钢管活性粉末混凝土界面粘结强度计算方法研究

为研究钢管活性粉末混凝土(RPC)的粘结滑移机理,对10个钢管约束RPC试件进行单轴推出试验,分析了试件的破坏特征、荷载-滑移曲线和钢管应变,探讨了长径比、径厚比以及RPC强度的影响规律,结果表明:套箍系数较小时,荷载-滑移曲线有明显的下降段,较大时未出现下降;粘结强度总体随径厚比的减小和长径比的增大而提高,RPC强度的影响不明显;当粘结应力达到粘结强度时,钢管的横向变形系数超过泊松比,其约束作用开始发挥。在此基础上,建立了钢管内压力与粘结应力的关系,并通过试验数据回归提出了钢管约束RPC粘结强度计算模型,公式计算与试验结果符合较好。

纤维聚合物筋混凝土粘结性能的基本问题

纤维聚合物筋与钢筋性能的差异 ,使纤维聚合物筋混凝土的粘结性能与钢筋混凝土的粘结性能存在明显不同 .根据纤维聚合物筋与混凝土之间的传力机理 ,讨论了粘结应力、纤维聚合物筋应力以及锚固长度之间的关系 ,建立了纤维聚合物筋混凝土粘结计算的基本公式 .在总结国内外已有的纤维聚合物筋与混凝土粘结滑移本构模型的基础上 ,提出了粘结滑移的连续曲线本构模型 .该模型以粘结滑移曲线的三个关键点为基础 ,物理概念明确、光滑连续 .最后 ,讨论了锚固长度的计算问题 。

不同截面类型钢管RPC界面粘结性能对比研究

本项目主要完成了30根圆钢管和15根方钢管RPC界面粘结强度试验,研究不同截面类型对钢管RPC界面粘结强度的影响,通过对比试验得出钢管RPC界面作用的主要影响因素的规律性的统一表达,对方形、圆形两种截面钢管活性粉末混凝土界面粘结滑移性能及工作机理进行了深入研究,得到了钢管RPC界面粘结强度理论解的计算公式,并对不同截面钢管RPC界面粘结强度进行了对比分析,通过对比试验得出了钢管RPC界面作用的主要影响因素,为工程设计奠定了基础,也为有限元分析提供试验数据。

压型钢板-混凝土组合楼板粘结试验研究

压型钢板-混凝土组合楼板因其具有刚度大、延性好、施工方便、经济效益优越等特点,目前在我国得到较为广泛的应用。通过对3种共27块(2W、3W、BONDECK各9块,2W、3W为开口板,BONDECK为缩口板)镀锌压型钢板-混凝土组合楼板的试验研究,分析了不同剪跨下,混凝土强度、压型钢板厚度、组合楼板厚度等因素对组合楼板极限承载力的影响,总结了压型钢板-混凝土组合楼板剪切-粘结破坏的形态及受力变形性能,利用回归分析提出了以混凝土抗拉强度特征值ft表征的剪切-粘结承载力计算公式。

Experimental research on mechanical properties of prestressed truss concrete composite beam encased with circular steel tube

Tests of 4 simply supported unbonded prestressed truss concrete composite beams encased with circular steel tube were carried out. It is found that the ratio of the stress increment of the unbonded tendon to that of the tensile steel tube is 0.252 during the using stage,and the average crack space of beams depends on the ratio of the sum of the bottom chord steel tube's outside diameter and the secondary bottom chord steel tube's section area to the effective tensile concrete area. The coefficient of uneven crack distribution is 1.68 and the formula for the calculation of crack width is established. Test results indicate that the ultimate stress increment of unbonded tendon in the beams decreases in linearity with the increase of the composite reinforcement index β0. The pure bending region of beams accords with the plane section assumption from loading to failure. The calculation formula of ultimate stress increment of the unbonded tendon and the method to calculate the bearing capacity of normal section of beams have been presented. Besides,the method to calculate the stiffness of this sort of beams is brought forward as well.

Synergistic effect of a new wedge-bond-type anchor for CFRP tendons

In order to improve the anchoring force of anchors for carbon fiber reinforced polymer(CFRP) tendons further, a new wedge-bond-type anchor for CFRP tendons was developed. The increment in anchoring force induced by the clamping segment of anchor was studied. Taking the deformation of all parts in clamping segment in the transverse direction into consideration, the calculation formula for the increment of anchoring force was proposed based on the linear elastic hypotheses. The proposed model is verified by experiments and conclusions are drawn that the anchoring force is influenced mainly by the inclination angle of clamping pieces, the length of clamping part and the thickness of bonding medium. Especially, the thickness of bonding medium should be lowered in design to improve the synergistic effect of anchors.

A Model for Agglomeration in Bio-fuel Fired Fluidized Bed

A mathematical model has been developed to describe the agglomeration process in bio-fuel fired fluidized bed combustor. Based on the balance mechanism of the adhesive force caused by liquid bonding between two parti- cles and the breaking force induced by bubbles in the fiuidized bed, the model considers modified Urbain model and chemical equilibrium calculations using FactSage modeling. This model prediction accounts for the evolve- ment of the adhesive and breaking forces, and clearly demonstrates that the different composition of ash, the in- creasing liquid phase matter and the fiuidization velocity cause defluidization in fluidized bed. In this model, it is the first time to hypothesize that the bonding stress between two particles is proportional to mass fraction of liq- uid phase and inversely proportional to the diameter of particles and viscosity of liquid phase. The defluidization time calculated by this model shows good agreement with that from the experimental data.

Effects of gas compressibility and surface roughness on the flow in microfluidic devices

With the development of the micro-electro-mechanical system (MEMS),the flow characteristics in micro-channels have drawn increasing attention.In this paper,numerical simulations are conducted to investigate the flow characteristics of compressible flow through micro-channels and micronozzles.An improved surface roughness viscosity model is used to simulate the effect of surface roughness on micro-channels flow characteristics.Using this model,better agreements between the computational results and the experimental data are found.The result indicates that the surface roughness is one of the important factors affecting the flow characteristics of gas through micro-channels.The numerical investigation on the expansion channel shows that by using the laminar model that considers surface roughness,the computational results and experimental data are consistent when Re<450,whereas deviation increases when Re>450.Based on the synthetic model with considerations of turbulence viscosity and surface roughness,the numerical results and the experimental data are identical.