An I-girder (ISMB) in scaffolding and shuttering is a steel beam with an I-shaped cross-section used as a horizontal support to carry the load of shuttering and fresh concrete. It is placed on top of scaffold standards, props, or trestles, and the formwork panels rest directly on it. The I-shaped profile provides very high bending resistance and rigidity, allowing it to span longer distances between supports without sagging, even under heavy loads.