工民建混凝土施工的质量控制措施

本文通过阐述混凝土施工质量控制的重要意义,着重分析影响混凝土质量的主要原因,提出混凝土施工质量的具体控制措施。

土建施工建设中的混凝土施工技术探讨

随着当前社会的高速发展,我国城市化水平逐步加强,越来越多的地区开始建造更多的施工工程,但是在开展土建施工建设时,混凝土技术仍旧存在着很大问题。虽然混凝土技术在目前我国发展中已经得到了非常大的提高,但是在实际施工时,混凝土施工技术及质量较差,就会直接影响到整体施工的效果。为了确保土建工程顺利开展,并且混凝土施工质量符合社会对于土建工程的实际,帮助混凝土施工技术逐步提高。

关于建筑工程混凝土施工技术的难点及对策探讨

科技在进步,技术在发展,建筑行业相比之前更是有着飞速的发展。此篇文章主要对混凝土施工技术的难点和在建筑施工过程中施工技术方面存在的一些问题以及施工的技术方法及措施进行分析探讨。

浅谈混凝土施工质量的控制措施

本文就混凝土的工艺要求、施工队伍的素质、原材料的质量等因素都是混凝土施工的质量控制的一天难题。

高标号混凝土浇筑过程中的裂缝控制与防治措施

现阶段,现浇高标号混凝土施工技术在房屋建筑中的应用, 在一定程度上提升了房屋建筑施工效率。房屋建筑工程现浇高标号混凝土裂缝包括温度收缩裂缝、材料干缩裂缝、不均匀沉降裂缝多种类型,多分布在建筑现浇高标号混凝土楼板底面、顶面与支座位置, 对建筑现浇高标号混凝土楼板质量造成了较大的负面影响。因此,本文重点研究房屋建筑现浇高标号混凝土施工中裂缝技术控制,不仅可以推动我国建筑工程行业的发展,还可以促进相关学科的发展,为今后的科研工作奠定基础。

混凝土路面施工技术在公路施工中的应用及质量控制措施

当前的改革面对城市农村的双向发展现状可以概括为围绕着新农村施工实施农村改革。本文主要以公路上的施工作为主要探讨对象,其中公路混凝土的施工工作成为大篇幅谈讨论的重点,在如今的农村经济发展中,便利化的交通网要求交通路面必须保证质量符合规范,在这样的实际前提之下,混凝土路面的实施工作必须要有一个合理的质量控制以及施工应用管理的标准,所以本文主要通过整合施工过程的应用问题在质量控制应达到的规范进行进入探讨。

The Ceneri Base Tunnel＂ Construction Experience with the Southern Portion of the Flat Railway Line Crossing the Swiss Alps

This paper summarizes the experience that was gained during the construction of the 15.4 km long Ceneri Base Tunnel （CBT）, which is the southern part of the fiat railway line crossing the Swiss Alps from north to south. The project consisted of a twin tube with a diameter of 9 m interconnected by cross- passages, each 325 m long. In the middle of the alignment and at its southern end, large caverns were excavated for logistical and operational requirements. The total excavation length amounted to approx- imately 40 km. The tunnel crossed Alpine rock formations comprising a variety of rock typologies and several fault zones. The maximum overburden amounted to 850 m. The excavation of the main tunnels and of the cross-passages was executed by means of drill-and-blast （D＆B） excavation. The support con- sisted of bolts, meshes, fiber-reinforced shotcrete and, when required, steel ribs. A gripper tunnel boring machine （TBM） was used in order to excavate the access tunnel. The high overburden caused squeezing rock conditions, which are characterized by large anisotropic convergences when crossing weaker rock formations. The latter required the installation of a deformable support. At the north portal, the tunnel （with an enlarged cross-section） passed underneath the A2 Swiss highway （the major road axis connect- ing the north and south of Switzerland） at a small overburden and through soft ground. Vertical and sub- horizontal jet grouting in combination with partial-face excavation was successfully implemented in order to limit the surface settlements. The south portal was located in a dense urban area. The excavation from the south portal included an approximately 220 m long cut-and-cover tunnel, followed by about 300 m of D＆B excavation in a bad rock formation. The very low overburden, poor rock quality, and demanding crossing with an existing road tunnel （at a vertical distance of only 4 m） required special excavation methods through reduced sectors and special blasting techniques in order to limit the blast-induced vibrations. The application of a comprehensive risk management procedure, the execution of an intensive surface survey, and the adaptability of the tunnel design to the encountered geological conditions allowed the successful completion of the excavation works.

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.

A Survey of Steel Arch Bridges in China

A review of the current status and progress of steel arch bridges in China is presented in this paper. The existing steel arch bridges in China were analyzed in terms of steel material, span, structure type, main arch rib form and construction method. The comparison with CFST arch bridges and RC arch bridges is also conducted. It is shown that steel arch bridge has gain rapid development in China since 2000, characterized by long main spans. As for the span, most of the steel arch bridges have a span less than 250 m, while when the span exceeds 350 m, steel arch bridges are strongly competitive against CFST or RC arch bridges. Over 80% of the bridges are through and half-through bridge types, and the arch ribs are hingeless structures. The rise-to-span ratios of the arches are mainly between 1：4 and 1： 5. Most of the arches use solid box ribs, and a small portion of arches use truss ribs in which box sections are mostly adopted for the truss members. The cantilever method and scaffolding method are the two main construction methods used, but some other construction methods have also been developed.

Research and application of schemes for constructing concrete pillars in large section finishing cut in backfill coal mining

Based on the technology of controlling surrounding rock deformation by constructing concrete pillars in large section finishing cut in backfill coal mining, the characteristics of vertical stress on concrete pillars and main factors influencing pillar stability are analyzed. By building a Winkler elastic foundation mechanical model for the support system constituted of coal pillar, backfill body and concrete pillars, mechanical calculation on stability of concrete pillar is carried out to evaluate the pillar stability and safety. Seven numeral models in three schemes with different pillar sizes, inter-row distances and compression ratios at the stopes were analyzed through numerical simulation according to width reduction principle. The practice of finishing cut at IIIB44 workface at Yangzhuang coal mine shows that： when the actual compression ratio is 86.5%, construction size inside the finishing cut is 2000 mm x 2000 mm and the interval between concrete pillars is 2000 mm x 2000 mm, the pillars can be stable with the maximum movement of two sides of each pillar being only 83 mm and 54 mm, which achieves the expected effect.

The construction design and practice of Three Gorges Project

The construction of Three Gorges Project (TGP) is characterized by large construction scale,high construction intensity and complexity in technology.In view of various technical difficulties such as navigation in construction period,two river closures,high-intensity concrete and earth-rock construction,high-intensity construction and demolition of RCC (roller compacted concrete) cofferdam in stage III and immediate navigation of double-line five-step shiplock after impoundment of reservoir,the scheme of river diversion during construction is adopted,namely "diversion in 3 stages,open channel navigation and cofferdam power generation".The practice and innovation achievements in river diversion during construction as well as earth-rock and concrete construction are presented emphatically.

Influence of concrete differential aging time on the construction phases analysis of the Fenghua River Bridge

The Fenghua River Bridge is a major structure on the highway between Hengzhang and Guojiachi, which is to be built with a four-span prestress concrete (PC) box girder and symmetrical cantilever castings. In this paper, a finite element method (FEM) model is set up to study the effects of concrete differential aging time on the construction phases of the Fenghua River Bridge by calculating the vertical displacement of the folding segment of the middle span and the longitudinal bending moment of Pier 12#. In the model, the girders are classified into 150 changing sections based on the desgn scheme, and their construction is to be carried in 16 phases respectively to build 12 blocks connected by a side folding segment and a middle folding segment, covered with a second dead load and in completion for 20 years. It is found that the internal forces and deformations of the concrete structures at the aging time of 60 d are quite different from those of 0 d aging time while the behaviors of the structures of 120 d aging time is nearly the same as those of 60 d aging time― the differences are so small that can be neglected, suggesting that the creep develops obviously about one month after the cement is hardened and the development fades later on.

Influence of construction interfaces on dynamic characteristics of roller compacted concrete dams

To study the influence of construction interfaces on dynamic characteristics of roller compacted concrete dams(RCCDs),mechanical properties of construction interfaces are firstly analyzed. Then, the viscous-spring artificial boundary(VSAB) is adopted to simulate the radiation damping of their infinite foundations, and based on the Marc software, a simplified seismic motion input method is presented by the equivalent nodal loads. Finally, based on the practical engineering of a RCC gravity dam, effects of radiation damping and construction interfaces on the dynamic characteristics of dams are investigated in detail. Analysis results show that dynamic response of the RCC gravity dam significantly reduces about 25% when the radiation damping of infinite foundation is considered. Hot interfaces and the normal cold interfaces have little influence on the dynamic response of the RCC gravity dam.However, nonlinear fracture along the cold interfaces at the dam heel will occur under the designed earthquake if the cold interfaces are combined poorly. Therefore, to avoid the fractures along the construction interfaces under the potential super earthquakes,combination quality of the RCC layers should be significantly ensured.

Key Technologies in the Design and Construction of 300 m Ultra-High Arch Dams

Starting with the Ertan arch dam （240 m high, 3300 MW） in 2000, China successfully built a total of seven ultra-high arch dams over 200 m tall by the end of 2014. Among these, the ]inping 1 （305 m）, Xiaowan （294.5m）, and Xiluodu （285.5 m） arch dams have reached the 300 m height level （i.e., near or over 300 m）, making them the tallest arch dams in the world. The design and construction of these 300 m ultra-high arch dams posed significant challenges, due to high water pressures, high seismic de- sign criteria, and complex geological conditions. The engineering team successfully tackled these chal- lenges and made critical breakthroughs, especially in the area of safety control. In this paper, the author summarizes various key technological aspects involved in the design and construction of 300 m ultra- high arch dams, including the strength and stability of foundation rock, excavation of the dam base and surface treatment, dam shape optimization, safety design guidelines, seismic analysis and design, treatment of a complex foundation, concrete temperature control, and crack prevention. The experience gained from these projects should be valuable for future practitioners.

Linear monitoring for cast-in-place reinforced concrete arch bridge construction

Linear monitoring is an important link of bridge construction control,which is conducted in key processes of construction to ensure the security of bridge in construction procedure. Combining with main arch construction monitoring program of No. 2 bridge in north district of Changbai international tourism resort,main content and key technologies are recommended. Considering the various influential factors during the construction process,linear adjustment is handled to ensure that the stress and linear of main arch meet design requirements.

Study on Life Prediction Model of Concrete Dam Based on Dry Zoning and Damage Theory

Concrete dam construction, reservoir impoundment and operation are a complicated and long-term process. During the course of this process dam suffers lots of factors including changing temperature, humidity, deformation, loads and restraints around dam. With time going by, damage to darn concrete happens. As a result, the strength, stiffness and resistance of concrete will decrease accompanying with damage accumulation and dam structure performance behavior and lifetime will be shorten or even destructed. At present, most of researches focus on concrete material itself and seldom consider effects of water content for concrete structures. That is apparently inconsistent with the actual situation. In engineering practice, it is urgently needed to assess existing dam structure damage state considering dry zoning in concrete. Through taking C30 dam concrete as standard specimen, alternate freezing and thawing tests are undertaken and changing law of time-dependent concrete damage state resulting in alternate wetting and drying has been studied in this paper. And then calculation formulas of time-dependent concrete damage evolution process considering alternate wetting and drying under condition of freeze-thaw cycle tests are established. Combining with four parameters Hsieh-Ting-Chen （ H -T-C ） model, some relevant factors or parameters are obtained through indoor testing and life prediction model of concrete dam based on dry zoning and damage theory is put forward which provides technical supports for dam safety evaluation and management of sustainable development.

Intelligent compaction theory of high roller compacted concrete dam

The concept and realization process of intelligent compaction for the construction of high roller compacted concrete dam were presented, as well as the theory of monitoring and intelligent feedback control. Based on the real-time analysis of the compaction index, a multiple regression model of the dam compactness was established and a realime estimation method of compaction quality for the entire work area of roller compacted concrete dam was proposed finally. The adaptive adjustment of the roiling process parameters was achieved, with the speed, the exciting force, the roller pass and the compaction thickness meeting the standards during the whole construction process. As a result, the compaction quality and construction efficiency can be improved. The research provides a new way for the construction quality control of roller compacted concrete dam.

Crucial technologies in the design of Xiluodu Super High Arch Dam

Some super high arch dams （ SHADs）, like Xiluodu Arch Dam, after their heights reaching the magnitude of 300 m, confront lots of technical challenges in design and construction. Several crucial technologies of 6 SHADs will be reviewed and discussed in this and consecutive papers, including Xiluodu, Jinping I in China, Baktiary in Iran, ete. , on the topics of the research method, criterion for evaluation and engineering application of dam safety analysis and evaluation, reasonable dam base interface, dam shape optimization, comprehensive treatments of complex foundation, anti-seismic engineering, dam construction material, concrete placement and temperature control, instrumentation and monitoring of dam operation, etc. This paper will mainly focus on the overall safety of SHADs, reasonable dam base interface analysis and evaluation and their engineering application.

Artificial Stone in France （1830-1930）： A Materialbetween Modernity and Tradition

1920s and 1930s architecture has often been associated with the use of modern materials, such as reinforced concrete, glass and steel, mainly thanks to the role given them by the historiography of the modern, of presenting a break with former tradition and of spreading the need of architectural renewal. The study of architecture from the point of view of construction techniques evidences, instead, how architectural renewal started earlier, during the 19 century and involved the whole realm of building, even tradition-associated materials, such as wood and stone. Indeed, artificial stone （which appeared in early 19 century） represents--above all in France--a link between traditional construction in stone and the newborn reinforced-concrete technique, so as to underline the gradual shift from 19 century construction codes to the new industrial construction techniques, which in the 1920s and 1930s tend to overlap and blend, in this way determining a material continuity of modern and 19 century architecture.

Numerical Staged Construction Analysis of Precast Concrete Bridge

The paper discussed about the staged construction analysis of two-span precast-girder bridge considering time dependent effects, namely creep and aging of concrete. Results obtained showed that it is very important to consider construction stage in the analysis of bridge because of stress resultants which are important in design process and very different from those obtained without the consideration of construction stage. This fact is especially important for bridges, because construction period continues along time and loads may change during the construction period and after.