Orthotropic steel decks are widely used in bridge construction due to their high strength-toweight ratio. However, they are particularly prone to fatigue cracking at welded joints, an issue intensified by increased traffic and heavier vehicles over time. This poses significant challenges for the maintenance and safety of ageing steel bridges, both in the Netherlands and internationally. This thesis investigates a novel strengthening method using blind bolted steel plates to enhance the fatigue performance of orthotropic steel decks. The central research question is: To what extent can a strengthening solution with blind bolted steel plates contribute to the extension of the fatigue life of orthotropic steel decks? A case study of the Second Van Brienenoord Bridge forms the focus of the research. Two fatigue-critical details within the heavy traffic lane are identified and targeted for strengthening. The strengthening solution involves attaching a thin steel plate to the existing deck using blind bolts, offering a lightweight and practical alternative to conventional methods such as Ultra High Performance Concrete (UHPC) overlays. A detailed finite element model of the bridge deck is developed in GSA Oasys to analyse hot spot stresses under fatigue loading before and after strengthening. A parametric model is also developed using Grasshopper to efficiently generate and assess different strengthening schemes by varying design parameters: plate thickness, bolt size, bolt spacing, number of bolt rows, and transverse bolt configuration. A comprehensive parametric study identifies plate thickness as the most influential factor in reducing hot spot stresses. Interactions between parameters, such as bolt arrangement and plate thickness, are identified. Based on these findings, a selection of promising strengthening schemes is made for further evaluation. These schemes are assessed using three criteria: fatigue life extension, added weight, and estimated installation time. Additionally, static verifications under thermal loading and heavy vehicle loading (Eurocode Load Model 2) are performed to ensure that the bolts do not fail prematurely in shear. Some schemes require denser bolt patterns at plate edges to pass these checks. The most effective schemes achieve over 60% reduction in hot spot stresses and extend fatigue life by up to 30 years, with moderate weight and relatively quick installation times. In conclusion, this research demonstrates that blind bolted steel plate strengthening can effectively enhance the fatigue performance of orthotropic steel decks, providing a cost-efficient and quick to implement solution. The use of blind bolts enhances applicability by enabling one-sided installation, even above closed stiffeners. The methodology and insights developed here can guide future applications in bridge maintenance. Recommendations for further research include experimental testing to validate bolt preload and slip resistance, more detailed fatigue damage assessments based on full stress histories, and investigation of the strengthening method’s applicability to varying deck geometries and damage levels. Practical aspects such as the interaction between deck and strengthening plate, emergency repair potential, and long-term durability should also be explored.