MODARES TECHNICAL AND ENGINEERING
Year:2002 | Volume:- | Issue:8|Papers Count:15

Cantilever beam mathematical models can be used for simulating the dynamic behavior of structures with the same support conditions and with high natural periods of vibrations. In this paper the transverse vibrations of hollow circular cantilever tapered beams with and without a mass at tip are studied. An exact and parametric method for computing the natural frequencies and mode shapes are presented using Bessel function. Modal effective mass and distribution of shear forces and bending moments are studied in the first three modes. The non dimensional frequency coefficients are calculated for change in tapers and increase in axial load. The exact and approximate solutions are obtained using computer program designed using Mathematical software. The exact solutions are compared with those calculated using the Rayleigh - Ritz approximate method and the given formula in Iranian code of practice for seismic resistance design of buildings.

In this paper, results of a series of static and dynamic tests performed on Shiraz silty clay, are presented. Using these test results, the effect of dynamic loading in reducing the stiffness and consequent degradation of the soil is illustrated. Different factors affecting the rate of reduction of soil stiffness are investigated. Among these factors the effects of reconsolidation pressure, cyclic strain amplitude and number of load cycles on the soil behavior are studied and empirical relationships correlating the soil stiffness to these factors are derived. Variation of soil damping ratio during cyclic loading is also highlighted. The normalized behavior of Shiraz silty clay, under both static and dynamic loading is investigated.

Reinforced concrete deep beam refer to a beam with relatively large depth in comparison with shallow beam. They are divided to three types: 1- Simply Supported 2- Continuous and 3- Fixed ended. They have high rigidity because of their large depth and when, the use of shallow beams are not economical. deep beams are used. They are usually used in highrise buildings, offshore structures. bridges silos, dam etc.The experimental results indicate that common mode of failure is shear, but flexural, bearing and buckling may occur. Therefore in analysis of the beam shear mode of failure and nonlinear behaviour are considered.In this paper, the experimental results of twelve continuous deep beam loaded from the top mid centre, tested at Tarbiat Modarrs University and Housing Research Centre are analysied. In the analysis all the important codes such as ACI, CIRIA etc. together with reported methods and two proposeal methods (Truss and Force Equilibrium) are used. The validity of proposed methods are controlled with test results of other researcher. The comparison of the results indicate that the proposed methods are safe, relaiable accuroed and simple.

ome two-parameter models for analysis of plates and beams on elastic foundation are discussed in this paper. Filoneko and Borodich , Pasternak and two-parameter layer models are given. Also, simplified elastic continuum and their governing equations due to Nogami and Vlasov are introduced. Then, a plate element on two-parameter elastic foundation is presented for three dimensional finite element analysis. In order to show the efficiency of the suggested method, some examples are solved.

Cyclones are conventional equipment for eliminating particulates from gas flows.Cyclones’ design is simple and they are reliable. However their efficiency for particulates less than 10 micrometer is very low. For this reason other equipment are used in industry. One of the efficient systems for eliminating particulates from gas, is cyclone-scrubbers. Cyclone-scrubber consists of a cyclone and a liquid that is injected by a pneumatic nozzle into gas entrance duct. Cyclone acts as a space for interaction between liquid and particles and a trap for the liquid-particle. Steady state and a long resident time for a specific particulate, lead to high removal efficiency for sub-micron particles. One of the advantages of cyclone-scrubber is low water usage. The ratio of liquid to gas is 0.2-0.5, which is less than other types of scrubbers (0.5-5.0).In this experiment, removal efficiency of cyclone for 4.5,9.0 and 13.0 m/s entrance velocity, were 85.5, 85 and 89.9%. In cyclone-scrubber, for the same conditions, the removal efficiency were 85.2, 95.6 and 97.4%. Removal efficiency for particles of 0.5 micron in cyclone was 3% while in cyclone-scrubber it was 63% with l/g=0.2.

The purpose of this study is to define some mechanical properties of concrete having pozzolan of west of Joopar with Kerman cement factory types 2 and 5 and their comparison with the control concrete.First by the termogravimetry test (TG), the pozzolanic activity index was determined. In order to find the optimum percentage of Joppar’s pozzolan different concrete mixes with 0 to 40 percentages of pozzolan by cement weight for six cases were made and tested for compression, at the ages of 7 and 28 days. Other variable parameters studied were; two curing conditions and two constant water-cement ratios.Now, to define the mechanical properties of concrete having optimum percentage of Joopar’s west pozzolans, the pozzolanic and the control specimens were cast and cured under the defined humidity conditions and tested for compressive, and flexural strengths and the modulus of elasticity at the ages of 28 and 90 days. Whereas to study the shrinkage the standard specimens were cast and the strain reading were taken at different ages (up to 90 days) after fixing the Demec advises on the surfaces of the concrete specimens.As the use of pozzolan as a cement replacement, needs to increase the quantity of water in the mix, therefore to reach a constant water-cement ratio, a super plasticizer were used. The results show that, the use of Joopar’s west pozzolan as a cement replacement caused both the quality and the mechanical properties to improve. It is also shown that, the amount of shrinkage is reduced for the pozzolanic specimens whereas, the modulus of elasticity is reduced comparing with those of the control concrete. Therefore for a particular aim, such an improvement can be useful.

The coarse grain materials such as riverbed alluvials are widely used in earth structures. There fore determination of their static and dynamic behavior is an important factor in the earth Structural analysis. Based on the results of this research, it can be shown that there are not any identical relation between the grain strength and the soil internal friction angle, but amount of fines in soil plays an important role in the strength of soil. In the cyclic triaxial tests also, the amount of fines (under 0.075mm) as an important effect on the soil stiffness. For example, increasing the fines to 14 percent increases the damping ratio and decreases the shear modulus considerably. Also based on findings of this research, it can be concluded that only by performing static tests, the Secant modulus of elasticity and then the shear modulus of coarse grained materials in the small Strains , (10-6 to 10-3) can be estimated without performing the cyclic tests.

Correlations between plasticity index (LL, PL ,PI), compaction effort and compaction characteristics (ωopt,γdmax) are of most importance in soil mechanics. Clays with different plastic properties are collected from different regions in Azarbaijan and Gorgan. These soils have been compacted with different compaction methods (Standard Proctor, Modified Proctor and Reduced Compaction). Then changes in the compaction characteristics due to variation of plastic properties and compaction effort have been investigated. Man made clayey soils are produced from the natural collected soils. These soils had constant fine grain percent ages. The effect of fine grains on compaction characteristics has been studied in these samples. In this research it has been concluded that increasing of compaction effort has different effects on improving of maximum dry density. Soils with high PI are more affected with compaction effort than low PI clays. Compaction curves shape showed that in clays with high PI the concaveness of the compaction curve is low and their sensitivity to water content variation are less than those of high PI clays.

In order to investigate the effect of different parameters on dimensions of scour hole Downstream of a flip bucket, extensive experiments were conducted. Effect of parameters like: radius of bucket, drop height, tail water depth and unit discharge have been investigated. It was observed that dimensions of scour hole is a function of radius of bucket, drop height, tail water depth and unit discharge. Dimensionless equations for prediction of scour hole dimensions are introduced.