Product Line Architecture (PLA) is the main tangible element shared by all products of a Software Product Line (SPL); it covers common functionality and the required variability of SPL products. Responding to industrial practice, this paper proposes a reactive refactoring bottom-up process to build a PLA from existing similar software product architectures of a domain, expressed by UML logical views. An architecture is represented by a connected graph or valid architectural configuration (P, R), where P and R represent components and connectors of the product. This process constructs a graph (RG) for each product, organized by levels, containing intermediate valid configurations or connected induced sub-graphs of (P, R). A candidate PLA is automatically constructed followed by an optimization process to obtain the PLA using the domain quality model. The refactoring process is applied to a case study in the robotics industry domain. Automatic parts of the process are tool supported.