## 4 Discussion--Challenges and Opportunities for the Bridges of Peru
### Challenges in New Digital Technology Tools to Support Bridge Construction  
Currently, a series of digital tools are being implemented in Peru to improve aspects of efficiency and precision in bridge infrastructure construction activities. Thus, in many projects, the installation of prefabricated or modular structural elements in both concrete and steel is being implemented. In the case of concrete, prestressed concrete beams or slabs and post-tensioned concrete, which allows for longer-span beams reaching 40 m, are used. Regarding steel elements, some sections or segments are part of the deck of cable-stayed bridges or suspension bridges, where 10 m long units can be assembled and mounted as modular pieces. On the other hand, there is the use of BIM (Building Information Modeling), which consists of a 5D virtual model of the bridge infrastructure to be built, studying the progress of the project both on the spatial scale and on the temporal scale. A virtual three-dimensional model is generated with all the structural elements and their environment, also coupling a fourth 1D dimension with the construction processes and programming over time, and finally adding a fifth 1D dimension by adding construction costs and expenses to the model [19, 20, 21]. Finally, it is important to mention the use of UAVs or drones to support the construction aspects of bridge projects, where it is possible to (i) make topographic surveys of the study sector using LiDAR systems, (ii) take photographs of the construction process and analyze its evolution over time, generating a 3D model using photogrammetry, and (iii) generate heat maps of the built infrastructure and identify areas of failure or weakness of sensitive or vulnerable structural elements through the use of thermal cameras. The use of UAVs allows for significant time savings in generating 3D models and avoids the risk of personnel accidents when accessing complex construction conditions [22, 23, 24, 25, 26]. The first example is the Nanay Cable-Stayed Bridge Project, where the BIM (Building Information Modeling) and DfMA (Design for Manufacturing and Assembly) methodologies were implemented. The application of these methodologies in this project was a cutting-edge milestone in Peru, since it was the first time that a large-scale infrastructure project had implemented this new construction concept in the country. The lack of significant sources of aggregates for concrete in the project location (jungle of Peru) was an important factor in selecting composite \"steel-concrete\" solutions, allowing the designer to minimize the use of concrete. In this sense, a composite cable-stayed bridge was the concept with a competitive edge solution [27, 28]. The Nanay cable-stayed bridge was designed to be built using successive cantilevers with 10 m segments, symmetrically, on each side of each of the pylons. The project considered that the assembly of the steel structure was carried out using mobile lifting systems. Each steel structure module is made up of two main lateral plate girder beams of 1.5 m height and an interior central beam of 0.3 m height, transverse beams spaced every 3.5 m, stiffeners, bolts and shear connectors. On the other hand, the deck slab was designed to be made from reinforced concrete, which is made up of prefabricated panels that are monolithically joined together by means of concrete joining strips built in situ. In addition, the substructure of the Nanay bridge is made up of an abutment and a pylon on each side of the Nanay River. The foundation is deep, using piles dug 60 m deep and with a diameter of 2 m. Finally, the bridge accesses, both on the left and right banks, are of a frame type with reinforced concrete columns and a crossbeam. For the execution of the piles, an operations platform was previously prepared, which had to be 2 m above the water table or the maximum water level for the construction period. The construction of the piles was not carried out within the Nanay River. To achieve this, the span and total length of the bridge were increased.