Vibration Assessment on Various Distance to Demolition Works

Vibration has been a serious problem to be discussed over the past years. Vibration has caused cosmetic damages to buildings and annoyance to the occupants of the building. Sources of vibration are usually produced by construction work, traffic, seismic effect and human activities. In this paper, the amplitude of vibration caused by demolition has been analyzed and the level of vibration and level of damage caused have been determined. Besides, the effect of the vibration strength due to distance from the source has also been studied. The vibration data due to demolition work was obtained and analyzed by using MATLAB software. The analyzed data in graphical form were compared with the Gordon vibration criteria to obtain the vibration limit and the level of vibration damage according to DOE (Malaysia) standard as well. The results indicated that the vibration at 1m distance and 10m distance from the vibration source will cause minor damage to the building whereas the vibration at 25m distance from the source is at the caution level. By comparing the Gordon vibration criteria curve, the vibration from 1m, 10m and 25m distance from the demolition vibration source are not suitable for sensitive equipment. This study also proved that the vibration strength will decrease as the distance from the source increases due to the loss of vibration energy during the propagation of vibration waves. Hence, the further the distance from the source, the weaker the strength of the vibration and lower level of damage on surrounding buildings.

Study on the Vibration Effect of Short Footage Blasting Load on Surrounding Rock-Support Structure of Tunnel

In the excavation process of a drilling and blasting tunnel, it takes multiple blasting excavations to form, so it is inevitable to produce multiple blasting impact loads, which will cause certain vibration damage to the surrounding rock-support structure. To solve this problem, based on the attenuation formula of blasting vibration wave and considering the cumulative effect of short footage blasting load, the radial displacement formula of surrounding rock particles is derived, and the analytical solution of vibration velocity field is obtained by using the method of separating variables. Then, taking Cuobuling station of Qingdao Metro as the engineering background, the finite element software is used to simulate the tunnel excavation process under the action of short footage multiple blasting. The vibration damage impact of multiple blasting loads on the surrounding rock-supporting structure is analyzed from the accumulated displacement value and vibration velocity cumulative value of the excavation tunnel. The results show that the damage accumulation effect is produced in the surrounding rock of each section during the blasting construction, among which the accumulation is the largest at the arch bottom. With the increase of blasting times, the damage of the surrounding rock is still accumulating gradually. Compared with the first blasting, the peak value of vibration velocity of the second blasting increased by 114%, and with the increase of blasting times, the variation trend of maximum vibration velocity of the measuring point showed an upward trend, but the subsequent vibration acceleration decreased. Under the condition of grade V surrounding rock, when the thickness of the concrete spray layer is 350 mm, the maximum displacement cumulative value of each measuring point in profile 1-1 is reduced by about 50.4% compared with that without support. According to the displacement nephogram of the concrete spray layer, the displacement of the concrete spray layer accumulates after three times of blasting, which affects the stability of the supporting structure. Finally, an example analysis is carried out and compared with the analytical model results to verify the accuracy of the mechanical model.

Computation of Critical Submergence Depth to Avoid Surface Vortices at Vertical Pumps Intakes

The pumping station became widely used in many fields. Free surface vortices at intakes of pumps are not favorable. It may cause noise, excessive vibration, damage to the pumping structure, reduction in efficiency and flow for hydro-turbines, etc. One of the important problems encountered during the pump intake design is the depth of submergence and other design parameters to avoid strong free-surface vortices formation. This study aims to compute the critical submergence depth with some geometrical and hydraulic limitations by using Computational Fluid Dynamic (CFD) package. The mathematical model was validated with a laboratory model that had been conducted. The model of three intake pipes was investigated under five different submergence depth (S), three different spaces between intake pipes (b), and five different suction velocities (v). The results showed the best operation cases when the space between intake pipes (b) equal to 4D, the submergence depth of water is equal or greater than 1.25 from the bell mouth diameter of intake pipe (D), and the suction velocity less than 2 m/s. The worst case was when the space between the suction pipe (b) was (2D), in this case, the vortex appeared at submergence depth (S/D = 2) with suction velocity 3 m/s.

The evaluation of vibration damage in fresh apricots during simulated transport

The transportation of fruits over longer distances could lead to damage fruits such as apricots. The present study was conducted to evaluate the effect of transportation factors including the vibration frequencies (17 and 20 Hz), the vibration time (15 and 30 minutes), the fruit cultivar (Shahroudi and Urdoobad), and the package type (2 types) on the apricot damage. An electro-dynamic lab vibration simulator was used to simulate the road transportation and a fruit damage index (FDI) was used as a criterion to evaluate the damage based on the classifying bruises into five different categories. The statistical analysis indicated that, except for the package type, the other factors (apricot cultivar, frequency, and vibration duration) had a significant effect on the FDI (P < 0.01). The vibration damages considerably changed by the apricot cultivar and increased by the frequency and duration. The results indicated that the Urdoobad cultivar was more resistant to the damage and could be used for export purposes to transport in distances more than 1,000 km. The maximum damages occurred at a frequency and duration of 17 Hz and 30 min in the Shahroudi cultivar, respectively.