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Innovative hybrid reinforcement constituting conventional longitudinal steel and FRP stirrups for improved

Mostafa FAKHARIFAR,Ahmad DALVAND,Mohammad K. SHARBATDAR,Genda CHEN,Lesley SNEED

《结构与土木工程前沿（英文）》 2016年 第10卷 第1期   页码 44-62 doi: 10.1007/s11709-015-0295-9

摘要： The use of fiber reinforced polymer (FRP) reinforcement is becoming increasingly attractive in construction of new structures. However, the inherent linear elastic behavior of FRP materials up to rupture is considered as a major drawback under seismic attacks when significant material inelasticity is required to dissipate the input energy through hysteretic cycles. Besides, cost considerations, including FRP material and construction of pre-fabricated FRP configurations, especially for stirrups, and probable damage to epoxy coated fibers when transported to the field are noticeable issues. The current research has proposed a novel economical hybrid reinforcement scheme for the next generation of infrastructures implementing on-site fabricated FRP stirrups comprised of FRP sheets. The hybrid reinforcement consists of conventional longitudinal steel reinforcement and FRP stirrups. The key feature of the proposed hybrid reinforcement is the enhanced strength and ductility owing to the considerable confining pressure provided by the FRP stirrups to the longitudinal steel reinforcement and core concrete. Reinforced concrete beam specimens and beam-column joint specimens were tested implementing the proposed hybrid reinforcement. The proposed hybrid reinforcement, when compared with conventional steel stirrups, is found to have higher strength, stiffness, and energy dissipation. Design methods, structural behavior, and applicability of the proposed hybrid reinforcement are discussed in detail in this paper.

关键词： FRP     ductility     confinement     seismic     shear    

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Flexural and longitudinal shear performance of precast lightweight steel–ultra-high performance concrete

《结构与土木工程前沿（英文）》 2023年 第17卷 第5期   页码 704-721 doi: 10.1007/s11709-023-0941-6

摘要： In this study, the flexural and longitudinal shear performances of two types of precast lightweight steel–ultra-high performance concrete (UHPC) composite beams are investigated, where a cluster UHPC slab (CUS) and a normal UHPC slab (NUS) are connected to a steel beam using headed studs through discontinuous shear pockets and full-length shear pockets, respectively. Results show that the longitudinal shear force of the CUS is greater than that of the NUS, whereas the interfacial slip of the former is smaller. Owing to its better integrity, the CUS exhibits greater flexural stiffness and a higher ultimate bearing capacity than the NUS. To further optimize the design parameters of the CUS, a parametric study is conducted to investigate their effects on the flexural and longitudinal shear performances. The square shear pocket is shown to be more applicable for the CUS, as the optimal spacing between two shear pockets is 650 mm. Moreover, a design method for transverse reinforcement is proposed; the transverse reinforcement is used to withstand the splitting force caused by studs in the shear pocket and prevent the UHPC slab from cracking. According to calculation results, the transverse reinforcement can be canceled when the compressive strength of UHPC is 150 MPa and the volume fraction of steel fiber exceeds 2.0%.

关键词： precast steel–UHPC composite beam     flexural performance     longitudinal shear performance     parametric study     transverse reinforcement ratio    

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Displacement-based seismic design of high-strength concrete frame columns

ZHANG Guojun, LIU Jianxin, LU Xilin

《结构与土木工程前沿（英文）》 2008年 第2卷 第1期   页码 93-101 doi: 10.1007/s11709-008-0006-x

摘要： Based on the testing results of 108 high-strength concrete columns under constant axial loading and horizontal cyclic loading, the relations between the drift ratio at yield, the maximum displacement drift, the limiting displacement drift, the ductility ratio of testing columns and shear span-to-depth ratio, axial compression ratio, confining reinforcement characteristic values, the ratio of cover area to confined core area as well as longitudinal reinforcement ratio are discussed in this paper. Then the relations between limiting displacement drifts and axial compression ratio, confining reinforcement characteristic values and the ratio of cover area to confined core area are analytically regressed. Subsequently the relations between confining reinforcement characteristic values and axial compression ratio, the limiting displacement drift, and the practical formula used to calculate confining reinforcement characteristic values are put forward. In the end the minimum confining reinforcement characteristic values in the dense hoop regions of high-strength concrete columns are presented by comparatively analysis, and compared with ones in the design code (GB 50010-2002, P. R. China).

关键词： horizontal cyclic     longitudinal reinforcement     design     loading     constant    

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Limit of axial force ratio and requirement for stirrups of RC columns with special shape

WANG Yiqun, XU Yidong, ZHAO Yanjing, CHEN Yunxia

《结构与土木工程前沿（英文）》 2007年 第1卷 第2期   页码 176-181 doi: 10.1007/s11709-007-0019-x

摘要： Thousands of columns with special shape are analyzed by nonlinear numerical methods. The ductility is calculated to investigate the limit of the axial force ratio and circumstantial requirement for stirrups of an reinforced concrete (RC) column with special shape, in the point of view of the characteristic value for providing stirrup. The limit of the axial force ratio of columns with special shape in relation to the characteristic value of the stirrup is obtained. Then, the effect of stirrup arrangement on the ductility of the RC column is discussed in case of buckling of the longitudinal reinforcement and constraint concrete columns. The complete requirement for stirrups of RC column with special shape is given.

关键词： reinforced concrete     circumstantial requirement     buckling     stirrup     longitudinal reinforcement    

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Numerical investigation and analysis of heat transfer enhancement in channel by longitudinal vortex based

TAO Wenquan, WU Junmei

《能源前沿（英文）》 2008年 第2卷 第1期   页码 71-78 doi: 10.1007/s11708-008-0001-x

摘要： 3-D numerical simulations were presented for laminar flow and heat transfer characteristics in a rectangular channel with vortex generators. The effects of Reynolds number (from 800 to 3 000), the attack angle of vortex generator (from 15° to 90°) and the shape of vortex generator were examined. The numerical results were analyzed based on the field synergy principle. It is found that the inherent mechanism of the heat transfer enhancement by longitudinal vortex can be explained by the field synergy principle, that is, the second flow generated by vortex generators results in the reduction of the intersection angle between the velocity and fluid temperature gradient. The longitudinal vortex improves the field synergy of the large downstream region of longitudinal vortex generator (LVG) and the region near (LVG); however, transverse vortex only improves the synergy of the region near vortex generator. Thus, longitudinal vortex can enhance the integral heat transfer of the flow field, while transverse vortex can only enhance the local heat transfer. The synergy angle decreases with the increase of Reynolds number for the channel with LVG to differ from the result obtained from the plain channel, and the triangle winglet performs better than the rectanglar one under the same surface area condition.

关键词： inherent mechanism     integral     surface     rectanglar     longitudinal    

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Analytical and numerical investigation into the longitudinal vibration of uniform nanotubes

null

《机械工程前沿（英文）》 2014年 第9卷 第2期   页码 142-149 doi: 10.1007/s11465-014-0292-z

摘要：

In recent years, prediction of the behaviors of micro and nanostructures is going to be a matter of increasing concern considering their developments and uses in various engineering fields. Since carbon nanotubes show the specific properties such as strength and special electrical behaviors, they have become the main subject in nanotechnology researches. On the grounds that the classical continuum theory cannot accurately predict the mechanical behavior of nanostructures, nonlocal elasticity theory is used to model the nanoscaled systems. In this paper, a nonlocal model for nanorods is developed, and it is used to model the carbon nanotubes with the aim of the investigating into their longitudinal vibration. Following the derivation of governing equation of nanorods and estimation of nondimensional frequencies, the effect of nonlocal parameter and the length of the nanotube on the obtained frequencies are studied. Furthermore, differential quadrature method, as a numerical solution technique, is used to study the effect of these parameters on estimated frequencies for both classical and nonlocal theories.

关键词： continuum theory     differential quadrature method     nanorod     longitudinal vibration    

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Experimental investigation and design of aluminum columns with longitudinal welds

Yun WU, Qilin ZHANG

《结构与土木工程前沿（英文）》 2011年 第5卷 第3期   页码 366-373 doi: 10.1007/s11709-011-0101-2

摘要： This paper presents an experimental investigation of longitudinally welded aluminum alloy I-section columns subjected to pure axial compression. The specimens were fabricated using 6061-T6 heat-treated aluminum alloy. The test program included 20 column tests which were separated into 2 test series of different types of welding sections. Each test series contained 10 columns. All the specimens were welded using the Tungsten Inert Gas welding method. The length of the specimens ranged from 442 to 2433 mm in order to obtain a column curve for each test series. The observed failure mode for the column tests includes mainly flexural buckling around the minor axis and the major axis by applying support except for one column (ZP1217-1) which buckled in the local zone and some columns which failed in the weld. The test strengths were compared with the design strengths predicted by the European Code and China Code for aluminum structures. The purpose of this paper is to present the tests results of two typically longitudinally welded I-section columns, and to check the accuracy of the design rules in the current specifications.

关键词： aluminum alloy     longitudinal weld     heat-affected zone (HAZ)     reduced strength zone (RSZ)     buckling     column     experimental study    

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Discontinuous mechanical behaviors of existing shield tunnel with stiffness reduction at longitudinal

《结构与土木工程前沿（英文）》 2023年 第17卷 第1期   页码 37-52 doi: 10.1007/s11709-022-0920-3

摘要： An analytical model is proposed to estimate the discontinuous mechanical behavior of an existing shield tunnel above a new tunnel. The existing shield tunnel is regarded as a Timoshenko beam with longitudinal joints. The opening and relative dislocation of the longitudinal joints can be calculated using Dirac delta functions. Compared with other approaches, our method yields results that are consistent with centrifugation test data. The effects of the stiffness reduction at the longitudinal joints (α and β), the shearing stiffness of the Timoshenko beam GA, and different additional pressure profiles on the responses of the shield tunnel are investigated. The results indicate that our proposed method is suitable for simulating the discontinuous mechanical behaviors of existing shield tunnels with longitudinal joints. The deformation and internal forces decrease as α, β, and GA increase. The bending moment and shear force are discontinuous despite slight discontinuities in the deflection, opening, and dislocation. The deflection curve is consistent with the additional pressure profile. Extensive opening, dislocation, and internal forces are induced at the location of mutation pressures. In addition, the joints allow rigid structures to behave flexibly in general, as well as allow flexible structures to exhibit locally rigid characteristics. Owing to the discontinuous characteristics, the internal forces and their abrupt changes at vulnerable sections must be monitored to ensure the structural safety of existing shield tunnels.

关键词： tunnel–soil interaction     discontinuous analysis     longitudinal joints     existing shield tunnel     Timoshenko beam     Dirac delta function    

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Range of ecological impact of highway construction in the Longitudinal Range-Gorge Region, China

Jie LIU, Fan CHEN, Haiqing GENG, Xinxin QIU, Binbin CAI,

《环境科学与工程前沿（英文）》 2010年 第4卷 第3期   页码 349-360 doi: 10.1007/s11783-010-0027-2

摘要： The major features of different road sections were identified. Methods quantitatively determining the ecological impact of highway construction were discussed, and a demonstration was presented. The Dabao highway (from Dali to Baoshan) and the Sixiao highway (from Simao to Xiaomengyang) passing through the Longitudinal Range-Gorge Region were used as examples in this paper. For the normal road sections having no important species to protect, a method of ecosystem health assessment was introduced to calculate the overall range of the ecological impact of highway construction. For the road sections having plants or soils of interest, indexes were selected and the range of impact was determined using mathematical methods such as regression analysis and variance analysis. The range of impact on animal populations was also discussed in terms of the minimum living areas required by animal populations and the fragmentation caused by highway construction. The results indicate that the zones impacted by highway construction were composed of both regular and anomalous figures, the range of impacts for different landforms of the two sample highways were substantially different; highway construction had dramatic effects on roadside ecosystem health; the impact on soil factors of farmland was greater than 200 m, and the distance may exceed 1000 m when important large animals were considered.

关键词： range of impact     quantitative analysis     highway construction     Longitudinal Range-Gorge Region    

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Numerical analysis on heat transfer enhancement by longitudinal vortex based on field synergy principle

WU Junmei, TAO Wenquan

《能源前沿（英文）》 2007年 第1卷 第3期   页码 365-369 doi: 10.1007/s11708-007-0055-1

摘要： Three-dimensional numerical simulation results are presented for a fin-and-tube heat transfer surface with vortex generators. The effects of the Reynolds number (from 800 to 2 000) and the attack angle (30º and 45º) of a delta winglet vortex generator are examined. The numerical results are analyzed on the basis of the field synergy principle to explain the inherent mechanism of heat transfer enhancement by longitudinal vortex. The secondary flow generated by the vortex generators causes the reduction of the intersection angle between the velocity and fluid temperature gradients. In addition, the computational evaluations indicate that the heat transfer enhancement of delta winglet pairs for an aligned tube bank fin-and-tube surface is more significant than that for a staggered tube bank fin-and-tube surface. The heat transfer enhancement of the delta winglet pairs with an attack angle of 45º is larger than that with an angle of 30º. The delta winglet pair with an attack angle of 45º leads to an increase in pressure drop, while the delta winglet pair with the 30º angle results in a slight decrease. The heat transfer enhancement under identical pumping power condition for the attack angle of 30º is larger than that for the attack angle of 45º either for staggered or for aligned tube bank arrangement.

关键词： computational     inherent mechanism     staggered     decrease     transfer surface    

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A new automatic convolutional neural network based on deep reinforcement learning for fault diagnosis

《机械工程前沿（英文）》 2022年 第17卷 第2期 doi: 10.1007/s11465-022-0673-7

摘要： Convolutional neural network (CNN) has achieved remarkable applications in fault diagnosis. However, the tuning aiming at obtaining the well-trained CNN model is mainly manual search. Tuning requires considerable experiences on the knowledge on CNN training and fault diagnosis, and is always time consuming and labor intensive, making the automatic hyper parameter optimization (HPO) of CNN models essential. To solve this problem, this paper proposes a novel automatic CNN (ACNN) for fault diagnosis, which can automatically tune its three key hyper parameters, namely, learning rate, batch size, and L2-regulation. First, a new deep reinforcement learning (DRL) is developed, and it constructs an agent aiming at controlling these three hyper parameters along with the training of CNN models online. Second, a new structure of DRL is designed by combining deep deterministic policy gradient and long short-term memory, which takes the training loss of CNN models as its input and can output the adjustment on these three hyper parameters. Third, a new training method for ACNN is designed to enhance its stability. Two famous bearing datasets are selected to evaluate the performance of ACNN. It is compared with four commonly used HPO methods, namely, random search, Bayesian optimization, tree Parzen estimator, and sequential model-based algorithm configuration. ACNN is also compared with other published machine learning (ML) and deep learning (DL) methods. The results show that ACNN outperforms these HPO and ML/DL methods, validating its potential in fault diagnosis.

关键词： deep reinforcement learning     hyper parameter optimization     convolutional neural network     fault diagnosis    

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Hole quality in longitudinal–torsional coupled ultrasonic vibration assisted drilling of carbon fiber

Guofeng MA, Renke KANG, Zhigang DONG, Sen YIN, Yan BAO, Dongming GUO

《机械工程前沿（英文）》 2020年 第15卷 第4期   页码 538-546 doi: 10.1007/s11465-020-0598-y

摘要： Carbon fiber reinforced plastic (CFRP) composites are extremely attractive in the manufacturing of structural and functional components in the aircraft manufacturing field due to their outstanding properties, such as good fatigue resistance, high specific stiffness/strength, and good shock absorption. However, because of their inherent anisotropy, low interlamination strength, and abrasive characteristics, CFRP composites are considered difficult-to-cut materials and are prone to generating serious hole defects, such as delamination, tearing, and burrs. The advanced longitudinal–torsional coupled ultrasonic vibration assisted drilling (LTC-UAD) method has a potential application for drilling CFRP composites. At present, LTC-UAD is mainly adopted for drilling metal materials and rarely for CFRP. Therefore, this study analyzes the kinematic characteristics and the influence of feed rate on the drilling performance of LTC-UAD. Experimental results indicate that LTC-UAD can reduce the thrust force by 39% compared to conventional drilling. Furthermore, LTC-UAD can decrease the delamination and burr factors and improve the surface quality of the hole wall. Thus, LTC-UAD is an applicable process method for drilling components made with CFRP composites.

关键词： longitudinal–torsional coupled     ultrasonically drilling     CFRP     thrust force     hole quality    

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Sensitivity analysis and numerical experiments on transient test of compact heat exchanger surfaces

REN Hesheng, LAI Lingjun, CUI Yongzheng

《能源前沿（英文）》 2008年 第2卷 第4期   页码 374-380 doi: 10.1007/s11708-008-0079-1

摘要： A single-blow transient testing technique considering the effect of longitudinal heat conduction is suggested for determining the average convection heat transfer coefficient of compact heat exchanger surface. By matching the measured outlet fluid temperature variation with similar theoretical curves, the dimensionless longitudinal conduction parameter , the time constant of the inlet fluid temperature , and the number of heat transfer units can be determined simultaneously using the Levenberg-Marquardt nonlinear parameter estimation method. Both sensitivity analysis and numerical experiments with simulated measurements containing random errors show that the method in the present investigation provides satisfactory accuracy of the estimated parameter , which characterizes the heat transfer performance of compact heat exchanger surfaces.

关键词： coefficient     dimensionless longitudinal     longitudinal     temperature     conduction    

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Lung function and air pollution exposure in adults with asthma in Beijing: a 2-year longitudinal panel

《医学前沿（英文）》 2022年 第16卷 第4期   页码 574-583 doi: 10.1007/s11684-021-0882-1

摘要： The effect of air pollution on the lung function of adults with asthma remains unclear to date. This study followed 112 patients with asthma at 3-month intervals for 2 years. The pollutant exposure of the participants was estimated using the inverse distance weight method. The participants were divided into three groups according to their lung function level at every visit. A linear mixed-effect model was applied to predict the change in lung function with each unit change in pollution concentration. Exposure to carbon monoxide (CO) and particles less than 2.5 micrometers in diameter (PM2.5) was negatively associated with large airway function in participants. In the severe group, exposure to chronic sulfur dioxide (SO2) was negatively associated with post-bronchodilator forced expiratory flow at 50%, between 25% and 75% of vital capacity % predicted (change of 95% CI per unit: −0.34 (−0.55, −0.12), −0.24 (−0.44, −0.03), respectively). In the mild group, the effect of SO2 on the small airways was similar to that in the severe group, and it was negatively associated with large airway function. Exposure to CO and PM2.5 was negatively associated with the large airway function of adults with asthma. The negative effects of SO2 were more evident and widely observed in adults with severe and mild asthma than in adults with moderate asthma. Patients with asthma react differently to air pollutants as evidenced by their lung function levels.

关键词： lung function     asthma     air pollution     adult    

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Punching of reinforced concrete slab without shear reinforcement: Standard models and new proposal

Luisa PANI, Flavio STOCHINO

《结构与土木工程前沿（英文）》 2020年 第14卷 第5期   页码 1196-1214 doi: 10.1007/s11709-020-0662-z

摘要： Reinforced concrete (RC) slabs are characterized by reduced construction time, versatility, and easier space partitioning. Their structural behavior is not straightforward and, specifically, punching shear strength is a current research topic. In this study an experimental database of 113 RC slabs without shear reinforcement under punching loads was compiled using data available in the literature. A sensitivity analysis of the parameters involved in the punching shear strength assessment was conducted, which highlighted the importance of the flexural reinforcement that are not typically considered for punching shear strength. After a discussion of the current international standards, a new proposed model for punching shear strength and rotation of RC slabs without shear reinforcement was discussed. It was based on a simplified load-rotation curve and new failure criteria that takes into account the flexural reinforcement effects. This experimental database was used to validate the approaches of the current international standards as well as the new proposed model. The latter proved to be a potentially useful design tool.

关键词： punching shear strength     reinforced concrete     slabs     reinforcement ratio    

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标题 作者 时间 类型 操作

Innovative hybrid reinforcement constituting conventional longitudinal steel and FRP stirrups for improved

Mostafa FAKHARIFAR,Ahmad DALVAND,Mohammad K. SHARBATDAR,Genda CHEN,Lesley SNEED

期刊论文

Flexural and longitudinal shear performance of precast lightweight steel–ultra-high performance concrete

期刊论文

Displacement-based seismic design of high-strength concrete frame columns

ZHANG Guojun, LIU Jianxin, LU Xilin

期刊论文

Limit of axial force ratio and requirement for stirrups of RC columns with special shape

WANG Yiqun, XU Yidong, ZHAO Yanjing, CHEN Yunxia

期刊论文

Numerical investigation and analysis of heat transfer enhancement in channel by longitudinal vortex based

TAO Wenquan, WU Junmei

期刊论文

Analytical and numerical investigation into the longitudinal vibration of uniform nanotubes

null

期刊论文

Experimental investigation and design of aluminum columns with longitudinal welds

Yun WU, Qilin ZHANG

期刊论文

Discontinuous mechanical behaviors of existing shield tunnel with stiffness reduction at longitudinal

期刊论文

Range of ecological impact of highway construction in the Longitudinal Range-Gorge Region, China

Jie LIU, Fan CHEN, Haiqing GENG, Xinxin QIU, Binbin CAI,

期刊论文

Numerical analysis on heat transfer enhancement by longitudinal vortex based on field synergy principle

WU Junmei, TAO Wenquan

期刊论文

A new automatic convolutional neural network based on deep reinforcement learning for fault diagnosis

期刊论文

Hole quality in longitudinal–torsional coupled ultrasonic vibration assisted drilling of carbon fiber

Guofeng MA, Renke KANG, Zhigang DONG, Sen YIN, Yan BAO, Dongming GUO

期刊论文

Sensitivity analysis and numerical experiments on transient test of compact heat exchanger surfaces

REN Hesheng, LAI Lingjun, CUI Yongzheng

期刊论文

Lung function and air pollution exposure in adults with asthma in Beijing: a 2-year longitudinal panel

期刊论文

Punching of reinforced concrete slab without shear reinforcement: Standard models and new proposal

Luisa PANI, Flavio STOCHINO

期刊论文