Papers by Keyword: Structural Damage

Abstract: The northern coastal region of Ecuador was affected by a moment magnitude M_w7.8 strong earthquake on April 16, 2016, with a recorded PGA of 1.41 g close to the epicenter. The earthquake was named “Pedernales” because the epicenter was near this small town located in the coastal province of Manabí, with a hypocentral depth of 21 km. Two strong aftershocks of M_w6.7 and M_w6.9 were felt a month later and they continued the destruction caused by the main event. Ecuador is located in a seismic zone with a long history of major earthquakes that have caused a lot of destruction in the last six centuries, the main seismic source comes from the subduction of the Nazca Plate under the South American Plate, but there are also crustal earthquakes and volcanism on the Andes Mountains that cross the country from north to south. In the northern coastal province of Esmeraldas a powerful earthquake of moment magnitude M_w8.8 was recorded in 1906, with a rupture area that has caused strong earthquakes in the 20^th and 21^st centuries. This paper describes the seismological aspects and the recorded strong ground motions, the geotechnical and infrastructure performance, site amplification and liquefaction on a few places, structural damage and collapse of buildings, extensive non-structural damage (mainly large damage to masonry walls) at high-rise buildings in cities near (100 km) and far away (270 km) from the epicenter, due to local soil conditions and flexible framed reinforced concrete structures.

Abstract: Protection of historical roof trusses is an important part of efforts to protect our cultural heritage. These timber structures carry a lot of information about used tools, technologies or construction processes. Roof trusses are generally threatened by many dangers, which could cause irreparable damage and loss of the carried information. Wood destroying insects and fungi are the gravest threat to historical roof trusses in our climatic conditions. Their spreading depends on several specific (interior) conditions. These include critical moisture content in the wood, relative humidity, amount of natural light and ventilation. In addition to these commonly monitored parameters (and their critical levels) we also must not forget the influence of local geography, biotope or orientation to the cardinal. This paper describes temporal fluctuations of some of the mentioned physical parameters in a historical roof truss with regard to external climatic conditions and orientation to the cardinal.

Abstract: Efficiently and accurately predicting structural dynamic response and damage to external blast loading is a big challenge to both structural engineers and researchers. Theoretical investigation on this problem is complex as it involves non-linear inelastic material properties, effect of time varying strain rates, uncertainties of blast load calculations and the time-dependent structural deformations. Experimental investigation can provide valuable data for locating the damage and establishing the damage criteria. The damage curves generated from the extensive experimental study can provide quick assessment of the structural status. However, such blast experiments always involve safety concern and can be beyond the affordability. Besides this, the correlation of the experimental data with predictive method is difficult since it requires a large number of tests to generate damage curves. Compared with the theoretical and experimental study, numerical simulation does not involve any safety concern and is cost-effective. With verified material model and element model, numerical simulation could be powerful supplement to the experimental tests. However, numerical simulation of structural responses under blast and impact loading could be time and resource consuming. Even with modern computer technology and computational mechanics method, detailed modelling and numerical simulation of responses of structures subjected to blast loadings are still often prohibitive. To address this issue, in the present study, an efficient numerical method is proposed to reliably calculate structural response and damage to blast loadings.

Abstract: This paper adapts finite element analysis of dynamic structure to analysis airfoil based on the phenomenon that torsion coupling may happen to airfoil during flying,, which verifies flutter mechanism of swing under subsonic and transonic condition. Modal frequency error can be changed into stiffness error by error analysis. The errors of bending and torsion frequency are verified by adjusting stiffness and mass distribution. Meanwhile the concept of modal strain energy is introduced to character and identify different positions and structures of damages.

Abstract: The main threats that endanger the historical roof trusses in our geographical conditions are wood decaying fungi and wood destroying insects. For these threats to occur and spread across the historical roof truss, several criteria have to be fulfilled within the indoor environment. These critical criteria include wood moisture, relative humidity, amount of daylight and airflow. In addition to these monitored parameters and their critical values, we must not forget the impact of local geographical specifications and wider dependencies. This article is focuses on comparison of theoretical knowledge in this area with in-situ measurements of historical roof trusses on several reference buildings – churches and chapels in Southern Moravia. These were chosen due to their long-lasting nature and circumstances of the construction. The influence of specific local conditions (especially indoor environment) on the extent of damage is also examined in addition to general comparison.

Abstract: Over decades phased array antenna technique attracts much more attention in Lamb wave based structural damage detection. Lamb wave generated by the piezoelectric wafers omnidirectionally could be steered at a specific direction during its propagation. Thus, the wave beam steering and focusing has been established, the location of structural damage is done with pulse-echo method by wave propagation. However, the detection accuracy will decrease as side bands energy leakage during wave propagation, so, signals to be generated have to be modified by window tone burst in order to concentrate energy in main bands and minimize the effect of dispersion side bands. In this paper, signals modified by Hanning-windowed tone burst was used to decrease the effect of side bands energy leakage, the results improved the detection accuracy better than signals without window tone burst and show good agreement with theoretical results. Meanwhile, a numerical simulation of aluminium plate demonstrates that phased array antenna technique is feasible in structural damage detection.

Abstract: Space frame structure of no damage and injury finite element models were established with ANSYS, and analyze 3D curvature mode as well three-dimensional vibration mode variety rate of the space rigid frame based on modal analysis. Curvature mode and three-dimensional vibration mode variety rate as the labeled amount was selected and applied to structural damage. The calculated results showed that the first-order curvature mode not only identify against single or multiple damage location, but also determine the initial degree of injury, and the axial curvature mode is better than the horizontal curvature mode for damage identification; The calculated results also showed that the variety rate of the first-order vibration mode can identify against damage location. Methods were provided by identifying the space frame structural damage of the curvature mode or three-dimensional vibration mode variety rate.

Abstract: First establish a dynamic model of tower crane in the load lifting process, the lifting load is solved under two work conditions.Then establish the FEM(finite element analysis) model of the tower crane under the normal and the damage condition. Get the dynamic displacement of the normal and the damage status under the lifting dynamic load. With wavelet packet decomposition and SVM(Support vector machines) multi-classification algorithm, a multi-fault classifier is constructed, and applied to the fault diagnosis of tower body. The results of the study show that the multi-fault classifier has such advantages as simple algorithm and excellent capability of fault classification, and it can not only diagnose the structural damage status, but also determine the positions of structural damage. This will be a new search on tower crane structural health diagnosis.

Abstract: A series of CT-triaxial shear tests were conducted on expancive soil specimens under controlled suction and confining pressure as 50kPa and 100kPa. The derivative and axial stress in each stage and CT images of inner structure of specimens were obtained .The results show that the different damage location and damage degree on expansive soil samples have different effect on soil mechanical property. The deviatoric stress of smaller damage area sample is larger than of bigger damage area specimen when the damage locates at the same place. The deviatoric strain is independent of the damage degree of samples. The CT images show that with the axial strain increasing, the fissures in soil close gradually, the density of soil increases, and the deformation of samples gets larger with the increase of confining pressure.

Abstract: This article describes the history of the development of structural damage, and an overview of current research status at home and abroad based on modal analysis of structural damage identification, reviewed in recent years the structure of the early damage recognition technology, from the application point of view of definition of indicators and indicators on the current some indicators of a comprehensive analysis and evaluation, further analysis of the feasibility of several modes of indicators to identify structural damage diagnosis, pointing out that the modal parameters of structural indicators to the validity and accuracy of damage identification and the need to further address the problem. The research will provide a reference for the application of modal analysis method to detect structural damage diagnosis in order to ensure early discovered the damage and accurately identify the site of injury repair in a timely manner.