Context: Modern software systems often are distributed, run on virtualized platforms, implement complex tasks and operate on dynamically changing and unpredictable environments. Such systems need to be dynamically reconfigured or evolve in order to continue to meet their functional and non-functional requirements, as load and computation need to change. Such reconfiguration and/or evolution actions may cause other requirements to fail. Objective: Given models that describe with a degree of confidence the requirements that should hold in a running software system, along with their inter-dependencies, our objective is to propose a framework that can process these models and estimate the degree requirements hold as the system is dynamically altered or adapted. Method: We present an approach where requirements and their inter-dependencies are modeled using conditional goal models with weighted contributions. These models can be translated into fuzzy rules, and fuzzy reasoners can determine whether and to what degree, a requirement may be affected by a system change, or by actions related of other requirements. Results: The proposed framework is evaluated for its performance and stability on goal models of varying size and complexity. The experimental results indicate that the approach is tractable even for large models and allows for dealing with models where contribution links are of varying importance or weight. Conclusion: The use of conditional weighted goal models combined with fuzzy reasoners allowed for the tractable run-time evaluation of the degree by which system requirements are believed to hold, when such systems are dynamically altered or adapted. The approach aims to shed light towards the development of run-time requirements verification and validation techniques for adaptive systems or systems that undergo continuous, or frequent evolution. (C) 2016 Elsevier B.V. All rights reserved.