Proposal for the Identification of Rigid and Flexible Diaphragms in Reinforced Concrete Structures

The results obtained from the analysis of twenty-eight structural models allowed quantifying the impact of diaphragm condition on the global seismic response of reinforced concrete buildings. Scenarios with and without diaphragm rigidity were compared, considering three key variables: lateral drift, base shear, and overturning moment. The modeled structures correspond to five-story buildings with three-meter inter story heights and plan geometries with aspect ratios ranging from one to four. Regular configurations showed drift differences below 1 %, while irregular configurations exhibited variations of up to 6.83 %. Base shear increased by up to 2.62 %, and overturning moment by up to 4.65 % when diaphragm flexibility was considered. These results show that geometric rigidity directly influences inter story deformation and, consequently, the distribution of internal forces. In addition, two complementary methodologies were applied to classify diaphragm behavior: a visual approach based on the interpretation of modal shapes, and a quantitative approach based on the calculation of average relative error. Both methods yielded fully consistent classifications across all models, validating the robustness of the proposed criterion and demonstrating its applicability to identify rigid or flexible diaphragms based on modal response, without the need for lateral loading. This methodology can be directly implemented in structural modeling platforms, enabling a more accurate characterization of the seismic behavior of buildings with complex geometries. A precise classification of diaphragm behavior is essential for realistic seismic analysis and safe structural design. However, current engineering practice lacks standardized technical or quantitative criteria to support this modeling decision. The proposed 5% threshold proved effective for identifying deformable diaphragms in structures with irregular mass or stiffness distributions. This contribution offers a structured and replicable tool for seismic evaluation, helping to avoid oversimplifications in modeling. Its application within commercial platforms can enhance the dynamic characterization of buildings with complex geometries, ultimately contributing to more reliable and safer structural designs.