# A Review of the Network Arch Bridge
## 5 Conclusions  
This paper provides a review of the literature published on network arch bridges and provides insight into the evolution of the network arch from the middle of the last century to the present day. An extensive review of the literature on the subject was presented. The purpose of this paper was to answer whether the NAB is a suitable structure for all ranges of spans, from small to very large ones, and whether it could have a beneficial impact in the construction industry from an environmental perspective. The main conclusions of this study can be formulated as follows:  
* The network arches had spans varying from 30 m up to 380 m for bridges already built and 420 m for a bridge under construction at the time; the already-built structures prove the reliability of network arches for spans varying from small to very large ones. * The discussion at this point could be whether the NAB is still a good idea for very small spans. No published research was found to compare the overall cost of the NAB to another type of structure in terms of materials and overall price of the bridge for spans smaller than 100 m; however, the experience of the authors with a 36 m NAB built in Romania, the Unirii Bridge at Maieru, is that it was less costly than a competing alternative. * Numerous published papers show a reduction in the materials used for 100 m network arches compared to arches with vertical hangers; other research published and structures already open to traffic prove the possibility of using sustainable materials for the arches or the hangers, such as timber of carbon fiber reinforced plastic. Both arguments demonstrate the potential the structural system has to align the bridge industry with the policy of net-zero CO\({}_{2}\) emissions by 2050, at least in part. * Some of the structures mentioned throughout the paper, including the Sixth Street Viaduct in Los Angeles, the Perry Bridge in New Zealand or the River Irwell Crossing in the United Kingdom showcase the possibility of combining esthetic requirements with structural efficiency. The limitations of this review include the fact that no insight into the technological challenges of erecting a network arch bridge were given. The authors feel that many details on the technology have been given in the papers published by Prof. [PERSON] and papers presenting different structures. We decided not to include this aspect in the present review. Future research directions can be explored when discussing the network arch. Looking at the Sixth Street Viaduct in Los Angeles, a network arch with the arches slightly inclined outward of the plane of symmetry, the bridge can be seen as an evolution of the structural form toward a butterfly arch bridge; further research into the behavior of such a structural system should be considered. Stability analyses were performed for different structures, but an extension of the buckling design procedure from EC3 for arches with vertical hangers to network arches is needed. Extended research into the behavior of small span NABs with a reduced number of hangers can be considered. The authors are already looking into it. For pedestrian network arch bridges, one interesting finding worth investigating in the future is that the rise-to-span ratio should be larger, 0.2 to 0.3 instead of 0.15 to 0.2. No definitive answer has been obtained yet as to whether a change in curvature at the springs of the arch can reduce the overall cost of the bridge or not. Using third-order analysis, a group of researchers found that additional tension in the hangers, above the force from self-tensioning, decreases the value of the critical load factor. Such a finding is also worth investigating in the future. As can be inferred from the points mentioned above, the research and development of the network arch is still ongoing.