Link Slab [PIG]

A link slab is a continuous deck segment cast across the joint between two simply supported spans and debonded from the girders for a short length each side, so the deck joint over the pier can be eliminated. Only the deck is made continuous — the girders keep rotating independently at their own bearings — so the slab is driven by the imposed end rotations of the two adjacent spans rather than by direct load.

This is a different detail from a continuity diaphragm, which makes the girders continuous.

The slab is anchored on the two decks it joins. Its plan geometry — width, edge positions, edge alignments and the skew of its end faces — is taken from those decks' own cross-sections rather than typed in, so it follows a widening, flared or curved deck automatically. Thickness is the only cross-sectional value entered here.

The two decks must not already be continuous at this joint

A deck that is continuous at the joint ties it rigidly in all six degrees of freedom, including rotation, which is the opposite of what a link slab does — the slab would be present but carry nothing, and the end rotations the design is based on would no longer be real.

Set Continuous at End to No on the down-station deck and Continuous at Start to No on the up-station deck. The object reports an issue if both are left continuous.

General

Deck (Down Station): The deck on the lower-station side of the joint. Select it from the model; the slab reads this deck's end cross-section for its own geometry on that side. A value is required.

Deck (Up Station): The deck on the higher-station side of the joint, selected the same way. The two decks must meet at the same support line — that shared boundary is what defines the joint station and its skew, which is why no support line is entered separately.

Material: The material of the link slab itself, assigned from the materials defined under Properties. For the NYSDOT detail this is a UHPC mix. A value is required.

Thickness: Depth of the link slab, measured downward from the top of deck. This is a partial-depth band cast into a blockout, not the full deck depth — the value is typically much smaller than the deck thickness. Must be greater than zero.

Debonded Zone Length: The total length of the debonded zone, measured along the alignment (Read-only). It is the void the two deck pours leave at the joint, taken from each deck's own Offset From Support Line so that the modelled concrete and the length the design is based on can never disagree.

How to change the debonded zone length

Because this value is derived, adjust it by moving the two decks' cross-section Offset From Support Line entries — the down-station deck's last offset and the up-station deck's first. That is the same edit that widens or narrows the blockout on the drawing, and this value follows it.

If the two decks meet at the pier the void is zero and the object reports an issue: pull their concrete ends apart rather than overriding the number.

Debond Length (Down Station): The distance from the support line back to the down-station deck's concrete end (Read-only). This is the actual debond length on that side, which equals half the debonded zone only when the two deck offsets happen to be equal and opposite.

Debond Length (Up Station): The distance from the support line forward to the up-station deck's concrete start (Read-only). Together with the value above it accounts for the whole debonded zone.

Reinforcement

Longitudinal Bar: The longitudinal reinforcing bar running through the link slab across the joint, assigned from the rebars defined under Properties. This is the reinforcement the slab's flexural capacity is checked against.

Longitudinal Bar Spacing: Centre-to-centre spacing of the longitudinal bars, measured across the width of the slab. Must be greater than zero.

Rebar Material: The material assigned to the link slab reinforcement, selected from the materials defined under Properties.

FEA

Release Composite Action in Debond Zone [No/Yes]: Controls whether the debonded zone is represented in the finite element model. When set to Yes, the slab is tied to the girders across the joint by equal-degree-of-freedom constraints that carry the selected translations but leave the rotations free — the slab moves with the girder while taking no moment from it, which is what a bond breaker does. When set to No, no constraints are generated and the joint behaves as the decks alone define it.

Generated Ties: The number of equal-degree-of-freedom constraints this slab actually emits (Read-only). Ties are generated from the deck mesh nodes on each side of the joint, so the count is the smaller of the two decks' edge node counts. A zero here means the joint is not being tied at all and is worth investigating before analysing.

Debond Tie Tx [Free/Tied]: Whether the tie carries longitudinal translation across the joint. Only editable when Release Composite Action in Debond Zone is set to Yes. A real bond breaker also slips longitudinally, so this is exposed rather than fixed.

Debond Tie Ty [Free/Tied]: Whether the tie carries transverse translation across the joint. Only editable when Release Composite Action in Debond Zone is set to Yes.

Debond Tie Tz [Free/Tied]: Whether the tie carries vertical translation across the joint. Only editable when Release Composite Action in Debond Zone is set to Yes.

Debond Tie Rx [Free/Tied]: Whether the tie carries rotation about the longitudinal axis. Leave this free to keep the two spans moment-independent, which is the behavior a link slab is designed for. Only editable when Release Composite Action in Debond Zone is set to Yes.

Debond Tie Ry [Free/Tied]: Whether the tie carries rotation about the transverse axis. This is the rotation the girder ends take at the joint; tying it makes the spans continuous and defeats the detail. Only editable when Release Composite Action in Debond Zone is set to Yes.

Debond Tie Rz [Free/Tied]: Whether the tie carries rotation about the vertical axis. Only editable when Release Composite Action in Debond Zone is set to Yes.

Quantities

Volume: The concrete volume of the link slab, calculated from the modelled geometry (Read-only).

Weight: The weight of the link slab, calculated from its volume and the assigned material (Read-only).

Referencing Objects

Structure States: The construction staging objects that reference this link slab (Read-only). An entry appears here once the slab has been assigned a casting stage.