Analysis and optimisation of structural timber vaulted floors for ultra-low carbon building structures

: (Alternative Format Thesis)

Abstract

The construction sector faces increasing pressure to reduce embodied carbon while meeting the growing global demand for floor area. Floors contribute a large proportion of the structural mass and embodied carbon in multi-storey buildings, making them a critical target for material efficiency. Engineered timber products offer a renewable alternative to concrete and steel; however, conventional timber floor systems are bending-dominated and therefore limited by timber’s tensile capacity and serviceability performance, often requiring deep structural sections that restrict their feasibility at longer spans. In contrast, arches and vaults transfer load primarily through compression-dominated membrane action, providing significant geometric stiffness and enabling more efficient use of material.

This thesis investigates whether combining the sustainability benefits of timber with the geometric efficiency of vaulted forms can deliver a structurally efficient, low-carbon, and cost-effective floor system. A practical two-way spanning solution is proposed comprising a shallow cross-laminated timber (CLT) groin vault supported on columns, with horizontal thrust restrained by a grid of steel ties. Ribs with granular infill are introduced to provide a level walking surface and to enhance vibration performance.

A novel computational optimisation framework is developed in which the structural geometry is optimised with respect to a single objective function, defined as either embodied carbon or cost, explicitly accounting for fabrication stage contributions, including material wastage, adhesive use, labour, and steel, and subject to strength, stiffness, and vibration serviceability constraints. The framework is first applied to glue-laminated timbe arches, demonstrating substantial reductions in embodied carbon and cost relative to straight bending-dominated beams. Building on this, the optimisation is extended to two-way spanning CLT groin vaults, enabling optimal configurations to be identified.

To validate the optimisation framework, a quarter scale CLT groin vault prototype is designed, fabricated, and destructively tested, the first known CLT vault to undergo such testing. A practical forming method using straight lamellas bent over a reusable former is established, demonstrating a practical fabrication methodology while accounting for spring-back and moisture induced effects. The first experimental vibration study of a CLT groin vault is then conducted using electrodynamic shaker testing, showing that granular infill can nearly double damping of the floor system.

Date of Award	22 Apr 2026
Original language	English
Awarding Institution	University of Bath
Supervisor	Will Hawkins (Supervisor), Antony Darby (Supervisor) & Tim Ibell (Supervisor)