Resilient performance of self-centering hybrid rocking walls with curved interface under pseudo-static loading

Frame and rocking wall(FRW)structures have excellent resilient performance during earthquakes.However,the concrete at interfacial corners of rocking walls(RWs)is easily crushed due to local extreme compression during the rocking process.An innovative RW with a curved interface is proposed to prevent interfacial corners from producing local damage,enhancing its earthquake resilient performance(ERP).The precast wall panel with a curved interface is assembled into an integral self-centering hybrid rocking wall(SCRW)by two post-tensioned unbonded prestressed tendons.Moreover,two ordinary energy dissipation steel rebars and two shear reinforcements are arranged to increase the energy dissipation capacity and lateral resistance.Two SCRW specimens and one monolithic reinforced concrete(RC)shear wall(SW)were tested under pseudo-static loading to compare the ERPs of the proposed SCRW and the SW,focusing on studying the effect of the curved interface on the SCRW.The key resilient performance of rocking effects,failure modes,and hysteretic properties of the SCRW were explored.The results show that nonlinear deformations of the SCRW are concentrated along the interface between the SCRW and the foundation,avoiding damage within the SCRW.The restoring force provided by the prestressed tendons can effectively realize self-centering capacity with small residual deformation,and the resilient performance of the SCRW is better than that of monolithic SW.In addition,the curved interface of the SCRW makes the rocking center change and move inward,partially relieving the stress concentration and crush of concrete.The rocking range of the rocking center is about 41.4%of the width of the SCRW.

Role of End-ring Configuration in Shaping IE4 Induction Motor Performance

The performance characteristics,particularly the starting performance of direct line-fed induction motors,which are mainly influenced by the design of the rotor,are crucial considerations for end-users.It is quite a challenging issue for motor manufacturers to enhance the starting performance of existing mass-produced motors with minimal modifications and expenses.In this paper,a simple and cost-effective method to improve the starting performance of a commercial squirrel-cage induction motor(SCIM)is proposed.The influence of geometric parameters of the end-ring on the performance characteristics,including starting(locked rotor)torque,pull-up and break down torque,starting current,rotor electric parameters,current density,power losses,and efficiency have been comprehensively investigated.It has been revealed that among the other end-ring design parameters,the ring thickness has a significant effect on the performance characteristics.An optimal end-ring thickness is determined,and its performance characteristics have been compared to those of its initial counterpart.Numeric and parametric analyses have been conducted using a 2D time-stepping finite element method(FEM).The FEM results were validated using experimental measurements obtained from an 11 kW SCIM prototype.

Fragility Curves of Existing RC Buildings Based on Specific Structural Performance Levels

In seismic risk mitigation policies, fragility functions of existing buildings play a fundamental role. In this paper, a procedure to develop analytical fragility curves for Moment Resisting Frame Reinforced Concrete buildings is presented. The design of the selected building typologies was performed according to the codes at the time of construction using force-based methods and the state of the practice at the time of construction. A total of 216 building classes were defined, considering different ages, number of storeys, infill panels, plan dimensions, beam stiffness, and concrete strength. The investigated buildings can be considered low-engineered buildings, using no seismic codes or old seismic codes. The seismic capacity of the selected models representing the existing RC buildings has been evaluated through non-linear dynamic simulations. Seismic response has been analyzed, considering various peak and integral intensity measures and various response parameters, such as ductility demands and Interstorey Drift Ratio (IDR). A new relationship among structural performance, damage levels and interstorey drift ratios for each studied type is introduced, which is calibrated using the damage levels described in EMS98. It is important to highlight that in this study, different thresholds of IDR have been associated with different typologies, considering their different ductility member levels after their different structural responses. Fragility Curves (FCs) for the studied structural types are set up, developed and discussed.

Direct tension and fracture resistance curves of ultra high performance marine composite materials

Fracture behavior is one of the most important,yet still little understood properties of ultra-high performance cementitious composites(UHPCC),a new marine structural engineering material. Research on the fracture and direct tension behavior of UHPCC was carried out.The constitution law of UHPCC was divided into three phases:pre-partial debonding,partial debonding,and pullout phases.A direct tension constitution law was constructed based on the proposed fiber reinforcing parameter as a function of fiber volume fraction,fiber diameter and length,and fiber bonding strength.With the definition of linear crack shape,the energy release rate of UHPCC was derived and the R-curve equation was calculated from this.Loading tests of UHPCC using a three-point bending beam with an initial notch were carried out.The predictions from the proposed R-curve were in good agreement with the test results, indicating that the proposed R-curve accurately describes the fracture resistance of UHPCC.Introduction of a fiber reinforcement parameter bridges the fracture property R-curve and micro-composites’ mechanics parameters together.This has laid the foundation for further research into fracture properties based on micro-mechanics.The proposed tension constitution law and R-curve can be references for future UHPCC fracture evaluation.

Comparative Thermal Performance in SiO_(2)–H_(2)O and (MoS_(2)–SiO_(2))–H_(2)O Over a Curved Stretching Semi-Infinite Region: A Numerical Investigation

The investigation of Thermal performance in nanofluids and hybrid nanofluids over a curved stretching infinite region strengthens its roots in engineering and industry.Therefore,the comparative thermal analysis in SiO_(2)–H_(2)O and(MoS_(2)–SiO_(2))–H_(2)O is conducted over curved stretching surface.The model is reduced in the dimensional version via similarity transformation and then treated numerically.The velocity and thermal behavior for both the fluids is decorated against the preeminent parameters.From the analysis,it is examined that the motion of under consideration fluids declines against Fr and
.The thermal performance enhances for higher volumetric fraction and
.Further,it is noticed that thermal performance prevailed in(MoS_(2)–SiO_(2))–H_(2)O throughout the analysis.Therefore,(MoS_(2)–SiO_(2))–H_(2)O is better for industrial and engineering uses where high heat transfer is required to accomplished different processes of production.

Vibration isolation performance analysis of a bilateral supported bio-inspired anti-vibration control system

To achieve better anti-vibration performance in a low frequency region and expand the range of vibration isolation,a bilateral supported bio-inspired anti-vibration(BBAV)structure composed of purely linear elements is proposed,inspired by the motion form of bird legs and the nonlinear extension and compression of muscles and tendons.The kinematic relations and nonlinear dynamic model considering vertical and rotational vibrations are established.The loading capacity and equivalent stiffness are investigated with key parameters.The amplitude-frequency characteristics and force transmissibility are used to evaluate the stability and anti-vibration performance with the effects of the excitation amplitude,rod length,installation angle,and spring stiffness.The results show that the loading requirements and resonant characteristics of the BBAV structure are adjustable,and superior vibration isolation performance can be achieved readily by tuning the parameters.The X-shaped vibration structure is sensitive to the spring stiffness,which exhibits a wider vibration isolation bandwidth with smaller spring stiffness.Besides,depending on the parameters,the nonlinear behavior of the BBAV system can be interconverted between the softening type and the hardening type.The theoretical analysis in this study demonstrates the advantages and effectiveness of the vibration isolation structure.

Assessment of the curving performance of heavy haul trains under braking conditions

To study the curving performance of trains, 1D and 3D dynamic models of trains were built using nu- merical methods. The 1D model was composed of 210 simple wagons, each allowed only longitudinal motion; whereas the 3D model included three complicated wagons for which longitudinal, lateral, and vertical degrees of freedom were considered. Combined with the calculated results from the 1D model under braking conditions, the behavior of draft gears and brake shoes were added to the 3D model. The assessment of the curving performance of trains was focused on making comparisons between idling and braking conditions. The results indicated the following： when a train brakes on a curved track, the wheel-rail lateral force and derailment factor are greater than under idling conditions. Because the yawing movement of the wheelset is limited by brake shoes, the zone of wheel contact along the wheel tread is wider than under idling conditions. Furthermore, as the curvature becomes tighter, the traction ratio shows a nonlinear increasing trend, whether under idling or braking conditions. By increasing the brake shoe pressure, train steering becomes more difficult.

Seismic fragility analysis of highway bridges considering multi-dimensional performance limit state

Fragility analysis for highway bridges has become increasingly important in the risk assessment of highway transportation networks exposed to seismic hazards. This study introduces a methodology to calculate fragility that considers multi-dimensional performance limit state parameters and makes a first attempt to develop fragility curves for a multi-span continuous (MSC) concrete girder bridge considering two performance limit state parameters: column ductility and transverse deformation in the abutments. The main purpose of this paper is to show that the performance limit states, which are compared with the seismic response parameters in the calculation of fragility, should be properly modeled as randomly interdependent variables instead of deterministic quantities. The sensitivity of fragility curves is also investigated when the dependency between the limit states is different. The results indicate that the proposed method can be used to describe the vulnerable behavior of bridges which are sensitive to multiple response parameters and that the fragility information generated by this method will be more reliable and likely to be implemented into transportation network loss estimation.

Seismic evaluation of rocking structures through performance assessment and fragility analysis

Numerical studies have been conducted for low- and medium-rise rocking structures to investigate their efficiency as earthquake-resisting systems in comparison with conventional structures. Several non-linear time-history analyses have been performed to evaluate seismic performance of selected cases at desired ground shaking levels, based on key parameters such as total and flexural story drifts and residual deformations. The Far-field record set is selected as input ground motions and median peak values of key parameters are taken as best estimates of system response. In addition, in order to evaluate the probability of exceeding relevant damage states, analytical fragility curves have been developed based on the results of the incremental dynamic analysis procedure. Small exceedance probabilities and acceptable margins against collapse, together with minor associated damages in main structural members, can be considered as superior seismic performance for medium-rise rocking systems. Low-rise rocking systems could provide significant performance improvement over their conventional counterparts notwithstanding certain weaknesses in their seismic response.

Characterization of Surface Hardness and Microstructure of High Performance Concrete

The relationship between compressive strength obtained by universal testing machine and rebound value obtained by the hammer of high performance concrete was systematically investigated at the macro level. And a model of high performance concrete strength curve was established from them. At the micro level, the microstructure, hydration products and pore structure of concrete surface were analyzed by scanning electron microscopy（SEM）, comprehensive thermal analysis（TG-DSC） and mercury intrusion porosimetry（MIP）, respectively. The effect of carbonation on surface strength was also investigated. The results showed that the concrete surface hardness layer grew rapidly at early stage and then stabilized at last with ongoing curing age; the rebound value and compressive strength of concrete with slag were higher than those of concrete with the same content of fly ash. In addition, the strength curve obtained by the least square method can satisfy the local standard requirements with an average relative error of 8.9% and a relative standard deviation of 11.3%. When the carbonation depth was 6 mm, the compressive strength calculated by national uniform strength curve was 25 PMa higher than that by high performance concrete.

Performance-based system seismic assessment for long-span suspension bridges under two-level seismic hazard

Since there are few studies on the performance-based seismic evaluation of the long-span suspension bridge system under two-level earthquake hazard in Chinese code,the developed procedure of this study can be regarded as a general program to assess the seismic performance of the overall system for long-span suspension bridges.In the procedure,the probabilistic seismic demand models of multiple bridge components were developed by nonlinear time-history analyses incorporating the related uncertainties,and the component-level fragility curves were calculated by the reasonable definition of limit states of the corresponding components in combination with seismic hazard analysis.The bridge repair cost ratios used to evaluate the system seismic performance were derived through the performance-based methodology and the damage probability of critical components.Furthermore,the repair cost ratios of the overall bridge system that was retrofitted with fluid viscous dampers for the main bridge and changed restraint systems for the approach bridges were compared.The results show that peak ground velocity and peak ground acceleration can be selected as the optimal intensity measurements of long-span suspension bridges using the TOPSIS(technique for order preference by similarity to an ideal solution).The bridge repair cost ratios can serve as accurate evaluation indicators to provide an efficient evaluation of retrofit measures.The seismic evaluation of long-span bridges is misled when ignoring the interaction of adjacent structures.However,the repair cost ratios of a bridge system that has optimum seismic performance are less sensitive to the relative importance of adjacent structures.

Influence of graphene on the anti-corrosion performance of epoxy-based coatings

In this work, graphene-modified epoxy-based anti-corrosion coatings were prepared and the influence of graphene on the anti-corrosion performance of the epoxy-based coatings was investigated with water contact angle test ,chemical solution immersion test, and electrochemical test. The water contact angle and chemical solution resistance of the epoxy-based coatings were improved with an increase in graphene content from 0 to 0.4%. These results prove that addition of graphene can significantly improve the hydrophobicity and impermeability of epoxy- based coatings. However, when the graphene content was increased to 0.5%, the performance of the epoxy-based coatings decreased because of graphene aggregation. Tafel polarization results show that graphene addition can significantly reduce the corrosion current density and corrosion potential of epoxy-based coatings, which enhance their anti-corrosion performance.

Seismic fragility analysis of composite frame structure based on performance

Steel-concrete composite structures that share the advantages of both steel structure and concrete structure have been developed rapidly and used widely. It has been a popular structure in high-rise buildings in recent years. Although more and more composite structures have been used in earthquake area, only a few literatures about fragility analysis of this type of structure are available. In this paper, a fragility analysis method based on performance is proposed, in which both the uncertainty due to variability in structures and ground motion are considered. Seismic fragility analysis is performed for a 15-story composite beam-concrete-filled square steel tube column frame by the proposed method. The top-drift-angle and the story-drift-angle are used as quantitative indexes to define the four different performance levels. Then seismic demand probability analysis is carried out and fragility curves are derived to assess the seismic performance of this type of structure.

A Review of Geothermal Type-Curves with Damage Effect: A Case of Practical Apply to a Mexican Geothermal Field

A review of the art state was developed about the inflow relationships and their application for reservoir characterization. The theoretical development of the methodology for determining the damage effect using type-curves of the inflow relationships was shown. We show the process followed for achieve the geothermal type-curve affected with damage for reservoirs with mean salinities of 30000 ppm and temperatures up to 350℃. This type-curve was applied using measurement production data in a Mexican geothermal field. According with the obtained results is shown that the methodology for determining the damage effect using production measurements is a sure alternative for the damage effect calculation. It was used an alternative methodology in order to validate the damage presence and the obtained results were consistent. Last thing shows that both methodologies can be combined as a confident manner.

Loon Nest Viability Model: A Performance Indicator for Improving Water-Level Regulation of Large Water Bodies

Rule curves dictating target water levels for management have been implemented in several water bodies in North America over the last 70 years or more. Anthropogenic alterations of water levels are known to affect several components of wetland ecosystems. Evaluating the influence of rule curves on biological components with simple performance indicators could help harmonize water level management with wetland integrity. We assessed the potential of using the probability of common loon nest viability as a performance indicator of long-term impacts of rule curves on nesting wetland birds. We analyzed the outcome of rule curves on the probability of loon nest viability in Rainy Lake and Namakan Reservoir, 2 regulated water bodies located along the Ontario-Minnesota border. The analysis was focused on 4 hydrological time series between 1950 and 2013: 2 sets of time series simulating rule curves used to manage the water bodies in the past decades (referred to as the 1970RC and 2000RC), one of the historical measured water levels, and one of computed natural water levels. The probability of loon nest viability under the 1970RC was 2× higher than under natural conditions in both water bodies. The probability was also 2× higher under the 2000RC than under the 1970RC in the Namakan Reservoir but not in Rainy Lake. The rule curves generally improved conditions for nesting loons in both water bodies. The presented performance indicator can be used to evaluate future rule curves before they are implemented in the Rainy-Namakan or other similar systems.

B-Spline曲线聚风装置直线翼垂直轴风力机启动性能数值模拟

为了提升直线翼垂直轴风力机的启动性能,基于B-Spline曲线生成方法,提出一种具有流线型轮廓的聚风装置,将其分别安装在风轮顶端和底端,用以提升风轮附近的来流风速,使风轮汲取更多风能,达到更易启动的特点.选取聚风装置的5个结构参数进行设计:聚风装置与风轮间隙距离ΔL、底圆半径R_(1)、顶圆半径R_(2)、入口角度α_(1)和出口角度α_(2).设计方法采用二次旋转正交组合筛选最优模型,通过三维数值模拟研究聚风装置参数对直线翼垂直轴风力机启动性能的影响,获得了最佳外形参数组合.此外,对有无加装聚风装置的直线翼垂直轴风力机进行了静态三维数值模拟.结果表明,通过添加具有外凸流线型轮廓的聚风装置,直线翼垂直轴风力机的启动性能有显著提升.在风速较低的情况下,性能改善更加明显.聚风装置可使直线翼垂直轴风力机的平均启动力矩系数最大增加38.8%,峰值平均启动力矩系数最大可增加31.2%.

叶顶间隙对多级轴流压气机性能退化的影响

以某F级燃机压气机为研究对象,考虑燃机实际运行过程中腐蚀和磨损作用导致的压气机叶顶间隙变化,通过三维数值模拟方法开展了不同腐蚀/磨损状态下多级轴流压气机的性能退化机理研究,分析了叶顶间隙变化对多级轴流压气机性能的影响规律。结果表明:叶顶间隙增大会导致压气机特性曲线整体向质量流量减小的方向偏移,使得压气机的质量流量、效率及压比均产生一定程度的衰退;随着叶顶间隙的增大,压气机峰值效率逐渐降低,喘振裕度明显降低;叶顶间隙增大会导致压气机通道内的流动分离加剧,动叶叶顶间隙变化对压气机流动分离的影响更严重;静叶吸力面尾缘附近的流动分离导致形成低马赫数区,同时逆流的低速涡团导致叶根附近的损失显著增大,造成压气机性能衰退。

钢-UHPC轻型组合结构短栓钉抗剪性能试验研究

通过6个钢-超高性能混凝土(ultra-high performance concrete,UHPC)轻型组合结构短栓钉推出试验,对其抗剪承载力、破坏形态、栓钉应变及荷载-滑移曲线进行了研究,探讨了栓钉直径、长度、数量以及界面黏结对短栓钉抗剪性能的影响规律.结果表明:所有试件均为栓钉根部剪切破坏,UHPC板除栓钉根部沿承压方向部分UHPC压碎外,其余部分保持完好,UHPC可以抵抗栓钉传递的高压应力;栓钉根部截面屈服后应力强化阶段明显,栓钉发生剪切破坏时,栓钉根部上侧应变超过3500με;长径比为2.0的短栓钉在UHPC中也能发挥全部强度;所有试件的荷载-滑移曲线分为弹性、弹塑性和塑性3个阶段,所有短栓钉的最大滑移量均小于4 mm,工程应用时应按照弹性剪力连接件进行设计;栓钉直径对栓钉抗剪性能提高最显著,直径16 mm的栓钉比直径13 mm的栓钉的抗剪承载力和极限滑移分别提高了46.4%和11%,弹性刚度和塑性刚度分别提高了35.8%和59.1%,增加栓钉长度和界面黏结能有效提高栓钉的剪切刚度,长径比为3.0的栓钉比长径比为2.5的栓钉的弹性刚度提高了12.3%,界面有黏结试件比界面无黏结试件的弹性刚度提高了17.4%;相同间距内,合理增加更多栓钉有利于提高整体抗剪强度,但会降低延性变形能力.最后,结合实验数据和国内外UHPC中栓钉推出试验结果,建立了UHPC中栓钉荷载-滑移曲线和抗剪承载力预测表达式,计算值与试验值吻合良好.

船用钢/铝爆炸焊过渡接头的疲劳试验

为了测试船用钢/铝爆炸焊过渡接头的疲劳性能,基于有限元方法,以钢/铝过渡接头为研究对象,重点研究过渡接头结合界面的疲劳强度,设计由3种材料组成的爆炸焊过渡接头试样,并结合数值仿真,对过渡接头试样在试验载荷下的受力进行分析,得到应力集中和容易疲劳失效的位置。结合试验研究,开展不同应力等级下过渡接头的疲劳试验,获取试样疲劳断裂数据,结合数值仿真和试验研究得到爆炸复合过渡接头整体应力分布和失效部位。通过疲劳试验发现试样断裂面均出现在铝合金和纯铝的界面处;通过试样疲劳循环次数拟合得到了名义应力的S-N曲线。该研究成果可用于指导船用爆炸复合结构的疲劳寿命预报,为船舶轻量化设计提供参考。

栓钉型弧形双钢板混凝土组合板的抗爆性能试验与数值分析

弧形双钢板混凝土组合结构由钢板、混凝土与连接件协同作用,具有更优异的抗震和抗爆性能,被应用于超高层结构、海洋平台和核电设施中。利用试验和数值分析方法研究了栓钉型弧形双钢板混凝土组合结构的破坏模式和损伤机理,参数化分析了爆炸距离、钢板厚度、拱高和栓钉间距对其抗爆性能的影响。结果表明:在爆炸荷载下,栓钉型弧形双钢板混凝土组合板整体表现良好,仍具有较高的承载能力。增加爆炸距离和钢板厚度能有效减小混凝土的损伤和组合板的跨中挠度;减小拱高,混凝土损伤区域从以压缩破坏为主逐渐转换为以拉伸破坏为主,混凝土损伤更严重,组合板跨中挠度变大;减小栓钉间距会增大混凝土塑性损伤程度,但组合板的跨中挠度减小。研究结果可为弧形双钢板混凝土组合结构的设计提供参考。