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1

Comparison study on seismic isolation design of RC frame structure based on two different codes

Zhang Junyi, Li Jiawei, Zhang Zhiqiang

Archives of Civil Engineering

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2024

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Vol. 70, nr 2

387--401

EN

With the development of building seismic isolation technology and the official release of the Isolation Code in September 2021, seismic isolation design in China will now rely on two foundational codes: the Seismic Code and the Isolation Code. This paper take a ceramic jar storage of the RC frame structure as the research object, and carry out the seismic isolation design based on the separated calculation design method of the Seismic Code and the unitary calculation design method of the Isolation Code respectively, and clarify the control index of the Isolation Code is the story drift angle. The maximum displacement is reduced by 37.5%. In terms of material consumption, the Isolation Code leads to a 5.94% decrease in concrete usage, accompanied by a 13.97% increase in steel consumption, resulting in an overall cost increase of 4.98%. The findings indicate that seismic isolation design, guided by the Isolation Code, substantially mitigates the seismic response of the superstructure. The damage extent to structural members is reduced by 15-20%, promoting enhanced safety and repairability. The outcomes of this study offer valuable insights for future seismic isolation designs in RC frame structures.

2

Study on the stress intensity factor of a compact specimen under the pre-compressed load condition

Wu Dongquan, Liu Zixiang, Li Dinghe, Zhang Zhiqiang, Chen Jianguo

Journal of Theoretical and Applied Mechanics

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2023

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Vol. 61 nr 1

37--47

EN

Structural components are often operated under combined stress conditions (primary and secondary stresses), but the stress levels generated by residual stress (or secondary stress) is hardly ever evaluated. Hence, stress intensity factors at the crack tips of a compact tension (CT) specimen under a pre-compressed load condition are analyzed using the finite element method. Then, the average residual stress intensity factor is calculated and analyzed. As the crack length α0/W increases, the average residual stresses σave/σ0 grows under the same pre-compression load. σave/σ0 increases rapidly at a low range of the pre-compression load but tends to a constant in a high range of the load. The distribution of the average residual stress intensity factors Kave and Κave/σ0 of the CT specimen with same crack length under different pre-compression loads have the same tendency. Additionally, the distribution of Κave and KFEM under different pre-compression loads are also similar. Nevertheless, Kave estimated by the average residual stress is too conservative and not accurate, and the method is complex, which depends on the analysis of simulation. Therefore, a simple method for calculating Mode I stress intensity factor K for this model is presented. A group of examples is presented to verify the accuracy of the method.

3

Study on constraint effect and creep crack initiation of plate containing elliptical embedded cracks

Wu Dongquan, Liu Zixiang, Li Yupeng, Li Dinghe, Zhang Zhiqiang

Journal of Theoretical and Applied Mechanics

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2023

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Vol. 61 nr 3

545--557

EN

In this study, a plate structure containing elliptical embedded cracks loaded under high temperature is studied. The constraint effect and creep crack initiation of the plate con- taining embedded cracks are discussed by using the finite element method based on the creep ductility exhaustion model. It is indicated that the highest constraint level or the load-independent parameter Q* is observed at the endpoint of the ellipse major axis of an elliptical embedded crack, and the constraint levels increase with crack length or depth, which represents a worse condition for the structure, such as higher stress concentration and greater danger of failure for a larger crack depth ratio a/t or crack length ratio a/c. Moreover, under the creep condition, the embedded crack with a larger a/t, a/c or loadings is accompanied with a higher crack driving force, which can accelerate creep damage, creep cracking initiation (CCI) and shorten the creep crack initiation (CCI) time. Additionally, an empirical prediction equation and engineering approach to the constraint parameter and the CCI time for elliptical embedded cracks are proposed, and the engineering approach to the CCI time is validated.

4

Numerical study on compression properties of semi-reentrant filled tubular structures

Wu Dongquan, Li Dinghe, Zhang Zhiqiang, Chen Jianguo

Journal of Theoretical and Applied Mechanics

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2023

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Vol. 61 nr 2

233--244

EN

In this study, a semi-reentrant structure (SR) filled with different tubular structures, includ- ing tube, triangular and rectangle structures were designed. The tubular structures were perfectly assembled into semi-reentrant cells to avoid swaying in the semi-reentrant cell. The geometric relations and relative density for these structures were established. For the out-of-plane and in-plane compressions, SR filled tubular structures exhibited different de- formation patterns compared to those of SR or pure fillers. A constraint effect was found between the filler tubular and container SR. With fillers contained inside the SR structures, the plateau stresses for three conditions were all promoted compared to those of SR. The best out-of-plane compression resistance occurred in the SR filled rectangle which might be caused by larger interaction areas between the SR and rectangular structures. The (specific) energy absorption of the SR filled tube compressed out-of-plane was the largest. The peak and plateau stress of the SR filled triangle was the largest compared to other structures when compressed in plane due to stability of the triangle. It was found that the plateau stress, energy absorption and specific energy absorption of SR filled triangle was the largest, while that of SR filled rectangle was the lowest.

5

Feasibility study on contact heating warm forming of 7075-T6 aluminum alloy

Sun Lu, Zhang Zhiqiang, Song Zhenkun, Ren Mingwen, Jia Hongjie

Archives of Civil and Mechanical Engineering

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2023

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Vol. 23, no. 3

art. no. e209, 2023

EN

7075 aluminum alloy is becoming an ideal material for the manufacture of vehicle body parts due to the demands for energy-saving and lighter vehicles. To solve the problem that the strength of 7075-T6 aluminum alloy decreases due to over-aging after warm forming, contact heating warm forming (CHWF) technology was proposed in this work. Contact heating is a fast and efficient heating method that can make the blank reach the target temperature in a very short time. In this work, the effect of contact heating on the mechanical properties and microstructures of 7075-T6 aluminum alloy after warm forming and paint-baking (PB) was studied. It only took about 11.5 s to heat the 2 mm 7075 aluminum alloy sheet to 200 ℃ by contact heating, and the strength and the hardness of the formed parts could reach 94% and 92.5% of T6 condition, respectively. In contrast, the heating furnace needed 690 s to heat the sheet to 200 °C, and the strength and the hardness of the formed parts were 87% and 85.4% of T6 condition, respectively. Due to the fast heating rate of contact heating (17.5 ℃/s), the atoms and vacancies in the matrix did not have time to undergo diffusion and aggregation, so that the precipitates could not coarsen obviously. As a result, most of the η' precipitates in the T6 condition were retained. However, long-term heating in the furnace led to the transformation of η' precipitates into coarse η phase and the loss of strength and hardness.

6

Assessing and controlling of boulder deep-hole blasting-induced vibrations to minimize impacts to a neighboring metro shaft

Zhang Zhiqiang, Li Yonglong, Wang Shuo, Zhang Heng, Qian Yang

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 2

421--440

EN

When a metro is constructed by the shield method in the strata containing boulder group, it is prone to some engineering problems such as serious cutter wear, deformation of the cutter holder head, damage of the cutter spindle, which seriously affects the construction efficiency and bring enormous problems to the shield construction. This paper proposes the vibration reduction measures for the boulder deep-hole blasting to meet the construction safety. To achieve this purpose, the field test was applied to investigate the vibration response of adjacent building under five blasting areas. Then, three-dimensional numerical model was employed to discuss the vibration characteristics of the boulder and adjacent buildings under vibration reduction measures. The results show that increasing the damping hole and the isolation hole and changing the charging layout of the blasting areas can blast the boulder under the condition of ensuring effective and safe construction. Damping hole and isolation hole have a positive role in the control and attenuation of blasting stress wave. All of them have good vibration reduction effect, and the vibration reduction efficiency is more than 90%. The double row damping holes with 12.7 cm diameter and 20 cm spacing have good vibration reduction effect and economic benefit. When double row damping holes are used, the maximum particle velocity of the shaft structure under the influence of blasting stress wave is 1.47 cm/s, which is within the reasonable safety range.