Experimental study of a highway bridge with shape memory alloy restrainers focusing on the mitigation of unseating and pounding

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.

Underestimated Methane Emissions from Solid Waste Disposal Sites Reveal Missed Greenhouse Gas Mitigation Opportunities

1.Introduction Cities are responsible for approximately 70%of all anthropogenic greenhouse gas(GHG)emissions and about 60%of all anthropogenic methane(CH4)emissions[1,2].Solid waste disposal sites(including landfills and dumpsites),which are prevalent in global cities,emit CH4 generated from the anaerobic biodegradation of municipal solid waste(MSW).Notably,the proportions of CH4 emissions from disposal sites surpass 50%of the total CH4 emissions in some megalopolises[3].CH4 has a high global warming potential(GWP),being 28 times stronger than carbon dioxide(CO_(2))over a 100-year period and 80 times stronger over a 20-year period[4].Understanding and mitigating CH4 emissions from solid waste disposal sites is particularly pertinent and pressing,considering that the latest Synthesis Report from the Intergovernmental Panel on Climate Change(IPCC)emphasizes that the current pace of mitigation and adaptation policies and measures falls short of restraining global temperature rise to under 1.5℃ within the 21st century[4].More than 150 countries signed the Global Methane Pledge at the United Nations Climate Change Conference in Glasgow(COP26),which aims to reduce global annual CH4 emissions by 30%by 2030,compared with emissions in 2020[5].

用于抵抗扭转采取边缘弹性约束下的单轴压缩下板材极限强度:一种新的综合方法

The ultimate strength of platings under compression is one of the most important factors to be addressed in the ship design.Current Rules for ship structural design generally provide explicit strength check criteria against buckling for simply supported and clamped platings.Nevertheless,ship platings generally exhibit an intermediate behaviour between the simple support and the clamped conditions,which implies that the torsional stiffness of supporting members should be duly considered.Hence,the main aim of this study is the development of new design formulas for the ultimate strength of platings under uniaxial compression,with short and/or long edges elastically restrained against torsion.In this respect,two benchmark studies are performed.The former is devoted to the development of new equations for the elastic buckling coefficients of platings with edges elastically restrained against torsion,based on the results of the eigenvalue buckling analysis,performed by Ansys Mechanical APDL.The latter investigates the ultimate strength of platings with elastically restrained edges,by systematically varying the plate slenderness ratio and the torsional stiffness of supporting members.Finally,the effectiveness of the new formulation is checked against a wide number of finite element(FE)simulations,to cover the entire design space of ship platings.

SCIENCE AND TECHNOLOGY

Brain-Machine Interface System Unveiled at Zhongguancun Forum The NeuCyber Array BMI System,a self-developed brain-machine interface(BMI)system from China,was unveiled at the opening ceremony of the 2024 Zhongguancun Forum(ZGC Forum)on April 25 in Beijing.At the forum,a video demonstration revealed a remarkable feat:a monkey,with its hands restrained and soft electrode filaments implanted in its brain,grasped a strawberry with an isolated robotic arm that was controlled by simply using its"thoughts."

Differential tectonic evolution and formation mechanism of three subsags in Wenchang Sag of Pearl River Mouth Basin,South China Sea

Notable differences in the structural characteristics and evolution of three adjacent sub-sags,i.e.,the Wenchang sub-sags A,B,and C,on the downthrown side of the Zhu IlI South Fault in the Wenchang Sag,are significant as they affect the formation and distribution of the oil and gas in these three sub-sags.However,the differences in their tectonic evolutions and formation mechanisms have not yet been adequately explained.In this paper,stress analysis,equilibrium profiles,and paleogeomorphic restora-tion,are used to investigate the dynamic settings,formation mechanisms,and influencing factors of the structural deformation related to the formation of the Wenchang Sag based on interpretation of seismic data.The results of the stress analysis suggest clockwise deflection of the regional tensile stress direction from a WNW-ESE trend during the Early Paleocene to NW-SE and NNW-SSE trends during the Eocene,to a nearly N-S trend during the Oligocene,and finally to a NNE-SSW trend during the Miocene.This clockwise rotation of the regional tensile stress direction led to the formation of a dextral strike-slip stress component parallel to the NE-trending Zhu I South Fault.This strike-slip stress component formed a releasing bend in sub-sag A,and may be associated with the continuous subsidence of a thick sedimentary layer in sub-sag A.It also created a restraining bend in sub-sag B,which underwent multiple structural inversions during its extension and subsidence and has a relatively s mall sedimentary thick-ness.The double restraining bend in sub-sag C is considered to have been strongly uplifted and eroded in response to this strike-slip stress component.Four obvious structural inversions in sub-sag B are iden-tified in this paper.These structural inversions correspond to the last four regional tectonic movements.This interpretation suggests that the formation of the structural inversions was likely related to the strong tensile stress and the small intersection angle between the direction of the regional tensile stress and the pre-existing boundary fault.The rotation of the tensile stress direction was responsible for the strike-slip movement on the pre-existing boundary fault and the formation of the releasing bend and restraining bend,which controlled the structural evolutions of the sub-sags.This reasonably explains the differential tectonic evolution of these three sub-sags in the Wenchang Sag,and provides a crucial idea forstructuralanalysisof similarbasins.

Macrophage fumarate hydratase restrains mtRNA-mediated interferon production

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.

Effects of connection types and elevated temperature on the impact behaviour of restrained beam in portal steel frame

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.

Vibration Control of an Experimental Flexible Manipulator Against Input Saturation

Dear Editor, This letter considers the control problem of an experimental flexible manipulator in position tracking, vibration suppression, and saturation compensation. Based on the backstepping technology and a Nussbaum function, we develop an anti-windup control to restrain the manipulator’s vibration, realize the desire trajectory tracking, and eliminate the saturation.

Analytical solutions for the restraint effect of isolation piles against tunneling-induced vertical ground displacements

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.

少年外交官 毕生外交梦

As the saying goes,in the prime of life,teenagers should be more energetic and unrestrained.At various CDMUN(中报模拟联合国)conferences,she seized every opportunity which can improve herself and composed(组成)her youth with actions.

Parametric study on performance of bridge retrofitted by unseating prevention devices

Over the past decade, seismically induced damage to bridges has been widely reported following major earthquakes such as the 1994 Northridge, 1995 Kobe and 1999 Chi-Chi events. Since these earthquakes, restrainers and stoppers have been installed on bridges to prevent unseating and excessive displacements, respectively. Alternatively, column jacketing has also been proven to be effective. However, the enhanced shear strength may result in extra retrofitting works on the footing. For bridges damaged in the Chi-Chi earthquake, investigations revealed that most bridge columns experienced none-to-minor damage in the longitudinal direction. The reason for this unexpected performance was the construction practice of using a rubber bearing, which is an unbolted design that may slide under large lateral forces. In this paper, parametric studies on simply-supported bridges retrofitted by a restrainer or concrete shear key along the longitudinal and transverse axes were carried out. The research focuses on finding suitable combinations of the design force and gap spacing so the restrainer and concrete shear key can be used as an unseating prevention device, with respect to the allowable column damage in terms of displacement ductility under near-fault type earthquakes. A two-lane PCI-girder bridge was selected as the benchmark model. In the longitudinal direction, a total of nine combinations considering yielding strength and gap spacing for the restrainer were analyzed; while parameters for the concrete shear key were divided into three shear force levels and three gap spacings. In the transverse direction, a similar approach was adapted, except smaller gap spacing was used. For each of the above mentioned earthquakes, seven input ground motions were selected and their PGAs were adjusted to 0.36g and 0.45g as the Design earthquake and Maximum Considerable Earthquake, respectively. Based on the results of nonlinear time history analyses, proper parameters to design the restrainers and concrete shear keys are obtained. Responses obtained from numerical simulations under the Chi-Chi earthquake leaded to new implications to design those devices. Restrainer should not exceed its breaking strain and sufficient unseating length will be needed always. Concrete Shear key was determined by considering both displacement demand of the superstructure and displacement ductility of the column at the same time. Further study is needed to provide optimal design parameters for use in performance based bridge design.

英语单词扩展对比记忆法

在英语学习中,常会遇到一些词,其前或其后加上一两个字母后,意思大不相同,学生容易将它们相混淆。若将它们放在一起记忆,既利于比较,又容易记住,现在举例如下: 1.arc,arch,archaeology arc弧,arch拱门,archaeology考古(学) 你可以这样记这些单词:先在墓室壁上画个arc,然后再开个arch,就可以进行archaeology了。 2.tact,tract,abstract。

A LOOP DRAWBEAD RESTRAINING FORCE MODEL IN SHEET METAL DEEP DRAWING PROCESS

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.

Observation and Study of Land Surface Parameters over Gobi in Typical Arid Region

According to the need of popular land surface process models, characteristics and rules of some key land surface process and soil parameters over Gobi in typical arid region of Northwest China are analyzed by using the data observed during the intensive observation period of the Dunhuang Land–Surface Process Field Experiment (DLSPFE) (May–June 2000). Using the relative reflection as weighting factor, the weighted mean of the surface albedo over Dunhuang Gobi in typical arid region is calculated and its values are 0.255 ± 0.021. After canceling the interference of the buildings, the mean values of the roughness length averaged with logarithm is 0.0019 ± 0.00071 m. After removing the influence of the oasis, the soil wetness factor computed with data under condition of no precipitation is 0.0045. After removing the influence of the precipitation , the mean values of the soil heat capacity over Dunhuang Gobi in typical arid region is 1.12 × 106 J m−3K−1, a bit smaller than the values observed in HEIFE. But the soil heat diffusivity and conductivity are about one of those observed in HEIFE. The soil water content over Dunhuang Gobi in typical synoptic condition is very little and does not exceed 1% basically.

Mathematical modeling and full-scale shaking table tests for multi-curve buckling restrained braces

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.

Seismic performance of cable-sliding friction bearing system for isolated bridges

During past strong earthquakes, highway bridges have sustained severe damage or even collapse due to excessive displacements and/or very large lateral forces. For commonly used isolation bearings with a pure friction sliding surface, seismic forces may be reduced but displacements are often unconstrained. In this paper, an alternative seismic bearing system, called the cable-sliding friction bearing system, is developed by integrating seismic isolation devices with displacement restrainers consisting of cables attached to the upper and lower plates of the bearing. Restoring forces are provided to limit the displacements of the sliding component. Design parameters including the length and stiffness of the cables, friction coefficient, strength of the shear bolt in a fixed-type bearing, and movements under earthquake excitations are discussed. Laboratory testing of a prototype bearing subjected to vertical loads and quasi-static cyclic lateral loads, and corresponding numerical finite element simulation analysis, were carried out. It is shown that the numerical simulation shows good agreement with the experimental force-displacement hysteretic response, indicating the viability of the new bearing system. In addition, practical application of this bearing system to a multi-span bridge in China and its design advantages are discussed.

Effects of fibers on expansive shotcrete mixtures consisting of calcium sulfoaluminate cement,ordinary Portland cement,and calcium sulfate

The mining industry often uses shotcrete for ground stabilization. However, cracking within shotcrete is commonly observed, which delays production schedules and increases maintenance costs. A possible crack reduction method is using expansive shotcrete mixture consisting of calcium sulfoaluminate cement(CSA), ordinary Portland cement(OPC), and calcium sulfate(CS) to reduce shrinkage. Furthermore, fibers can be added to the mixture to restrain expansion and impede cracking. The objective of this paper is to study the effects of nylon fiber, glass fiber, and steel fiber on an expansive shotcrete mixture that can better resist cracking. In this study, parameters such as density, water absorption, volume of permeable voids, unconfined compressive strength(UCS), splitting tensile strength(STS), and volume change of fiber-added expansive mixtures were determined at different time periods(i.e. the strengths on the 28 th day, and the volume changes on the 1 st, 7 th, 14 th, 21 st, and 28 th days). The results show that addition of fibers can improve mixture durability, in the form of decreased water absorption and reduced permeable pore space content. Moreover, the expansion of the CSA-OPC-CS mixture was restrained up to50% by glass fiber, up to 43% by nylon fiber, and up to 28% by steel fiber. The results show that the STS was improved by 57% with glass fiber addition, 43% with steel fiber addition, and 38% with nylon fiber addition. The UCS was also increased by 31% after steel fiber addition, 26% after nylon fiber addition, and16% after glass fiber addition. These results suggest that fiber additions to the expansive shotcrete mixtures can improve durability and strengths while controlling expansion.

An Efficient Method for Local Buckling Analysis of Stiffened Panels

The local buckling of stiffened panels is one of possible failure modes and concerned by engineers in the preliminary design of lightweight structures. In practice,a simplified model,i.e.,a rectangular plate with elastically restrained along its unloaded edges,is established and the Ritz method is usually employed for solutions. To use the Ritz method,however,the loaded edges of the plate are usually assumed to be simply supported. An empirical correction factor has to be used to account for clamped loaded edges. Here,a simple and efficient method,called the quadrature element method(QEM),is presented for obtaining accurate buckling behavior of rectangular plates with any combinations of boundary conditions, including the elastically restrained conditions. Different from the conventional high order finite element method(FEM),non-uniformly distributed nodes are used,and thus the method can achieve an exponential rate of convergence. Formulations are worked out in detail. A computer program is developed. Improvement of solution accuracy can be easily achieved by changing the number of element nodes in the computer program. Several numerical examples are given. Results are compared with either existing solutions or finite element data for verifications. It is shown that high solution accuracy is achieved. In addition,the proposed method and developed computer program can allow quick analysis of local buckling of stiffened panels and thus is suitable for optimization routines in the preliminary design stage.

Assessment of early-age cracking of high-performance concrete in restrained ring specimens

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.

EXPERIMENTAL TESTING OF DRAW-BEAD RESTRAINING FORCE IN SHEET METAL FORMING

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.