Ferdowsi Civil Engineering
Year:2018 | Volume:31 | Issue:1 (21) |Papers Count:9

Moment-resisting steel frames (MRSFs) have high ductility, however, suffer from low lateral stiffness and large lateral drifts. Recently, a new LFRS called knee-braced moment frame (KBMF) has been introduced in the literature in which the seismic behavior of an ordinary moment frame is improved using some knee elements as structural ductile fuses in the vicinity of beam-to-column moment connections. In this research, seismic behavior of some 3, 6 and 10 stories KBMFs with different span numbers are studied using nonlinear static and dynamic time-history analyses. The results show that the overstrength factor as well as behavior factor of KBMFs are considerably larger than the corresponding factors for MRSFs. Furthermore, it was observed that the column axial demands in KBMFs – except for the top stories-are smaller than those proposed in the Seismic Provisions for MRSFs.

In this paper, new algorithm is proposed for fictitious mass of Dynamic Relaxation (DR) method with viscous damping. First, the incremental equations are derived for DR procedure. By using the transformed Gershgö rin theory, new boundaries are achieved for fictitious mass. This formulation leads to a new algorithm for viscous DR method. For evaluating the efficiency of the proposed method, some 2D and 3D truss and frame structures are analyzed by elastic linear and geometrically nonlinear behaviors. Results show that the proposed scheme for fictitious mass improves the convergence rate of DR method so that the suggested algorithm presents the structural response with less iteration in comparison with other common DR techniques.

Developing three dimensional vortices at river meander causes severe erosion at the toe of the outer bank and deposition at the inner bank. The flow altering measures which have been presented so far are installed on the bed and are subject to failure due to progress of scour hole at their toe. Therefore in the present study the performance of immersion vanes, which are installed above the bed, are experimentally investigated. To reach such goal a movable physical model of 180 degree Karoon river bend was constructed. Different tests at Froude number equal to 0. 20 (=corresponded to the Karoon 2-years flood occurrence discharge) at six different vanes angles equal to 10, 20, 30, 40, 50, and 60 degrees was carried out. The general results show that the immersion vanes are effectively shifted the scour hole from the bank toe to the middle of the bend while no scour is observed at the base of the vanes. By comparing the bed topographic variations after tests it was found that at 40 degrees vane angle the toe scour hole is smaller and developed much farther from the outer bank compare to the other vane angles.

The evaluation of the country past earthquakes show that many reinforced concrete buildings in Iran are not earthquake-resistant. Damage to buildings against earthquakes, changing land use, changing guidelines and the development of building, are among the reasons that necessitate the retrofitting. In this research, retrofitting the reinforced concrete frames with conventional concentric and eccentric and buckling restrained braces was analyzed and by changing the distance between core and steel sheath, the effect of these parameters on the behavior of bracing and consequently the structural behavior has been studied. The results showed that by increasing the distance between the core and steel sheath, the deformability of steel core of buckling restrained braced frame is reduced, and localized strength degradations are caused in the retrofitted structure that it was observed reduce of structural energy dissipation by 5-20 %.

This research compares the influence of different kinds of lime on the amount and time of swelling pressure of bentonite. In the present research, constant volume method was used for measurement of samples of bentonite soil mixed with 3 % of quick and hydrated lime compacted at 2 – 3 % dry of optimum water content and after curing period of 0, 1, 7, 28 and 90 days. The results showed that adding quick lime to bentonite decreased the magnitude of swelling pressure, the time to reach to primary swelling pressure, time rate of secondary swelling pressure and both stress and strain controlled swelling indices more effectively than the use of hydrated lime. It was also determined that the values of these parameters decreased further with increase in curing period. Traditional quick lime had the least slope of secondary swelling pressure with time. The slope of secondary swelling pressure with time for samples stabilized with industrial quick lime were lower than those which were stabilized with industrial hydrated lime.

The characteristics of PP and PVA FRC specimens under impact and flexural tests with totally 56 specimens were investigated in this paper. The test results indicated that effective parameters of impact were significantly increased and the specimen behavior were improved. The strength and energy absorption of rectangular specimens were respectively increased by 54 and 200% when the PVA fiber percentage was twice. Final strength PVA specimen with 3% fiber was 87% higher that of PP specimen with same fiber percentage. The impact strength of specimens reinforced with PVA fiber was three times of same specimen reinforced with PP fiber.

This study investigated the effect of alkaline solution-to-slag ratio on permeability of Alkali-Activated Slag Concrete (AASC). Concrete, as the most widely used building material, has an undeniably important role in development of economic and civic infrastructure. Alkali activated slag cement is an environmentally friendly alternative to Portland cement, which can be produced by using an alkaline solution to activate the binding effect of the blast furnace slag. Permeability of concrete has a direct impact on its durability, so in this study a series of tests were arranged to examine the effect of alkaline solutionto-slag ratio on water impermeability, chloride permeability, short-term and total water absorption and compressive strength of AASC specimens. In experimental study four concrete mixes with alkaline solutionto-slag ratios of 0. 4, 0. 45, 0. 50, and 0. 55 were considered. One mix made by ordinary Portland cement were also considered for comparison of results. In addition, The images taken from samples AASC and Ordinary Portland Cement Concrete (OPCC) by means of scanning electron microscopy (SEM) were used to study the comparison of microstructure. The results showed that the alkaline solution/slag ratios of 0. 45 and 0. 50 are the optimum values for AASC production from the durability and permeability point of view.

Previous studies on the behavior of clayey soil mixed with granular materials shows that major researches has been done under low confining stress level so that they almost exhibit behavior similar to normally consolidated clayey soils and by increasing content of granular materials both of the shear strength and excess pore water have been raised. In some researches, the results are inconsistent and the effect of grain size of granular materials is not clear. To study the behavior of these soils comprehensively, a series of consolidated undrained triaxial tests carried out on the clay and clay – sand mixtures under a wide range of confining stresses. The results show that the behavior of these soils depends on sand content and grain size. Adding 60% sand to clay, the shear strength increases and the mixtures consist of fine sand has lower strength in comparison with those of including coarse sand. It also observed that dependent on content and size of sands, the behaviors of specimens change from contractive to dilative one. So that at low confining stresses, by an increase in sand content from 0% to 60%, the behavior of samples change from contractive to slight dilation and then it is observed heavily dilation at samples include 60% sand.

Using continuity plates in the balance of the tensile and compressive beam's flanges in the box column is for satisfying stiffness and strength criteria according to terms of the 2800 code and the tenth issue of national building regulations. Since in box columns due to section closure, lack of vision and inappropriate viewing angles performance of the continuity plates inside the column has many problems, continuity plates removed from the box column and rigidity of connection provide by stiffeners from outside welded the joint and their Installation is more simple than continuity plates. For this purpose connectivity models without continuity plates, connection with continuity plates, connection with trapezoidal external stiffener, connection with internal stiffener including networks of horizontal bar and the proposed new connection which includes of the external stiffeners, concrete and networks of horizontal bar by ANSYS software modeling and analyzed. Graph of force – displacement of models is drawn based on monotonic and cyclic analyzes and on their have been determined rigidity, strength, ductility, energy dissipation as well as the location of plastic hinges in every connection. The analysis determined that the proposed new connection with the acquisition of rigidity 96. 18, ductility 7. 04, ultimate strength 89. 45 ton and transferred the plastic hinge into the area far from connection, therefor it is a good alternative for continuity plates.