水闸工程大体积混凝体施工质量控制研究

本文着眼于水闸工程大体积混凝体施工质量控制问题展开探讨,笔者结合个人在这方面的一些实践工作经验提出几点思考和建议,希望借阅者能够积极提出改进意见。

浅谈大体积混凝土施工技术

大体积混凝土工程在建筑中占的比重越来越大,混凝土施工技术,对建筑物有很大影响,因此,在施工过程中应熟练掌握混凝土施工技术。

体外预应力混凝土梁力学特性分析

采用杆系有限元理论 ,建立了体外预应力混凝土梁在荷载作用下全过程非线性分析的计算方法 ,并编制了相应的计算机程序。结果表明 ,该方法是可靠的。为进一步深入研究体外预应力结构提供了依据。

体外预应力高强混凝土两跨连续梁模型试验

为研究预应力和混凝土材料对高强度混凝土体外预应力连续梁的力学行为的影响 ,设计并完成了 4片体外预应力高强度混凝土连续梁模型的静载试验。试验结果表明 :体外预应力连续梁的裂缝分布和发展规律与无粘结预应力梁相似 ;采用钢纤维提高负弯矩区的开裂载荷是有效的 ,而且利用钢纤维增强可在一定程度上限制裂缝发展并在卸载后使裂缝闭合 ;普通钢筋对分散裂缝和限制裂缝发展有利。

混凝土的劣化对钢筋混凝土桥梁结构耐久性的影响

21世纪以来,随着社会的发展,科学技术的发展,力学性能已不再占据主导地位,人们对现代混凝土的耐久性能的关注是与日俱增。在现代化的社会的创建中,混凝土的耐久性在各种大型工程施工建设中占有很重要的地位,我们有必要进行深入研究。随着混凝土的广泛应用,由混凝土带来的一些问题也逐渐显现出来。我们必须从根源上去寻找产生问题的原因。一项工程的优劣不仅仅是以实际使用年限也能客观反映出整项工程,而是要从其整体结构的力学性能来评定的优劣。在现代社会中,随着混凝土行业的逐步发展,我们要注重对矿渣水泥、干湿循环、氯离子寝室破坏影响程度和对混凝土碳化的影响进行深入研究。

土建施工中混凝土施工技术分析

随着经济不断的发展,我国社会的科技水平正在不断的提升,促使我国建筑行业发展的速度也是越来越快,在土木工程建设施工的建设中,混凝土的施工技术在施工中起着重要作用,在整个工程中,混凝土施工是重要环节,所以土建施工中混凝土施工的好坏决定着土建工程的质量好坏。由于当今经济快速发展,建筑施工正在火热的进行中,所以在施工时对混凝土施工要格外重视。本文主要针对混凝土施工技术进行了分析。

混凝土结构设计方法及其优化措施

近些年我国在建筑中投入资金和精力非常多,建筑的弊端也日渐突出。混凝土结构的凸显给建筑带来了新的力量的同时也带来了建筑的相关问题。我们应高谈质量关,提高思想的觉悟,把混凝土的建设缺陷改善好,把建筑做大做强。

浅谈混凝土在土建施工中技术分析

现如今经济的发展带动了我国产业突飞猛进的发展,其中对土建施工的建筑质量以及施工安全、技术等问题提出了新的要求,施工技术与施工材料的好坏直接影响着建筑质量。其中,混凝土是土建施工中的重要施工材料,为了提升在土建施工建设中我国混凝土施工技术的应用水平,保证土建施工项目的有序进行,本文首先分析了土建工程混凝土施工现状,重视混凝土施工技术及材料的研发及创新,就现阶段土建施工建设中的混凝土施工技术要点展开探讨,希望为现代土建行业的发展提供技术支持。

京沪高速铁路32米双线单箱梁的灌捣技术

根据大型箱梁的结构特点,通过与传统混凝土浇筑工艺的比较,提出了新的灌捣顺序及工艺和注意事项。

Strength of circular concrete columns under concentric compression

An experimental study, in which six columns were loaded concentrically toinvestigate the behavior of reinforced normal strength and high strength circular columns underconcentric compression, is described. The concrete strengths of the columns were 30 MPa and 60 MPa.The primary variables considered were the concrete strength and the amount of transversereinforcement. Test results indicate that smaller hoop spacing provides higher column capacity andgreater strength enhancement in a confined concrete core of columns. For the same lateralconfinement, high strength concrete columns develop lower strength enhancement than normal strengthconcrete columns. Both the strength enhancement ratio (f'_(cc) /f'_(co)) and the column capacityratio (P_(test)/P_o) were observed to show linear increase variations with rho_s f_(yt)/f'_c incircular columns.

Improved designed method of pervious concrete based on optimal volume ratio of paste to aggregate

An improved design method of pervious concrete was proposed to lower the deviation between the designed and actual porosity and maintain both mechanical property and permeability of pervious concrete. The improved design method is mainly based on the optimal volume ratio of paste to aggregate(VRPA), which was determined by testing the average thickness of cement paste coating aggregate. The performances of pervious concrete designed by the traditional method and the improved one were compared. The results show that with the increase of designed porosity, the reduction of compressive strength and flexural strength of pervious concrete designed by the improved method is significantly smaller than those designed by the traditional one. The maximum deviation between the designed and actual porosity of the pervious concrete by the improved method is only 1.54%, which is far less than 8.7% obtained by the traditional one. Micro-structural analysis shows that the porous distribution of pervious concrete designed by improved method exhibits better uniformity.

Complete splitting process of steel fiber reinforced concrete at intermediate strain rate

The complete splitting process of steel fiber reinforced concrete （SFRC） at intermediate strain rate was studied by experiment. The basic information of a self-developed SFRC dynamic test system matching with lnstron 1342 materials testing machine was given, and the experiment principle and the loading mode of cubic split specimen were introduced. During the experiment, 30 cubes of 150 mm×150 mm×150 mm and 36 cubes of 100 mm×100 mm×100 mm, designed and prepared according to C20 class SFRC with different volume fractions of steel fiber （0, 1%, 2%, 3%, 4%） were tested and analyzed. At the same time, the size effect of SFRC at intermediate strain rate was investigated. The experimental study indicates that SFRC size effect is not influenced by the loading speed or strain rate. When the steel fiber content increases from 0 to 4%, the splitting strength of SFRC increases from 100% to 261%, i.e. increasing by 161% compared with that of the common concrete. The loading rate increases from 1.33 kN/s to 80.00 kN/s, and the splitting tensile strength increases by 43.55%.

Ion-transport characteristics of new-old concrete composite system

New-old concrete composite system usually exists in concrete repairing structure.In the present work,series of experiments were carried out to investigate permeability and ion diffusion properties of new-old concrete composite by measuring 6-hour coulomb charge and chloride diffusivity.The interrelation among transport properties of new-old composites,new,and old concretes was also discussed.Results indicate that the permeability and chloride diffusivity of new-old concrete composite system closely interrelate to the corresponding new concrete and old concrete.The interfacial transition zone between new concrete and old concrete greatly influences the transport property of new-old concrete system.Compared with the corresponding new concrete and old concrete lower permeability and diffusivity values for the new-old concrete composites can be achieved by choosing suitable new concrete.It is possible to design the tailor-made new-old concrete composite system for repair given the transport property.

Experimental investigation of axially loaded steel fiber reinforced high strength concrete-filled steel tube columns

An experimental study on the compressive behavior of steel fiber reinforced concrete-filled steel tube columns is presented. Specimens were tested to investigate the effects of the concrete strength, the thickness of steel tube and the steel fiber volume fraction on the ultimate strength and the ductility. The experimental results indicate that the addition of steel fibers in concrete can significantly improve the ductility and the energy dissipation capacity of the concrete-filled steel tube columns and delay the local buckling of the steel tube, but has no obvious effect on the failure mode. It has also been found that the addition of steel fibers is a more effective method than using thicker steel tube in enhancing the ductility, and more advantageous in the case of higher strength concrete. An analytical model to estimate the load capacity is proposed for steel tube columns filled with both plain concrete and steel fiber reinforced concrete. The predicted results are in good agreement with the experimental ones obtained in this work and literatures.

Experimental study on mechanical property of stiffening-ribbed-hollow-pipe cast-in place reinforced concrete girderless floor

Stiffening-ribbed-hollow-pipe cast-in place reinforced concrete girderless floor is a new-style hollow girderless floor system. Model experimental researches of simply-supported floor and four-corners bearing floor have been done on this new kind of floor system in this paper. The experiment results show that the floor system has good mechanical property such as high bearing capacity, big rigidity and good tensility. A theoretical method is presented in this paper that the stiffening-ribbed-hollow-pipe girderless floor can be analyzed by being converted equivalently to orthotropic solid slab. It is indicated that the method is correct and reasonable according to the contrast between theoretical calculated results and experimental measured results. The theoretical results coincide with the measured results well.

A^2O工艺参数及对出水质量的影响

A2O处理工艺对于脱氮除磷效果是非常优异,因此,在全世界得到广泛应用,本文的主要目的分析了A2O工艺主要参数,及综述了A2O工艺参数对出水质量的影响。

Real-Time Temperature Control for High Arch Dam Based on Decision Support System

It is important and difficult to control the temperature of mass concrete structure during high arch dam construction.A new method with decision support system is presented for temperature control and crack prevention.It is a database system with functions of data storage,information inquiry,data analysis,early warning and resource sharing.Monitoring information during construction can be digitized via this system,and the intelligent analysis and dynamic control of concrete temperature can be conducted.This method has been applied in the construction of the Dagangshan Arch Dam in China and has proven to be very convenient.Based on the decision support of this system and the dynamic adjustment of construction measures,the concrete temperature of this project is well-controlled.

Comparison Research of Bed Joints Construction and Bed Joints Reinforcement on Shear Parameters of AAC Masonry Walls

The work presents the results of tests on the shear parameters of walls made of AAC （autoclaved aerated concrete, fb = 4.0 N/mm2） on the system mortar for thin M5 and M10 joints （fm = 6.1 N/mm2 and fro = 11.9 N/mm2） and on polyurethane glue and also walls without mortar （dry masonry）. The wall compression strength （on mortar M5 class） （per EN 1052-1：2000） amounted tofc,mv= 2.97 N/mm2 （fk = 2.48 N/mm2）, elastic modulus was Ecru = 2,040 N/mm2. Various structure of bed joints and head joints were applied and the following were used as reinforcement： steel trusses of EFZ 140/Z 140 type （Z1 type） and meshes made of plastics （Z2 type）. Based on the tests carried out with regard to unreinforced elements, it was shown that the filling in of head joints with mortar had an advantageous effect on the values of cracking and destruction stresses. While, with the use of reinforcement, advantageous increase of stress was obtained only when the mortar was laid twice on both bed surfaces of masonry units. The application of reinforcement in the bed joints when the mortar was laid only on one bed joints surface of the masonry units reduced the values of cracking and destruction stresses in relation to the values obtained in the unreinforced walls.

Retrofitting of RC Slabs Against Explosive Loads

With the increase of terrorist bomb attacks on buildings, there is a need to develop advanced retrofitting techniques to strengthen structures against blast loads. Currently, several guidelines including an Australian version for retrofitting reinforced concrete (RC) structures are available for the design of retrofitting systems against seismic and monotonic loads using steel or fibre reinforced polymer (FRP) plates that can be either adhesively bonded to the surface or near surface mounted to the concrete cover. However, none of these guidelines provide advice suitable for retrofitting structures subjected to blast loads. In this paper, numerical models are used to simulate the performance of retrofitted RC slabs subjected to blast loads. Airblast pressure distributions on the surface of the slabs estimated in a previous study are used as input in the analysis. A material damage model developed previously for concrete and an elastoplastic model for steel bars are employed in this research for modelling reinforced concrete behaviour due to explosive loads. The material models and blast loading are coded into a finite element computer program LS-DYNA3D to do the analysis. With the numerical model, parametric studies are conducted to investigate RC slabs retrofitted by either externally bonded or near-surface mounted plates or GFRP sheets subjected to blast loads. Discussion is made on the effectiveness of the retrofitting system for RC slabs against blast loads.

Experimental study on the compressive strength of grouted concrete block masonry based on nondestructive detection methods

Existing nondestructive detection methods were adopted to test the compressive strength of grouted concrete block masonry,i.e.the rebound method,pulling-out method and core drilling method were employed to test the strength of block,mortar and grouted concrete,respectively.The suitability of these methods for the testing of strength of grouted concrete block masonry was discussed,and the comprehensive strength of block masonry was appraised by combining existing nondestructive or micro-destructive detection methods.The nondestructive detection test on 25 grouted concrete block masonry specimens was carried out.Experimental results show that these methods mentioned above are applicable for the strength detection of grouted concrete block masonry.Moreover,the formulas of compressive strength,detection methods and proposals are given as well.