Blast Response of Concrete Encased Carbon Composite H-Beam Columns

Abstract

The response of concrete columns is highly dependent upon their internal reinforcement configuration when subjected to a short duration and high intensity loadings, such as one resulting from a detonation event. In recent times, structural engineers have pursued concrete column designs featuring encased steel and/or composite laminate H-beams, as an alternative to traditional longitudinal and transverse (shear) steel reinforcement. Encased beam reinforcement alters shock wave propagation characteristics in the through-thickness direction of the structural element, thus resulting in unique failure phenomena when compared to traditional columns of equivalent quasi-static strength. In this study, the Lattice Discrete Particle Model (LDPM) is initially reformulated for detonation events, implemented in a commercial finite element solver, and validated using experimental data. The model is then employed to investigate the dynamic behavior of three concrete columns with differing internal structures: traditionally reinforced with 25-millimeter Grade 60 rebar, encased A992 steel H-beam, and encased carbon fiber composite laminate H-beam. LDPM is formulated to simulate concrete at the mesoscale -- the length scale of the coarse aggregate used in concrete mixtures. Composed of polyhedral cells connected through a lattice of nonlinear fracturing struts, LDPM accurately and precisely captures the failure behavior at the mesoscale level. For this study, a typical 40-MPa concrete is used for all LDPM concrete material input. Linear beam elements with displacement degrees-of-freedom tied to LDPM nodes are used to model embedded rebar, whereas shell elements are employed to simulate the encased sections. The columns are subjected to two ranges of blast loads simulated via realistic pressure distributions along the column height and on all four exposed vertical surfaces. A comparison of the overall column performance is provided through quantitative analysis of mid-span responses as well as qualitative comparison of the overall failure modes. Results show that the encased beam column design provides a significant improvement with respect to the dynamic, post failure performance compared to that of the traditionally reinforced concrete column design.