Simulation of a bridge deck construction using precast beams supported in Virtual Reality technology

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1 Simulation of a bridge deck construction using precast beams supported in Virtual Reality technology Luís Filipe Duarte Viana Technical University of Lisbon IST. Dep. Civil Engineering and Architecture Abstract In the execution of bridge decks or viaducts, several construction methods are adopted. In this Thesis the construction methods most frequently applied in bridge decks using precast beams are presented. For the considered work a 4D (3D + time) geometric model was implemented in a virtual reality environment, which simulates the construction of a deck, allowing the visualization and interaction with the several steps and key elements intervening in this process. For the conception of the virtual model, an analysis of the construction components, steps inherent to the process and his sequence as well as the type e and operation mode of the required equipment was performed. Based on that analysis, a 3D geometric modeling of the different elements that characterize the construction place was performed and a coding sequence was established that could allow simulating the construction activity in an interactive way. The model is interactive, allowing the user to have access to the different phases of the constructive process, thus obtaining distinct visualizations both in time and space through the lifetime of the construction, improving that way the understanding of this constructive method. The model has a didactic character and may be used as a support in the formation of students and professionals in the study area of Bridges. Keywords: Bridges, construction methods, precast beams, Virtual Reality 1. Introduction In Civil Engineering there are several construction methods used in the execution of bridge decks. This work analyses several methods, with special focus in the constructive method used in bridge decks using precast beams. In the execution of Civil Engineering projects it is frequently used pre-fabricated elements, since they include several advantages in urban areas, works over railways and in general in areas where the placement of the falsework is difficult. By using pre-fabricated elements it allows a quicker and more economic construction and at the same time it avoids constrictions in important areas. The present work intends to contribute to the promotion of this construction methodology through the presentation of a visual simulation in 1

2 a virtual environment. For the execution of the virtual simulation the Virtual Reality (VR) technology was used. This technology presents advantages in the communication mode allowing the user to interact with the 4D model and thus allowing to access different visualization modes of the model both in time and space. 2. Deck using precast beams The pre-fabrication of works of art began in the 20 th century, in the 30 s and for many years it was limited to transversal section beams with little slender. These beams were used in small span bridges, between 15 to 20 meters and in his fabrication it was used pre-stressed steel wires. At the time the means of transportation and elevation were limited and it was difficult to obtain concretes with resistances superior to 35/40 Mpa [1]. In the 50 s this technique was used in a more intensive way, supported by the development of the means of transportation, elevation with higher capacity and also due to the advances in the pre-stressing technology [2]. The pre-fabrication in bridges presents several advantages, such as: good concrete quality of the pieces produced; economic advantages resulting in the utilization of optimized forms and pattern solutions with great repetition; reduction of the bottlenecking at the construction place and the shortage of construction deadlines; less formwork and shoring for the deck construction; bigger safety since the number of tasks in the construction place are reduced. The construction of the bridge deck using precast beams presents an equidistant distribution of the isolated elements, complemented with a slab responsible for the continuity of the deck surface. The precast beams are in general built with the same span length, with each span formed by several beams connected on top by an in situ concreted slab and transversely connected by cross beams located over the bridge supports. The slab can be executed in situ with the usage to falsework or by pre-slabs, which can improve the overall structural resistance or just be used as formwork during the concreting of the deck slab. The most common transversal sections in these types of beams are in the I (figure 1) or U shape. The shape of the section is determined by several constraints, such as: manufacturing procedure; the prestressing system utilized (pre-tensioning or post-tensioning); mean of transportation and assembly; construction method of the deck slab. Figure 1 - Transversal section of the bridge deck with I shaped beams [2]. 2

3 3. Constructive process of the deck with precast beams The constructive method applied to bridges with precast beams may present differences concerning the way of placing the precast beams, the type of solution adopted for the connection between elements and in the execution of the slabs. The first step consists in the placing of precast beams, which can be done using cranes (figure 2, a) or a launcher (figure 2, b). a) b) Figure 2 Placing of precast beams: a) using two cranes [2]; b) using a launcher [3] After placing the precast beams in their final position, several connection solutions can be used between these elements and the structure: Isostatic decks: formed by independent spans, separated by dilation joints, simply supported over the pillars by support apparatus; Isostatic decks with continuous slab: the precast beams are assembled over independent definitive supports, concreting afterwards the deck slab, which is the only element that establishes the continuity between spans; Continuous decks with reinforcement steel: the continuity is done by the placing of continuous reinforcement steel in the slab over the supports and of the concreting of the space between beams creating a cross beam; Continuous decks with connection executed outside the supports: various constraints may determine the execution of bridges with a span extension that makes unachievable its execution with precast beams of length equal to the span length. In these cases a connection between beams located outside the supports can be established, using prestressing, reinforcement passive steel, sheet metal or carbon based synthetic fibers; Continuous decks with monolithic connection between beams and pillars: this solution presents some economic advantages since it allows the suppression of support apparatus and a better usage of the available materials; Continuous decks using longitudinal pre-stressing: applying pre-stressing can be made using pre-tensioning, post-tensioning or by using both techniques. Using pre-tensioning has the advantage of guaranteeing bigger protection against the corrosion of the reinforcement 3

4 steel, offered by the concrete, when compared to the protection offered by the grout injection to the pre-stressing reinforcement steel using pre-tensioning. Once the continuity between spans is completed, the deck slab is concreted. For the slab there are two types of execution possible: With fixed falseworks at the precast beams: in this process metallic structures, usually tubular, are assembled and fixed to the beams flanges for formwork support. The concreting is done using traditional processes; Solution using pre-slabs: this method consists in substituting the formwork and support structure of the previous solution for reinforced or pre-stressed concrete slabs, with a width that usually varies from 6cm to 10cm. These pre-slabs may be used as lost formwork in the construction phase, which allows supporting only the concrete of the slab shape at the construction place. It can also be used as collaborating formwork, which has similarly the formwork function during the construction phase but also resistance functions during the services phase. 4. Geometrical modeling of the deck and equipment After analyzing the different types of decks and constructive methods, a frequent situation to be modulated in virtual space was selected. The deck is characterized by I shaped beams, hoisted by cranes and complemented with collaborating pre-slabs. Initially, a tridimensional geometrical modulation is performed in all elements necessary to realize the pretended visual simulation. The modulated example corresponds to a highway-profile bridge formed by five spans. The central spans have a 30 meter extension while the lateral spans have a 24 meter extension. The transversal section of the deck is characterized by eight I shaped precast beams for each span. Figure 3 Transversal section of the deck. 4

5 The tridimensional modeling is initiated with the generation of the scenery surrounding the construction place, followed by the modeling of several construction elements: pillars and abutments; tower staircases; work platforms; definitive and provisory support equipment; two cranes, needed to hoist the precast beams. Figure 4 shows the configuration of a generic precast beam transversal section used and the respective 3D model. From Figure 4 it can be observed: at the beam surface, the stirrups (in red) support the resistance and connection of different age concretes; the armors (in yellow) reinforce the connection rectification between precast beams; the suspension armor (in blue), necessary for the beam hoisting. Figure 4 Transversal section and precast beam model. Figure 5 illustrates the geometric model for the two pre-slab types used in the virtual model. The bracket pre-slab is placed in the lateral areas of the deck s transversal section and the central pre-slab placed between beams. Figure 5 Bracket and central pre-slab models Finally the cross beam is modulated, including the reinforcements and the formwork necessary for the concreting of the cross girder, the deck ordinary reinforcements and the slab concreting. In order to enhance the perception of reality, some elements of the finishing were also used. 5

6 5. Programming of the construction method in Virtual Reality Then, it was established the programming of the construction visual simulation using for that purpose a Virtual Reality (VR) informatics system called Eon Studio TM ( According to the programming approach followed, initially the surrounding scenery is inserted in the virtual space (Figure 6), which is composed by the land, secondary road, river, pillars and abutments. Figure 6 Beginning of the simulation and visualization of the surrounding scenery. The simulation of the construction activity continues with the insertion of complementary elements to the construction place (Figure 7): the tower staircase (to provide access to the top of the piers); the work platforms (which provides backup to the movement and execution of tasks by the workers). Figure 7 Visualization of the tower staircase and work platforms. 6

7 In the virtual space the positioning of the definitive support apparatus is simulated, followed by the positioning of the provisory supports on the top of the piers and abutments (Figure 8). Figure 8 Positioning of the definitive and provisory support apparatus. Each beam is elevated using two cranes situated in the construction site and then placed over the provisory support apparatus (Figure 9). Figure 9 Insertion of the precast beam over the provisory supports using two cranes. The simulation of the constructive process continues with the installation of the pre-slabs over the precast beams (Figure 10). Figure 10 Pre-slabs positioning. 7

8 The cross girder are executed after the slab have passed through the deform work process. The formwork of each cross beam was placed over the piers. In this programming phase it was verified that, due to the high number of pre-slab defined reinforcement, the camera movement in the virtual environment was very slow, mainly due to the heavy workload in the drawing files. Thus, in the next phases it was decided not to present the pre-slab reinforcement and the precast beams stirrups. Figure 11 illustrates the formwork and reinforcement placing in one of the cross girder. Afterwards, the reinforcement of the slab are placed and the slab concreting is initiated (Figure 11). Finally, the cross girders are concreted, making the structure continuous. After, the cross girders deform work is initiated as illustrated in Figure 11. Figure 11 Cross girder and slab visualization. 8

9 Once the deck construction is concluded, the supports are removed. The finishes are then executed on the deck s superior part, in order to allow vehicle circulation on the bridge (Figure 12). Figure 12 Removal of the support apparatus and complete deck visualization. At last, all tower staircases are removed as well as the work platforms. Figure 12 illustrates the superior and inferior deck visualization after the work completion. 6. Conclusions In this work some constructive processes were analyzed, related to bridge decks using precast beams and an interactive model that simulates the activity inherent to the execution of the deck was applied, using one of the most frequently deployed methods for this type of topology. For creation of the model a VR technology was used in order to create an interactive application. The Virtual Reality allows to create a constructive sequence both in time and space through the interaction with the 3D representative models of equipment and components, simulating the deck construction progression, which increments the overall understating of the construction process. The 4D virtual model (3D plus time) offers several advantages, allowing a more deep perception of the relationship between the construction components and the phasing of the work, leading to a better spatial understanding about the moving of the equipment and construction components positioning, than to the traditional graphic documentation drawings of the construction project, which are sometimes unclear and difficult to analyze. 9

10 References [1] J.N. Camara Pré-fabricação de Pontes e Viadutos, in Communication about Pre-fabricated Structures organized by Empresa Prefabricados Castelo, 18 January, 2011 [2] C. F. F. Sousa Continuidade estrutural em tabuleiros de pontes construídos com vigas pré-fabricadas. Soluções com ligação em betão armado. Dissertation for the Masters degree in Civil Engineering Structures, FEUP, [3] F. Leonhardt Basic Principles of the Construction of Concrete Bridges, Volume 6. Interciência, RJ, [4] A. J. Reis Bridges. Discipline notes. AEIST, 2006 [5] Stefan Woksepp - Virtual Reality in Construction - Tools, Methods and Processes, Phd Thesis, Sweeden, November, 2007 [6] A.Z. Sampaio, P.G.Henriques Virtual Reality technology applied on the visual simulation of construction activities. The Open Construction & Building Technology Journal, Mathew Honan, Editorial Director, Bentham Science Publishers Ltd., Vol. 2, pp7-14, [7] A. Z. Sampaio, P. G. Henriques, P. Studer, R. Luizi Interaction with virtual 3D models in order to visualize the construction processes of wall and a bridge. CC-2005, The tenth international Conference on Civil, Structural and Environmental Engineering Computing, B. H. V. Topping, Rome (Italy),