PSI - Issue 22

Elise Zgheib et al. / Procedia Structural Integrity 22 (2019) 25–32 Elise Zgheib – Wassim Raphael / Structural Integrity Procedia 00 (2019) 000 – 000

27 3

RH

relative humidity

h 0

notional size

f cm

Mean compressive strength of concrete at 28 days

2. Evaluation of Eurocode 2 creep model 2.1. Eurocode 2 creep predictions

The compliance which is the total load-induced strain (elastic strain plus creep strain) at age t per unit stress caused by a unit uniaxial sustained load applied since loading age t 0 , (Gandomi et al. (2016)), can be predicted according to Eurocode 2 model, (Eurocode 2 (2004)), using Eq. (1):

  E cm28 t, t 0 

E cm t 0 1

 

J t, t 0





 

(1)

This study treats the long-term creep compliance. Therefore, the creep compliances are calculated at the time when the creep curves have reached their asymptotic value which is considered in this study after 3000 days of applying the external load to the concrete element. 2.2. Experimental database Rush and Wagner have compiled the first data collection at the Technical University of Munich (T.U.). This limited database became the basis for the first CEB creep and shrinkage model. Another collected data was included into Branson and Christiason’s paper underlying the 1971 ACI -209 Model. The first large world-wide creep and shrinkage database was collected at the Northwestern University (NU) by Bažant and Panula (1978). This database established from American and European institutions consisted of approximately 400 creep tests and 300 shrinkage tests and was included in the papers presenting the BP Model, ( Bažant and Panula (1978) ). A joint ACI-RILEM committee was organized, during the international ACI Fall 1979 Convention, to extend the Northwestern University database. This work was pursued and led to the RILEM-ACI 209 database in 1992. Some further additions to the database were done, at NU, by Bažant and Li (2008) and by Kim (2010). The latest database was assembled at Northwestern University during 2010-2013, (Hubler et al. (2015b)), mainly under the support of the U.S. Department of Transportation. Information was extracted from many reports, conference proceedings and journal articles. This database is constituted of approximately 1433 creep tests and 1827 shrinkage tests. The tests in this database are performed using different concrete mix composition and placed in various environmental conditions. These parameters include water to cement ratio, cement type, aggregate to cement ratio, concrete strength, effective thickness, relative humidity, temperature, age at loading, sustained stress, etc. 2.3. Methods of evaluation Based on this large experimental database and in order to study the accuracy of Eurocode 2 compliance predictions, the Eurocode 2 compliance is calculated for each test in the database. Then the predicted values are compared to the experimental measurements using the CEB statistical methods which were proposed by Muller and Hilsdorf. The CEB mean deviation M CEB The CEB mean deviation method calculates an average gap, (ACI 209.2R-08 (2008)), using the following formulas: 2.3.1.