Design Recommendations for Bonded Anchors under Fire Conditions Using the Resistance Integration Method (original) (raw)
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Engineering Structures, 2020
European guidelines for fire performance evaluation of post-installed anchoring systems are limited to mechanical (e.g., expansive, undercut) mechanisms of load transfer and the steel failure mode, whereas the adhesive bond mechanism remains unaccounted for in chemically bonded anchors. Furthermore, current evaluation methods do not account for the influence of practical testing conditions on temperature profiles along the bonded depth. This paper presents 3D finite element thermal simulations of chemically bonded anchors in uncracked concrete exposed to ISO 834 fire conditions with comparisons to experimental specimens. Five parameters representing application and testing conditions are investigated to assess their influence on temperature profiles along the embedment depth of bonded anchors. A numerical model is proposed based on the results of the numerical simulations to determine thermal data necessary for predicting the load-bearing capacities of bonded anchors using the Resistance Integration Method. The model adopts Eurocode material properties for concrete and steel, with 3D analysis yielding conservative capacity prediction compared to physical fire tests. 3D and 2D simulation results are compared, demonstrating that modelling using 2D heat transfer analysis yields inaccurate temperature profiles compared to 3D modelling. After experimental validation of the proposed model, additional parameters are explored in a numerical parametric study: embedded depth, external length of the anchor element, insulation of the anchor element, and insulation of the concrete element. Results show that the embedded depth has a significant influence on temperature profiles along the bond. Moreover, the external length of the anchor influences temperature profiles, but not beyond 20 mm from the concrete surface.
Applied Sciences
Under fire conditions, bonded anchors often exhibit pull-out failure due to the thermal sensitivity of polymer-based adhesives. However, progress in manufacturing has allowed the development of more thermoresistant mortars, enhancing the probability of observing concrete-related failure modes at high temperature. For concrete cone failure, Annex D (Informative) to the European Standard EN 1992-4 provides a method to determine the characteristic fire resistance. This method is based on ISO 834-1 fire ratings and on limited experimental data without inclusion of bonded anchors. To remedy these shortcomings, the present contribution aims to provide the first experimental analyses on the concrete cone failure of bonded anchors loaded in tension and exposed to ISO 834-1 fire conditions, as well as heating with a relatively slower rate. The recorded ultimate loads show that the loss of capacity depends on the embedment depth, failure mode and heating scenario. Regarding exposure to ISO 83...
Evaluation of PIRs Post-Fire Pull-Out Strength in Concrete Exposed to ISO 834-1 Fire
Materials, 2021
Post-installed rebars (PIRs) using mortar can offer bond strength at ambient temperature equal or higher to that of cast-in place rebars. However, high temperatures have the effect of weakening the bond, typically governed by the chemical and physical properties of the mortar which is often sensitive to temperature increase. Therefore, the behavior of PIRs in a fire situation becomes vulnerable. Moreover, after exposure of PIRs to high temperature, the heat transfer continues during the post-fire phase, which might endanger the construction after a fire event. In order to evaluate the evolution of the pull-out capacity during fire, Pinoteau et al. have developed the bond resistance integration method (Pinoteau’s RIM) to predict the bond resistance value of a rebar subjected to various temperatures in accordance with the fire exposure curves. Therefore, accurate temperature profiles during the post-fire phase are needed to ensure a correct calculation of the post-fire behavior of the...
Numerical investigations on post-fire bond behaviour of reinforcement in concrete
RILEM Technical Letters
Reinforced concrete (RC) structures may be subjected to accidental fire loads during their service life. In such a case, it is essential to have appropriate methods for the estimation of post-fire performance. One of the vital aspects for the performance of RC structures is adequate steel-to-concrete bond. The bond behaviour under ambient conditions is very well established. However, an appropriate model for the assessment of the post-fire bond capacity is still lacking. In order to provide more insight into the bond performance after fire, a 3D FE numerical study using a thermo-mechanical model with temperature dependent microplane model for concrete is performed. The effects of concrete cover, confinement through stirrups, fire duration and exposure type on post-fire bond performance are investigated using beam-end specimen. The results show a strong degradation of post-fire bond capacity, which is primarily attributed to the irreversible damage of concrete cover resulting from he...
Fire Rating of Post-Installed Anchors and Rebars
CivilEng
Fire safety is a critical performance aspect of construction products, and post-installed anchors and rebars are no exemption in that regard. During their service life, anchors and rebars are subjected to different kinds of load actions, so they have to be qualified and designed for critical safety performance. While the qualification guidelines for static and seismic loading have matured to conclusive requirements over the past two decades, the requirements for determining the resistance to fire are just about to consolidate. This contribution strives to provide clarity on the fire rating of post-installed anchors and rebars. For this, the current status of the regulations, as well as the underlying background, is reviewed after a brief introduction. Typical examples of fire ratings in the field of post-installed anchors and rebars are given, and recent research undertaken to close the last regulative gaps is briefly presented.
Behavior of bonded anchors in concrete under fire
2021
Perhaps the most straightforward classifier in the arsenal or machine learning techniques is the Nearest Neighbour Classifier-classification is achieved by identifying the nearest neighbours to a query example and using those neighbours to determine the class of the query. This approach to classification is of particular importance because issues of poor run-time performance is not such a problem these days with the computational power that is available. This paper presents an overview of techniques for Nearest Neighbour classification focusing on; mechanisms for assessing similarity (distance), computational issues in identifying nearest neighbours and mechanisms for reducing the dimension of the data. This paper is the second edition of a paper previously published as a technical report [14]. Sections on similarity measures for time-series, retrieval speed-up and intrinsic dimensionality have been added. An Appendix is included providing access to Python code for the key methods.
International Journal of Adhesion and Adhesives, 2011
The high bonding capacity of polymer adhesives has encouraged their application for anchoring steel bars into concrete for structural purposes. However, high temperatures have the effect of weakening the bond and endangering the construction under a fire situation. This paper evaluates bond resistance to temperature by means of pull-out tests performed with a constant tensile load on the steel bar and a progressive temperature increase of the bond throughout the test until a failure temperature is reached. Two testing programs were performed using separate heating technologies: electric oven and gas furnace, which mainly differ by their heating speed, in order to assess the influence on bond failure at high temperature. The study describes thermal characteristics and phenomena such as vaporization in different concrete zones near the anchor in both of the testing devices (electric and gas).
Tensile Behavior of Chemically Bonded Post-Installed Anchors in Low-Strength Reinforced Concretes
After the 1999 Kocaeli Earthquake, the use of chemically bonded post-installed anchors has seen a great growth for retrofits in Turkey. Currently, chemically bonded post-installed anchors are designed from related tables provided by adhesive manufacturers and a set of equations based on laboratory pullout tests on normal or high strength concretes. Unfortunately, concrete compressive strengths of existing buildings, which need retrofit for earthquake resistance, ranges within 5 to 16 MPa. The determination of tensile strength of chemically bonded anchors in low-strength concretes is an obvious prerequisite for the design and reliability of retrofit projects.