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1

Experimental of buckling restrained brace hysteretic performance with carbon fiber wrapped in concrete

Fang Yuan, Lv Lei, Gao Yuqiang, Fu Zhongqiu

Archives of Civil Engineering

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2024

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Vol. 70, nr 1

527--541

EN

Buckling restrained brace is an important structure for improving the seismic resistance of structures. Conducting research on new types of buckling restrained brace can improve the seismic performance and reliability of buckling resistant support. Four different types of buckling restrained braces specimens were designed and manufactured: cross-shaped square steel pipe members, cross-shaped round steel pipe members, cross-shaped carbon fiber members, and in-line carbon fiber members. By conducting quasi-static tests, the force displacement hysteresis curves, skeleton curves, stiffness degradation, equivalent viscous damping coefficient, and energy dissipation ratio of four different types of buckling restrained brace were analyzed. The research results showed that all four buckling restrained brace specimens have good hysteresis performance. The load-bearing capacity and energy consumption performance of the three specimens of square steel pipe, round steel pipe and carbon fiber with the same core unit are the same, but the inline type is worse than the cross type. The core unit specimen with a width of 80 mm is about 60% higher in bearing capacity and energy consumption than a specimen with a width of 50 mm. The core unit of some specimens undergoes multi-wave buckling. For carbon fiber specimens, the CFRP is prone to breakage due to the lateral thrust of the restraining unit. Therefore, steel hoop or stirrup should be added to the end to improve the restraint effect when designing and manufacturing.

2

Seismic behavior of interior polyvinyl chloride-carbon fiber-reinforced polymer-confined concrete column-ring beam joints

Yu Feng, Wang Shisi, Fang Yuan, Zhang Nannan, Wang Yan, Nuermaimaiti Maimaiti

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 1

art. no. e49, 2023

EN

Eleven interior polyvinyl chloride (PVC)-carbon fiber-reinforced polymer (CFRP)-confined concrete (PCCC) column-ring beam joints are fabricated and experimentally investigated. The impacts of axial compression ratio, frame beam reinforcement ratio, CFRP strips spacing, ring beam width and ring beam reinforcement ratio, on seismic behaviors are analyzed. All specimens show obvious failure signs, and the frame beam reinforcement ratio exerts a degree of effect on failure positions, exhibiting different failure modes, such as shear failure in the joint zone, shear-bending failure at the junction and bending failure at the frame beam. The experimental results show that the hysteresis curves are relatively full, which have roughly experienced four stages as elastic, elastic-plastic, stable and decline stages, reflecting that the interior joints have considerable seismic behavior. The increment of ring beam reinforcement ratio or ring beam width enhances the load capacity, mitigates degradation of strength and stiffness. The peak load increases by 38.63% as the ring beam reinforcement ratio increases from 0.88 to 1.5%. When the ring beam width increases from 75 to 125 mm, the peak load increases by 37.24%. Appropriately increasing axial compression ratio can raise the load capacity, alleviate strength degradation, and enhance the initial stiffness. As the axial compression ratio increases from 0.2 to 0.4, the peak load increases by19.41%. The joints with larger frame beam reinforcement ratio show higher load capacity, while the frame beam reinforcement ratio exerts marginal impacts on strength and initial stiffness degradation. The existing classical shear models and specification design formulae are used to evaluate the shear capacity of the interior joints, and the reasons for the deviations of prediction results are expounded, which provides the theoretical basis and useful reference for the subsequent establishment of a new shear capacity formula of the joints.

3

Experimental study on flexural capacity of PVA fiber-reinforced recycled concrete slabs

Yu Feng, Li Xu, Song Jie, Fang Yuan, Qin Yin, Bu Shuangshuang

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 4

518--541

EN

The flexural tests were conducted on 21 polyvinyl alcohol (PVA) fiber-reinforced recycled concrete slabs to investigate the influences of the reinforcement ratio, the PVA fiber content, the replacement ratio of recycled coarse aggregate (RCA) and the span-thickness ratio on the mechanical behaviors. The failure mode of the PVA fiber-reinforced recycled concrete slabs was the yielding of the longitudinal tensile reinforcement, slight crushing of concrete in the compression zone, and pulling out or breaking of PVA fiber at cracking position. The ultimate moment, cracking moment, moment corresponding to 0.2 mm-crack width and yield moment decreased as the replacement ratio of RCA or the span-thickness ratio increased while they increased as the reinforcement ratio or the PVA fiber content increased. Considering the impact of the PVA fiber content and the replacement ratio of RCA, the calculation formulas for conveniently predicting the flexural capacities of the PVA fiber-reinforced recycled concrete slabs were proposed. The formula prediction results were in good agreement with the test data.

4

A migration based location method using improved waveform stacking for microseismic events in a borehole system

Mao Qinghui, Azeem Tahir, Zhang Xuliang, Zhong Yu, Fang Yuan, Zhang Yunxiao

Acta Geophysica

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2020

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Vol. 68, no. 6

1609--1618

EN

The migration-based microseismic event location methods using waveform stacking algorithms are widely used for hydrofracturing monitoring. These methods have the advantage of not requiring the accurate frst arrival time around a detected event, which is more suitable for noisy data than classical travel time-based methods. However, accuracy of these methods can be afected under the condition of relatively low signal-to-noise ratio (SNR). Therefore, in order to enhance the location accuracy of microseismic events in a borehole system, we have proposed a migration-based location method using improved waveform stacking with polarity correction based on a master-event technique, which optimizes the combination way of P- and S-wave waveform stacking. This method can enhance the convergence of the objective function and the location accuracy for microseismic events as compared to the conventional waveform stacking. The proposed method has been successfully tested by using synthetic data example and feld data recorded from one downhole monitoring well. Our study clearly indicates that the presented method is more viable and stable under low SNR.