Numerical calculations are presented to describe the behavior of a composite beam in which the concrete slab does not predominate and the neutral axis of the transformed section is well into the steel section. The general behavior of such a beam is examined and some inadequacies of the present code illustrated.

On Composite Beams

Modeling R/C Columns in Fire according to Different Constitutive Models for Heated Concrete

The sensitivity of the structural response to variations of material and cross sectional geometrical parameters is investigated for reinforced concrete structures under fire loading. A relatively low cost 2D corotational layered beam finite element is employed in a reduced latin hypercube sampling framework for this purpose. The structural response is assessed in terms of vertical deflection versus time, failure time and cross sectional stress/strain distribution using standard fire curves. The numerical models represent experimentally tested cases in the literature and operate with experimentally derived parameter sets, when possible. A minimum set of three RVs, the bottom concrete cover thickness, steel and concrete yield stregths, out of the initial full set of 12 are identified that drastically reduces the number of RVs and thus the stochastic computation’s cost, while keeping a reasonable envelop for the results. The relationship between structural behavior, material degradation and data extracted from the cross sectional behavior is also successfully established and used to explain why the random set can be reduced to three parameters.

Probabilistic investigation of reinforced concrete structures under fire loading accounting for material and geometric uncertainties

The structural response of slender reinforced concrete (RC) structures may be highly nonlinear due to cracking, reinforcement yielding, and geometrically nonlinear effects. While advanced models can simulate the detailed response of such structures, they are generally ill-suited for limit state verification in practical design scenarios due to a high computational and modeling effort. A design-oriented method for evaluating the geometrically linear response of cracked RC wall structures was recently presented and demonstrated to allow the analysis of large-scale models with more than 2400 finite shell elements within minutes on a standard personal computer. This paper proposes a design-oriented numerical method for efficient instability analysis of slender RC wall structures, also enabling the inclusion of thermal effects. Based on a two-step linearized buckling analysis, the method first determines the geometrically linear structural response by solving the complementary energy minimization problem, including, if relevant, thermal strains and reduced material stiffness. This solution is used to derive the sectional stiffness upon which a linearized buckling problem is formulated and subsequently solved as a linear eigenvalue problem. The model is validated using examples with exact solutions, and its applicability to large-scale models is demonstrated through an example with a four-story stairwell modeled using more than 3200 finite elements. 

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/suco.202200883

Design‐oriented nonlinear‐elastic buckling analysis of reinforced concrete wall structures using convex optimization

Comparative study on failure mechanism of multi-storey planar composite frames with RC beams to CFST columns subjected to compartment fire

Fire is a critical risk in reinforced concrete (RC) structures and appropriate structural resistance against it has to be ensured. In this contribution, an approach using corotational layered beam ...

Fabian M Paz Gutierrez

Papers

Computational analysis of reinforced concrete structures subjected to fire using a multilayered finite element formulation