Sustainable structural design optimization - prestressed concrete beams

• Main Author: Ng, Kok Hang
• Other Authors: Teoh Bak Koon
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2024
• Subjects: Engineering; Prestressed concrete; Sustainability
• Online Access: https://hdl.handle.net/10356/177422
• Institution: Nanyang Technological University

The dynamic interaction between urban and earth systems meant that inputs made by either system often produce a cascading impact on the other. The adverse effects of climate change which is largely driven by human activities are being felt across global communities in profound manners. Imperatively, the construction sector has been identified as a major contributor to global greenhouse gas emissions. While new technologies and research have been made to reduce the carbon emissions during the operational phase, there is significant room for improvement regarding embodied carbon (EC) emissions which has become an influential contributor to global emissions. This project focuses on the sustainable optimization of prestressed concrete beams with respect to the EC. A parametric study was first conducted to examine the beam parameters that will influence the amount of EC normalized to the structural capacity. A series of 2D and 3D graphs were generated to highlight the impact of varying each parameter on the allowable live load and EC per unit of live load. Subsequently, a case study was carried out to determine the optimum beam span length for an expressway bridge that will result in the lowest overall EC for the bridge system. The case study utilized design guidelines from the Land Transport Authority and Eurocode 1 (traffic load) to create a practical bridge design scenario. The parametric study established that the beam length plays a pivotal role in controlling the amount of EC per unit of structural capacity while the prestressing force is less dominant for the range of parameters studied. In addition, beams with a span length exceeding 34 m, height shorter than 1100 mm or prestressing force less than 5000 kN should be avoided as a very high EC will be produced with respect to it’s structural capacity. The case study revealed that for an 18 m wide bridge, a 3-beam layout generates lesser overall EC than a 4-beam layout and a beam length (thus column spacing) of 20 to 26 m is likely to produce the lowest EC for the bridge system. The findings from this project can be used by structural engineers to minimise the EC emissions associated with the construction industry by prudent selection of the prestressed beam parameters during the initial design. The author hopes that the sustainable design guidelines provided in this paper will inspire deeper research into other beam parameters such as the tendon profile that will also influence the EC of the structure.