جستجوی مقالات مرتبط با کلیدواژه « near-field record » در نشریات گروه « عمران »

In this research, a review was conducted on the characteristics of strong ground motions in near-fault zones, as well as the analysis of its effects on seismic behavior of mid-rise structures with two types of earthquake resistant skeletons. The studied structural models are mid-rise 10 story buildings with bundled tube frame and 3d moment frame. Also, the analytical capability of the modal pushover analysis (MPA) method has been studied on the estimation of structural response parameters. The maximum inter-story drift, axial force, roof maximum displacement of the studied structures was determined by conducting nonlinear dynamic time history (NTH) analyses and MPA method under the effects of an ensemble of lateral loads. An analytical comparison was accomplished among the obtained results.

This paper presents a computational approach to the analytical performance of modal pushover method (MPA) in predicting nonlinear response parameters of tall buildings compriding hybrid framed tube with large scale zipper elements. The accuracy of the results based on MPA is evaluated by comparing the benchmark responses obtained through conducting two sets of nonlinear time history analyses (NLRHA). Also, the effect of higher modes on the structural response parameters is measured by considering three computational vectors of the ordered lateral loading prepared according to the participation of the basic mode as well as the first 3 and 5 transitional modes, separately. In this study, the determination of the target displacement in MPA was set based on the results of NLRHA under two groups of near and far field records. The variation range of response parameters of the three high-rise 30storey studied structures was evaluated based on conducting a series of MPA as well as NLRHA analyses. The computational outputs of the MPA are compared with the results of the NLRHA (as exact values) and the standard error percentage is estimated. Evaluation of the results represented in this study demonstrates the relatively desirable computational capability of the MPA method in predicting the behavior characteristics of tall building structures with symmetric and regular rigid skeleton at plan and height. Moreover, it was observed that the presence of large-scale zipper elements in resistant system can reduce the seismic response parameters and also relatively increases the overall dynamic stability of high-rise structural skeleton.

In this study, the nonlinear behavior of a studied 20story steel bundled tube frame structure is evaluated under applying the assumed incidence angles to the imposed directions of near-field records. Additionally, the related effects on the stability of the studied structure subjected to the probable forming of progressive collapse, have been studied too. The results of this research were obtained based on conducting nonlinear dynamic time history analyses. Four assumed incidence angle case studies were considered to an ensemble of three-component earthquake records. Moreover, three-member removal situations were also assumed for the selective column elements of the studied structure subjected to all chosen ground motions.The results of this study show that the structural response parameters have a relatively larger amplitude under removing of the corner column at the first story, than the other two cases of column removal which to be assumed at 10th story and also for the middle column of the outer frame. Furthermore, the structural responses did not change significantly with the increase of the incidence angle from 0° to 45°. The obtained results show that the formation of plastic hinges and inelastic zones in the structure would indicate high deformation demands at the middle stories and also the induced demand variation decreases along upward of the height. Additionally, removing of the corner column would result in the formation of more plastic hinges, which cause relatively greater structural damages and gradually reduces the stability of the studied structure. It is worth noting that the structural response parameters under each element removal and subjected to strong near-field records, remains in a relatively stable domain. Furthermore, the variation of response parameters did not exceed the life safety limit.

The study includes an analytical approach to the issue of improving the seismic performance of the frame tube resistant skeleton. In this regard, the use of large-scale zipper elements in resisting skeleton of structures is investigated. Add a configuration of these elements only on the lower floors of structures can be a positive effect on reducing the parameters of the dynamic response of combined frame tube structures. Reduction of inter story drift and permanent drift, Creating downward trend in absolute acceleration and relative velocity graphs of the center of mass, Reducing non-linear rotation of panel zones, Represents the better performance in the skeletal configuration of a prototype tall frame-tube structure. Three 30-story building of frame tube skeleton and two configurations in combination with large-scale zipper elements selected and designed. A set of nonlinear analysis for side loading of these structures are done based on a choice of five powerful earthquake records. The presence of high-energy pulses and extensive acceleration spike with a combination of high speed pulses in selected time history records, is characterized by the modelling of near-fault ground motions. The skeleton of selected structures is designed based on the sixth and tenth National Building Regulations and the 2800 (Fourth Edition). Evaluation of the results showed that presence of large-scale configuration Zipper-Elements in the lower decks, Create an integrated behavior mechanism and the continuity of the seismic performance in tall building rigid skeleton. Showing the stable structural dynamic behavior of structures, particularly in large velocity pulse range, Along with reducing drift parameter, are the most important characteristics of such infrastructure in resistant skeleton tall buildings.

The aim of this research is to study the parameters of nonlinear dynamic behavior of steel tall buildings having a compound braced-tube resistant skeleton with belted trusses in higher levels. For this purpose, four 30-story study models have been designed in 3D. The first study model has a resistant skeleton without a belted truss. Yet, the remaining three structural models, each have a belted truss in higher levels with layouts of one, two and three stories, respectively. Numerical study results of this research are acquired according to a set of time-history nonlinear analyses on the mentioned study models. The chosen ensemble of three-component ground motions includes six highly powerful near-field records and one far-field record. Assessing study results reveal that applying belted trusses in tall braced-tube skeletons would lead in a remarkable increase in stiffness and a growth in the capability to absorb the earthquake’s kinetic energy. This issue also results in a large decrease in lateral displacement and dynamic drift of the structure and will therefore cause an increase in using the axial capacity of peripheral columns of the structure plan. Thus it becomes possible to introduce the application of resistant structures with belted trusses in structural skeletons of high-rise buildings, especially in areas with high seismicity as a suitable and efficient alternative plan compared to other structural systems.

Steel moment frame and bracing panels compound structures are suitable systems for medium-height resistant skeletons due to their desirable ductility along with high rigidity when facing large dynamic forces caused by earthquakes. In this research, the seismic behavior of two 10-story buildings with compound systems of moment frame/eccentrically braced frames as well as moment frame/eccentrically braced frame with zipper elements are evaluated. The evaluation and changes of the seismic response parameters of the studied models are based on performing nonlinear time history analyses. The studied models are designed according to the fourth edition of seismic design provisions in Code 2800, plus the 6th and 10th issues of the Iranian National Building Regulations. Following the results of this research, it has been recognized that the existence of large coherent pulses in the time history of powerful earthquakes affects the response parameters of the building to a great extent. The results of this research includes the analytical process in the graphs related to maximum push of the drift, floors acceleration and velocity of the studied structural models and also the time history of story’s drift and axial force of the columns. The results show that seismic responses and demands under near-field records have a bigger appearance than the corresponding effects obtained exposed to far-field records.