Deformation Model for Reinforced and Cracked Prestressed Concrete

Changes in ACI 318-19 and elsewhere to the effective moment of inertia I-e, used for computing the immediate deflection of reinforced (non-prestressed) concrete, have led to renewed interest in the serviceability conditions related to deflection. The focus of this study is to extend the approach adopted by ACI 318 for reinforced concrete to prestressed concrete. A review of basic concepts used to formulate a rational model for computing the short-and long-term deformation of rein forced concrete forms the basis of a deformation model for prestressed concrete cracked under service loads. Two viable alternatives expected to provide a reasonably consistent prediction of the deformation are evaluated. One approach employs an offset in the cracked section response to develop an expression for I-e used to compute the deformation relative to the offset, while the other approach treats deformation from the load and prestressing separately. Factors affecting the deflection of prestressed concrete are assessed and help explain why comparing the existing and proposed models with test data might not always lead to reliable predictions.