STRUCTURE AND STEEL
Year:2015 | Volume:11 | Issue:17|Papers Count:8

Pounding problem between fixed-based structures due to large earthquakes may cause local damages or lead to the structure’s total collapse. Inadequate gap distance between structures could influence pounding between adjacent structures. Limited studies could be found on pounding analysis of modern systems as based-isolation buildings. In the present paper, we have modeled two adjacent structures, fixed base building and base isolated one in order to assess the effects of near and far properties of earthquakes on their response. Results show that critical impact could occur when mean period (Tm) is close to the natural period of structures. Also, if the highs of adjacent structures are nearer to isolated structures, the effects of near field earthquakes would increase. As a results, with increasing the height of adjacent structure, the amount of affected impact force in near-field motions is amplified 4 times more than far-field ones.

After Northridge earthquake, many researches were introduced low cycle fatigue as one of the reasons of failure of connections under cyclic earthquake loads.The most of the studies of low cycle fatigue in flexural steel frame structures, has been experimentally and analyticaly done in local scale. Therefore, the evaluation of all critical points of structure and the effect of seismic parameters in global scale is necessary. In the present study modelling and dynamical analisys of an flexural steel frame and also the effect of low cycle fatigue under various earthquakes in the mentioned frame connections has been investigated. The amount of damage or decrease in fatigue life has been properly coordinated with response of various earthquakes. On the other hand, the result shows that the increase of the first acceleration of earthquake leads to increase of damage due to fatigue in connections. Also, as time of earthquake decreases down to 68 percent, the fatigue damage in connection has been decreases about 17 percent.

In this study to evaluate the effect of high-strength steel and energy-absorbing steel in moment frame structures, a numerical investigation was undertaken of column-tree moment connections with three type of steels as ST37, ST19 and ST52. Also, in order to improve steel moment connections, the possibility of replacing the proposed model has been analyzed by common popular models. The results show acceptable ductility and energy absorption capacity and also stable hysteresis curves in the models which have been made of light steel in the plastic zone. As a result, using ST37 steel in plastic hinges of connections which were made of ST52 steel, increase the ductility (36%) and energy absorption (5.8%) in compared with column-tree connections which are fully made of ST37. Also applying ST19 in plastic hinges of ST37 connections will bring more ductility in a range of 64 percent and will increase the energy absorption. Accordingly, this study recommends this column-tree connection with combined steels as a good alternative for rigid connections.

Concentrically braced frames are among the most common systems due to ease of implementation and low cost compared to the moment resisting frames, however non-ductile behavior after buckling of compression element is noticeable. So, various research projects have been conducted to deal with this shortcoming. In this paper, the effect of steel angle in slit brace is considered to prevent its buckling. Stresses and displacement of structures using nonlinear static analysis by finite element software "ABAQUS" are evaluated. Results indicate improved cyclic performance and ductility of CBF systems. In addition, comparing the hysteresis loop of the proposed sample with that of normal braces shows symmetric and stable rational behavior where strength and stiffness degradations are not observed in the displacement up to about 3 cm while the normal brace buckles in about 1 cm.

In this study, the behavior of slip-critical connection of steel beam to CFT column has been analytically studied by using and not using web stiffeners in beam. In the studied connections, steel beam and triangular stiffeners attached on its flanges are installed on both sides of connection by the end-plate and passing rods through the column. In this study, 5 specimens with different number and arrangement of beam web stiffeners have been designed by AISC 2011 specifications and modeled with the finite element software of ABAQUS and subjected to static and cyclic loadings. To achieve correct trend of analytical modeling in software, the results obtained from a tested experimental specimen have been compared with stimulated analytical one and have been evaluated. In addition to proving the appropriate behavior of the connection under cyclic and static loading, the analytical study of the designed specimens confirm the significant effect of beam web stiffeners on the performance of studied connection.

Coupled steel plate shear walls are an extension of the steel plate shear wall (SPSW) system. Limited research and lack of appropriate methodology to analyze and design such system has led to less understanding of the behavior and conservative design requirements. In this paper the conventional elastic design approach for the system is introduced and performance-based plastic design (PBPD) method is developed for seismic design of this system. In order to evaluate the design method, 12 samples of 6 and 12-story structures with 30, 45 and 60 percent coupling and different coupling beam length are designed using this methodology. To evaluate the performance of sample structures a nonlinear static analysis is conducted. Steel plates are modeled with nonlinear orthotropic membrane elements. The results showed that the proposed design method, would lead to further insight into the structural behavior, more control over the design and achieve performance targets.

In this research, the performance abilities of tube type lateral load resistant framed systems are studied in order to assess the dynamic response of mid-rise steel structures under effects of far and near-field ground motions. For this purpose, three 10 story structural models with separated framed tube based skeletons were selected and designed. The structural models have been designed according to the Iranian seismic code 2800 (3rd edition). The main criterion which was considered to select powerful ground motions for performing nonlinear time history analyses is the existence of energized coherent velocity pulses as well as high amplitude acceleration spikes in the time history of each earthquake record. Assessment of the analytical results should emphasize on the importance of both lateral displacement and drift parameters which must be taken into account during the design phase. Furthermore, it was concluded that the maximum drift demand is more than 0.035 and the upper level of rotation of rigid connecting zones was obtained more than 5 percentages of a radian. As a general note, it was concluded that the seismic response parameters of mid-rise steel framed tube structures are intensively influenced by those strong earthquake records which contain forward directivity effects and are able to emerge long period pulses in their time histories.