Time-dependent nonlinear analysis of prestressed concrete cable-stayed girders and other concrete structures
Creators: name: Khalil, Mahmoud S. A.
Publisher: name: University of Calgary
Year: 1979
Subjects: subject: TA 440 K46 1979 Microfiche
subject: Structural engineering
subject: Prestressed concrete construction
subject: Strains and stresses
subject: Bridges, Concrete - Models

description: The objective of this investigation is to develop and implement an accurate method for the analysis of time-dependent effects in prestressed concrete structures built in stages. The analysis utilizes a step-by-step method in which the period under study is divided into a finite number of time intervals some of which coincide with the addition of new structural members, application of loads or changes in end conditions. New creep and shrinkage models are proposed. Creep is considered to be composed of a recoverable component and an irrecoverable or flow component. The creep model requires the stress information at the end of one previous interval only thus obviating the necessity of storing the entire previous stress history and the computation cost penalty associated with that requirement. Emphasis is placed on the analysis of prestressed concrete cable-stayed bridge systems. The analysis of cable-stayed systems is presented in detail including non-linear behaviour due to cable sag, combined axial load and bending moments in the girder and towers and large displacements. A computer program is developed. The program is capable of handling composite as well as non-composite prestressed concrete plane frames. A concrete member may be composed of up to three layers of concrete of different creep and shrinkage properties with prestressed and non-prestressed reinforcement. The effect of both static and dynamic temperature fields on creep is accounted for. Non-linear differential shrinkage is handled by replacing the non-linear distribution by a tri-linear diagram. Non-linear temperature gradiant and the associated non-linear creep strains are treated similarly. Four applications are presented. A prestressed concrete cablestayed bridge is analyzed for time-dependent effects during construction as well as after completion with non-linearities accounted for. A multistorey post-tensioned frame is investigated for the effects of deferring the column-to-slab connections until after prestressing of floors. A post-tensioned multi-·bay frame with a reinforced concrete closure strip is analyzed and the stresses in the closure strip are investigated for various time and column stiffness parameters. A circular tank wall with hoop prestress is studied for the effect of delaying the wall to base connection until some time after prestressing. The program produces stresses at the extreme fibres of concrete members, stresses in prestressed and non-prestressed steel, internal forces in non-concrete members and displacements at the joints. The results of the application examples show clearly the significance of creep and shrinkage of concrete and relaxation of prestressing steel in structures built in stages and subject to continuous variations in geometry, loads and end conditions. The computer program is fairly general and is capable of handling a wide range of prestressed concrete structures.