The moment resisting frames (MRF) are one of the three main structural steel typologies used for seismic design of steel frames. They are characterized as the most ductile structural type possessing a large number of possible dissipative zones, following the fact that plastic hinges can develop both in the beams and the columns. Possessing the feature of being the most ductile type, these structures exhibit very large deflections before the structural damage occurs. Additionally, the strength and stiffness deterioration of the steel material due to cyclic loading increases the effect of the lateral forces and represents the most realistic behaviour of this structural system. Hence, in this research study an improved approach using updated material model for evaluating the steel MRFs' behaviour is implemented in order to tackle the deficiency in the assessment of this type of structures. Firstly, the modelling is performed using the nonlinear beam -column elements with distributed plasticity for both the beams and the columns. Then, the same frame model is developed using the elastic beam -column elements ending with zero-length plastic hinges modelled by a stiffness deteriorating steel material referred to as Ibarra -Krawinkler (IK) model. Two sets of seven acceleration records are chosen as realistic earthquake loading to represent the medium hazard seismicity (MH) and high hazard seismicity (HH) scenarios. Incremental nonlinear dynamic analysis of the frames is conducted by scaling the records in order to attain various levels of relative intensities. They are extracted from the database and scaled to match the EC8 elastic spectra for the two hazard scenarios.

This article presents the advantages of using preloaded bolts in connections of steel structures. First we discussed the main differences between preloaded bolts and shear bolts. Then we explained the categories of shear connections and the categories of friction surfaces, along with their associated surface preparation and slip factor. To connect theory and codes with experiment, we showed the basic expressions used to calculate the design resistance of preloaded bolts and compared the design resistance of shear bolts. The slip factor was tested according to EN 1090-2:2008, Annex G, for two series of specimens, identical to those used in bridges in the Republic of Albania.

The self‐centring system presented in this paper is a novel damage control technique designed to improve the resilience of concentrically braced frames (CBF) under seismic action. Namely, traditional CBFs can undergo large residual drifts following an earthquake event which can limit the opportunity for cost‐effective repair of the structure. Additionally, the gusset plates connecting the brace members to beams and/or columns can experience substantial rotations as a result of the compression buckling of the bracing members. Through the utilisation of post‐tensioning strands placed between flanges of beams, the novel self‐centring concentrically braced frame (SC‐CBF) system can return the frame to its original position after significant inelastic deformations experienced during large earthquakes, resulting in minimum residual drifts. In this paper, shake table testing of the aforementioned SC‐CBF system subjected to realistic earthquake loading is presented. The research is carried out as part of the H2020 “Seismology and earthquake engineering research infrastructure alliance for Europe” SERA project. Four sets of bracing configurations, incorporating varying square hollow section (SHS) braces and gusset plates were utilised in the shake table testing. Uniaxial loading with varying shake table accelerations was executed and the structural response evaluated using data from strain gauges (SG), load cells (LC), displacement transducers and accelerometers. The measured results provide information on the important parameters such as the tensile and compressive strength of the braces, post‐buckling capacity, gusset plate strains and post‐tensioning force. These findings are then presented and the crucial local and global response performance emphasised.

The self-centring concentrically braced frames (SC-CBF) present an innovative structural typology for improved behaviour of the steel structures to earthquake loading. Namely, the SC-CBFs present an advanced technological solution for minimization of the residual drifts at concentrically braced frames which are quite substantial following high intensity seismic action. This structural type’s main characteristic is the re-centring of the frame following the earthquake loading in the initial vertical position, thus reducing the post-earthquake cost and time for retrofitting. It also reduces the material used for repair since the only elements needing retrofitting remain the diagonal braces that undergo many cyclic loadings under the earthquake excitation and develop plastic hinges. However, in order to validate this behaviour, many experimental investigations are required. For that purpose, this study addresses previous, current and future experimental testing considerations and shows the results and potential findings. Firstly, the previous experimental studies involving quasi-static and shake table testing are presented. Then, a virtual experimental procedure is presented in order to tackle the most demanding aspects of calibration and parameter estimation for the simulation of dynamic structural response. The various types of experimental procedures are then combined in order to form a complete methodology for estimation of the main characteristics of the novel system and proceeding to a code conforming evaluation procedure. A combination of these experimental methodologies is the ultimate method for developing reliable numerical simulation model, as well. The calibrated model is subjected to reliability analysis in order to estimate the probability of failure for predefined failure scenarios. Finally, the numerical model is used for developing several archetype structures and thorough parametric study for EC conform design procedure.

The response of structures exposed to earthquakes is mainly defined by the stiffness, capacity and ductility of the structural elements which is governed by their dimensions and the material properties. The buildings’ seismic performance is essential for their earthquake resilience especially beyond safety point defined by the building code. The main philosophy of modern codes is to increase the earthquake resiliency of the buildings. Unfortunately, Macedonia is one of the last European countries where designing the structures according to outdated codes is allowed. The older national seismic codes have not been modified in view of the implementation of the most recent knowledge. In this sense, there are no strict limits to prevent the design of rectangular columns with an unsuitable ratio of the section sides. Mainly, due to the need for greater open space and flat interior walls, the columns are designed as rectangular where the lower section side is oriented along a larger span. This results in decrease of the global structural capacity in that direction affecting its response under earthquake excitation. In order to investigate the influence of the ratio of section sides of a rectangular column on seismic performance of building structures, an existing RC frame structure was chosen for analysis. The results of the performed seismic assessment of the selected structure by nonlinear static analysis, emphasize the importance of choosing square shaped columns or rectangular columns with appropriate arrangement in plan even for low-rise buildings. Based on the analysis’ results, we conclude that designers need to pay more attention when choosing columns’ cross section dimensions and orientation to achieve an acceptable building resilience against earthquakes.