Numerical analysis of the effect of embedment depth on the geometry of the cone failure

This paper presents the results of a numerical FEM analysis of the effect of embedment depth on the extent of the failure zone (cone failure) under the effect of an undercut anchor. For the establishment of the other affecting quantities, the formation of the value of the cone failure angle of the rock medium depending on the embedment depth was analysed. The problem is interesting as regards aspects of rock mass loosening during pull-out of undercut anchors. As a result of the analysis, a significant effect of embedment depth on propagation and the extent of cone failure has been found. The increasing value of embedment depth significantly decreases the extent of the failure zone measured on a free rock surface. The increasing value of cone failure angle limits the potential interaction of failure zones in multi-anchor systems.

Influence of Different Fiber Dosages on the Behaviour of Façade Anchors in High-Performance Concrete

The behaviour of façade anchors in high performance fiber reinforced concrete (HPFRC) has not been investigated in sufficient detail in recent years. The regulations in the European Technical Approvals also do not fully describe the load-bearing capacity of anchor systems. Due to the increase in the production of HPFRC elements, it is necessary to analyse the impact of added fibers in the concrete composition on the behaviour of anchors. In particular, the behaviour of anchors in filigree façade elements, which is one of the main application areas of the programme of polypropylene (PP) fiber-reinforced concrete, is therefore analysed. With a sufficient content of PP fibers surrounding the steel anchors oriented in an optimal direction, the fibers may enhance both the load-bearing capacity of anchors and the ductility of concrete. However, unfavourable effects on the installation process or even on the load-bearing capacity may also occur due to unfavourable fiber orientation. Therefore, tensile and punching tests were carried out in uncracked concrete with different types of anchor systems containing a tension anchor and an adjustable spacer bolt. The PP fiber content of the concrete component varied during the tests.

Experimental Study of Post Installed Rebar Anchor Systems for Concrete Structure

This study investigated the effectiveness of several types of adhesives used in post-installed rebar connections as a bonding agent between steel reinforcement bars and old concrete under pull out test. The experimental samples were; cylindrical samples of (150 mm dia. × 300 mm high) with anchors rebar of varying diameter (12 and 16 mm), different embedded length (100 and 150) mm with different holes’ diameters. The strategy of control were cast-in-place rebar concrete specimens while other samples are post-installed rebar concrete specimens of varied chemical adhesives as bonding agents, namely KUT EPOXY ANCHOR ‘NS’ and SIKAFLOOR169. The output showed that the different adhesives yielded closed pull-out load values. It is found that the pull-out capacity (bond strength) is increased by increasing the embedded length, the diameter of the rebar and slightly with the diameter of the hole. In addition, the failure mode of post-installed rebar concrete was governed by the embedded length and the area of contact with the adhesives. On the other hand, the larger diameter of rebar favors splitting or failure of concrete due to higher strength in binder-rebar interface compare to the binder-concrete interface. The results showed that the pull-out load was increased by (26 % and 32 %) as the rebar diameter increased from 12 mm to 16 mm for KUT “NS” and SIKAFLOOR respectively. The hole diameter had slightly effect of the pull out load where the average of increment was only 6 %. Finally, the bonding strength is considerably depended on the embedded length and less affected by the type of epoxy.

A Technic for Ground Anchor Force Determination from Distributied Strain Using Fiber Optic OFDR Sensor with the Rejection of a Temperature Effect

Anchor systems are widely used to stabilize soil slope and suppress slope failure. Thus, monitoring conditions of an anchor system is important to prevent disasters due to slope failure. The slope condition can be indirectly monitored by sensing the tensile force applied to the anchor because the slope deformation directly affects the anchor force. Previously, we propose a way to monitor the tensile force of the anchor by measuring the strain field on a bearing plate using a distributed fiber optic sensor (OFDR) and experimentally demonstrate that the anchor force has a large correlation with the strain distribution on the bearing plate. However, it was found that a spatial variation of the strain and thermal strain due to temperature change makes it difficult to get a reliable correlation coefficient. In this study, we newly propose a way to get a reliable correlation coefficient between the anchor force and the strain field on the bearing plate. We install a distributed optical fiber sensor in two concentric circles on the bearing plate and measure circumferential strain distribution. We take average values of the strain field in each circle as representative strain values minimizing the spatial variation and takes a difference of the two strains to exclude the temperature effect. We experimentally demonstrate that the proposed method gives a reliable correlation coefficient between the anchor force and the strain field on the bearing plate. This technique can be applied to various anchor systems to monitor the anchor force and manage the anchor systems safely.

Experimental Study on FRP-to-Concrete Bonded Joints with FRP Sheet Anchor System

Fiber-reinforced polymer (FRP) has been widely used for retrofitting and strengthening concrete structures over the past two decades. Because concrete members retrofitted by externally bonded FRP sheets can fail prematurely in debonding because of the fracture between FRP and concrete, FRP tensile strength cannot be fully utilized in engineering practices. Numerous useful investigations have been conducted to develop effective anchor systems to restrict FRP debonding. Thus, an FRP sheet-anchor system was developed and observed to be one of the most effective and convenient anchor systems. The FRP sheet-anchor system is applied to reinforced concrete beams strengthened with U-wrapping and side-bonded FRP configurations in few design guidelines. However, only a few investigations have focused on the failure mechanism of the FRP sheet-anchor system in the existing literature. Therefore, the main objective of this study is analyzing the effect of the carbon FRP (CFRP) sheet-anchor system on the bonding behavior of the CFRP-concrete interface, particularly the effect of the width and stiffness of the CFRP sheet-anchor system. In addition, the anchor-strengthened stage is defined by the load-slip response, which is different from that of specimens without the CFRP sheet-anchor system. Based on the experimental results, three linear stage models of the bond-slip constitutive relationship are proposed in this study.

Consistent Time-to-Failure Tests and Analyses of Adhesive Anchor Systems

Motivated by tunnel accidents in the recent past, several investigations into the sustained load behavior of adhesive anchors have been initiated. Nevertheless, the reliable lifetime prediction of bonded anchor systems based on a relatively short testing period still represents an unsolved challenge due to the complex nonlinear viscoelastic behavior of concrete and adhesives alike. This contribution summarizes the results of a comprehensive experimental investigation and systematically carried out time-to-failure analysis performed on bonded anchors under sustained tensile load. Two different adhesive materials that find widespread application in the building industry were used, one epoxy and one vinylester based. Performed experiments include full material characterizations of concrete and the adhesives, bonded anchor pull-out tests at different loading rates, and time-to-failure sustained load tests. All anchor tests are performed in a confined configuration with close support. After a thorough review of available experimental data and analysis methods in the literature, the experimental data are presented with the main goal to (i) provide guidance for the analysis of load versus time-to-failure test data, and (ii) to derive a set of recommendations for efficient time-to-failure tests having in mind the needs associated with different analysis techniques. Finally, a new approach based on a sigmoid function, previously used only for concrete, is for the first time applied to bonded anchors systems and compared to the established regression models.