Strut and tie model optimization for reinforced concrete bridge pier head structure using a genetic algorithm

Abstract

Strut and tie model (STM) is more suitable to design the pierhead structures which resist high shear forces transferred
from the girders. These pierhead structures behave like the disturbed regions as in reinforced concrete deep beam. The design
of the struts and ties elements requires the initial geometry configuration of the truss model where its boundaries are limited by
the shape of the pier head structures. To find the optimum topological shape of the truss model, the genetic algorithm (GA)
optimization technique is used in this paper. The objective functions in the GA optimization consisted of minimizing the usage
of concrete and steel reinforcement material and ensuring all the stress ratios of the strut and tie elements are less than equal
to unity. Both prestressed and non-prestressed pierheads are investigated in this paper. The use of prestressing in the pierhead
structures reduces the stresses in the main tension tie significantly. Some shear tie and compression struts members also have
almost zero stresses due to the presence of prestressing forces. For these elements with zero stresses, the elements can be
removed and reduces the concrete and rebar materials usage. Furthermore, the genetic algorithm optimization is found to be
successful to ensure all the stress ratio in the members to be less than equal to unity.