Simplified modified tension chord model: An alternative crack width calculation model to Eurocode 2 and fib model codes

Abstract

This paper proposes a new design code formulation for calculating crack widths for regular and more special reinforced concrete (RC) members. The more comprehensive Modified Tension Chord Model (MTCM) has been simplified (SMTCM) to facilitate an alternative method for calculating crack widths to Eurocode 2 and fib Model Codes. The model is based on mechanical principles without empirical modifications and is benchmarked against a previously published experimental crack width database. The SMTCM predicts crack widths quite as accurately as the MTCM and provides a broader range of applicability, such as for large covers and RC ties having arbitrary rebar configurations and thus a better crack width model than the current design codes for RC ties. In addition, there are no openings for ambiguous interpretations of the calculations, which can increase the risk of obtaining two different crack widths from two different designers. To further justify the SMTCM code formulation and concept, several RC ties with experimental crack width profiles were used and discussed. The results show a considerable difference between the crack width profile at the surface and at the reinforcement location, depending on the concrete cover and rebar size. These observations are interesting regarding durability design and requirements and show that the approach using a maximum design crack width at a specific surface as a decisive parameter should be further investigated, especially for large concrete covers.