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Showing 36 results for Columns

Mazloom M., Ramezanian Pour A.a.,
Volume 2, Issue 1 (3-2004)

This paper presents the long-term deformations of reinforced high-strength concrete columns subjected to constant sustained axial forces. The objective of the study was to investigate the effects of binder systems containing different levels of silica fume on time-dependent behaviour of high-strength concrete columns. The experimental part of the work focused on concrete mixes having a fixed water/binder ratio of 0.35 and a constant total binder content of 500 kg/m3. The percentages of silica fume that replaced cement in this research were: 0%, 6%, 8%, 10% and 15%. The mechanical properties evaluated in the laboratory were: compressive strength secant modulus of elasticity strain due to creep and shrinkage. The theoretical part of the work is about stress redistribution between concrete and steel reinforcement as a result of time-dependent behaviour of concrete. The technique used for including creep in the analysis of reinforced concrete columns was age-adjusted effective modulus method. The results of this research indicate that as the proportion of silica fume increased, the short-term mechanical properties of concrete such as 28-day compressive strength and secant modulus improved. Also the percentages of silica fume replacement did not have a significant influence on total shrinkage however, the autogenous shrinkage of concrete increased as the amount of silica fume increased. Moreover, the basic creep of concrete decreased at higher silica fume replacement levels. Drying creep (total creep - basic creep) was negligible in this investigation. The results of the theoretical part of this researchindicate that as the proportion of silica fume increased, the gradual transfer of load from the concrete to the reinforcement decreased and also the effect of steel bars in lowering the concrete deformation reduced. Moreover, the total strain of concrete columns decreased at higher silicafume replacement levels.
B. Behnam, M.h. Sebt, H.m. Vosoughifar,
Volume 4, Issue 2 (6-2006)

By identifying the damage index of a structure, in addition to a correct understanding from real behavior of the structure, the required criterion for strengthening would be given. Researchers have given many relations for determination of damage index but such relations have been based upon laboratory methods which challenge their usage in a broad term. In this paper two new methods are given for calculation of damage index. Surveying the first crack limit and total structure failure is based upon the formation of plastic joints in the first column and basic floor columns. To give a qualitative simple and functional damage index, the functional method was given in the form of a qualitative method with statistical analysis and collection of different views. Using this method is very simple and meantime offers suitable accuracy. With a numerical study on three models it was made clear that the difference of new method with amended method of Papadopolos in approximate 3%. This shows that given qualitative method is suitable to be used in a broad terms.
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.
Sassan Eshghi, Khashaiar Pourazin,
Volume 7, Issue 1 (3-2009)

Confined masonry buildings are used in rural and urban areas of Iran. They performed almost satisfactory

during past moderate earthquakes of Iran. There is not a methodology in Iranian Seismic Code (Standard 2800-3rd

edition) to estimate their capacities quantitatively. In line with removing this constraint, an attempt is made to study

in-plane behavior of two squared confined masonry walls with and without opening by using a numerical approach.

These walls are considered based on Iranian Seismic Code requirements. Finite element 2D models of the walls are

developed and a pushover analysis is carried out. To model the non-linear behavior of the confined masonry walls, the

following criteria are used: (1) The Rankine-Hill yield criterion with low orthotropic factor to model the masonry

panel (2) The Rankine yield criterion to model reinforced concrete bond-beams and tie-columns (3) The Coulomb

friction criterion with tension cutoff mode to model the interface zone between the masonry panel and reinforced

concrete members. For this purpose, the unknown parameters are determined by testing of masonry and concrete

samples and by finite element analysis. Comparing the results show that the initial stiffness, the maximum lateral

strength and the ductility factor of walls with and without opening are different. Also, the severe compressed zones of

the masonry panels within the confining elements are found different from what are reported for the masonry panels

of infilled frames by other researchers. This study shows that a further investigation is needed for estimating capacity

of confined masonry walls with and without opening analytically and experimentally. Also where openings, with

medium size are existed, the confining elements should be added around them. These issues can be considered in the

next revisions of Iranian Seismic Code.

M. Saiidi, C. Cruz, D. Hillis,
Volume 8, Issue 1 (3-2010)

Three unconventional details for plastic hinges of bridge columns subjected to seismic loads were developed,

designed, and implemented in a large-scale, four-span reinforced concrete bridge. Shape memory alloys (SMA),

special engineered cementitious composites (ECC), elastomeric pads embedded into columns, and post-tensioning

were used in three different piers. The bridge model was subjected to two-horizontal components of simulated

earthquake records of the 1994 Northridge earthquake in California. The multiple shake table system at the University

of Nevada, Reno was used for testing. Over 300 channels of data were collected. Test results showed the effectiveness

of post-tensioning and the innovative materials in reducing damage and permanent displacements. The damage was

minimal in plastic hinges with SMA/ECC and those with built in elastomeric pads. Conventional reinforced concrete

plastic hinges were severely damaged due to spalling of concrete and rupture of the longitudinal and transverse

reinforcement. Analytical studies showed close correlation between the results from the OpenSEES model and the

measured data for moderate and strong earthquakes.

Kabir Sadeghi,
Volume 9, Issue 3 (9-2011)

An energy based damage index based on a new nonlinear Finite element (FE) approach applicable to RC structures subjected to cyclic, earthquake or monotonic loading is proposed. The proposed method is based on the evaluation of nonlinear local degradation of materials and taking into account of the pseudo-plastic hinge produced in the critical sections of the structure. A computer program is developed, considering local behavior of confined and unconfined concretes and steel elements and also global behavior and damage of reinforced concrete structures under cyclic loading. The segments located between the pseudoplastic hinges at critical sections and the inflection points are selected as base-models through simulation by the proposed FE method. The proposed damage index is based on an energy analysis method considering the primary half-cycles energy absorbed by the structure during loading. The total primary half-cycles absorbed energy to failure is used as normalizing factor. By using the proposed nonlinear analytical approach, the structure's force-displacement data are determined. The damage index is then calculated and is compared with the allowable value. This damage index is an efficient means for deciding whether to repair or demolish structures after an earthquake. It is also useful in the design of new structures as a design parameter for an acceptable limit of damage defined by building codes.  The proposed approach and damage index are validated by results of tests carried out on reinforced concrete columns subjected to cyclic biaxial bending with axial force.

A. Kaveh, O. Sabzi,
Volume 10, Issue 3 (9-2012)

In this paper a discrete Big Bang-Big Crunch algorithm is applied to optimal design of reinforced concrete planar frames under

the gravity and lateral loads. Optimization is based on ACI 318-08 code. Columns are assumed to resist axial loads and bending

moments, while beams resist only bending moments. Second-order effects are also considered for the compression members, and

columns are checked for their slenderness and their end moments are magnified when necessary. The main aim of the BB-BC

process is to minimize the cost of material and construction of the reinforced concrete frames under the applied loads such that

the strength requirements of the ACI 318 code are fulfilled. In the process of optimization, the cost per unit length of the sections

is used for the formation of the subsequent generation. Three bending frames are optimized using BB-BC and the results are

compared to those of the genetic algorithm.

A. A. Maghsoudi, H. Akbarzadeh Bengar,
Volume 10, Issue 4 (12-2012)

In order to lighten the prestressed concrete solid members, nowadays, it is possible to make use of the advantage of HPC (fc'>60

MPa) as well as replacing the solid section with a PSC thin-walled section for certain members such as circular and box columns.

Using the strength theory of ACI, a numerical procedure along with a computer program was developed for the analysis of such

sections subjected to axial compression or tension load and bending moments. The program solves for all possible variables such

as, concrete compressive strength (fc'= 60-100 MPa), type of prestressed steel, concrete cover, ratio of wall thickness to the section

dimensions and the PS steel arrangements to satisfy the given loading cases, thus leading to an optimal cost solution. However,

since the cross section is thin-walled circular or box and the PS steel is located at discrete points along the periphery of a circle

or rectangle, the equations of equilibrium are complex for hand computations (especially for circular section) but suitable for

computer program. So, by use of MATLAB software the interaction diagrams were also drawn for the analysis of such sections

for all mentioned variables. The use of prestressed thin-walled column diagrams is a safe and easy tool for the analysis of such

columns. Finally, the accuracy of the proposed method is demonstrated by comparing its results to those of the available

experimental values and is indicate that the proposed method predict very well the capacity of prestressed thin-walled column.

Seyed B. Beheshti-Aval,
Volume 10, Issue 4 (12-2012)

A comparison between design codes i.e. ACI and AISC-LRFD in evaluation of flexural strength of concrete filled steel tubular

columns (CFTs) is examined. For this purpose an analytical study on the response of CFTs under axial-flexural loading is carried

using three-dimensional finite elements with elasto-plastic model for concrete with cracking and crushing capability and elastoplastic

kinematic hardening model for steel. The accuracy of the model is verified against previous test results. The nonlinear

modeling of CFT columns shows that the minimum thickness that recommended by ACI and AISC-LRFD to prevent local buckling

before the steel shell yielding for CFT columns could be decreased. The comparison of analytical results and codes indicates that

the accuracy of ACI method in estimation of axial-flexural strength of CFT columns is more appropriate than AISC-LRFD. The

ACI lateral strength of CFTs is located on upper bond of the AISC-LRFD’s provisions. AISC-LRFD estimates the lateral strength

conservatively but ACI in some ranges such as in short columns or under high axial load levels computes lateral strength in nonconservative

manner. Supplementary provisions for post local buckling strength of CFT columns should be incorporated in high

seismic region. This effect would be pronounced for column with high aspect ratio and short columns.

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.
H. Rahami, A. Kaveh, M. Ardalan Asl, S. R. Mirghaderi,
Volume 11, Issue 4 (12-2013)

In the process of structural analysis we often come to structures that can be analyzed with simpler methods than the standard approaches. For these structures, known as regular structures, the matrices involved are in canonical forms and their eigen-solution can be performed in a simple manner. However, by adding or removing some elements or nodes, such methods cannot be utilized. Here, an efficient method is developed for the analysis of irregular structures in the form a regular structure with additional or missing nodes or with additional or missing supports. In this method, the saving in computational time is considerable. The power of the method becomes more apparent when the analysis should be repeated very many times as it is the case in optimal design or non-linear analysis.
H. Shakib, Gh. R. Atefatdoost,
Volume 12, Issue 1 (3-2014)

An approach was formulated for the nonlinear analysis of three-dimensional dynamic soil-structure interaction (SSI) of asymmetric buildings in time domain in order to evaluate the seismic response behavior of torsionally coupled wall-type buildings. The asymmetric building was idealized as a single-storey three-dimensional system resting on different soil conditions. The soil beneath the superstructure was modeled as nonlinear solid element. As the stiffness of the reinforced concrete flexural wall is a strength dependent parameter, a method for strength distribution among the lateral force resisting elements was considered. The response of soil-structure interaction of the system under the lateral component of El Centro 1940 earthquake record was evaluated and the effect of base flexibility on the response behavior of the system was verified. The results indicated that the base flexibility decreased the torsional response of asymmetric building so that this effect for soft soil was maximum. On the other hand, the torsional effects can be minimized by using a strength distribution, when the centre of both strength CV and rigidity CR is located on the opposite side of the centre of mass CM, and SSI has no effect on this criterion.
A. R. Habibi, Keyvan Asadi,
Volume 12, Issue 1 (3-2014)

Setback in elevation of a structure is a special irregularity with considerable effect on its seismic performance. This paper addresses multistory Reinforced Concrete (RC) frame buildings, regular and irregular in elevation. Several multistory Reinforced Concrete Moment Resisting Frames (RCMRFs) with different types of setbacks, as well as the regular frames in elevation, are designed according to the provisions of the Iranian national building code and Iranian seismic code for the high ductility class. Inelastic dynamic time-history analysis is performed on all frames subjected to ten input motions. The assessment of the seismic performance is done based on both global and local criteria. Results show that when setback occurs in elevation, the requirements of the life safety level are not satisfied. It is also shown that the elements near the setback experience the maximum damage. Therefore it is necessary to strengthen these elements by appropriate method to satisfy the life safety level of the frames.
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.
Guray Arslan, Melih Hacisalihoglu, Muzaffer Balci, Muzaffer Borekci,
Volume 12, Issue 2 (6-2014)

The main cause of structural damage in buildings subjected to seismic actions is lateral drift. In almost all reinforced concrete (RC) structures, whether designed with walls or frames, it is likely to be the code drift limits that control the design drift. The design drift limits and their contribution to damage may be represented indirectly through the material strain limits. The aim of this study is to investigate the seismic design indicators of RC columns using finite element analyses (FEA). The results of FEA have been compared with the results of experimental studies selected from literature. It is observed that the lateral load-deflection curves of analyzed columns are in agreement with the experimental results. Based on these lateral load-deflection curves, the drift limits and the material strain limits, given by the codes as performance indicator, are compared. It is observed that the material strain limits are non-conservative as performance indicator of RC columns, compared to the drift limits.
Mohsen Shahrouzi, Amir Abbas Rahemi,
Volume 12, Issue 2 (6-2014)

Well-known seismic design codes have offered an alternative equivalent static procedure for practical purposes instead of verifying design trials with complicated step-y-step dynamic analyses. Such a pattern of base-shear distribution over the building height will enforce its special stiffness and strength distribution which is not necessarily best suited for seismic design. The present study, utilizes a hybrid optimization procedure to seek for the best stiffness distribution in moment-resistant building frames. Both continuous loading pattern and discrete sizing variables are treated as optimization design variables. The continuous part is sampled by Harmony Search algorithm while a variant of Ant Colony Optimization is utilized for the discrete part. Further search intensification is provided by Branch and Bound technique. In order to verify the design candidates, static, modal and time-history analyses are applied regarding the code-specific design spectra. Treating a number of building moment-frame examples, such a hyper optimization resulted in new lateral loading patterns different from that used in common code practice. It was verified that designing the moment frames due to the proposed loading pattern can result in more uniform story drifts. In addition, locations of the first failure of columns were transmitted to the upper/less-critical stories of the frame. This achievement is important to avoid progressive collapse under earthquake excitation.
A. Kaveh, M.s. Massoudi ,
Volume 12, Issue 2 (6-2014)

Formation of a suitable null basis is the main problem of finite elements analysis via force method. For an optimal analysis, the selected null basis matrices should be sparse and banded corresponding to sparse, banded and well-conditioned flexibility matrices. In this paper, an efficient method is developed for the formation of the null bases of finite element models (FEMs) consisting of tetrahedron elements, corresponding to highly sparse and banded flexibility matrices. This is achieved by associating special graphs with the FEM and selecting appropriate subgraphs and forming the self-equilibrating systems (SESs) on these subgraphs. Two examples are presented to illustrate the simplicity and effectiveness of the presented graph-algebraic method.
M. L. Li, Q. Chun-Xiang, Z. Yong-Hao,
Volume 12, Issue 2 (4-2014)

It introduced an innovative bioengineering method of consolidating incompact sand by urea-hydrolysis producing calcite cementation under the inducement of urease producing microbe. In the paper it discussed the effects of cementation methods and time on porosity and mechanical properties of microbe-inspired cementing sand columns. Method A adopted reaction fluid gravitational permeating and external pressing and method B adopted reaction fluid gravitational permeating and outlet intermittent plugging method. 28-day sand columns prepared by method A exhibited stronger mechanical properties than those prepared by method B, considering of the compressive strengths and three-point flexural strength as well. Pore volume fractions of sand columns prepared by method A reduced with an increase in cementation time which represented the bulk densities of sand columns were improved positively with time. The compressive strengths and the flexural strengths of sand columns prepared by method A increased with time. All these improved mechanical properties were attributed to the fact that the increasing amount of microbe inspired calcite precipitation with time consolidated sand columns by filling or bridging in sand gaps.
S. Karimiyan, A. Moghadam, A. . Husseinzadeh Kashan, M. Karimiyan,
Volume 13, Issue 1 (3-2015)

Plan irregularity causes local damages being concentrated in the irregular buildings. Progressive collapse is also the collapse of a large portion or whole building due to the local damages in the structure. The effect of irregularity on the progressive collapse potential of the buildings is investigated in this study. This is carried out by progressive collapse evaluation of the asymmetric mid rise and tall buildings in comparison with the symmetric ones via the nonlinear time history analyses in the 6, 9 and 12 story reinforced concrete buildings. The effect of increasing the mass eccentricity levels is investigated on the progressive collapse mechanism of the buildings with respect to the story drift behavior and the number of beam and column collapsed hinges criteria. According to the results, increasing the mass eccentricity levels causes earlier instability with lower number of the collapsed hinges which is necessary to fail the asymmetric buildings and at the same time mitigates the potential of progressive collapse. Moreover, the decreasing trend of the story drifts of the flexible edges is lower than those of the stiff edges and the mass centers and the amount of decrement in the story drifts of the stiff edges is approximately similar to those of the mass centers.
H. B. Ozmen, M. Inel, S. M. Senel, A. H. Kayhan,
Volume 13, Issue 1 (3-2015)

Seismic performance and loss assessment studies for stock of buildings are generally based on representative models due to extremely large number of vulnerable buildings. The main problem is the proper reflection of the building stock characteristics well enough by limited number of representative models. This study aims to provide statistical information of structural parameters of Turkish building stock for proper modeling using a detailed inventory study including 475 low and mid-rise RC building with 40351 columns and 3128 beams for member properties. Thirty-five different parameters of existing low and mid-rise Turkish RC building stock are investigated. An example application is given to express use of given statistical information. The outcomes of the current study and previous studies are compared. The comparison shows that the previous studies have guidance for limited number of parameters while the current study provides considerably wide variety of structural and member parameters for proper modeling.

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