Can you explain to the visitors what your patent relates to?

Our patent The strenghening of a stress ribbon by external prestressing is Czech Patent No. 308602. It is a method of strengthening a bridge structure made of a stress ribbon by external prestressing with spatial crossing of cables at the abutments. It is assumed that the external prestressing placed under the existing structure will create a "safety net" which, in the case of failure of the existing structure, will significantly increase its ductility, catch the fragments of the structure and prevent brittle fracture due to corrosion damage to the original prestressing reinforcement. The patented system ensures that the result will be only excessive deformation of the structure, not its collapse.

Where did you use the patent?

The technical solution was developed and verified on the construction of a suspension footbridge over the Morava River in Kroměříž, which was strengthened and renovated between 2019 and 2021. Considering three other similar constructions built in the Czech Republic, it can be assumed that it will be used again on two or three other constructions of this type in the Czech Republic. This assumption is supported by the performed diagnostics of stress ribbon structures in the Czech Republic with similar conclusions as in the case of the bridge in Kroměříž. Described patent solution is currently being used in a project of strengthening of the footbridge over the Ohře River in Radonice nad Ohří.

What is the essence of it?

The strengthening of the stress ribbon structure by external pretension with crossing at the abutments involves the installation of new external cables under the existing bridge structure. The external prestressing may consist of two cables, one on each side of the cross-section of the structure. The geometry of the external cables corresponds to a second degree parabola with a span and sag equivalent to the strengthened structure. The height of the fixture for the installation of the external tendons corresponds to the distance from the external cables to the existing structure. It is due to different curvature of the parabola of the stress ribbon structure and the external tendons. The new prestressing cable system consists of cables primarily protected by a passivation grease with a plastic cover, which are secondarily protected by a cover made of corrosion-resistant metal. The space between the cover and the individual strands is filled with self-compacting micro-concrete. The original abutments are drilled through with cable ducts at the locations of the newly designed cables. The diameter of the holes is determined based on the quantity of the new external prestress. The lengths of the designed ducts should be kept to a minimum with respect to the reinforcement of the original abutments. This is accomplished by an appropriate arrangement of external cables with crossing each other in front of the abutments. The crossing of the cables is realized by using a spatial saddle made of concrete, which keeps the radial forces from pretension by its compressive capacity. The crossing also ensures that the radial forces from the outer cables are directed into the mass of the substructure as they arc around the abutment and that both cables have the same centre of gravity at the crossing point.

Can the patent be used elsewhere?

There are a great number of similar stress ribbon structure in the world. Several structures have been built in the USA, Canada, Portugal, Great Britain, Japan, etc. Therefore, further possible applications abroad can be expected. To establish collaboration and offer the patented solution abroad is the next challenge of the research team. This statement can be supported by the collaboration on the design of these constructions in the USA and Canada, in which the research team has already actively participated.

The questions were answered by the co-author of the patent doc. Ing. Ladislav Klusáček, CSc.