This paper was produced for the 2019 NAFEMS World Congress in Quebec Canada
The additive manufacturing of concrete is an active area of research in recent years. It can be expected that in the future it becomes a standard method of construction of buildings or infrastructure projects. As such it will be important to perform the standard safety checks and verification as required by the building codes and standards. The simulation of the construction process and accurate modelling of material curing and strength development in the early ages of the material is crucial for the verification of the structural stability and safety during the construction as well as during its service life.
The paper presents a procedure of such an analysis on the basis of nonlinear FEM, and it describes all extra features that are needed for such a simulation. These are mainly modelling of the detailed construction process of the structure, time variable load and suitable nonlinear constitutive equations for times ranging from fresh to mature concrete conditions. The newly developed computation modules are implemented into software ATENA (Cervenka et al 2018), which is later also used to compute a few sample analyses. The structure is first modelled at its final size and shape neglecting its construction process. Then, based on the prescribed motion of the printing head, a time for the activation of each element is calculated. The next step is the simulation of the manufacturing process. It is carried out at time steps, whereby at each step at a given time the FE model of the structure consists of active elements only and the rest is ignored.
For the modelling of the concrete material, the fracture-plastic material model of Cervenka & Papanikolaou (2008) is used. This material model combines orthotropic smeared crack model for tensile (fracturing) response and plasticity-based model for compression (plastic) behaviour. This material is formulated in a fully incremental form, and is extended for the purpose of this work to take into consideration the time dependent material parameters of the very young hardening concrete. The material parameters of the fracture-plastic material model are expressed as a function of time. The paper also describes the derivation of the required time dependent formulas for the material parameters.
During the printing process the structure is loaded by self-weight and shrinkage, both dependent on time. When the load is assembled it is automatically introduced into the appropriate time load functions.
Two sample analyses at the end of this paper demonstrate the performance and the applicability of the developed model. It is shown that the presented analysis is simple for use and it provides reasonably good results for a variety of digitally printed structures from the selected pilot projects.
The presented work is part of an international research project digiCON2, where the presented approach will be used to optimize the path and speed of the printing process and for the verification of the structural stability of the printing process.
|Date||18th June 2019|
|Organisation||Cervenka Consulting s.r.o.|