Durability design of prestressed concrete structures

Based on the durability characteristics of prestressed concrete structures,the durability limit states of carbonation and chloride ion attack are defined, respectively.Durability predicting models on the basis of reliability mathematics and stochastic processes areconstructed, and the pure theoretical formulae of failure probability of prestressed concretestructures are analyzed. In addition, a simple durability design method for carbonation ofstructures is put forward. According to the analysis, the durability of prestressed concretestructures is superior to that of traditional structures. The research also indicates that theconcrete cover prescribed in the current code (GB 50010-2002) is not adequate. The rational coverthickness should notbe less than 35 or 45 mm according to carbonation or chloride ion attack,respectively.

Three-dimensional Analysis of Prestressed Concrete Offshore Wind Turbine Structure Under Environmental and 5-MW Turbine Loads

A concrete gravity base structure may not be suitable for offshore weak soil because of its heavy weight. Therefore, a conceptual model for a concrete offshore wind turbine structure suitable for weak soils is proposed. The proposed model is composed of a prestressed concrete(PSC) supported by a pile foundation. For a three-dimensional analysis of the large concrete structure, wave pressures based on the diffraction wave theory are developed using a three-dimensional solid finite element method. Static and dynamic analyses were performed to achieve the conceptual model of a PSC structure subjected to ocean environmental loads and a 5-MW turbine load on southwest coast in Korea. From the analysis, the maximum displacement and stresses of the proposed model did not exceed the allowable values from design standard, and the first mode of natural frequency of the structure was in a safe range to avoid resonance. The proposed model has enough structural stability to withstand external loads, and it is expected to be used in locations suitable for concrete gravity structures.

Tensile force correction calculation method for prestressed construction of tension structures

Factors such as errors during the fabrication or construction of structural components and errors of calculation as- sumption or calculation methods, are very likely to cause serious deviation of many strings’ actual prestressing forces from the designed values during tension structure construction or service period, and further to threaten the safety and reliability of the structure. Aiming at relatively large errors of the prestressing force of strings in a tension structure construction or service period, this paper proposes a new finite element method (FEM), the "tensile force correction calculation method". Based on the measured prestressing forces of the strings, this new method applies the structure from the zero prestressing force status approach to the measured prestressing force status for the first phase, and from the measured prestressing force status approach to the designed prestressing force status for the second phase. The construction tensile force correction value for each string can be obtained by multi-iteration with FEM. Using the results of calculation, the strings’ tensile force correction by group and in batch will be methodic, simple and accurate. This new calculation method can be applied to the prestressed correction construction simulation analysis for tension structures.

Probabilistic Assessment of Pitting Corrosion Effect on Flexural Strength of Partial Prestressed Concrete Structures in a Chloride Environment

Like reinforced concrete （RC） structure, Prestressed concrete （PC） structures cannot escape from corrosion related problems, especially when they are subjected to very aggressive environment, such as chloride environment. The corrosion of PC and RC structures can take place if the concrete quality is not adequate, the concrete cover is less than that specified in the design, poor detailing during design and construction. For RC structures, corrosion in the reinforcing steel generally leads to serviceability problems （staining, cracking and spalling of concrete）. By contrast, for PC structures, corrosion of prestressing strands may initiate structural collapse due to higher stress levels in the steel and smaller diameter of the prestressing steel. Research on corrosion effect on concrete structure has mainly considered the effect of corrosion have on reinforced and full prestressed concrete structure. In this study, a structural framework will be developed to predict the flexural strength of partial prestressed concrete structures in a chloride environment. The corrosion model previously developed for reinforced and prestressed concrete structures will be combined to predict the effect of corrosion has on partial prestressed concrete structures. Note that in partial prestressed concrete structures, both non prestressing steel （passive） and prestressing （active） reinforcement are utilized to carry the load. The framework developed will be combined with probability analysis to take into account the variability of parameters influencing the corrosion process. This approach allows more accurate prediction of service life of partial prestressed concrete structures in a chloride environment.

Study on damage-stress loss coupling model of rock and prestressed anchor cable in dry-wet environment

The loss of anchoring force is one of the problems to be solved urgently.The anchorage loss is a key factor causing the failure of anchoring engineering,so it is crucial to study the time-dependent variation of anchoring force.Alternating dry and wet(D-W)conditions have a significant effect on deformation of rock.The anchoring system is composed of anchoring components and rock mass,and thus rock deformation has a significant impact on the loss of anchoring force.Quantifying rock deformation under the effects of D-W cycles is a prerequisite to understanding the factors that influence loss of anchoring force in anchor bolts.In this study,we designed an anchoring device that enabled real-time monitoring of the variation in strain during D-W periods and rock testing.Nuclear magnetic resonance(NMR)measurements showed that under D-W conditions,the increment in porosity was smaller for prestressed rock than unstressed rock.The trends of prestress loss and strain variation are consistent,which can be divided into three characteristic intervals:rapid attenuation stage,slow attenuation stage and relatively stable stage.At the same stress level,the rate of stress loss and strain for the soaking specimen was the highest,while that of the dried specimen was the lowest.In the same D-W cycling conditions,the greater the prestress,the smaller the strain loss rate of the rock,especially under soaking conditions.The characteristics of pore structure and physical mechanical parameters indicated that prestress could effectively suppress damage caused by erosion related to D-W cycles.The study reveals the fluctuation behavior of rock strain and prestress loss under D-W conditions,providing a reference for effectively controlling anchoring loss and ideas for inventing new anchoring components.

Life cycle detection of prestress in large prestressed reinforcement structures

To monitor the stress state of prestressed reinforcement in large reinforcement prestressed structure, two sensing structures, namely the direct spiral-winding structure and sawtooth modulated structure, were designed based on the ordinary communication optical fiber. The sensing theories were analyzed, and the experimental studies were also carried out. The quasi-distributed sensing system based on optical time domain reflective technology was established. The detection wavelength and spatial resolution were analyzed, and the estimation formula of maximal number of sensing point was also given. The results show that the system can realize the quasi-distributed test of measurand with single fiber, which helps to simplify the in-out wires. Moreover it can take on the important task of long-term and continuous monitoring of prestress, which helps to realize the life cycle detection of prestress, and play an important role in the estimating of bridge health state.

Shear Behavior of Novel Prestressed Concrete Beam Subjected to Monotonic and Cyclic Loading

Prestressed steel ultrahigh-strength reinforced concrete(PSURC) beam is a new type of prestressed concrete beam, which not only has a considerable compressive strength attributed to the ultrahigh strength concrete, but also ensures a certain degree of ductility at failure due to the existence of structural steel. Five of these beams were monotonically tested until shear failure to investigate the static shear performance including the failure pattern, loaddeflection behavior, shear capacity, shear crack width and shear ductility. The experimental results show that these beams have superior shear capacity, crack control ability and shear ductility. To study the shear performance under repeated overloading, seven PSURC beams were loaded in cyclic test simultaneously. The overall shear performance of cycled beams is similar to that of uncycled beams at low load level but different at high load level. The shear capacity and crack control ability of cycled beams at high load level are reduced, whereas the shear ductility is improved. In addition, the influences of variables including the degree of prestress, stirrup ratio and load level on the shear performance of both uncycled and cycled beams were also discussed and compared, respectively.

Dynamic calculation model and seismic response for frame supporting structure with prestressed anchors

A dynamic calculation model of frame supporting structures with prestressed anchors for the slope stability is proposed. The frame and soil are closely contacted in the role of prestressed anchors and they cannot be separated along the whole slope. The lateral displacement of frame and soil is nearly in phase. The movement characteristic satisfies the theory of elastic foundation beam. The frame is treated with elastic foundation beam in this model. The influence of prestressed anchors is simplified as linear spring and damped system related with velocity. Under the condition of horizontal earthquake excitation, the equation of vibration response is established by using the model of dynamic Winkler beam and the analytical solutions are obtained for simple harmonic vibration. This method is applied to a case record for illustration of its capability, in order to verify the method, 3D nonlinear FEM (ADINA) is used to analyze the seismic performance of this case, the comparative results show that the design and the analysis are safe and credible by using the proposed method. The calculation model provides a new way for earthquake analysis and seismic design of slope stability supported by frame structure with prestressed anchors.

Seismic Performances of Large-Span Prestressed Concrete Frame Structure by Shaking Table Tests

The seismic performances of the large-span prestressed concrete frame structure of bunker bay of thermal power plant under different intensity level was investigated by shaking table tests.A 1/8 microconcrete nonfull weight scaled model was designed according to the prototype structure and the conditions of laboratory.Three kinds of scaled ground motion accelerations were employed as seismic excitations.White noise was input in the structure through each seismic wave applied.The experimental results indicate that the structure is safe to endure seven degree intensity as required in Chinese codes.The natural vibration frequency of the structure is decreasing with the increasing of the seismic intensity,the natural vibration frequency of the structure decreases by about 24.5%,and the structural stiffness reduces by nearly 44% in seven degree intensity of seldom occurred earthquake.The damage at the top of column in the first floor is the most serious,the weak part of the structure is at the first floor,and the strong beam/weak column phenomenon appeared obviously,so this kind of large-span prestressed concrete frame should not be used in a high intensity district.

Editorial: Special subject on the mechanical behavior of thermal protection materials and structures

The thermal protection materials and structures are widely used in hypersonic vehicles for the purpose of thermal insulation, and their mechanical behavior is one of the key issues in design and manufacture of hypersonic vehicles. It is our great pleasure to present the seven papers in this special subject of Theoretical ＆ Applied Mechanics Letters （TAML） and introduce the recent progresses on the mechanical behavior of thermal protection materials and structures by the authors.

Role of Ordering Energy in Formation of Grain Structure and Special Boundaries Spectrum in Ordered Alloys with L12 Superstructure

It was revealed that an average energy of special boundaries is proportional to APB energy in the alloys with the L12 superstructure. This fact proves the appearance of the GAPBs in the planes of location of special boundaries in coincidence sites of ordered alloys. It was determined that the more energy of special boundaries in ordered alloys, the more energy of complex stacking fault. There is a correlation between the distribution of special boundaries as a function its relative energy and ordering energy: the more ordering energy, the more degree of washed away of distribution. The correlation between average relative energy of special boundaries and ordering energy was detected: the more ordering energy, the more average energy of special boundaries. The reverse dependence between ordering energy and average number of special boundaries in grains limited by boundaries of general type was discovered.

Global Topological Structure of a Class of Plane Homogeneous Fifth System with Six Special Direction

In this paper, a class of plane homogeneous fifth system with six special direction is studied, and the global topological classification and coefficient conditions is discussed.

The Role of Special Economic Zones in Enhancing Enterprise’s Export Structures:The Perspective of Industry Complexity

Special economic zones(SEZs)help provide the momentum for China’s economic growth.This paper studies the influence of SEZs on enterprise’s export structures from the perspective of production complexity using data from the China Industry Business Performance Database(CIBPD)collected between 2000 and 2007.We found that enterprises in SEZs have a higher export propensity and volume due to more complexity.Also,enterprises with more complexity outside SEZs show a higher export propensity and volume depending on the number of SEZs near them and the radiation effect of the SEZs.Similarly,high and new-tech industrial development zones perform more prominently in this regard.

On Speciality Structure for Musical Education in Colleges

In general, the overall goals for musical education in colleges include but are not limited to, to make the students become talents with ability to adapt specialized requirements by state, capacity to perform with artistic doctrines, capability to solve problems in teaching and research, ability to adapt to reform in musical education at schools, and ability to promote music in society.Based on examination of history of musical education, and reference by contemporary authors, this paper intends to elaborate basic speciality structure for musical education students by approaches of analysis, deduction and induction and so on and so forth. The paper mainly focus on the necessity, importance, practical nature and relevance. Particular attention has been paid to model called ＂speciality plus versatility＂ based on advice from students, schools and society as well.

Analysis on Governance Structure of Farmers' Specialized Cooperatives in Sichuan Province

In this paper, 87 farmers' specialized cooperatives in Sichuan Province were investigated firstly, and then their governance structure was analyzed from the aspects of authority, decision-making mechanism, supervision mechanism and executive body based on the corporative governance structure in narrowest sense, finally corresponding policy suggestions for improving the governance structure of farmers' specialized cooperatives in Sichuan Province were put forward. It is concluded that human control is serious within farmers' specialized cooperatives; inner supervision is effective; council has great effects on governance structure; the cooperatives give limited incentive to managers.

Application of laminated vierendeel truss in high-position transfer story structure

To meet the demands for large space and flexible compartmentation ofbuildings, laminated vierendeel trasses are adopted in high-position transfer story structures.First the bearing characteristics are analyzed, in which reasonable stiffness ratio of the upperchord, middle chord, and lower chord is derived. Then combined with an actual engineering model (1:8similar ratio), the static loading and pseudo-dynamic tests of two models for laminated vierendeeltrass used in transfer story structures are conducted, in which one model adopts reinforcedconcrete, and the other adopts prestressed concrete and shape steel concrete. Seismic behaviors areanalyzed, including inter-story displacement, base shear-displacement skeleton curves, andequivalent viscosity-damping curves. A program is programmed to carry out the elasto-plastic dynamicanalysis, and displacement time-history curves of the two models are derived. The test and analysisresults show that the laminated vierendeel trass with prestressed concrete and shape steel concretehas excellent seismic behaviors. It can solve the disadvantages of laminated vierendeel trussesused in transfer story structures. Finally, some design suggestions are put forward, which can bereferenced by similar engineering.

Evaluation of Governance Structure of Farmers' Specialized Cooperatives

In this paper,from the authority,decision-making body,supervisory body and implementing body,we analyze the governance structure evaluation indicators of farmers' specialized cooperatives,using objective and subjective combination weighting approach.And we draw the following conclusions:the rate of return of profits for membership,frequency of council convened and the number of members of board of supervisors have a great impact on the governance structure of cooperatives; the insider control phenomenon in cooperatives is more serious and the level of incentives is limited.Finally we put forward corresponding policy recommendations.

预应力在我国大跨度结构中的应用研究综述

为了提高大跨度结构的正常使用性能,通常在混凝土结构中施加预应力.结果表明,预应力混凝土结构具有更好的使用性、耐久性和大跨度适用性,其中预应力混凝土空心板结构在不显著降低承载力和刚度的前提下明显减小结构自重,预应力型钢混凝土梁(板)结构采用较小的截面尺寸即可满足承载力和刚度的需求.开发城市地下空间是解决城市用地紧张的有效手段,我国地下大跨空间常用的结构形式主要包括密排框架(肋梁)结构、折板或拱形结构、变截面(加腋)板结构、预应力混凝土结构、型钢-混凝土组合结构和Y形柱结构6种形式,相比之下,跨度较大时宜采用预应力结构.

基于客观结构化临床考试的情景模拟式教学在手术室专科护士培训中的应用

目的探讨基于客观结构化临床考试(objective structured clinical examination,OSCE)的情景模拟式教学在手术室专科护士培训中的应用效果。方法选取参加郑州大学第一附属医院手术室专科护士培训的78名学员为研究对象。按照培训时间先后顺序,将2021年4月-6月参加培训的40名学员作为对照组,将2022年4月-6月参加培训的38名学员作为观察组。对照组采用常规情景模拟式教学,观察组采用基于OSCE的情景模拟式教学,比较2组操作考核成绩、临床思维能力。结果观察组操作考核中患者核查交接、手术体位安置、职业暴露防护的考核成绩均好于对照组(t=4.616,P<0.001;t=3.004,P=0.004;t=3.574,P=0.001),观察组临床思维能力得分高于对照组(t=7.309,P<0.001)。结论将基于OSCE的情景模拟式教学应用于手术室专科护士培训,有助于提高其操作技能和临床思维能力,值得临床推广应用。

要素禀赋改善、产业结构优化与特殊类型地区共同富裕

特殊类型地区是推进高质量发展的重点区域,建构“以要素禀赋改善为支撑,产业结构转型升级为引擎,协同驱动区域共同富裕”的逻辑框架,计量分析要素禀赋和产业结构耦合协调度,实证检验三者之间互动关联并探讨其理论蕴含,有益于加快构建支持特殊类型地区振兴发展的政策体系和长效机制。结果表明,产业结构调整在要素禀赋影响特殊类型地区振兴发展的过程中发挥中介作用;实现要素禀赋与产业结构的耦合协调可以更好推进区域共同富裕,二者耦合协调程度在要素禀赋促进区域共同富裕过程中发挥门槛效应;要素禀赋及其与产业结构耦合协调度发挥正向作用时,其滞后一期变量对促进区域共同富裕具有阻滞作用。据此针对要素品质提升、产业结构高阶演进以及政府与市场作用协同发挥等领域给出相关建议,力争推动特殊类型地区在要素禀赋改善与产业结构优化良性互动中实现高质量发展。