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.

Repair of the existing buildings has always been a great challenge for the building companies and for the civil engineering scientists, as well. When there is no available design documentation, a chain of activities precede to the main design for repair: measuring, in situ geotechnical investigations, determination of the quality and quantity of the built-in materials with various methods, etc. An example for repair and strengthening of the existing structure of a car service in Skopje, Republic of Macedonia, is presented in this paper, as well as a new steel structure for overbuilding.

Extended end-plate bolted connections as moment-resistant connections between beam and column usually fall in the semi-rigid partial strength category. Simplicity, duplication, and economy made this joint widely used in steel frame structures. This type of joint is prevalent nowadays which requires knowledge of the entire nonlinear moment-rotation behaviour of the joints. Using ABAQUS FE software in this paper, a three-dimensional finite element model (FEM) is developed to identify the effect of different geometrical parameters on the behaviour of extended end-plate bolted connection with four bolts per horizontal row as a semi-rigid beam-to-column joint. The component method which, is adopted in Eurocode 3, parts 1-8, provides detailed application rules for the design of bolted end-plate connections when most of them are limited to configurations with two bolts only in each horizontal row, without column web stiffeners. By using the finite element model, a parametric study is conducted to study the influence of column web stiffeners (compression and tension stiffeners, K stiffeners, and double web stiffeners) on three main properties of extended end-plate bolted connection, moment capacity (Mj,Rd), initial rotational stiffness (Sj.in) and rotation capacity (Φcd) under monotonic loading, using finit element (FE) analyses. The analytical research work, done here gives specific attention to the characterization of joint ductility, which is one of the critical behaviours of semi-rigid connections compared with rigid or pinned ones based on finite element analyses.

The behaviour of the semi-rigid joints can be obtained by laboratory tests or by an appropriate finite element analysis. This paper describes the process of modelling joints in the SOFISTIK software package and their calibration method.The verification of the results obtained from the 3D models is performed with values obtained from laboratory tests. In the framework of the modelling and calibration process of the models, all parameters that influence the accuracy of the results are being reviewed.Analyzes performed with well-calibrated mathematical models including finite elements based on experimental research within certain parameters allow a large number of parametric analyzes to be faster and more economical if performed exclusively by laboratory tests.