JOURNAL OF SCHOOL OF ENGINEERING
Year:2007 | Volume:19 | Issue:1 (CIVIL ENGINEERING ISSUE)|Papers Count:12

Variation of behavior factor of reinforced concrete moment resisting frames (RC-MRFs) with high and medium ductility level is investigated upon the effect of concrete confinement for two soil types and hazard levels. For this purpose concrete stress-strain curve in tension and compression for confined and unconfined concrete is studied and then the best modified model was selected for the nonlinear static analysis of RC-MRF through IDARC computer program. Dead load and 20% of live load was applied as gravity loading upon which the lateral load was distributed according to the generalized power distribution method along the height of the frames. Based on ATC-19, the analysis was carried out using idealized capacity diagram on the basis of stiffness degradation model as well as equal elasto-plastic dissipated energy model, for both confined and unconfined concrete of appropriate frames. The results indicate that the behavior factor of confined frames are different from those of unconfined frames, and also vary with respect to the aspect ratio of the frames.

The Iranian Concrete Code (ICC) specification suggests a simple expression that is a function of story height for estimating tension flange effective width in flanged reinforced concrete (RC) shear walls. Other influential variables sush as drift level, wall width, and the level of axial load are not addressed in the ICC expression. A detailed finite element model is used to investigate the effect of these parameters on the tension flange effective widt. The finite element accounts for nonlinear concrete behavior and is validated through conmparisons to test data. The analytical results show that the tension flange effective width is strongly dependent on all the variables investigated. Implications of the presented data regarding existing guidelines are discussed and provisions are suggested that are suitable for implementation in performance-base design criteria.

Stress-strain behavior of clay soils, commonly, is indicated by explicit mathematical models. The models can not consider all of circumferential and experimental conditions, i.e., consequent stress-strain curves do not contain any secondary property of soil. Theory of Fuzzy sets and Fuzzy systems is a powerful tool to consider environmental impacts on stress-strain behavior. In this paper, a fuzzy model is provided, using a data set collected from Karkheh and Siazakh soil samples, in South west of Iran, which express stress-strain behavior of clay soils more accurately. The study consists of three parts: application of theory of fuzzy sets and fuzzy inference is reviewed firstly, then, stress-strain behavior of clay soils is explained. Implementation of fuzzy inference system to predict stress-strain relation of clay soils is expressed finally.

FEMA273 provisions relate maximum deformation demands to performance levels, while such relations have not been provided for cumulative deformation demands of the elements. On the other hand, the factor of cumulative deformation demand may be regarded as a criterion for damage level, which can present a different feature of the structure response under maximum deformation demands. In order to compare the parameters of maximum and cumulative demands, a case study was implemented on 4, 10 and 25 story and 3 bay frames under Manjil earthquake ground motion. In this study three maximum responses and cumulative drift response of the frames’ stories have been measured and evaluated. The cumulative damage results, corresponding to Life Safety and Collapse Prevention levels, are of great importance and may affect higher performance levels, such as repairable damages. The rate of damage, applied to the structure, is evaluated by damage indexes (which are function of structure ductility, the energy dissipated in the structure, period, number of loading cycles, maximum story displacement limit and etc.) and its numerical value is related to the damage applied to an element or to whole the structure based on a certain classification. In this study maximum story displacement limit (Ddps,i) is presented as an index of structural damage in story level. It was resulted that the estimation of cumulative deformation demands in inelastic structures (subjected to long duration ground motions with considerable effects of higher modes and due to the increase in the number of inelastic cycles) is an important and critical factor in evaluation of Steel Moment Resisting Frames’ demands. It was also seen that the difference between maximum values and cumulative plastic deformation (caused by maximum demand locations in height of the structure or due to the amplitude of relative demands between different stories) is considerably increased in top stories of the structure, which can be ascribed to the increase in number of inelastic cycles in top stories and to the higher mode effects.

Investigation on the volume change behavior of sands is one of the most important issues in Geotechnical engineering. Formulation and mathematical modeling for prediction of the stress –strain and strength of soils under various stress conditions, especially saturated sands under cyclic loading, requires a profound understanding of the volume change behavior of soils. Despite having many apparent advantages, most of the behavioral models developed by researchers loose their efficiency in predicting soil behavior in unloading  path. In this paper, after presenting discussion on the volume change mechanism, it is shown that the total volume change in granular soils can be divided into 3 different components. For each of the component, a new and rational relation is introduced; the sum of which is considered as the total volume change under loading or unloading condition. In order to investigate the variation of stress ratios and stress-dilatancy under triaxial loading conditions, a new comprehensive model is introduced using the new volume change relation mentioned above. The accuracy and efficiency of the proposed model is examined by comparison of the experimental results on  sands available in the literature and those predicted by the present model. It is shown that the proposed model predicts well the soil behavior under various stress or sand density conditions.

In the past, Geomorphologic Instantaneous Unit Hydrograph (GIUH) had been proposed as a tool to generation of flood hydrographs from storm rainfall data. Nowadays, Spatial Unit Hydrograph is used instead, with making use of Geographic Information Systems (GIS). First, watershed is divided into small square cells, and then routing of runoff from each cell to the basin outlet is calculated using the first passage time response function based on the mean and variance of the flow time distribution, which is derived from advection- dispersion transport equation. The flow velocity for ground surface cells is calculated by Overton’s equation and for channel flow cells by Manning’s equation based on the local slope, roughness coefficient and hydraulic radius. The total direct runoff at the basin outlet is obtained by superimposing all contributions from every grid cell. The model is tested on kameh catchment in Khorasan Razavi state. Results are in excellent agreement with the measured hydrograph at the basin outlet. Sensitivity analysis shows that parameters of channel roughness coefficient and minimum slope threshold have larger influence than parameter of thershold of drainage area in delineating channel networks on peak discharge, time to peak and on the outflow hydrograph, Since the model accounts for spatially distributed hydrologic and geophysical characteristics of the catchments, it has great potential for study of the influence of changes in land use or soil cover on the hydrologic behavior of a river basin.

To obtain the more accurate response of the arch dam in frequency domain, the dynamic analysis should be carried out by imposing the dam-foundation rock interaction effects. To do so, the foundation rock is usually considered as a substructure, and its impedance matrix is computed separately. In this article, the impedance matrix for the static case is obtained by utilizing the three-dimensional boundary element method, and so, the flexibility effect of the foundation rock is imposed. In this approach, the geometry of canyon could be quite arbitrary and this has become possible due to the fact that a 3D boundary element formulation is applied for foundation rock domain. In the results section, the seismic responses of a real arch dam are presented, and they are verified by the results of the well-known finite element method. It should be mentioned that the analyses are performed by the special purpose program developed.

This article is an investigation to determine mixture proportion of high strength structural light weight concrete in order to reduce the weight of concrete by using expanded aggregate clay (Leca), which in Iran is produced by industry. In order to reach to high strength concrete mineral and chemical admixtures additives have been used. Also stone powder has been used to reduce porosity and to increase compressive strength. Regarding the performance of this type of concrete, the variables in different mix designs are as follow: The ratio of water to cementitious materials, the amount of light weight aggregate to the total volume of concrete, the amount of cement and stone powder. Test for compressive strength, indirect tensile strength and flexural strength were carried out on the specimens. The specimens made in the concrete laboratory of Mazandaran University were kept under the water. In order to investigate the effect of curing on the compressive strength of these types of concrete from each mix design some specimens were kept in the open air. The results of this research show that by using light weight aggregate (Leca) it is possible to reach to a light weight structural concrete with dry unit weight of 1610 – 1965 kg/m3 with cube compressive strength of 34 to 71 MPa. Also, it has been observed the role of stone powder for the improvement of mechanical properties of concrete with light weight aggregate is very important.

The great potential accidents’ risk involved on and in the vicinities of bridges, has been gradually more evident by vehicles’ technology progress and the increase in their obtainable speed and acceleration. This risk is related to the high number of accidents and casualties, which are caused by hitting roadside obstacles and/or prolabsus to the nearside valleies, rivers, lakes, etc. In this research-work the physical and traffic characteristics related to nineteen bridges, which are selected from initially twenty five nominated bridges in rural roads in the province of khorasan; were collected. Then a set of mathematical operations including development and expansion of statistics regression models, which possess the capabilities of predicting accident frequencies in accordance with effective independent variables; were carried out. The results show that among physical and mathematical bridges’ characteristics, the reduction of shoulder width has the highest impact on the bridge traffic safety. The traffic mixed interaction and intervention and also the bridge width, are almost equally the next most effective factors.In the process of this research-work for the first time, a “Bridge Safety Index” model, which is specifically generated, for Iran rural roads; is developed. This model can be economically beneficial and generate important decision-making results, including prediction of bridges’ traffic safety, optimization of bridges’ rehabilitation and maintenance expenditures, and defending related financial resources.

One of the most important factors in satisfactory composite action of a repair system, is its adhesion to the substrate concrete. Although some methods such as pull-off have been studied and used for the assessment of the bond strengths of the repair systems, but the values obtained are influenced by the method of loading, substrate concrete texture, failure planes, etc. This paper presents the results of the application of friction-transfer method for assessing the bond strengths of different cementitious, polymer added and resinous repair materials. Substrate concrete used in this research included both saw cut and split/sand blasted surfaces. Since the surface strength of the saw cut concrete is much higher than the split surfaces, the sawn surface was considered for a better assessment of the true bond strength. Based on the optimization method analysis of the results, it is recommended that, when mixed failures are involved, 10 percent should be added to the bond strengths measured on rough surfaces. Application of the multiple regression analysis, also suggests the use of an equation for a better assessment of the bond strengths. In this equation, in addition to the failure stress, the percentages of repair, bond and concrete failures have been accounted for.