Parameter identification as the basis for finite element simulations of ultimate limit states of concrete hinges

Abstract

Reinforced concrete hinges, subjected to eccentric compression, are failing in a ductile fashion (Schlappal et al. 2017). Three-dimensional Finite Element simulations are prime candidates for a more detailed analysis of this interesting structural behavior. Such nonlinear simulations, however, typically require pocedures for updating of the underlying models. They involve fitting of input parameters such that the output of the simulations agree with experimental measurements (Kalliauer et al. 2017). In the present contribution, it is investigated to which extent fitting procedures, involving time-consuming nonlinear three-dimensional Finite Element simulations, can be avoided. Therefore, input parameters are identified by combining (i) results from destructive and nondestructive compression tests on plain concrete specimens, (ii) results from centric and eccentric compression tests on concrete hinges subjected to serviceability loads, (iii) a multiscale model for tensile failure of concrete, and (iv) linear-elastic twodimensional Finite Element simulations. Parameter identification aims of (i) quantifying the influence of damage of concrete (resulting from restrained shrinkage prior to structural testing) on the elastic stiffness, the tensile strength, and the fracture energy, and of (ii) determination of the characteristic triaxiality of the compressive stress states, prevailing in the neck region, in order to ensure modeling of the triaxial compressive strength of concrete in accordance with regulations of Eurocode 2. After parameter identification, a nonlinear three-dimensional Finite Element simulation of the bearing capacity tests by Schlappal et al. ( 2017) is carried out. The obtained numerical results agree well with experimental observations. This underlines the usefulness of the presented parameter identification strategy.

Modeling and design of concrete hinges under general loading

“…Nonlinear finite element (NLFE) analyses can help understanding the complex three-dimensional behavior of concrete hinges and contribute to their adequate design. 12,13 However, such analyses require expertise and considerable modeling time, and their results can be very sensitive to parameters often unknown during the design phase. 14 Therefore, it is essential to provide reliable mechanical models for the behavior of concrete hinges that-even if NLFE analyses are carried out in detailed design-can be used as initial design (to be checked by NLFE) and as a plausibility check of the NLFE results.…”