火灾后钢骨超高强混凝土柱抗震性能的研究

从高温后钢材及混凝土力学性能、高强混凝土材料力学性能、火灾后的钢骨混凝土柱力学性能3个方面进行了论述,介绍了目前国内外钢骨超高强混凝土结构抗火研究的主要进展及成果。     

预应力混凝土结构抗火性能的研究进展

对预应力混凝土结构抗火性能的国内外最新研究进展进行较系统的综述与分析:研究预应力高强钢丝、钢绞线和新型纤维增强塑料(FRP)筋在高温下以及高温后的受力性能,总结相应的计算模型;探讨预应力混凝土梁和预应力混凝土板的抗火性能,并重点分析预应力混凝土框架在火灾作用下的受力特性;最后,对今后预应力混凝土结构抗火性能研究的发展趋势作了展望。     

Investigating the unexposed surface temperature criteria of standard ASTM E119

Information and data were obtained to evaluate the unexposed surface temperature criteria of standard ASTM E119. The investigation consisted of: (1) reviewing literature to obtain information on the development of ASTM E119 and the unexposed surface temperature rise criteria, (2) conducting fire tests to obtain temperature data on slabs with various materials placed on the unexposed surface and (3) conducting ignition tests on these materials to obtain their approximate temperature at ignition. The information and data increased the knowledge concerning the relationship between the unexposed surface temperature rise criteria of ASTM E119 and the ignition temperature of common combustible materials.Winner of the 1985 Harry C. Bigglestone Award for Excellence in Written Communication of Fire Protection Concepts. Reference: Kenneth J. Schwartz and T. T. Lie, Investigating the Unexposed Surface Temperature Criteria of Standard ASTM E119,Fire Technology, Vol. 21, No. 3, August 1985, p. 169.     

A Numerical Study on the Thermo-mechanical Response of a Composite Beam Exposed to Fire

This study presents an analytical framework for estimating the thermo-mechanical behavior of a composite beam exposed to fire. The framework involves: a fire simulation from which the evolution of temperature on the structure surface is obtained; data transfer by an interface model, whereby the surface temperature is assigned to the finite element model of the structure for thermo-mechanical analysis; and nonlinear thermo-mechanical analysis for predicting the structural response under high temperatures. We use a plastic-damage model for calculating the response of concrete slabs, and propose a method to determine the stiffness degradation parameter of the plastic-damage model by a nonlinear regression of concrete cylinder test data. To validate simulation results, structural fire experiments have been performed on a real-scale steel–concrete composite beam using the fire load prescribed by ASTM E119 standard fire curve. The calculated evolution of deflection at the center of the beam shows good agreement with experimental results. The local test results as well as the effective plastic strain distribution and section rotation of the composite beam at elevated temperatures are also investigated.     

高强、超高强混凝土抗火性研究进展综述

回顾了国内外高强混凝土和超高强混凝土抗火性研究进展,并展望了超高强混凝土(特别是活性粉末混凝土)的下一步研究方向。高强混凝土的高温强度损失与普通混凝土基本类似,但其主要弱点是高温爆裂,可采用聚合物纤维或钢纤维予以抑制。活性粉末混凝土抗火性研究的主要目标应是抑制高温爆裂,减小乃至消除高温爆裂发生的可能性。需要进一步研究宏观断裂性能与微观结构特征,建立活性粉末混凝土抗火性改善的机理,提出确保抗火性的技术途径。     

高强混凝土的抗火灾高温性能研究概述

综述目前高强混凝土的抗火灾高温性能的研究进展,并对聚丙烯纤维、橡胶粉、钢纤维等对改善高强混凝土的高温性能情况进行比较,指出研究中所存在的问题和今后的研究发展方向,对高强混凝土的高温性能研究和应用起到指导作用.     

Flexural behavior of high-strength,steel-reinforced,and prestressed concrete beams

To study the flexural behavior of prestressed concrete beams with high-strength steel reinforcement and high-strength concrete and improve the crack width calculation method for flexural components with such reinforcement and concrete, 12 specimens were tested under static loading. The failure modes, flexural strength, ductility, and crack width of the specimens were analyzed. The results show that the failure mode of the test beams was similar to that of the beams with normal reinforced concrete. A brittle failure did not occur in the specimens. To further understand the working mechanism, the results of other experimental studies were collected and discussed. The results show that the normalized reinforcement ratio has a greater effect on the ductility than the concrete strength. The cracking- and peak-moment formulas in the code for the design of concrete (GB 50010-2010) applied to the beams were both found to be acceptable. However, the calculation results of the maximum crack width following GB 50010-2010 and EN 1992-1-1:2004 were considerably conservative. In the context of GB 50010-2010, a revised formula for the crack width is proposed with modifications to two major factors: the average crack spacing and an amplification coefficient of the maximum crack width to the average spacing. The mean value of the ratio of the maximum crack width among the 12 test results and the relative calculation results from the revised formula is 1.017, which is better than the calculation result from GB 50010-2010. Therefore, the new formula calculates the crack width more accurately in high-strength concrete and high-strength steel reinforcement members. Finally, finite element models were established using ADINA software and validated based on the test results. This study provides an important reference for the development of high-strength concrete and high-strength steel reinforcement structures.     

圆钢管超高强混凝土应力-应变关系研究

在40根圆钢管超高强混凝土短柱轴压试验研究的基础上,将钢管超高强混凝土视为一新型组合材料,建立其应力-应变关系曲线的理论特征参数(极限强度、平台强度以及峰值应变)计算方法.通过比较发现,现有钢管混凝土的相应计算公式不适用于圆钢管超高强混凝土.最后,推导建立了圆钢管超高强混凝土短柱轴压应力-应变关系的三段式曲线方程,并验证了该方程理论曲线与试验曲线吻合良好.     

震损钢筋混凝土平面框架结构抗火性能研究

为明确混凝土框架结构受地震破坏造成的几何损伤对其遭受地震次生火灾后耐火性能退化规律的影响,分析总结震害资料以及抗震实验记录,将混凝土保护层剥落、残余变形作为混凝土结构的震损形式,通过数据统计与回归分析的方法确定损伤尺寸,从而建立了两层两跨震损钢筋混凝土平面框架有限元模型,得到了框架结构变形特点和受火位置、轴压比、层间位移角对平面框架结构耐火极限的影响规律。     

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.     

型钢高强混凝土柱抗剪承载力RBF神经网络预测方法及参数分析

在已有文献有关试验的基础上,引入径向基(RBF)网络理论,提出了型钢高强混凝土柱抗剪承载力RBF神经网络预测方法.以混凝土强度等级、剪跨比、轴压比和配箍率为输入参数,混凝土柱的抗剪承载力为输出参数,建立精确RBF神经网络模型,以多组不同试验数据分别作为训练样本和检验样本,对网络进行训练和检验,并把仿真结果与采用非线性最小二乘法拟合公式的计算结果进行了比较.在文中所提方法的基础上,对型钢高强混凝土的抗剪承载力进行的参数分析结果表明,用训练成熟的RBF网络进行仿真,避免了诸多人为因素的影响,大大提高了结果的精度,使计算更加准确、高效.参数分析还表明,型钢高强混凝土柱的抗剪承载力随着混凝土强度、轴压比和配箍率的增大而增大,但随着剪跨比的增大而减小,并且剪跨比对柱的抗剪能力的影响最大,轴压比、混凝土的强度和配箍率则趋于同等重要影响程度.     

Fire Endurance of High Strength Concrete Columns

In buildings, fire represents one of the most severe environmental conditions, and therefore, should be properly accounted for in the design of high strength concrete (HSC) structural members. The increased use of HSC in buildings has raised concerns regarding the behavior of such concrete in fire. In particular, spalling at elevated temperatures, as identified in studies by a number of laboratories, is a main concern.In this paper, results from an experimental program on the fire resistance of HSC columns are presented. The factors that influence the thermal and structural behavior of HSC concrete columns under fire conditions are discussed. Data from this study indicate that the type of aggregate, concrete strength, load intensity, and detailing and spacing of ties have an influence on the fire resistance performance of HSC columns. Further, the test results show that tie configuration (bending of ties at 135°, ties and provision of cross ties) and closer tie spacing has a significantly beneficial effect on the fire resistance of HSC columns. The results presented will generate data on the fire resistance of HSC columns, and contribute to identifying the factors that influence the behavior of HSC columns.     

预应力活性粉末混凝土梁抗火性能试验研究

活性粉末混凝土(RPC)是超高性能建筑材料,与高强预应力筋结合形成的预应力RPC梁具有显著的承载、变形和耐久性能优势,但预应力RPC梁的火灾安全性能是制约其广泛应用的关键问题之一。鉴于预应力RPC梁的火灾安全性亟待研究,以荷载水平、预应力筋保护层厚度、预应力筋类型、预应力度等为试验参数,设计制作了8个预应力RPC简支梁,开展了恒定荷载ISO 834标准升温条件下受火试验。获得了梁内温度变化、挠度 受火时间曲线、有效预应力、裂缝开展、爆裂分布及深度等试验数据,研究了火灾高温损伤演化规律和破坏模式。结果表明：干热养护可有效抑制RPC高温爆裂,受火试件保持了良好的完整性;荷载水平和预应力筋保护层厚度是影响预应力RPC梁抗火性能的关键因素,随荷载水平的减小和预应力筋保护层厚度的增大,耐火极限显著提高;荷载水平为0.5、预应力筋保护层厚度不小于45mm可满足2.0h的耐火极限要求;同等条件下有黏结预应力RPC梁的抗火性能优于无黏结预应力RPC梁;常温下按适筋梁设计的预应力RPC梁火灾下易发生少筋破坏。     

高强箍筋约束高强混凝土柱的抗轴压性能

为了研究高强箍筋约束高强混凝土柱的抗轴压性能,定量分析该类型柱的强度和变形提高程度,进行了31根高强箍筋约束高强混凝土方形截面柱的轴心受压试验。在试验的基础上,分析箍筋强度、箍筋间距和箍筋形式对其强度和变形性能的影响;结合国内外试验数据,通过回归分析提出高强箍筋约束高强混凝土峰值强度和极限应变的计算公式。     

有粘结与无粘结预应力混凝土框架结构抗火性能比较研究

从平面框架结构入手 ,通过试验分析 ,对比研究了有粘结和无粘结预应力混凝土结构在不同温度、不同荷载、不同预应力度及不同张拉应力下的火灾反应。研究了预应力混凝土结构在火灾中的特性 ,提出了提高预应力混凝土结构抗火性能的一些建议。     

碳纤维布用于改善斜向受力高强混凝土柱抗震性能的研究

基于 8根高强混凝土柱在周期反复荷载作用下受力性能的试验 ,本文编制了矩形截面高强混凝土双向压弯构件全过程受力分析计算机程序 ,对影响碳纤维布抗震加固效果的因素进行了分析 ,理论计算结果与试验结果吻合较好。在此基础上 ,本文进一步分析了斜向受力情况下碳纤维布包裹层数、轴压比、荷载角等因素对抗震加固效果的影响。试验结果与电算结果均表明 ,在一定范围内横向缠裹碳纤维布可显著改善高强混凝土柱的延性。     

高强箍筋高强混凝土短柱抗震性能试验研究

为了研究高强箍筋约束高强混凝土短柱在地震作用下的抗震性能,采用建研式加载装置,通过14根高强混凝土短柱试件的低周反复加载试验,研究了高强箍筋约束高强混凝土短柱的破坏形态、滞回性能、骨架曲线、变形和延性、耗能能力以及高强箍筋的应力发挥水平和受剪承载力计算等,分析了轴压比、剪跨比、箍筋强度、箍筋间距、箍筋形式和混凝土强度等因素对短柱破坏形态、滞回性能和承载力的影响。结果表明：短柱破坏形态受设计参数的影响有剪切破坏和剪切黏结破坏两类;与普通强度箍筋混凝土短柱相比,高强箍筋高强混凝土短柱在节约材料的同时具有优越的抗震性能和抗倒塌能力;达到极限荷载后,箍筋的应变发展较快,高强箍筋的强度发挥充分,短柱的抗震性能明显改善;通过对高强箍筋应力取值进行适当修正,采用GB 50010-2010规范公式计算高强箍筋高强混凝土短柱的受剪承载力是可行的。     

内置高强角钢的方钢管再生块体混凝土柱轴压及耐火性能试验研究

为了在不增加用钢量的前提下,明显改善钢管混凝土柱的耐火性能,同时确保其常温轴压性能基本不降低,针对内置高强角钢的方钢管再生块体混凝土柱,开展了6根短柱(边长300 mm、高度900 mm)的轴压试验以及3根足尺柱(截面边长320 mm、高度3 770 mm)的耐火试验,研究了废旧混凝土块体取代率(0、30%)、角钢强度等级(Q345、Q690)、角钢至钢管净距(10、20、30 mm)等因素对柱轴压性能的影响,分析了内置高强角钢、角钢至钢管净距(10、30 mm)等因素对柱耐火性能的影响。研究表明:在总用钢量基本不变的情况下,通过适当减薄钢管并在管内设置高强角钢且二者之间预留一定净距,可使方钢管再生块体混凝土柱的耐火极限提高了200%以上;同时,其轴压承载力和延性指标都有所提高,初始刚度基本不变或有所提高;在用钢量完全相同的情况下,适当增加高强角钢至钢管内壁的净距可使柱的耐火极限进一步提高,而轴压承载力变化不大;针对该类柱改进的轴压承载力实用计算方法,计算结果与试验结果之间的偏差较小。     

无粘结部分预应力高强混凝土梁裂缝宽度计算

通过２６根无粘结部分预应力高强混凝土梁,研究了影响裂缝宽度的主要因素。将无粘结部分预应力高强混凝土梁在使用荷载作用下的受力状态转化为偏心受压构件的受力状态,求解非预应力筋的应力,然后采用现有规范裂缝宽度计算公式来求无粘结部分预应力高强混凝土梁的裂缝宽度,计算结果与试验结果吻合较好。     

高强箍筋约束高强混凝土轴心受压应力-应变全曲线研究

为研究高强箍筋约束高强混凝土的受压力学性能,进行了高强箍筋约束高强混凝土棱柱体试件的轴心受压试验,分析了配箍率、箍筋屈服强度和箍筋形式对约束高强混凝土应力-应变曲线的影响。结果表明：高强箍筋在约束混凝达到其峰值应力时并未屈服,根据其受力机理提出了有效侧向应力和相应的高强箍筋应力的计算方法;高强箍筋可在约束混凝土应力-应变曲线下降段提供更有效的侧向约束,曲线下降较为平缓。在试验研究和理论分析的基础上,提出了约束高强混凝土的强度和变形的计算式,建议了高强箍筋约束高强混凝土的应力-应变全曲线方程,理论曲线与实测曲线吻合较好。