Applied Mechanics and Materials Vols. 249-250

Abstract: Failure mechanism of perilous rock and its corresponding dynamic parameters is one of the basic theoretical questions for the security alert implement about collapse disaster. Focusing on the dominant fissure of perilous rock, it is divided into linking patch and locked patch, and the constitutive model of dominant fissure is proposed. Based on the energy principle, it proposes the deformation energy formula of perilous rock with dominant fissure’s creeping displacement. On the mutation theory, it establishes the failure cusp mutation model of perilous rock, and the calculating formulas of creeping displacement on failure starting point and end point and the controlling factors of dynamic instability are gained. With scientific theory, elastic energy releases and transforms to the elastic and impulsive kinetic energy at the moment of dynamic instability, and a method to calculate the violent-slide velocity and acceleration on collapse mass at that moment is proposed. Practical examples indicate that this method is useful in engineering practice.

Abstract: Noise filtering of impact load spectrum is the key to ensure the impact load of debris flow during the control engineering design of debris flow. As the laboratory impacting test indicates, noise effect in pulse impact force spectrum can be denoised using Daubechie(dbN)and Symlet(symN)wavelet methods, both of which contain hard threshold method and soft threshold method. Analyzed the pulse impact force of non-viscosity debris flow testing results by wavelet denoising method, the testing conditions are A-3(whose grain size is range from 0.3cm to 0.8cm), B-3(whose grain size is range from 0.8cm to 1.5cm) and C-3(whose grain size is range from 1.5cm to 3.0cm),all of whose solid phase ratio are 0.16.The analyzing results show that the denosing effect adopting Db5 wavelet function is superior to ones adopting Sym2 wavelet function, meanwhile, the denosing effect adopting hard threshold method is superior to ones adopting soft threshold method. The results also indicate that the bigger the solid phase ratio is, the bigger the Signal Noise Ratio is, the better the wavelet denosing effect is. These results could provide scientific basis for further accurate experimental study to ensure impact load of non-viscosity debris flow.

Abstract: In order to insure the safety and stability of the existed dam body and dam curtain during the diversion tunnel excavation, the vibration velocities were analyzed based on in-site blasting vibration monitoring. Result shows that the elevation difference between explosion point and monitoring points has a great impact on the vibration velocity in addition to single fire dynamite and blast center distance. During data analysis, the traditional empirical formula of attenuation of blasting earthquake must be amended. Through contrasting and analyzing, the amended formula of attenuation of blasting earthquake wave is precise relatively. At the same time, two collapses during the diversion tunnel excavation were analyzed based on the characteristics of layered rock mass and fault distribution, and the explosion parameters were optimized, so that the damage effect of blasting vibration was controlled effectively. This research also takes a good effect in other similar works.

Abstract: As one of the most popular materials used in construction, concrete is prone to superficial flaws, such as crack, due to the load-bearing and external environment. This research manually made cracks of 2 mm with 100 mm length and 30 mm depth on concrete vessels as specimens. Subsequently, bacteria, specifically B. pasteurii, was used in crack rehabilitation to enhance the compression strength of the repaired concrete. The mixture of microbes, urea medium, and urea-CaCl2 medium was added to a sludge and fine aggregate with a weight ratio of 0.6:1:1 to be the repairing material for crack rehabilitation. Crack rehabilitation was conducted by injected the mixture into the test samples after 90 days curing in saturated lime solution. In addition to the traditional test – compression test, scanning electron microscope (SEM) was used to examine the structure composition of the microbe-repaired concrete for calcium carbonate crystal formation. Various rectangular and polygonal crystals were observed in the SEM photographs of the microbe-repaired concrete samples with high bacterial concentrations demonstrated that bacteria can induce calcium carbonate precipitation to complete crack rehabilitation. The results prove that high concentration of bacterial broth induced a great amount of calcium carbonate precipitate and improved the concrete strength of the microbe-repaired samples.

Abstract: Previous researchers have tried to predict the response of different types of structures under elevated temperatures. The results are important in preventing the collapse of buildings in fire. Post-fire status of the structures is also of interest for ensuring the safety of rescue workers during the fire and in the post-fire situations. Determining the extent of the structural damage left behind a fire event is necessary to draw up adequate repair plans. Connections play an important role on the fire performance of different structures. Due to the high cost of fire tests, adequate experimental data about a broad range of connections is not available. A vulnerable type of such connections to fire is the weld connections between I-shape beams and cylindrical columns in oil platform topsides. Considering the high probability of fire in oil platforms, study of the behaviour of these connections at elevated temperatures and in the post-fire, is of great importance. In the current study, eight small scale experimental fire tests on welded connections between I-shape beams and cylindrical columns have been conducted. Four tests are aimed at investigating the structural performance of this connection at elevated temperature. In other tests, post-fire behaviour of these connections has been studied to investigate their residual structural strength.

Abstract: The influence of the structure parameters on the anti-impact performances of the reinforced concrete slab is studied in the article. The reinforced concrete model is established by using ANSYS 13.0/LS-DYNA and nonlinear finite element theory and the parameterized modeling is achieved. The results show that the increase of the thickness of the slab and the steel bar diameter result in the enhancement of impact resistant capability of the slab; a appropriate quantity of reinforcement is significant; Increasing the concrete strength has a distinct impact on the slab’s impact resistance when using relatively low strength concrete. However the influence becomes weak after the concrete strength comes to C60 and higher. The fruits are useful to the designing of reinforced concrete slabs.

Abstract: The rock fragmentation process is the interaction process between TBM and rock mass, which is affected by TBM specifications, such as thrust force, cutter tip width and profile, cutter spacing, RPM, and torque, and rock mass properties mainly including rock material strength, rock brittleness, joint spacing and orientation. In this study, based on the systematic study of the existed rock constitutive model achievements and introduction of rock breaking mechanism, main failure mode of rock in the breaking process of disc cutter is added and revised in order to meet the actual situation. The method of establishing numerical model of disc cutter breaking process is introduced. After the dynamic simulation, we can obtain that geotechnical interface disturbance insulted by disc cutter. Based on plenty of experiments, it confirms reliability of numerical methods and provides a method to study cutting performance for different geological conditions.

Abstract: The aim of the present research is to assess the dynamic performance of bond-slip between reinforcing steel bar and concrete. Precisely, the sensitivity of the bond stress-displacement relationship in the interface between reinforcing steel bar and concrete to strain rate is investigated. In this paper, the reinforcing steel bar/concrete specimens were tested in dynamic push-out experiments with modified split Hopkinson pressure bar (SHPB) system. The incident bar was used to apply compressive loading to single steel bar embedded in a surrounding concrete. Using this technique, the debonding progress was analyzed. Besides, the effect of loading rate and effective depth on the push-out tests was studied with the impact velocities in the range of 9 m/s - 29 m/s. It is seen that maximum push-out force increases with increasing loading rate. In addition, the dynamic interface bond force does not proportionally increase with the effective depth of steel bar.

Abstract: This is a case study of cottage housing in Taiwanese military dependents’ villages that are primarily wooden structures with brick walls. When a fire ignited in one of these structures, sufficient air on the exterior of the building promoted the rapid ignition of the wooden structure. Because residents were a woman and child who lacked fire safety and escape knowledge, the fire resulted in two deaths. When fires ignite in wooden structures, toxic particulates in the smoke generated from the burning and decomposition spread rapidly because of thermal buoyancy effect, causing difficulties for escape and rescue. This research utilizes the fire dynamics simulator (FDS) software to simulate the fire scenario to discuss the impacts of smoke diffusion at a fire site and analyze the main causes of the fire. We also provide suggestions in the hope of offering information on fire safety precautions for this structure type to prevent future similar disasters.

Abstract: This paper describes the reliability analysis of a concrete containment for VVER 440 under a high internal overpressure considering nonlinear behavior of reinforced concrete structure. The probabilistic safety assessment (PSA) aims at an assessment of the probability of the concrete structure failure under the excessive overpressure. The non-linear analysis of the concrete structures was taken. The uncertainties of the loads level (long-time temperature and dead loads), the material model (concrete cracking and crushing, behavior of the reinforcement and liner), degradation effects and other influences following from the inaccuracy of the calculated model and numerical methods were taken into account in the response surface method (RSM). The results of the reliability analysis of the NPP structures are presented.