矿粉粒度及反应温度对高磷鲕状赤铁矿制备碳化铁的影响

基于对50根弯曲破坏钢筋混凝土圆柱低周反复试验结果的分析,建立了完整滞回环的数学表达式并推导得出等效阻尼比计算模型;以双柱墩桥梁为例,说明了建立桥梁整体结构等效阻尼比与墩柱端部塑性铰等效阻尼比关系的方法。研究表明,完整滞回环数学表达式较好地反映了弯曲破坏钢筋混凝土圆柱的滞回特性,得到的等效阻尼比模型计算结果与试验结果符合较好;采用建立的桥梁整体结构等效阻尼比与墩柱端部塑性铰等效阻尼比的关系进行pushover分析更能反映实际情况。采用等效阻尼比模型算得的目标位移与基于Rosenblueth模型和Kowalsky模型算得的位移之间存在较大差距。     

THE ORGANIZED DEVELOPMENT TREND OF CEMENT CONCRETE

Cement concrete is the building material which is widely and lar-gely used.Congenital deficiency of cement concrete is brittleness.Adding a little polymer into cement concrete can improve its brittleness and function and even provide concrete with new function.This is an organized development trend of cement concrete.     

Experimental Study on Moment Modulation of Prestressed Frames

Based on the experimental study of two prestressed frames in redistribution of Internal force, it can be concluded that the dominating influence factors on moment modulation are the relative height of equivalent compression zone, the secondary moment, the ratio of beam rigidity to column and development of cracks in the top of columns.The secondary moment is very important in modulation of frames. Especially, the secondary moment will governing the modulation when the relative height of equivalent compression zone is large enough.     

Cause Analysis and Treatment Measure on Cracks in New Reinforced Concrete Restricted by Old Web Concrete

In this paper, the cause analysis about cracks on the new concrete web poured in multi -span continuous box -girder of a main bridge was introduced. This bridge is a prestressed concrete one with variable cross sections and an 80 -meter main span. When casting reinforced concrete in large volume in box girder during vehicle transport service, the shrinkage cracks in cast -in place reinforced web concrete were formed due to the restriction of old web concrete. Then, the control measure taken on these cracks is discussed.     

混凝土拉压强度尺寸效应的细观非均质机理

为了从材料细观非均质角度揭示混凝土强度尺寸效应机理,建立了混凝土细观单元等效非均质力学模型,开展了立方体抗拉、抗压强度尺寸效应细观数值模拟研究。研究结果表明：混凝土强度尺寸效应根源于材料细观非均质性,随着模型尺寸的增加,混凝土材料细观单元弹性模量变异系数增大,材料细观非均质性增强,大尺寸模型内部存在更多的低强度单元或缺陷,导致混凝土立方体抗拉、抗压强度降低,极限应变减小,脆性增大;混凝土损伤破坏由少量集中区域,发散扩展形成多条非贯通的裂纹带;数值模拟结果与尺寸效应实验数据相吻合。     

外掺植物纤维对冻融作用下植被混凝土抗剪强度的影响

[目的]研究外掺2种植物纤维对冻融作用下植被混凝土抗剪强度的影响,为植被混凝土生态防护技术在高寒地区的应用提供科学依据。[方法]参考相关标准(GB/T50082-2009)中的慢冻法,采用2因素3水平全面交叉试验开展研究。[结果]未掺植物纤维的植被混凝土,冻融后黏聚力显著减小,内摩擦角变化不明显。掺入植物纤维可使经受5次冻融循环作用后植被混凝土的内摩擦角平均增加5°左右,并且随植物纤维掺量的增加,内摩擦角变化无明显规律,黏聚力则呈先增加后减小的趋势。表明纤维加筋对黏聚力的贡献存在临界掺量。棕纤维掺量对黏聚力的影响比黄麻纤维掺量更为敏感。[结论]外掺植物纤维可有效改善植被混凝土抵抗冻融破坏的能力,棕纤维和黄麻纤维的建议掺入比为0.6%和0.6%,具备推广应用前景。     

济南建邦黄河公路大桥主桥斜拉桥辅助墩顶超重主梁施工控制措施

济南建邦黄河大桥主桥是一座三塔、双索面的预应力混凝土梁斜拉桥,跨度布置为53.5＋56.5＋2×300＋56.5＋53.5m,中塔处为塔梁墩固结。主梁采用前支点挂篮进行施工,边跨合龙段位于过渡墩与辅助墩之间,中边跨合龙有一定难度。墩助墩顶主梁较重,施工难度大,本文主要介绍了该桥辅助墩顶超重主梁施工的方法及控制的措施。     

Modeling of Punching Failure Initiated by Concrete Splitting at Longitudinal Bar Level for Slabs without shear reinforcement

A new punching failure model has been developed for thinner slabs (≤120 mm thick) yet with a larger reinforcement ratio (＞085). On the assumption that the trigger of ultimate failure is the loss of dowel action caused by concrete splitting along the horizontal surface at longitudinal bar level, an equilibrium equation was established and an upper bound solution was obtained. The computation of punching shear capacity shows that for a total of 194 specimens collected, the mean and the coefficient of variation are 1072 and 0.250 respectively. As for the 116 members (out of all 194 ones) with the above character, it is found that there is little change of the mean (equal to 1017) yet an apparent decrease in the coefficient of variation (equal to 0184), which justifies the proposed hypothesis and refined mode in estimating punching resistance of such members.     

Boundary Element Method for Time-dependent Chloride Diffusion and the Chloride Distribution in Concrete

The process of chloride diffusion in concrete is time-dependent.The boundary element method (BEM) with a time-dependent diffusion coefficient is presented for chloride diffusion in concrete based on the suitable transformation of variables.The fundamental solution of the partial differential equation for time-dependent chloride diffusion in concrete is developed,and the compensation length of the diffusion field is defined as well as the compensation coefficient.The scheme of BEM with a time-dependent diffusion coefficient is developed.Two examples are given to demonstrate the accuracy and efficiency of the presented method and the rationality and the importance of the compensation length for the method.     

Experimental Analysis of Fire Resistant Performance of Concrete Frame with Damage Caused by Weak Earthquake

Two monolayer concrete frames with the same reinforcement, KJ1 and KJ2, were designed. KJ1 was designed to simulate low cyclic reversed loading test under weak earthquake. Besides, the fire response test, including temperature rising and lowing, was made by fixing the axial compression ratio of the column. For KJ2, the fire response test at the fixed axial compression ratio was made. The deformation response of the concrete frames in fire was studied. Comparative analysis of the apparent phenomenon, temperature curves, bearing capacity change of the frames were made based on the test results of KJ1 and KJ2. According to the simplified temperature distribution, the ultimate bearing capacity of the column under the high temperature was preliminarily determined. It is illustrated that the calculation results and finally test phenomenon are consistent according to the simplified section.