Evaluation of the creep coefficients of the HKBD and JSCE code concrete creep prediction models

Creep of concrete is an important design consideration. National design codes therefore provide empirical based models for the estimation of creep deformation. Such models generally estimate a creep coefficient (?) and an elastic modulus (E) of the concrete, both of which are used to predict the creep strain at any age. The creep coefficient (?) is the ratio of the creep strain (?c) to the elastic strain (?e). Extensive research, by the author, on the accuracy of 14 international code-type creep prediction models concluded that the creep coefficient component (?) of prediction models correlated highly significantly with the predicted creep and, on that basis, justifies further investigation of its accuracy. This paper assesses the accuracy of the creep coefficients (?) predicted by the Hong Kong Code of Practice for Structural Use of Concrete (HKBD, 2013) and the Japan Society of Civil Engineers Standard Specification for Concrete Structures (JSCE, 2007). In the case of the JSCE, two models were considered, the one applicable to normal strength concretes (referred to as JSCE) and the other applicable to high strength concretes (> 55 MPa), referred to as JSCE HS. The accuracy of the models was evaluated by comparing the predicted with the actual (measured) creep coefficients (?), over a period of approximately six months, on a range of concretes under laboratory-controlled conditions, for six mixes (comprising three aggregate types and two water-cement ratios). The JSCE HS Model, which considered the least factors of the models investigated, was the most accurate model, yielding an overall coefficient of variation (?_all) of 30.6 %. The HKBD Model was the least accurate with a ?_all of 45.2 %, being only slightly less accurate than the JSCE Model (which yielded a ?_all of 43.1 %). The results of this investigation were compared to those of 16 other models.