Computational Damage Measure for RC Frame Structures Under Seismic Loading

Abstract eng:
In the earthquake areas, the priority task in seismic design is to fulfill the safety requirements with respect to the expected earthquakes. These safety requirements will differ from each other according to the type of the earthquake and structure. For that reason, most codes for seismic design, assessment and retrofitting use the performance-based seismic design concept. In that concept, performance levels are specified ranging from fully operational to near collapse and earthquake design forces are classified. Such performance levels are then associated with a damage state with respect to a given earthquake. At that, either descriptive criteria or displacements are utilized for the damage extent instead of an explicit damage index. The aim of this work is to overview existing damage indices and to define new explicit damage indices which may be used as seismic design criteria for reinforced concrete frames. Both local and global damage indices to be defined will range between 0 (no damage) and 1 (failure or collapse). They will be suitable for static, cyclic and dynamic computer analysis in order to be used with various existing design procedures. The necessary computer analyses are carried out by means of the finite element program (FRAME) developed in-house within the MATLAB environment. In that program, classical rectangular beam elements are used. Elasto-plastic bilinear moment-curvature relationships are used for the nonlinear material model including hysteretic behaviour under cyclic and dynamic loading. The stiffness matrices of the elements are obtained by use of the spread plasticity model along the length. The Newmark-Beta method with constant average acceleration is applied for the step-by-step time integration of the governing equations. The cyclic global damage index is proposed to be composed of the separate global damage indices during positive and negative load cycles. Several test problems have been analysed to check the sensitivity of the computational global damage measure for cyclic and dynamic loadings.

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