A hammerhead pier cap is a cap on a single column whose two cantilevers carry the superstructure loads from the bearings to the column. The cantilevers are short, so the bearings sit close to the column and beam theory does not apply. The whole cap is a D-region and is designed with a strut-and-tie model under ACI 318 Chapter 23, AASHTO LRFD 5.8.2 or Eurocode 2. The pier-coping template in AStrutTie builds the strut-and-tie model from the cap dimensions and bearing positions, then checks the strength of every strut, tie and nodal zone, and the anchorage lengths, against the selected code.
The load travels to the column along a short, direct path. Each bearing reaction reaches the column through an inclined strut, and a tie at the centroid of the top bars carries the tension that develops along the top of the cap. When the live load sits on one side only, the unbalanced moment can put one side of the column in tension; the column's longitudinal bars can then be modeled as a tie extended into the cap for the analysis.
Three checks usually govern the safety of the cap. The top tie carries the largest tension and must be anchored at the cap tips, where little length remains beyond the outer bearing. The node under the outer bearing that anchors this tie (CCT) can fail under the load on the bearing plate, so it must always be checked. And when the cap is modeled simply, with struts running straight from each load point to the column, a strut can end up nearly parallel to the tension tie depending on the cantilever length. Because a strut and a tie cannot act in nearly the same direction, ACI 318 requires an angle of at least 25° between a strut and a tie meeting at a node.
- When it applies: short cantilevers with the bearings close to the column — the whole cap is a D-region
- The model: inclined struts from each bearing to the column, with a top tie at the centroid of the top bars
- Live load on one side only: the column's longitudinal bars can be modeled as a tie extended into the cap
- What usually governs: the top tie and its anchorage at the tips, the CCT node under the outer bearing, and the strut–tie angle
- A strut and a tie meeting at a node: at least 25° apart (ACI 318 §23.2.7)
- In AStrutTie: the pier-coping template builds the model and checks strut, tie and nodal-zone strength and anchorage