Advancing the sustainable and acoustic design of concrete structures
Open Access
- Author:
- Broyles, Jonathan
- Graduate Program:
- Architectural Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 22, 2024
- Committee Members:
- James Freihaut, Program Head/Chair
Nathan Brown, Chair & Dissertation Advisor
Ryan Solnosky, Major Field Member
Rebecca Napolitano, Major Field Member
Michelle Vigeant-Haas, Major Field Member
Andrew Barnard, Outside Unit & Field Member - Keywords:
- concrete floors
embodied carbon
acoustic insulation
impact sound insulation
sustainability - Abstract:
- The building and construction sector contributes 35-40% of global carbon emissions, with concrete attributed to around 7% of global carbon emissions. With the substantial volume of concrete used in building floor systems, design practitioners and engineers are increasingly tasked to identify concrete floor systems with the least amount of embodied carbon (EC) emissions. A prominent EC reduction pathway is through the removal of structurally unnecessary concrete material in floors. This low-carbon pathway is directly applicable in the selection of more material-efficient concrete floor systems in buildings, as several concrete systems exist that are more material-efficient than conventional concrete slabs. Further concrete material reductions can be realized at the component scale when optimization frameworks are employed to determine non-traditional floor forms that improve upon the material efficiency of conventional systems. While existing concrete floor systems can reduce the EC emissions by up to 50%, greater EC savings can be achieved through the design of optimized components. However, challenges have hindered both the selection of low-carbon conventional concrete floor systems and the realization of optimized components. Material-efficient concrete floor systems have been designed, engineered, and constructed for many years; however, identifying the floor system with the lowest EC emissions has been restricted due to the variety of floor system types, the bevy of possible design scenarios, and the uncertainty of the carbon footprint of concrete mixtures. Additionally, the selection of a low-carbon floor system can happen in early-stage design phases, potentially restricting the consideration of alternative systems, especially when design parameters are loosely defined. Furthermore, the design of a concrete floor system may be controlled by non-structural objectives. Secondary objectives such as fire-resistance, acoustic insulation, and vibrations may influence the design of a concrete floor structure, further complicating the selection of a low-carbon concrete system. These limitations currently impede how designers can identify which concrete floor system has the largest EC savings when considering various design scenarios and performance goals. While optimized concrete components have been found to achieve material savings up to 70% when compared to conventional concrete slabs, their implementation has been restricted because floors influence additional design performance goals. Several researchers have evaluated how secondary considerations, like walking vibrations, can be influenced by the design of optimized components, yet air- and structure-borne insulation performance has been less studied. Although air-borne sound insulation of optimized concrete floors can be adequately estimated using analytical expressions, a high-resolution numerical model is necessary to quantify impact sound insulation. However, computational resource restrictions limit simulating the full-frequency radiated sound power needed to evaluate impact insulation. An additional challenge when evaluating optimized floors for acoustic insulation is that the existing sound transmission metrics have known functional limitations that can inflate or penalize the true acoustic performance of a concrete component. As a result of these challenges, little research has evaluated the performance of optimized concrete components for acoustic performance and other design goals. This dissertation responds to these research gaps by deriving equations and design tools to aid in the selection of a low-carbon concrete floor system, developing a new simulation method to quantify impact sound insulation, and proposing new sound transmission metrics to improve the acoustic assessment of optimized concrete components. At the building system scale, multivariate polynomial regression models, which encompass many design scenarios, were trained to estimate EC for ten conventional concrete systems tailored to the two early design phases to better inform the selection of a low-carbon floor system. A subset of the concrete floors was then evaluated for fire resistance, air-borne sound insulation, and walking vibrations to evaluate how the inclusion of additional design objectives affected which floor system had the lowest EC for six unique design scenarios. To improve the assessment of structure-borne sound insulation of optimized components, experimental results were used to validate a numerical model used to quantify impact sound insulation performance, with new acoustic transmission metrics proposed to improve the performance rating and customizability of optimized structural components. Finally, the simulation method to quantify impact sound and proposed transmission metrics were applied to a case study of shaped one-way slabs to demonstrate how comprehensive assessments of optimized concrete components can inform building practitioners on complex floor design trade-offs, and to evaluate the design benefits of optimized components when compared to an equivalent conventional floor system.