Øystein Ulvestad is a Norwegian structural engineer and BIM developer who uses Tekla Structures to model bridges in 3D. We spoke to him about the benefits of modeling in Tekla during the design phase of a bridge.
Ulvestad has been working with Tekla software for almost 20 years. In the first part of his career, he used it to design steel trusses, connections and other structures for industrial buildings. He then joined an infrastructure group that was using Tekla Structures to make concrete bridges. Since then, Ulvestad has designed around 30 bridges with the software. Today, he leads the bridge design team at Sweco, the engineering consultancy behind the Randselva Bridge project - winner of the 2020 Tekla Global BIM Awards. Randselva is a 634-meter-long cantilever concrete bridge built exclusively on the basis of BIM models, without drawings.
Ulvestad and his team use Tekla Structures together with the Grasshopper visual programming language and the RHINOCEROS CAD application. Structural engineers generally use Grasshopper for parametric modeling: a digital practice that uses rules and parameters to create complex geometries. The bridge geometry is first created in Grasshopper and Rhino, before the design is imported into Tekla Structures. Here the attributes are added, and the design is optimized. Parameter changes made in Grasshopper can be immediately reflected in Tekla Structures.
"Tekla works very well in combination with parametric design," says Ulvestad. "Your design becomes much more flexible, and human error can be eliminated. What's more, the parametric script is reusable."
Patented Tekla concreting technology
Ulvestad says that before the advent of drawing-free designs, a bridge the size of the Randselva would normally have required the production of around 250 traditional drawings. When the transfer of information is based on a BIM model, then it is very important to be able to model concrete objects with millimeter precision. Tekla Structures achieves this by intelligently merging concrete elements of the same type to create concrete objects. Any overlapping volume is eliminated, and properties can be assigned to this new concrete object, making planning much easier than it used to be. This is one of the many patented features in Tekla.
"The bridge I'm working on at the moment has more than 200 concreting objects," he says. "When you're building something this big, it's not feasible or possible to do all the concreting at the same time. So you need to divide up your project and pour in phases. That's why we model all the concrete bridges we design in Tekla." Tekla Structures is a fantastic tool for this, because merging and splitting concrete objects is easy," says Ulvestad. "Tekla also visualizes the concreting phases - or construction sequences - very well. This is vital in large, complex structures like bridges. It makes life on the construction site much easier too, as the builders then have the exact quantities and dimensions of concrete and reinforcement for all the pours."
Ulvestad says that being able to visualize the geometry of the concrete at the start of the project allows him to design and detail the structure much more accurately.
"On complex projects, we work together with the contractor to find out which machines and forms will be used for specific pours, and we factor this into our design tool," he says. "The concreting geometry often dictates the shape of the reinforcement, so concreting modeling is a big advantage when you're looking to get more accurate reinforcement designs."
Made for parametric design
Ulvestad says that Tekla's automatic concreting fusion feature is particularly useful when designing concrete bridge abutments and hammers - both of which are modeled using a number of different fusion shapes.
"When it comes to concreting and its complexity, cantilever sequences are always difficult to model," he says. "You have walls, slabs, indents and bubbles. The different elements are modeled separately, but Tekla Structures merges them into a single concrete object. "Designing a concrete bridge is a 200,000-piece puzzle that you can't predict the end result of when you first start producing it," says Ulvestad. "No two concrete phases are alike, and modeling them without parametric design would be almost impossible. "Fortunately, the integration between Grasshopper, Rhino and Tekla frameworks is very well developed, so we had very few problems modeling unique concreting phases and designs. Tekla's ability to merge elements sharing the same concrete phase property gives us flexibility. Some elements can be designed in Grasshopper, some within Tekla, but they can all merge to form a single pour object. Tekla is easy to work with."
Tekla Structures was instrumental for Ulvestad and his team in designing the Randselva Bridge without any drawings. Based on a concrete beam design using the balanced cantilever method, the bridge rests on six piers ranging from five to 42 meters. Around 200,000 reinforcements are inside the concrete added in 200 separate concreting phases.
