| A two-dimensional constitutive law for behavior of concrete under load has been developed in this dissertation. Concrete is a composite material made up of two components: mortar and aggregate. Experimentalists have identified that the interaction between these two components, at the local level, governs the macroscopic behavior of concrete. The proposed model describes the fabric of a representative sample using the notion of a class of contacts, each class having a common orientation of the contact normal to the particle-mortar interface. Each class is further broken down into cracked and bonded contacts. Cracked contacts allow slip along the interface and are modeled as granular material. Bonded contacts do not allow slip along the plane of contact.; In developing the model, first the overall stresses are related to the interface forces at the microlevel. Simple constitutive relations are used to relate the rate of change of the local interface forces, for both cracked and bonded contacts, to the local velocity gradient. Finally, macroscopic constitutive equations are postulated using a Taylor-averaging method. An incremental procedure is needed due to the nonlinearity of the material behavior.; Results for monotonic compression, as well as for cyclic compression, are presented and show good qualitative agreement with published test data. |
