Minnesota Department of Transportation (MnDOT) tasked WSP with inspecting and evaluating a series of pier caps on approach spans of two sister bridges that carry Trunk Highway (TH) 77 bridge over the Minnesota River. These pier caps were relatively shallow supported on two rectangular columns. The initial load rating analysis performed using traditional Strut-and-Tie Method (STM) resulted in poor ratings (given the geometrical restraints for STM analysis set forth by AASHTO LRFD (i.e., minimum angle between struts and ties). The sectional method gave better results, but it was still unsatisfactory in shear. 

The WSP team developed a full 3D Finite Element modeling framework for these caps that leveraged solid elements to simulate concrete and discrete modeling of all internal reinforcement. Based on observed state of stresses in the as-designed model, cracks were then introduced into the model to approximate the state of non-linearity. Presence of these discontinuities in the concrete continuum allowed for development of a realistic stress field and shear transfer mechanism within concrete by effectively engaging internal reinforcement. The refined analysis indicated presence of a viable load path through evaluation of the 3D state of stresses, which resulted in satisfactory shear load ratings according to LRFR methodology.

Learning Objectives:

1) Recognize the limitations of traditional shear evaluation methods (STM and sectional approaches) for shallow concrete pier caps under AASHTO LRFD geometric constraints.

2) Understand how refined 3D finite element modeling—including discrete reinforcement and crack representation—can reveal realistic shear load paths in reinforced concrete bridge components.

3) Apply results from advanced 3D FE analyses to support bridge load rating decisions, demonstrating how viable load paths can lead to satisfactory shear ratings under LRFR when conventional methods are insufficient.

Speakers

Soroush Fakhri Yazdi: Vice President, Structures Manager, Washington DC

Soroush Fakhri Yazdi is an achievement-oriented senior structural engineer with an exceptional educational background and extensive finite element analysis experience. Recognized for superior research, problem-solving, and design skills, Soroush has over 16 years of experience in project management, review, and design of highway structures in several states. Soroush’s teaching experience at GMU’s Civil Engineering Department underscores his expertise and dedication to the field. His ability to impart knowledge in complex subjects such as Structural Analysis, Soil Mechanics, Steel Design, and Reinforced Concrete Design was recognized by the department, leading to an assignment to join the faculty as an Adjunct Professor.

Amir Gheitasi: Vice President, Structures Manager, Baltimore, MD

Amir Gheitasi has diverse experience involving analysis, design, evaluation, and rehabilitation of bridges and highway structures, including long-span steel plate girders, curved steel plate girders, steel box girders, prestressed concrete girders, precast and cast-in-place concrete segmental, cable-stayed, and steel truss bridges. In addition, Amir is experienced in time-dependent staged-construction analysis, non-linear finite element analysis, soil-structure interaction, seismic analysis, load rating, load testing and structural monitoring. In addition, he has experience in precast-prestressed concrete and vertical industry and has provided services for design, construction, and rehabilitation of parking garages, data centers, and residential buildings. Amir has been involved with both highway and railroad bridge projects across north America with international exposure, along with progressive experience towards business development, project management and alternative delivery. Amir has also been actively involved in industry technical committees and has a proven track record of publications and presentations in peer-reviewed journals and conferences.