Especially (older) city tunnels which were built using a cut and cover method have been constructed by means of steel and/or concrete roof beams with a concrete slab or a composite steel/concrete slab on top of the beams. Quite frequently the space between the beams is utilised to install pipes, cable trays and other services. In case of a refurbishment of such a tunnel the protective membrane system is both technically and commercially the most feasible option.

The protective membrane system consists out of a steel frame which is suspended from the load bearing structure or, depending on the span of the ceiling, can be supported along the walls only.

The designer of the suspended steel frame has two options for the horizontal load bearing members:
1. the use of C, Z or omega profiles
2. the use of a trapezoidal steel decking,

Typically the design of such a suspended steel frame is conducted by a local structural engineer.

From below the PROMATECT^®- T boards will be screwed to the suspended steel frame, either the profiles or the trapezoidal steel sheets.

Further technical information is available at the Promat technical department.