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Showing 11 results for Footing

H. Ghiassian,
Volume 2, Issue 1 (3-2004)

A study of bearing capacity and compressibility characteristics of cohesive soil, reinforced by geogrid and supporting square footing loads has been conducted. The lack of adequate frictional resistance between clay and reinforcing elements was compensated by using a thin sand layer (lens) encapsulating the geogrid sheet. In this way, tensile forces induced in the geogrid were transferred to the bulk clay medium through the sand particles and soil reinforcement was improved Experiments were conduced on two sets of specimens, one set of 1 x 1 x 1 m dimension and the footing size of 19 x 19 cm (series A), and the other set of 0.15 x 0.15 x 0.15 m dimension and the footing size of 3.7 x 3.7 cm (series B). The loading systems for the above specimens were stress controlled and strain controlled respectively. All specimens were saturated and presumably loaded under an undrained condition. The results qualitatively confirmed the effectiveness of the sand lens in improving the bearing capacity and settlement characteristics of the model footing. In series A, the maximum increase in the bearing capacity due to the presence of the sand lens was 17% whereas in series B, the amount of increase was 24%. The percentage reductions in the settlement for these results were 30% and 46% respectively.
S. Eshghi, V. Zanjanizadeh,
Volume 5, Issue 3 (9-2007)

This paper presents an experimental study on seismic repair of damaged square reinforced concrete columns with poor lap splices, 90-degree hooks and widely spaced transverse bars in plastic hinge regions according to ACI detailing (pre.1971) and (318-02) using GFRP wraps. Three specimens were tested in “as built” condition and retested after they were repaired by glass fiberreinforced plastic sheets. They were tested under numerous reversed lateral cyclic loading with a constant axial load ratio. FRP composite wraps were used for repairing of concrete columns in critically stressed areas near the column footings. Physical and mechanical properties of composite wraps are described. Seismic performance and ductility of the repaired columns in terms of the hysteretic response are evaluated and compared with those of the original columns. The results indicated that GFRP wraps can be an effective repair measure for poorly confined R/C columns due to short splice length and widely spaced ties with 90-degree anchorage hooks. Both flexural strength and ductility of repaired columns were improved by increasing the existing confinement in critical regions of them.
A. R. Majidi, A.a. Mirghasemi, M. Arabshahi,
Volume 9, Issue 4 (12-2011)

In the current study, an effort is made to determine three dimensional bearing capacity of rectangular foundations using Discrete

Element Method. The soil mass is modeled as discrete blocks connected with Winkler springs. Different factors affect the geometry

of failure surface. Six independent angles are used to define the failure surface. By trial and error, the optimum shape of failure

surface beneath the foundation can be found. The paper includes the derivation of the governing equations for this DEM based

formulation in three dimensional state as well as parametric sensitivity analyses and comparison with other methods. Moreover,

using the current method, bearing capacity coefficients are presented for various friction angles and foundation aspect ratios.

S. N. Moghaddas Tafreshi, Gh. Tavakoli Mehrjardi, M. Ahmadi,
Volume 9, Issue 4 (12-2011)

The results of laboratory model tests and numerical analysis on circular footings supported on sand bed under incremental

cyclic loads are presented. The incremental values of intensity of cyclic loads (loading, unloading and reloading) were applied

on the footing to evaluate the response of footing and also to obtain the value of elastic rebound of the footing corresponding

to each cycle of load. The effect of sand relative density of 42%, 62%, and 72% and different circular footing area of 25, 50,

and 100cm2 were investigated on the value of coefficient of elastic uniform compression of sand (CEUC). The results show that

the value of coefficient of elastic uniform compression of sand was increased by increasing the sand relative density while with

increase the footing area the value of coefficient of elastic uniform compression of sand was decreases. The responses of footing

and the quantitative variations of CEUC with footing area and soil relative density obtained from experimental results show a

good consistency with the obtained numerical result using “FLAC-3D”.

A. Asakereh, S.n. Moghaddas Tafreshi, M. Ghazavi,
Volume 10, Issue 2 (6-2012)

This paper describes a series of laboratory model tests on strip footings supported on unreinforced and geogrid-reinforced sand
with an inside void. The footing is subjected to a combination of static and cyclic loading. The influence of various parameters
including the embedment depth of the void, the number of reinforcement layers, and the amplitude of cyclic load were studied.
The results show that the footing settlement due to repeated loading increased when the void existed in the failure zone of the
footing and decreased with increasing the void vertical distance from the footing bottom and with increasing the reinforcement
layers beneath the footing. For a specified amplitude of repeated load, the footing settlement is comparable for reinforced sand,
thicker soil layer over the void and much improved the settlement of unreinforced sand without void. In general, the results
indicate that, the reinforced soil-footing system with sufficient geogride-reinforcement and void embedment depth behaves much
stiffer and thus carries greater loading with lower settlement compared with unreinforced soil in the absent of void and can
eliminate the adverse effect of the void on the footing behavior. The final footing settlement under repeated cyclic loading becomes
about 4 times with respect to the footing settlement under static loading at the same magnitude of load applied.

A. R. Rahai, S. Fallah Nafari,
Volume 11, Issue 4 (12-2013)

The seismic behavior of frame bridges is generally evaluated using nonlinear static analysis with different plasticity models hence this paper tends to focus on the effectiveness of the two most common nonlinear modeling approaches comprising of concentrated and distributed plasticity models. A three-span prestressed concrete frame bridge in Tehran, Iran, including a pair of independent parallel bridge structures was selected as the model of the study. The parallel bridges were composed of identical decks with the total length of 215 meters supported on different regular and irregular substructures with non-prismatic piers. To calibrate the analytical modeling, a large-scale experimental and analytical seismic study on a two-span reinforced concrete bridge system carried out at the University of Nevada Reno was used. The comparison of the results shows the accuracy of analytical studies. In addition, close correlation between results obtained from two nonlinear modeling methods depicts that the lumped plasticity approach can be decisively considered as the useful tool for the nonlinear modeling of non-prismatic bridge piers with hollow sections due to its simple modeling assumption and less computational time.
J. Nazari Afshar, M. Ghazavi,
Volume 12, Issue 1 (1-2014)

The Stone-column is a useful method for increasing the bearing capacity and reducing settlement of foundation soil. The prediction of accurate ultimate bearing capacity of stone columns is very important in soil improvement techniques. Bulging failure mechanism usually controls the failure mechanism. In this paper, an imaginary retaining wall is used such that it stretches vertically from the stone column edge. A simple analytical method is introduced for estimation of the ultimate bearing capacity of the stone column using Coulomb lateral earth pressure theory. Presented method needs conventional Mohr-coloumb shear strength parameters of the stone column material and the native soil for estimation the ultimate bearing capacity of stone column. The validity of the developed method has been verified using finite element method and test data. Parametric studies have been carried out and effects of contributing parameters such as stone column diameter, column spacing, and the internal friction angle of the stone column material on the ultimate bearing capacity have been investigated.
H. Shahnazari, M. A. Shahin, M. A. Tutunchian,
Volume 12, Issue 1 (1-2014)

Due to the heterogeneous nature of granular soils and the involvement of many effective parameters in the geotechnical behavior of soil-foundation systems, the accurate prediction of shallow foundation settlements on cohesionless soils is a complex engineering problem. In this study, three new evolutionary-based techniques, including evolutionary polynomial regression (EPR), classical genetic programming (GP), and gene expression programming (GEP), are utilized to obtain more accurate predictive settlement models. The models are developed using a large databank of standard penetration test (SPT)-based case histories. The values obtained from the new models are compared with those of the most precise models that have been previously proposed by researchers. The results show that the new EPR and GP-based models are able to predict the foundation settlement on cohesionless soils under the described conditions with R2 values higher than 87%. The artificial neural networks (ANNs) and genetic programming (GP)-based models obtained from the literature, have R2 values of about 85% and 83%, respectively which are higher than 80% for the GEP-based model. A subsequent comprehensive parametric study is further carried out to evaluate the sensitivity of the foundation settlement to the effective input parameters. The comparison results prove that the new EPR and GP-based models are the most accurate models. In this study, the feasibility of the EPR, GP and GEP approaches in finding solutions for highly nonlinear problems such as settlement of shallow foundations on granular soils is also clearly illustrated. The developed models are quite simple and straightforward and can be used reliably for routine design practice.
M. Haghbin,
Volume 12, Issue 4 (12-2014)

This research examines the behavior of soil-reinforced piles and applied loads based on the analytical method and by using the numerical results of FLAC3D software for comparison with the analytical results. The analysis was based on a method called virtual retaining wall, the following into consideration: an imaginary retaining wall that passes the footing edge the bearing capacity of footing on reinforced soil with piles, which was determined by applying equilibrium between active and passive forces on virtual wall and a pile row that exists beneath the shallow foundation. To calculate the lateral pile resistance here, an analytical equation was then required. The main objective of this paper is to determine the percentage of applied load on pile. Similarly, the effect of adding pile in various positions relative to the present footing (underpinning) was studied in this research. The various parameters of this study included pile length, vertical distance of pile head to shallow footing, pile distance to center of footing and location of the pile. Finally, the findings were compared with the numerical results of FLAC3D and the formerly presented experimental results. Results show that the analytical method, while being close to other methods is more conservative.

Mohammad Reza Lotfizadeh, Mohsen Kamalian,
Volume 14, Issue 2 (3-2016)

A study has been conducted on the bearing capacity of strip footings over sandy layered soils using the stress characteristic lines method. Traditional bearing capacity theories for specifying the ultimate bearing capacity of shallow foundations are based on the idea that the bearing layer is homogenous and infinite. However layered soils are mainly happening in practice. The stress characteristic lines method is a powerful numerical tool in order to solve stability problems in geotechnical engineering. In the present paper, an appropriate algorithm is derived for estimating the static bearing capacity of strip footing located on two layered soils using the stress characteristic lines method. Some numerical and experimental examples are presented in order to validate the proposed algorithm. Some graphs and equation are presented for initial estimating the effective depth of strip footings located on two layered soils.

Maryam Haghbin,
Volume 14, Issue 7 (10-2016)

In the present research, an analytical method is applied to determine the bearing capacity of strip footing on two layers of the soil. Bearing capacity of the footing is calculated according to soil resistance beneath the foundation and virtual retaining wall method. In the said method, the active and passive force on the retaining wall are considered equal on the edge in order to determine the bearing capacity of the footing. Regarding two layers of soil, the active and passive forces of each layer is found and their resultant is applied to calculate footing bearing capacity. This method has many advantages including the possibility to determine the depth of rupture surface of the soil beneath the footing, and to study the effect of the soil second layer on footing bearing capacity. Moreover, the effect of soil improvement beneath the footing as well as the depth and width of compacted area on bearing capacity of footing are also studied here in this research. In general, the studied parameters in this project consist of soil layers thickness, soil cohesion and friction angle, footing depth and width, the width of compacted soil beneath the footing, and the depth of underground water. By programming in MATLAB, the calculation and deduction was fulfilled. The results were compared with the bearing capacity of the footing on one layer of the soil in various situations in order to study the effect of various parameters in two layers of the soil. Finally, this bearing capacity of the footing was compared with the previous experimental methods and reliable results were obtained.

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