# A Review of the Network Arch Bridge
## 4 Research on Network Arch Bridges  
### Network Arch Bridges in Timber  
The first network arch in timber, Steien Bridge in Norway, was opened to traffic in 2016 [46, 47], and to this day, it is the longest NAB with gulam arches, with a span of 88.2 m. The other network arches in timber are also in Norway; two of the bridges are road bridges with spans of 70 m and 34 m, and one a footbridge with a 52 m span. Even though Steien Bridge was the first timber NAB to be built, researchers' interest into the use of gullam for network arches started years before. At the 8 th International Conference on Timber Engineering, TCTE, held in Lahti, Finland, in 2004, [PERSON] and [PERSON] presented two papers [46, 47] investigating an analysis of a network arch bridge with gullam arches with a span of 80 m. The conclusion in [46] was that if the overall stability of the system could be proven, the design could be viable. The deck solution adopted was presented in [47], having as its starting point the deck of a timber bridge already built. In ref. [47], a 3D model was investigated with respect to the in-plane and out-of-plane buckling analysis. The similarities and differences between the 2D analysis [46] and the 3D analysis were presented, and the overall conclusion was that the suggested design had sufficient stability properties [47].  
In 2012, a master's thesis was presented at Lund University investigating gullam arches [48]. The study had some limitations, but it proved again the possibility of using timber as the material of choice for the arch.  
One year later, in 2013, at the International Conference on Timber Bridges held in Las Vegas, Nevada, USA, the first network arch built with timber arches was presented [42], and [PERSON] and [PERSON] presented the first of a series of papers investigating gullam NABs. In ref. [49], a scaled laboratory model of a bridge was presented, together with measured and numerically obtained vibrational modes, in the vertical and horizontal directions, of the timber deck. [PERSON], under the supervision of Prof. [PERSON], continued her studies and received her PhD from the Norwegian University of Science and Technology in 2017. In her doctoral thesis, [PERSON] studied the case of an NAB with a light timber deck in transverse crossbeams [50] and introduced new hanger arrangements suitable for this type of bridge: the modified radial pattern and the \"spoked wheel configuration of hangers\". In the spoked configuration, there are two sets of inclined hangers that have a coinciding point of fastening on the arch, while their fastening point on the deck is in the same longitudinal plane but in different points on the crossbeam; that leads to the hangers being inclined in and out of the plane of the arch. She also made a scaled model of one of the proposed configurations that was tested and used to calibrate numerical models. The results of the study [49] were published in a series of papers [51, 52, 53, 54]. In ref. [55], the steps taken to choose the actual configuration of a network arch timber footbridge were presented, starting with the hanger configuration evaluated in the first step to other aspects involving the bridge design and erection. The case shown was the Vala Footbridge in Norway, with a span of 52.5 m, a width of 5.9 m and an arch rise of 8.4 m.  
Another group compared a gulam arch they developed with a similar steel arch to determine the environmental benefits of timber arches using life-cycle assessment [56]. With the only modification in the bridge being the arch, the timber arch had a reduction of CO2 emissions of 20% compared to a similar steel arch.  
The most recent study published on timber NABs is a master's thesis from Sweden [57] assessing the performance of timber arch footbridges with different hanger configurations.