Analysis of auxiliary ribs in steel–concrete joint of hybrid girder

• Stress intensity and loading eccentricity of the joint are reduced by auxiliary ribs.
• Efficient T-ribs inserted in trough ribs result in 50% stress dispersal effect.
• Auxiliary ribs with abrupt tip weaken orthotropic steel deck with troughs.
• Modified trough–auxiliary rib joint decreases 60% stress concentration.
• Effective length of auxiliary ribs is two to four times concrete slab thicknesses.

The auxiliary ribs are utilized to reinforce the steel–concrete joints (SCJs) of hybrid girders. However, the demands of the ribs and the design of orthotropic steel decks with the auxiliary ribs are not addressed in design specifications. Solid element models are used to study the auxiliary ribs of the SCJ. The joints with and without auxiliary ribs are analyzed to clarify the demands and the reinforcing effects of the ribs. Stress dispersal efficiency of three typical auxiliary ribs is investigated. The trough–auxiliary rib (TA) joint is analyzed to check the steel deck design assumption and the approach to suppress stress concentration is discussed. The effective length of the auxiliary ribs is studied considering the geometric variations. Results show that the auxiliary ribs enlarge the steel deck and narrow the steel–concrete centroid deviation. The auxiliary ribs disperse about 50% axial force and the stress transmission of the joint is improved. The T-rib inserted in the trough is efficient to reinforce the SCJ with the effective length of 2–4 times the concrete slab thickness. The TA joint with abrupt tip suffers stress concentration and the safety margin of the steel deck is reduced. The joint is improved with about 60% hot spot stress decrease using the gentle tip with crossbeam constraint.