Challenges and Considerations for the Retrofit of Existing Structures for Progressive Collapse

Abstract

The present paper discusses the challenges of retrofitting buildings to meet current progressive collapse guidelines. The knowledge of the structural capacity depends on the quality of information available. The existence of original drawings greatly facilitates the understanding of the design intent. However, drawings are not always available and information must be also obtained through on-site testing. A case study of the retrofit of a 5-story flat plate concrete structure is presented, where the floor slabs are hung from a new steel girder located above the roof using high strength steel rods. Neglecting the contributions of the existing structure, the failure mode of this system is ductile beam flexural mode. However, the analysis presented show that a brittle shear failure at the slabs can occur when the existing concrete column and its reinforcement are incorporated into the analysis.