Author(s):
A. Laskar, J. Wang, T.C. Hsu, Y. Mo
Publication Date
January 2007
Abstract
Prestressed concrete I-beams are used extensively as the primary superstructure components in Texas highway bridges. This research intends to solve one of the most troublesome problems in prestressed concrete, namely shear. The problem arises from the lack of a rational model to predict the behavior of prestressed concrete structures under shear action and the various modes of shear failures. Because of this deficiency, all the guidelines for shear design, such as ACI Codes and AASHTO Specifications, are empirical and have severe limitations. The research work was divided into two phases: Phase One consisted of developing the constitutive laws for prestressed concrete membrane elements and developing an analytical model for predicting the shear behavior of such elements. Crack simulation tests were first performed on rectangular prestressed beams to find the same cracking pattern of post tensioned concrete with conduits as that in pre-tensioned concrete without conduits. Ten prestressed concrete panels (two series of five panels each) were tested. The first series of five panels was tested under sequential loading. The results of these tests were used to establish the constitutive relationships of materials (concrete and prestressing tendons). The second series of panels was tested under pure shear (a special case of proportional loading) to study the shear behavior of prestressed concrete membrane elements. Finally the Softened Membrane Model for Prestressed Concrete (SMM-PC) was developed to predict the response of prestressed concrete membrane elements under shear loading Phase Two of the research dealt with testing of fuIl-scale prestressed concreted I-beams and developing a new simplified equation for the shear design of prestressed concrete girders. Five TxDOT Type-A beams were designed, cast and tested to study their behavior in web shear and flexural shear failures. The results of these tests, along with the constitutive laws of prestressed concrete (developed in Phase One), were used to develop a new simplified equation for shear design of prestressed girders. Results of other prestressed beams available in literature were also considered to validate the design equation. The shear capacities of all the tested and referred beams were obtained using the new design equation and compared with the shear capacities obtained using ACI and AASHTO guidelines. Four design examples were prepared to illustrate the application of the new equation for design of prestressed girders. The new design equation was thereby extended to include non-prestressed girders. An example showing the design of a non-prestressed girder using the new equation was also completed. The research findings proved that the shear capacities of prestressed beams depended mainly on the compressive strength of concrete and the shear span to depth ratio of the beams. The effect of the amount of prestressing force and the angle of the failure planes of the beams on their shear capacities is insignificant.
Report Number:
0-4759-1
Keywords:
Beams, Constitutive Laws, Design Equation, full-scale tests, Membrane Elements, prestressed concrete, Shear Provisions
Link(s):
Document/Product
http://tti.tamu.edu/documents/0-4759-1.pdf
Publication/Product Request
TTI reports and products are available for download at no charge. If an electronic version is not available and no instructions on how to obtain it are given, contact the TTI Library.