Structural behaviour of precast and post-tensioned concrete system under column removal scenarios

• Main Author: Tran, Manh Ha
• Other Authors: Tan Kang Hai
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2024
• Subjects: Engineering
• Online Access: https://hdl.handle.net/10356/177319
• Institution: Nanyang Technological University

In the past few decades, progressive collapse has become a growing concern in building design, particularly following the Oklahoma City bombing in 1995 and the September 11 attacks on the World Trade Centre in New York in 2001. Although numerous studies have been conducted on this problem, most of them have focused on cast-in-situ concrete, steel, and composite structures. Only a few studies have been carried out on post-tensioned precast concrete (PTPC) structures. In particular, there is almost no study on 3D PTPC beam-slab substructures. Therefore, it is crucial to conduct a comprehensive research program on PTPC substructures under column removal scenarios. The backbone of the research program is to analyse all the load-resisting mechanisms of 3D models, while 2D models play a role at the sub-structural level for 3D models. Firstly, preliminary research studies are presented to determine the best methodology and data measurement for the experimental program. Two simple yet effective and reliable approaches to predict the structural behaviour of 3D beam-slab systems are proposed, including (i) an analytical method and (ii) a simplified finite element model based on grillage analysis. Both approaches were validated against published test results. The proposed two approaches incorporate all the load-resisting mechanisms in both the beams and the slabs, providing more accurate predictions of the load-displacement curves for the considered sub-structures. Subsequently, an experimental research program is proposed and conducted to study the resisting mechanisms of PTPC structures under progressive collapse. The experimental programme consists of three main test series conducted under quasi-static loading conditions. The first test series investigated the combined effects of PT tendon and wet connection on load-resisting mechanisms of 2D PTPC beam-column sub-structures under a middle column removal scenario (MCRS). In addition, the influence of basic parameters such as unbonded and bonded PT tendons, T-beam effect, and boundary conditions was studied in detail. In the second series, both 2D and 3D PTPC sub-structures were subjected to an edge column removal scenario. High-tensile strength PT tendon greatly enhanced capacity in primary beams of both 2D and 3D specimens. In the 3D sub-structure, PT primary beam carried the major load, while the contribution of secondary beams and slabs was moderate. The third part focuses on a 3D PTPC beam-slab sub-structure subjected to an internal column removal scenario. Under a twenty four-point loading system simulating UDL conditions, all load-resisting mechanisms of primary and secondary beams and slabs were mobilized to resist applied loads. In addition to experimental investigations, numerical studies corresponding to the three-test series were conducted. Component-based models (CBM) were developed for 2D sub-structures with PT tendon. CBMs considered the interaction behaviour between the tendon and the grout through an innovative bond-slip model. The CBMs showed close agreement with the test results in terms of the first peak load (CAA) and ultimate capacity (CA). Furthermore, simplified finite element (FE) models based on grillage theory were proposed for 3D PTPC beam-slab sub-structures. These models showed reliability and provided quick predictions of the response of the 3D sub-structures. Finally, a design approach is developed for 2D and 3D PTPC sub-structures. The approach can serve as a convenient tool to facilitate a quick initial assessment on behaviour of 2D and 3D sub-structures, as this approach does not require computational resources as FE modelling. Most importantly, the approach can be easily implemented by a few simple steps, thereby providing a simple and yet robust tool for structural engineers to calculate progressive collapse resistance of PTPC structures for missing column scenarios.