AMIRKABIR JOURNAL OF CIVIL ENGINEERING (AMIRKABIR)
Year:2010 | Volume:42 | Issue:2|Papers Count:12

Now a days, improvement of human life and requirements to make suitable space cause to making structures with confident and safe seismic behaviror in earthquake, economical and architectural aims. In this way, eccentric braced frames with high ductility that innovated by Popov in 1977 are very useful. In this research, visual behavior of this systems of structures ecentrice braced frames (EBF) with R factor studying has been considered. The base method in this research for studying R factor is investigation of ductility and extra resistance in frames by capacity spectra of structures resulted from static nonlinear analysis. For reaching this idea, the structural cases with public construction method have been considered. Finally, the results showd that the structures designed by Iranian standard code NO.2800-84 rules are weak in acceptance of allowed ultimate deforming and resistance of earthquake design force in standard 2800-84. So, for reaching to suitable seismic behavior of structure in earthquake, lower R factor and lower allowed displacement for design of this structures should be used.

This paper presents an analytical approach for probabilistic assessment of inter-structure fire following ignitions. In this method, unlike the conventional methods which are based on statistical ignition rate, various sources of ignitions and their associated uncertainties are taken into consideration. Using probabilistic algorithms, ignition probabilities for each source of ignition as well as overall ignition probabilities for each building are estimated. A GIS-based computer software are designed and implemented based on the proposed approach in order to estimate regional ignition probability. A scenario-based approach is used in this model in order to remove potential sources of probabilistic correlation. However, the model is capable of providing full probabilistic ignition results using a Monte Carlo simulation approach. Using the proposed model, the built environment data as well as seismotectonic of northern Iran are used in order to estimate preliminary ignition probabilities for district 3 in northeastern Tehran.

In many geological structures, the matrix permeability is negligible and the fractures are the main flow paths. The fluid flow and particle transport through rock fracture are increasingly important research topics mainly to the demands for design, operation and safety assessments of underground/ surface constructions. In this paper, single-phase fluid flow through a rock fracture is studied. Computational domain for an artificial three-dimensional fracture is generated and used for numerical fluid flow simulations. Both laminar and turbulent flow simulations are performed by using finite element method for a wide range of inlet velocities. The calculated average pressure drops, between consecutive vertical sections are compared to describe the flow rate dependant pressure drop. The simulations results show that, (i) the predicted static pressure drop for turbulent flow simulation was roughly 3% to 17% more than laminar simulation at Reynolds number of 4.5 to 89.5, respectively, and (ii) the Forchheimer law is fitted very well to flow simulation results and critical Reynolds number of 15 is suggested.

Settlement in the saturated sands after seismic loading is one of the important phenomenons, because of induced damages after the earthquake loading. In this study, the effects of plastic fines on volumetric response were evaluated after cyclic loading in saturated sands. All of the tests were performed by cyclic triaxial tests and strain-controlled method. The results show increasing in excess pore pressure affects on volumetric response after cyclic loading even at the excess pore pressure less than its value to liquefaction. In the sand-kaolinite mixtures for excess pore pressure ratio (ru) less than 60%, the volumetric compressibility of the specimens contain 10% and 20% kaolinite is near to it's of clean sands but their excess pore pressure value around the liquefaction are a little more than clean sands (~2% to 2.5%). At the lower excess pore pressure, the specimens contains 30% kaolinite show the volumetric strain 4 times greater then other specimens.

In spite of the fact that different methods are available for dynamic analysis of concrete dams, researchers are still studying other more efficient alternatives. Modal approach can highly improve the efficiency of analysis, since the response of dam must be generally calculated for several earthquake ground motion records. In this paper, two different methods have been considered for dynamic analysis of concrete gravity dams including dam-reservoir interaction (with pressure degrees of freedom for fluid domain). The coupled modal approach utilizes the coupled modes of the system for the analysis, and the decoupled modal approach employs the decoupled modes of system for this purpose. Calculation of the coupled modes involves some complications, due to its corresponding unsymmetrical eigen-problem induced. However, dynamic equation of motion can be solved very efficiently by using this method. In decoupled approach, the symmetry in the assumed corresponding eigen-problem results in faster calculation of modes. The equation of motion can also be solved with reasonable speed in this method.In the last part of this paper, analysis of a typical dam-reservoir system is performed by both methods mentioned above. Both of these approaches have shown to be very efficient and have their own advantages at point of view of the calculation cost and memory allocations.

The properties of the surface and the core, due to the hydration heat development, are normally different in mass concrete. In the present paper, hydration heat regime was applied on a cabinet contain specimens, with 0.3 water/cement ratio, to examine the influence of heat development on strength properties. Natural pozzolan, fly ash and silica fume were used, as partial replacement for cement in the predetermined specimens. The samples were taken after 1, 2 and 5 days from cabinet, to simulate surface and core of mass concrete, and then were cured in special conditions. The results indicated that strength of the natural pozzolan and fly ash samples, which were taken after 2 days from heat cabinet, attained maximum strength. While, strength of the silica fume specimens promoted when 1-day remolding time was used. Furthermore, silica fume adversely diminished compressive strength of the core specimens.

On the end of 1970s.The concept of (Ca/Cc) was developed by Mesri et al. in order to analyze the secondary compression settlements. There is a general acceptance in the (Ca/Cc) concept after many investigations made with different soil specimens.We have found no studies signifying the properties of secondary compression of the soils in various part of Iran considering constant (Ca/Cc) concept, also there were no reports on the value of (Ca/Cc) ratio on Iran's soils. So, in this paper the secondary compression behavior of Iran’s soils was investigated through the performance of a series of conventional and long-duration one-dimensional consolidation tests conducted on undisturbed samples from six different sites in the central and northern parts of Iran. The characteristics of secondary compression index were examined, and the relationship between the coefficient of secondary compression, (Ca), and the compression index (Cc), was established for all of these soils. The results of comparison between secondary compression index equations and (Ca/Cc) ratio concept show the ability of this concept to estimating the secondary compression index of samples.

As the use of Self Compacting Concrete becomes common, the risk of exposing it to elevated temperatures increases. However, few investigations have been reported on the mechanical properties of SCC when it is exposed to elevated temperatures. Mechanical properties of SCC containing Pumice (P) at elevated temperatures up to 800oC were experimentally investigated in this paper. Four different mix designs, Traditional Concrete (TC), SCC and two other SCC mixtures containing pumice as a replacement for both cement and filler were produced. At the age of 28 days, the specimens were placed in an electrical furnace and heating was applied at the rate of 2.5 (oC/min) up to the desired temperature. Maximum temperatures of 200, 450, 600 and 800oC were maintained for 2 hr. Then, the specimens were allowed to be cooled in the furnace and subsequently tested for compressive strength, rebound hammer, ultrasonic pulse velocity and weight loss. The residual compressive strength of SCC mixture containing pumice as a filler replacement almost was higher than the other mixtures up to 800oC.

Double-I-built-up columns are used in most of existing steel moment frames. The traditional moment connection of I-beam to these columns is made using flange plates. Due to flexibility of column cover plate, these connections behave as partially restrained, semi-rigid and brittle connections. Vertical stiffeners are proposed for upgrading the connection.To compare the behavior of the connection before and after upgrading, non-linear finite element models of one-sided sub-assemblage is being analyzed under cyclic loading. Hysteretic moment-rotation curves and stress and strain contours of traditional and retrofitted models were compared. The results show that, vertical stiffeners modify the force transferring mechanism and reduce the deformation of column cover plate, which improve connection behavior considerably.

This paper discusses performance of tall steel structures with dual system (comprised of SMRFs and Intermediate RC shear walls) in near-fault ground motions according to acceptance criteria introduced in FEMA356 and ATC40. Achieving this purpose and in comparison with far-fault ground motions and evaluating acceptability of push-over analyses in performance based design method some nonlinear time history analyses under near-field and far-field records and some nonlinear static analyses are performed. Thereafter acceptance criteria of structures is checked. The results show that despite of appropriate performance of dual system under far-fault excitations structural performance is not acceptable under near-fault ground motions because of inadmissible story drifts. Deficiency of Iranian code (Standard No.2800) in exhibition of critical load combination for column’s seismic design and inadequacy of push-over analysis in demonstrating tall buildings performance are other results of this study.

In this study, a non-plastic silt is grouted by sodium silicate in an electrokinetic cell. The silicate solutions are injected through the reservoir next to the anode electrode. The injection of Na- silicate solution increases the strength adjacent to the anode electrode between 5 to 8 times compared with the base soil. Increasing silicate concentration generates lower increase in strength across the specimen. This means that decreasing the silicate concentration increases the penetration length of the grout. Neglecting the results for anode side of the specimens, the maximum increase in strength has been observed for injection of 5% silicate solution through the anode with acid in the cathode chamber. The obtained strength is 3.3 to 4.0 times greater than the strength of the base soil with the highest penetration length.The application of this technology for increasing the strength of the soil underneath an existing foundation or generation of pile through the soil is proven.

Shear Panel system is one of the most useful passive control methods, in which shear panel devices are installed between node of chevron braces and flange of the floor beam. In this paper, the effect of using shear panels or vertical link beams on seismic energy dissipation is numerically investigated. Using shear panel system, the seismic behavior of 2D, 5 and 8-story frames was improved. Analyses were conducted by Seismo-Struct software. In this way, base shear, top story displacement and maximum acceleration of the floors in 5-story frames were reduced respectively 29, 70 and 62%, while in 8-story frames these parameters were reduced respectively 43, 27 and 40%. Story drifts were mostly reduced and became uniform. In all parameters, effectiveness of using SPS, Shear Panel System, in 5-story frame was more than that in 8-story frame. In fact by using SPS, in addition to increasing the ductility of the structures with decreasing seismic demand, seismic behavior of structures was improved. Finally, using shear panel is highly recommended as an easy to use and efficient way consistent with construction condition in the country for seismic design of new steel building structures and also for seismic retrofit of existing steel buildings.