Narrow Results

To explore the influence of liquid nitrogen (LN${}_2)$ cooling on the structural damage and failure characteristics of coal, a series of structural experiments, uniaxial compression tests, and crack morphology characterization experiments were carried out in this study. Based on the fractal theory, the pore structure damage and failure characteristics of the coal before and after the LN₂ cooling treatment were compared. After the LN₂ treatment, the structural damage inside the coal increases. Compared to the untreated coal, the fractal dimensions of the total pores, seepage pores, and adsorption pores in the LN₂-treated coal decrease by 0.88%, 0.24%, and 5.16%, respectively. The results indicate that the LN₂ cooling treatment can increase the connectivity of pores, especially adsorption pores. The internal structure damage of the coal induced by the LN₂ treatment reduces its compressive strength and elastic modulus by 27.86% and 32.62%, respectively. Simultaneously, it can be found that the fragments fractal dimension of the coal decreases by 9.53%, and the fractal dimension of the induced fracture surface increases from 2.134 to 2.151 after the LN₂ treatment. By the LN₂ treatment, the distribution of fragments becomes more uniform, and the complexity of the generated fracture surface increases. Therefore, the LN₂ cooling treatment can increase the effective seepage path and the contact area between the crack and the coal matrix to promote the gas flow and enhance the gas desorption in the coal matrix. The experimental results also show that the damage of the single LN₂ treatment on the coal is limited. LN₂ cycling treatment is suggested to use to improve the efficiency of the coalbed methane extraction because that it can give full play to the multiple cracking effects of LN₂ on the coal.

In the degradation evaluation process of the crane girder structure under moving loads, the complex vibration response and low accuracy of health index standards are the main factors limiting the performance of the evaluation method. A method for identifying and evaluating damage to crane girder structures under moving loads has been proposed. In this method, optimized empirical wavelet transform (EWT) is used for decomposing the vibration signal of the crane girder structure to obtain sensitive components. A health indicator based on power spectrum maximum sequence is constructed by combining structural vibration simulation and response characteristics analysis under moving loads. A degradation index acquisition scheme based on an optimized sparse autoencoder is proposed, which utilizes a simulated annealing algorithm to optimize the model parameters of the sparse autoencoder. The effectiveness of the proposed method is verified through girder structure crack tests under moving loads.

Simultaneous identification of vehicle load and structural damage is an issue of practical significance in structural health monitoring and maintenance of in-service concrete bridges. However, most methods proposed in history to deal with this engineering issue are solely based on data from a single source of structural vibration response measurement, which are subjected to problems such as incomplete understanding of the structural health, the computational inefficiency and the easy failure of the monitoring system. To this end, this paper proposes a new method of synthesizing data generated from two different types of sensors (the strain gauges and the accelerometers) to simultaneously identify the vehicle load and the structural damage which is established on the theories of weigh-in-motion method based on the strain influence line. The new method, which is supposed to be able to well solve the problems with the traditional approaches disseminated to the profession, is formulated in a flowchart for use, and applied to the actual Renyihe Bridge (a concrete rigid-frame continuous highway bridge with spans of 80 m + 4 × 145 m + 80 m) to validate its effectiveness. The results suggest that the new method is of high accuracy in use in low vehicle speed scenarios and superior to the traditional simultaneous identification approach based on unitary structural acceleration sensing.

On 15 June 1995, an earthquake of moment magnitude M_w=6.4 occurred in the western part of Corinthiakos Gulf, Greece, causing the loss of 26 human lives and inflicting considerable damage mainly in the northern part of Peloponnessus. Particularly damaged was the town of Aigio with its environs. The only strong motion instrument in operation at the time of the mainshock in the town of Aigio recorded a horizontal acceleration as high as 0.54 g — the highest ever recorded in Greece — in the vicinity of a collapsed building. The main characteristic of the recorded strong ground motion is the pulse-like shape of its most intensive part, with a period of about 0.45 sec. The macroseismic observations are in good agreement with the distribution of the peak horizontal acceleration — recorded at epicentral distances from 18 km to 78 km, and both sets of data imply anisotropic radiation of seismic waves by the source. The tremor and its largest aftershock (M_w=5.6), which followed about 15 minutes later, caused total or partial collapse of a few buildings and heavily damaged several more. However, despite the very high recorded accelerations — the highest recorded in Greece — and the highest response spectra resulting from them, damage was not as much as one might have expected, considering the poor earthquake design and construction practices under which the majority of the buildings in the town and its surroundings had been built. This earthquake demonstrated among others, the great improvement in seismic behaviour of buildings effected by the application of the revised Greek Seismic Design Code of 1984, along with the importance of strength reserves of existing buildings in alleviating the consequences of strong ground motions.

Hongkou Town is located north of Dujiangyan City, around 27 km away to the northeast of the epicenter of Wenchuan Earthquake on May 12, 2008. The middle segment of the central fault, that is the Yingxiu-Beichuan Fault of the Longmenshan Fault belt, passes through the town, along which almost every form of surface ruptures is developed. The quake also resulted in 73 of the town's residents dead or missing and 95% of its buildings or infrastructures damaged, including the collapse of Gaoyuan Bridge. Its estimated intensity was around XI. On the other hand, in Shenxigou Village and Gaoyuan Village, many houses successfully withstood the quake.

In this paper, the authors examine why the latter houses withstood the earthquake well. Based on field investigation and local geology, especially fault configuration in the area, a detailed description is given on the characteristics of surface rupture and structural damage in the two villages and an attempt is made to correlate fault movement with structural damage. The results show that: (1) Fault movement or surface rupture may be affected by local geological configuration and topography. Compression can lead to local strike-slip movement. (2) Structural damage is associated with fault movement. Strike-slip movement causes less damage to structures, while in the adjacent area of fault with thrust movement, the structures in the hanging-wall can be more easily damaged than the ones on the footwall, i.e. hanging-wall effects. An area located on the footwalls of two nearly parallel faults may result in a "safer island," where structural damage is much lighter that those outside the island. (3) Apart from shaking effect, site effects should also be considered in structural design.

An earthquake of Mw = 7.0 occurred on October 30, 2020, in the Aegean Sea near Samos Island, which caused severe structural damage in Bayraklı, Izmir (Türkiye), located around 70 km from the epicenter. To investigate the source, path, and site effects, ground motions recorded in Western Anatolia are simulated using the stochastic finite-fault method based on a dynamic corner frequency approach. The input model parameters are calibrated using the recorded motions at selected 10 stations within an epicentral distance of less than 100 km. The soil amplifications are modeled using horizontal-to-vertical spectral ratios and generic amplification factors. At most stations, including a few within Izmir Bay, amplitudes and frequency contents are modeled closely. Minor discrepancies within particular frequency bands can be attributed to insufficient representation of the local site effects. Finally, distributions of observed and simulated felt intensities are found to be consistent.