普通强度高性能混凝土的高温性能试验研究

为确保混凝土结构的抗火性,对普通强度高性能混凝土高温性能进行试验,探讨普通强度高性能混凝土的高温爆裂与力学性能。结果表明,普强高性能混凝土与高强高性能混凝土类似,湿含量和密实度是影响其高温爆裂的主要因素。当湿含量超过临界值时,爆裂几率随湿含量上升而增大;混凝土越密实,爆裂越严重。体积分数0.05%的聚丙烯纤维可防止普强高性能混凝土发生高温爆裂,纤维掺量越高,高温损伤程度越小。聚丙烯纤维对残余力学性能有一定的改善作用。     

高性能混凝土火灾条件下抗爆裂性能的研究

采用 15 0mm× 15 0mm× 3 0 0mm的普通混凝土、高性能混凝土及分别掺有聚丙烯纤维、引气剂和二者复合掺加的高性能混凝土 ,在 2 0～ 45 0℃范围内进行高性能混凝土火灾高温下的抗爆裂性能的研究。试验结果表明 ,聚丙烯纤维的加入可以大大提高高性能混凝土的抗爆裂性能 ,单独加入引气剂及复合掺加聚丙烯纤维和引气剂的抗爆裂效果并不理想。回弹试验表明 ,经受火灾高温后的高性能混凝土的残余力学性能呈一空间分布     

网状聚丙烯纤维和PVA纤维对高性能混凝土高温性能的影响

本文研究了含湿量和纤维对高性能混凝土高温爆裂和高温后残余力学性能的影响。研究结果表明,含湿量是影响高性能混凝土高温爆裂的主要因素。高性能混凝土发生爆裂的温度范围是350~450℃,爆裂的临界含湿量为63%~75%。试件含湿量越高,试件爆裂的频率和损伤程度越大。单掺体积分数为0.05%的网状聚丙烯纤维或PVA纤维即可防止高性能混凝土发生高温爆裂,纤维掺量越高,高性能混凝土高温损伤程度越小。单掺网状聚丙烯纤维和PVA纤维改善了高性能混凝土高温后残余抗压强度、残余劈拉强度和残余断裂能。     

高温后混凝土在复杂应力状态下的变形和强度特性的试验研究

本文对普通混凝土经高温后在两向压荷载作用下的变形和强度特性进行了试验研究。试件尺寸为１００ｍｍ×１００ｍｍ×５０ｍｍ。试验过程中测得了混凝土在常温，１５０℃～６００℃等５个温度级作用后的应力─应变关系曲线，分析了主任应力。及其对应的应变随温度的变化规律以及在温度作用后混凝土的二轴强度．应力一应变关系，最大应力处的应变等随主压应力比的变化规律，观察了试件的破坏形态，给出了相应的强度准则。     

深圳俊园梁式转换层施工技术

深圳俊园工程地上４７层 ,高１６１ｍ ,建筑面积７．５９万ｍ２,于１１层上设有梁式转换层。转换层建筑面积１４９０．７ｍ２,层高５．０ｍ ,共用钢筋６２０ｔ,混凝土强度等级为Ｃ５０。框支梁设计共５４根（图１）。在转换层中 ,框支梁４００ｍｍ×２５００ｍｍ和８００ｍｍ×２５００ｍｍ主要分布在建筑物四角处 ;框支梁９００ｍｍ×２５００ｍｍ、１０５０ｍｍ×２５００ｍｍ、１５００ｍｍ×２５００ｍｍ、１６００ｍｍ×２５００ｍｍ主要分布在核心筒周围 ;４根框支梁２０００ｍｍ×２５００ｍｍ分布在建筑物四周 ,长度达３０ｍ ,该梁…     

21m跨拱板仓库屋盖的预制和安装技术

浙江金华国家粮食储备库是国家重点工程项目 ,由６幢６０ｍ×２１ｍ、３幢９０ｍ×２１ｍ仓库组成 ,总建筑面积１３８５７ｍ２,主体由６２０ｍｍ厚中空砖墙 ,檐高８ｍ ,屋盖为２１ｍ跨薄壳板梁 ,每块拱板长２３．２ｍ ,宽１．１９ｍ ,底板纵向内配１２ ｊ５预应力筋、肋梁（２０ｍｍ×１５０ｍｍ）上下各６ ｊ５。拱板上弦均为纵向６＠２００、横向４＠２００非预应力筋 ,板厚４０ｍｍ ,混凝土设计强度等级为Ｃ３５（图１）。由于拱板跨度大 ,薄壳板梁均为预应力结构 ,制作、安装难度较大。１拱板台座１．１预制场地为节省造价 ,根据场地情…     

粮库拱板高处原位现浇施工

河南新县、新蔡等地国家粮食储备库工程 ,其屋盖结构设计均为预制１８ｍ跨拱板屋架。拱板下弦安装标高７．８００ｍ ,拱板平面尺寸为１９．９４ｍ×１．９８ｍ ,矢高１．８０ｍ（图１）。其下弦板为平板 ,板厚４０ｍｍ ;上弦板为抛物线弧板 ,板厚５０ｍｍ。上弦板和下弦板的两侧均为７０ｍｍ×１５０ｍｍ的肋梁 ,上下弦板间每隔１．８ｍ用４０ｍｍ厚预制隔板连接。拱板分布筋均为４ＬＬ５５０＠１５０冷轧带肋钢筋 ,混凝土强度等级上下弦板为Ｃ４０ ,隔板Ｃ２０。由于拱板屋架跨度大 ,构件壁薄 ,结构刚度差 ,给制作、运输和吊装带来困难 ,经…     

聚丙烯纤维混凝土板火灾后性能变化规律研究

通过模拟火灾现场材料表面实际升温曲线,对普通混凝土板及不同掺量聚丙烯纤维混凝土板进行火灾实验,结果表明:不同于高性能混凝土中常出现的高温爆裂现象,普通混凝土在经历高温与冷却的过程后,内外部温度梯度应力使其出现很大的裂缝。而通过掺加聚丙烯纤维可有效地缓解裂缝宽度,降低高温对普通混凝土的损伤。同时,通过测试高温前后混凝土板底面及侧面回弹值发现,由于混凝土板内部与侧面温度值在空间内分布不同,进而造成混凝土材料回弹值的损失也不一样,使得混凝土板残余力学性能呈空间分布,且与温度场有着直接的关系。     

利用楔劈拉伸试验研究混凝土的断裂特性

利用改进了的楔劈拉伸试验方法,对尺寸为２００ ｍ ｍ ×２００ ｍｍ ×１００ ｍ ｍ 的小型试件在不同的预制裂缝（ 初始裂缝）下的混凝土的开裂、裂缝稳定扩展进行了研究．试验结果表明,利用Ｓｈａｈ 等人提出的双参数模型所求得的混凝土稳定断裂韧度ＫｓＩｃ 与混凝土的初始裂缝长度ａ０ 无关,同时还发现混凝土临界裂缝尖端张开位移ＣＴＯＤｃ 及裂缝过程区长度ａｅ 与初始裂缝长度ａ０ 成反比关系．由于该方法所得到的结果同相应的三点弯曲试验所得到的结果几乎一致,因此其有可能成为判断混凝土失稳断裂材料参数的方法．     

框架节点处不同强度等级混凝土的施工措施

某工程地下１层,地上２２～２７层,总高１１９ｍ,建筑面积３００００ｍ２,纵向的大跨度梁（１８．５ｍ）采用后张钢绞线预应力梁,其尺寸为ｂ×ｈ×ｌ＝６００ｍｍ×８５０ｍｍ×１８５００ｍｍ;横向连系梁尺寸为ｂ×ｈ×ｌ＝４００ｍｍ×１０００ｍｍ×７８００ｍｍ,楼板厚１１０ｍｍ。框架柱的直径为１６５０ｍｍ。柱及预应力梁混凝土强度等级为Ｃ５５,剪力墙为Ｃ４０,非预应力梁及板为Ｃ３０,混凝土强度等级较多,给拌制、运输和浇筑都带来很多不便（图１）。１施工方案（１）采用预拌混凝土（商品混凝土）,由搅拌站负责配合比设计和试配,…     

Fire performance assessment of HPLWC hollow core slabs through full-scale furnace testing

High-Performance Light-Weight Concrete (HPLWC) is used for many structural applications when superior strength and low self-weight of the structural components are required. Among these applications there are thin floor structures, like hollow core slabs, that require characteristics of lightness, relatively high resistance and superior durability. Although the fire performance of normal strength concrete hollow core slabs has been extensively studied, the behavior of HPLWC hollow core slabs has not been suitably investigated.The paper reports the results of two full-scale furnace tests on HPLWC hollow core slabs. Each of them involved one panel with an applied load and one without load. The evolution of temperature inside the slabs was measured along with the load bearing capacity under fire conditions. During the first test severe spalling occurred in the loaded slab while during the second one, performed on slabs cured for some months under dry conditions, spalling did not occur. Finite elements simulations were also carried out in order to support the interpretation of the experimental results. Experimental and numerical investigations gave insight into the fire performance of HPLWC hollow core slabs and highlighted the influence of dry curing conditions in reducing the spalling and increasing the fire resistance.     

自密实混凝土结构抗火研究进展

对近年来自密实混凝土结构抗火研究进展作了总结,包括自密实混凝土高温材性试验和足尺自密实混凝土构件的抗火性能试验研究。从自密实混凝土高温下和高温后的力学性能、热工性能和应力-应变关系等方面入手,总结和分析了已有研究所取得的成果和尚存的一些问题。分析表明：高温下自密实混凝土质量和抗压强度损失严重,通过添加不同添加剂可使其得到改善。由于其密度高,在高温下自密实混凝土比普通混凝土更易发生高温爆裂,加入纤维可以有效抑制爆裂但会降低抗压强度。高温爆裂的抑制和抗压强度降低的平衡研究,自密实混凝土结构高温后损伤鉴定和修复加固,以及自密实混凝土加固结构的防火保护措施研究等是今后一段时间自密实混凝土结构抗火研究领域值得关注的课题。     

预应力混凝土结构抗火研究进展

总结了近年来预应力混凝土结构抗火研究进展,包括预应力筋高温力学性能、预应力混凝土梁板抗火试验、足尺预应力混凝土梁板抗火性能、活性粉末混凝土高温力学性能、高温下混凝土的爆裂规律、CFRP布加固混凝土梁板抗火性能、预应力混凝土梁板以及用耐高温无机胶粘贴CFRP布加固的混凝土梁板抗火设计方法等,分析了预应力混凝土结构和CFRP布加固混凝土结构抗火研究中尚存在的一些问题。分析表明：大尺度预应力混凝土梁的抗火性能优于小尺度梁,用耐高温无机胶替代环氧类有机胶粘贴CFRP布加固混凝土梁板并以此提高结构的抗火性能是可行的,大尺度预应力构件及预应力整体结构的抗火性能及其抗火设计方法等是今后一段时间预应力混凝土结构抗火研究领域值得关注的课题。     

混凝土高温试验及高温后抗压残余强度研究

介绍混凝土高温试验过程和试验现象。对高温后混凝土的抗压强度进行了力学性能测试，得到高温后混凝土试块的抗压残余强度。综合4种高温后混凝土抗压残余强度公式，通过曲线图形与本试验结果进行对照比较，找出一致性较优公式。     

高强混凝土受火后湿扩散特性研究

采用PCK法测量了高强混凝土受火后的吸水率 ,用以表征混凝土受火后的渗透性及高温时的温扩散能力。研究表明 ,随着受火温度升高、恒温时间延长 ,试件吸水率增大 ,且温度的影响更敏感 ;PP纤维掺入后可提高试件的湿扩散能力 ,从而降低爆裂度 ,但也削弱了受火后混凝土抗环境介质渗透的能力 ;硅灰混凝土结构更为密实 ,湿扩散能力低 ,更易爆裂。验证了蒸气压是爆裂的主要原因     

Improvement of residual compressive strength and spalling resistance of high-strength RC columns subjected to fire

This paper investigates the spalling properties of high-strength concrete in order to improve the residual compressive strength and spalling resistance in specimens subjected to 3 h of unloading fire conditions. This study consists of three series of experiments with eighteen different specimens varying in fiber type and content, finishing material and simultaneous fiber content and lateral confinement. They were fabricated to a 300 × 300 × 600 mm mock-up size. Results of the fire test showed that the control concrete was explosive, while the specimens that contained more than 0.1 vol% of polypropylene (PP) and polyvinylalcohol (PVA) fibers were prevented from spalling. One specimen, finished by a fire endurance spray, exhibited even more severe spalling than the control concrete. The specimen containing 0.1 vol% of PP fiber and using a confining metal fabric at the same time, showed the most effective spalling resistance; in particular, the residual compressive strength ratio was even higher than that of the control concrete before the fire test. It was demonstrated that adding fibers in concrete prevented the spalling occurrence and confining metal fabric around the main bars of concrete specimens can secure the strength of structures during the conditions of elevated temperature.     

The structural behavior and simplified thermal analysis of normal-strength and high-strength concrete beams under fire

The objective of this study is to investigate the effects of concrete compressive strength and cover thickness on the structural behavior of reinforced concrete (RC) beams under fire. For this purpose, four normal-strength and high-strength concrete test beams were fabricated and tested under the ISO 834 standard fire curve to point of the failure. The test set-up was designed to evaluate the heat distribution and displacement changes of simply supported beams subjected to sustained loads under fire. Test results for normal-strength and high-strength concrete beams were compared for each of the test variables. The test results show that the relationships between time and temperature distributions in the beam sections are very similar and are unrelated to the strength of the concrete, with the exception of the upper part of the beam section. They also showed that the rates of deflection increase for both normal-strength and high-strength concrete beams is very similar before spalling but becomes remarkably high for high-strength concrete beams after spalling. A simplified model was proposed to determine the effect of spalling on the temperature gradient of a high-strength concrete beam. The results of finite difference method (FDM) analysis using this proposed model showed a section temperature gradient that was similar to that of the test results.     

双向面内约束混凝土板火灾试验及数值分析

为研究混凝土板在双向面内约束作用下的火灾行为,对4块混凝土矩形板进行恒载-升温条件下的火灾试验,获得试验板沿板厚的温度场分布、钢筋温度、板平面内外变形、板角约束力和破坏模式等规律。在此基础上,编程对试验板的温度场、变形行为和薄膜机理进行数值分析。结果表明：对于双向面内约束板,其裂缝模式与简支板和单向约束板不同;面内约束作用致使混凝土板后期变形及变形速率增大;不同面内约束下混凝土板具有不同的薄膜机理;相比单向面内约束,双向约束作用更不利于混凝土板受拉薄膜效应发展。     

The behaviour of reinforced concrete slabs in fire

In this paper a robust model is presented based on the previous layer procedure developed by the author to also take into account the effects of concrete spalling on the behaviour of concrete slabs under fire conditions. In this study, a detailed analysis of a uniformly loaded reinforced concrete slab subject to different degrees of concrete spalling under a standard fire regime is first carried out. Further, a series of analysis of floor slabs with different degrees of concrete spalling is also performed on a generic reinforced concrete building. A total of 16 cases have been analysed using different degrees of spalling on the slabs, with different extents and positions of localised fire compartments. It is clear that adjacent cool structures provide considerable thermal restraint to the floor slabs within the fire compartment. And it is evident that the compressive membrane force within the slabs is a major player in reducing the impact of concrete spalling on the structural behaviour of floor slabs in fire.