Local and global effects of forward directivity

Ranija istraživanja pokazuju da pomaci tla u blizini rasjeda djeluju vrlo destruktivno na građevine smještene poprečno na plohu loma rasjeda. Zbog uobičajenog korištenja okvira otpornih na savijanje te zbog značaja snažnih pomaka u blizini rasjeda, u ovom se radu razmatraju utjecaji pulsirajućih pomaka tla dugog perioda (Tpulse>0,7s) na lokalno i globalno ponašanje pet uzoraka čeličnih okvira otpornih na savijanje, uzimajući u obzir varijacije zbog promjene visine modela. Rezultati pokazuju da se kod primarnog udara globalni i lokalni zahtjevi modela povećavaju za 1,1 do 2,6 puta tj. za 1,2 do 3,5 puta.Previous studies have revealed that near-fault ground motions perpendicular to the fault slip are very destructive for structures. Due to the common use of moment resisting frames and the importance of near-fault strong motions, the local and global effects of long-period (Tpulse>0.7s) pulse-like ground motions are studied on 5 samples of steel moment resisting frames by considering variations in the height of models. Results obtained show the forward directivity increases global and local demands of models for about 1.1 to 2.6, and 1.2 to 3.5 times, respectively

Study of Stiffness Effect of Panel Zone on Ductility of RBS Joint

Beam to column joint fractures on steel structures in Northridge earthquake produced some worries about the reliability of steel connections. Brittle fracture of bending joints indicated that ductility of construction materials doesn't ensure structure ductility, and structure geometry, loading type, and other specifications influence structure behavior. Stress (strain) concentration due to seismic moment changes may prevent distribution of plastic zone around joint, and this can be a justification for joint brittle fracture. RBS joint is one that came after Northridge earthquake, which is known as dog bone joint. In this kind of joint, by minimizing section of beam flange near support area (in which possibility of plastic joint formation is more), plastic joint is transferred from column side and joint area to inside beam and at proper interval with joint. To design this joint and achieve the goal of formation and development of plastic hinge in reduced area, many parameters must be considered. Panel zone is one of the most effective parts of a rigid steel joint. Resistance and stiffness value of panel zone has a large effect on behavior and performance of joints. This paper studies these kinds of joints and effects of changes in panel zone using cross-shaped substructure and ANSYS software. Regarding to the studies it was indicated that weak panel zone doesn't develop plastic hinge in beam, so collapses merely occurs in panel zone and joint area. In specimens with strong panel zone, because of elastic behavior of panel zone, all substructure energy is wasted in beam, so panel zone is not used efficiently

Study of inter story drift demands of multi-story frames with RBS connection

RBS connections are one of the most common deformable connections in the world. The plastic hinge will be placed in a conducted mode at a specific area in the beam using this type of connection. It is worth to mention that reducing the sectional area of the beam flange, in general, will cause a reduction in the strength and lateral stiffness of the structure. Hence, the effect of fabrication of the RBS connection, on the frame stiffness and lateral displacement of steel bending frames is analyzed. Regarding the high effect of drift on building’s damages, the effect of fabrication of RBS connections on increasing or decreasing of the frame drift are analyzed. In order to investigate the effect of fabrication of RBS connections, the results of RBS connection are compared with the results of cover plate connection. Keywords: Steel rigid connection; RBS connection; Cover plate connection; Drift; Time History

Comparative Evaluation of Behavior Factor of SMRF Structures for Near and Far Fault Ground Motions

In common design codes, earthquake loads are reduced by a coefficient (behavior factor) which depends on nonlinear seismic performance of structure during earthquake event. Nonlinear performance of structures depends on structural properties and ground motion characteristics. There are different methods for estimation of seismic response parameters such as behavior factor. One of the approaches is using incremental dynamic analysis. This paper gives estimations of behavior factor for special moment-resisting steel frames under near and far fault records using incremental dynamic analyses. Three moment resisting frames with, 3, 6, and 10 stories, are considered for evaluations employing two performance levels (Life Safety and Collapse Prevention). One aspect of difference among earthquake records is existence of velocity pulse in their time-history. This issue is investigated through evaluation of R factor for three frames. It is shown that behavior factor for near fault records is averagely 23% less than far fault records

Introducing teacher action research to language teachers: a new movement in language pedagogy

The main premise of this paper is to highlight the significance of teacher action research in language pedagogy as a tool for English teachers to ameliorate their teaching process. This study seeks to investigate two distinct objectives. First it aims to introduce three types of professional actions in teacher action research (TAR) to a group of English language teachers during pre-service and in-service TAR course program and learn its contributions to their professional development. Secondly, it aims at assessing and evaluating teachers' self-reported changes in knowledge and attitudes towards TAR through a retrospective pre-test. As for the second aim of the study, the researchers also seek to discover possible relationship(s) between variables such as teachers' level of education, their teaching experience, knowledge and attitudes towards TAR (both after and before being familiar with its concept and practice)

The Effect of Local Fuse on Behavior of Concentrically Braced Frame by a Numerical Study

The concentrically braced frames (CBFs) are one of the most widely used lateral load-resisting systems. Seismic performance of these structures has a weakness that is due to the brace buckling at a lower loading than the ultimate compressive loading capacity. In this paper, attempt is made to enhance the seismic response of CBFs through utilizing a local fuse. For this purpose, first the formulation of fuse area and length are presented. Then based on this formulation, several numerical models have been built and analyzed to examine the effect of implementing this fuse on seismic response of CBFs. From the analyses results, it is found that if the reduced cross-section fuse (RCF) is properly designed and also the end of brace is fixed, the CBFs with equal energy dissipation capacity, that are equipped with this fuse exhibit a better ductility than the customary CBFs