**3.1. Bridge deck composed of prefabricated beams**

The construction method for decks composed of prefabricated elements is frequently chosen in construction works over railway lines, and, in general, in areas where the placement of trusses is difficult. This is because these bridges offer several advantages in urban areas, as they allow quick and economical construction without generating significant local constraints [1]. In a bridge deck, the prefabricated beams present an equidistant distribution. The slab complemented "in situ" uses pre‐slabs as lost shuttering and as reinforcement during service, contributing to the structural strength of the deck. The most common cross‐sectional type of the prefabricated beams is an I‐shape.

The first step of the constructive method consists of placing the prefabricated beams on the pillars and can be carried out by means of cranes (**Figure 8**). The connection between the beams is made using pre‐slabs.

The 4D virtual model that was implemented presents the construction of a deck composed of 4 precast I‐beams, lifted by cranes onto the pillars and supplemented with composite pre‐slabs [13]. Initially, 3D geometric models of all the elements necessary to simulate the construction process were created, including the surroundings of the construction site, the pillars, the stair towers, the worker platforms, the provisional and the definitive supports and two cranes needed to lift the precast beams (**Figure 9**). The 3D model of a prefabricated beam includes reinforcements running out of the beam.

**Figure 8.** Placement of precast beams and pre‐slabs.

**Figure 9.** 3D models of beams, pillars, stair towers and worker platforms.

In order to establish the principal characteristics of each construction method, to define the type and quantity of the construction components needed to be modelled for the simulation of each construction work and, also, to perform the correct sequence of operations, the bibliographies concerning the three methodologies of bridge construction were consulted [12–14]. Based on this information, the 3D model of each type of bridge was generated and the corresponding sequence animation of each construction process was programmed. Because specialists in construction processes and bridge design were consulted in the implementation of these 4D models, the final product is efficient and accurate. Through direct interaction with the models, the progress of the actual construction process of the bridges can

The construction method for decks composed of prefabricated elements is frequently chosen in construction works over railway lines, and, in general, in areas where the placement of trusses is difficult. This is because these bridges offer several advantages in urban areas, as they allow quick and economical construction without generating significant local constraints [1]. In a bridge deck, the prefabricated beams present an equidistant distribution. The slab complemented "in situ" uses pre‐slabs as lost shuttering and as reinforcement during service, contributing to the structural strength of the deck. The most common cross‐sectional type of

The first step of the constructive method consists of placing the prefabricated beams on the pillars and can be carried out by means of cranes (**Figure 8**). The connection between the beams

The 4D virtual model that was implemented presents the construction of a deck composed of 4 precast I‐beams, lifted by cranes onto the pillars and supplemented with composite pre‐slabs [13]. Initially, 3D geometric models of all the elements necessary to simulate the construction process were created, including the surroundings of the construction site, the pillars, the stair towers, the worker platforms, the provisional and the definitive supports and two cranes needed to lift the precast beams (**Figure 9**). The 3D model of a prefabricated beam includes

be monitored.

64 Structural Bridge Engineering

**3.1. Bridge deck composed of prefabricated beams**

the prefabricated beams is an I‐shape.

reinforcements running out of the beam.

**Figure 8.** Placement of precast beams and pre‐slabs.

is made using pre‐slabs.

The virtual simulation of the construction activity starts with the presentation of the workplace, followed by the insertion of additional elements, such as the stair towers (for access to the top of the pillars) and the work platforms (which allow the workers to move around and complete their tasks). The sequences of activities in the virtual space are as follows (**Figure 10**):


**Figure 10.** Construction sequence deck composed with prefabricated beams.

After finalizing the construction of the deck, the provisional support devices are removed, and all complementary elements necessary for road traffic are placed above the deck. The complete bridge can now be observed from any point of view (**Figure 11**). The model allows the user to use the zoom sufficiently well in order to understand the final configuration of the bridge.

**Figure 11.** Views of the complete deck.

#### **3.2. Incremental launching method**

Another interactive model for the construction of bridge decks was created. The construction of bridge decks using the incremental launching method has existed from the 60s. This method consists of casting segments of the bridge deck in a provisional formwork, and then, each segment is pushed forward along the bridge axis. This method is used in viaducts crossing high valleys. The cross section of the bridge must have a constant height, and the most suitable type of cross section is the box girder.

Using the VR model is possible to follow the visual simulation of the construction sequence and to learn how the equipment is moved [15]. In order to perform correctly, the construction simulation activity every construction components and equipment was generated as 3D models (**Figure 12**), and the EON studio, a VR‐based software, was used [16].

The main steps of the construction process are as follows (**Figure 13**):


For the following segments, the process is identical. In the final phase of the construction the worksite yard is removed. Finally, all the finishing elements are positioned. Because consid‐ eration was given during its development, both to technical knowledge and to its use in education, in particular how and what to show, the 4D model could be an important teaching tool to illustrate bridge construction issues during training. The application is designed, not only as a learning tool, but also for use by professionals involved in the construction of these types of bridges. Note that a film was created showing the interaction with the VR/4D model (available in [14]).

**Figure 12.** 3D models of the construction elements and landscape.

**Figure 13.** Sequence of the incremental launching process.
