Antiseismic stirrups

Stirrups constitute one of the most crucial factors affecting the quality and the earthquake resistant strength of buildings. Three are the major reliability parameters of stirrups:
a. The appropriate hooks at its free edges. Hooks are absolutely necessary for the proper behavior of stirrups especially during an intense seismic incident, when concrete spalling occurs, leaving hooks to be the only anchoring mechanism.

b. The pin diameter used for their bending. Stirrups must be bend in rolls with a diameter at least equal to 4Ø, i.e. for Ø 10 they must have a diameter greater or equal to D = 40 mm.

c. The distance between the legs of a closed stirrup. These must be placed no more than 200 mm apart from each other (e.g. a column 500x500 must have three stirrups at each layer).

A column with 10% fewer rebars has around 10% lower capacity strength. However, if we remove even a single intermediate stirrup, the capacity strength of that same column will be lowered even by 50%. This happens because the stirrup’s removal doubles the buckling length of the rebars previously enclosed by it.

In a seismic event, columns always fail in the same way:

a. When stirrups open, concrete disintegration in the column’s head or foot occurs.

b. Once the stirrups’ ends open, longitudinal reinforcement buckles and concrete disintegration take place.

Common stirrups are produced by hand; consequently their application has no limitations. Practically this means that they can be used in every type and size of columns.

Spiral form stirrups are produced by special CNC machines and they can be used in a wide range of column types and sizes. Practically the produced stirrups size depends on the machine’s largest dimension.

Robot stirrups are produced with the use of CNC machinery like the ones used for the production of spiral form stirrups. Their sole difference is that each complete circle produces one only individual stirrup.

SIDEFOR stirrups are produced as uniform stirrup cages ready for the positioning of the longitudinal reinforcement rebars. Like the “robot” stirrups, they are composed of individual stirrups (formed by one complete circle) welded to holding or sacrificial wires of a Ø5.5 diameter. Their main characteristic is their industrialised production, they are ready-to-use but they are available in specific shapes and dimensions.

ForSteel stirrups are exactly like the SIDEFOR stirrups; their only difference is that the holding wires are of a Ø6 diameter.

Cellular stirrups are closed section (no loose ends) stirrups that are composed by many simple cells or one composite cell. They can be assembled either industrially with the use of longitudinal holding wires or manually, as the common stirrups. These stirrups are patented technology of pi-SYSTEMS in most countries around the world. At present, cellular stirrups are in an experimental stage for their further development.