Partitioned modelling for nonlinear dynamic analysis of RC buildings under earthquake loading

1. Partitioned modelling for nonlinear dynamic analysis of RC buildings under earthquake loading B.A. Izzuddin, L. Macorini and G. Rinaldin www.imperial.ac.uk/csm

2. Overview • Introduction • Nonlinear dynamic analysis of RC buildings • Partitioned modelling for parallel processing • Application study • Conclusion

3. Introduction • Retrofitting and strengthening RC buildings in earthquake regions • Nonlinear dynamic analysis for seismic assessment • Accuracy vs computational demand • Partitioned modelling on distributed memory HPC • Overcoming memory bottleneck for large-scale structures • Reduced simulation time through parallelisation

4. Nonlinear dynamic analysis of RC buildings • Interactions between frame, floor slabs and lateral resistance system • Geometric and material nonlinearity • Modelling of frame members with 1D elements • Fibre elements with nonlinear material models • Modelling of floor slabs and shear walls with 2D elements • Step-by-step time-integration scheme • Accuracy, stability and dissipation of higher modes (e.g. HHT) • Prohibitive memory and computational demands for real RC buildings

5. Partitioned Modelling for Parallel Processing Case 2: A parent and a child partition (parent also models a part of structure made with other elements) Case 3: A parent and a child partition (Same as case 2 but parent and child roles reversed) Case 1: A parent and 2 child partitions (parent has only partition super elements) Placeholder super-element on parent side Dual partition super-element on child side

6. Partitioned Modelling for Parallel Processing • Child partitions represented in parent by placeholder super-elements • Parent and child partitions processed in parallel • Child partition wrapped by dual super-element along interface boundary • Parallelisation through communication between placeholder/dual super-elements • Effective recovery of super-element resistance/stiffness via frontal solution method • Benefits of partitioned modelling approach using distributed memory HPC • Overcoming memory bottlenecks and parallel element computations in subdomains • Additional performance benefits due to parallelisation of frontal solution with reduced front widths

7. Application Study • Irregular 4-storey RC building • Modelling of beams/columns with 1D elements of fibre-type • Modelling of floor slab diaphragm action using equivalent planar bracing units • Geometric and material nonlinearity • Seismic excitation in two horizontal X-Y directions

8. Application Study • Three computational models with different number of partitions • Model (A): monolithic (1 process) • Model (B): 4 child partitions (5 processes) • Model (C): 14 child partitions (15 processes) • Partition interface boundaries at column locations for models (B) and (C) • Small number of parent nodes compared to child partitions • Effective for reducing communication overhead between processes • Avoids wall-clock time being imposed by solution of equations at parent level • Ideal speed-up equal to number of child partitions

9. Application Study • Identical accuracy for monolithic and partitioned models • Excellent speed-up for partitioned models • Exceptional speed-up for Model (C) exceeding number of child partitions • Considerable reduction in front width • Effective implementation of parallel frontal solver on distributed memory HPC systems

10. Conclusion • Nonlinear dynamic analysis of buildings subject to earthquake loading • Computational demand can be prohibitive for real structures • Partitioned modelling approach for parallel HPC • Based on parent/child partitions and associated processes • Identical accuracy to monolithic approach with use of dual super-elements for recovery of condensed resistance/stiffness at partition interface boundary • Computational benefits in terms of speed-up and overcoming memory bottleneck • Application to 4-storey RC building subject to earthquake loading • Exceptional speed-up of 27 with only 14 child partitions • Additional benefits arising from effective parallelisation of frontal solver leading to reduced front widths • Practical prospect for nonlinear seismic assessment of real structures

11. Partitioned modelling for nonlinear dynamic analysis of RC buildings under earthquake loading B.A. Izzuddin, L. Macorini and G. Rinaldin www.imperial.ac.uk/csm