Procedure to investigate the suitability of safety barriers of containment level H4b on bridge. Part 1- Procedure to investigate the suitability of safety barriers of containment level H4b on bridges. The protective devices are of special importance when equipping bridge structures if a possible truck accident can pose a risk to passers-by. Modern protective devices quickly reach their limits in situations where accidents occur, involving very heavy trucks and where the accident situation is unfavourable. The basic requirement for the use of protective devices in Germany is a positive test in accordance with DIN EN 1317. Furthermore, the forces of a protective device which are applied to the dome and the supporting support structure need to be known for both new bridges and when carrying out bridge repairs so that a structural design can be carried out in an economically viable but nevertheless safe manner. The aim of this research project is the testing of protective devices on bridges which have a high containment capacity pursuant to DIN EN 1317 and thereby determine the applied forces. At the same time, knowledge should be gained of the behaviour of the protective devices with a very high containment capacity in situations where space is restricted. In the scope of this research project, six protective devices have provided proof of their serviceability pursuant to DIN EN 1317. The 27 collision tests which were carried out on 14 systems proved that the development of protective devices with a very high containment capacity and restricted range of action is difficult. Should there be additional boundary conditions e.g. noise abatement measures of continuation along the route, it becomes apparent that none of the tested systems that exist today can be put to universal use. On the contrary, it has to be determined in each individual case, whether a system can be used and if so, which one. With this in mind, it is recommended that a close coordination of the bridge planning is carried out together with the route planning in order to obtain solutions which make sense and are safe for traffic. If possible, planning of a bridge should also take the protective device and all of the other boundary conditions into account. A subsequent separate planning of the protective device or even the taking of it into account as the final structural element can result in a suitable protective device not being available. The force measurements are based on individual events but nevertheless reproduce the action variables that are applied during the collision process and therefore confirm the previous findings. The measured values serve as a basis for the working on recommendations concerning the actions for which the bridges are to be measured, on which the protective devices which are the subject of discussion here, are to be installed. The variable of the values shows that the actions with H4b systems are up to 6 times higher than the current load approach in the DIN technical report 101 “Actions”, version from 2003. It was therefore possible to acquire important benchmarks for the future measuring of new bridges or the re-equipping of existing ones. The results have already been taken into account in the extrapolation of the new DIN technical report from 2009. The tested protective devices which are presented here meet the containment capacity and passenger protection requirements, in addition to them also including force measurements. Further developments which also meet additional requirements such as are included in this report would have been desirable. As the traffic safety requirements do not remain the same, but adapt in accordance with the development requirements, it will continue to be the case in the future that a further development of the protective devices with a very high containment capacity will be necessary. The demands placed on the containment capacity increase, if heavy vehicles with higher loads are to be driven on the roads for example. Part 2 - Test results and evaluation of safety of containment level H4b on bridges. The falling of trucks off bridges can especially be hazardous should persons frequently be underneath the bridge. The primary protective device which serves to prevent falling that is used in Germany is the simple spaced safety barrier with a post clearance of 1.33m (SSSB 1.33) with banister and a galvanized steel cable in the handrail, on the basis of which the safety barrier and the banister jointly achieve the containment capacity. Concrete protective walls are also used. The SSSB 1.33 with banister has been subjected to a collision test which was carried out by the BASt in accordance with the latest requirements of the new European DIN EN 1317 standard “vehicle restraint systems on roads”. The system has proven that it is capable of preventing heavy vehicles with a maximum weight of around 13 tonnes from falling off bridges. This protective device is constructed in such a manner that it is also able to restrain cars without difficulty and turn the vehicle back without placing the passengers at any considerable risk. These protective devices quickly reach their limits however should accidents occur involving very heavy trucks and if the accident situation should be unfavourable. This is why the BASt has cooperated with the BMVBS in order to carry out tests with the aim of providing protective devices which are also able to prevent very heavy trucks from falling from bridges. The essential aspects here were the stipulation of technical boundary conditions for the development of protective devices by the industry and the development of suitable test procedures which are suitable for ensuring the usability on German bridge structures. In the scope of this project, it was possible to prove in collision tests for the first time that protective devices which achieved the highest containment level as defined in DIN EN 1317 for very heavy trucks can be installed on bridge structures in Germany without there being any need to fear unacceptable damage being caused to the bridge domes. It was also possible to measure the forces which act on the structure in the event of a collision occurring. It is the case that a collision test is only an individual result but these measurements show the extent of the actions that are applied during the collision process. The measured values served as the basis for the making of a recommendation for the determination of the actions (forces and moments) which is necessary if protective devices with a very high containment capacity are to be installed on the structure. The exact values of the determined action variables have specific validity for the tested protective device. The value variables can therefore be transferred to other protective devices which have a very high containment capacity rate on bridges. The recommendation provides for actions which are around 3-4 times higher than the current load base specified in DIN technical report 101 “Actions”. (Author/publisher)
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