This paper presents a multi-agent based simulation framework for cognitive systems engineering of socio-technical systems. Comprehensive design analysis of socio-technical systems requires modeling of various aspects of the work environment and of behavior and performance of humans. This framework provides a distinct focus on the work-environment, specifying it as a coherent collection of declarative models spanning its multiple aspects. Compared to traditional methods in cognitive systems engineering, aggregating multiple aspects allows greater detail and scale in modeling socio-technical systems. This also addresses design issues that cut across individual aspects, thus enabling a comprehensive what-if analysis of the system. Humans are computationally modeled as proactive and interactive agents operating within their work-environment. Emergent behavior of the system in response to design changes in both humans and their work environment can thus be simulated. The framework is illustrated through an example in air traffic control. The framework can be applied to problems in enterprise re-engineering, organizational structuring, etc.