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Showing 25 results for Lateral Load

Kheyr Aldin A., Mortezaei A.r.,
Volume 2, Issue 1 (3-2004)
Abstract

Structural walls are used extensively in moderate- and high-rise buildings to resist lateral loads induced by earthquakes. The seismic performance of many buildings is, therefore, closely linked to the behavior of the reinforced concrete walls. The analytical models used in this paper are developed to study the push-over response of T-shaped reinforced concrete walls andinvestigate the influence of the flange walls on laterally loaded walls and nonlinear behavior of shear walls, namely strength, ductility and failure mechanisms. A layered nonlinear finite element method is used to study the behavior of T-shaped and rectangular (barbell) shear walls. This paper introduces a computer program to practically study three-dimensional characteristics of reinforced concrete wall response by utilizing layered modeling. The program is first verified bysimulated and reported experimental response of 3-D reinforced concrete shear walls. Subsequently, a study considering eighteen analytical test specimens of T-shaped and barbell shear walls is carried out. Finally, based on analytical results, a new equation for minimum ratio of shear wall area to floor-plan area is proposed.
M.kazem Sharbatdar,
Volume 6, Issue 1 (3-2008)
Abstract

FRPs (fiber reinforced polymer) possess many favorable characteristics suitable and applicable for construction industry when compared with steel reinforcement. There are new ideas to use FRPs as longitudinal or transverse reinforcement for new concrete elements particularly for bridge decks or beams. Although high tensile strength of FRP is main characteristic for applications at both areas, its weakness to bending and linear stress-strain behavior with virtually no ductility, makes it vulnerable to probably premature failures under reversal tension-compression loading during earthquake. A pilot research project has been conducted to explore the characteristics of large-scale cantilever concrete beams reinforced with FRP re-bars and grids and were tested under either simulated cyclic loading or monotonically increasing lateral loading. This paper presents the test parameters and results obtained during research. The analytical relationships are compared with those recorded experimentally, and test results showed the diagonal cracks and either rupturing of FRP bars in tension or stability failure in compression bars at long or short shear span beams. The comparison of nominal moment capacities between analytical and experimental values confirms that plane section analysis is applicable to FRP reinforced concrete members.
A.r. Rahai, M.m. Alinia, S.m.f Salehi,
Volume 7, Issue 1 (3-2009)
Abstract

Concentric bracing is one of the most common lateral load resistant systems in building frames, and are

applied to many structures due to their manufacturing simplicity and economics. An important deficiency in the

bracing members is their irregular hysteretic loops under cyclic loading. In order to overcome this problem, it is

advised to restrain braces against buckling under compression, since buckling restrained frames dissipate a large

amount of energy. One method to restrain braces against buckling is to cover them with concrete. A proper covering

can prevent the core from buckling and provide similar capacities whether in tension or compression which would

produce regular hysteric curves. In this study, the behavior of buckling restrained braces (BRB) has been investigated

by considering different types of surrounding covers. The steel core is encased in concrete with different coverings. The

covering types include steel tubes, PVC pipes, and FRP rolled sheets. Experimental and numerical analyses were

implemented. According to the results, PVC pipes and FRP sheets are suitable alternatives to steel pipes. Furthermore,

the behavior of several types of steel cores was assessed since, applying steel with high ductility promotes the energy

dissipation of the brace. Finally, the effect of the separating layer between the steel core and the concrete on the

performance of bracing was evaluated.


A.r. Khaloo, I. Eshghi, P. Piran Aghl,
Volume 8, Issue 3 (9-2010)
Abstract

In this paper the response of cantilevered reinforced concrete (RC) beams with smart rebars under static lateral loading has been numerically studied, using Finite Element Method. The material used in this study is SuperelasticShape Memory Alloys (SE SMAs) which contains nickel and titanium elements. The SE SMA is a unique alloy that has the ability to undergo large deformations and return to their undeformed shape by removal of stresses. In this study, different quantities of steel and smart rebars have been used for reinforcement andthe behavior of these models under lateral loading, including their load-displacement curves, residual displacements, and stiffness, were discussed. During lateral loading, rebars yield or concrete crushes in compression zone in some parts of the beams and also residual deflections are created in the structure. It is found that by using SMA rebars in RC beams, these materials tend to return to the previous state (zero strain), so they reduce the permanent deformations and also in turn create forces known as recovery forces in the structure which lead into closing of concrete cracks in tensile zone. This ability makes special structures to maintain their serviceability even after a strong earthquake


A. Kaveh, N. Farhoodi,
Volume 8, Issue 3 (9-2010)
Abstract

In this paper, the problem of layout optimization for X-bracing of steel frames is studied using the ant system (AS). A new design method is employed to share the gravity and the lateral loads between the main frame and the bracings according to the requirements of the IBC2006 code. An algorithm is developed which is called optimum steel designer (OSD). An optimization method based on an approximate analysis is also developed for layout optimization of braced frames. This method is called the approximate optimum steel designer (AOSD) and uses a simple deterministic optimization algorithm leading to the optimum patterns and it is much faster than the OSD. Several numerical examples are treated by the proposed methods. Efficiency and accuracy of the methods are then discussed. A comparison is also made with Genetic algorithm for one of the frames.


Ali Kaveh, Omid Sabzi,
Volume 9, Issue 3 (9-2011)
Abstract

This article presents the application of two algorithms: heuristic big bang-big crunch (HBB-BC) and a heuristic particle swarm

ant colony optimization (HPSACO) to discrete optimization of reinforced concrete planar frames subject to combinations of

gravity and lateral loads based on ACI 318-08 code. The objective function is the total cost of the frame which includes the cost

of concrete, formwork and reinforcing steel for all members of the frame. The heuristic big bang-big crunch (HBB-BC) is based

on BB-BC and a harmony search (HS) scheme to deal with the variable constraints. The HPSACO algorithm is a combination of

particle swarm with passive congregation (PSOPC), ant colony optimization (ACO), and harmony search scheme (HS)

algorithms. In this paper, by using the capacity of BB-BC in ACO stage of HPSACO, its performance is improved. Some design

examples are tested using these methods and the results are compared.


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

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.


F.r. Rofooei, M. R. Mirjalili, N. K. A. Attari,
Volume 10, Issue 4 (12-2012)
Abstract

The nonlinear static procedures (NSPs) proposed by design codes do not lead to reliable results especially for tall buildings.

They generally provide inconsistent estimates of inelastic seismic demands, especially for the top floors due to their inabilities in

considering the higher modes effects. In this paper, a new enhanced pushover procedure is proposed which is based on the

envelope of the structural responses resulting from two separate pushover analyses as a combination rule. Also, the suggested

pushover analyses are performed using a newly proposed modal load pattern, i.e., the Modal Spectra Combination (MSC), and

the ASCE41-06 required first mode load pattern. The MSC load pattern is consisted of a number of mode shapes combined with

appropriate weighting factors that depend on their modal participation factors, modal frequencies and design spectral values. A

number of 2-D steel moment resisting frame models with different number of stories are used to investigate the efficiency of the

proposed method. The inter-story drifts and the maximum plastic beam moment and curvature responses are used as a measure

to compare the results obtained from the nonlinear time-history analyses (NL-THA) and some other NSPs. The results obtained

through rigorous nonlinear dynamic analyses show that the application of the proposed method leads to acceptable results for

steel MRF systems in comparison to other available enhanced NSPs. The OpenSees program is used for numerical analysis.


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

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. Shakib, Gh. R. Atefatdoost,
Volume 12, Issue 1 (3-2014)
Abstract

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.
R. Vidjeapriya, V. Vasanthalakshmi, K. P. Jaya,
Volume 12, Issue 1 (3-2014)
Abstract

The present study focuses on the performance of precast concrete beam-column dowel connections subjected to cyclic loading by conducting experiments. In this study, one-third scale model of two types of precast and a monolithic beam-column connection were cast and tested under reverse cyclic loading. The precast connections considered for this study is a beam-column connection where beam is connected to column with corbel using (i) dowel bar and (ii) dowel bar with cleat angle. The experimental results of the precast specimens have been compared with that of the reference monolithic connection. The sub-assemblage specimens have been subjected to reverse cyclic displacement-controlled lateral loading applied at the end of the beam. The performance of the precast connections in terms of the ultimate load carrying capacity, post- elastic strength enhancement factor, load-displacement hysteresis behaviour, moment-rotation hysteresis behaviour, energy dissipation capacity, equivalent viscous damping ratio and ductility factor were compared with that of the monolithic beam-column connection. The monolithic specimen was found to perform better when compared to the precast specimens in terms of strength and energy dissipation. In terms of ductility, the precast specimen using dowel bar and cleat angle showed better behaviour when compared to the reference monolithic specimen.
P. Vahabkashi, A. R. Rahai, A. Amirshahkarami,
Volume 12, Issue 1 (3-2014)
Abstract

Piles or drilled shafts used in bridge foundation, waterfronts, and high rise buildings are generally subjected to lateral loads. In order to study the effect of concrete pile geometry on the structural behavior in layered soils, several models with different shapes and dimensions for piles and different properties for two soil layers with variable thickness were selected and analyzed using the finite difference method. The performance of piles situated in layered granular soil with different compaction and thicknesses were studied in two cycles of lateral loading and unloading. The applied finite difference procedure is also validated based on experimental and published results. The pile head displacement of different models due to their overall deformation and rotation were calculated under maximum loading. For a comparison of pile head displacement due to their overall deformation and rotation in different models, the "performance index” is defined as the ratio of “displacement due to deformation” to the “total displacement”.
A. H. Eghbali, K. Fakharian,
Volume 12, Issue 1 (1-2014)
Abstract

Portland cement can be mixed with sand to improve its mechanical characteristics. Many studies are reported in literature on this topic, but the effect of principal stress rotation has not been investigated yet. Considering the inherent anisotropy of most sands, it is not clear whether the added cement shall contribute to equal increase in strength and stiffness at vertical and horizontal directions or not. Furthermore, it is not well understood how the cement as an additive in non-compacted (loose) sand compared to compacted (dense) sand without cement, contribute to improving the material behavior in undrained condition such as limiting the deformations and the liquefaction potential. In this research, undrained triaxial and simple shear tests under different stress paths are carried out on different mixtures of Portland cement (by adding 1.5, 3 and 5 percent) with clean sand to investigate the effect of principal stress rotations. The triaxial test results revealed that the cement mixture reduces the anisotropy, while it improves the mixture mechanical properties compared to compacted sand without cement. The results of the simple shear tests validated the triaxial test results and further clarified the effect of the  parameter or rotation of principal stresses on the behavior of cemented sand mixtures.
Guray Arslan, Melih Hacisalihoglu, Muzaffer Balci, Muzaffer Borekci,
Volume 12, Issue 2 (6-2014)
Abstract

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)
Abstract

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.
S. Karimiyan, A. Moghadam, A. . Husseinzadeh Kashan, M. Karimiyan,
Volume 13, Issue 1 (3-2015)
Abstract

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. Liu, M. He, J. Guo, Zh. Hou, Y. Shi,
Volume 13, Issue 2 (6-2015)
Abstract

Self-centering pier (SCP) has been viewed as a remarkable accomplishment which is able to sustain major lateral loading with reduced structure damage in seismic engineering. Stiffness deterioration observed in experiment is vital for the seismic performance of self-centering concrete pier. In this contribution, the associated stiffness deterioration with respect to the structural damage is modeled in a modified analytical model for SCP comprehensively. In the proposed modified theoretical model, the lateral force-displacement relation associated with the stiffness reducing is analyzed. Three damage factors are introduced in the stiffness deterioration analysis to illustrate the damage evolution caused by gradually increasing lateral displacement. The proposed modified quasic-static model with damage evolution or stiffness deterioration has been validated against an experiment we conducted, where a good agreement is clearly evident. Subsequently, a parametric investigation focusing on aspect ratio, initial pre-tension, and ratio of ED (Energy Dissipator) was conducted to evaluate the hysteretic behavior of SCP under quasi-statically cyclic loading.
A. Komak Panah, A.h. Khoshay,
Volume 13, Issue 2 (6-2015)
Abstract

To increase the safety of structures against strong ground motions and their life due to environmental issues on the earth and saving in terms of materials, it is necessary to expand and upgrade seismic resistant systems. However, more cost-effective systems which have sufficient influence on the seismic performance of structures and also more compatibility with the regional conditions, will be more desirable than other systems. One of the seismic resistance systems is seismic isolation. In the event of interest in using the seismic isolation system for a mounted building on piles, the costly construction of piles and isolation equipment shall be provided simultaneously. The seismic isolating using sleeved-piles which is generally used in combination with various damper systems, can help to overcome this issue. In this research a seismic isolator system using sleeved-pile has been studied while considering the damping behavior of the soil-rubber mixture as the only source of damping. To investigate the proposed system, a series of tests including static lateral load test, dynamic free and forced vibration tests, were performed on a model pile in a field laboratory which has been constructed for this purpose. According to results of tests the proposed system has a good deformation ability and damping characteristics, and as a method of seismic isolation is completely efficient.
H. Tekeli, E. Atimtay, M. Turkmen,
Volume 13, Issue 3 (9-2015)
Abstract

In this paper, an approximate method is proposed for determining sway of multistory RC buildings subjected to various types of lateral loads. The calculation of both fundamental period and stability index in RC building requires the sway term at each story level. Using approximate method design engineers can estimate sway terms at each story level. The developed analytical expressions are inserted into fundamental period and stability index equations to replace the sway terms, which yields modified equations for fundamental period and stability index without any sway terms. It is fairly easier to employ these equations developed by eliminating all sway terms. Results obtained from the equations are remarkably close to those generated by the related computer program. Consequently, design engineers can reliably use the simple equations to calculate stability index and fundamental period, which enables the determination of these parameters without referring to the complex sway terms. The capability and accuracy of the proposed equations are demonstrated by a numerical example in which computer program results are compared with the proposed methodology.
Guray Arslan, Muzaffer Borekci, Muzaffer Balci, Melih Hacisalihoglu,
Volume 14, Issue 3 (4-2016)
Abstract

The contribution of concrete to inelastic deformation capacity and shear strength of reinforced concrete (RC) columns failing in shear has been investigated extensively by various researchers. Although RC members are designed to have shear strengths much greater than their flexural strengths to ensure flexural failure according to the current codes, shear degradation of RC columns failing in flexure has not been studied widely. The aim of this study is to investigate the shear degradation of RC columns using finite element analyses (FEA). The results of FEA are compared with the results of experimental studies selected from literature, and it is observed that the lateral load-deflection curves of analysed columns are compatible with the experimental results. Twenty-six RC columns were analysed under monotonically increasing loads to determine the concrete contribution to shear strength. The results of analyses indicate that increasing the ratio of shear to flexural strength reduces the concrete contribution to shear strength of the columns.



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