Design of cross-girders and slabs in ladder deck bridges

Abstract

Deck slabs in ladder decks span longitudinally between transverse cross-girders and the primary function of these cross-girders is to support the deck slab. The girders may, however, need to perform the secondary function of preventing the slab from buckling in compression. The concrete deck slab of a ladder deck can have a very large transverse span between main girders. This large unsupported width can lead to buckling of the slab in compression unless it is prevented from doing so by transverse girders. If the spacing of the cross-girders is large, it is still possible for second-order bending moments to develop in the slab under the effects of global compression. This paper sets out guidance on the limiting spacing of main girders and cross-girders to avoid consideration of second-order effects and also the means of determining second-order effects in slabs and cross-girders when this becomes necessary.