International Concrete Abstracts Portal

Adhesive-bonded anchors are increasingly adopted as structural fasteners for connections to hardened concrete. Due to their reliance on chemical bond, the tensile capacity of adhesive anchors is uniquely dependant on a number of factors [1]. These factors include the geometric parameters of the anchorage system, installation conditions, and adhesive bond strength which is manufacture dependent. Due to the complexity of these factors and their interaction in contributing to the tensile capacity of adhesive concrete anchors, it has proved to be difficult to evaluate their tensile strength. The design guidelines of anchorages using cast-in-place and post-installed mechanical anchors is discussed in ACI 318-08, Appendix D [2]. While, bonded anchors are used extensively in practice, they have not yet been incorporated into the design provisions of ACI 318-08 [3]. The worldwide database containing 2,878 tests of the anchors’ tensile capacity was provided to the authors by Dr. Ronald A. Cook, of ACI Committee 355 on Anchorage to Concrete. The aim of this study is to estimate the tensile strength of concrete adhesive anchors in uncracked concrete using artificial neural networks (ANNs) subject to bond failure and the effect of different parameters on it. As a result of this study, the ANN model will be able to capture the complex relationship between the adhesive bond stress and geometric parameters that compose the anchorage system.

The best fire protection strategies for structural components are useless if connections lack the necessary fire resistance. Many current European Technical Approvals for anchors in concrete provide details on duration of fire resistance based on EOTA Technical Report 020 – Evaluation of Anchors in Concrete Concerning Resistance to Fire – published in 2004. This report delineates testing, evaluation and design requirements for anchors subject to fire exposure. It addresses post-installed mechanical anchors, adhesive anchors and plastic anchors and includes a simplified design approach that considers all relevant concrete failure modes as well as pull-out failure and the steel resistance. The failure modes relevant for normal service conditions also apply under fire exposure. Nevertheless, as temperatures increase the yield point of steel drops significantly. Stainless steels exhibit superior resistance to elevated temperature over carbon steels; however, in general, the reduction in the steel strength is greater than that associated with concrete breakout or pull-out failure. Thus, in most cases, steel failure is the governing parameter in the design, although concrete failure may control in case of shallow embedment, anchor groups or close to the edge. The simplified design method to determine the steel capacity under fire exposure provided by the EOTA Technical Report 020 and by the pre-standard CEN/TS 1992-4 ‘Design of fastenings for use in concrete’ yields often very conservative results. Therefore the leading brands in fastening technology perform fire tests according to the regime given in TR 020, which result in design values which are sometimes as much as three times as high as the values according to the simplified prediction.

Numerical simulation has become a powerful tool for supporting the development of innovative fastening products. The information on the failure mechanism developing during the load transfer from fasteners to concrete can be obtained and analyzed by simulation, which offers the basic requirement for designing innovative fasteners. During the last 15 years Hilti Corporation has developed a simulation tool based on the finite element method and concrete material models to support the fastener design process. In this paper various simulation examples for typical post-installed anchors, particularly for adhesive anchors, are presented. Numerical simulations are carried out for single anchors and anchor groups consisting of four adhesive anchors loaded in tension. The simulation results are discussed and compared with experimental data. The comparison shows a good agreement.

Adhering carbon fiber (CF) sheets onto RC piers is one of the effective seismic strengthening methods. When the pier has an irregular shape such as I-shaped cross section, CF sheets cannot be adhered continuously around the pier. In such cases, the edge of the CF sheets have to be fixed with steel angles and anchor bolts in conventional fixing method. Therefore, an alternative fixing method using CF-anchors consisted of bundles of CF strands and fan shaped was developed and practically applied. One end of the CF-anchor spreaded like a fan was adhered to the CF sheet and other end is embedded in a hole drilled in the concrete member and fixed with injected epoxy resin. Applying this CF-anchor for the reinforcement of the concrete piers, it is necessary to design the adhesive load of the adhered part and the pull-out load of the embedded CF-anchor corresponding to the amount of the CF sheets. This paper describes the design of CF-anchors based on the experimental results for the adhesive load of the adhered part and the pull-out load of the embedded CF-anchor.

Scope of this study is to estimate the reliability of bonded anchor systems. Furthermore, the use of a factor K in order to account the effect of sustained loading on a fastening’s failure probability pf, is discussed. As a general standard in structural engineering, it was assumed that the extreme failure probability of pf = 10-6 per year applies to fastenings as well. By use of the factor K, which can be considered as an index of safety reserves as well, the sensitivity of the investigated system to variations of particular parameters can be captured. In order to define the range of K the input parameters were elaborated statistically considering their mean values, variations and types of distribution. Apart from that, the influence of different input parameters was determined through a parametric study. The statistic input of the study was obtained either from the Probabilistic Model Code (Joint Committee of Structural Safety) or from experimental measurements. Final aim was to find a value for the factor K that guarantees a failure probability of pf = 10-6.