大跨度预应力混凝土结构施工质量控制研究

由于预应力混凝土的施工技术是一项专业性强、操作要求严、技术含量高的工作,所以预应力混凝土的质量控制对于结构施工的优劣起到至关重要的作用,进而影响到整个工程质量的好坏。鉴于此,本文从施工前、施工中和完工后三个阶段分析和归纳了预应力混凝土施工质量控制的要点,以期对工程实践起到参考和指导的作用。     

117大厦超厚板箱体单元现场拼装焊接的动态模拟

考虑到巨型箱型柱截面净尺寸大、壁厚、组装隔板多等特点,施工时需控制局部变形及整体变形,以保证构件几何尺寸精度。运用有限元软件,结合117大厦地下室核心巨柱焊接实例,对箱型柱80mm超厚板的焊接温度场及应力场进行动态模拟。计算结果表明:焊接热源的影响区域仅限于焊缝附近区域,而远离焊缝的区域基本维持在室温状态;随着焊接热源的移动,焊缝区域逐步达到屈服状态而发生塑性变形,但钢材仅发生弹性变形;简化模型的周边最大位移在毫米的数量级上,一定程度上可以认为焊接对与模型相连的构件的影响很小。     

北方寒冷地区农村住宅炕居新模式研究

随着社会的进步,农民已不再满足传统热炕的方式,因传统方式不仅增加开支、浪费能源,而且造成了严重的环境污染.开发和推广新式炕既可以实现节约能源、降低污染的目的,又可以实现供暖费用的降低,具有一定的实践价值和经济效益.同时又可以保护环境,促进农房建设的现代化.     

A new technique to measure the temperature of a rotating motor shaft

In the present study, a new technique has been developed for the measurement of the temperature of a motor shaft rotating at high speed. A radiation thermometer could be useful as one of the methods of measuring the surface temperature of said shaft. However, if the cross-sectional diameter of the motor shaft is small, it is necessary to closely approach the shaft rotating at high speed when measuring the temperature. The present paper reports the successful measurement of the local surface temperature and the temperature rise time of a motor shaft with a diameter of 10 mm diameter, rotating at high speed, by utilizing the potential of the melting points of different chemical reagents. The measurements were carried out at a distance of 1 m from the shaft, overcoming the difficulty in the use of a radiation thermometer.     

Assessing the effects of soil grading on the moisture content-dependent thermal conductivity of stabilised rammed earth materials

New data for both the dry-state and the moisture content-dependent thermal conductivity of cement-stabilised rammed earth (SRE) materials is presented. For highly compacted SRE materials, no correlation was found between thermal conductivity and dry density or void ratio. The thermal conductivity of SRE materials increases linearly with the saturation ratio, S_r of the material and can be expressed as λ¹, the moisture content-dependent thermal conductivity. The sensitivity of λ¹ to an increase in the saturation ratio of SRE materials varies according to soil grading. The influence of grading parameters on λ¹ can cause material variations of approximately 0.8 m² K/W. The experimental data has been applied to standard SRE wall design configurations and the effect of wall moisture content on the total thermal resistance has been shown. The R-value of an SRE wall irrespective of cavity insulation can vary by as much as 0.13 m² K/W.     

A framework for risk-informed decision support in electricity distribution companies utilizing input from quantitative risk assessment

Electricity distribution companies are to an increasing extent using risk assessment methods in their asset management practices. This paper presents an overall framework for risk-informed decision sup-port where simplified risk analysis methods are used for initial risk assessment, and quantitative risk analysis methods are used to perform more in-depth studies for selected problems. Quantitative risk assessment methods are far more laborious compared to simplified analyses, so it is important that such analyses are performed only to a limited number of risk problems.     

Shrinkage cracking of styrene butadiene polymeric emulsion‐modified concrete using rapid‐hardening cement

This study was performed to resolve the problem of cracks caused by the rapid hydration heat produced during the early setting stages of rapid‐hardening cement. To address the hydration heat of rapid‐hardening cement, we prepared a modified rapid‐hardening cement using calcium sulfoaluminate clinker combined with a styrene butadiene (SB) polymer. The performance of SB polymeric emulsion‐modified concrete made from modified rapid‐hardening cement was assessed by determining shrinkage (change in length, and plastic and autogenous shrinkage). The modified rapid‐hardening cement in combination with SB polymeric emulsion effectively reduced cracking. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Seismic design of concentric braced frames

In this paper some modifications to the design procedure, currently implemented in the modern European seismic code for ductile cross concentric braced frames (X-CBFs), are proposed. The code procedure is aimed to obtain a ductile and dissipative ultimate behaviour by imposing that the yielding of diagonal members occurs before the damage and premature failure of beams, columns and connections (capacity design); this approach, involving overstrength requirements and diagonal slenderness limitations, strongly affects the design of CBFs and generally leads to oversized structural solutions, thus suggesting a high weight premium related to the capacity design. The approach proposed by the authors in this paper consists of some modifications to the current design provisions of the European seismic codes, with the major aim of controlling the overstrength requirements to the non-dissipative members of braced frames, thus reducing the associated structural weight premium while preserving a satisfactory inelastic behaviour. In order to assess the reliability of the proposed approach, the results of non-linear FE analyses are presented in the paper with reference to three, and six‐ and nine‐storey buildings, for which different structural solutions are designed according to the current and the proposed approaches.     

Probabilistic assessment of tunnel construction performance based on data

A probabilistic model for estimating tunnel construction time is learnt with data from past tunnel projects. The model is based on the Dynamic Bayesian Network technique. The model inputs are determined through an analysis of data from three tunnels built by means of the conventional tunneling method. The data motivate the development of a novel probability distribution to describe the excavation performance. In addition, the probability of construction failure events and the delay caused by such failures are estimated using databases available in the literature. The model is applied to a case study, in which it is demonstrated how observations from the tunnel construction process can be included to continuously update the prediction of construction time.     

Onsite 3D marking for construction activity tracking

This article presents an innovative onsite 3D marking approach for tracking the progress of construction activities using an Ultra Wide Band (UWB) positioning system. The 3D marking approach is used to track activities that could not be tracked previously using object-based tracking models, including welding and inspection activities for pipelines. A field experimentation study on an industrial-type building construction project was conducted to demonstrate the method and evaluate its performance in a construction environment and a software application was developed using MATLAB to automate the data analysis and progress estimation procedure. The results of the field experiments confirmed the feasibility of the developed 3D marking approach for tracking a number of construction activities, such as welding and inspection, which are not associated with the addition or movement of objects on a site and therefore could not be tracked using traditional object-based models.