Abstract

ABSTRACT

Mechanical Performance Prediction and Retrofitting Technique of Heritage Timber Beams
Reza Abbasi Malekabadi, Ph.D.
Concordia University, 2025
Heritage timber buildings with cultural value often suffer from age-related deterioration, serviceability issues, load modifications, and gaps in code guidance for assessment and strengthening. This thesis developed an integrated framework to (i) predict the mechanical performance of in-situ Heritage timber beams and (ii) retrofit them using practical, minimally destructive techniques while retaining residual capacity if strengthening is lost. The methodology is executed in two Phases. Phase I (Evaluation) compiles a database for 44 full-scale Heritage beams (collected from Quebec and Ontario) with Non-Destructive Tests (NDTs), including density, dynamic MOE, cavity, and destructive bending test. Then, the material properties and mechanical performance of beams are assessed through two different methods. The first method established a comparison pathway via New/Simulated New Counterpart (SNC) beams for statistical inference testing. A Null-hypothesis protocol is used to investigate whether Heritage and New/SNC beams are mechanically comparable in terms of flexural strength, supporting a novel method that substitutes for NDTs. The technique allows destructive tests to be conducted on New beams and their results to be attributed to in-situ Heritage beams. The second approach developed and formulated NDT results in relation to mechanical performance to directly obtain the required assessment needs.
Phase II (Strengthening) evaluated Near-Surface-Mounted Glass Fibre Reinforced Polymer (NSM-GFRP) retrofits on full-scale Heritage members, varying rebar length, ratio, and configuration. The four-point bending procedure measured capacity gains, neutral-axis shifts, and failure modes. Furthermore, an allowable-strengthening criterion is derived by adapting ACI 440.2R to timber to maintain a safe residual capacity if FRP is suddenly lost. Beyond testing, complementary analytical formulations, Bernoulli-based sections, moment–curvature models with simplified equilibrium, and a Whitney-type compression block calibrated to the experiments, support design and interpretation. These models bridge the gap between measured behaviour and design prediction, incorporating plasticized depth and neutral-axis movements.
Future work proposes a dual system (local post-tensioning and FRP) for cases where the flexural demand exceeds the allowable FRP limit, aiming to increase stiffness, enhance drift control, and incorporate self-centring capabilities.
The results show that calibrated NDT and destructive data enable Heritage-friendly assessment, and NSM-GFRP retrofits deliver substantial flexural gains, ranging from 30% to over 140%, depending on development length and configuration, while altering damage progression (e.g., delaying tension-governed rupture and changing failure modes). The proposed maximum allowable FRP limits provide a conservation-minded bound on intervention. Collectively, the thesis contributes to: (1) a full-scale Heritage beam database; (2) an NDT-to-mechanics and statistical equivalence pathway for in-situ assessment; (3) evidence-based NSM-GFRP guidance at full scale; and (4) allowable-strengthening and analytical tools with a proposed post-tensioned dual system concept for durable, reversible, and safer conservation practice.