Designing Ternary Laves Phase-Based Eutectic Alloys CrFeNbx with Excellent Strength, Toughness, and Thermal Stability

Yunlong Xue,Yuxuan Wang,Haohua Sun,Na Feng,Liang Yuan 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.2

Three ternary Laves phase-based eutectic alloys CrFeNbx(x = 2.0, 2.35, 2.7) were designed successfully by combining thebinary phase diagrams and thermodynamics calculations. With the increasing Nb content, the solidified microstructuresevolved from the primary (Cr, Fe)2Nb plus the eutectic (Cr, Fe)2Nb/Nbss in the CrFeNb2.0,via the full eutectic (Cr, Fe)2Nb/Nbss in the CrFeNb2.35,and finally to the primary Nbss plus the eutectic (Cr, Fe)2Nb/Nbss in the CrFeNb2.7. The full eutectic(Cr, Fe)2Nb/Nbss of the CrFeNb2.35was found with outstanding thermal stability, and the lamellar eutectic was quitestable even under the heat-treatment of 1273 K/48 h. The compression strength and fracture toughness increased firstly anddecreased subsequently with the increase of Nb content, which reached their maximums of 2.54 GPa and 18.25 MPa·m1/2,respectively, in the CrFeNb2.35. The excellent combination of compression strength and fracture toughness in the CrFeNbx(x = 2.0, 2.35, 2.7) were attributed to the synergistic effects of Laves phase strengthening, interface strengthening, solidsolution strengthening, alloying toughening and Nbss phase toughening mechanisms.

Shear behavior and shear capacity prediction of precast concrete-encased steel beams

Yunlong Yu,Yong Yang,Yicong Xue,Yaping Liu 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.36 No.3

A novel precast concrete-encased steel composite beam, which can be abbreviated as PCES beam, is introduced in this paper. In order to investigate the shear behavior of this PCES beam, a test of eight full-scale PCES beam specimens was carried out, in which the specimens were subjected to positive bending moment or negative bending moment, respectively. The factors which affected the shear behavior, such as the shear span-to-depth aspect ratio and the existence of concrete flange, were taken into account. During the test, the load-deflection curves of the test specimens were recorded, while the crack propagation patterns together with the failure patterns were observed as well. From the test results, it could be concluded that the tested PCES beams could all exhibit ductile shear behavior, and the innovative shear connectors between the precast concrete and cast-in-place concrete, namely the precast concrete transverse diaphragms, were verified to be effective. Then, based on the shear deformation compatibility, a theoretical model for predicting the shear capacity of the proposed PCES beams was put forward and verified to be valid with the good agreement of the shear capacities calculated using the proposed method and those from the experiments. Finally, in order to facilitate the preliminary design in practical applications, a simplified calculation method for predicting the shear capacity of the proposed PCES beams was also put forward and validated using available test results.

Cyclic tests on RC joints retrofitted with pre-stressed steel strips and bonded steel plates

Yunlong Yu,Yong Yang,Yicong Xue,Niannian Wang,Yaping Liu 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.75 No.6

An innovative retrofit method using pre-stressed steel strips and externally-bonded steel plates was presented in this paper. With the aim of exploring the seismic performance of the retrofitted RC interior joints, four 1/2-scale retrofitted joint specimens together with one control specimen were designed and subjected to constant axial compression and cyclic loading, with the main test parameters being the volume of steel strips and the existence of externally-bonded steel plates. The damage mechanism, force-displacement hysteretic response, force-displacement envelop curve, energy dissipation and displacement ductility ratio were analyzed to investigate the cyclic behavior of the retrofitted joints. The test results indicated that all the test specimens suffered a typical shear failure at the joint core, and the application of externally-bonded steel plates and that of pre-stressed steel strips could effectively increase the lateral capacity and deformability of the deficient RC interior joints, respectively. The best cyclic behavior could be found in the deficient RC interior joint retrofitted using both externally-bonded steel plates and pre-stressed steel strips due to the increased lateral capacity, displacement ductility and energy dissipation. Finally, based on the test results and the softened strut and tie model, a theoretical model for determining the shear capacity of the retrofitted specimens was proposed and validated.

Shear strength prediction of concrete-encased steel beams based on compatible truss-arch model

Yicong Xue,Chongxin Shang,Yong Yang,Yunlong Yu,Zhanjie Wang 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.43 No.6

Concrete-encased steel (CES) beam, in which structural steel is encased in a reinforced concrete (RC) section, is widely applied in high-rise buildings as transfer beams due to its high load-carrying capacity, great stiffness, and good durability. However, these CES beams are prone to shear failure because of the low shear span-to-depth ratio and the heavy load. Due to the high load-carrying capacity and the brittle failure process of the shear failure, the accurate strength prediction of CES beams significantly influences the assessment of structural safety. In current design codes, design formulas for predicting the shear strength of CES beams are based on the so-called “superposition method”. This method indicates that the shear strength of CES beams can be obtained by superposing the shear strengths of the RC part and the steel shape. Nevertheless, in some cases, this method yields errors on the unsafe side because the shear strengths of these two parts cannot be achieved simultaneously. This paper clarifies the conditions at which the superposition method does not hold true, and the shear strength of CES beams is investigated using a compatible truss-arch model. Considering the deformation compatibility between the steel shape and the RC part, the method to obtain the shear strength of CES beams is proposed. Finally, the proposed model is compared with other calculation methods from codes AISC 360 (USA, North America), Eurocode 4 (Europe), YB 9082 (China, Asia), JGJ 138 (China, Asia), and AS/NZS 2327 (Australia/New Zealand, Oceania) using the available test data consisting of 45 CES beams. The results indicate that the proposed model can predict the shear strength of CES beams with sufficient accuracy and safety. Without considering the deformation compatibility, the calculation methods from the codes AISC 360, Eurocode 4, YB 9082, JGJ 138, and AS/NZS 2327 lead to excessively conservative or unsafe predictions.

Experimental study on shear performance of partially precast Castellated Steel Reinforced Concrete (CPSRC) beams

Yong Yang,Yunlong Yu,Yuxiang Guo,Charles W. Roeder,Yicong Xue,Yongjian Shao 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.21 No.2

A new kind of partially precast or prefabricated castellated steel reinforced concrete beam, which is abbreviated here as CPSRC beam, was presented and introduced in this paper. This kind of CPSRC beam is composed of a precast outer-part and a cast-in-place inner-part. The precast outer-part is composed of an encased castellated steel shape, reinforcement bars and high performance concrete. The cast-in-place inner-part is made of common strength concrete, and is casted with the floor slabs simultaneously. In order to investigate the shear performance of the CPSRC beam, experiments of six CPSRC T-beam specimens, together with experiments of one cast-in-place SRC control T-beam specimen were conducted. All the specimens were subjected to sagging bending moment (or positive moment). In the tests, the influence of casting different strength of concrete in the cross section on the shear performance of the PPSRC beam was firstly emphasized, and the effect of the shear span-to-depth ratio on that were also especially taken into account too. During the tests, the shear force-deflection curves were recorded, while the strains of concrete, the steel shapes as well as the reinforcement stirrups at the shear zone of the specimens were also measured, and the crack propagation pattern together with the failure pattern was as well observed in detail. Based on the test results, the shear failure mechanism was clearly revealed, and the effect of the concrete strength and shear span-to-depth ratios were investigated. The shear capacity of such kind of CPSRC was furthermore discussed, and the influences of the holes on the steel shape on the shear performance were particularly analyzed.

Theoretical and experimental study on shear strength of precast steel reinforced concrete beam

Yong Yang,Yicong Xue,Yunlong Yu 국제구조공학회 2019 Steel and Composite Structures, An International J Vol.32 No.4

With the aim to put forward the analytical model for calculating the shear capacity of precast steel reinforced concrete (PSRC) beams, a static test on two full-scale PSRC specimens was conducted under four-point loading, and the failure modes and strain developments of the specimens were critically investigated. Based on the test results, a modified truss-arch model was proposed to analyze the shear mechanisms of PSRC and cast-in-place SRC beams. In the proposed model, the overall shear capacity of PSRC and cast-in-place SRC beams can be obtained by combining the shear capacity of encased steel shape with web concrete determined by modified Nakamura and Narita model and the shear capacity of reinforced concrete part determined by compatible truss-arch model which can consider both the contributions of concrete and stirrups to shear capacity in the truss action as well as the contribution of arch action through compatibility of deformation. Finally, the proposed model is compared with other models from JGJ 138 and AISC 360 using the available SRC beam test data consisting of 75 shear-critical PSRC and SRC beams. The results indicate that the proposed model can improve the accuracy of shear capacity predictions for shear-critical PSRC and cast-in-place SRC beams, and relatively conservative results can be obtained by the models from JGJ 138 and AISC 360.

Flexural behavior and flexural capacity prediction of precast prestressed composite beams

Manxin Hu,Yong Yang,Yunlong Yu,Yicong Xue 국제구조공학회 2022 Structural Engineering and Mechanics, An Int'l Jou Vol.84 No.2

In order to improve the cracking resistance of reinforced concrete and give full play to the advantages of prefabricated assembly structure in construction, prestressed reinforced concrete composite beam (PRCC) is proposed. Through the bending static test of seven I-shaped beam specimens, the bending failure modes and bearing capacity of PRCC and reinforced concrete composite beam are compared and analyzed, and the effects of prestress size, prestressed reinforcement layout and prestress application sequence on the flexural behavior of PRCC beams are studied. The results show that the cracking load and ultimate load of PRCC beams significantly increased after prestressing, and prestressed tendons can effectively control the crack development. With the increase of prestressing degree, the deformation resistance and bending stiffness of PRCC beams are increased. The application sequence of prestress has little influence on the mechanical properties of PRCC beams. The crack width, stiffness and normal section bearing capacity of PRCC beam are analyzed, and the calculated results are in good agreement with the experimental results.

Post-fire test of precast steel reinforced concrete stub columns under eccentric compression

Yong Yang,Yicong Xue,Yunlong Yu,Zhichao Gong 국제구조공학회 2019 Steel and Composite Structures, An International J Vol.33 No.1

This paper presents an experimental work on the post-fire behavior of two kinds of innovative composite stub columns under eccentric compression. The partially precast steel reinforced concrete (PPSRC) column is composed of a precast outer-part cast using steel fiber reinforced reactive powder concrete (RPC) and a cast-in-place inner-part cast using conventional concrete. Based on the PPSRC column, the hollow precast steel reinforced concrete (HPSRC) column has a hollow column core. With the aim to investigate the post-fire performance of these composite columns, six stub column specimens, including three HPSRC stub columns and three PPSRC stub columns, were exposed to the ISO834 standard fire. Then, the cooling specimens and a control specimen unexposed to fire were eccentrically loaded to explore the residual capacity. The test parameters include the section shape, concrete strength of inner-part, eccentricity ratio and heating time. The test results indicated that the precast RPC shell could effectively confine the steel shape and longitudinal reinforcements after fire, and the PPSRC stub columns experienced lower core temperature in fire and exhibited higher post-fire residual strength as compared with the HPSRC stub columns due to the insulating effect of core concrete. The residual capacity increased with the increasing of inner concrete strength and with the decreasing of heating time and load eccentricity. Based on the test results, a FEA model was established to simulate the temperature field of test specimens, and the predicted results agreed well with the test results.

Experimental investigation on shear capacity of partially prefabricated steel reinforced concrete columns

Yong Yang,Yang Chen,Jintao Zhang,Yicong Xue,Ru-yue Liu,Yunlong Yu 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.28 No.1

This paper experimentally and analytically elucidates the shear behavior and shear bearing capacity of partially prefabricated steel reinforced concrete (PPSRC) columns and hollow partially prefabricated steel reinforced concrete (HPSRC) columns. Seven specimens including five PPSRC column specimens and two HPSRC column specimens were tested under static monotonic loading. In the test, the influences of shear span aspect ratio and difference of cast-in-place concrete strength on the shear behavior of PPSRC and HPSRC columns were investigated. Based on the test results, the failure pattern, the loaddisplacement behavior and the shear capacity were focused and analyzed. The test results demonstrated that all the column specimens failed in shear failure mode with high bearing capacity and good deformability. Smaller shear span aspect ratio and higher strength of inner concrete resulted in higher shear bearing capacity, with more ductile and better deformability. Furthermore, calculation formula for predicting the ultimate shear capacity of the PPSRC and HPSRC columns were proposed on the basis of the experimental results.

Seismic performance of RC columns with encased prefabricated high-strength CFST core

Yong Yang,Dongde Sun,Yicong Xue,Yunlong Yu,Kang An,Yang Chen 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.39 No.6

This paper proposed an innovative RC column with encased prefabricated high-strength concrete filled steel tube core, and four RC columns with encased prefabricated high-strength CFST core and a RC control-column were tested under lateral low cyclic loading. All specimens were evaluated by the cracks developments, failure patterns, hysteretic behavior, skeleton curves, strength and stiffness degradation, ductility and energy dissipation capacity. The effects of stirrup ratio and welding studs of prefabricated CFST core were investigated in details. The experiment results indicated that compared with the RC control-column, the performances of RC columns with encased prefabricated high-strength CFST core, including the hysteretic behavior, strength degradation, ductility and energy dissipation, were significantly improved. Higher stirrup ratio of the RC column with encased prefabricated high-strength CFST core leaded to higher ductility and more satisfactory energy dissipation capacity, stiffness degradation. Studs could effectively combine prefabricated high-strength CFST core and surrounding concrete, which significantly increase the integrity of RC column with encased prefabricated high-strength CFST core. Based on the test results, a numerical model was established to further analyze the cyclic behavior of the test specimens, and the numerical results agreed well with the test results, which showed the feasibility for the further parametric study. Finally, on the basis of the plastic stress theory, a calculation model for seismic bending moment capacity of RC column with encased prefabricated high-strength CFST core was established, and the results obtained form the formulas showed good agreement with the experiments.