This paper presents a simplified elastic continuum method for calculating the restraint effect of isolation piles on tunneling-induced vertical ground displacement,which can consider not only the relative sliding of t...This paper presents a simplified elastic continuum method for calculating the restraint effect of isolation piles on tunneling-induced vertical ground displacement,which can consider not only the relative sliding of the pile‒soil interface but also the pile rowesoil interaction.The proposed method is verified by comparisons with existing theoretical methods,including the boundary element method and the elastic foundation method.The results reveal the restraining mechanism of the isolation piles on vertical ground displacements due to tunneling,i.e.the positive and negative restraint effects exerted by the isolation piles jointly drive the ground vertical displacement along the depth direction from the original tunneling-induced nonlinear variation situation to a relatively uniform situation.The results also indicate that the stiffness of the pile‒soil interface,including the pile shaft‒surrounding soil interface and pile tip-supporting soil interface,describes the strength of the pile‒soil interaction.The pile rows can confine the vertical ground displacement caused by the tunnel excavation to the inner side of the isolation piles and effectively prevent the vertical ground displacement from expanding further toward the outer side of the isolation piles.展开更多
Metabolic rewiring underlies the effector functions of macrophages1-3,but the mechanisms involved remain incompletely defined.Here,using unbiased metabolomics and stable isotope-assisted tracing,we show that an inflam...Metabolic rewiring underlies the effector functions of macrophages1-3,but the mechanisms involved remain incompletely defined.Here,using unbiased metabolomics and stable isotope-assisted tracing,we show that an inflammatory aspartate argininosuccinate shunt is induced following lipopolysaccharide stimulation.The shunt,supported by increased argininosuccinate synthase(ASS1)expression,also leads to increased cytosolic fumarate levels and fumarate-mediated protein succination.Pharmacological inhibition and genetic ablation of the tricarboxylic acid cycle enzyme fumarate hydratase(FH)further increases intracellular fumarate levels.展开更多
Based on the background of structural protection and Disaster Reduction Engineering, the dynamic behaviour and failure mechanism of restrained beams in portal steel frames in localised fire are investigated via experi...Based on the background of structural protection and Disaster Reduction Engineering, the dynamic behaviour and failure mechanism of restrained beams in portal steel frames in localised fire are investigated via experimental measurement and numerical simulation techniques. Comprehensive parametric studies are carried out to discuss the influence of end connection types, temperature, impact velocity,impact mass and span-to-depth ratio(SDR) on the dynamic response of the beams. The characteristics of deformation, internal force and energy distribution about the restrained beams and its joints are investigated. A temperature dependent criterion for evaluating the frame joint performance is proposed to measure the degree of performance degradation and impact resistance of the joint. The dynamic displacement amplification factor in different temperature environments are proposed for the different beam end constraint types and SDRs. Results of the experimental and numerical analysis show that the welded connection(WC) of three typical joint types is the strongest, and the extended endplate connection(EEC) is the weakest in terms of the impact resistance performance. With regard to the failure mode of the joint, the failure positions of the WC and the welded-bolted connection are located in the inner web of the column. Meanwhile, the EEC is located in the connection position between the beam and the endplate. Three different internal force stages and two obvious critical temperature boundaries of the restrained beams emerge with the increase in temperature, and they have significant characteristics in terms of deformation trend, internal force transfer and energy distribution. During the impact, a phenomenon known as “compression arch action” develops into “catenary action” with the increase in deflection in the frame beam mechanism.展开更多
Accurate estimates of ductility demands on buckling-restrained braced frames(BRBFs)are crucial to performance-based design of BRBFs.An analytical study on the seismic behavior of BRBFs has been conducted at the ATLSS ...Accurate estimates of ductility demands on buckling-restrained braced frames(BRBFs)are crucial to performance-based design of BRBFs.An analytical study on the seismic behavior of BRBFs has been conducted at the ATLSS Center,Lehigh University to prepare for an upcoming experimental program.The analysis program DRAIN-2DX was used to model a one-bay,four-story prototype BRBF including material and geometric nonlinearities.The buckling- restrained brace(BRB)model incorporates both isotropic and kinematic hardening.Nonlinear static pushover and time- history analyses were performed on the prototype BRBF.Performance objectives for the BRBs were defined and used to evaluate the time-history analysis results.Particular emphasis was placed on global ductility demands and ductility demands on the BRBs.These demands were compared with anticipated ductility capacities.The analysis results,along with results from similar previous studies,are used to evaluate the BRBF design provisions that have been recommended for codification in the United States.The results show that BRB maximum ductility demands can be as high as 20 to 25.These demands significantly exceed those anticipated by the BRBF recommended provisions.Results from the static pushover and time- history analyses are used to demonstrate why the ductility demands exceed those anticipated by the recommended provisions. The BRB qualification testing protocol contained in the BRBF recommended provisions is shown to be inadequate because it requires only a maximum ductility demand of at most 7.5.Modifications to the testing protocol are recommended.展开更多
In sheet metal forming, drawbeads are often used to control uneven material flow which may cause defects such as wrinkles, fracture, surface distortion and springback. Appropriate setting and adjusting the drawbead ...In sheet metal forming, drawbeads are often used to control uneven material flow which may cause defects such as wrinkles, fracture, surface distortion and springback. Appropriate setting and adjusting the drawbead force is one of the most important pa- rameters in sheet metal forming process control. This paper derives the model of loop drawbead restraining force (DBRF) using plastic forming theory, and gives the min imum blankholding force. Experiments are carried out to verify the proposed DBRF model. The good agreement between the calculated values and experiments data justi- fies the proposed loop drawbead restraining force model.展开更多
Buckling restrained braces (BRBs) have been widely applied in seismic mitigation since they were introduced in the 1970s. However, traditional BRBs have several disadvantages caused by using a steel tube to envelope...Buckling restrained braces (BRBs) have been widely applied in seismic mitigation since they were introduced in the 1970s. However, traditional BRBs have several disadvantages caused by using a steel tube to envelope the mortar to prevent the core plate from buckling, such as: complex interfaces between the materials used, uncertain precision, and time consumption during the manufacturing processes. In this study, a new device called the multi-curve buckling restrained brace (MC-BRB) is proposed to overcome these disadvantages. The new device consists of a core plate with multiple neck portions assembled to form multiple energy dissipation segments, and the enlarged segment, lateral support elements and constraining elements to prevent the BRB from buckling. The enlarged segment located in the middle of the core plate can be welded to the lateral support and constraining elements to increase buckling resistance and to prevent them from sliding during earthquakes. Component tests and a series of shaking table tests on a full-scale steel structure equipped with MC-BRBs were carried out to investigate the behavior and capability of this new BRB design for seismic mitigation. The experimental results illustrate that the MC-BRB possesses a stable mechanical behavior under cyclic loadings and provides good protection to structures during earthquakes. Also, a mathematical model has been developed to simulate the mechanical characteristics of BRBs.展开更多
This paper presents an experimental study to investigate the performance of shape memory alloy(SMA) restrainers for mitigating the pounding and unseating of highway bridges when subjected to seismic excitations.Mechan...This paper presents an experimental study to investigate the performance of shape memory alloy(SMA) restrainers for mitigating the pounding and unseating of highway bridges when subjected to seismic excitations.Mechanical property tests of the SMA wire used in the restrainers are conducted first to understand the pseudo-elastic characteristics of the material.Then,a series of shaking table tests are carried out on a highway bridge model.The structural responses of the highway bridge model equipped with SMA restrainers,installed in the form of deck-deck and deck-pile connections,are analyzed and compared with the uncontrolled structures.The test results of this study indicate that the SMA restrainers are not only effective in preventing unseating but also in suppressing the seismic-induced pounding of the highway bridge model used in this study.展开更多
High-performance concrete (HPC) is stronger and more durable than conventional concrete. However, shrinkage and shrinkage cracking are common phenomena in HPC, especially early-age cracking. This study assessed earl...High-performance concrete (HPC) is stronger and more durable than conventional concrete. However, shrinkage and shrinkage cracking are common phenomena in HPC, especially early-age cracking. This study assessed early-age cracking of HPC for two mixtures using restrained ring tests. The two mixtures were produced with water/binder mass ratio (mw/mB) of 0.22 and 0.40, respectively. The results show that, with greater steel thickness, the higher degree of restraint resulted in a higher interface pressure and earlier cracking. With steel thickness of 6 mm, 19 mm, and 30 mm, the age of cracking were, respectively, 12 days, 8 days, and 5.4 days with the mw/mB = 0.22 mixture; and 22.5 days, 12.6 days, and 7.1 days with the mw/mB= 0.40 mixture. Cases of the same steel thickness show that the ring specimens with a thicker concrete wall crack later. With the mw/mB = 0.22 mixture, concrete walls with thicknesses of 37.5 mm, 75 mm, and 112.5 mm cracked at 3.4 days, 8.0 days, and 9.8 days, respectively; with the mw/mB = 0.40 mixture, the ages of cracking were 7.1 days, 12.6 days, and 16.0 days, respectively.展开更多
Due to complexities of draw-bead restraining force calculated according to theory and depending on sheet metal forming properties experiment testing system, a simplified method to calculate draw-bead restraining force...Due to complexities of draw-bead restraining force calculated according to theory and depending on sheet metal forming properties experiment testing system, a simplified method to calculate draw-bead restraining force is put forward by experimental method in cup-shaped drawing process. The experimental results were compared with numerical results and proved agreement. It shows the method is effective.展开更多
A pile-restrained pontoon-plate floating breakwater is proposed in this paper. The laboratory physical-model tests are conducted to investigate the wave-dissipation property and heave-motion response of a model. The i...A pile-restrained pontoon-plate floating breakwater is proposed in this paper. The laboratory physical-model tests are conducted to investigate the wave-dissipation property and heave-motion response of a model. The influence of the model's geometric parameters including relative pontoon width, plate width, number of plates and pontoon draft on wavedissipation performance and heave-motion response are discussed, as well as the correlation between these two factors. The result indicates that wave-dissipation performance of the proposed structure is better than the pontoon structure: its transmission coefficient and heave-motion height are reduced by 0.2 and 0.3, respectively, in comparison with those of the pile-restrained pontoon model at a relative pontoon width of 0.2.展开更多
Our preliminary study demonstrated that neuropeptide Y (NPY)/nestin-positive cells exhibit a consistent spatial distribution in the hippocampus of normal adult rats. However, following severe acute and chronic stres...Our preliminary study demonstrated that neuropeptide Y (NPY)/nestin-positive cells exhibit a consistent spatial distribution in the hippocampus of normal adult rats. However, following severe acute and chronic stress-induced impaired learning and memory, synchronous decreased expression of nestin and NPY takes place in the hippocampus, and the underlying mechanisms remain unclear. In the present study, acute and chronic stress rat models were established using combined restrained and inverted stress. Results showed that learning and memory significantly decreased in acute and chronic stress rats. In addition, hippocampal cells were damaged, in particular in the acute stress rats, and nestin and NPY expression, as well as the number of NPY/nestin-positive cells in the CA3 region, significantly decreased. Furthermore, mature neurofilament 200-positive neurons were absent in the chronic stress rats. The NPY and cytoskeletal protein system equally contributed to stress-induced early learning and memory deficits as well as sustained cerebral iniurv in the adult hippocampus.展开更多
Steel frames equipped with buckling restrained braces(BRBs)have been increasingly applied in earthquake-prone areas given their excellent capacity for resisting lateral forces.Therefore,special attention has been paid...Steel frames equipped with buckling restrained braces(BRBs)have been increasingly applied in earthquake-prone areas given their excellent capacity for resisting lateral forces.Therefore,special attention has been paid to the seismic risk assessment(SRA)of such structures,e.g.,seismic fragility analysis.Conventional approaches,e.g.,nonlinear finite element simulation(NFES),are computationally inefficient for SRA analysis particularly for large-scale steel BRB frame structures.In this study,amachine learning(ML)-based seismic fragility analysis framework is established to effectively assess the risk to structures under seismic loading conditions.An optimal artificial neural network model can be trained using calculated damage and intensity measures,a technique which will be used to compute the fragility curves of a steel BRB frame instead of employing NFES.Numerical results show that a highly efficient instantaneous failure probability assessment can be made with the proposed framework for realistic large-scale building structures.展开更多
This paper addresses the free transverse vibrations of thin simply supported nonhomogeneous isotropic rectangular plates of bilinearly varying thickness with elastically restrained edges against rotation. The Gram-Sch...This paper addresses the free transverse vibrations of thin simply supported nonhomogeneous isotropic rectangular plates of bilinearly varying thickness with elastically restrained edges against rotation. The Gram-Schmidt process has been used to generate two-dimensional boundary characteristic orthogonal polynomials, which have been used in the Rayleigh-Ritz method to study the problem. The lowest three frequencies have been computed for various values of nonhomogeneous parameters, thickness parameters, aspect ratio and flexibility parameters. A comparison of the results with those available in the literature has been made. Three-dimensional mode shapes for the specified plate have been presented.展开更多
The extracts from leaves of Manglietia insignis (Wall) Blume, Manglietia chingii Dandy and Manglietia yuyuanensis Law were prepared by organic solvent extraction and their components were analyzed by GC/MS and quant...The extracts from leaves of Manglietia insignis (Wall) Blume, Manglietia chingii Dandy and Manglietia yuyuanensis Law were prepared by organic solvent extraction and their components were analyzed by GC/MS and quantified. Meanwhile, the free radicals restraining activities were detected. The 21 compounds in M. insignis, 36 compounds in M. chigii and 20 compounds in M. yuyuanensis were identified. There were 11 common components in the extracts from three Manglietia species, and 12 components in two Manglietia species. The results of relative contents of every component in three extracts showed that the main constituents of M. insignis were terpenoids and alkene, amounting to 38.93%, followed by alkane (28.18%), the nitrogen containing compounds (15.73%) and aromatic compounds (7.23 %). The main constituents of leaf extract from M. chingii were the terpenoids and alkene, carboxylic acid, alkane and aromatic compounds, amounting to 30.22%, 14.17%, 13.87% and 13.29%, respectively, The main constituents of M. yuyuanensis were alcohol compounds, the terpenoids and alkene, and aromatic compounds, amounting to 28.00%, 25.38% and 18.00% respectively. The results showed that the three extracts had strong function of restraining oxygen free radicals. The ultra oxygen anions activity was restrained at the highest level, when the three extracts were diluted by hundred-fold, whereas the restraining capacity of hydroxyl free radicals reached maximum, when the three extracts were diluted by twenty-fold. The above results provide scientific evidences for further approaching the ecological healthy function of three MangUetia species展开更多
An image segmentation algorithm of the restrained fuzzy Kohonen clustering network (RFKCN) based on high- dimension fuzzy character is proposed. The algorithm includes two steps. The first step is the fuzzification ...An image segmentation algorithm of the restrained fuzzy Kohonen clustering network (RFKCN) based on high- dimension fuzzy character is proposed. The algorithm includes two steps. The first step is the fuzzification of pixels in which two redundant images are built by fuzzy mean value and fuzzy median value. The second step is to construct a three-dimensional (3-D) feature vector of redundant images and their original images and cluster the feature vector through RFKCN, to realize image seg- mentation. The proposed algorithm fully takes into account not only gray distribution information of pixels, but also relevant information and fuzzy information among neighboring pixels in constructing 3- D character space. Based on the combination of competitiveness, redundancy and complementary of the information, the proposed algorithm improves the accuracy of clustering. Theoretical anal- yses and experimental results demonstrate that the proposed algorithm has a good segmentation performance.展开更多
To investigate the early-age behaviors of concrete under a restrained condition, a set of apparatus was developed. In this way, the tensile creep and other early-age properties can be investigated in depth. By measuri...To investigate the early-age behaviors of concrete under a restrained condition, a set of apparatus was developed. In this way, the tensile creep and other early-age properties can be investigated in depth. By measuring the modulus of elasticity of concrete, synchronous shrinkage of concrete and steel rings and free shrinkage of concrete, the deformations of concrete ring can be quantified respectively. The experimental results show the tensile stress in concrete is time-dependent, and the stress at cracking is much lower than the tensile strength at that age; the tensile creep plays an important role in relaxing the tensile stress and postponing the cracking of concrete.展开更多
The element-free Galerkin method is proposed to solve free vibration of rectangular plates with finite interior elastic point supports and elastically restrained edges.Based on the extended Hamilton's principle for t...The element-free Galerkin method is proposed to solve free vibration of rectangular plates with finite interior elastic point supports and elastically restrained edges.Based on the extended Hamilton's principle for the elastic dynamics system,the dimensionless equations of motion of rectangular plates with finite interior elastic point supports and the edge elastically restrained are established using the element-free Galerkin method.Through numerical calculation,curves of the natural frequency of thin plates with three edges simply supported and one edge elastically restrained,and three edges clamped and the other edge elastically restrained versus the spring constant,locations of elastic point support and the elastic stiffness of edge elastically restrained are obtained.Effects of elastic point supports and edge elastically restrained on the free vibration characteristics of the thin plates are analyzed.展开更多
BACKGROUND:Motor vehicles crashes(MVCs) are the leading cause of injury related morbidity and mortality in developed countries. Recent evidence proves that properly used child seat belts can dramatically reduce the ri...BACKGROUND:Motor vehicles crashes(MVCs) are the leading cause of injury related morbidity and mortality in developed countries. Recent evidence proves that properly used child seat belts can dramatically reduce the risk of severe and life-threatening injury from MVCs. There are rarities of thought and inspiration regarding the use of child seat belts in our society and region,therefore we lack of data regarding factors and paucity of usage of child seat belts in motor vehicles. This study aimed to assess the knowledge and attitudes of child seat belt usage among the educated population in Karachi,Pakistan.METHODS:Altogether 304 employees were investigated. They were employees of Aga Khan University who were using their cars and having children younger than 10 years old. A cross sectional observational study was designed,and a 36-item questionnaire in English was used to collect data on participants' demographic details,designation,educational level,economic status,validity of driving license,number of children and cars,availability of adult seat belts and child seat belts along with their functionality,awareness,knowledge and attitude toward its use,and reason of not using these devices. SPSS version 20 for Windows was used to analyze the data and the Chi-square test was used.RESULTS:Totally 290 participants were recruited with a response rate of 72%(212). Of 212 participants,126(59%) were male. 154(72.6%) participants had valid driver licenses,and 154(72.6%) had adult seat belts in their vehicles. Only 32(15%) reported regular use of adult seat belts. Although 168(79.2%) participants had some knowledge about child restrains(CRs),only 65(22%) had CRs in their cars. Eighty-two(38.7%) participants got the knowledge about CRs and seat belts from media. Mothers were more concerned about the use of CRs than fathers. Only 14(6.6%) parents were found to use both adult and child seat belts all the time. Of the 157 parents who did not us use CRs,42 considered unnecessary,35 lacked relevant knowledge. But 15 parents used CR against their children's wills.CONCLUSIONS:The pattern of CR usage among the employees at Aga Khan University,Karachi is dictated by the unavailability of CR,followed by ignorance,inconvenience,and nonacceptance by their children. The important issue of CR has consistently been ignored over the years and it has never gained enough popularity in Pakistan.展开更多
Hydration process, crack potential and setting time of concrete grade C30, C40 and C50 were monitored by using a non-contact electrical resistivity apparatus, a novel plastic ring mould and penetration resistance meth...Hydration process, crack potential and setting time of concrete grade C30, C40 and C50 were monitored by using a non-contact electrical resistivity apparatus, a novel plastic ring mould and penetration resistance methods, respectively. The results show the highest resistivity of C30 at the early stage until a point when C50 accelerated and overtook the others. It has been experimentally confirmed that the crossing point of C30 and C50 corresponds to the final setting time of C50. From resistivity derivative curve, four different stages were observed upon which the hydration process is classified; these are dissolution, induction, acceleration and deceleration periods. Consequently, restrained shrinkage crack and setting time results demonstrated that C50 set and cracked the earliest. The cracking time of all the samples occurred within a reasonable experimental period thus the novel plastic ring is a convenient method for predicting concrete's crack potential. The highest inflection time(t_i) obtained from resistivity curve and the final setting time(t_f) were used with crack time(t_c) in coming up with mathematical models for the prediction of concrete's cracking age for the range of concrete grade considered. Finally, an ANSYS numerical simulation supports the experimental findings in terms of the earliest crack age of C50 and the crack location.展开更多
Buckling-restrained braces (BRBs) have recently become popular in the United States for use as primary members of seismic lateral-force-resisting systems. A BRB is a steel brace that does not buckle in compression b...Buckling-restrained braces (BRBs) have recently become popular in the United States for use as primary members of seismic lateral-force-resisting systems. A BRB is a steel brace that does not buckle in compression but instead yields in both tension and compression. Although design guidelines for BRB applications have been developed, systematic procedures for assessing performance and quantifying reliability are still needed. This paper presents an analytical framework for assessing buckling-restrained braced frame (BRBF) reliability when subjected to seismic loads. This framework efficiently quantifies the risk of BRB failure due to low-cycle fatigue fracture of the BRB core. The procedure includes a series of components that: (1) quantify BRB demand in terms of BRB core deformation histories generated through stochastic dynamic analyses; (2) quantify the limit-state of a BRB in terms of its remaining cumulative plastic ductility capacity based on an experimental database; and (3) evaluate the probability of BRB failure, given the quantified demand and capacity, through structural reliability analyses. Parametric studies were conducted to investigate the effects of the seismic load, and characteristics of the BRB and BRBF on the probability of brace failure. In addition, fragility curves (i.e., conditional probabilities of brace failure given ground shaking intensity parameters) were created by the proposed framework. While the framework presented in this paper is applied to the assessment of BRBFs, the modular nature of the framework components allows for application to other structural components and systems.展开更多
基金support by the National Natural Science Foundation of China(Grant Nos.52108376 and 51908371)China Postdoctoral Science Foundation(Grant No.2022T150436).
文摘This paper presents a simplified elastic continuum method for calculating the restraint effect of isolation piles on tunneling-induced vertical ground displacement,which can consider not only the relative sliding of the pile‒soil interface but also the pile rowesoil interaction.The proposed method is verified by comparisons with existing theoretical methods,including the boundary element method and the elastic foundation method.The results reveal the restraining mechanism of the isolation piles on vertical ground displacements due to tunneling,i.e.the positive and negative restraint effects exerted by the isolation piles jointly drive the ground vertical displacement along the depth direction from the original tunneling-induced nonlinear variation situation to a relatively uniform situation.The results also indicate that the stiffness of the pile‒soil interface,including the pile shaft‒surrounding soil interface and pile tip-supporting soil interface,describes the strength of the pile‒soil interaction.The pile rows can confine the vertical ground displacement caused by the tunnel excavation to the inner side of the isolation piles and effectively prevent the vertical ground displacement from expanding further toward the outer side of the isolation piles.
文摘Metabolic rewiring underlies the effector functions of macrophages1-3,but the mechanisms involved remain incompletely defined.Here,using unbiased metabolomics and stable isotope-assisted tracing,we show that an inflammatory aspartate argininosuccinate shunt is induced following lipopolysaccharide stimulation.The shunt,supported by increased argininosuccinate synthase(ASS1)expression,also leads to increased cytosolic fumarate levels and fumarate-mediated protein succination.Pharmacological inhibition and genetic ablation of the tricarboxylic acid cycle enzyme fumarate hydratase(FH)further increases intracellular fumarate levels.
基金supported by the National natural Science Foundation of China [grant numbers 12172198, 11272189 and 52078283]Youth Innovation Technology Project of Higher School in Shandong Province [grant number 2019KJG015]。
文摘Based on the background of structural protection and Disaster Reduction Engineering, the dynamic behaviour and failure mechanism of restrained beams in portal steel frames in localised fire are investigated via experimental measurement and numerical simulation techniques. Comprehensive parametric studies are carried out to discuss the influence of end connection types, temperature, impact velocity,impact mass and span-to-depth ratio(SDR) on the dynamic response of the beams. The characteristics of deformation, internal force and energy distribution about the restrained beams and its joints are investigated. A temperature dependent criterion for evaluating the frame joint performance is proposed to measure the degree of performance degradation and impact resistance of the joint. The dynamic displacement amplification factor in different temperature environments are proposed for the different beam end constraint types and SDRs. Results of the experimental and numerical analysis show that the welded connection(WC) of three typical joint types is the strongest, and the extended endplate connection(EEC) is the weakest in terms of the impact resistance performance. With regard to the failure mode of the joint, the failure positions of the WC and the welded-bolted connection are located in the inner web of the column. Meanwhile, the EEC is located in the connection position between the beam and the endplate. Three different internal force stages and two obvious critical temperature boundaries of the restrained beams emerge with the increase in temperature, and they have significant characteristics in terms of deformation trend, internal force transfer and energy distribution. During the impact, a phenomenon known as “compression arch action” develops into “catenary action” with the increase in deflection in the frame beam mechanism.
文摘Accurate estimates of ductility demands on buckling-restrained braced frames(BRBFs)are crucial to performance-based design of BRBFs.An analytical study on the seismic behavior of BRBFs has been conducted at the ATLSS Center,Lehigh University to prepare for an upcoming experimental program.The analysis program DRAIN-2DX was used to model a one-bay,four-story prototype BRBF including material and geometric nonlinearities.The buckling- restrained brace(BRB)model incorporates both isotropic and kinematic hardening.Nonlinear static pushover and time- history analyses were performed on the prototype BRBF.Performance objectives for the BRBs were defined and used to evaluate the time-history analysis results.Particular emphasis was placed on global ductility demands and ductility demands on the BRBs.These demands were compared with anticipated ductility capacities.The analysis results,along with results from similar previous studies,are used to evaluate the BRBF design provisions that have been recommended for codification in the United States.The results show that BRB maximum ductility demands can be as high as 20 to 25.These demands significantly exceed those anticipated by the BRBF recommended provisions.Results from the static pushover and time- history analyses are used to demonstrate why the ductility demands exceed those anticipated by the recommended provisions. The BRB qualification testing protocol contained in the BRBF recommended provisions is shown to be inadequate because it requires only a maximum ductility demand of at most 7.5.Modifications to the testing protocol are recommended.
文摘In sheet metal forming, drawbeads are often used to control uneven material flow which may cause defects such as wrinkles, fracture, surface distortion and springback. Appropriate setting and adjusting the drawbead force is one of the most important pa- rameters in sheet metal forming process control. This paper derives the model of loop drawbead restraining force (DBRF) using plastic forming theory, and gives the min imum blankholding force. Experiments are carried out to verify the proposed DBRF model. The good agreement between the calculated values and experiments data justi- fies the proposed loop drawbead restraining force model.
基金Science Council in Chinese Taipei Under Grant No.NSC 94-2211-E-035-015
文摘Buckling restrained braces (BRBs) have been widely applied in seismic mitigation since they were introduced in the 1970s. However, traditional BRBs have several disadvantages caused by using a steel tube to envelope the mortar to prevent the core plate from buckling, such as: complex interfaces between the materials used, uncertain precision, and time consumption during the manufacturing processes. In this study, a new device called the multi-curve buckling restrained brace (MC-BRB) is proposed to overcome these disadvantages. The new device consists of a core plate with multiple neck portions assembled to form multiple energy dissipation segments, and the enlarged segment, lateral support elements and constraining elements to prevent the BRB from buckling. The enlarged segment located in the middle of the core plate can be welded to the lateral support and constraining elements to increase buckling resistance and to prevent them from sliding during earthquakes. Component tests and a series of shaking table tests on a full-scale steel structure equipped with MC-BRBs were carried out to investigate the behavior and capability of this new BRB design for seismic mitigation. The experimental results illustrate that the MC-BRB possesses a stable mechanical behavior under cyclic loadings and provides good protection to structures during earthquakes. Also, a mathematical model has been developed to simulate the mechanical characteristics of BRBs.
基金Earthquake Engineering and Engineering Vibration Laboratory Foundation,Institute of Engineering Mechanics, China Earthquake Administration Under Grant No.2009a1the National Natural Science Foundation of China under Grant No.50878071
文摘This paper presents an experimental study to investigate the performance of shape memory alloy(SMA) restrainers for mitigating the pounding and unseating of highway bridges when subjected to seismic excitations.Mechanical property tests of the SMA wire used in the restrainers are conducted first to understand the pseudo-elastic characteristics of the material.Then,a series of shaking table tests are carried out on a highway bridge model.The structural responses of the highway bridge model equipped with SMA restrainers,installed in the form of deck-deck and deck-pile connections,are analyzed and compared with the uncontrolled structures.The test results of this study indicate that the SMA restrainers are not only effective in preventing unseating but also in suppressing the seismic-induced pounding of the highway bridge model used in this study.
文摘High-performance concrete (HPC) is stronger and more durable than conventional concrete. However, shrinkage and shrinkage cracking are common phenomena in HPC, especially early-age cracking. This study assessed early-age cracking of HPC for two mixtures using restrained ring tests. The two mixtures were produced with water/binder mass ratio (mw/mB) of 0.22 and 0.40, respectively. The results show that, with greater steel thickness, the higher degree of restraint resulted in a higher interface pressure and earlier cracking. With steel thickness of 6 mm, 19 mm, and 30 mm, the age of cracking were, respectively, 12 days, 8 days, and 5.4 days with the mw/mB = 0.22 mixture; and 22.5 days, 12.6 days, and 7.1 days with the mw/mB= 0.40 mixture. Cases of the same steel thickness show that the ring specimens with a thicker concrete wall crack later. With the mw/mB = 0.22 mixture, concrete walls with thicknesses of 37.5 mm, 75 mm, and 112.5 mm cracked at 3.4 days, 8.0 days, and 9.8 days, respectively; with the mw/mB = 0.40 mixture, the ages of cracking were 7.1 days, 12.6 days, and 16.0 days, respectively.
基金Supported by Science and Technology Development Foundation of Shanghai (015211009).
文摘Due to complexities of draw-bead restraining force calculated according to theory and depending on sheet metal forming properties experiment testing system, a simplified method to calculate draw-bead restraining force is put forward by experimental method in cup-shaped drawing process. The experimental results were compared with numerical results and proved agreement. It shows the method is effective.
基金supported by the National Natural Science Foundation of China(Grant No.50479054)
文摘A pile-restrained pontoon-plate floating breakwater is proposed in this paper. The laboratory physical-model tests are conducted to investigate the wave-dissipation property and heave-motion response of a model. The influence of the model's geometric parameters including relative pontoon width, plate width, number of plates and pontoon draft on wavedissipation performance and heave-motion response are discussed, as well as the correlation between these two factors. The result indicates that wave-dissipation performance of the proposed structure is better than the pontoon structure: its transmission coefficient and heave-motion height are reduced by 0.2 and 0.3, respectively, in comparison with those of the pile-restrained pontoon model at a relative pontoon width of 0.2.
基金the Natural Science Research Project from Bureau of Public Health of Sichuan Province,No. 090194the Natural Science Research Project of Science Technology Bureau of Luzhou,No. 090102
文摘Our preliminary study demonstrated that neuropeptide Y (NPY)/nestin-positive cells exhibit a consistent spatial distribution in the hippocampus of normal adult rats. However, following severe acute and chronic stress-induced impaired learning and memory, synchronous decreased expression of nestin and NPY takes place in the hippocampus, and the underlying mechanisms remain unclear. In the present study, acute and chronic stress rat models were established using combined restrained and inverted stress. Results showed that learning and memory significantly decreased in acute and chronic stress rats. In addition, hippocampal cells were damaged, in particular in the acute stress rats, and nestin and NPY expression, as well as the number of NPY/nestin-positive cells in the CA3 region, significantly decreased. Furthermore, mature neurofilament 200-positive neurons were absent in the chronic stress rats. The NPY and cytoskeletal protein system equally contributed to stress-induced early learning and memory deficits as well as sustained cerebral iniurv in the adult hippocampus.
基金Financial support received from the Scientific Research Fund of Institute of Engineering Mechanics,China Earthquake Administration under Grant No.2019EEEVL05the National Key Research and Development Program of China under Grant No.2016YFC0701106the National Natural Science Foundation of China under Grant No.51578473 are gratefully acknowledged.
文摘Steel frames equipped with buckling restrained braces(BRBs)have been increasingly applied in earthquake-prone areas given their excellent capacity for resisting lateral forces.Therefore,special attention has been paid to the seismic risk assessment(SRA)of such structures,e.g.,seismic fragility analysis.Conventional approaches,e.g.,nonlinear finite element simulation(NFES),are computationally inefficient for SRA analysis particularly for large-scale steel BRB frame structures.In this study,amachine learning(ML)-based seismic fragility analysis framework is established to effectively assess the risk to structures under seismic loading conditions.An optimal artificial neural network model can be trained using calculated damage and intensity measures,a technique which will be used to compute the fragility curves of a steel BRB frame instead of employing NFES.Numerical results show that a highly efficient instantaneous failure probability assessment can be made with the proposed framework for realistic large-scale building structures.
文摘This paper addresses the free transverse vibrations of thin simply supported nonhomogeneous isotropic rectangular plates of bilinearly varying thickness with elastically restrained edges against rotation. The Gram-Schmidt process has been used to generate two-dimensional boundary characteristic orthogonal polynomials, which have been used in the Rayleigh-Ritz method to study the problem. The lowest three frequencies have been computed for various values of nonhomogeneous parameters, thickness parameters, aspect ratio and flexibility parameters. A comparison of the results with those available in the literature has been made. Three-dimensional mode shapes for the specified plate have been presented.
基金This paper was supported by the National "Eleven .Five" Scientific and Technological Supporting project "Test and demonstration for typical region city forest construction technol-ogy(2006BAD03A19) "
文摘The extracts from leaves of Manglietia insignis (Wall) Blume, Manglietia chingii Dandy and Manglietia yuyuanensis Law were prepared by organic solvent extraction and their components were analyzed by GC/MS and quantified. Meanwhile, the free radicals restraining activities were detected. The 21 compounds in M. insignis, 36 compounds in M. chigii and 20 compounds in M. yuyuanensis were identified. There were 11 common components in the extracts from three Manglietia species, and 12 components in two Manglietia species. The results of relative contents of every component in three extracts showed that the main constituents of M. insignis were terpenoids and alkene, amounting to 38.93%, followed by alkane (28.18%), the nitrogen containing compounds (15.73%) and aromatic compounds (7.23 %). The main constituents of leaf extract from M. chingii were the terpenoids and alkene, carboxylic acid, alkane and aromatic compounds, amounting to 30.22%, 14.17%, 13.87% and 13.29%, respectively, The main constituents of M. yuyuanensis were alcohol compounds, the terpenoids and alkene, and aromatic compounds, amounting to 28.00%, 25.38% and 18.00% respectively. The results showed that the three extracts had strong function of restraining oxygen free radicals. The ultra oxygen anions activity was restrained at the highest level, when the three extracts were diluted by hundred-fold, whereas the restraining capacity of hydroxyl free radicals reached maximum, when the three extracts were diluted by twenty-fold. The above results provide scientific evidences for further approaching the ecological healthy function of three MangUetia species
基金supported by the National Natural Science Foundation of China(61073106)the Aerospace Science and Technology Innovation Fund(CASC201105)
文摘An image segmentation algorithm of the restrained fuzzy Kohonen clustering network (RFKCN) based on high- dimension fuzzy character is proposed. The algorithm includes two steps. The first step is the fuzzification of pixels in which two redundant images are built by fuzzy mean value and fuzzy median value. The second step is to construct a three-dimensional (3-D) feature vector of redundant images and their original images and cluster the feature vector through RFKCN, to realize image seg- mentation. The proposed algorithm fully takes into account not only gray distribution information of pixels, but also relevant information and fuzzy information among neighboring pixels in constructing 3- D character space. Based on the combination of competitiveness, redundancy and complementary of the information, the proposed algorithm improves the accuracy of clustering. Theoretical anal- yses and experimental results demonstrate that the proposed algorithm has a good segmentation performance.
基金the National Natural Science Foundation of China (50678054)
文摘To investigate the early-age behaviors of concrete under a restrained condition, a set of apparatus was developed. In this way, the tensile creep and other early-age properties can be investigated in depth. By measuring the modulus of elasticity of concrete, synchronous shrinkage of concrete and steel rings and free shrinkage of concrete, the deformations of concrete ring can be quantified respectively. The experimental results show the tensile stress in concrete is time-dependent, and the stress at cracking is much lower than the tensile strength at that age; the tensile creep plays an important role in relaxing the tensile stress and postponing the cracking of concrete.
基金Project supported by the National Natural Science Foundation of China (Grant No.10872163)the Natural Science Foundation of Education Department of Shaanxi Province (Grant No.08JK394)
文摘The element-free Galerkin method is proposed to solve free vibration of rectangular plates with finite interior elastic point supports and elastically restrained edges.Based on the extended Hamilton's principle for the elastic dynamics system,the dimensionless equations of motion of rectangular plates with finite interior elastic point supports and the edge elastically restrained are established using the element-free Galerkin method.Through numerical calculation,curves of the natural frequency of thin plates with three edges simply supported and one edge elastically restrained,and three edges clamped and the other edge elastically restrained versus the spring constant,locations of elastic point support and the elastic stiffness of edge elastically restrained are obtained.Effects of elastic point supports and edge elastically restrained on the free vibration characteristics of the thin plates are analyzed.
文摘BACKGROUND:Motor vehicles crashes(MVCs) are the leading cause of injury related morbidity and mortality in developed countries. Recent evidence proves that properly used child seat belts can dramatically reduce the risk of severe and life-threatening injury from MVCs. There are rarities of thought and inspiration regarding the use of child seat belts in our society and region,therefore we lack of data regarding factors and paucity of usage of child seat belts in motor vehicles. This study aimed to assess the knowledge and attitudes of child seat belt usage among the educated population in Karachi,Pakistan.METHODS:Altogether 304 employees were investigated. They were employees of Aga Khan University who were using their cars and having children younger than 10 years old. A cross sectional observational study was designed,and a 36-item questionnaire in English was used to collect data on participants' demographic details,designation,educational level,economic status,validity of driving license,number of children and cars,availability of adult seat belts and child seat belts along with their functionality,awareness,knowledge and attitude toward its use,and reason of not using these devices. SPSS version 20 for Windows was used to analyze the data and the Chi-square test was used.RESULTS:Totally 290 participants were recruited with a response rate of 72%(212). Of 212 participants,126(59%) were male. 154(72.6%) participants had valid driver licenses,and 154(72.6%) had adult seat belts in their vehicles. Only 32(15%) reported regular use of adult seat belts. Although 168(79.2%) participants had some knowledge about child restrains(CRs),only 65(22%) had CRs in their cars. Eighty-two(38.7%) participants got the knowledge about CRs and seat belts from media. Mothers were more concerned about the use of CRs than fathers. Only 14(6.6%) parents were found to use both adult and child seat belts all the time. Of the 157 parents who did not us use CRs,42 considered unnecessary,35 lacked relevant knowledge. But 15 parents used CR against their children's wills.CONCLUSIONS:The pattern of CR usage among the employees at Aga Khan University,Karachi is dictated by the unavailability of CR,followed by ignorance,inconvenience,and nonacceptance by their children. The important issue of CR has consistently been ignored over the years and it has never gained enough popularity in Pakistan.
基金Funded by National Natural Science Foundation of China(Nos.51478200 and 51178202)
文摘Hydration process, crack potential and setting time of concrete grade C30, C40 and C50 were monitored by using a non-contact electrical resistivity apparatus, a novel plastic ring mould and penetration resistance methods, respectively. The results show the highest resistivity of C30 at the early stage until a point when C50 accelerated and overtook the others. It has been experimentally confirmed that the crossing point of C30 and C50 corresponds to the final setting time of C50. From resistivity derivative curve, four different stages were observed upon which the hydration process is classified; these are dissolution, induction, acceleration and deceleration periods. Consequently, restrained shrinkage crack and setting time results demonstrated that C50 set and cracked the earliest. The cracking time of all the samples occurred within a reasonable experimental period thus the novel plastic ring is a convenient method for predicting concrete's crack potential. The highest inflection time(t_i) obtained from resistivity curve and the final setting time(t_f) were used with crack time(t_c) in coming up with mathematical models for the prediction of concrete's cracking age for the range of concrete grade considered. Finally, an ANSYS numerical simulation supports the experimental findings in terms of the earliest crack age of C50 and the crack location.
基金Federal Highway Administration Under Grant No. DDEGRD-06-X-00408
文摘Buckling-restrained braces (BRBs) have recently become popular in the United States for use as primary members of seismic lateral-force-resisting systems. A BRB is a steel brace that does not buckle in compression but instead yields in both tension and compression. Although design guidelines for BRB applications have been developed, systematic procedures for assessing performance and quantifying reliability are still needed. This paper presents an analytical framework for assessing buckling-restrained braced frame (BRBF) reliability when subjected to seismic loads. This framework efficiently quantifies the risk of BRB failure due to low-cycle fatigue fracture of the BRB core. The procedure includes a series of components that: (1) quantify BRB demand in terms of BRB core deformation histories generated through stochastic dynamic analyses; (2) quantify the limit-state of a BRB in terms of its remaining cumulative plastic ductility capacity based on an experimental database; and (3) evaluate the probability of BRB failure, given the quantified demand and capacity, through structural reliability analyses. Parametric studies were conducted to investigate the effects of the seismic load, and characteristics of the BRB and BRBF on the probability of brace failure. In addition, fragility curves (i.e., conditional probabilities of brace failure given ground shaking intensity parameters) were created by the proposed framework. While the framework presented in this paper is applied to the assessment of BRBFs, the modular nature of the framework components allows for application to other structural components and systems.