Examples of defects of pre-tensioned concrete roof beams in Poland

The beginning of the use of pre-tensioned precast concrete elements, including roof girders, in Poland, dates back to the mid-1950s. Until the 1980s, these were mainly original constructions of Polish concrete designers. After a dozen or so years of economic collapse, there was a rebirth related to the entry of international concerns for the prefabrication of concrete onto the Polish market. The brought know-how, and an extensive marketing campaign resulted in the revival of interest in pre-tensioned precast concrete structures. Refreshing also required the experience of the construction companies, which resulted in a lot of defects especially in the first period, mainly of executive and assembly nature, sometimes in connection with design errors. The article focuses on pre-tensioned roof beams (girders and purlins) concerning the entire period of their application from the mid-20th century to the present day. Selected cases of design, executive, assembly and application errors were presented. The authors based on their own experience from numerous expert opinions, hence the selection of presented cases is somewhat subjective. Nevertheless, the paper includes both typical problems observed in many objects as well as individual cases of very significant defects or damages. Due to the limited volume of the text, the description of repairs or strengthenings used in individual cases was omitted, and attention was focused on identifying the causes of the defects described.