混凝土叠合板的板端受剪承载力分析

混凝土叠合板的预制底板外伸钢筋会给其制作和安装带来不便,但是否可以取消预制板底外伸钢筋存在争议。根据中国和美国的现行相关标准,建立了叠合板板端可能出现的受剪破坏模式及相应的受剪承载力计算公式,并通过算例分析了未留设预制底板外伸钢筋时,叠合板跨度、活荷载与后浇层最小厚度的关系。

工业化建筑技术与实践

在社会经济高速发展的推动下,建筑发展日新月异,人们对居住的要求也不断提高,而生态环境保护与传统施工工艺之间的矛盾日益突出,落后的人力资源又制约了施工技术的进步。为解决这些问题,在发达国家中已普遍应用的工业化建筑模式被引起关注并开始在我国一些工程项目上实践运用。建筑工业化模式即以工业化的生产方式来进行建筑建设,其中大量运用到预制混凝土构件亦称PC,本文对于PC特点→PC设计→PC模具→PC生产→PC运输→PC施工→PC验收的整个流程中各个环节的内容和注重点做了详细介绍。

Experimental study of pre-cracked concrete subjected to cryogenic freeze-thaw cycles based on an LNG concrete tank

To investigate the mechanical properties of concrete under the leakage condition for a liquefied natural gas storage tank,cryogenic freeze-thaw cycle tests were performed under liquid nitrogen refrigeration and water immersion melting.The effects of the cryogenic temperature,freeze-thaw cycle,pre-crack,and addition of steel fiber on the compressive strength,flexural strength,and splitting tensile concrete strength were analyzed.The experimental results show that the width of pre-cracks tends to expand after freeze-thaw cycles.When the freezing temperature is -80℃,the relative width of the pre-cracks expands by 1 to 2 times.However,when the freezing temperature is -120℃,the relative width of the pre-cracks expands by 2 to 5 times.Compared with the specimens without steel fibers,the specimens with steel fibers can still maintain a relatively complete appearance structure after the mechanical property tests.The compressive strength,flexural strength,and splitting tensile concrete strength decrease with the drop in the freezing temperature.After adding steel fibers,all of the three strengths increased.

Cyclic test and numerical study of seismic performance of precast segmental concrete double-columns

The comparative research on the seismic performance of grouted sleeve connected pier(GS)and prestressed precast segmental concrete pier(PC)is mostly carried out by numerical simulation.In this study,the GS pier and the PC pier of the new railway project from Hetian to Ruoqiang are taken into consideration.Two kinds of 1/5-scale assembled double-column specimens are made,and the quasi-static tests are carried out.The overall seismic performance of the two spliced piers is studied,and compared in terms of failure mechanism,bearing capacity,ductility,stiffness and energy dissipation capacity.The results show that the failure modes of both GS pier and PC pier are characterized by bending.However,the specific failure location and form are different.The GS pier presents a complete hysteretic curve,large equivalent stiffness and strong energy dissipation capacity.The hysteretic area of the PC pier is small.However,it has good self-reset ability and quasi-static residual displacement.Finite element models are set up using DispBeamColumn fiber elements and ZeroLength elements.The models that are calibrated with the test data can effectively simulate the damage development under monotonic loading.The load−displacement curves are in good agreement with the backbone curves of the test results.

BIM-based construction technologies for precast foamed lightweight concrete wallboards

To promote the visualisation and informatisation of the construction process of precast foamed lightweight concrete wallboards(PFLCWs),from the analysis of the construction requirements of PFLCWs,three key construction technologies based on building information modelling(BIM),namely,parameterised modelling for the PFLCW layout design,drawing generation to draw the PFLCW layout and quantity statistics for extracting PFLCW quantities,are proposed.Then,a reinforced concrete(RC)frame infilled with PFLCW is considered the test model to verify the feasibility of the aforementioned technologies.The results show that PFLCW layout design can be accomplished rapidly and visually using parameterised modelling technology.The PFLCW layout diagram can be generated directly using drawing generation technology.The proposed quantity statistics technology enables the automatic export of PFLCW bills of quantities.The built parameterised model helps construction workers rapidly and intuitively understand the specific layout details of PFLCWs.Moreover,the generated layout drawing and the bills of quantities based on the parameterised model can guide the production and on-site installation of PFLCWs.The research conclusions can serve as a practical guide and technical support for PFLCW engineering applications.

Operation Phase Problems of Prefabricated Residential Buildings with Integrated Autoclaved Aerated Concrete Panel Walls

Growing technical problems with the maintenance of precast concrete housing stock result in the search for efficient repair methods. The paper analyses the effects of flaws in the design concept and assembly accuracy of integrated AAC （autoclaved aerated concrete） panel walls, type GWO （Gazobetonowa Wielka P｜yta Ostonowa which means large cover panel from aerated concrete in English）, used as curtain walls in a system of precast concrete housing blocks erected in Lublin. The results of in-situ observations and laboratory tests of the panel walls have been described, and the opinion on the further use of these elements has been presented. As for the analysed case, there is no possibility of replacing damaged elements, thus, additional reinforcement with steel tendons has been proposed as a repair measure.

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.

Comparison and Finite Element Analysis of Steel or Synthetic Fiber Reinforced Precast, Prestressed Beams

Usage of fiber reinforced concrete to replace shear reinforcement has become more common in the precast industry in recent years. In some cases, the use of steel fibers could be problematic because of corrosion, hence, synthetic material could be a suitable alternative material solution. Thus, it would appear logical to undertake a comparison of these fibers＇ load bearing capacity to determine suitability in each case. In this paper, the bending and the shear tests of four large-scale and prestressed beams made of steel or synthetic fiber reinforced concrete without stirrups are presented. The post-cracking residual tensile strength diagram of the fibers, according to RILEM （International Union of Laboratories and Experts in Construction Materials, Systems and Structures） TC162, is given and the experimental behavior of the fiber solutions is compared. The modified fracture energy method is used to define an advanced material model for the fiber reinforced concrete in the finite element analysis. The numerical calculations and the test results are compared in terms of crack propagation and the loading-deflect＇ion process. As a consequence, both steel and synthetic fibers seem to be good alternatives to replace the stirrups. However, the behavior of each fiber is not the same. The numerical calculation provided a good approximation for the real scale tests.

预制砼组合桩－基础加固的新方法

基础加固历来是令人头痛的难题，最近国外推出了一种小型的预制砼组合桩，成功地解决了这个问题，本文仅对此作一简单的介绍，以供同仁借鉴和参考。

Experimental investigation on dynamic mechanical characteristics and microstructure of steam-cured concrete

Steam-cured concrete is widely used to manufacture prefabricated units of high-speed railway foundation structure such as girder and track slab.The dynamic mechanical property of steam-cured concrete is one of the key properties affecting service performance of high-speed railway foundation structure.In the present paper,serial macro/micro-experiments were carried out to investigate the dynamic elastic modulus,shear modulus,damping ratio,and microstructure of steam-cured concrete.The relationships between compositions,curing regime,microstructure,and dynamic properties of steam-cured concrete as well as the corresponding mechanisms were discussed.The results indicate that steam-cured concrete in early age has a larger dynamic elastic modulus and shear modulus as well as a smaller damping ratio compared with standard-cured concrete.On the contrary,at a later age a slightly smaller dynamic elastic modulus and a larger damping ratio of steam-cured concrete are observed.Addition of mineral admixture results in a bit lower dynamic elastic modulus and damping ratio of concrete than that of the control specimen without mineral admixtures.The achievements can provide some fundamental suggestions for materials parameters selection during structural design of steam-cured concrete precast element.