Despite timber’s potential as a sustainable building material, its application in high-rise construction remains limited due to structural, dynamic, and connection-related challenges, as well as high material costs. As a result, the realisation of timber high-rise buildings remains financially and technically complex. Hybrid timber–concrete systems offer a promising solution by combining the strengths of both materials, potentially improving feasibility while maintaining significant advantages in terms of CO2 impact. However, the optimal implementation of such hybrid systems remains unclear. Key uncertainties include the structural performance in terms of achievable height and net floor area, cost-effectiveness, and actual impact in terms of CO2. Exploring these trade-offs through distinct design alternatives is essential to understand how both materials can be effectively combined in high-rise construction.
This research aims to investigate the CO2 impact and material cost implications of hybrid timber–concrete design approaches for high-rise buildings of varying heights. Based on this aim, the main research question is formulated: What is the influence of different complementary timber lateral stability systems on the material costs and CO2 impact of timber high-rise structures with a concrete core? To answer this question, the study first explores existing timber high-rise projects and challenges, then develops a representative base model and structural variants.
The base model features a square floor plan and consists of TCC floors, glulam beams and columns, slotted-in steel connections, and a concrete core. Two design variants were developed by adding timber-based lateral stability systems to this base configuration: one with perimeter bracing in two configurations, and one with timber outrigger structures. These additions aim to enhance lateral stiffness, allowing for a reduction in core size and potentially increasing the net floor area for taller building configurations.
The structural variants with varying heights are analysed using a parametric workflow combining Grasshopper, SCIA Engineer, and Excel in an iterative process. Key elements are verified according to Eurocode-based criteria, including overall deflection. Each iteration is assessed by plotting net floor area against material cost and CO2 sequestration. Net floor area is used as the main performance indicator, as it better captures the functional value of a design and reflects the influence of increasing core size at greater heights.
The results show that the need for larger cores at greater heights leads to a reduction in net floor area, with corresponding increases in material cost and CO2 sequestration per square metre. These indicators are strongly correlated: greater timber use leads to both higher cost and higher CO2 storage. A configuration with dense perimeter bracing showed the most consistent performance gains at greater heights by maintaining a smaller core, increasing net floor area, and improving cost-efficiency. In contrast, the use of concrete columns improved space and cost efficiency but resulted in net CO2 emissions, underlining the sensitivity of outcomes to material choice.
