Wall Strength Research Articles

Research on Floor Heave Mechanisms and Control Technology for Deep Dynamic Pressure Roadways

In order to study the influencing factors of floor deformation and floor heave mechanisms of deep mining roadways, this paper takes the deep dynamic pressure mining roadway of a mine as the engineering background and adopts a research method combining theoretical analyses, numerical simulations and field observations to study the influence of various factors on floor deformation and floor heave mechanisms. It is determined that the influencing factors on floor heave are a large buried depth, a long duration of dynamic pressure, unique characteristics of the surrounding rock and an insufficient support strength. A bearing mechanics model of the roadway floor beam is established, and it is determined that the displacement of the roadway floor is negatively correlated with the elastic modulus and floor thickness and positively correlated with the buried depth of roadway, the roadway width and the width of fracture zone. A numerical simulation method is used to study the influence of the original geological conditions, strengthening the elastic modulus of floor, strengthening the strength of the side wall rock and increasing the thickness of the floor rock on the displacement of the roadway floor. It is determined that increasing the thickness of floor rock controls the floor heave the most, followed by strengthening the elastic modulus of the floor rock and then strengthening the strength of the side walls. The results of the numerical simulation agree well with those of the theoretical analysis. After the control method of “bottom lifting + bottom angle bolt + floor bolt ” is adopted on site to treat the floor heave, the floor heave volume of the roadway is small during the service period of the 303 working face return air roadway, which meets the application requirements of the roadway. Meanwhile, the theoretical analysis and numerical simulation results are indirectly verified.

Shear Strength of Reinforced Concrete Squat Walls

Squat shear walls are widely used in various structures to resist earthquake loads. However, the relevant design expressions found in building codes and literature do not incorporate the influence of all crucial parameters and provide inconsistent peak shear strength estimations. This study adopts the artificial neural network (ANN) to predict the peak shear strength of squat walls using an extensive database that includes the results of 487 walls with wide-ranging test parameters. The ANN models consider the effect of concrete strength, the wall aspect ratio, vertical and horizontal reinforcements, vertical reinforcement of boundary elements, and axial load ratio. These accurately predicted the available test results. They implemented it to carry out parametric and sensitivity analysis to investigate the effect of the main parameters on the peak strength and to give information about the factors that contribute most to the shear response. In addition, a softened strut and tie method is proposed, considering the variables that substantially influence the shear strength. A nonlinear regression analysis is employed to determine the coefficients of the proposed model using the available database. The performance of the proposed model is measured using the existing models, which results in the best favorable agreement with the test results. Doi: 10.28991/CEJ-2023-09-02-03 Full Text: PDF

Higgsless simulations of cosmological phase transitions and gravitational waves

First-order cosmological phase transitions in the early Universe source sound waves and, subsequently, a background of stochastic gravitational waves. Currently, predictions of these gravitational waves rely heavily on simulations of a Higgs field coupled to the plasma of the early Universe, the former providing the latent heat of the phase transition. Numerically, this is a rather demanding task since several length scales enter the dynamics. From smallest to largest, these are the thickness of the Higgs interface separating the different phases, the shell thickness of the sound waves, and the average bubble size. In this work, we present an approach to perform Higgsless simulations in three dimensions, producing fully nonlinear results, while at the same time removing the hierarchically smallest scale from the lattice. This significantly reduces the complexity of the problem and contributes to making our approach highly efficient. We provide spectra for the produced gravitational waves for various choices of wall velocity and strength of the phase transition, as well as introduce a fitting function for the spectral shape.

Research and Practice of Rebar Engineering Quantity Calculation for Underground Diaphragm Wall of Intercity Railway Based on BIM and Planar Representation Method of Rebar

Underground diaphragm wall is a typical form of deep foundation support for intercity railroad, which has the characteristics of high wall strength, high stiffness and large amount of steel reinforcement. In the process of quantity calculation, there are problems such as unreasonable calculation method of reinforcement quantity and inaccurate and non-uniform calculation results. This paper briefly discusses the research on quantity calculation based on BIM model by combining the classification form of underground diaphragm wall, sorting out the rules of quantity calculation and steel flat method labeling. It also discusses the functions of the rebar information extraction system based on the rebar flat method labeling and the flow structure of the rebar quantity calculation process of intercity railroad underground diaphragm wall based on BIM and rebar flat method labeling. Finally, the accuracy of the calculation results of the diameter, length and number of longitudinal bars, hoop bars and tension bars of the underground diaphragm wall of the intercity railroad is compared with the traditional calculation mode by combining the calculation model. The data showed that the accuracy rate of calculation based on BIM and steel flat marking method was higher than that of traditional calculation mode, and the accuracy rate of BIM and steel flat marking method reached 97.9% on average, while the accuracy rate of traditional calculation mode was only about 85% on average. Therefore, it is verified that the calculation of intercity railroad underground diaphragm wall reinforcement based on BIM and steel flat method has good effect.

Model trees and stepwise regressions for accurate in-plane shear strength predictions of partially grouted masonry walls

The behaviour of partially grouted (PG) masonry shear walls is complex due to masonry's anisotropic nature and the nonlinear interactions among its constituents. Currently available code- and research-based shear strength equations provide highly variable results when predicting the in-plane shear strength of PG masonry walls. It is crucial to develop a greater understanding in this area, as sudden shear failures of masonry walls can lead to catastrophic losses of human life and property. This study presents the development of several new in-plane shear strength models for PG masonry walls using stepwise regression and model trees with data compiled from 292 experimentally tested walls. The models are found to significantly outperform existing code- and research-based shear strength equations. It was found that, of the variables studied, the most significant ones are the axial load, wall geometry, compressive strength of mortar, and area of interior vertical reinforcement.

A Collapse Strength Model for a 7” Crescent-Worn Casing Connection Considering Sealing Integrity

Collapse failure under external pressure is one of the common failure forms of casing. Much research has been performed on the casing body, but few on the threaded connection, in view of the general belief that the threaded connection has a thicker wall and larger collapse strength than the casing body. However, under external pressure, the sealing capacity of a worn casing connection will decrease due to deformation of the sealing structure, so the influence of sealing ability should be considered to determine the collapse strength of casing. In this paper, we established a three-dimensional finite element model of a 7” crescent-worn casing connection and calculated the collapse strength of the connection under different wear depths. Meanwhile, the stress distribution characteristics on the sealing surface were obtained and the influence of wear on the sealing performance of the casing connection under external pressure was analyzed. The results showed that when the wear rate exceeds a certain value, the collapse strength of the connection based on sealing integrity was lower than that of the casing body. Based on these, a collapse strength model for a 7” crescent-worn casing connection considering sealing integrity was developed and a safety evaluation method of the collapse strength of the worn casing string was proposed.

Seismic performance evaluation of steel and GFRP reinforced concrete shear walls at high temperature

Fire-induced structural damage to the seismic performance of reinforced concrete shear walls is critical in the event of a fire-earthquake scenario. However, only few researchers have studied the seismic performance of reinforced concrete shear walls at high temperatures. This study focuses on the seismic performance of fiber reinforced concrete shear walls at high temperatures by using finite element (FE) software, ABAQUS. The experimental test available in a literature on seismic behavior of shear walls exposed to fire and thermal properties of glass fiber reinforced polymer (GFRP) bars were used to validate the FE model and showed good agreement and thus used in the simulation.The FE results showed that exposure of RC shear wall to fire reduced the strength of the wall. The strength of walls at the maximum applied drift of 3.2% with concrete cover thicknesses of 20 mm, 25 mm, and 30 mm was dropped by about 70%, 76%, and 85% of the reference shear wall, respectively. Similarly, the strength of RC walls was reduced by about 80%, 75%, and 68% of the reference shear wall for the duration of fire exposure of 30 min, 60 min, and 120 min, respectively. Additionally, the strength of walls due to one side, two sides, or all sides’ exposure to fire was decreased by about 68%, 56%, and 50% of the reference shear wall, respectively. It can generally be concluded that the fire exposure sides has largely affected the strength of the shear wall compared to the other parameters and GFRP bars were more sensitive to temperature than steel bars.

Investigation of the real contact area of tensile fractures with different normal stresses and sizes by using pressure-sensitive films

More than 240 experimental tests were conducted and the characteristics of real contact area of the mated tensile fractures were investigated by using pressure-sensitive films. The effects of normal stress, fracture size as well as rock type on the real contact area of mated tensile fractures were evaluated and discussed. The results show that the real contact area of the mated rock fractures has a parabolic increasing relationship with the normal stress ratio (the ratio of the applied normal stress on the fracture surface to the uniaxial compressive strength of the joint wall). Also, the size of the tensile fracture can affect its real contact area, and the larger the applied normal stress is, the more significant the size effect of the rock fracture on the real contact area is. Furthermore, lithology has a significant influence on the real contact area of the structural plane, which is also related to the applied normal stress. Under the same stress condition, the real contact areas of shale and granite fractures are the smallest, while that of green sandstone fractures is the largest. By analyzing the nominal normal stress and the real normal stress on rock fractures, it was found that even if the nominal normal stress applied on the rock fractures is only 1.5 MPa, the average real normal stresses can reach 20 MPa ∼ 45 MPa, which is about 15–30 times the nominal applied normal stress. The contact characteristics of tensile fractures were analyzed by adopting the cutting methods. It was revealed that within a mated tensile fracture, the smaller the JRC of an area is, the larger the real contact area will be. The results of this study are of great significance for revealing the characteristics and laws of the contact areas of tensile fractures, and the 248 sets of data specimens obtained from the tests can provide important support or reference for establishing mechanical models for rock mass contact.

Numerical Investigation of the Effects of Opening on the Strength of Masonry Wall

Masonry is used as a construction material since old age. It is a cheaper construction material compared to R.C.C. and also requires comparatively less construction skills. During an earthquake, the masonry wall constructed following the codal provisions shows preliminary behaviour in the in-plane direction of wall and it has lesser deformation in the out-of-plane direction of the wall. Although, the strength and stiffness of the Un-Reinforced Masonry (URM) walls were reduce due to sizes and positions of openings, the relationship between the seismic capacity of the walls and the position and size of opening in walls are not clear. Researchers in the past mostly explored the in-plane behaviour of solid masonry wall without opening. Considering the openings in these walls can significantly affect the strength of the masonry wall. Hence, in the present study, an attempt is made to understand the effect of varying opening sizes (4 different combinations of door and/or window openings) in unreinforced masonry wall using finite element software CATIA. From this software, URM walls were modeled and load based quasi-static analysis were done in in-plane direction. The collapse mechanisms of the masonry walls and crack patterns are studied from the analysis and a key output from this work is the characterization of the relationships between the sizes and positions of openings and the in-plane performance of masonry walls.

Experimental and Numerical Study on Unreinforced Brick Masonry Walls Retrofitted with Sprayed Mortar under Uniaxial Compression

The use of shotcrete or sprayed mortar is a common construction alternative to retrofit unreinforced brick masonry (URM), and extensive research has already been carried out in this area. However, most studies have been conducted on lateral strength, for example, eccentric compression or seismic forces. On the other hand, there are few studies about uniaxial compression, and the results of most studies confirm a strong relationship between the thickness of the retrofitting layer and whether it is a double-sided retrofitting section. However, most studies are exclusively experimental, with few samples, and lack numerical analysis; therefore, deeper research is required on this issue. In this sense, this paper combined experiments and finite element (FE) simulations to further study the uniaxial compression. A series of cyclic uniaxial compression experiments on URM retrofitting with sprayed mortar were performed. The experimental results were used to calibrate the FE model. Using these calibrated FE models, more variable parameters were run so that more reference results could be obtained. Moreover, the resulting damageable model of FE will be useful for studying the behavior in the inelastic phase. Results found that the compression strength of most composite walls retrofitted with sprayed mortar increases with the thickness of the sprayed layer and can improve the construction defects of the masonry itself. An over-thin sprayed layer reduces the range of the elastic phase of the composite wall. This phenomenon tends to stabilize with increasing thickness. The ultimate strength of the composite masonry is generally positively correlated with the overall increase in the thickness of the sprayed mortar but may cause a negative contribution to the ultimate strength of the composite masonry when the sprayed layer is too thin. The contribution of double-sided spraying to the ultimate strength of the composite wall was not as large as expected, but the contribution to the improvement of the elastic modulus of the wall was significant.

A STUDY ON TSUNAMI-RESISTANT REINFORCEMENT EFFECT OF REINFORCED CONCRETE OUTER WALL BY FIBER REINFORCED SHEET

In the 2011 Tohoku Earthquake, many buildings were collapsed or overturned, and a number of outer concrete walls were broken by the hydro dynamic pressure due to Tsunamis. Out-of-plane strength of wall are usually not concerned in the seismic design and a few static loadings tests verify the actual nonlinear out-of-plane response of concrete walls. In a past study, an out-of-plane strength of outer concrete walls damaged by 2011 Tohoku Tsunami was evaluated based on the plastic hinge mechanism. In this study, the strength evaluation method is verified by the hydro static loading test on the concrete walls, and the out-of-plane strength are compared by the test between the bare concrete walls and walls reinforced with the polyester fiber sheets.

The effect of polyurethane foam glue on the strength and deformability of aerated concrete masonry when using it as a masonry mortar

The article presents the results of experimental studies of masonry made of cellular concrete blocks of autoclave hardening YTONG produced by JSC «Kcell-Aeroblock-Center» on the adhesive composition (polyurethane glue) Dryfix (POLYPAG AG). The tests included comprehensive studies of the strength and deformability of masonry walls made of cellular concrete blocks, under various types of stress state of structures: central and off-center compression of masonry walls, axial tension on bandaged and unbound seams, tensile bending on bandaged and unbound seams, shear with an assessment of tangential adhesion. Tests have confirmed the inconsistency of the technology of laying blocks of cellular concrete on the adhesive composition of Dryfix with incomplete filling of seams. This technology has a significant impact on the strength of the masonry during bending: the adhesion of the blocks to each other with such an adhesive composition applied to the surface of the block is significantly lower than the value obtained when testing the blocks for axial tension. According to the results of the experiments, the value of the temporary resistance to axial stretching along the unbound section (normal adhesion) of the masonry, the values of the calculated resistance of the masonry to stretching during bending along the unbound and tied sections, as well as the value of the calculated resistance of the masonry under central compression were determined.

Study on Seismic Performance of Cold-Formed Thin-Walled Steel-Straw Board Composite Wall with Diagonal Brace

The composite wall studied in this paper is based on the original cold-fonned thin-walled steel-straw board composite wall, which is set up with inclined braces and rigid inclined braces to improve its seismic performance. The factors of aspect ratio are analyzed, and the formula of shear bearing capacity of composite wall is deduced. The results show that: (1) When the height-width ratio of the composite wall is 2.4m×1.2m, 1.8m×1.2m and 1.2m×1.2m respectively, the yield strength of the composite wall is 35.78kN, 37.47kN and 54.23kN respectively. The yield strength of the former increases by 4.72 %, and the yield str ength of the latter increases by 44.73 %. (2) Using the effective strip method, the error of the derived shear capacity formula is not large, and the difference between the experimental value and the simulated value is not large, in order to provide some reference for the seismic design of this kind of cold-fonned thin-walled steel-strawboard composite wall with diagonal brace.

Lateral Resistance of Reinforced Light-Frame Wood Shear Walls

In light-frame timber construction, the shear wall is one of the most important components that provide resistance to lateral loads such as earthquakes or winds. According to KDS (Korea Design Standard) 42 50 10, shear walls are to be constructed using wood-based structural sheathing, with studs connected by 8d nails spaced 150 mm along the edge and 300 mm in the field. Even though small-scale residential timber building can be designed to exhibit seismic resistance using light-frame timber shear walls in accordance with KDS 42 50 10, only the abovementioned standard type of timber shear wall is available. Therefore, more types of timber shear walls composed of various materials should be tested to measure their seismic resistance, and the results should be incorporated into the future revision of KDS 42 50 10. In this study, the seismic resistance of shear walls composed of structural timber studs and wood-based structural sheathing with reinforced nailing is tested to evaluate the effects of the reinforcement. For the nailing reinforcement, shear wall specimens are constructed by applying nail spacings of 75–150 mm and 50–100 mm. For the shear wall specimens with one sheathing and reinforced nailing, the shear strengths are 1.7–2.0 times higher than that of the standard shear wall (nail spacing of 150–300 mm). The shear strength of the shear walls with sheathing on both sides is 2.0–2.7 times higher than that of the standard shear wall.

Experimental investigation of FRCM under shear loading

Fabric Reinforced Cementitious Matrix (FRCM) can be used to improve the shear strength of masonry walls. The contribution of the FRCM is evaluated, accordingly to existing standard, taking into account the FRCM-to-substrate bond strength and the tensile strength of bare fabrics, neglecting the mortar matrix. Nevertheless, to date, there are no experimental tests that provide the actual shear capacity of the FRCM alone and not bonded to the substrate. To this scope, a four-hinge articulated steel frame was designed to investigate the shear behaviour of small-scale square specimens, as well as the mechanism of shear stress transfer between the fabric and the mortar. This paper presents the outcomes of shear tests performed on four FRCM composites, comprising of two basalt fabrics embedded in either lime- or cement-based mortars, in order to assess the influence of the single components. Digital image correlation (DIC) was also used to determine the displacement fields, strains and to detect the crack pattern of the specimens.

STRENGTH ANALYSIS OF VERTICAL SECTION CERAMIC FENCE WALL

The article shows methods for determining the strength of masonry walls of a ceramic fence depending on the strength of ceramic bricks and mortar. In addition, in order to assess the strength of the ceramic brick wall during cutting, tests were carried out on prototypes made of ceramic solid bricks on a vertical horizontal seam of the mortar. Products made of ceramic bricks and hollow ceramic bricks showed a significant difference in the experimental values of cutting resistance in the section of contact with the data obtained in accordance with the norms. For laying hollow bricks, the movable values of the contact cross-section were 1.8 times higher than the calculated ones and 13 times higher than those established by them. The strength when cutting walls made of hollow bricks with a volume of 18% obtained on the basis of the experiment, respectively, when calculated according to the norms exceeded the growth by 2.6 and 3.5 times, respectively.

Analyzing the contribution of vasa vasorum in oxygenation of the aneurysmal wall: A computational study

The mechanisms of abdominal aortic aneurysm (AAA) formation and rupture are controversial in the literature. While the intraluminal thrombus (ILT) plays a crucial role in reducing oxygen flux to the tissue and therefore decreasing the aortic wall strength, other physiological parameters such as the vasa vasorum (VV) oxygen flow and its consumption contribute to altered oxygenation responses of the arterial tissue as well. The goal of this research is to analyse the importance of the aforementioned parameters on oxygen delivery to the aneurysmal wall in a patient-specific AAA. Numerical simulations of coupled blood flow and mass transport with varying levels of VV concentration and oxygen reaction rate coefficient are performed. The hypoperfusion of the adventitial VV and high oxygen consumption are observed to have critical effects on reducing aneurysmal tissue oxygen supply and can therefore exacerbate localized oxygen deprivation.

Reproduction and long-term monitoring of drying of mudbricks and small mudbrick walls for the preservation of the ancient mudbrick wall of Eleusis

The mudbrick wall remains preserved to date in the site of Eleusis are some of the largest preserved in Greece. Following an extensive investigation of the properties of existing mudbricks, material of similar properties from the archaeological site of Eleusis was used to reproduce mudbricks of similardensity with the ancient ones after drying with various concentrations of dry grass also from the archaeological site. Actual mudbricks were reproduced and brought to a final equilibrium condition under climatic conditions practically similar to those in Eleusis. Others were used to trim samples and measuremechanical properties to compare with original mudbricks, others were instrumented with suction and volumetric water content sensors in order to monitor mudbrick drying under climatic conditions and others in order to build small mudbrick walls with mortar from the same soil used to make the mudbricks. These small mudbrick walls included the mudbricks with internally installed suction and volumetric water content sensors and were also constructed with similar sensors in the mortar. This allowed monitoring of drying of the mortar until each whole mudbrick wall came to equilibrium and was then subjected to uniaxial compression under load control. Monitoring of mudbricks and mudbrick walls indicated that the higher the dry grass concentration, the higher the drying rate of the mudbricks; the lower the dry grass concentration the higher the probability of mudbrick cracking during drying; minimum required time for mudbrick and mudbrick wall drying for the particular soil used in the ancient mudbricks is not less than 5 weeks. Finally, uniaxial compression under load control on both samples trimmed from dried mudbricks and mudbrick walls indicated that uniaxial compression strength decreases with increasing dry grass concentration and mudbrick wall strength should be expected in the order of 70-80% that of the cubic samples trimmed from dried mudbricks and subjected to load rate control compression.

Probabilistic assessment of slope stability at ore mining with steep layers in deep open pits

Purpose. A methodology development for predicting the geomechanical situation when mining an ore deposit with steep-dipping layers, taking into account the uncertainty in determining the rock properties, which is a consequence of the rock mass heterogeneity. Methods. The assessment of the open-pit wall stability is based on a combination of numerical simulation of the rock stress-strain state (SSS) and probabilistic analysis. The finite element method is used to determine the changes in the SSS that occur at various stages of mining operations due to design changes in the overall open-pit slope angle. The elastic-plastic model of the medium and the Mohr-Coulomb failure criterion are implemented in the codes of the 3D finite element analysis program RS3 (Rocscience). Stochastic simulation is used to assess random risks associated with natural object state variations. Findings. The distribution of maximum shear strains, which localizes the real or potential sliding surfaces in the open-pit wall at various stages of ore mining, has been identified. Based on the Shear Strength Reduction procedure, the open-pit wall Strength Reduction Factor (SRF) has been determined. The probabilities of open-pit wall stability loss, as well as the decrease in the strength reduction factor below the standard level at all stages of the ore body mining, have been revealed. Originality. For the first time, for real mining-geological conditions of a deep ore open pit, the dependence of the strength reduction factor on the overall wall slope angle, which changes during mining of each steep layer, has been determined. For each stage of mining operations, for the first time, the probability of a decrease in the open-pit wall stability below the standard level has been determined based on stochastic simulation. Practical implications. The ratio between the open-pit contour characteristic (overall slope angle) and the probabilistic safety factor is the basis for practical solutions to ensure the efficiency and safety of mining at various stages of friable and hard overburden excavation, ore extraction, as well as for the subsequent optimization of the open-pit design contours.

Investigating the Retrofitting Effect of Fiber-Reinforced Plastic and Steel Mesh Casting on Unreinforced Masonry Walls.

Unreinforced masonry (URM) is one of the most popular construction materials around the world, but vulnerable during earthquakes. Due to its brittle nature, the URM structures may lead to a possible collapse of the wall of a building during earthquake events causing casualties. In the current research, an attempt is made to enhance the seismic capacity of URM structures by proposing a new innovative composite material that can improve the shear strength and deformation capacity of the URM wall systems. The results revealed that the fiber-reinforced plastic having high tensile and shear stiffness can significantly increase in-plane as well as out-of-plane bending strength of the URM wall. It was recorded that the bending moment of the prism increased up to 549.5% by increasing the bending moment from 490 N*mm to 3183 N*mm per mm deflection of prism upon using glass fibers. Moreover, the ductility ratio amplified up to 5.73 times while the stiffness ratio increased up to 4.16 times with the aid of glass fibers. Since the material used in this research work is low cost, easily available, and no need for any skilled labor, which is economically good. Therefore, the URM walls retrofitted with fiber-reinforced plastic is an economical solution.