Ultra-high-performance concrete with steel fibers (UHPC) stands out for its exceptional mechanical properties and high ductility. The addition of steel fibers improves the tensile strength, allowing for its use in the design of structural elements subject to bending. The use of rice husk ash (RHA) as a natural mineral addition in the UHPC mixture offers significant advantages in terms of environmental impact and mechanical properties. Therefore, this work experimentally investigates the effect of RHA as a partial replacement for active silica fume on the flexural tensile strength and compressive behavior of UHPC. Additionally, a parametric study was conducted to examine the impact of varying prism geometries on the flexural tensile strength of UHPC with and without CCR in ABAQUS version 6.14. The experimental results made it possible to calibrate the UHPC parameters using RHA for numerical simulations of UHPC behavior based on the concrete damaged plasticity (CDP) model. The results indicated an increase of 4% in the compressive strength and 20% in the flexural tensile strength of UHPC with the addition of RHA. Furthermore, the numerical extrapolations of the flexural tensile strength test show that increasing the dimensions of the prisms reduces the strength by up to 30% of UHPC with RHA, evidencing the influence of geometry on the results.

Timber beams have assumed a prominent role in contemporary structural engineering, driven by sustainability requirements and the advancement of engineered wood products. Despite the evident environmental and building advantages, the performance of timber beam elements under fire conditions remains one of the main design challenges, due to the strong nonlinearity of thermal behavior, progressive charring, and degradation of mechanical properties. In this context, numerical simulations have become a central tool for the thermal and thermomechanical assessment of timber beams exposed to fire. This study presents a technical and critical review of numerical approaches applied to timber beam elements, with emphasis on finite element–based models, thermal modeling strategies, representation of charring, thermomechanical coupling, and the use of reduced-order and surrogate models. The distinctive contribution of this work lies in an integrated and critical analysis of these approaches, explicitly articulating high-fidelity numerical models with reduced-order and symbolic models, aiming at their use as complementary tools in structural design. The analysis was conducted thematically, based on literature selected from major international databases, emphasizing modeling assumptions, levels of numerical complexity, and methodological limitations. The results indicate a predominance of transient finite element (FEM) models, widespread use of two-dimensional cross-sectional analyses, increasing adoption of enthalpy-based formulations for charring, and a prevalence of sequential thermomechanical coupling strategies. In contrast, the literature reveals strong heterogeneity in thermal parameters, limited standardization of validation procedures, restricted use of probabilistic approaches, and still incipient integration of reduced-order and symbolic models. It is concluded that future advances in the field depend on the standardization of modeling strategies, the expansion of thermal property databases, and, above all, the integration of high-fidelity models with interpretable reduced-order models, capable of supporting parametric analyses and performance-based structural design methodologies.

Hybrid timber–steel structural systems have emerged as promising solutions to enhance fire performance in sustainable construction. However, design-oriented predictive models capable of adequately representing their coupled thermomechanical behavior remain scarce. This study developed and validated a multiphysics finite element model to assess hybrid timber beams reinforced with embedded steel bars subjected to the standard ISO 834 fire curve. The model incorporates temperature-dependent thermal degradation, orthotropic plasticity of timber, elastoplastic behavior of steel, and geometric nonlinearity, and was validated against mechanical and thermal experimental references. A multivariate parametric study comprising 81 structural configurations was conducted to investigate the influence of beam geometry, steel area, and reinforcement positioning on load-bearing capacity and fire resistance time. The results indicate that metallic reinforcement significantly enhances structural resilience under fire exposure, with increases in time to failure exceeding 100% in optimized configurations. The steel acts as a residual load-redistribution mechanism during timber charring, compensating for the progressive reduction of the effective resistant cross-section. Bar diameter, positioning at h/6, and beam slenderness were identified as dominant variables. Through symbolic regression, an explicit analytical expression was derived to estimate fire resistance time, demonstrating high predictive accuracy with R2 ≈ 0.98 and MAPE ≈ 4.8%. The findings contribute to the development of performance-based design strategies for sustainable hybrid structural systems.