Following the previous analytical studies performed with ATENA software for a series of RC moment resisting frame models, it were used in the pre-processing stage the stress-strain relation laws for concrete and steel reinforcement. These mathematical and graphical relations represent a necessity in the current conditions of numerical analysis and imply a correct knowledge of the deformation mode of the „reinforced concrete” which is a composite material. Thus, it is desired through this research paper the theoretical exposition of: equivalent uniaxial law for concrete, biaxial compressive failure and tensile failure consideration laws for concrete, bilinear with hardening law for steel reinforcement, cycling steel reinforcement model and steel reinforcement bond model. Finally, it will be possible to validate the correctness of the analytical RC frame systems through the experimental results of the optimal RC frame model after seismic platform testing.

Reinforced concrete (RC) frame systems represent one of the structural solutions used in seismic zones by engineers. For this reason, the importance of knowing the real seismic response for these types of structures is essential and presents the research problem studied in this article. Thus, the seismic response for two storey axial RC frame (one bay-one span) system was studied using nonlinear static analysis in ATENA software. The structural degradation of the two storey RC frame system was investigated for several steel reinforcement possibilities and three distinct RC beams cross sections. Particular attention was paid to RC beam-column joints degradation areas and to seismic energy dissipation mechanism in the marginal regions of the RC columns. Thus, it was observed a nonlinear inelastic response in the potential degradation zones with contrary effects with respect to the specified conclusions in the current seismic design norms. Also, it was studied the RC slab bending stiffness influence to horizontal structural elements (RC beams) and to vertical structural elements (RC columns) alongside the cracking mode for horizontal static actions and RC slab local degradation beside RC beam-column joint area. In these conditions, conclusions regarding the seismic response of the moment resisting (MR) RC frame system with low height regime designed according to the current seismic code were specified and an unsatisfactory seismic response was proved.

For monolithic reinforced concrete structures, it is known that beams and slabs form a common body, so that the stiffness of the dissipative elements (beams) increases significantly. Also, it is known the fact that the beams are the principal structural dissipative elements. In these circumstances, it will try through numerical simulations (nonlinear calculation) a theoretical reproduction of a recently executed structure, so as to take into consideration the effect of excess rigidity brought to the horizontal dissipative structural elements (beams). It will be pursued the dissipation mode of seismic energy through plastic deformations (formation the punctual plastic hinges at the end zones of the beams and especially at the end regions of the columns).

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Cold-formed steel structures represent a suitable alternative to classical, by now, structural solutions considering the recycling/reuse tendency worldwide as part of the circular economy paradigm. The paper presents a new design approach for CFS profile joints to accurately predict their realistic behavior, based on experimental and numerical investigation of two types of connectors frequently used in the construction industry for manufacturing joints made of CFS profiles: steel-steel pop-rivets (SSPR) and self-tapping screws (STS). The experiments carried out in the case of T-joints subjected to tensile forces tested both solutions. Another significant parameter of the research was the thickness of the steel sheet used to make the CFS profiles. A number of 20 specimens of T-joints made of Cold-Formed Steel (CFS) profiles in total were tested. These consist of five specimens for each of two types of steel sheet thicknesses. The results are relevant for designers because they provide relevant data concerning the limited axial rigidity of T-joints, which are an important instrument in numerical models for achieving the optimum design of the structural system in terms of strength and overall rigidity. Experimental tests calibrate the numerical model that accounts for the axial stiffness of the hinged joints between the CFS profiles. The main parameters of the research are the thickness of the steel sheet and the connector type. The calibrated numerical model used in a case study highlights the advantages of the new approach compared to the classical design procedure based on a conventional hinged connection. Based on the results, the conclusion is that, besides the geometry of the joint and the connector type, the joint stiffness plays a crucial role in the overall behavior of the structural system and should be accounted for in the design process.