A Benchmarking of Models and Methods for Simulating the Seismic Response of Reinforced Concrete
Presented By: Ercan Serif Kaya
Affiliation: University of California,
Description: Authors: E. S. Kaya, I. Talebinejad, J. Hong, P. Chang, T. Nguyen, V. Jafari Azad, M. Reardon, O. Jaradat, E. Taciroglu1
Abstract:
Simulating the nonlinear response of reinforced concrete structures under mechanical loads is a frequent task encountered in civil engineering design and risk assessment. Depending on the application, different modeling and analysis approaches are adopted. The present study explores the validity brackets for these alternatives, primarily in the context of dynamic or quasi-static analyses that reach or exceed deformations at the capacity of reinforced concrete. Three main branches of modeling approaches are explored—namely, models that adopt (i) lumped plasticity macroelements (e.g., plastic hinges), (ii) kinematics hypothesis of beams, plates, or shells (e.g., Bernoulli-Euler beams with “fiber-based” cross-sections), and (iii) continuum models (e.g., concrete damage plasticity models). Several benchmark problems involving well-instrumented laboratory-scale models of common structural elements and plain concrete specimens are devised to compare modeling options. Additional benchmark problems involving more complex (and very large) specimen geometries are also developed using practical engineering applications as inspiration. These benchmark problems are used to compare different modeling and analysis options with each other in terms of accuracy (when test data are available) and computational efficiency. An effort is also made to translate input among different modeling options. Particular focus is directed to determining differences in pushover versus cyclic types of analyses, mesh dependency of predictions, and strain localization issues.
The Sensitivity of Nonlinear Finite Element Modeling Results to the Input Parameters in Low-rise Shear Walls
Presented By: Asa Bassam
Affiliation: Sargent & Lundy
Description: This study investigates the sensitivity of nonlinear finite element modeling (FEM) to input parameters in the analysis of low-rise reinforced concrete shear walls, with a focus on evaluating the reliability and accuracy of predicted seismic demands. Given the increased use of nonlinear FEM in performance-based seismic design and assessment, understanding how input parameters influence the model response is critical for ensuring dependable results, especially when applied to low-rise structural systems where shear behavior dominates. This research systematically examines a range of material and modeling parameters, including concrete compressive strength, reinforcement properties, shear retention factors, element discretization, and boundary condition assumptions. Using a parametric study on representative wall configurations, the influence of each input on key response indicators such as peak shear force, displacement capacity, and energy dissipation is quantified. Special attention is given to emerging modeling practices and tools that propose standardized or "recommended" input values. The numerical predictions using these standard parameters are compared to experimental results to assess their practical accuracy and potential limitations. Results indicate that certain parameters, particularly those governing shear stiffness and tension softening, exhibit high sensitivity and significantly affect model outcomes. Conversely, other inputs, such as axial load variation within typical design ranges, show minimal influence. The findings highlight the necessity of careful calibration and validation when adopting emerging nonlinear modeling technologies and stress the importance of prioritizing critical input parameters in design and assessment practices. The study offers insights into improving the reliability of nonlinear FEM for low-rise shear walls and provides guidance for engineers and researchers applying these models in both routine and seismic evaluation.
Implementation of Early-age Shrinkage Effects in the Numerical Analysis of Concrete Box Girder Bridges
Presented By: Pablo Hurtado
Affiliation: Simpson Gumpertz & Heger Inc.
Description: This study presents an in-depth investigation into the implementation of early-age shrinkage effects in the numerical analysis of concrete box girder bridges using advanced finite element modeling techniques and emerging computational technologies. Early-age shrinkage, particularly in post-tensioned concrete structures, can induce significant internal stresses and cracking, especially in restrained elements such as the webs of box girders. These effects, if not accurately accounted for, may compromise long-term durability, serviceability, and load-carrying capacity. The research integrates state-of-the-art modeling approaches to simulate early-age behavior, including time-dependent material properties, moisture gradients, thermal effects, and restraint conditions, within a nonlinear finite element framework. Using advanced software platforms capable of capturing the coupled hygro-thermo-mechanical behavior of concrete at early ages, the study evaluates the stress development and potential cracking in the webs of box girder bridges during the critical curing period. The numerical models incorporate realistic construction sequences, boundary conditions, and material models aligned with current international guidelines and experimental data. A parametric study is conducted to assess the influence of variables such as ambient temperature, hydration kinetics, curing methods, and cross-sectional geometry on shrinkage-induced stresses. Results reveal that early-age shrinkage can lead to significant tensile stresses in the web regions, especially where geometric restraints are high, potentially initiating microcracking before the application of live loads.
Practical Resolutions and Considerations of Response Spectrum Analysis in Concrete Structures and Foundations
Presented By: George Ghaly
Affiliation: Westinghouse
Description: Response Spectrum Analysis (RSA) has been a cornerstone in seismic design since its development, providing a simplified method for evaluating the seismic response of structures based on their natural frequencies and mode shapes. Initially developed for linear elastic systems, RSA allows engineers to estimate the maximum response to earthquake excitations without performing time-history analysis. Over time, it has been integrated into various seismic design codes, including those for concrete structures, to guide the design of elements under dynamic loading.
However, RSA has inherent limitations in practical applications, particularly when assessing concrete structures and foundations. One of the key challenges is the loss of directional specificity in the resultant forces, which can lead to underestimating or misrepresenting internal forces. This issue is compounded when differentiating between compression and tensile stresses, a critical aspect of concrete design. Structural codes provide provisions to address these differences, yet RSA may fail to capture the nuanced behavior of concrete, especially under non-linear conditions.
Additionally, RSA may struggle with accurately predicting the direction and distribution of internal forces, including axial, shear, and flexural stresses, which are vital for section design and analysis. In particular, the combination of axial and lateral forces in concrete structures requires careful attention to the directionality of these forces for proper design of shear and flexural reinforcement. Shear design provisions in concrete codes require careful evaluation of the shear forces, including their interaction with other internal forces, which may be overlooked in RSA-based analysis.
This presentation will discuss the history and evolution of Response Spectrum Analysis, highlighting the practical resolutions and considerations in the design and evaluation of concrete structures. It will also explore how these evaluations impact the
Ensuring Confidence in Finite Element Analysis for concrete structures: Principles and Guidelines
Presented By: Abbas Mokhtar-zadeh
Affiliation: M3 Engineering & Technology Corporation
Description: Ensuring confidence in Finite Element Analysis (FEA) for concrete structures is essential for reliable design, assessment, and forensic investigations. Achieving this confidence requires a structured approach that integrates fundamental principles, rigorous verification, and practical validation techniques. This presentation will focus on strategies to enhance the trustworthiness of FEA results and how engineers can practically achieve high confidence levels in their analyses. Key aspects include model formulation, appropriate element selection, meshing strategies, boundary conditions, and material modeling—particularly for nonlinear behavior and cracking. Special emphasis will be placed on verification and validation (V&V) processes, including benchmarking against experimental data, performing sensitivity analyses, and identifying sources of uncertainty. Practical methods to quantify confidence levels, such as error estimation, mesh refinement studies, and convergence checks, will be discussed. Real-world case studies will demonstrate how improper assumptions can undermine confidence in FEA results and how best practices can mitigate these risks. Additionally, industry standards and guidelines that help engineers establish robust and dependable FEA workflows will be highlighted. Attendees will gain actionable insights into improving the reliability of their models, making informed decisions based on FEA results, and ensuring confidence in structural performance predictions.