21.02: Strengthening of orthotropic steel decks using UHPC: UHPC‐concrete instead of asphalt layer for additional at least 50 years in service

Abstract

ABSTRACTOrthotropic steel bridge decks for slender and long spanned girder bridges were frequently built in the 60ties and 70ties of the last century in Europe. In the design of such bridge decks only the ultimate load carrying capacity was considered, without fatigue aspects. Due to the dramatic increase of heavy traffic in the European road network, sometimes the calculated remaining fatigue life is exhausted, after only 50 years of service life.In the paper the relevant results of a research project are presented, with the challenging aim to increase the service life of such orthotropic bridge decks to at least 50 years after strengthening. The research activities were based on a very slender orthotropic deck, with a slenderness of elr/tdp = 36 for the deck plate. Two significant details for fatigue of such a representative bridge deck have been analysed. Detail D1 represents the welded connection of the longitudinal rib to the deck plate and Detail D2 is the welded connection of the longitudinal rib to the cross girder. Extensive numerical studies were done for the strengthening solution with an UHPC‐concrete layer. First the present remaining service life was calculated using a finite element model of the steel deck. The beneficial effect of the asphalt layer is considered by an increased wheel contact area. The current fatigue load model FLM‐4 from the Eurocode with 5 lorry types and 3 different axle types was executed and the gross weight of each lorry type was adapted to weigh in motion measurements at an Austrian highway bridge. For determining the stress reduction factors in the details D1 and D2 after strengthening the finite element model had to be extended with the UHPC‐concrete layer. The concrete cracking was conservatively considered with an effective Young modulus Ec,eff = Ec/4. For both details at least 50 years in service can be guaranteed with an UHPC‐pavement that has a thickness of 80mm. Based on these studies full scale tests on an orthotropic deck specimen were done, including overload effects (increased axle loads) and severe temperature effects (simulation of a cold rain event on a very hot summer day) to stimulate concrete cracking. The full scale tests together with the numerical studies showed very good results with regard to the remaining fatigue life. Therefore in the near future a prototype application on an Austrian highway bridge is intended.