# Visualization of Distributed Plasticity in Concrete Piles Using OpenSeesPy
## 1 Introduction and Background
### State of the Art in Fiber Modeling and Visualization  
More refined finite element analyses (FEAs) have demonstrated that whatf-soil interaction behavior can be accurately assessed using both 2D approaches [15; 16; 17; 18; 19] and 3D simulations [20; 21; 22; 23]. However, the time required to develop detailed numerical models, combined with high computational demands and the need for extensive calibration campaigns to achieve accurate results, can be quite restrictive for practical applications. To address the limitations of both detailed FEAs and simplified lumped plasticity models, distributed plasticity (fiber-based) formulations have gained prominence in the seismic analysis of RC whart structures. These models discretize cross-sections into concrete and steel fibers, each governed by nonlinear constitutive laws. When implemented within force-based beam-column elements [24; 25], they capture the progressive development of inelasticity along member lengths under varying axial forces and bending moments. This is essential for modeling whart structures, where nonlinear soil-structure interaction, P-\(\delta\) effects, and vertical inertial forces affect seismic response [13]. Fiber modeling of reinforced concrete pile elements and their connections has been reported in both building and bridge applications, demonstrating good agreement with experimental results in capturing deformation, damage progression, and evaluating repair techniques [12; 26; 27; 28; 29; 30; 31; 32]. Recent studies have demonstrated the superior predictive capabilities of fiber models for marine infrastructure. For example, [PERSON] et al. [33] implemented 2D fiber models to analyze damage-resistant pile-to-whart connections under both static and dynamic loading, finding that these configurations outperformed conventional detailing in terms of seismic performance. [PERSON] [34] evaluated the in-ground plastic hinge length and found that, for clays, it increases with lower-bound soil properties and decreases with upper-bound values relative to the nominal case. This finding supports the need for conducting separate analyses using different plastic hinge lengths for the two seismic design levels, in order to more realistically estimate displacement capacity at each level. [PERSON] et al. [35] conducted detailed 3D seismic simulations of a pile-supported whart using nonlinear fiber-section beam-column elements for both the deck and piles, coupled with soil macro-elements to capture pile-soil interaction and kinematic effects under liquefaction conditions. More recently, the same author [36] developed a refined 3D OpenSees model incorporating realistic free-field boundary conditions and coupled pile springs to evaluate performance under two seismic hazard levels defined in ASCE 61-14 (Contingency and Design Earthquake levels). Their fiber model results indicated that, even under strong ground shaking, computed pile strains remained well below code-specified limits. In a subsequent study, [PERSON] et al. [37] extended the analysis to crane-whart interaction, concluding that the crane influences the static response of the whart pile foundation prior to shaking, and this effect carries over into dynamic response during seismic events. [PERSON] and [PERSON] [11] investigated the effect of corrosion in prestressed concrete (PC) bars on the seismic performance of a pile-supported whart using fiber sections through the Scientific ToolKit for OpenSees (STKO) [38]. STKO is a graphical pre- and post-processor that facilitates the creation, visualization, and analysis of finite element models using OpenSees, enabling model development and interpretation through an user interface. They concluded that distributed plasticity yields more accurate pushover curves compared to those from idealized concentrated hinge approaches. Despite the advantages, the adoption of fiber models in routine engineering practice remains limited due to perceived complexity, greater computational demands, and lack of standardized workflows.