火灾后钢筋混凝土梁损伤识别及试验研究

为得到火灾后钢筋混凝土简支梁动力特性用于识别其损伤,本文基于厚板积分理论提出火灾后以刚度为转换变量的梁自由振动方程,并考虑了弹性模量改变,中性轴上移及配筋率对其产生的影响。然后提出以频率为识别指纹对梁损伤后的位置及程度进行识别的新方法。最后结合梁的火灾试验及动力试验验证了理论的正确性。     

基于CS-SVM的混凝土梁火灾损伤识别方法

为确定钢筋混凝土梁的受火损伤程度,采用布谷鸟搜索(CS)算法优化支持向量机(SVM),提出一种以受火时间为指标的火灾损伤识别方法.首先,建立适用于T型简支梁的火灾损伤识别方法,用T型简支梁数值模拟验证了该方法的有效性,通过与SVM识别结果对比发现,CS-SVM识别结果更加接近真实受火时间.然后,在简支梁火灾损伤识别算法...     

基于临近差分曲率差值指标的简支梁损伤识别方法

为方便有效地进行简支梁的损伤识别,基于对称集中加载和结构静力位移数据的采集,以梁体的局部抗弯刚度和剪切刚度为损伤识别参数,通过理论推导提出了一个基于中心差分曲率指标的损伤识别新指标——临近差分曲率差值Di(difference of nearby difference curvature,DNDC),并建立了相应的损伤...     

基于移动加载的简支梁损伤识别方法

为了更简便、有效地实现简支梁结构的损伤识别,考虑荷载施加的便利性,提出了一种基于移动加载(包含3种加载方式)、能处理初始刚度离散性的损伤识别方法:首先,以等长度的区间为单位来描述抗弯刚度的局部性;然后,建立了3种移动加载方式(单个集中荷载移动、轴重不相等的双轴车辆移动、轴重相等的双轴车辆移动)及相应的加载制度,在各工况下都只需采集简支梁的跨中挠度数据;最后,建立方程可求解出各区间的局部抗弯刚度值,通过对比简支梁损伤前后的抗弯刚度值可以识别出损伤信息。结果表明:本方法可以方便、有效地区分出简支梁局部抗弯刚度的自身离散性和损伤引起的局部抗弯刚度变化,确定真实损伤的位置和程度。     

连续梁火灾损伤定性识别方法研究

为研究多种损伤工况下钢筋混凝土连续梁火灾损伤程度,以简支梁火灾损伤识别方法为基础,针对传统方法依靠样本数量较多、损伤识别效果较差等缺点,提出3跨连续梁火灾损伤定性识别方法。通过对理论计算值施加5%的白噪声确定试验值,验证方法可行性。研究结果表明,3跨连续梁火灾损伤定性识别方法精度较高,能够较好地预测结构损伤。     

基于曲率模态和柔度曲率的变截面钢梁多损伤静态识别

以具有损伤位置不同但损伤刚度相同的变截面悬臂梁和简支梁为研究对象,通过结构模态分析,以曲率模态和柔度曲率为识别参数,计算各种工况下仅用第1阶模态参数的多损伤识别结果并进行了对比.     

低温下钢结构裂缝损伤识别方法(Ⅱ)

利用截面抗弯刚度的降低来模拟这种裂缝损伤,并以简支梁为研究对象,分别针对单位置及其多位置损伤,利用有限元分析软件计算得到简支梁的位移模态,再通过应变和位移之间具有二阶导数的关系,对简支梁进行了应变模态分析。     

基于挠度法的钢筋混凝土简支梁损伤识别研究

根据静、动载作用下的简支梁挠度数据,求解了结构的挠度差曲率和,对受拉钢筋局部锈蚀混凝土简支梁的损伤识别进行了研究,理论分析和有限元仿真表明:该方法可以识别结构的损伤位置和损伤程度,提高简支梁检定的准确度.     

基于模态应变能的桥梁损伤识别

桥梁结构损伤识别是对桥梁结构进行安全性评定的一个重要环节。文中以模态应变能变化率作为损伤定位的判别参数,对桥梁结构的损伤进行定位,以简支梁为数值模拟对象,说明该方法能够比较准确地对结构损伤进行定位识别和损伤程度评估。     

梁结构的损伤识别方法研究

针对桥梁结构多为简支梁和连续梁的形式,文章使用了柔度差法对粱结构的损伤识别进行了研究.文章首先分别推导了一阶振型变化率和柔度差的识别理论;然后使用ansys有限元分析软件对简支粱和连续粱进行了损伤数值模拟,并使用此两种识别指标进行损伤识别;最后比较了两种指标的识别效果.文章还对梁结构的多处损伤进行了研究.结果表明:对于...     

基于模态柔度相对变化量的结构损伤识别

介绍了支持向量机的分类算法,构造了基于模态柔度相对变化量的损伤识别指标,并将此指标作为支持向量机的特征参数进行训练和结构的损伤识别,通过对简支梁仿真计算及试验结果表明：支持向量机对结构损伤的识别有着良好的抗噪性能,该方法对梁的损伤位置有较高的识别能力。     

Probabilistic Evaluation of Structural Fire Resistance

The work described herein seeks to investigate a probabilistic framework to evaluate the fire resistance of structures given uncertainty in the fire load and structural resistance parameters. The methodology involves (i) the identification and characterization of uncertain parameters in the system, (ii) a stochastic analysis of the thermo-mechanical response of the structure, and (iii) the evaluation of structural reliability based on a suitable limit state function. The methodology is demonstrated through the analysis of a protected steel beam using Monte Carlo simulation with embedded finite element simulations. Model dimensionality is reduced using a response sensitivity analysis, and limit state functions are defined based on limiting deflection criteria used in fire resistance tests. Results demonstrate that the 1-h rated beam resists a natural fire exposure with a failure probability of less than ten percent, although additional discussion is warranted regarding what might be considered an acceptable level of risk in structural fire design. The study also demonstrates that probabilistic analysis of structural fire resistance provides an enhanced understanding of the factors affecting the resistance of structures to fire and offers a means for rationally improving structural designs to meet target performance objectives.     

基于振动传递率的损伤识别仿真研究

为研究基于振动传递率的损伤识别方法的可行性,以一钢悬臂梁为例,进行了多种仿真试验,分别研究了振动传递率的可重复性、损伤敏感性和损伤位置敏感性。仿真试验结果显示:振动传递率不依赖于结构激励荷载;对损伤具有较强的敏感性;能识别结构损伤位置。相对于多位置损伤识别相比,其对于单位置损伤识别具有更好的效果。     

Numerische Simulation des Verhaltens von Betontragwerken unter Brandeinwirkung

Numerical Simulation of the Response of Fire Exposed Concrete Structure The proposed numerical model for concrete and reinforced concrete structures subjected to fire comprises the transient thermal and mechanical analysis considering the temperature dependent material properties of concrete and reinforcing steel within the framework of the phenomenological approach of the Eurocode 2, part 1‐2. A concrete model, based on the combination of plasticity and damage theory, serves as the basis for the material model of concrete for high temperatures. For reinforcing steel a standard elastic‐plastic material model is employed. The proposed model is validated by the numerical simulation of fire tests on plain concrete specimens and by the numerical simulation of a large scale fire test on a reinforced concrete slab. Furthermore it is used to determine the structural integrity of a tunnel structure, put up by the cut‐and‐cover method, exposed to fire.     

连续刚构桥箱梁火灾损伤检测与评估

火灾产生的高温会对钢筋混凝土桥梁造成严重的影响,致使桥梁中普通钢筋和预应力钢筋强度降低和混凝土质量下降。该文结合工程实例,介绍预应力混凝土连续刚构桥箱梁火灾后的损伤检测方法和评估方法,为火灾后桥梁的管理维护提供参考。     

广东某工程火灾后鉴定及修复

某工程经过火灾后,结构剪力墙、梁、板、柱混凝土及钢筋均产生不同程度的损伤。根据现场遗留物烧损情况推定火场温度,并根据国内外混凝土构件受损综合评定办法,将构件受损程度分为四级:轻度受损、中度受损、严重受损和危险结构。通过检测分析,给出了不同受损级别构件的鉴定结果以及修复措施,而且通过了竣工验收。     

悬臂梁损伤的支持向量机识别研究

针对结构损伤识别中,损伤与其影响因素之间的复杂非线性关系,提出了结构损伤识别的支持向量机方法。支持向量机是一种基于统计学理论的机器学习算法,本文以模态频率作为损伤标识量,通过支持向量机建立了损伤程度和频率之间的支持向量机模型,并以悬臂梁的损伤为例进行了计算分析,结果表明提出的方法是科学,可行的。     

Multi-source information fusion applied to structural damage diagnosis

This study aims to import multi-source information fusion (MSIF) into structural damage diagnosis to improve its validity. Two structural damage identification methods based on MSIF are put forward, one of which is to fuse two or more structural damage detection methods by MSIF and another of which is the improved modal strain energy method by multi-mode information processing based on MSIF. Through a concrete plate experiment it is proved that, if two methods are integrated by character-level information fusion, structural initial damages can be more accurately identified than by a single method. In a simulation of a concrete box beam bridge, it is indicated that the improved modal strain energy method has a nice sensitivity to structural initial damages and a favorable robusticity to noise. These two structural damage diagnosis methods based on MSIF have good effects on structural damage identification and good practicability to actual structures.     

经一麻五灰地仗处理的木梁三面受火耐火极限试验研究

传统木结构建筑木构件表面通常采用地仗处理进行保护,而地仗处理对木构件耐火性能的影响规律尚不清晰。为此,通过4组10根三面受火木梁耐火极限的对比试验,研究了截面尺寸、持荷水平、是否地仗处理等因素对木梁耐火极限的影响规律,提出了剩余截面法计算木梁耐火极限,并提出了木梁热力耦合数值分析模型。结果表明,三面受火木梁耐火极限随持荷水平的增加明显降低,当持荷比由30%增加至50%时,木梁耐火极限降低19.6%~31.7%,平均降低17.5min;三面受火木梁耐火极限随截面尺寸增加显著提高,当截面尺寸由100mm×200mm增加至200mm×400mm时,耐火极限提高95.1%~107.8%,平均增加40.0min;木梁表面经一麻五灰地仗处理后,耐火极限提高21.3%~429%,平均提高15.8min。不同持荷水平和截面尺寸木梁内部距离边缘相同位置处的温度变化相近,表面采用一麻五灰地仗处理可显著延缓木梁内部温度的上升速率,木梁两个方向的炭化速度平均值为0.54mm/min,与未作表面处理的木梁相比降低19.4%。基于剩余截面法和数值模拟得到的三面受火木梁耐火极限预测值与试验值的误差在±15%以内,基本满足工程精度要求。     

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.