Load-bearing capacities of SFRC elements accounting for tension stiffening with modified moment-curvature relations

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Title: Load-bearing capacities of SFRC elements accounting for tension stiffening with modified moment-curvature relations

Author(s): Peter Heek; Peter Mark

Publication: Special Publication

Volume: 310

Issue:

Appears on pages(s): 301-310

Keywords: Tension stiffening bond factor, effective tension area, optimization methods, non-linear analysis.

Date: 3/17/2017

Abstract:
The application of steel-fibre-reinforced concrete (SFRC) with or without additional steel bars has been growing recently in structural engineering. To accurately predict both holistic load-deflection curves and the redistribution of stresses in statically indetermined systems, calculation methods that take non-linear stress-strain relations and tension stiffening into account are favoured. Here, a moment-curvature-based approach for SFRC is proposed. In contrast to conventional tri-linear moment-curvature relations, all four stages: initially uncracked concrete, crack formation, stabilized cracking and yielding of reinforcement, are incorporated explicitly employing optimization methods. On the cross-sectional level, general and dimensionless diagrams have been derived to read the strain state w.r.t. bending moment and mechanical reinforcement ratio, two factors to account for the fibre effectiveness and the ratio of concrete cover to the effective depth. Thereby, tension stiffening is considered adapting a modified stress-strain relation of rebar. Since crack spacing of SFRC elements with additional reinforcement compared to conventionally reinforced concrete is reduced, the effective tension area and the tension stiffening bond factor have been modified. To verify the new approach, experimental load-deflection curves from literature are recalculated by numerical integrations of the obtained moment-curvature relations. The results are in good accordance. The paper summarizes the major findings of the contribution “Non-linear analysis of SFRC elements bearing capacities accounting for tension stiffening by means of modified moment-curvature relations” by the same authors published in (Heek/Mark, 2014).