现浇混凝土结构外观质量缺陷及裂缝处理措施

本文根据厦门某花园现场施工监理发现，在结构混凝土施工过程中，混凝土表面常会出现各种外观质量缺陷和裂缝。为提高混凝土的强度，改善混凝土结构的使用性能，延长混凝土结构的使用寿命，文中对现浇混凝土外观质量缺陷提出补救处理意见，并对现浇混凝土结构产生裂缝的原因进行分析，进一步提出预防措施和出现裂缝的处理办法。     

柴油机机体横隔板断裂失效分析

针对高速大功率柴油机机体横隔板断裂失效现象,应用断裂力学和有限元方法,提出了机体横隔板断裂力学有限元分析的基本方法,建立了合理的含有裂纹的二维有限元模型,进行了静载荷作用下两种不同加载方式的分析,得到了柴油机机体横隔板的应力强度因子K、J积分,并考察了横隔板在静载荷作用下的承载能力;采用3种复合型裂纹扩展准则,预测了裂纹扩展方向,预测结果与横隔板的实际断裂情况相吻合,证明了该方法的正确性,对今后柴油机机体设计有一定的借鉴价值.     

Fuzzy set based crack diagnosis system for reinforced concrete structures

This paper presents a computer assisted crack diagnosis system for reinforced concrete structures which aids the non-expert to diagnose the cause of cracks at the level of an expert in the general inspection of structures. The system presented adapts fuzzy set theory to reflect fuzzy conditions, both for crack symptoms and characteristics which are difficult to treat using crisp sets. The inputs to the system are mostly linguistic variables concerning the crack symptoms and some numeric data about concrete and environmental conditions. Using these input data and based on built-in rules, the proposed system executes fuzzy inference to evaluate the crack causes under consideration. The built-in rules were constructed by extracting expert knowledge, primarily from technical books about concrete and concrete cracks. We implemented the proposed system in a computer program with a graphic user interface for actual utilization in practical business fields. When applied to cracks actually diagnosed by experts, the proposed system provided results similar to those obtained by experts, and we expect that this system can be used as an effective crack diagnosis tool for both experts and non-experts in the regular inspection of RC structures.     

沥青路面裂缝检测图像处理算法研究

针对经典图像处理算法对沥青路面裂缝的检测效果不佳,以及神经网络等智能算法不易实现的弊端,通过分析沥青路面的裂缝特性,提出了一种适用于沥青路面裂缝检测的图像处理新算法。该算法通过构造8个方向模板的Sobel算子对沥青路面裂缝进行检测,并结合迭代阈值分割算法和全方位膨胀形态学方法对边缘检测后的图像进行处理,能够很好地获得沥青路面的裂缝特性。最后,在VisualC 6.0编程环境下进行了算法实现。结果表明,裂缝边缘的连接和检测效果较好,为沥青路面裂缝的分析和管理提供了技术基础。     

Extension of FCM to plain concrete beams with vertical tortuous cracks

Fictitious crack model has been appropriately modified to make it applicable for plain concrete beams with vertical tortuous cracks. A number of tortuous cracks are generated considering the crack deviations as random variable based on the maximum aggregate size. Instead of a straight-line crack in FCM a number of simulated tortuous cracks are replaced to model the roughness of fracture surface of concrete. Plain concrete beams with such tortuous cracks are analyzed to study the effect of the tortuousity of the cracks on the various fracture parameters.     

In situ observation of crack propagation in ESP (engineered stress profile) glass

Important features of the ESP (engineered stress profile) glasses are the crack arrest and multiple cracking phenomena that occur even in an unstable stress field. In this work a detailed “in situ” observation of crack observation and analysis was performed with the aim to examine crack propagation in detail and relate it to the residual stress field produced by ion exchange and to the final mechanical performances of the material. The results showed that the peculiar residual stress field with a maximum below the surface is responsible for the formation of a multitude of stable cracks on the tensile surface of the glass that evolved into through-thickness flaws. The propagation within the material is limited by the increasing compressive residual stress, which also leads to kinking of the cracks in a direction parallel to the surface. The observed fracture phenomena are also responsible for a shielding effect that makes the measured failure resistance of ESP glass larger than predicted by simplistic single crack models.     

4号板坯连铸机铸坯表面纵裂的控制

根据4号板坯连铸机投产后的生产实践，分析了连铸板坯发生表面纵裂的原因，提出并实施了减少表面纵裂的措施。     

Numerical analyses for the prediction of the splitting strength of beams loaded perpendicular-to-grain by dowel-type connections

The paper presents a parametric numerical study on the splitting strength of timber beams loaded perpendicular-to-grain by dowel-type connections. The main aims of the numerical investigations are: (1) find out the influence of main connection parameters on the splitting strength of beams; (2) compare the above evaluated influences with the ones proposed by the first author in a recently developed semi-empirical prediction formula. The first part of the paper presents the mentioned new semi-empirical prediction formula which has been developed by means of a survey on experimental data from literature. The formula is presented in its main aspects and later its prediction capability is discussed and compared with the ones of formulae embodied in new European and German design codes for timber structures. The second part of the paper reports the main results of parametric numerical analyses carried out in the framework of Linear Elastic Fracture Mechanics (LEFM) by means of a crack propagation approach. The analyses are performed on beams of different size loaded at mid-span by both single and multiple dowel connections. The main investigated parameters are the connection width (l _r), the connection depth (h _m), and the number of rows of fasteners (n). They are analysed for different beam heights (h) and for different distances of the most distant row of fasteners from beam loaded edge (h _e). The numerical results are compared with available experimental test data and with the relationships embodied in the above-mentioned semi-empirical prediction formula.

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Résumé L’article présente les résultats d’une étude numérique paramétrique qui analyse la résistance à la fissuration de poutres en bois chargées perpendiculairement aux fibres de connexions, avec des connecteurs cylindriques. Le but principal de cette étude numérique est: (1) déterminer l’influence des paramètres principaux des connexions sur la résistance à fissuration des poutres; (2) comparer les résultats obtenus avec les résultats proposés par Ballerini dans une formule récente de prédiction semi-empirique. La première partie de l’article présente la formula citée de prédiction semi-empirique développée sur base d’une analyse des données expérimentales disponibles dans le texte. La formule est illustrée dans ses aspects principaux et par la suite sa capacité prévisible est comparée avec celle des formules adoptées par les récentes normes européennes et allemandes pour les structures en bois. La seconde partie de l’article reprend les principaux résultats de l’analyse numérique paramétrique développés dans le domaine de la Mécanique de la Fracture Linéaire Elastique (LEFM) à l’aide d’analyses avec propagation de fissure. Les analyses concernent des poutres de différentes dimensions chargées en ligne de connexions avec un ou plusieurs connecteurs cylindriques. Les paramètres principaux étudiés sont la largeur (l_r), la hauteur (h_m) et le nombre de lignes des connecteurs (n) de la connexion. Les analyses concernaient des poutres de différentes hauteurs (h) et placés à différentes distances par rapport au bord des poutres de la ligne des connecteurs plus éloignée (h_e). Les résultats numériques sont comparés avec les données expérimentales disponibles et les études prévues par la formule citée de prédiction semi-empirique.

     

Structural Health Monitoring of Railroad Wheels Using Wheel Impact Load Detectors

This paper proposes two quantitative criteria for removing railroad wheels from service, based on real-time structural health monitoring trends that are developed using data collected from trains while in service. The data is collected using wheel impact load detectors (WILDs). These impact load trends are able to distinguish wheels with a high probability of failure from high-impact wheels with a low probability of failure. The trends indicate the critical wheels that actually need to be removed, while at the same time allowing wheels that aren’t critical to remain in service. As a result, the safety of the railroad will be much improved by being able to identify and remove wheels that have high likelihood of causing catastrophic failures.     

Experimental and numerical analysis of delamination growth in double cantilever laminated beams

Delamination crack growth in laminated composites is investigated using experiments and finite element (FE) models. Tests are performed on cross-ply graphite/epoxy specimens under static conditions. The load-displacement response is monitored in the tested coupons along with crack length. The FE models employ a cohesive layer that is used to simulate the debonding and crack propagation. The cohesive parameters are calibrated from the experimental load-displacement curves. Crack growth and strain measurements are compared with those from the FE models. The predicted results from the FE models are in good agreement with the test results. The same modeling approach is also used to simulate crack propagation in the transverse direction of a notched laminate. The proposed FE analysis with cohesive layers can simplify fracture toughness assessment in multilayered specimens.