نشریه سازه و فولاد
سال هشتم شماره 15 (پاییز و زمستان 1393)

While working with slip critical connections, one of the most critical factors for high strength bolts is to achieve to a specific value of pretension. This pretension varies depending on several factors such as condition of thread, nonlinear local behavior (head, thread, nut, and other components of the connection), lubrication, and dynamic frictional effect of tightening speed. The current study addresses one of these factors which is the dynamic effect of tightening speed of the bolt performed by automatic machines. In this respect, four samples were carefully examined in laboratory showing that the friction factor of bolt tightening with minimum speed is smaller than the same with average speed. The results indicate that lower tightening speed with smaller torques concludes to a higher pretention, while increasing the tightening speed results in a greater friction factor and nut factor, and consequently, making it difficult to reach to the needed pretention.

After northridge earthquake in 1994, different details for constructing new moment resisting connections to attain a ductile behavior under earthquake excitations were recommended. As a substitution instead of welded moment resisting connections, researchers recommended the utilization of post-tensioned moment connections in moment resisting frames to resist against earthquake loading. Post-tensioned connections are composed of high-strength steel cables which are erected parallel to the beam web and then are crossed through the column and finally would be fixed at the column’s flange face. Firstly, steel cables create compression between beam and column flanges, secondly they provide the resisting moment of connections against applied service loads and eventually these cables would cause self-centering of columns, which means that the columns would get back to their initial position after they are tilted by earthquake excitation. Moreover, two steel angle sections are added at the top and bottom surfaces of these connections, in order to dissipate the earthquake energy in the joint area. In this paper, in addition to introduction of this Connections, the modeling mode for them with the OPENSEES software and evaluation of accuracy of modeling results compared with experimental results, evaluated the Seismic demand of Post-Tensioned Steel Moment Resisting Frames by change in Post-Tensioned effect parameters for 4,7 and 10 story under time history dynamic analysis. The results indicate that reduced frames seismic demand with increasing force and the number of Post-Tensioned cables, thickness of angles and decreasing the ratio of length to thickness of angles.

Steel Plate Shear Walls in recent decades as a lateral load resisting system of buildings, especially tall buildings have been discussed. Using this system in tall buildings requires a detailed analysis on behavior of Steel Plate Shear Walls. In tall buildings, bending deformations are more effective. So in this research, three-story Steel Plate Shear Walls are analyzed by modified - slop deflection method which considers bending deformations. The plates in this system are equaled by diagonal springs. Plate - frame interaction method is used for calculating plate stiffness. The process of analysis is conducted in a programming language in order to reduce analysis time. Analytical results in compare with finite element analysis show incorrect assumption in plate - frame interaction method for making complete diagonal tension field in post-buckling phase should be modified. After modifying, analytical results in compare with finite element analysis show good coincidence.

In field studies of one hundred under construction steel skeletons was found that over 70 percent of these frames contain operational defects in the welded connection of braces. Since in Iran, most steel skeletons are made in situ and then installed, therefore, the lack of accuracy in installing end plates of braces during the assembly causing the braces are not fully fitted on end connection plates and thus leading to form gap between braces and the end plates. Unfortunately, the welders to solve the problem, put rebar in the gap between the brace and the connection plate, and then fill it with welding. In this research to quantify the effects of the aforementioned problem in the strength of welded joint, both theoretical and experimental investigations were carried out. The standard welded connection and the welded connection with the rebar as filler were modeled by the ABAQUS finite element software and exerted by tensile force. Similar test samples were prepared and tensile tests were performed. This study shows that in both methods, theoretical and experimental, the strength of welded joint with a rebar as filler is 30 to 33 percent lower than the resistance of the standard welded joint. The result suggests that the need for care and supervision of those involved in the construction of the steel frames related to the technical principles in welding, and in particular welding of braces should be important and serious issues.

The performance of connections has a significant importance in a steel structure. Designing and executing of connections without adequate accuracy can cause failure not only on the connection but even on the connection members. As a result this may have destructive effects on the whole structure. So an accurate perception of connection behavior is necessary for a safe and economical design. In this paper, static and seismic behavior of recommended splice Iran National Code is examined and contrast with behavior common splices. With finite element software, static and seismic behavior three types of splices including bearing, covering with filler plate and covering with section transfer and the collapse performance, the way of connection fracture, cyclic and static resistance of connected column are considered in this paper. The results of investigation show that recommended column splice mentioned in the 10th, has the most Focus stress of transfer part and low resistance than spliced column with filler plate and covering plate. The collapse performance of examined columns is of local buckling in transfer plate or other part of columns.

Most energy dissipation system have some limitations and drawbacks such as difficulties related to ageing, durability, complexity of the installation, maintenance and placing permanent displacements after strong earthquakes. Characteristics such as large strain range without any residual deformation, high damping capacity, excellent re-centering, high resistance to fatigue and corrosion and durability have made shape memory alloy an effective damping device or part of base isolators. This paper investigates the seismic performance of an elastomeric bearing type base isolation system utilizing the shape memory alloys. To provide this investigation, a nonlinear structural model has been developed. The results of dynamic time history analyses reveal the significant characteristics of the proposed structural isolation system. This smart base isolation utilizes the different responses of shape memory alloys at several levels of strain to control the displacements of the rubber bearing and base shear at excitation level. Furthermore the proposed based isolation systems has enhanced performance in terms of response reduction and re-centering capacity.

One of the most common types of the bolted connections is the Endplate connection. Understanding of the structural behavior of connections and good knowledge of the power transmission by them and more accurate understanding their behavior for modeling and analysis and accurate monitoring on their implementation is necessary. In this study, component method is used for I beam-to-CFT column connection with end plate. Then, by comparing the results of behavior of the beam-to-column connection with experimental method, modeling accuracy of the modeled samples is investigated under monotonic loading. Analysis results shows that the moment - rotation curves of the experimental sample and mathematical model are reasonably close to each other and so we can use this method for the parameterization of this type of connection with reasonable accuracy.