Transverse member properties

[Persepolis260593]

I have a query regarding the correct method of accounting for the section properties of transverse members near diaphragm / support line positions on high skew orthogonally constructed deck grillage models. It appears to me that if members are given uniform properties along that prototype strip then parts of the deck in the triangular regions are represented more than once. My view would be to reduce the grillage member stiffness locally about the diaphragm location (which would be modelled separately appropriate to its dimension and strength ) instead of applying uniform section properties across the transverse strip. The bridge deck being modelled is a concrete slab comprised of prestressed beams with in situ concrete infill. A stiffening diaphragm is proposed to tie the prestressed beams together about the support line. Another question altogether and unconnected to the above is whether a slab would much benefit from a edge stiffening given that the depth of fill is uniform throughout the slab. In which case a nominal stiffness may be provided along the support line member and uniform section properties to the transverse members can be provided.

Bridge data:

Span: 13m
skew: 60 deg

Any advice to the above would be greatly appreciated.

cheers

 

[Persepolis260593]

I believe I have a solution from Hambly Bridge deck behaviour "It might appear that if members are given uniform properties, the parts of the deck in the triangular regions are represented more then once. If the orthogonal members are assumed to represent the typical deck construction, they should have typical section properties. No reduction in the grillage member stiffness is necessary as since the strip of prototype it represents is not tapered and does not terminate at a point. The edge trimming grillage member should be given the stiffness appropriate to its additional stiffness coincident with its line in the prototype. If the prototype is a slab with no special end of edge stiffening, the skew grillage member is given a nominal stiffness. However, if there is a stiffening diaphragm or edge beam built into or on to the deck, the equivalent grillage member should be given the stiffness appropriate to the dimensions and strength of the actual stiffening member with the part of the slab that participates is flange."

In summary a diaphragm here serves no purpose as the depth of section would be uniform across the rest of the slab. The section in theory could be deeper, but in any case I believe the correct method would be to assume a nominal stiffness along the skew line and have uniform stiffness properties for the transverse members.