The limitations of linear static analysis in the seismic design gave rise to non-linear static analysis or Pushover analysis. Pushover analysis can demonstrate how progressive failure in buildings really occurs and identify the mode of final failure. Pushover Analysis can also predict potential weak areas in the structure, by tracking the sequence of damages of every member in the structure (using something called ‘hinges’).
With the advent of Finite Element software in the world of seismic engineering, we have reached a stage where seismic design based on linear elastic analysis is no longer sufficient, and a dedicated non-linear analysis of the structure is required.
The linear approach uses the concept of Response Reduction factor R. When we design a structure for say, R=3, it implies that only 1/3rd of the seismic force is taken by the Limit State Capacity of the structure and further deflection is taken by the ductile capacity of the structure. However, we rarely analyze the ductile part and only fulfill the reinforcement detailing guidelines for the part. This is due to various challenges faced while analyzing the ductile capacity, such as changes in the stiffness of elements due to cracking and yielding, P-delta effects, changes in the final estimated seismic force, etc.
The elastic analysis fails to account for the resulting redistribution of forces during the progressive yielding or even predict the failure mechanisms in the structure. A non-linear static analysis that considers the inelastic behavior of the structure can predict these more accurately.
The need for this non-linear analysis to predict the performance of the structure beyond the elastic limit gave rise to Pushover analysis (PA). Using this method, we can demonstrate how progressive failure in buildings really occurs and identify the mode of final failure. Pushover Analysis can also predict potential weak areas in the structure, by tracking the sequence of damages of every member in the structure (using something called ‘hinges’).
Pushover analysis can provide the following advantages:
Let us see some of the similarities and differences between conventional seismic analysis (SA) and Pushover Analysis (PA). We will begin with the similarities.
With that idea, let us discuss some of the differences between the two methods:
Conventional Seismic Analysis results are mostly used for the design of structure, thus the loads available in the load combinations are factored, however, PA simulates the behavior of the structure under actual loads, therefore, the loads applied are not factored.
Fig 1. Typical Hinge Location in a structural model
Fig 2. Typical Flexural Hinge, showing IO (Immediate Occupancy), LS (Life Safety), and CP (Collapse Prevention)
Fig 3. A typical substructure (pier/pier cap) section
Midas Civil offers a built software, General Section Designed (GSD) to find the Moment-curvature function for the cross-section of the pier.
Pushover hinge is assigned to both the columns
Pushover Global analysis control