The workflow demonstrates seismic nonlinear time-history analysis of a reinforced concrete bridge pier using SOFiSTiK. The aim is to evaluate the pier’s seismic performance by modelling material nonlinearity (plastic hinges) and performing dynamic response analysis under real earthquake excitation.
Workflow Steps:
- Plastic Hinge Modelling
- Define the backbone curve (moment-rotation) from the pushover analysis.
- Use the Modified Takeda model for hysteretic behaviour (reinforced concrete).
- Assign strain-based performance categories for concrete and reinforcement (e.g., fully operational → life safety).
- Nonlinear Time-History Analysis Setup
- Verify the actual normal force in the columns via linear static analysis (dead load + superstructure).
- Perform modal analysis to obtain eigenfrequencies (needed for Rayleigh damping).
- Define earthquake input (El Centro record) scaled to gravitational units.
- Include material degradation via the effective stiffness factor (18%).
- Use Newmark time integration with adaptive stepping for convergence.
- Execution of Analysis
- Activate physical + geometrical nonlinearity.
- Run dynamic analysis with a 20-second simulation and a 0.02-second time step.
- Monitor hinge response (moment-rotation hysteresis) and header beam displacement.
- Post-Processing and Performance Evaluation
- Use SOFiSTiK GRAPHIC to check:
- Strain-based criteria (3 levels for concrete/reinforcement).
- Rotation-based criteria (yielding P, ultimate U, failure X).
- Identify exceedance of performance levels (e.g., PL3 reached at 3.1 s in the bottom hinge).
- Interpret results to determine the safety and performance of the structure.
- Use SOFiSTiK GRAPHIC to check:
Key Insights
- The modified Takeda model effectively captures the RC cyclic behaviour.
- Performance-based criteria allow localised damage assessment.
- Integration of static, modal, and dynamic analyses ensures a realistic seismic response.
- An effective stiffness factor is critical for simulating degradation.
