Implementation of BIM for Bridge Design A Case Study

Transcription

1 Implementation of BIM for Bridge Design A Case Study Yi-Min Chen 1, Chih-Wen Chen 2 and Shang-Hsien Hsieh 3 1 Engineer, BIM Center, Sinotech Engineering Consultants, LTD., Taipei, Taiwan 2 Manager, BIM Center, Sinotech Engineering Consultants, LTD., Taipei, Taiwan 3 Professor, Department of Civil Engineering, National Taiwan University, Taipei, Taiwan ABSTRACT: To date, in building construction industry, BIM (Building Information Modeling) is already a mature methodology and technology. However, it is not yet the case in design and construction of civil infrastructure, including bridge design, due to the lack of information modeling standards and difficulties in handling irregular shapes and complex geometries of the bridges. This study investigates how to use integrated CAD/BIM approaches to model a reinforced concrete extradosed bridge with rice-shape towers in design and then to retrieve all required information from the BIM model to facilitate bridge construction. INTRODUCTION During the past few years, Building Information Modeling (BIM) has already become the most popular technology in the AEC industry. It not only enhances the quality of communication between different stakeholders throughout construction lifecycle but also reduces the time and the labor by advancing visualization from 2D drawings into 3D parametric models. The more times design requirements change, the more significant benefits we can get from BIM applications. Owners, designers and contractors are all fascinated and eager to implement BIM into their business processes to improve the workflow and quality of construction. Taiwan s government has also noticed the trend and its Public Construction Commission, Executive Yuan is now asking for BIM implementation in large public construction projects (i.e. over NT$ 200 millions) in Taiwan. However, current cases that use BIM mostly concentrate on building construction projects and only few of them are civil infrastructure cases. The reasons for this are mainly the following. First, unlike building structures, information modeling standards for civil infrastructure are still

2 lacking. Second, the most common BIM modeling tools currently support only components on a certain plane or floor but there is usually no fixed plane for placing model objects in civil infrastructure cases. Although we may work around the problem by placing all model objects manually, the result is lack of flexibility for adapting future model changes. When there is a need to change design requirements, the model must be rebuilt instead of just being modified. The solution should be to use parametric objects which can be modified by simply adjusting the parameters to accommodate changes in design requirements. Since it is much easier to create parametric geometry in CAD than in BIM software, we would use this feature to handle components with complex shapes in CAD. Other components will still be built in BIM software. Finally, we coordinate all model components in BIM software and extract required information for construction. In the case study presented here, this integrated CAD/BIM approach was used to model a parametric reinforced extradosed bridge with information to facilitate bridge construction. MODELING WITH COMPONENT DECOMPOSING METHOD To model a parametric component, this study uses a component decomposing method in CAD. Take a rectangle column as an example, the column is essentially a cuboid which could be modeled by extruding a rectangle along the path of its height, or more specifically, along a curve which radius is infinite large. In other words, the rectangle and the curve could be seen as the input objects for defining the cuboid. Also, the rectangle and the curve can be further decomposed into lines and points placed on certain planes (See FIG. 1). Once again, the lines and points can be treated as the input objects for defining the rectangle and the curve that in turn are the input objects for the cuboid. Different kinds of cuboids can then be created by modifying these input objects that serve as the parameters of the cuboid. The same method is applied to the construction of all kinds of parametric components including civil infrastructure components by decomposing components into proper planes, curves and points as parameters.

3 FIG. 1 Component decomposing method A CASE STUDY ON THE BAIMI BRIDGE Baimi Bridge (See FIG. 2) is a reinforced extradosed bridge located in Su'ao, eastern Taiwan. It is part of the ongoing Suhua Highway Improvement Project (or simply called the Suhuagai project), which is for major improvement of dangerous sections of Suhua Highway where only two lanes are available with low speed limit. The Suhuagai project is divided into 3 parts. The first part is from Su'ao to Dong'ao, 9.7 kilometers in length; the second part is from Nan'ao to Heping, with 20 kilometers in length; and the last part is from Heping to Daqingshui, with 9.1 kilometers in length. The Baimi bridge is in the first part, starting from the mileage at 3k+320m to that at 3k+660m and has two (2) pylons (or towers), which are labeled P38 and P39, supported by 48 cables in total. The length of the central span between P38 to P39 is 150 meters long; each of the two side spans is 95 meters long; so the total length of the bridge is 340 meters. The total width of the bridge roadway is 18.5 meters. The cross-section of box girder is trapezoidal and hollow (see Fig. 3). The bridge is notable for the twin rice-shape pylons. The design inspiration comes from the literal meaning of the place, named "white rice" in Chinese (pronounced as Baimi in Mandarin). The bridge is expected to become the landmark of the Baimi Village once the project is completed. Because the horizontal alignment is composed of one transition curve (or called spiral) and one circular curve with changing elevation of the vertical alignment, each cable has different angles in horizontal and

4 vertical directions, making it difficult to calculate the positions of cables. Besides, we also would like to know the accurate rebar weights in the two pylons for estimating the cost for construction. Therefore, the solution used in this case study is to create the bridge BIM model of actual size and then retrieve the information from the model to assist construction tasks. The process is described later. FIG. 2 The Baimi bridge Major BIM Goals Two goals for BIM applications (or uses) are set in this case study: 1. Calculating positions of all 48 cables. 2. Estimating rebar weights of the two pylons. CAD/BIM Tools In this study, we choose Tekla Structures and Rhino plus Grasshopper as the modeling tools. Tekla Structures is known as a good BIM modeling tool for structural engineering, especially for structural detailing. Rhino plus Grasshopper is known for modeling parametric precise freeform surfaces which use NURBS (Non-uniform rational B-spline) mathematical representation of 3D geometry. In this case study, Tekla Structures is used to create structural detailing components including bolts, stiffeners, and rebars. Rhino plus Grasshopper is used to create the trapezoidal box girder and the related parts of the girder, including barriers, guardrails, asphalt concrete pavement, and cables. Bridge Girder Modeling To model the trapezoidal box girder parametrically, we use the decomposing method mentioned earlier. The modeling steps are described below: 1. Divide the alignment by specific distance depending on the need of the modeling precision to get all split points and tangent vectors. The smaller distance we set,

5 the more precise model we get. 2. Create normal planes by using spilt points as the origins and tangent vectors as the normal vectors of the normal planes. 3. Rotate the normal planes by aligning the X-axis with the horizontal plane. 4. Create SOL (setting out line), PG (profile grade) and other vertices in terms of the design requirements to construct the cross-sections (see FIG. 3). 5. Align each cross-section to the corresponding normal plane along the alignment (see FIG. 4). 6. Create trapezoidal box girder by lofting all cross-sections along the alignment. In this case study, alignment, division spacing, slopes, cross-section shapes are the input objects for building the box girder. By modifying or adjusting the input objects, we could get different modeling results, e.g. replacing the trapezoidal cross-section with a rectangle cross-section will result in a rectangular box girder. FIG. 3 Vertices on the cross-section of the box girder

6 FIG. 4 Align each cross-section to the corresponding normal plane Rebar Modeling Modeling rebars in the rice-shape pylons is not an easy task because the cross-sections of the pylon vary in shape while the elevation changes. This means that we cannot just copy and paste one stirrup type, but hundreds of stirrup types instead, to different locations. The solution used in this study is described as follows: 1. Export the pylons as meshes. 2. Use Rhino to open those meshes. Extract edges of the pylons determined by the shape of the stirrup (see FIG. 5). 3. Divide edges by rebar spacing to get vertices for the paths of stirrups. 4. Draw stirrups by connecting corresponding vertices in Tekla Structures. 5. Divide the inner edge and the outer edge of the pylon by specific vertical distance depending on the need of modeling precision to get the split points (see FIG. 6). 6. Draw lines by connecting the split points at the same elevation.

7 7. Divide lines according to the need of the longitudinal rebar number. 8. Draw longitudinal rebars by connecting the vertices from step Set all attributes, including the hook angle, bend diameter, cover, bar diameter, hook length and grade, to create stirrups of the exact size (see FIG. 7). FIG. 5 Process for creating stirrups of pylon FIG. 6 Process for creating longitudinal rebars of pylon

8 FIG. 7 Modeling of rebars in pylon using Tekla Structures CONCLUSIONS After the BIM model is built, the information needed can be retrieved from the model. The definition of the angles is shown in FIG. 8. There are 3 angles to be calculated in this case study. α 1 is the angle between the cable and the normal plane of the horizontal alignment of the bridge at the point where the pylon locates. α 2 is the angle between the cable and the normal plane of the alignment at the joint position. θ is the angle between horizontal plane and the cable. L and R mean the left-hand side and the right-hand side, respectively, when one drives along the alignment direction. Cables from No. 61 to No. 72 are with the pylon at P38, and the rest are with the pylon at P39. The results are shown in Table 1 and Table 2. FIG. 8 Definition of cable angles

9 Table 1 Angles retrieved from the BIM model (P38) P38 No θl αl αl θr αr αr Table 2 Angles retrieved from the BIM model (P39) P39 No θl αl αl θr αr αr Table. 3 shows the amount of rebars placed in the pylon at P38 (same amount in the pylon at No. 39). The total rebar weight is tons (see Table 3 for more details) which does not include the weight of the rebar splicing and waste from cutting. This weight can be regarded the minimum weight of actual rebar usage that the construction team can use for cost estimation. Table. 3 The amount of rebars in pylon Rod Number #14 #10 #6 #5 Sum Weight(t) % 65.3% 0.2% 33.4% 1.1% -- The case study shows the benefit of using BIM in the bridge design phase. That is the information needed for construction is usually difficult to obtain from 2D drawings, such as the spatial positions of the cables and the total weight of rebar, but can be retrieved more easily from the BIM model. However, when compared to

10 building construction cases, application of BIM to civil infrastructure cases currently would require well organized preparation and planning, high-level modeling skill (such as parametric modeling with the component decomposing method) and even programming and scripting skills. ACKNOWLEDGEMENT Our special thanks to Shara Tsai (Senior Engineer in Sinotech Engineering Consultant, LTD) and Cheng-Chong, Wang (Project Manager of Baimi Bridge Construction Project) for the great support on this research. REFERENCES Eastman, C. M. (2011). BIM handbook: A guide to building information modeling for owners, managers, designers, engineers and contractors. Hoboken, NJ: Wiley. "Grasshopper." - Algorithmic Modeling for Rhino( "Tekla Open API: Connect Applications to Tekla Structures." (