The SEeMOREEffect research project investigates the influence of system reduction on the seismic behavior of steel-concrete composite frames. The aim is to analyze the effects of the reduction of complex frame structures in test setups and to develop reliable FE-models for the prediction of the earthquake behavior of moment-resisting frames (MRFs) within complex structures.

Main focus:

• Analysis of system reduction: Investigation of how the reduction of complex frame structures in test setups influences the seismic load-bearing behavior of innovative composite structures.

• Investigation of CFST and CFDST columns: Evaluation of the seismic capacity of MRFs with concrete-filled tubular steel columns (CFST) and concrete-filled double-tubular columns (CFDST) to optimize slender, heavy-duty and fast construction methods in building construction.

• Surrogate model integration: Development of analytical approaches to capture the system reduction effects for integration into a surrogate model for the analysis of the seismic behavior of global frame structures.

• Model development: Creation and validation of reliable FE models that take into account the observed effects of system reduction and can represent the seismic behavior of frame structures.

Previous studies have analyzed the behavior of these structures through experimental tests on individual component groups, such as T- and cross-connections. However, these tests are often simplified and do not reflect the real conditions in the overall structure of a building and are predominantly proprietary. Field observations and investigations on frame substructures show that additional effects, such as the limitation of axial deformation of beams by floor slabs and adjacent columns, influence the seismic capacity. These effects cannot be taken into account in the substructure experiments, which is why larger frame structures are being investigated as part of this research project. As a continuation of previous research projects of the chair, e.g. SEISMICCOLUMNS, STUBSEISMIC and CFSHSC, a further focus is on the investigation of the seismic behavior of MRFs built with Concrete-Filled-Double-Steel-Tube (CFDST) columns and composite steel beams. The composite behavior and the influence on the load-bearing behavior of CFDST compared to normal steel tube columns (Concrete-Filled-Steel-Tube (CFST)) is analyzed. This is relevant because there is a lack of high-quality test data to draw appropriate conclusions on the stiffness, stability and ductility of earthquake-resistant frame structures with this construction method. Both experimental and numerical studies are planned in order to understand and quantify the observed effects.

The experimental tests will investigate the ductility and energy absorption capacity of the joints as well as the influence of frame action, plate effects, failure mechanisms and plastic rotation capacity of the MRF composites under seismic loading. Monotonic pushover and cyclic tests will be performed on realistic frame structures, including a 2-bay 1-story frame structure with reinforced composite floor slabs. Comparative tests on simplified subassamblies, such as T- and cross-test specimens with CFST and CFDST composite columns respectively, are also planned. In this way, the differences between the real framework conditions and the simplified test conditions can be quantified. In parallel, numerical studies are carried out in which fiber- and continuum-based finite element models are developed and validated on the basis of the test results. The numerical simulations are intended to contribute to a deeper understanding of the load-bearing behavior of the composite columns and enable statements to be made about force and deformation variables that cannot be measured or observed. The models enable detailed analyses of the deformations, shear distortions, stresses and axial forces in the structures. The parameter range of the experimental results is supplemented and extended by additional parameter investigations. This allows the system effects and the factors influencing the reduction of the frame structure to be evaluated both quantitatively and qualitatively. The results form the basis for the development of suitable connections for corresponding composite frame structures in seismic applications.