Showing papers on "Embedment published in 2020"

Experimental pull-out tests and design indications for strength anchors installed in masonry walls

Abstract: This study deals with the identification of the mechanical behavior of chemical anchors embedded in masonry walls. 108 pull-out tests are carried out in five types of masonry walls built with clay brick or vertically perforated units with cement mortar. Different parameters are taken into account: embedment depths, masonry type, anchor position (injection either in brick units or in mortar joints). The axial load capacity and the failure mode are observed for each test. The results are examined by means of elastic and plastic models assessing the efficiency of anchors installed in headers, stretchers or mortar joints. The anchors injected in mortar joints are shown to have much greater pull-out capacity than that found for anchors in bricks. Passing from 90 to 160 mm of embedment depth, a minimum increase by 40% of pull-out strength is observed. The most common failure modes are the sliding failure, which occurs for short anchors or weak masonry, and mixed sliding/cone failure, for long anchors or strong masonry. An analytical model is proposed to design anchors in order to avoid or at least to limit brittle masonry failures and to identify the field of application of uniform stress models.

Analysis of the Rock Failure Cone Size Relative to the Group Effect from a Triangular Anchorage System.

Abstract: This study employs the numerical analysis and experimental testing to analyze the fracturing mechanics and the size of rock cones formed in the pull-out of a system of three undercut anchors. The research sets out to broaden the knowledge regarding: (a) the potential of the undercut anchor pull-out process in mining of the rock mass, and (b) estimating the load-carrying capacity of anchors embedded in the rock mass (which is distinctly different from the anchorage to concrete). Undercut anchors are most commonly applied as fasteners of steel components in concrete structures. The new application for undercut anchors postulated in this paper is their use in rock mining in exceptional conditions, such as during mining rescue operations, which for safety considerations may exclude mechanical mining techniques, mining machines, or explosives. The remaining solution is manual rock fracture, whose effectiveness is hard to assess. The key issue in the analyzed aspect is the rock fracture mechanics, which requires in-depth consideration that could provide the assistance in predicting the breakout prism dimensions and the load-displacement behavior of specific anchorage systems, embedment depth, and rock strength parameters. The volume of rock breakout prisms is an interesting factor to study as it is critical to energy consumption and, ultimately, the efficiency of the process. Our investigations are supported by the FEM (Finite Element Method) analysis, and the developed models have been validated by the results from experimental testing performed in a sandstone mine. The findings presented here illuminate the discrepancies between the current technology, test results, and standards that favor anchorage to concrete, particularly in the light of a distinct lack of scientific and industry documentation describing the anchorage systems’ interaction with rock materials, which exhibit high heterogeneity of the internal structure or bedding. The Concrete Capacity Design (CCD) method approximates that the maximum projected radius of the breakout cone on the free surface of concrete corresponds to the length of at the most three embedment depths (hef). In rock, the dimensions of the breakout prism are found to exceed the CCD recommendations by 20–33%. The numerical computations have demonstrated that, for the nominal breakout prism angle of approx. 35% (CCD), the critical spacing for which the anchor group effect occurs is ~4.5 (a cross-section through two anchor axes). On average, the observed spacing values were in the range of 3.6–4.0.

Planar Mechanical Metamaterials with Embedded Permanent Magnets.

Abstract: The design space of mechanical metamaterials can be drastically enriched by the employment of non-mechanical interactions between unit cells. Here, the mechanical behavior of planar metamaterials consisting of rotating squares is controlled through the periodic embedment of modified elementary cells with attractive and repulsive configurations of the magnets. The proposed design of mechanical metamaterials produced by three-dimensional printing enables the efficient and quick reprogramming of their mechanical properties through the insertion of the magnets into various locations within the metamaterial. Experimental and numerical studies reveal that under equibiaxial compression various mechanical characteristics, such as buckling strain and post-buckling stiffness, can be finely tuned through the rational placement of the magnets. Moreover, this strategy is shown to be efficient in introducing bistability into the metamaterial with an initially single equilibrium state.

Vertical vibration of a rigid circular disc embedded in a transversely isotropic and layered poroelastic half-space

Abstract: Fundamental solution for the time-harmonic vertical vibration of a rigid circular disc embedded in a transversely isotropic and layered poroelastic half-space is developed using a semi-analytical method. First, based on the Green's function of the time-harmonic vertical circular load embedded in the layered half-space, function of the corresponding annular ring load is determined via the method of superposition. Then the disc-medium contact area is discretized into annular ring elements with unknown densities which are determined via an integral least-square approach. Finally, the dynamic vertical compliance is derived by virtue of the equilibrium between the applied load on the disc and the resultant contact stress. Based on the derived fundamental solution, selected numerical examples on the dynamic vertical compliance are presented to investigate the influence of the surface hydraulic condition, fluid saturation, embedment depth of the disc, material anisotropy, material layering, and input frequency.

Numerical Analysis of the Deformation Performance of Monopile under Wave and Current Load

Abstract: The research on the deformation mechanism of monopile foundation supporting offshore wind turbines is significant to optimize the design of a monopile foundation under wave and current load. In this paper, a three-dimensional wave-pile-soil coupling finite element model is proposed to investigate the deformation mechanism of monopile undercurrent and fifth-order Stokes wave. Different from the conventional assumption that there is no slip at the pile-soil interface, Frictional contact is set to simulate the relative movement between monopile and soil. Numerical results indicate that under extreme environmental conditions, the monopile foundation sways within a certain range and the maximum displacement in the loading direction is 1.3 times the displacement in the reverse direction. A further investigation has been made for a large-diameter pipe pile with various design parameters. The finite element analyses reveal that the most efficient way to reduce the deflection of the pile head is by increasing the embedment depth of the monopile. When the embedment depth is limited, increasing the pile diameter is a more effective way to strengthen the foundation than increasing the wall thickness.

Centrifuge and numerical modeling of moving traffic surface loads on pipelines buried in cohesionless soil

Abstract: The main aim of this research was to investigate the mechanism of deformation of buried pipe under traffic moving load and the suitability of the modified Spangler-Iowa formula, coupled with the Boussinesq theory of load transmission through elastic media in predicting the deformation of these buried structures. This study employed reduced-scale physical model tests in a geotechnical centrifuge, numerical back-analysis using ABAQUS software and a numerical prediction for a hypothetical case. The hypothetical case consisted of a steel pipe buried in cohesionless soil under moving surface loads. Nine centrifuge tests were carried out for three different embedment ratios in dense, medium and loose sand. The tests results demonstrated that the formulas used for pipeline projects, the modified Spangler-Iowa formula together with the Boussinesq theory, are somewhat conservative for all densities analyzed and that the degree of conservatism increases with both embedment ratio and with the stiffness of the soil the pipe rests.

Bond Behavior of Reinforcing Steel Bar and Geopolymer Concrete

Abstract: The study investigated the bond behavior of reinforcing bar and geopolymer concrete as a function of rebar diameter, embedment length, concrete cover and compressive strength. The effect of...

Numerical modelling of timber and timber joints: computational aspects

Abstract: Timber joints with their simultaneous ductile and brittle failure modes still pose a major challenge when it comes to modelling. Wood is heterogeneous and highly anisotropic. It shows ductile behaviour in compression and brittle behaviour in tension and shear. A 3D constitutive model for wood based on continuum damage mechanics was developed and implemented via a subroutine into a standard FE framework. Embedment and joint tests using three different wood species (spruce, beech and azobe) were carried out, and the results were compared with modelling outcomes. The failure modes could be identified, and the general shape of the load–displacement curves agreed with the experimental outcomes.

Bond of Reinforcement Cable in 3D Printed Concrete

Abstract: The use of high strength steel cables directly entrained into printed concrete during the printing process, has previously been introduced as a method to provide reinforcement to objects being manufactured through a layer-extrusion based 3D concrete printing process. The bond between the cable and the cementitious mortar is a crucial parameter for the structural performance of such reinforcement, and was hence subject of a detailed study presented in this paper. The bond performance was studied in direct and flexural pull-out tests on cast and printed specimens and further analyzed by microscopic analysis of the bond surface. Two effects were identified that significantly decrease the bond strength. Firstly, chemical reactions create a spongy interface of poor strength. Secondly, the flow of mortar around the cable tends to create a cavity underneath the cable which reduces the effective bond surface. Mortar viscosity, nozzle design and filament pressure, were thus identified as important parameters for the bond quality. The average bond quality seems to reduce with embedment length. As a consequence, cable breakage was not achieved, in spite of considerable embedment lengths that were tested. Likely, this was caused by the cumulative probability of critical defects along the increasing embedment length, in combination with a non-constant shear distribution. All test series showed significant scatter. It was concluded that, although this reinforcement method is promising as it can potentially provide sufficient post-cracking strength, the bond quality must be improved considerably both in terms of average strength and reduction of scatter.

Design Embedment Strength of Plybamboo Panels Used for GluBam

Abstract: The embedment behavior of plybamboo panels under dowel-type connections used for glued, laminated bamboo (GluBam) structures, was experimentally studied, following the half-hole loading met...

Vertical vibration of piles in viscoelastic non-uniform soil overlying a rigid base

Abstract: This paper presents an analytical methodology that provides the dynamic response of an elastic pile embedded in viscoelastic non-uniform soil overlying a rigid base, when subjected to a harmonic vertical load. The non-uniform soil comprises two parts, featuring independent properties: the substratum soil, below the pile toe, is represented by a viscoelastic layer of finite thickness resting on rigid bedrock, while the soil surrounding the pile shaft is modelled as a series of infinitesimally thin independent viscoelastic layers. Following validation of the methodology, where we show that the presented solution degenerates to published solutions for simpler pile embedment conditions, we use results of a parametric investigation to discuss the mechanisms governing the dynamic response of the non-uniform soil–pile system. The presented solution allows modelling realistically the contribution of end-bearing resistance to vertical vibrations of piles in cases of practical interest when non-linearity effects can be effectively ignored.

Improved discrete element modeling for proppant embedment into rock surfaces

Abstract: Brinell indentation tests were performed on Montney siltstone, and the results were compared with discrete element indentation simulations that use the micro-parameters calibrated using compression test data from the same siltstone samples. The simulated proppant indentation into the rock surface can be 15% less than the laboratory measurements. A lower effective particle–particle modulus and thus a lower Young’s modulus are needed in discrete element models for proper simulation of indentation. An equation to find the appropriate value of Young’s modulus for indentation simulation is proposed using Brinell indentation tests including 198 laboratory tests and 32 discrete element simulations. This equation can improve the prediction of Young’s modulus and thus the particle–particle effective modulus for indentation simulations to match the measured force–indentation depth curve in the laboratory. Using the improved micro-parameters, a parametric analysis of the influence of rock Young’s modulus and proppant particle size on proppant embedment was performed. An equation to estimate Brinell hardness as a function of Young’s modulus and closure stress was derived. A practical procedure was developed to predict proppant embedment from the estimated hardness. The predictions agree with the laboratory measurements in a case study on the Montney Formation.

Radial basis function surrogate model-based optimization of guardrail post embedment depth in different soil conditions:

Abstract: For guardrail designers, it is essential to achieve a crashworthy and optimal system design. One of the most critical parameters for an optimal road restraint system is the post embedment depth or ...

Effects of embedment side and loading direction on embedment strength of cross-laminated timber for smooth dowels

Abstract: Embedment strength is a decisive mechanical property of the dowel-type connection in cross-laminated timber (CLT) structures. Dowels can be installed in the plane or/and narrow side of CLT, which may result in different dowel embedment strength. To investigate the effects of embedment side and loading direction on the embedment strength of CLT, six groups of cubic specimens with predrilled half-holes, including three embedment positions and two loading directions, were tested according to the ASTM D5764-97a half-hole test method in this study. It was found that the embedment side, loading direction and the thickness ratio of transverse layer (TRTL) of CLT had significant influences on CLT embedment properties. The load-deformation behaviors and failure modes of each group were significantly different. The existence of transverse layers could reduce the embedment strength and improve the ductility of CLT under embedment tests. When only one layer bore the load parallel to the grain of wood, the crack occurred along the grain of this layer. When the transverse and longitudinal layers shared the dowel embedment load jointly, CLT had a better ductility. For dowels installed in the narrow side, the maximum and minimum embedment strength values were 37.66 MPa and 12.55 MPa, respectively. For dowels installed in the plane side, the embedment strength decreased with the increase in TRTL. The embedment strength of CLT calculated by the existing design models was different from the experimental values. These findings are important to providing a safe and efficient joint to achieve more efficient use of CLT products.