Wall Joints Research Articles

DIMENSIONAL SYNTHESIS OF ACTIVE SUSPENSION CAB MECHANISM LINKS

One of the directions of the heavy duty machine is the operator cabin construction, which provides a high level of comfort. Adequate control of active suspension drives can reduce low frequency and large amplitude vibrations occurring in a number of cabin degrees of freedom. The main link of the mechanism is the platform with cab suspended on two rockers and one actuator. Article proposes methods for determining the length of suspension arms, the width of the platform and centres of the joints, which are connected to the suspension. It has been proved for the flat case that if the momentary centre of rotation of the platform relative to the machine frame is located inside the road roughness zone is a single drive can effectively reduce transverse vibration and angle vibration around the longitudinal machine axis. Further conditions that determine links size are to prevent from peculiar positions, to avoid collision between cab wall and suspension joints. Presented relations between the height of the waist rough roads, wheelbase machine, cab mounting height on the machine and the dimensions of the link suspension mechanism. Presented dimensional calculation results cab suspension links dedicated to Caterpillar 924 GZ loader. Assuming the vertical driving cab calculated inaccuracy of its transverse displacements. Presented the results showing influence of the cab assembly height on the cabin mounting links dimensions.

New Method for Shear Strength Determination of Unfilled, Unweathered Rock Joint

Replicas were produced of 20 natural rock joints with different roughness. Factors affecting shear strength were examined and direct shear tests were performed using the replica joints to determine their quantitative shear strength characteristics. Results from the shear tests were best fitted by the power law equation, τ = Aσ n , where τ is the shear strength and σ n is the normal stress, and regression coefficients A and B were determined. The coefficient A (equal to τ when σ n is 1 MPa) is defined as the friction angle, and B, which determines the curvature of the plot of shear versus normal strength, is a factor that reduces the shear strength. The physical and mechanical properties of the coefficients A and B were defined, and the relationship between these coefficients and the factors affecting shear strength, such as roughness and joint wall strength, were analyzed quantitatively. A new equation, τ = σ n tan[ϕ b + ϕ J + s n], was suggested to measure and predict shear strength accurately based on results from these analyses, where ϕ b is the basic friction angle, ϕ J is the joint roughness angle, and s n is the shear component. Although the new shear strength equation is nonlinear, it is as simple to use as a linear equation and the shear strength can be estimated using only three easily measurable parameters (ϕ b , ϕ J , and σ j , the joint wall compressive strength). The failure envelope estimated using the new shear strength equation not only closely matches the measured shear strength, but also reflects the nonlinear relationship between the normal stress and shear strength.

Experimental Study on the Shear Strength of Sandy Clay Infilled Regular Rough Rock Joints

Infill materials in rock joints usually cause a reduction in the joint shear strength. The shear behavior of rock discontinuities depends upon whether they are clean and unfilled or filled, so this concern invites accurate understanding of the shear behavior and strength of infilled joints. A series of constant normal load direct shear tests was performed to investigate the shear strength of artificial samples with infilled rough joint surfaces having different asperity and infill characteristics. The current study focuses on the effects of factors that influence the shear strength of infilled rock joints samples, with emphasis on forward and reverse shearing. In the forward cycle, the front joint wall is compressed and possibly sheared, and the back side fill is unbonded from the joint surface and slightly disturbed. In the reverse cycle, the disturbed and weakened back side fill is under shearing. The effect of the normal stress on the joint is studied, as this factor plays an important role on the shear behavior of infilled rock joint samples. The results show that joints with low asperity angle exhibit higher shear strength during the forward shearing cycle than the reverse cycle, but in joints with steeper asperity angle, the reverse cycle exhibits greater shear strength. In the reverse cycle, the joint infill has less influence compared to the effect of the rougher surface and higher asperity inclination, even in higher normal stress.

Direct Measurement of the Contact Normal Stress Distribution between Two Smooth Joint Surfaces

The shear strength of rock joints is highly depended upon the failure mode of joint asperity. At lower normal stress slide-up of one asperity up over another mode, however at high normal stress the joint asperities are sheared off at the base. This research uses pressure measurement film to directly measure the contact normal stress between smooth joint surfaces. It demonstrates that the density of color impression is capable of capturing the normal stress distribution behavior. The contact normal stress distribution during shearing is changed. After shearing, the contact stress becomes large. This increase in contact normal stress is to fracture the joint wall material.

Model for the shear behavior of rock joints under CNL and CNS conditions

Empirical models for the shear behavior of rock joints are suggested from the results of direct shear tests using a servo-controlled shear testing machine. Cement mortar replicas of rock joints are tested while varying the normal stiffness, initial normal stress, joint roughness coefficient and joint wall compressive strength. The test results are analyzed to investigate the effects of loading conditions and material properties on the surface resistance index and normal displacement behavior of the joints. In this study, the ratio of the shear stress to normal stress was defined as the surface resistance index because it shows friction-related characteristics between joint surfaces. Empirical models of the surface resistance index and normal displacement behavior are suggested. In the empirical models, dimensionless terms are adopted to avoid the scale effect and thus enhance the applicability of the suggested models. The suggested models can be applied to predict the shear behavior of rock joints, including pre-peak and post-peak shear stress levels, regardless of the loading condition. To verify the suggested models, additional shear tests of the rock joints and cement mortar replica specimens are carried out, and the performance of the models is compared with those of other models such as Barton׳s empirical model. The suggested models are applied to the test results of previous studies. The predictions of the suggested models corresponded well with the experimental results for the overall stress levels.

A conceptual model for the peak shear strength of fresh and unweathered rock joints

Several criteria have been proposed over the years in order to predict the peak shear strength of rock joints. The most widely used criterion is the JRC–JCS criterion by Barton. It says that changes in the peak shear strength originate from surface roughness, joint wall compressive strength and normal stress. A limitation with this criterion is that the contribution from roughness could be overestimated for natural and mismatched joints if the joint roughness coefficient, JRC, is estimated based on the direct profiling method. To account for this effect, Zhao introduced the joint matching coefficient, JMC, which accounts for the matedness of the joint. In addition to this, it is known that the scale of the sheared joint could affect the peak shear strength. However, no criterion exists that describes how roughness, matedness and scale interact. In this paper, a conceptual model is proposed. The model is based on adhesion and fractal theory, measurements of surface roughness and the anticipated variation of the number and size of the contact points. The model proposes how the compressive strength and the roughness of the joint surface together with the matedness of the joint interact in order to form the shear strength of the joint under constant normal load conditions. The model also suggests an explanation for the scale effect of rock joints with respect to the surface roughness.

Thermal Cracking of the Cylindrical Tank under Construction. II: Early Age Cracking

AbstractThe subject of this paper is a phase numerical analysis of early-age cracking of a reinforced concrete (RC) cylindrical tank wall, with a nominal unit capacity of 8,300 m3, under construction. Numerical calculations are based on the model that can analyze the behavior of such structures, including the temperature development originating from heat hydration, external conditions, the development of shrinkage, and mechanical properties in time. A viscous-elastic concrete model with cracking was used. The real state of cracked wall segments 8 and 9 (Part I) is compared with the results of the numerical calculations. Moreover, the cracks’ localization and sequence of cracking as a result of the numerical analysis is discussed. Based on the achieved numerical results, the design solutions of vertical construction joints in which the degree of reinforcement is increased to ensure their water-tightness (despite the use of a sealing tape) negatively affect the cracking state of the jointed walls. This is ...

Hydro-mechanical coupling mechanism on joint of clay core-wall and concrete cut-off wall

The joint of clay core-wall and concrete cut-off wall is one of the weakest parts in high earth and rockfill dams. A kind of highly plastic clay is always fixed on the joint to fit the large shear deformation between clay core-wall and concrete cut-off wall, so the hydro-mechanical coupling mechanisms on the joint under high stress, high hydraulic gradient, and large shear deformation are of great importance for the evaluation of dam safety. The hydro-mechanical coupling characteristics of the joint of the highly plastic clay and the concrete cut-off wall in a high earth and rockfill dam in China were studied by using a newly designed soil-structure contact erosion apparatus. The experimental results indicate that: 1) Shear failure on the joint is due to the hydro-mechanical coupling effect of stress and seepage failure. The seepage failure will induce the final shear failure when the ratio of deviatoric stress to confining pressure is within 1.0–1.2; 2) A negative exponential permeability empirical model for the joint denoted by a newly defined principal stress function, which considers the coupling effect of confining pressure and axial pressure on the permeability, is established based on hydro-mechanical coupling experiments. 3) The variation of the settlement before and after seepage failure is very different. The settlement before seepage failure changes very slowly, while it increases significantly after the seepage failure. 4) The stress-strain relationship is of a strain softening type. 5) Flow along the joint still follows Darcian flow rule. The results will provide an important theoretical basis for the further evaluation on the safety of the high earth and rockfill dam.

Corrosion Mechanism of 316L Stainless Steel in a Expansion Joint of Blast Furnace Gas Pipeline in a Power Plant

Severe corrosion phenomenon appeared in an expansion joint of blast furnace gas (BFG) pipeline after booster fan in a power plant. The sediment adhered to the inner wall of the expansion joint was analyzed by ion chromatography. The corrosion site of expansion joint was examined by scanning electron microscope (SEM), and the behavior of electrochemical corrosion of stainless steel electrode was discussed through electrochemical impedance spectroscopy (EIS) and polarization curve. The results reveal that the leaching solution of the sediment is a kind of strong electrolyte solution. Along with the increase of immersion period, the impedance of stainless steel electrode decreases dramatically, the impedance spectroscopy experiences such a procedure that a single capacitive reactance arc gradually develops into the contraction of inductive reactance and then tends to be two capacitive reactance arc, which indicates that pitting corrosion transfers from induction period to evolution period until metastable pitting translates into stable pitting. There exists no passive area in polarization curves of stainless steel and shows the characteristics of active dissolution. In conclusion, the failure of the expansion joint stainless steel shows typical pitting characteristic.

Numerical Simulation of the Process of Fracture of Echelon Rock Joints

The effect of joint overlap on the full failure behavior of a rock bridge in the shear-box test was numerically investigated by means of the particle flow code in two dimensions (PFC2D). Initially, the PFC2D was calibrated by use of data obtained from experimental laboratory tests to ensure the conformity of the simulated numerical model’s response. Furthermore, validation of the simulated models was cross-checked with the results from direct shear tests performed on non-persistent jointed physical models. By use of numerical direct shear tests, the failure process was visually observed and the failure patterns were seen to be in reasonable accordance with experimental results. Discrete element simulations demonstrated that macro shear fractures in rock bridges are because of microscopic tensile breakage of a large number of bonded discs. The failure pattern is mostly affected by joint overlap whereas the shear strength is closely related to the failure pattern. The results show that non-overlapping joints lost their loading capacity when nearly 50 % of total cracks developed within the rock bridge whereas the overlapping joints lost their loading capacity as soon as cracks initiated from the joint walls. Furthermore, progressive failure or stable crack growth was seen to develop for non-overlapped joints whereas brittle failure or unstable crack growth was seen to develop in overlapped joints.

Effect of stress distribution on the tool joint failure of internal and external upset drill pipes

Detailed investigation was carried out on the tool joint failure of the internal & external upset (IEU) GSS105 drill pipes. Stresses were analyzed using 2D finite element method (FEM) for the threaded tool joint of the drill pipe under the combined loading conditions containing preload, tensile and bending loads. The stress concentration factors in the pin and box were calculated. Results showed that the maximum stress concentration occurred at the roots of the first tooth from the pin tool joint shoulder of the drill pipe. Fractographic observation revealed that the tool joint failure of the drill pipe was caused by fatigue crack nucleated at the tooth root and propagated through the wall of the tool joint. The deterioration of the fatigue resistance of the tool joint is related to dogleg region where severe cyclic bending load exists due to the local deviation of the drill pipe from the vertical line.

Numerical modeling of composite beam to reinforced concrete wall joints: Part I: Calibration of joint components

This paper presents the first part of a numerical study to simulate composite beam to reinforced concrete wall joints using the finite element software ABAQUS. In detail, several benchmark examples dealing with different components of the joint are simulated in the validation and calibration process of the finite element package. Moreover, these simulations consider the analysis of: (i) type of finite element, 3D solid first and second order elements; (ii) material constitutive law for steel and concrete; (iii) interactions, reinforcement–concrete bond, composite behavior and mechanical contact. The validation of the simulated benchmark examples is accomplished by means of convergence studies and comparison with experimental tests. The accuracy obtained within these benchmark examples puts in evidence the appropriate simulation of the different phenomena to be dealt within the analysis of composite beam to reinforced concrete wall joints in a companion paper.

Numerical modeling of composite beam to reinforced concrete wall joints: Part II: Global behavior

This paper presents the second part of a numerical study that aims to reproduce the behavior of a novel type of joint between a composite beam and reinforced concrete wall using the finite element software ABAQUS. The joint configuration was developed within the RFCS project “InFaSo”, which provided the experimental results. In a preceding paper, the calibration of the joint components modeling through benchmarking was presented. Next, a three-dimensional FE model is proposed to simulate stiffness, strength and rotation behavior of the complete joint. The comparison between computation and experiments highlights the degree of accuracy of the proposed models. Subsequently, using the numerical data produced, the global behavior of the joint is further exploited. Finally, some parametrical variations put in evidence the influence of the longitudinal reinforcement bars in the composite beam, as the governing component, and analyze a variant of the joint configuration that aims to improve its performance.

울릉도 국수바위 주상절리의 형성과정과 자연유산적인 가치

울릉도 서면의 비파산에는 마치 국수가락과 같은 독특한 외관을 가진 조면암질 단애가 위치하고 있다. 이 단애는 외관상의 특징에 의해 국수바위라 명명되었으며 북쪽을 제외한 삼면에 단애가 발달하고 있고 각 면에서 아수직 방향의 주상절리를 뚜렷하게 보여주고 있다. 이 주상절리는 노출된 방향에 따라 형태 및 광물학적으로 상이한 특징을 보이고 있으며 이 경향은 동쪽 면과 서쪽면의 대조에서 두드러진다. 본문에서는 양 측면에 노출된 주상절리의 대조를 바탕으로 용암의 분출 이 후의 냉각과정에 대해 고찰하였다. 형태학적인 측면에서 동쪽 면은 서쪽 면에 비해 주상절리와 끌 구조의 간격이 좁고 절리면이 비교적 뚜렷하게 발달하고 있다. 그리고 광물학적인 측면에서 서쪽 면의 조면암은 동쪽 면에 비해 반정이 크고 취반상조직을 보이며 라쓰상의 사장석에 의한 트라카이틱조직이 미약하다. 이러한 차이점을 중심으로 하여 고온의 암체가 냉각될 때 보이는 전형적인 온도구배를 모델링하였으며, 그 결과 동쪽 면은 서쪽 면에 비해 암체의 바깥쪽에 해당하였을 것이라는 추론에 부합하였다. 국수바위의 주상절리는 경관적인 가치와 함께 조면암질 용암에서 발달하는 주상절리의 형성과정에 대한 학술적인 중요성으로 자연유산적인 보전가치가 높은 것으로 판단된다. Trachytic cliff showing a unique appearance like noodle is located in the Mt. Bipa, Seo-myeon, Ulleung island. This cliff is named 'Guksubawi'(means noodle-like rock) by its appearance. There is cliffs on three sides except north side and each side shows semi-vertical columnar joints obviously. This columnar joint has different character in appearance and mineralogy according to their direction and this tendency is remarkable in contrast between the east side and the west side. The consideration of the cooling processes after eruption of trachytic lava based on the contrast of both columnar joints dealt in the full text. In the morphological approach, the columnar joint on the east side has narrower space and chisel-like marks than the west side. And the joint walls are sharper on the east side than west side too. In the mineralogical approach, then, trachyte on the west side has bigger phenocrysts than the east side and is showing glomeroporphyritic texture and weak trachytic textures of lath of plagioclase. Around these differences between the east side and the west side, it modelled the typical temperature gradient while the cooling processes of hot rocks and the east side, consequently, corresponds to exterior of the entire trachytic volume. The columnar joint of the Guksubawi has the value of landscape and scientific importance about the forming processes of the columnar joint of trachytic lava, and so supposed it has enough values to preserved as natural heritage.

The Study on Static Force Behavior of Concrete Filled Steel Tube Lattice Wind Generator Tower Joints

In order to discuss the failure mechanism of concrete filled steel tube lattice wind generator tower joints. Based on the parameters of web member section form, and using nonlinear static numerical simulation, this dissertation research on the stressed complex joints. The results of the study show that the abdominal rod for circular steel tubes joint (JD1) is instability failure which is led to the local buckling of compressive bar; the abdominal rod for single angle steel (JD2) or double angle steel (JD3) joint is instability failure because of the local buckling of the joint board. Under the web members and joint boards all fitting their own capacity requirements, JD1 is very easy to make draw bar broken on both sides of the pillar tube wall region, JD2 and JD3 are apt to damage on the weak positions of joint board ends and pillar tube wall joint. In the three forms of web member joints, the best ultimate bearing capacity is JD1 , JD3 is the second and JD2 is minimum.

Joint Wall Mitigation and Compressive Sensing for Indoor Image Reconstruction

Compressive sensing (CS) for urban operations and through-the-wall radar imaging has been shown to be successful in fast data acquisition and moving target localizations. The research in this area thus far has assumed effective removal of wall electromagnetic backscatterings prior to CS application. Wall clutter mitigation can be achieved using full data volume which is, however, in contradiction with the underlying premise of CS. In this paper, we enable joint wall clutter mitigation and CS application using a reduced set of spatial-frequency observations in stepped frequency radar platforms. Specifically, we demonstrate that wall mitigation techniques, such as spatial filtering and subspace projection, can proceed using fewer measurements. We consider both cases of having the same reduced set of frequencies at each of the available antenna locations and also when different frequency measurements are employed at different antenna locations. The latter casts a more challenging problem, as it is not amenable to wall removal using direct implementation of filtering or projection techniques. In this case, we apply CS at each antenna individually to recover the corresponding range profile and estimate the scene response at all frequencies. In applying CS, we use prior knowledge of the wall standoff distance to speed up the convergence of the orthogonal matching pursuit for sparse data reconstruction. Real data are used for validation of the proposed approach.

Limit State Strength of Unreinforced Masonry Structures

This paper presents a new formula to estimate the ultimate lateral force of unreinforced masonry structures. The ratio of the wall's height to the wall's width is used to predict the ultimate lateral load of the wall. The coefficient is determined by the numerical implementation of an interface model to simulate the behavior of mortar joints in masonry walls. The numerical predictions are compared with the FEMA guidelines and the experimental data. The comparisons show that the loads that are predicted by the proposed formula have a lower error percentage than the FEMA guidelines. Thus, the proposed formula can be used to analyze unreinforced masonry structures.

Design model for composite beam‐to‐reinforced concrete wall joints

AbstractA design model for composite beam‐to‐reinforced concrete wall joints is presented and discussed in this paper. The model proposed is the component method extended to this type of joint. The characterization of the active components is therefore performed in terms of force‐deformation curves. In this type of joint, special attention is paid to the steel‐concrete connection where “new” components, not covered in EN 1993‐1‐8, are activated. The application of the model allows the designer to obtain the joint properties in terms of the moment‐rotation curve. The accuracy of the proposed model is verified by comparing it with available experimental and numerical results. The latter were developed in the FE program ABAQUS and previously validated by experimental results.

Earthquake-resistant performance investigation for rural buildings in Zhongxiang area, China

We carried out a census of the rural residential buildings of Zhongxiang area’s 17 towns. Next, we conducted a sample survey in four townships: Huji, Shipai, Zhangji, and Jiuli. According to the census and sample survey data of the rural residence buildings, we evaluated the quality and earthquake-resistant performance of the rural buildings for the various local rural residential structural types. The results showed that there are four main factors affecting the seismic performance of the local rural residences: (1) Foundations are not made appropriately (such as by compaction or some other fill) but are built directly in the farming soil. (2) Seismic measures are not completely implemented. Structure construction measures are not in place at the junction of the vertical and horizontal wall. The vertical wall joints are not the result of the same masonry techniques as the horizontal joints. There are no lintels above the door and window openings, or if there are any, the length of the lintels is less than 240 mm. (3) The brick masonry wall has low strength. The greatest housing wall mortar strength is between M 0. 4–1.5, much lower than the strength of the brick. (4) The building material and construction quality are poor. The quality of the mortar masonry wall is poor. The cracks between the bricks are uneven, even in the seams.

Mechanical response of discontinuities of different joint wall contact strengths

An intensive investigation was set up to study the mechanical response of discontinuities with different joint wall compressive strengths. Physical models were employed in order to perform the planned studies. Models were designed to contain profiles of regular artificial joints molded by five types of plaster mortars each of which representing a distinct uniaxial compressive strength. The compressive strengths of plaster specimens ranged from 5.9 to 19.5 MPa. These specimens were prepared considering to have discontinuities of regular triangular asperity profile and were so designed to achieve joint walls of different strength material combinations. Direct shear tests were carried out on joints, and variations of shear stiffness, normal stiffness, and residual friction angle were investigated in various states. Details of the experiments, obtained data, the performed analyses, and the results are presented in this paper.