• Virve Juhola

Structural design and concrete detailing by BIM for Trimble’s new Finland offices

The HQ of AINS Group, a major Finnish engineering office, is conveniently located very close to the office campus construction site in Espoo where Trimble’s new premises will take place. The company is providing the main structural and concrete designs for the A, B and C buildings of the project including the parking facilities. Structural design is done by modeling with Tekla Structures software, the Model Sharing functionality of which has been found an effective way of working for the large team at AINS. The cast-in-place and reinforced structures are also being modeled in Tekla.

“We’ve involved a large team of some 15 engineers to do the structural design and detailing of Trimble’s new offices,” says structural engineer Ulla Hakulinen in charge of the building information model. “We started the design already in the autumn of 2018, and the project kicked off officially in the spring of 2019, at which point we already had a model visually very like the current one. Obviously we’ve added plenty of details and accuracy since then.”

BIM specialist Kristiina Sulankivi joined the project as a supporting professional in June and structural engineer Arttu Yli-Pietilä in October 2019. The project manager and lead engineer of the project is AINS Group’s head of industrial and business premises unit in the capital area, Jukka Oja-Lipasti.

“In June we learned that the anchor tenant of the property will be Trimble,” Sulankivi recalls. “We wanted to use the best and most advanced tools in the project and decided to update to Tekla Structures version 2018. The transition was smooth despite the risk of having to redo some of the drawings.”

From left to right: Sulankivi, Hakulinen and Yli-Pietilä

Model Sharing is the modern way of working that significantly boosts modeling

“The transition to the new software version was indeed smooth,” Hakulinen confirms. “At the same time, we took Tekla Model Sharing into use instead of the multiuser mode. It is now faster to save changes, because the model is saved on one’s hard drive and only the changes are synchronized with the other users. Modeling is done in the same way as before. We are able to continue work even if the internet or LAN connection is lost because the model can always be synchronized later.”

“Model Sharing is the modern way of working and a much more agile way of sharing information,” Sulankivi says. “It now feels old-fashioned to have to wait for a turn to save in the multiuser mode. Model sharing supports remote working, too. We have found the technology reliable to use.”

AINS engineers have been modeling CIP and reinforcing bars for quite a while now

“I’ve mostly worked on cast-in-place structures, hollow-core slabs for vaults, and raft foundations, for which the modeling of the reinforcing bars and producing the drawings has functioned well,” Yli-Pietilä says. “The foundations, the sub-floor slab, a couple of vaulted ceilings in the basement, one vehicle ramp and one set of stairs will all be cast in place.”

“We have not yet used the new Tekla Structures Rebar Set in a project, but we are very interested to make use of it,” Sulankivi says. “It’s a major step forward in modeling when these tools meet their purpose reliably. We participate in Trimble’s User Feedback program to test the properties that we believe will be useful in future projects.”

“CIP structures often involve particular geometry, so we face the limits of the modeling tools faster compared to square prefabricated units,” Hakulinen explains. “The structural engineer usually decides together with the contractor or at least has a say in the decision on whether to use precast units or to cast in place.”

“For example, we thought over whether to cast in place the reinforced concrete slabs because the contractors want to avoid that as far as possible,” Yli-Pietilä says. “In certain cases CIP is an easier alternative if the unit in question is difficult to deliver or install.”

Sharing the model helps coordinate the steel and concrete structures

The AINS Group structural engineering team works in cloce cooperation with the steel supplier Ruukki and steel detailer Sweco design teams to coordinate the frame of the building.

“There are plenty of issues to address and coordinate regarding the structures,” Yli-Pietilä says. “We meet every other week to discuss structural matters with the help of the model. Although this building is pretty streamlined, there is plenty of detailing to consider. We use the steel design as a reference imported in IFC and vice versa. Our challenge is that we each use different versions of Tekla Structures. Meanwhile the main contractor NCC’s team is using the models on site. Fortunately the construction site for this project is so close to our offices that we can drop by if questions arise.”

“In addition to our standard project bank Sokopro, models have been imported to the Trimble Connect service which also functions as a type of project bank,” Sulankivi says. “Any project party can view the model, too, in Trimble Connect. We still print drawings for the site, and they are used for inspection sign-offs as required by the building authority. At the moment, we have approximately 2,200 precast unit drawings and more than 5,000 precast units in the model, despite not having modeled everything yet.”

“At best, we can have the unit from the factory on site in 3 to 4 days,” Hakulinen estimates.

Changes during and after the project influence modeling and its level of detail

“We strive at designing the main structures and building components as accurately as possible, but if we know there are bound to be changes in the project, accurate detailing too early just translates into redundant work,” Yli-Pietilä explains. “Once the design has been finalized, the more accurate detailing we can produce, the less need there is for design during assembly, although there will always be some deflections found on site.”

“The level of detail required by the client complies with the Finnish standard YTV3/4,” Hakulinen says. “However, there are areas in the building, such as the roofs of the shafts, where the openings do not need to be designed in such detail and can be left for the construction team to decide because they do not affect the functionality or the look of the building.”

“In the beginning of the project, we needed to take into account the lower layers of soil and the municipal engineering, for example the bridge designed for the City of Espoo, in order to fit all structures on the lot,” Hakulinen says. “We were able to use the bridge model as a reference in IFC format, as well as the ArchiCAD model by Architects Cederqvist & Jäntti, the electrical design by Optiplan, and the HVAC design by Ramboll. There are dozens of professionals modeling this project and sharing IFC files back and forth.”

“Furthermore, we needed to take into account that the block will be extended and that they may build a shopping centre at the end of the C building later,” Hakulinen says. “The structures have been designed to allow annexing another building, and the facades can be removed if need be. This means we were not able to extend the foundations too far outside the walls of the building. We needed to decide at this early stage where to place the wall of the next building, and this defines the space available for the structures."

The project also includes three air-raid shelters, for which the structures, reinforcements and wall openings have all been modeled.

“All wall openings of the air-raid shelters include unusually shaped recesses for which we could not model reinforcing bars using the rebar tools but needed to use the standard Tekla tools of Tekla, with which it took us more time. It would be convenient to have custom components for wall openings of various size, for example,” Hakulinen says.

From left to right: lead structural engineer and project manager Jukka Oja-Lipasti; engineer Samuli Rytömaa, steel detailing; engineer Ilpo Lakka, detailing and design reviews; engineer Arttu Yli-Pietilä, exceptionally demanding structures, slabs and site inspections, senior engineer Kalevi Kauppinen, roofs and complementary structures and design reviews; engineer Petteri Koskela, exceptionally demanding structures; engineer Petteri Karjalainen, building stability and structural calculations; engineer Ulla Hakulinen, in charge of the structural model and general design, project engineer Rami Nordlund, precast concrete units; engineer Joonas Saukkonen, precast concrete units, steel staructures and exterior structures: engineer Mariia Ovanesova, precast concrete units, steel and exterior structures; engineering assistant Anne Wall, dimensional drawings and precast concrete units. Missing from the photo: engineer Risto Korhonen, air-raid shelters and inspections on site, and assistant engineer Juhan-Petteri Laakso, exceptionally demanding structures.