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Title: Advances on Bond of Embedded Steel Reinforcement in the New Model Code 2020

Author(s): Giovanni Metelli

Publication: Web Session

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Appears on pages(s):

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DOI:

Date: 6/1/2020

Abstract:
This presentation summarizes the main open issues on bond which are under discussion in the TG2.5 “Bond and Material Models” of the International Federation for Structural Concrete (FIB). Some of these issues will be included in the Chapter 18 (“Bond of embedded steel reinforcement“) of the new fib Model Code which is likely to be published on 2020. This chapter will be organized in six main sections dealing with local bond slip law of embedded steel reinforcement for static and non‐static loading and for extreme thermal conditions, as well with the design rules for anchorage and lapped of steel reinforcement, of pretensioned prestressing tendons and of post‐installed reinforcements. Since nowadays one of the main issues for practitioners concerns the assessment of existing RC structures which have exhausted their service life, a new model is proposed on bond stress‐slip in case of corrosion. The bond strength may be related to the corrosion level and the local bond stress‐slip curve of corroded reinforcement can be approximated evaluated by shifting the uncorroded curve of MC2010 in the slip direction, depending on the corrosion level (weight loss) of rebars. Similarly, a new section with recommendation and comments will be added on the assessment of laps and anchorages and lapped joints in case of non‐compliant detailing or old rebars which may have different rib patterns and surface geometries, which may induce different bond properties, as occurs in many old structures. A design strength for anchorages of corroded rebars is also proposed. A new model will be proposed on bond affected by “fire” and “high temperatures”. The basic bond splitting model of MC2010 for reinforcement under ambient conditions will be taken as the basis for the model. For the reinforcing bars close to the surface, the bond capacity is significantly affected by the damage to the surrounding concrete due to fire. The residual bond capacity shall be calculated depending on the time and type.