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Mechanical behavior of laminated bamboo-timber composite columns under axial compression

Chen Si, Wei Yang, Wang Gaofei, Zhao Kang, Ding Mingmin

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 2

art. no. e72, 2023

EN

Bamboo is a fast-growing biobased building material with a high strength-to-weight ratio, and the combination of bamboo and wood provides an environmentally friendly alternative for building construction. A new type of laminated bamboo-timber composite column was proposed to improve the compressive performance of timber columns, which was expected to obtain better mechanical performance. Bamboo scrimber and Douglas fir were combined to form laminated bamboo-timber composite columns for the experimental study. Axial compression tests were carried out on 5 groups of 15 composite columns. The failure modes of the composite columns were assessed. The laws of axial displacement, lateral displacement, axial strain, ultimate bearing capacity and stiffness were analyzed. Finally, the bearing capacity of the composite columns was calculated by referring to the design specification for timber structures. The results indicated that the composite columns exhibited three failure characteristics. The ultimate bearing capacity and stiffness of the bamboo-timber composite columns increased with increasing amount of bamboo scrimber. The ultimate load of the bamboo-timber composite columns was increased by 23.0-94.6%, while the stiffness was increased by 9.1-38.4%. In addition, the bearing capacity of composite columns was calculated according to two standards. The experimental values of the bamboo-timber composite columns are in good agreement with the theoretical values, and the errors are within 8%.

2

Failure study of weathered granite based on critical slowing down theory and acoustic emission b-value

Huang Qizheng, Zhao Kang, Yan Yajing, Wu Jun, Nie Qiang, Chen Jiale, Xiao Weiling, Wang Huiping

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 3

art. no. e196, 2023

EN

To investigate the precursor characteristics of failure of weathered granite (WG), we conducted uniaxial compression tests on WG specimens using the RMT-150C rock mechanics testing system and the PCI-II acoustic emission (AE) device. We analyzed the AE parameters based on the critical slowing down (CSD) and AE b-value theoretical methods. The study shows that the peak strain value of WG under uniaxial compression is < 1% and the stress falls off rapidly after the peak, and the specimen mainly undergoes brittle failure. The failure process can be divided into four stages: compression stage, elastic deformation stage, plastic development stage, and post-peak failure stage, in which the compression stage lasts longer. The ringing count rate and its cumulative amount can effectively indicate the process of WG failure during loading. As the failure nears, microcracks within the WG accumulate and expand, leading to the appearance of macroscopic cracks. At the same time, the cumulative ringing count rate increases rapidly while the ringing count rate converges to the peak. Furthermore, the rapid increase of autocorrelation coefficient and variance obtained from the CSD theory analysis of ringing counts can be used as a precursor signal of WG failure. The “inflection point” before the sharp rise of the variance curve can be regarded as an early warning point of failure. Based on the characteristic that the b-value shows a large rate fluctuation decrease before the failure of WG, the autocorrelation coefficient and variance variation law obtained by CSD theory and the early warning point are analyzed simultaneously with the b-value variation law, which can accurately grasp the failure characteristics of WG in mines.

3

Deformation and failure laws and acoustic emission characteristics of low‑strength molybdenum ore

Zhao Kang, Yang Jian, Song Yufeng, Wang Qing, Zhao Kangqi, Ji Yongbo

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 2

art. no. e74, 2023

EN

Uniaxial compression acoustic emission (AE) tests were conducted on low-strength molybdenum ore (LSMO) to investigate its deformation and failure laws and AE characteristics. The stress-strain curve and AE parameter data of LSMOs were obtained by uniaxial compression AE test, and the relationships of stress, AE parameter, amplitude fractal dimension, and AE b value with loading time were analyzed accordingly to obtain the general law of their deformation and failure and a series of AE characteristics. The research shows that under the action of uniaxial stress, the failure mode of LSMOs mainly shows brittle failure, and the failure form mainly shows monoclinic shear failure. The stress-strain curve shows obvious plastic-elastic deformation, the plastic deformation time is long, and the division of each stage of deformation failure is not obvious. The simultaneous occurrence of large surges in ringing count and energy to higher orders of magnitude can be used as precursor information for failure destabilization of LSMOs. The evolution process of AE parameters of LSMO corresponds well with its deformation and failure process, and the variation pattern of ringing counts and energy shows a high consistency. With increasing stress, the amplitude correlation dimension and b value are mainly in the form of "falling-rising-falling-fluctuating". The results of the study can provide some theoretical basis for the assessment of the stability of the mine surrounding rock and the determination of a reasonable and effective reinforcement plan.

4

Structural behavior of prefabricated bamboo-lightweight concrete composite beams with perforated steel plate connectors

Wei Yang, Wang Zhiyuan, Chen Si, Zhao Kang, Zheng Kaiqi

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 1

239--259

EN

To reduce the self-weight of bamboo-concrete composite (BCC) beams and realize rapid industrial production, innovative assembled bamboo-lightweight concrete composite (ABLCC) beams are presented for use in engineering structures. To verify the structural performance of the ABLCC beams, a series of bending tests were performed on the bamboo beams, the cast-in-place bamboo-lightweight concrete composite (PBLCC) beams and the ABLCC beams. The effects of the thickness of the perforated steel plate, the connector spacing, and the construction technology on the BCC beams were investigated. The test results showed that the failure mode of the ABLCC beams was bamboo fiber cracking at the bottom of the mid-span. Compared with the benchmark bamboo beams, the bending capacity and stiffness of the ABLCC beams increased by 1.43–1.94 times and 2.20–4.16 times, respectively. Compared with the cast-in-place bamboo-lightweight concrete composite (PBLCC) beams, the bending capacity of the ABLCC beam was essentially the same, and the flexural stiffness increased by 1.18 times. The bending capacity, flexural stiffness and combination efficiency of the ABLCC beam increased with decreasing connector spacing. The increase in the thickness of the perforated steel plate did not have a substantial effect on the flexural stiffness of the ABLCC beam. Analytical and numerical methods were validated against the experimental results.