地下室侧墙预应力抗裂技术的研究

预应力技术作为一种主动抗裂措施是控制地下室侧墙开裂的有效途径之一。本文首先分析了地下室侧墙开裂考虑的因素，涉及到混凝土的收缩、温度的应力以及徐变的作用，并进一步研究了预应力抗裂设计过程中的预应力筋分段以及连接结构．

Effects of silicon content on microstructure and stress corrosion cracking resistance of 7050 aluminum alloy

Evolution of microstructure and stress corrosion cracking （SCC） susceptibility of 7050 aluminum alloy with 0.094%, 0.134% and 0.261% Si （mass fraction） in T7651 condition have been investigated. The results show that the area fraction of Mg2Si increases from 0.16% to 1,48% and the size becomes coarser, while the area fraction of the other coarse phases including Al2CuMg, Mg（Al,Cu,Zn）2 and A17Cu2Fe decreases from 2.42% to 0.78% with Si content increasing from 0.094% to 0.261%. The tensile strength and elongation of 7050-T7651 alloys is decreased with the increase of Si content by slow strain rate test （SSRT） in ambient air. However, electrical conductivity is improved and SCC susceptibility is reduced with the increase of Si content by SSRT in corrosion environment with 3.5% NaCl solution.

Influence of superplasticizers on the early-age crack resistance of concrete

In order to improve the early-age cracking resistance of concrete, different types of superplasticizers are used. Two types of polycarboxlic salt/acid superplasticizers and one retarding naphthalene superplasticizer are selected to investigate the influence of superplasticizers on the early-age cracking resistance of the concrete by using the slab test and the temperature-stress test. The results show that the polycarboxlic salt/acid superplasticizer cannot always improve the cracking resistance capacity of the concrete compared with the naphthalene superplasticizer, which is related to the chemical structure of the polycarboxlic salt/acid superplasticizer. High plastic tensile strength and dynamic elastic modulus at the early stage are beneficial to avoid cracking, and low hydration heat is also helpful. The evolutions of the drying shrilakage stress and the hydration heat temperature stress varying with time can be comprehensively evaluated by means of the slab test and the temperature stress test.

直桥和弯桥受力计算对比分析

为比较弯桥与直桥的设计差异,根据弯桥承受弯一扭耦合作用的受力特点,分别建立两组有限元计算模型,通过对比分析计算结果可知,弯桥在外力作用下支反力外侧大于内侧,预应力作用下较为突出。自重作用下扭矩内力表现为边跨梁端大于中跨梁端,桥台处最大。预应力作用下扭矩内力表现为中跨梁端大于边跨梁端。抗裂应力内外侧差异较大,外侧比内侧更为不利,分析了差异产生的原因,并根据计算结果和工程设计经验提出了设计构造措施。

Design and evaluation of epoxy asphalt geogrid stress- absorbing layer

In order to delay or eliminate the occurrence and expansion of the reflective cracking in the asphalt concrete overlay on old cement concrete pavement, an epoxy asphalt geogrid stress-absorbing layer（ EAGSAL） was designed. The EAGSAL consists of epoxy asphalt and fiberglass geogrid. The pull-out test, skewshearing test, bending beam test and fatigue test were conducted to evaluate the performance of the EAGSAL and a traditional stress-absorbing layer（ TSAL）. The results showthat the adhesive performance, shear performance, bending strength and fatigue performance of the EAGSAL with an optimal spraying volume of epoxy asphalt are better than those of optimally designed TSAL, and the maximum bending strain of the EAGSAL is very close to that of the TSAL. The EAGSAL has superior performance in reflective cracking resistance.Moreover, the EAGSAL with the optimal spraying volume of approximately 2. 0 L m^2 is thinner and lighter than the TSAL,which can decrease the thickness and improve the bearing ability of the whole pavement structure.

Crack initiation stress and strain of jointed rock containing multi-cracks under uniaxial compressive loading: A particle flow code approach

The ratio of crack initiation stress to the uniaxial compressive strength(SCI,B/SUC,B) and the ratio of axial strain at the crack initiation stress to the axial strain at the uniaxial compressive strength(B,UCB,CI,A,A/SSSS) were studied by performing numerical stress analysis on blocks having multi flaws at close spacing's under uniaxial loading using PFC3 D. The following findings are obtained: SCI,B/SUC,B has an average value of about 0.5 with a variability of ± 0.1. This range agrees quite well with the values obtained by former research. For joint inclination angle, β=90°,B,UCB,CI,A,A/SSSS is found to be around 0.48 irrespective of the value of joint continuity factor, k. No particular relation is found betweenB,UCB,CI,A,A/SSSS and β; however, the average B,UCB,CI,A,A/SSSS seems to slightly decrease with increasing k. The variability ofB,UCB,CI,A,A/SSSS is found to increase with k.Based on the cases studied in this work,B,UCB,CI,A,A/SSSS ranges between 0.3 and 0.5. This range is quite close to the range of 0.4to 0.6 obtained for SCI,B/SUC,B. The highest variability of ± 0.12 forB,UCB,CI,A,A/SSSS is obtained for k=0.8. For the remaining k values the variability ofB,UCB,CI,A,A/SSSS can be expressed within ± 0.05. This finding is very similar to the finding obtained for the variability of SCI,B/SUC,B.

连续箱梁节段悬臂支架现浇施工研究

箱梁节段悬臂支架现浇施工是利用落地支架替代挂篮悬臂施工浇筑的一种工法。施工工序决定了结构的计算和配筋方式,从力学角度解析了此工法在外荷载作用下的内力分布情况。结合某高架桥施工图设计,计算分析了自重、温度及支架局部沉降作用下悬臂状态梁体的应力分布情况,并据此提出了设计和施工要求,验算了使用阶段正、斜截面抗裂应力和承载力,结果均满足规范要求。提出了施工阶段的构造措施,最大限度减小裂缝的发生。