Tension Field Action in Hybrid Steel Girders

With the advent of HPS70W (70 ksi) steel, several bridges have been built, and many more will be built, using hybrid design provisions. One limit with hybrid girder design, which decreases the beneficial aspects, is that tension field action (TFA) is not allowed when determining the shear capacity. This is a severe shear capacity penalty for using hybrid girders. This paper proposes that tension field action should be allowed for hybrid girders and presents a modified moment-shear interaction. Hybrid tension field action would allow shear capacities well above what is currently allowed by AASHTO. With an increase in shear capacity, fewer transverse stiffeners will be necessary. A decrease in stiffeners allows for a more economical design of hybrid plate girders, substantial cost savings in material and fabrication and fewer fatigue details. The paper also presents planned experimental and finite element studies that are expected to verify the development of tension field action in hybrid girders and the capability of the proposed modified moment-shear interaction equation as a lower bound strength estimate.