Experimental Investigation on Effects of Bacterial Concentration, Crack Inclination Angle, Crack Roughness, and Crack Opening on the Fracture Permeability Using Microbially Induced Carbonate Precipitation

Uncontrollable leakage has significant effects on the safety of fractured rock mass, and microbially induced carbonate precipitation (MICP) is an effective way to control the seepage. In this study, four sets of seepage experiments are conducted on transparent rock-like specimens containing MICP filled single cracks to investigate the effects of bacterial concentration, crack inclination angle, crack roughness, and crack opening on fracture permeability. The experimental results show that calcium carbonate precipitation is produced when Sporosarcina pasteurii and cementing fluid are injected into the cracks, which can seal the cracks and reduce the permeability of the cracks. Moreover, the calcium carbonate produced by Sporosarcina pasteurii increases with increasing bacterial concentration. Furthermore, the fracture permeability of the MICP filled crack increases first and then decreases with increasing inclination, roughness, and opening of cracks. The experimental results provide a better understanding of the influence of different construction conditions on fracture permeability when the MICP technology is applied in rock engineering.

Study of plate vibrating in fluids having part-through crack at random angles and locations

This study presents the vibration characteristics of plate with part-through crack at random angles and locations in fluid. An experimental setup was designed and a series of tests were performed for plates submerged in fluid having cracks at selected angles and locations. However, it was not possible to study these characteristics for all possible crack angles and crack locations throughout the plate dimensions at any fluid level. Therefore, an analytical study is also carried out for plate having horizontal cracks submerged in fluid by adding the influence of crack angle and crack location. The effect of crack angle is incorporated into plate equation by adding bending and twisting moments, and in-plane forces that are applied due to antisymmetric loading, while the influence of crack location is also added in terms of compliance coefficients. Galerkin’s method is applied to get time dependent modal coordinate system. The method of multiple scales is used to find the frequency response and peak amplitude of submerged cracked plate. The analytical model is validated from literature for the horizontally cracked plate submerged in fluid as according to the best of the authors’ knowledge, literature lacks in results for plate with crack at random angle and location in the presence of fluid following validation with experimental results. The combined effect of crack angle, crack location and fluid on the natural frequencies and peak amplitude are investigated in detail. Phenomenon of bending hardening or softening is also observed for different boundary conditions using nonlinear frequency response curves.

Diffraction of elastic waves by a fluid-filled crack in a fluid-saturated poroelastic half-space

Summary An indirect boundary element method (IBEM) is developed to model the two-dimensional (2D) diffraction of seismic waves by a fluid-filled crack in a fluid-saturated poroelastic half-space, using Green's functions computed considering the distributed loads, flow, and fluid characteristics. The influence of the fluid-filled crack on the diffraction characteristics is investigated by analyzing key parameters, such as the excitation frequency, incident angle, crack width and depth, and medium porosity. The results for the fluid-filled crack model are compared to those for the fluid-free crack model under the same conditions. The numerical results demonstrate that the fluid-filled crack has a significant amplification effect on the surface displacements, and that the effect of the depth of the fluid-filled crack is more complex compared to the influence of other parameters. The resonance diffraction generates an amplification effect in the case of normally incident P waves. Furthermore, the horizontal and vertical displacement amplitudes reach 4.2 and 14.1, respectively. In the corresponding case of the fluid-free crack, the vertical displacement amplitude is only equal to 4.1, indicating the amplification effect of the fluid in the crack. Conversely, for normally incident SV waves at certain resonance frequencies, the displacement amplitudes above a fluid-filled crack may be lower than the displacement amplitudes observed in the corresponding case of a fluid-free crack.

Experimental study on composite mechanical properties of a double-deck prestressed concrete box girder

A series of tests were carried out on a scaled (1:8) double-deck prestressed concrete box girder in this study, aiming to study the structural response and failure mechanism of the box girder under prestressed axial compression, transverse bending, and torsion. The test results, such as the twist angle, crack development, and distortion of the box girder, were analyzed in detail. The results show that (1) the box girder eventually suffered lateral bending damage, and the cross-section of the support distorted severely; (2) torsional cracking occurred in the pure torsion region at the mid-span, but the longitudinal and transverse rebars did not yield, indicating that the pure torsion section of the box girder was still in the early stage of torsion failure; and (3) after the cracking of the box girder, stress redistribution phenomenon occurred, resulting in obvious nonlinear strain variations. Comparison of the longitudinal and transverse steel strains showed that transverse steel withstood the most shear stress during the early stage of torsion.

Slope Detection Based on Grating Sensors

<p class="0abstract"><span lang="EN-US">Because slope detection is often subject to various electromagnetic disturbances and weather limitations, there is an urgent need to develop a monitoring system that has the advantages of strong anti-electromagnetic interference capability, long service life, and small external environmental impact.</span><span lang="EN-US">Based on this demand, a real-time slope monitoring system based on fiber Bragg grating angle, crack, and osmotic pressure sensors is designed.</span><a name="OLE_LINK2"></a><a name="OLE_LINK1"></a><span lang="EN-US">The design idea is to use the sensitivity of FBG to the external stress, and the angle and crack penetrating pressure information are obtained from the offset of wavelength in different sensors to determine the stability of the slope.</span><span lang="EN-US">The design and implementation of the FBG slope monitoring system can better solve the existing problems in the slope monitoring, improve the ability to predict dangers, and strengthen the safety monitoring capability.</span><span lang="EN-US">The utility value of the system is high</span><span lang="EN-US">.</span></p>

Effect of Microstructure on the Thermal Conductivity of Plasma Sprayed Y2O3 Stabilized Zirconia (8 %YSZ)

In this paper, the effect of microstructure on the thermal conductivity of plasma-sprayed Y2O3 stabilized ZrO2 (YSZ) thermal barrier coatings (TBCs) is investigated. Nine freestanding samples deposited on aluminum-base superalloy are studied. Cross-section morphology such as pores, cracks, m-phase content, grain boundary density of the coated samples are examined by scanning electron microscopy (SEM) and electron back-scattered diffraction (EBSD). Multiple linear regressions are used to develop quantitative models which describe the relationship between the particle parameters, m-phase content and the microstructure such as porosity, crack-porosity, the length density of small-angle-crack and the length density of big-angle-crack. Moreover, the relationship between microstructure and thermal conductivity is investigated. Results reveal that the thermal conductivity of the coating is mainly determined by the microstructure and grain boundary density at room temperature (25 ℃) and by the length density of big-angle-crack, monoclinic phase content and grain boundary density at high temperature (1200 ℃).

EXPERIMENTAL AND ANALYTICAL COMPARISON OF TORSION, BENDING MOMENT AND SHEAR FORCES IN REINFORCED CONCRETE BEAMS USING BS 8110, EURO CODE 2 AND ACI 318 PROVISIONS

This study investigated the effect of combined actions of torsional moments, bending moments and shear forces in reinforced concrete beams with concrete compressive strength of 30N/mm2.The ultimate torsional moments, bending moments, and shear forces of the beams were determined experimentally, through a simple test arrangement set-up on fifteen beam specimens grouped from BC1 to BC5, three beam specimens in each group. The combined loads were induced by loading the test beams at an eccentricity of  from the beam’s principal axis at the mid-span, using Computerized Universal Testing Machine TUE-C-100. BS 8110, Euro code 2 and ACI 318 were used to calculate the ultimate torsional moments provided by both longitudinal and transverse reinforcements, bending moments and shear forces induced. The values obtained from the codes were compared with those of experimental results for validation. It was observed that Eurocode 2 predicted the highest bending moment of 21.1530kNm, the highest torsional moments of 9.8470kNm and 12.6193kNm, for torsional resistance provided by longitudinal and transverse reinforcements respectively, at an angle crack of 45°, while BS 8110 predicted the least values. ACI 318 predicted the highest value of internal shear forces that the beams possessed before yielding to the applied loads. http://dx.doi.org/10.4314/njt.v36i3.7

Numerical Analysis of the Performances of Bonded Composite Repair with Adhesive Band in Pipeline API X65

The technique of adhesively bonded composite patch repair has been successfully applied in pipeline of API X65 components repair and has recently been expanded to commercial pipeline industry. In the present paper, the crack growth behavior of cracked pipeline API X65 repaired with bonded composite patch was investigated. The finite element approach was applied in order to analyses the circumferential crack’s behavior repaired by a carbon-epoxy composite patch. The effects of the properties of the patch on the evolution of the stress intensity factor, according of angle crack tip, were discussed. The adhesive properties were optimized to increase the performance of the repair of structures by such reinforcement. Moreover, a relatively new method was developed to stop the external corrosion and the structurally reinforce steel pipes by external wrapping of damaged sections, using fibre reinforced polymer (FRP) materials. The results indicated that the defect width around the circumference had little impact on the ultimate rupture pressure of the repaired vessel. On the other hand, it was found that the defect width around the circumference was affected by the stress state in the underlying pipe substrate.

Mismatch Limit Loads of Circumferential Cracked Pipes With V-Groove Welds

The present work reports mis-match limit loads for V-groove welded pipe for a circumferential crack using finite element (FE) analyses. In our previous paper [14], closed-form solutions of mis-match limit loads were proposed for idealized butt weld configuration as a function of the strength mis-match ratio with only one geometry-related slenderness parameter. To integrate the effect of groove angles on mis-match limit loads, the geometry-related slenderness parameter has to be modified by relevant geometric parameters including groove angle, crack depth and root opening based on plastic deformation patterns in theory of plasticity. Circumferential through-wall cracks are located at the centre of the weld considering two different groove angles (45°, 90°). With regards to loading conditions, axial (longitudinal) tension is applied for all cases. For the parent and weld metal, elastic-perfectly plastic materials are used to simulate under-matching and over-matching conditions in plasticity. The overall results from the proposed solutions agree well with FE results.