## 4 Conclusions  
In this paper, investigations of the torsional load-bearing behavior of hollow box girders--which exhibit unique design properties due to the new LT-bridge construction method--are presented. A comparison was made between a reference girder, based on a conventional bridge design, and a girder designed according to the newly developedbridge building method, incorporating vertical joints without longitudinal reinforcement in the webs directly at the connection to the pier segment. This comparison was made to distinguish the torsional load-bearing behavior of the novel bridge superstructure from that of conventional designs. Since the torsion tests found in the literature only consider hollow box girders without joints or girders in segmental construction with unreinforced joints, a new scientific investigation was necessary. The presented analyses are intended to lay the foundation for further application of the LT-bridge construction method. Within this paper, the experimental investigations were first presented before being verified using mathematical methods. The following conclusions were drawn from these investigations:  
* The reference test specimen TSRef failed at a torsional moment of 551 kNm and an associated bending moment of 96 kNm, with the decisive crack occurring at a distance of 1.20 m from the restraint. The computational analysis presented almost exact agreement with the experimental investigations. However, it was observed that the girder did not fail at the restraint, where the associated bending moment was significantly higher (i.e., 161 kNm). It can be assumed that the vertical compressive stresses in the web--resulting on the one hand from the simulated deflection force of the prestressing and, on the other hand, from the reaction forces resulting from the compression struts from the webs on the restraint--increase the torsional load-bearing capacity. * The test specimen TSjoint, which represents the bridge superstructure of the new bridge construction method, was able to withstand higher torsional loads (i.e., up to 681 kNm) than the reference girder. This was only due to the adapted reinforcement layout with additional bars in the corner areas of the deck and bottom slabs. The fact that no premature failure occurred, despite the unreinforced joints at the connection to the restraint, can again be attributed to the vertical compressive stresses in the joints and webs which, on the one hand, hinder crack opening due to torsion and, on the other hand, ensure a shorter anchorage length of the longitudinal reinforcement abutting the joint. * Further investigations will focus on the influence of the vertical compressive stresses. Thus, for the next test series, it is planned to move the joint into the span section. * Another important point to be analyzed in future experimental studies is the influence of post-tensioning on the torsional behavior of girders according to the LT-bridge construction method. Since this investigation is beyond the scope of this paper, the analysis of the effects of post-tensioning was excluded for the time being. However, experiments with longitudinal post-tensioning will be carried out in the near future. Development of new bridge construction method, J.K., F.U. and M.R. ; torsion tests on hollow box girders, test conceptualization, M.R., F.U. and J.K.; methodology, M.R. ; investigation, M.R. ; analysis, M.R. ; writing, M.R. ; supervision, J.K. All authors have read and agreed to the published version of the manuscript. This research was funded by FFG, grant number 880272. Open-access funding by TU Wien. Not applicable. The data that support the findings of this study are available from the corresponding author upon reasonable request.