Mass Timber Hybrid Structure

Hybrid structures are becoming increasingly popular in the construction industry as they offer a unique combination of materials to create sustainable and efficient building solutions. Hybrid structures are those composed of different materials gathered to create unique building solutions, using the strengths of all materials combined. Regarding mass timber projects, hybrid structures are those designed with wood combined with concrete, steel or glass. These structures have many advantages and benefits, and can be used in various projects including new buildings, extension projects, retrofit or addition of floors upon the existing building.  

Mass Timber Hybrid Structure - Future of green construction movement

Several types of hybrid structures can be listed, when the goal is to have light, yet strong and sustainable structure:

  • Certainly the most common is wood-concrete system, consisting of prefabricated concrete panels placed into the timber frame. Concrete resists compression, while wood resists tensile forces. That way, they create rigid structure. If floor slabs are made of concrete too, they form a horizontal diaphragm that resists horizontal forces (earthquake and wind). 
  • Another type is post-tensioned timber system, in which steel rods or tendons are used to cause precompression in timber panel, preparing it to bear expected loads.
  • One of possible hybrid system can be made entirely of wood, consisting of light frame wooden structure combined with mass-timber elements.
mass timber hybrid

Hybrid structures are recommended to be used in retrofit and extension projects, where additional floors are expected to be built. In this case, mass-timber CLT slabs, combined with concrete beams and columns, make the extension of the building significantly lighter. Also, they are suitable for green solutions like green roofs, weakening the effects of urban heat island. 

Regarding benefits, hybrid structures contribute in many ways to sustainability and circular requirements:

  • Lighter structure means lighter foundations, less concrete, less CO2 emission, smaller  costs
  • Prefabrication of mass-timber elements means easier transport organization, less people needed to mount the elements on the construction site, less time needed, less embodied carbon, less waste and less noise pollution commonly present on the construction site
  • More efficient design, fabrication and mounting phases mean more efficient time frame and deadlines met as planned.

In the project for two commercial and residential buildings near Stockholm, we designed structure as combination of mass-timber, concrete and steel. Ground floor structure is made of steel columns and beams, due to heavy load from the upper floors, while slabs and walls are made of CLT panels. Upper floors are entirely designed in CLT panel walls – 14cm thick façade panels and 16cm thick interior bearing wall. Slabs span two structural fields and are 20cm high, which improves vibration resistance of the whole structure. 

mass timber hybrid

Elevator’s and stairs’ shafts, as well as stairs’ slabs, are entirely made of CLT panels exposed and visible in the interior space. Special sustainable effect is provided by green roofs inclined by 45 degrees. Green roofs improve thermal performances, decreasing the use of air-conditioning and heating systems, therefore decreasing costs and energy needed to maintain thermal comfort of the building. It is important to mention the compact form of the buildings, which decreases the energy losses during cold months and provide contemporary urban look. 

Hybrid structures offer many benefits, including lighter foundations, less concrete, and less CO2 emissions. They also offer prefabrication options that allow for easier transport organization, fewer people needed on the construction site, and a more efficient design, fabrication, and mounting process. This leads to more efficient timeframes and deadlines that are met as planned.

In conclusion, hybrid structures are a promising solution in the construction industry as they offer a combination of materials that can create sustainable and efficient building solutions. The use of wood-concrete and post-tensioned timber systems provide a balance of strength and durability, while also offering prefabrication options that can lead to a more efficient building process. The use of mass-timber, concrete and steel in the project near Stockholm is a good example of how hybrid structures can be used to create sustainable, energy efficient and visually appealing buildings. Hybrid structures are suitable for various types of projects, and can help to meet the growing demand for sustainable and circular building solutions