Deformation characteristics and failure modes of sandstones under discontinuous multi-level cyclic loads

2020 ◽  
Vol 373 ◽  
pp. 599-613 ◽  
Author(s):  
Kang Peng ◽  
Jiaqi Zhou ◽  
Quanle Zou ◽  
Yongjiang Zhang ◽  
Guowen Tan
2020 ◽  
Vol 10 (11) ◽  
pp. 3937
Author(s):  
Guang Li ◽  
Fengshan Ma ◽  
Jie Guo ◽  
Haijun Zhao

Deformation failure and support methods of roadways have always been critical issues in mining production and safety, especially for roadways buried in complex engineering geological conditions. To resolve these support issues of kilometer-depth roadways under high ground stress and broken rock mass, a case study on the roadways in the No. 2 mining area of Jinchuan Mine, China, is presented in this paper. Based on a detailed field survey, the deformation characteristics of the roadways and failure modes of supporting structures were investigated. It was found that the horizontal deformations were serious, and the primary support was not able to control the surrounding rock well. Additionally, a broken rock zone test was carried out, which indicated that a zonal disintegration phenomenon occurred around the roadways and the maximum depth of the fractured zone was more than 4.8 m. In order to effectively limit the deformation in the roadways, a new support scheme called the “multistage anchorage + concrete-filled steel tube” was put forward. To further assess the support behavior of the new method, we selected a test roadway in the research area, and numerical simulations and in-situ monitoring were conducted. The findings suggest that the roadway’s serious deformation under high ground stress and broken rock mass could be successfully controlled by the new control method, which can provide a reference for other engineering solutions under similar geological conditions.


Author(s):  
Sayan Sakhakarmi ◽  
Jee Woong Park

A traditional structural analysis of scaffolding structures requires loading conditions that are only possible during design, but not in operation. Thus, this study proposes a method that can be used during operation to make an automated safety prediction for scaffolds. It implements a divide-and-conquer technique with deep learning. As a test scaffolding, a four-bay, three-story scaffold model was used. Analysis of the model led to 1411 unique safety cases for the model. To apply deep learning, a test simulation generated 1,540,000 datasets for pre-training, and an additional 141,100 datasets for testing purposes. The cases were then sub-divided into 18 categories based on failure modes at both global and local levels, along with a combination of member failures. Accordingly, the divide-and-conquer technique was applied to the 18 categories, each of which were pre-trained by a neural network. For the test datasets, the overall accuracy was 99%. The prediction model showed that 82.78% of the 1411 safety cases showed 100% accuracy for the test datasets, which contributed to the high accuracy. In addition, the higher values of precision, recall, and F1 score for the majority of the safety cases indicate good performance of the model, and a significant improvement compared with past research conducted on simpler cases. Specifically, the method demonstrated improved performance with respect to accuracy and the number of classifications. Thus, the results suggest that the methodology could be reliably applied for the safety assessment of scaffolding systems that are more complex than systems tested in past studies. Furthermore, the implemented methodology can easily be replicated for other classification problems.


2014 ◽  
Vol 81 (11) ◽  
Author(s):  
Xiaofeng Chen ◽  
Bin Chen

Cells are subjected to cyclic loads under physiological conditions, which regulate cellular structures and functions. Recently, it was demonstrated that cells on substrates reoriented nearly perpendicular to the stretch direction in response to uni-axial cyclic stretches. Though various theories were proposed to explain this observation, the underlying mechanism, especially at the molecular level, is still elusive. To provide insights into this intriguing observation, we employ a coupled finite element analysis (FEA) and Monte Carlo method to investigate the stability of a cluster of slip bonds upon cyclic loads. Our simulation results indicate that the cluster can become unstable upon cyclic loads and there exist two characteristic failure modes: gradual sliding with a relatively long lifetime versus catastrophic failure with a relatively short lifetime. We also find that the lifetime of the bond cluster, in many cases, decreases with increasing stretch amplitude and also decreases with increasing cyclic frequency, which appears to saturate at high cyclic frequencies. These results are consistent with the experimental reports. This work suggests the possible role of slip bonds in cellular reorientation upon cyclic stretch.


2017 ◽  
Vol 21 (5) ◽  
pp. 631-642 ◽  
Author(s):  
Jianyang Xue ◽  
Lei Zhai ◽  
Yuze Bao ◽  
Rui Ren ◽  
Xicheng Zhang

This article presents the results of low cyclic loading tests on steel-reinforced recycled concrete inner-beam–column connections, including four 1:2.5 scaled specimens with different replacement rates of recycled coarse aggregates. The main objective of this study is to evaluate the seismic behavior of steel-reinforced recycled concrete inner-beam–column connection based on the seismic tests of the four specimens under low cyclic loads with vertical axial force. The main design parameter of the beam–column connections in this research is the recycled coarse aggregate replacement percentage. The crack status, failure modes, hysteresis loops, skeleton curves, energy dissipation, capacity stiffness of degradation, and ductility of steel-reinforced recycled concrete inner-beam–column connections are presented and analyzed. The results indicate that the main failure pattern of the steel-reinforced recycled concrete inner-beam–column connection is the shearing diagonal compression in the beam–column connection zone. As the recycled aggregate replacement percentage increases, both the bearing capacity and ductility of the steel-reinforced recycled concrete beam–column connections decrease to some extent. However, the seismic behavior of the steel-reinforced recycled concrete inner-beam–column connection does not degrade significantly compared with the ordinary steel-reinforced concrete beam–column connection.


2010 ◽  
Vol 25 (1) ◽  
pp. 167-173 ◽  
Author(s):  
Mingzhe An ◽  
Ziruo Yu ◽  
Meili Sun ◽  
Shuaiquan Zheng ◽  
Lei Liang

Author(s):  
Shervin Shameli Derakshan ◽  
Lina Zhou ◽  
Chun Ni

Wood shear walls are the main lateral load resisting systems in light wood frame buildings to resist the wind and seismic loads. Sheathing to lumber nail connections are regarded as the key components that control the resistance and failure modes of wood shear walls. Considerable experimental tests have been conducted on performance of nail joints or wood shear walls under both static and reversed cyclic loads. However, these tests were usually conducted under different loading speed causing specimen failure in 1 min to an hour. It is unclear how the loading speed will affect the test results of nail joints or wood shear walls. Research on these topics is limited. This paper aims to evaluate the effect of loading speed on the mechanical characteristics of nail joints. 72 specimens have been tested under various loading speeds, ranging from 0.05 mm/s to 0.5 mm/s for monotonic tests and 1.5 mm/s to 15 mm/s for reversed cyclic tests. The range of loading speed was selected based on the total estimated loading time that both monotonic and reversed cyclic tests fail within around 1 min to 10 min. Two groups of nail joints, comprising two common nail sizes and two sheathing thicknesses, were assessed under both monotonic and reversed cyclic loads. From the test results, the effect of loading speed on the mechanical properties of nail joints was determined.


Author(s):  
D. R. Kitchen ◽  
S. L. Linder ◽  
R. E. Omlor ◽  
P. F. Lloyd

Electromigration is a well known phenomenon in the aluminum films of an integrated circuit and occurs at elevated temperatures under the influence of current densities exceeding 10 amps/cm2. The failure modes are characteristically cracks, voids or hillocks in the metal lines, causing open-circuits. The majority of research in the electromigration of aluminum conductors examines the formation of these voids and hillocks in the linestripes. This is unfortunate since experiments have shown that short-circuits caused by whisker formation between adjacent stripes or between multi-level structures can be equally damaging to device performance. Most previous work has involved examining whiskers grown by annealing, however, very little work has been carried out on whiskers produced by electromigration. In this investigation aluminum whiskers formed by electromigration were studied with a transmission electron microsope to determine their crystallographic orientation.


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