Keywords: microplane model, initial anisotropy, anisotropic damage, cementitious composites, textile reinforced concrete, tension-stiffening effect.

Textile reinforced concrete (TRC) is a new composite material that consists of a fine grained concrete matrix reinforced with layers of textile fabric made out of for example alkali-resistant glass or carbon. In order to allow an efficient calculation, a smeared crack approach and an implicit representation of the reinforcement was applied. The model presented in this paper is based on the microplane damage model [1]. This microplane formulation can be placed in the framework of continuum damage mechanics. Within the model the stress and strain tensors are projected onto a set of generic microplanes with a defined orientation which makes it possible to apply unidirectional damage laws at the microplane-level. The overall macroscopic response is then obtained using the principle of energy equivalence.

The direction-dependent representation of the material structure into oriented micro-planes provides a flexible way to introduce the initial anisotropy [2,3]. In the present case the anisotropy is captured by the definition of orientation-dependent damage laws. The aim of this approach is to model both the tension-stiffening effect characteristic for TRC specimens in the reinforcement-direction as well as the strain softening behaviour in the non-reinforced direction. To achieve this, the damage laws of the microplanes with normal direction corresponding to the reinforcement-direction are associated with modified damage laws that exhibit a horizontal asymptote at the desired level of residual integrity. At this point the saturated crack pattern with multiple cracks in the reinforcement-direction has been reached. The transition from the reinforced direction to the non-reinforced direction can be described by an appropriate transition function. To exemplify the computational proceeding, a simple linear transition has been applied.

The proposed approach is reviewed in numerical simulations on the material point level for the two-dimensional case. The general procedure is motivated for the case for isotropic quasibrittle materials and is then extended to anisotropic materials using the example of a TRC specimen reinforced in one direction only. The results obtained should be regarded as a preliminary study of the model behavior. Nevertheless, it demonstrates the capability of the model to reproduce the transition from the reinforced to non-reinforced direction in terms of the stress-strain response.

1

Jirasek M., "Comments on microplane theory", Mechanics of Quasibrittle Materials and Structures, Hermes Science Publications, Paris, 55-77, 1999.

2

Ozbolt J., Li Y., Kozar I., "Microplane model for concrete with relaxed kinematic constraint", International Journal of Solid and Structures, Vol. 38, 2683-2711, 2001. doi:10.1016/S0020-7683(00)00177-3

3

Cusatis G., Beghini A., Bazant Z.P., "Spectral Stiffness Microplane Model for QuasiBrittle Composite Laminates: I. Theory", Journal of Applied Mechanics, ASME, in press, 2007. doi:10.1115/1.2744036

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