What if the construction of a 10-story hotel building could now be completed in less than 5 days? With the current deadlines known in the construction sector, this new possibility is more than interesting. When a structural researcher joins forces with a company that specializes in modular construction, nothing less than the future of construction is redefined.
Modular construction projects have been around for several years, mainly for low-rise buildings: schools, hospitals, mining camps, homes. But a new element has recently entered the equation: steel. Existing modular buildings are mostly wooden. Being able to build a ten-story modular structure that can withstand different loads, such as wind and earthquakes, required adaptations at the structural level. Charles-Philippe Lamarche, professor in the Department of Civil and Building Engineering, has worked for the past four years with his team, together with RCM Solutions Modulaires, to deliver the tallest modular steel structure in Canada. : the Holiday Inn of Gatineau. A 12-story structure.
Steel makes it possible to raise the highest modular structures, mainly thanks to its very high strength. The innovation is mainly in the intermodular connections, which allow the modules to fit together perfectly. Connectivity is ensured by a male-female mechanism that connects the column segments of the stacked modules. Like Lego blocks.
Ehsan Bazarchi, a doctoral student under Charles-Philippe and Professor Nathalie Roy, won the award for best presentation last May as part of the Center d’études interuniversitaire desstructures sous charges (CEISCE) annual conference at Polytechnique Montréal, for his presentation entitled “Canada’s Tallest Modular Building: Developing Structural Concepts to Resist Seismic, Wind and Transport Loads. »
The benefits of modules
Another innovative aspect that was presented in the research project is that, instead of transporting modules of around 30 feet, as is often the case, the research group and the company designed larger modules, the maximum length that our roads can travel: 66 feet ! Unprecedented in the industry. The participation of Mr. Serge Parent, associate professor in the Department of Civil Engineering and Building Engineering, was an important asset at this stage of the project. Each module has two hotel rooms with bathroom and hallway, and can be installed in less than 20 minutes. The idea is to be able to reduce the hours worked on site as much as possible and to be able to assemble the structure very quickly after delivery of the modules.
Still in the example of the hotel, the internal finishing of the modules is already done. Beds, coffee machines, tables, toilets, bathtubs, showers, counters, everything is already in place. And there are several other advantages in such a modular structure. As modules are built directly at the factory and then transported to construction sites, less labor is required, the environment is better controlled, products are standardized and construction time is reduced. The construction of the building is done much faster once on site, and there is much less waste produced, less noise pollution around and less road traffic nearby.
Concrete in some connections
In the proposed concept, the modules are stacked on top of each other vertically, and the columns are not fixed in the vertical direction. For this type of modular construction, it is possible, as in a chair that is difficult to pull when there is weight on it, to rely on the gravity loads of the upper floors and the friction between the elements to resist lateral loads (wind, earthquakes). However, when you reach the top of the building, there is not enough friction to prevent possible horizontal sliding on the upper floors.
From a safety point of view, this is correct, says the professor, as the slips are small and limited by the tolerance between the parts in the connectors. However, it is possible that some horizontal sliding occurs between the modules on the upper floors supporting less weight. These slips can cause some discomfort to users under wind loads such as hiss, creaks. To overcome this problem, the Department’s concrete specialists were called in: Professor Richard Gagné and Audrey Albert, Master’s student, developed an expansive mortar that, once injected into the connections, expands and prevents any movement in the connectors located on the upper floors.
For the time being, the modular concept includes reinforced concrete shear walls as a lateral load-bearing system. Since January, Charles-Philippe and his team have been working with RCM Solutions Modulaires and engineering firm Côté-Jean et Associés, a new partner, as part of the second phase of the project to integrate steel side load support systems. directly in the modules. This new technology will make it possible to completely prefabricate the structure in the factory and thus further increase the speed of construction and the profitability of the projects.
What motivates me in these projects, says the professor, is that they are things that have never been done, or rarely done, in the industry. A company offers you an idea for a project that must be completed in a certain time and that does not yet exist. It’s super motivating. We see all of this taking shape as the project progresses. For students, it is very rewarding too. A great experience!
Brand new metal aprons
At the same time, Charles-Philippe is also carrying out research with a company in Beauce that specializes in steel buildings, Métal Sartigan. We still touched on steel, but this time the innovation is in the metal decks, an important structural component of the roofs and floors, to which reinforcements have been added. Another novelty little seen in North America.
The innovation here is essentially in the depth of the decks, explains Professor Lamarche. Typically, we’re talking about 75mm deep and less. In this project, we have a 100 mm deep apron that was custom developed. These structural elements are quite complex to design due to certain instability phenomena that are not found in conventional decks. To overcome these instabilities, reinforcements must be added.
The initial design phase of the project was launched at Polytechnique Montréal by Professor Robert Tremblay and Research Professional Ali Davaran. Over the past three years, a research project following work done at Polytechnique has been initiated at the University of Sherbrooke to characterize the deck’s properties through large scale testing. The team on site is working to develop new design equations that will eventually be adopted into North American standards for deep decks like the one studied.
We are in the third year of the project, continues Professor Lamarche, and we have a better understanding of the behavior of the deck under vertical (gravity) and horizontal (wind, earthquake) loads. Large-scale laboratory testing and state-of-the-art digital modeling made it possible to deliver a first building with this new deck in fall 2021.
With this new technology, the roof joists can be spaced 12 feet apart instead of 6 or 8 feet. This has the effect of significantly reducing the amount of steel beams needed, given the greater strength of the deck. For an industrial or commercial building, this significantly reduces the steel tonnage and assembly of the structure is faster: saving time and materials.