Dangerous synergies causing failures of historical structures

The safety and reliability of historical structures or structures generally are typically assessed under “ideal” load or environmental service conditions. However, natural events and human activity or intervention during the life of historical structures may generate synergic effects which decrease their safety and even cause serious defects or failures. This paper presents selected situations involving combined time dependent degradation and sudden impacts of natural or artificial loads or human activity, identifies problems involved in coupling incompatible materials with weather or climate effects and incompatible remedial or strengthening work on historical structures. It further deals with a common problem: inadequate design, harmful interventions, and inadequate protection or preservation treatments. Lessons learned in practice and basic recommendations for preventing catastrophic results are presented.