Concrete material properties, namely Modulus of Elasticity, Creep, and Shrinkage, are highly dependent on mix designs and the properties of local aggregates. The material model used is based on NCHRP Report 496, Prestress Losses in Pretensioned High-Strength Concrete Bridge Girders. NCHRP Report 496 is the basis for the modulus of elasticity, creep, shrinkage, and prestress loss requirements in the AASHTO LRFD Bridge Design Specifications since 2005.

Modulus of Elasticity

The modulus of elasticity is computed as

NOTE: Prior to the AASHTO LRFD 7th Edition 2014 with 2015 Interims the modulus of elasticity was computed as

Creep

The creep coefficient is computed as

Shrinkage

The shrinkage strain is computed as

Aggregate Correction Factors

The modulus of elasticity, creep, and shrinkage equations all include two aggregate correction factors, K1 and K2. The modulus of elasticity, creep, and shrinkage equations are developed for a national averaged based on samples from Nebraska, New Hampshire, Texas, and Washington. The aggregate correction factors account for the effects of local aggregates. The values of K1 and K2 are determined by research.

A correction factor K1 = 1.0 corresponds to an equal average of all predicted values and all measured values. The correction factor K2 is based on the 90th percentile upper-bound and the 10th percentile lower-bound of a set of measured data.

NCHRP Report 496 provides modulus of elasticity aggregate correction factors for Nebraska, New Hampshire, Texas, and Washington.