STRUCTURE AND STEEL
Year:2008 | Volume:4 | Issue:3|Papers Count:12

Concrete filled steel tube columns (CFST) are a kind of composite columns according to advantages of CFST relative to reinforced concrete and steel columns. Use of these materials is common in recent years especially in high buildings, unnecessary of moulding, high ductility, proportionate resistance with low volume, economical, low deformation relative to steel columns are among advantages. In these columns, development of full load bearing capacity depends on, bond strength between steel and concrete, local buckling of steel encasing, ratio of side dimension of the column to steel thickness, D/t, length to dimension ratio, L/D and finally the shape of column.In this paper, effective parameters on CFST columns behavior are investigated experimentally by testing specimens in laboratory. For this experimentally research, twelve specimens loaded axially with enhancing cyclic lateral load. The results of experimental investigation are compared with regulation relations and proposal analytical relation of some of the researchers.

Steel plate shear walls have high capability for earthquake energy damping as a lateral load resisting system. Since the number of steel plate shear walls with stiffeners tests is limited, therefore the comparison of force modification factor and energy absorption of them relative to steel plate shear walls without stiffener has not published up to now. For this goal two steel plate shear wails specimens with stiffeners and without stiffener was tested. Also a moment frame specimen of surround plate was tested for comparing of force modification factor and energy absorption relative to steel plate shear wails. Results show that force modification factor of steel plate shear wall with stiffeners and without stiffener is 11.5 and 12.2. Steel plate shear wail energy absorption without stiffener in various displacements is about 20 to 36 percent less than one with stiffeners. In steel plate shear wails specimens with stiffeners and no stiffener the Portion of moment frame energy absorption is about 50 and 67 percent.

Cylindrical steel above ground tanks extensively used in oil refinery complexes and oil depots in Iran. Past earthquake experiences in Japan, U.S.A, and Turkey show that these tanks are very vulnerable to strong ground motions and the study of the vulnerability and strengthening of these tanks are very important. In this paper, 5 steel above ground tanks with different ratio of height to diameter (HID) have been studied and different failure mechanisms including elephant foot buckling, diamond elastic buckling, failure of roof due to fluctuation of fluid, sliding, overturning, up lift and unsymmetrical settlement were assessed using nonlinear analyses. International documented references such as ASCE and API650 standards and static, modal, spectral (linear) and time history (nonlinear) analyses is used in this study. Results of the analytical study show that the minimum tree board of tanks should be 13 percent of the tank Height to avoid of roof damage during an earthquake. In addition, tanks with a height to diameter ratio greater than 1.0 are unstable with the problem of overturning. Other failure mechanisms mentioned above are not dominant in the case studied tanks.

The purpose of this paper is determination of response modification factor of shaft supported concrete elevated water tanks using nonlinear static (pushover) and nonlinear dynamic analysis. At First, using incremental nonlinear time history analysis, the seismic capacity curve is obtained and structural response modification factor has been computed. Then response modification factor is computed using pushover analysis with several load patterns. Shear effect on structural behavior is evaluated using the new procedure. Finally, using the proposed analytical procedure, the response modification factor is calculated. In the analytical method the effects of P- D, type of loading, plastic hinge in shaft and effect of stiffness variability in height of shaft is considered. The result represents the validity of the proposed analytical procedure.

Researchers have shown that using viscous dampers can have influential role in controlling response of structures against wind, explosion and earthquake. Most of structures, with the help of ductility, resist severe earthquakes which cause damages to nonstructural and structural components. Using viscous dampers can reduce large displacements and accelerations of structures and consequently reduce the ductility demand. This research studies different process of designing, construction and experiments of viscous dampers with the capability of adjusting damping for determine their mechanical characteristics. These experiments have done for the first time in country. The results show an acceptable function of these dampers.

Braced frames are popular a type of steel frames in Iran. In these structures different kind of braced are used to resist lateral loads and all connections are considered as fix-type connections. In practice great care is taken, but it is not possible to construct fully fix-type connections and they are partially fixed, however, to be on the safe side this fixity is neglected.In this research, experimental behavior of the braced frame connection with scale of 0.5 under cyclic load has been investigated. This study has been performed under the same loading condition using three tests: 1- bare frame made of beam and columns; 2- frame with gusset plates; 3- x-braced frame (braced made of two U sections). Results show that connection in these type of frames, although neglected in calculations, have some fixity and with use of gusset plates this fixity becomes much more.

Eccentrically Braced Frames are increasingly used in the design and/or retrofit of new and existing buildings and bridges. Accordingly extensive research works in this area is undertaken worldwide. In this paper a new type of Eccentrically Braced Frames composed of two vertical links is introduced. In this regard Eccentrically Braced Frames with double vertical links (DV-EBFs) are first introduced; effective parameters on selection of vertical link length and its design criteria are then explained. To investigate seismic performance of this system, nonlinear analyses (material and geometric) under monotonic and cyclic loading were performed to verify seismic behavior and effects of length and number of stiffeners used in the vertical link. The results show adequate shear strength, ductility and stiffness especially in short links with enough stiffeners.