ضریب رفتار

The tunnel form buildings provide some advantages for medium to high-rise buildings that constructed by using a special tunnel form technique are commonly built in countries facing a substantial seismic risk. There are no special requirements for seismic design of this type of buildings, and some provisions of the concrete bearing wall system are used. None of the seismic codes addresses the R factor for tunnel‐form buildings directly. This study presents R factor of this structural system based on the nonlinear pushover analyses of 7 case studies using the ABAQUS software. The impacts of shear wall reinforcement ratio and its detailing on system ductility, load-carrying capacity and failure mechanism under seismic forces are evaluated. Influences aspect ratio and wall openings on the response are also discussed.

In recent decades the use of special truss moment frames has been developed as relatively new steel frame systems in high seismic zones. These frames dissipate the seismic energy through the specific ductile parts that are located near the middle of the span of the truss beam. In this study the response modification factor of steel moment frames with specific truss beams due to the ductility and over strength was determined. The analysis was carried out using linear static analysis (pushover). In order to consider the nonlinear behavior of the material in formation of the plastic hinge، it was used the elasto-plastic behavior and it was assumed that the plastic hinge are created at the top and bottom of the column and beam. The analyses are carried out for two types of the frames، Vierendeel and across diagonals frames. These frames are evaluated for two cases، two and three spans، and also for different stories، 3 to 8-story. The results are shown that the response modification factor of the Vierendeel frame is more than the across diagonal frame’s and has a better seismic performance. The results also show that the response modification factor is dependent on the height of the structure، so that this factor is increased with increasing the height of the structure.

In this paper، the seismic behavior of steel dual frames with large-scaled concentrically bracings have been evaluated at special ductility level، and then the ductility reduction factor and the over-strength reduction factor for this type of structural system have been calculated. To do so، multi-story buildings with large scaled X- bracing form were considered. Then، the push-over static analysis، non-linear incremental dynamic analysis and linear dynamic analysis were performed to determine the effect of building height on the behavior factor. This study shows that the seismic behavior، the ductility reduction factor and the over-strength reduction factor decrease when the number stories of building increase. But the decrease rate in ductility reduction factor is more than the decrease rate in over-strength reduction factor. Finally، the behavior factor for each building has been calculated separately and، mean values، 5. 0 and 7. 5 have been recommended for limit-states design and permissible (or Allowable) stress approaches، respectively.

Determining structural maximum deformation under earthquake excitation is an important problem in seismic design of structures. There are several approaches in order to estimate an acceptable accurate response for maximum drift of the structure in nonlinear region. Both ATC and FEMA approaches are good ideas to evaluate maximum drift but more simplified approaches should be applied in seismic design codes. Most of seismic design codes suggest a very simple relation for estimating maximum drift in design base earthquake. Iranian seismic code of practice (Standard No. 2800) proposes such a relation. In this paper a comparison between nonlinear dynamic results and code suggested relation is carried out. 3 scaled records have been used for analysis. Based on reduction factor calculated for the structure, a comparison has been carried out with the suggested factor in Iranian Code of Practice (Standard No. 2800).

Eccentrically braced frames have high stiffness and suitable energy damping against the lateral forces like the earthquake. In this bracing system, the required stiffness and formability of the frame is provided by the link beam, and are dependent on the details and characteristics of the link beam. In recent years, Eccentrically Braced Frames (EBF) has been utilized as a resistant system against the earthquake lateral forces. In this paper, using non-linear static analysis, the behavior factors of MRF, CBF, and EBF frames in some models are investigated. These studies are carried on three-storey, six-storey, and ten-storey models, statically linear and non-linear. The results indicate that the EBF behavior factor is largely affected by the link beam. It is also concluded by the investigating of relative and overall displacements of the mentioned models that these parameters are dependent greatly on the length of the link beam.

After the 1994 Northridge and 1995 Kobe earthquakes and the extensive damage in moment resisting connections side plate connection was introduced. This connection is able to hold plastic hinge far from the beam-column connection and has sufficient strength and ductility so plastic hinges can form in beams. The structure is expected to withstand large deformations resulting from lateral loads, this property of structures is defined as ductility. In order to include ductility in structure analysis and also to use entire capacity of the structure, the conception of R-factor is used in linear analysis. To evaluate the ductility and R-factor of a structure, use of nonlinear analysis is inevitable. In the present study models of dual systems with side plate connections, various types of bracing, different braced spans and lateral load distribution patterns has been nonlinearly analyzed using PERFORM-3D at different heights (4, 8 and 12 stories). Then using Uang method ductility, extra resistance and behavior factor of the models were obtained and compared. On the basis of this study, the side plate connection increases R-factor and as the number of bracing increases, R-factor increases as well. Studying chevron, diagonal and X bracing indicates that R-factor is the greatest for diagonal bracing and smallest for chevron bracing. Comparison of uniform, triangular and modal lateral loading patterns indicates that R-factor reaches its highest value for triangular lateral load distribution and the lowest value is obtained through triangular loading pattern.