Embedment

About: Embedment is a research topic. Over the lifetime, 2441 publications have been published within this topic receiving 31444 citations.

Utilization of soil nailing technique to increase shear strength of cohesive soil and reduce settlement

Abstract: This article deals with the assessment of the soil nailing technique with a vertical inclusion to improve the geotechnical parameters of cohesive soil. A series of unconfined compression tests and direct shear tests were carried out to establish the stress–strain relationship and strength characteristics of the reinforced clay sample by vertical steel nails. The shear strength performance of the new composite material was tested by varying the number of vertical inclusions, the embedment depth and the alignment radius. The results confirmed that the vertical bars/inclusions shared the vertical applied load with clay. Increase in the number of vertical inclusions significantly increases the shear strength and the stiffness with a remarkable reduction in settlement. When the clay samples were reinforced with six inclusions along the perimeter, the shear strength was increased to 231% for the embedment depth ratio equal to 0.85. To obtain the optimum effect in eliminating shear failure, the vertical inclusions should be extended to a deeper zone with sufficient numbers. It has been found that the vertical inclusions significantly influence the shear strength, and the brittle or general shear failure of the unreinforced sample can be diverted to partial/plastic shear failure.

Mechanism Analysis for Concrete Breakout Capacity of Single Anchors in Tension

Abstract: A correct estimation of the concrete breakout capacity of anchors under tensile loads would permit the nominal anchor strength to be controlled by ductile yielding. This paper develops a numerical technique based on the theory of plasticity to predict an optimum geometry of the failure surface and concrete breakout capacity of single anchors away from edges under tensile loads. In this technique, concrete is regarded as a rigid, perfectly plastic material obeying a modified coulomb failure criteria with effective compressive and tensile strengths. The failure mode is idealized as an assemblage of two rigid blocks separated by failure surfaces of displacement discontinuity. Minimization of the collapse load predicted by the energy equation produces the optimum shape of the failure surface geometry. A simplified solution is developed by approximating the failure surface as two straight lines. The effect of different parameters on the concrete breakout capacity of anchors is reviewed using the developed mechanism analysis, ACI 318-05, and test results of 501 cast-in-place and 442 post-installed anchor specimens. The shape of failure surface and concrete breakout capacity of anchors predicted by the mechanism analysis are significantly affected by the ratio between effective tensile and compressive strengths of concrete. For anchors installed in concrete having a low ratio between effective tensile and compressive strengths, a larger horizontal extent of failure planes in concrete surface is predicted by the mechanism analysis than recommended by ACI 318-05. Experimental concrete breakout capacity of anchors is closer to the prediction obtained from the mechanism analysis than ACI 318-05. ACI 318-05 provisions for anchors significantly underestimate the breakout capacity of cast-in-place and post-installed anchors having effective embedment depths exceeding 200 and 80 mm, respectively, installed in concrete of compressive strength larger than 50 MPa (7250 psi). The experiments also suggest that concrete breakout capacity of anchors slightly increases with the increase of the ratio of head diameter to effective embedment depth anchors.

3D FE Analysis of Anchor Bolts with Large Embedment Depths

Abstract: In engineering practice, headed anchors are often used to transfer loads into reinforced concrete members. Experience, a large number of experiments as well as numerical studies of anchors of different sizes confirm that fastenings are capable to transfer a tension force into a concrete member without using reinforcement. Provided the steel strength of the stud as well as the load bearing area of the head are large enough, a headed stud subjected to a tensile load normally fails by cone shaped concrete breakout. To better understand the crack growth and to predict the concrete cone pull-out failure load of headed studs for different embedment depths a number of experimental and theoretical studies have been carried out. Due to the fact that the tests with large embedment depths are rather demanding, most of the experiments were carried out for embedment depths that range from hef = 100 to 500 mm. For anchorages with larger embedment depths, which are relatively often used in the engineering practice, there are almost no experiments available. Consequently, for these fastenings the influence of the geometry (edge influence, influence of the anchor spacing, influence of the thickness of the concrete member, etc.) and type of loading (tensile, shear or combined) on the failure load and failure mode is not confirmed by experiments. In last two decades significant work has been done in the development and further improvement of numerical tools. These tools can be employed in the analysis of non-standard anchorages. Unfortunately, the objectivity of the numerical simulation depends very much on the choice of the material model. Therefore, the numerical results should be confirmed by experiments. In the present paper the results of a finite element study of fastenings which were designed for the application in nuclear power plants in Korea are presented. In the three-dimensional finite element analysis the code MASA, which is based on the microplane model for concrete, is performed. The numerical investigations were actually a part of an extensive test program. The results of the study were used to support a test program that had to be carried out for a non-standard fastening systems in which the anchor bolts with embedment depths that varied from 0.5 m to over 1.0 m were employed. Furthermore, the head sizes of the anchor bolts were much larger than that used in the standard pull-out experiments. The analysis was carried out for tensile and shear loads. For both cases the edge influence and the influence of the reinforcement was investigated. The numerical results are compared with test results, which were obtained afterwards. Therefore, the numerical study was a real benchmark test for the finite element code used in the numerical investigations. The calculated failure modes and failure loads shows very good agreement with measured data. It is interesting to observe that for some cases the measured and calculated data shows disagreement with the data obtained using current design code recommendations.