Simulation Analysis of Flexural Performance of Reinforced Concrete Beam in Salt-frost Environment

Considering the damage of concrete mechanical properties and bonding behavior between the steel bar and concrete after the freezing and thawing function in the numerical simulation, the nonlinear analysis on flexural performance of reinforced concrete beam which experiences different salt-frost cycles is conducted, and the evolution law of resistance performance of reinforced concrete beam is studied. It is shown that, in the salt-frost environment, the decrease of concrete mechanical properties is the main reason that causes the degeneration of RC beam on flexural performance, while the reduction of bonding property has an unobvious effect on the beam resistance performance. When the salt-frost cycles reach a certain level, the beam failure pattern would change from the under-reinforced failure to over-reinforced failure. The freeze-thaw damage of bonding property in the beam-ends anchorage zone has a certain effect on the beam resistance behavior, especially for the more serious freeze-thaw degree, the resistance performance of the beam reduces about 4% than the perfect anchor beam.     

原状黄土冻融过程抗剪强度劣化机理试验分析

通过对西安Q₃原状黄土在封闭系统冻融作用下的电镜扫描和直剪试验,研究了冻融作用对原状黄土微观结构和强度的影响。试验表明：冻融过程中原状黄土微观结构发生显著变化,大颗粒集粒数量明显减少,小粒径土颗粒所占比重增加,孔隙面积比增加。进一步基于损伤力学理论,得到微观结构冻融损伤度随冻融次数增加呈指数增加趋势,反映出冻融作用一定程度上破坏黄土体的结构强度,但多次冻融后黄土体结构强度趋于稳定的残余强度。冻融过程土样表面结构发生破坏,且含水率越高,土体表面特征破坏越严重。粘聚力随冻融次数增加呈指数衰减趋势,且含水率越高,粘聚力衰减幅值和速率越小;粘聚力随含水率增加表现出线性衰减特征,且冻融后粘聚力与含水率的变化规律近似重合;内摩擦角无明显规律性变化。粘聚强度冻融损伤系数随冻融次数增加呈指数增加趋势,随含水率升高有增大趋势。基于试验数据规律性,进一步提出了原状黄土粘聚强度劣化模型,该模型经试验验证可较好描述原状黄土粘聚强度劣化规律。     

Experimental Research on Concrete Strength under Freeze-thaw Recycle Action with Ultra-low Temperature

The concrete structure has been used in low and ultra-low temperature environment. But few researches are experienced on its properties under freeze-thaw recycles with ultra-low temperature. Based on the standard for test methods of long-term performance and durability of ordinary concrete, considering the influence of the times and minimum temperature of recycles, water-cement ratio and the external environment humidity, compressive and tensile strength of cubic concrete and scanning electron microscopy on the residual sample are experimented to explore the impact of freezing and thawing cycles under ultra-low temperature on its strength and microstructure. The results show that the role of cryogenic temperature for freeze-thaw cycles has a greater effect on concrete performance. With the temperature decreasing and water-cement ratio increasing, the damage tends to grow up. Consistent with the results of the strength tests, electron microscopy tests show that the pore size of mortar increases and the material becomes looser.     

Influences on Engineering Properties of AS Firming Agent Modified Soil by Freeze-thaw Cycles

To study the freeze-thaw durability of Aught-Set(AS) firming agent modified soil, a series of triaxial tests were conducted. The mutual relationships between stress-strain relationship, static strength, dynamic modulus and critical dynamic stress of AS firming agent modified soil and curing time, freeze-thaw cycles, cooling temperature were deeply analyzed. The results show that the unconfined compressive strength of 7 d is 75% than that of 28 d. The stress-strain curves of AS firming-agent modified soil are strain-softening and in brittle failure shape. The static strength, critical dynamic stress and resilient modulus decrease in exponential form with the increase of freeze-thaw cycles, and after 6 cycles of freezing and thawing, the trend is stable. Under the same dynamic stress, the cumulative plastic strain of samples develop from stable state to failure because of freezing and thawing. After many times of freeze-thaw cycles, the lower the negative temperature, the little influence on the mechanic properties.     

Stress Corrosion of Concrete Exposed to the Action of Freezing-thawing Cycles

Through the method of accelerated freezing-thawing and room-temperature corrosion, the stress corrosion of three kinds of concretes subjected to 5.0%MgSO4(in mass)solution was studied. The considered concretes include High Strength Concrete(HSC), High-Volume Mineral Admixture Concrete(HVMAC) and High Durable Concrete(HDC) added with high-volume mineral admixture, air-entraining agent, superplasticizer, fibers and expansion agent. The results showed that the relative dynamic elastic modulus of concrete went through strengthen and deterioration stages subjected to stress corrosion, whether the room temperature or freezing and thawing conditions. The length of time of these two stages are closely related with the experimental temperature. Freezing and thawing action significantly accelerated the process of sulphate stress corrosion damage. Under the action of freezing and thawing, stress corrosion strengthening the period length of HSC shorter 96%, deterioration section of the length of time shorter 88%, compared with the length of time at the corresponding room temperature. Deterioration section of the length of time of HVMAC is reduced by 98%, while the HDC reduced by 71%. The effect of freezing and thawing, HDC freezing-thawing cycles when the stress corrosion damage occurred were longer 1.5 times and 13 times than the HSC and HVMAC. Thus in the cold regions, HDC showed more resistance to sulfate stress corrosion.     

冻融作用下特定污染物的清洗试验研究

抽出处理法是目前修复土壤污染常用的方法之一,为了解决抽出处理法中对渗透性差的土中污染物和低浓度污染物效率低的问题,利用土体冻结过程中在一定的温度梯度和水分条件下未冻土侧水分（溶质）向冻结锋面迁移和冻融作用导致渗透性增强的特性,开展了基础试验。试验将混有模拟污染物NaCl溶液的粘土作为研究对象,结合传统的抽出处理法,实施了单向冻融试验和污染物清洗模型试验,探索了利用冻融现象清洗污染土壤的可行性。结果表明,冻融作用有助于提高污染物的抽出效率。     

改良冷冻法测定梨果实的石细胞含量

为了提高梨石细胞的提取效率,以黄金梨和茌梨的果实为试材,在冷冻提取方法的基础上,通过设置不同的冷冻时间和冻融次数来研究其对梨石细胞提取效果的影响。结果表明：所有处理中以处理（1）(3 h+3 h+3 h)反复冻融处理的提取效果最好,石细胞提取的量随着冻融次数的增加而增加,说明增加冻融次数有利于梨果实石细胞的提取;在冻融次数相同时,每次冷冻时间满足3 h后,再增加冷冻时间对提取效果影响不大。冷冻法提取石细胞效果与冻融次数密切相关,在满足基本的冷冻时间后,增加冻融次数可以显著提高梨石细胞的提取率。     

冻融作用对土壤氮转化影响的研究进展

氮素是限制植物生长的重要营养元素之一,其在土壤中转化程度受多种因素影响,作为中、高纬度或高海拔地区土壤氮转化的重要驱动力,冻融作用对于土壤氮转化过程也存在极大影响。本文基于国内外已有研究成果,概述了土壤冻融循环次数、结冻持续时间以及结冻强度对于土壤氮转化过程的影响。总结出冻融格局的改变对土壤氮转化关系的一般规律：随着冻融格局的改变,均有利于土壤氮的矿化;冻融强度的增加可显著提高土壤硝态氮的含量;冻融格局的改变也会提高N₂O的排放。     

冻融环境下钢筋与粉煤灰混凝土的粘结性能

通过对内贴应变片钢筋的直接拔出试验,分析冻融作用下粉煤灰掺量对钢筋与粉煤灰混凝土间粘结性能的影响,得出冻融循环作用对钢筋与粉煤灰混凝土之间粘结性能的影响规律。试验结果表明：钢筋与粉煤灰混凝土的粘结强度随粉煤灰掺量的增加而降低;当粉煤灰掺量一定时,随着冻融循环次数的增加,混凝土强度有所下降,钢筋与粉煤灰混凝土间极限粘结强度降低;当粉煤灰掺量较大,达到40%时,随冻融次数的增加,钢筋粉煤灰混凝土试件极限粘结强度的下降幅度明显减缓,极限粘结强度对应的滑移量增大。表明掺入较多粉煤灰可使试件的冻融损伤现象得到缓解,冻融环境下钢筋混凝土的粘结性能得到提高。     

冻融损伤对再生混凝土耐久性及与钢筋粘结性能分析

制作掺入引气剂和未掺入引气剂的100%粗骨料取代率的再生混凝土RC1和RC2两组试件以及掺入引气剂和未掺入引气剂的普通混凝土NC1和NC2两组试件,并分别对经过不同次数冻融循环试件的抗压强度、质量损失率、动弹性模量损失率进行研究。结果表明,冻融后各组试件的抗压强度、质量损失率及动弹性模量损失率均降低,对于添加引气剂的NC1和RC1两组试件损失较小,其中RC1组试件在200次冻融后抗压强度损失接近40%,质量损失率达0.5%,动弹性模量损失率38.5%。100%取代率并加入引气剂的ZRC组试件冻融后进行中心拨出实验,发生劈裂破坏和钢筋拔出破坏2种形式。再生粗骨料混凝土与钢筋的极限粘结应力均随冻融次数的增加而降低,200次冻融后极限粘结应力下降33.5,荷载滑移曲线既有上升段也有下降段。     

Reinforced Concrete Beam's Stiffness Degeneration Regulation and its Calculation Formula Under the Action of Fatigue Load

Fatigue failure is a fatal damage for the reinforced concrete structure bearing fatigue load repeatedly. That how to estimate or describe the degree of fatigue damage is a challenge in areas of structure damage and lifespan estimation. Structure's stiffness degenerates irreversibly along with the damage progress. There is a certain inherent relevance between stiffness degeneration and fatigue damage. A series of fatigue tests were carried out to study stiffness degeneration regulation due to its simplicity and feasibility. According to the test results, reinforced concrete beam's stiffness degeneration presents a three-stage rules obviously, and the stiffness degeneration curves accord with "S" style. Based on the stiffness degeneration regulation, the reinforced concrete beams' stiffness degeneration calculation formula is obtained by fitting experimental data. The formula has a perfect goodness of contact area with 10 test beams' experimental results, and it can describes reinforced concrete beams' stiffness degeneration perfectly. The formula can be used to forecast the deformation developing. Meanwhile, the residual life of the structure can be used to decision structure's fatigue fracture and the degree of performance degradation.     

草面温度在霜预报中的应用

为了避免农作物遇霜后遭受冻害,本研究采用草面温度对霜进行预测。利用连云港气象观测站2014—2016年逐时气象要素,包括气温、0 cm地温、露点温度、水汽压、气压以及2 min平均风速等气象要素作为影响连云港地区草面温度的关键因子,并以这6个要素作为属性特征,以草温作为标志量构建训练样本集,结合KNN数据挖掘算法构建草温预测模型,并根据草温判别是否有霜出现。结果表明：基于该算法构建的草温预测模型效果较好,预报平均误差1.2℃;根据草温预测霜的准确率高达90.2%,尤其对初终霜的预报具有很好的指示意义。因此,引入草温作为霜的预报指标,对于避免农作物遭受霜害具有十分重要的意义。     

苦瓜多糖的测定方法研究

为开发和利用苦瓜多糖,选用苯酚硫酸法和蒽酮硫酸法测定苦瓜多糖的含量;比较不同成熟度苦瓜中多糖的含量差别;比较冻融法制备的苦瓜汁粉及苦瓜渣粉中多糖含量。结果显示,对同一种样品利用苯酚硫酸法和蒽酮硫酸法测定,测定结果分别为28.00%和29.25%,苯酚硫酸法测定结果更为准确合理,可作为苦瓜中多糖含量测定的首选方法;测定不同成熟度苦瓜的多糖含量,发现苦瓜成熟度越高,多糖含量越低,说明苦瓜生理成熟阶段,苦瓜多糖是重要的呼吸基质之一;利用冻融法制备的苦瓜汁粉多糖含量为31.25%,苦瓜渣粉多糖含量为28.64%,说明冻融法获得的苦瓜汁没有起到完全分离苦瓜多糖的作用。     

早龄期混凝土蠕变模型比较

针对早龄期混凝土的蠕变松弛特性,以配比、强度以及不同加载龄期的混凝土蠕变试验数据为依据,对比研究了CEB-FIP模型、Muller模型、B3模型与笔者所建立变系数四参数Burgers模型的蠕变预测差异。研究结果表明:常用经验模型中,CEB-FIP模型具有较好的适应性,Muller模型对于高强混凝土的蠕变预测较好,基于固化理论的B3模型对于早龄期混凝土的蠕变预测值偏大,准确性较差。对比研究验证了变系数四参数Burgers模型中参数的物理意义与经验取值范围及其合理性与适用性。     

Prediction Analysis on Equivalent Resilient Modulus of Clay Subgrade of Water Network Intensive Areas

According to unsaturated soil basic theories, equilibrium moisture of clay subgrade is predicted based on the updated studies of soil suction and soil water characteristic curve. Also, the bilinearity constitutive experience model of resilient modulus of clay soil is presented by triaxial repeated loading tests in laboratory. Using above mentioned results, a prediction method of equivalent resilient modulus of clay subgrade is established by comprehensively considering subgrade moisture and stress condition. Then, based on the concrete engineering, the prediction function of equivalent resilient modulus of the clay subgrade is provided by taking ground water table and subgrade height as centers. Compared with the results of other traditional testing methods on the same test road, the new prediction method may be used in practice. The results provide new perspectives and standpoints to determine the equivalent resilient modulus mechanics features of clay subgrade structure from two aspects of equilibrium moisture and stress condition.     

A Modified Chloride Ion Diffusion Model in Concrete

Based on the analysis of influencing factors chloride ion diffusion in concrete and the simplified model induced by Fick's second law, a chloride ion diffusion model was established, in which , the influences of water-cement ratio, humidity, time, temperature, chloride ion binding capacity of concrete and freeze-thaw cycle are taken into consideration. The Validity of the new model is verified through the comparison of results between the proposed model and the existing analytic /numerical model. Compared with the analytic model, the proposed model can consider the seasonal change of humidity and temperature,and the time-variant effect of freeze-thaw cycle.Compared with the numerical model, the computational efficiency of the proposed model is higher.     

Deformation Feature of the Particle Improved Roadbed of Qinghai-Tibetan Railway

The design idea and the spot experimental scheme of the particle improved roadbed are analysed in detail and deformed law with time of the particle improved roadbed in the cycle of freezing and thawing. The results indicate that the deformation of the particle improved roadbed presents the corresponding frost - heave deformation with the cycle of freezing and thawing. As compared with the ventilated embankment, the particle improved roadbed can, to some extent, shorten the freezing period and ease the frost-heave deformation.     

基于隶属函数法的李涂白防寒措施筛选

为筛选较适宜的李涂白防寒措施,本研究以‘早红’、‘公主红’和‘吉红’3个李品种为试材,通过不同涂白剂及方法对李树体进行涂白预防冻害,测定枝条冻害级别、植株生长及果实品质等指标,利用正交设计及隶属函数法对防寒效果进行综合评价。结果表明,涂白可降低李树一年生枝冻害情况,促进萌芽及果实生长;筛选出‘公主红’李最佳涂白措施:树干涂白剂+0.5 g/kg纤维素,涂干100 cm。本研究结果可为寒冷地区李树抵御低温胁迫提供技术指导。     

基于灰色离散增量模型的人口预测-以安徽省望江县为例

人口系统是一个典型的灰色系统。根据1949-2005年望江县人口发展的最新统计资料,根据离散灰色增量模型,对未来望江县人口发展趋势进行预测研究,得出了望江县2010年和2020年的的人口预测值,并对该预测结果进行了精度检验与对比分析。通过与其他预测模型进行比较,反映了灰色预测模型具有较好的预测精度,有益于区域土地利用总体规划的制定。     

Differences between wheat genotypes in damage from freezing temperatures during reproductive growth

Cereal crops in the reproductive stage of growth are considerably more susceptible to injury from freezing temperatures than during their vegetative growth stage in the fall. While damage resulting from spring-freeze events has been documented, information on genotypic differences in tolerance to spring-freezes is scarce. Ninety wheat genotypes were subjected to a simulated spring-freeze at the mid-boot growth stage under controlled conditions. Spring-freeze tolerance was evaluated as the number of seeds per head at maturity after plants were frozen at −6 °C. Plants that froze, as confirmed by infrared (IR) thermography, died shortly after thawing and consequently the heads did not mature. Only in plants that had no visible freezing (super-cooled) were heads able to reach maturity and produce seeds. In plants that super-cooled four genotypes had significantly higher seed counts after being exposed to freezing than three with the lowest. In addition, significant differences between genotypes were found in whole plant survival among those that had frozen. Genotypes with high whole-plant freezing survival were not necessarily the same as the super-cooled plants with the highest seed counts. Spring-freeze tolerance was not correlated with maturity suggesting that improvement in freezing tolerance could be selected for without affecting heading date. Spring-freeze tolerance was not correlated with freezing tolerance of genotypes of plants in a vegetative state, either under non-acclimated or cold-acclimated conditions indicating that vegetative freezing tolerance is not a good predictor of spring-freeze tolerance.