematic and in-depth exploration. In this paper, the tensile properties of composite bars have been investigated by adequate experimental testing considering the type of inner steel bar and the thickness of the GFRP layer. Results show that although composite bars undergo elasticity, hardening, and failure stages under tensile loading, due to differences in interfacial bonding forces, the ultimate failure mode for composite bars with HPB300 inner steel bars is relative slippage, while for those with HRB400 inner steel bars, it is fracturing. While ensuring that composite bars have good initial elastic modulus and durability, it is preferable for the thickness of the external GFRP layer to be as small as possible. However, the thickness of the external GFRP layer of composite bars should not be less than 2 mm to prevent misalignment of the inner steel bars, which can negatively impact the tangent modulus during the hardening stage and the ultimate tensile strength. Furthermore, a stress–strain constitutive model for this composite bar was developed and validated. This model offers a universal framework for accurately representing the mechanical properties of the material across a wide range of research parameters.

In this study, the high-temperature test (i.e., temperature to 1000 °C) is conducted on 600 MPa seismic steel bars, and its residual mechanical properties and constitutive relations are investigated though three cooling rates, i.e., under air, furnace, and water-cooling conditions. Results show that three cooling methods have significant effects on the apparent characteristics of 600 MPa steel bars, when the heating temperature is greater than 600 °C. In addition, the ultimate and yield strength of steel bars have been significantly affected by different cooling methods, with increasing heating temperature. However, the elastic modulus is significantly not affected by temperature. Furthermore, the elongation rate after fracture and the total elongation rate at the maximum force do not change significantly, when the heating temperature is less than 650 °C. The elongation rate, after fracture, and the total elongation rate, at the maximum force, have different changes for three cooling methods. The degeneration of the stress–strain curves occurs when the heating temperature is high. The two-fold line, three-fold line, and Ramberg–Osgood models are developed based on the stress–strain curve characteristics of steel bars after cooling. The fire resistance of 600 MPa steel bars of reinforced concrete structure is analyzed, which provides a basis for post-disaster damage assessment, repair, and reinforcement of the building structure.

The steel bars account for a high percentage of material costs for the current construction projects. At the present time, most of the construction projects for the factories of thin‐film transistor liquid crystal display (TFT‐LCD) complete the transactions of steel bars when the suppliers ship the steel bars to the temporary storage/processing sites. This paper applies the buy‐in concept in the Theory of Constraint (TOC) on the supply chain of steel bars. In this study, suppliers are required to establish warehouses at the construction sites and complete the transactions when the formed and processed steel bars are shipped into the factory sites. The aim is to find a win‐win solution to meet with the expectations from constructors as they hope that there is no need to build up inventories but supply is ready at any time. Also, this paper compares and analyzes the traditional supply/inventory model of steel bars and the Demand‐Pull (D‐P) model under the TOC framework. It is proved that Vendor Management Inventory (VMI) in the D‐P model is able to more effectively manage steel bars as a material.

Reinforced-concrete (RC) structures are inevitably subjected to sustained loads during their service life. In the natural environment, the exposed surfaces of RC members often experience dry–wet cycles due to rainfall and tides. An important parameter in structural design is the the bond behaviour between steel bars and concrete, and this is affected by the coupled effect of sustained loads and dry–wet cycles. In this study, 32 RC beam specimens were subjected to different levels of sustained load (25%, 50% and 75% of ultimate load) and dry–wet cycles for a period of 120 d. The immediate slip and time-dependent slip (TDS) between the steel bar and concrete during testing were recorded and analysed. It was found that the TDS increased with an increase in the duration of sustained loading and greater sustained load levels resulted in larger TDSs. After long-term testing, the bond strength and bond stress–strain were investigated using a flexural-bond test. The results showed that bond strength increased due to the coupled effects of sustained load and dry–wet cycles. Based on the test results, an empirical model for steel bar–concrete TDS considering the effect of sustained load and dry–wet cycles was developed.

The application range of rubber-recycled aggregate concrete (RRAC), a new type of green building material, is currently limited due to performance defects, including low hardness, high water absorption, and poor adhesion. To expand its application in reinforced concrete structures, it is crucial to enhance the bonding performance between RRAC and steel bars. In this study, the effects of adding straight steel fibres (SSFs) and ring-type steel fibres (RSFs) to RRAC were investigated, in order to enhance the bonding performance. To investigate the impact of steel fibres (SFs) on the bonding properties of RRAC and steel bars, a total of 51 specimens were subjected to pull-out tests to systematically examine the impact of SSF and RSF dosages on the bonding performance. The results demonstrated that incorporating the optimal amount of SSFs and RSFs can significantly improve the bond strength and bond stiffness. Moreover, the combined use of SSFs and RSFs yielded even better enhancement effects. The RRAC exhibited remarkable performance, when the total content of SFs was 1.2% and the proportion of RSFs 75%. In this case, the bond strength and bond stiffness were enhanced by 3.7% and 53.88%, respectively. Finally, a bond–slip constitutive model for RRAC and steel bar was established. The combined use of SSFs and RSFs minimizes the limitations of poor mechanical properties in traditional RRAC and holds significant value for the widespread adoption and application of RRAC.

Experimental and numerical parametric study on flexural behavior of concrete beams reinforced with hybrid combinations of steel and BFRP bars

Bond-slip model of headed bar and its application to component-based model for precast concrete joints under accidental loads