18
1735-0522
190
Cyclic Performance of Buckling Restrained Composite Braces Composed of Selected Materials
Rahai
A.R.
Alinia
M.M.
Salehi
S.M.F
1
3
2009
7
1
0
0
10
05
2009
11
01
2014
Concentric bracing is one of the most common lateral load resistant systems in building frames, and areapplied to many structures due to their manufacturing simplicity and economics. An important deficiency in thebracing members is their irregular hysteretic loops under cyclic loading. In order to overcome this problem, it isadvised to restrain braces against buckling under compression, since buckling restrained frames dissipate a largeamount of energy. One method to restrain braces against buckling is to cover them with concrete. A proper coveringcan prevent the core from buckling and provide similar capacities whether in tension or compression which wouldproduce regular hysteric curves. In this study, the behavior of buckling restrained braces (BRB) has been investigatedby considering different types of surrounding covers. The steel core is encased in concrete with different coverings. Thecovering types include steel tubes, PVC pipes, and FRP rolled sheets. Experimental and numerical analyses wereimplemented. 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 energydissipation of the brace. Finally, the effect of the separating layer between the steel core and the concrete on theperformance of bracing was evaluated.
191
Collocation Discrete Least Square (CDLS) Method for Elasticity Problems
Naisipour
Mohammad
Afshar
Mohammad Hadi
Hassani
Behrooz
Rahmani Firoozjaee
Ali
1
3
2009
7
1
10
18
10
05
2009
A meshless approach, collocation discrete least square (CDLS) method, is extended in this paper, for solvingelasticity problems. In the present CDLS method, the problem domain is discretized by distributed field nodes. The fieldnodes are used to construct the trial functions. The moving least-squares interpolant is employed to construct the trialfunctions. Some collocation points that are independent of the field nodes are used to form the total residuals of theproblem. The least-squares technique is used to obtain the solution of the problem by minimizing the summation of theresiduals for the collocation points. The final stiffness matrix is symmetric and therefore can be solved via efficientsolvers. The boundary conditions are easily enforced by the penalty method. The present method does not require anymesh so it is a truly meshless method. Numerical examples are studied in detail, which show that the present methodis stable and possesses good accuracy, high convergence rate and high efficiency.
192
Diagonal Compression Criterion for Compression Reinforcement Ratio in HSRC Flexural Members
Maghsoudi
A.A.
Akbarzadeh Bengar
H.
1
3
2009
7
1
19
26
10
05
2009
11
01
2014
Limit to the tension reinforcement ratio in flexural high strength reinforced concrete (HSRC) members isbased on the requirement that tension failure as sufficient rotation capacity are ensured at ultimate limit state.However, the provisions for the total amount of longitudinal reinforcement ratio ( and ) are not associated withany rational derivation. In this paper, a quantitative measure to evaluate an upper limit to the compressionreinforcement ratio of flexural HSRC members is proposed. The quantitative criterion to can be derivedfrom i) steel congestion and ii) considerations that are related to the diagonal compression bearing capacity of themembers. In this paper it is shown that, when shear loading is dominant, the limit to is set by the diagonalcompression criterion. Parameters that affect this limit are deeply investigated and the expressions were derived fordifferent end conditions, to provide an additional tool for a better design and assessment of the flexural capacity ofHSRC members.
193
Size Effects in Reinforced Concrete Flanged ShearWalls
Mortezaei
Alireza
Kheyroddin
Ali
1
3
2009
7
1
27
40
10
05
2009
11
01
2014
The work presented in this paper investigates the causes of size effects in structural-concrete members. It isbased on the use of a finite-element model found to yield realistic predictions of structural-concrete behavior in allcases investigated to date. In fact, the previous use of this model in investigations of size effects in reinforced-concretebeams indicated that such effects reflect the dependence of load-carrying capacity on small unintended eccentricitiesof the applied load and/or load-induced anisotropy, rather than, as widely considered, on fracture-mechanicscharacteristics. The present work extends the scope of the above investigation so as to include the case of reinforcedconcrete flanged shear walls, the behavior of which is already established experimentally. It is found that, unlike theflanged shear walls with a height-to-length ratio larger than 2, the shear walls investigated in the present work, incontrast with the interpretation given to recently published experimental findings, are size-effect independent.
194
A Hybrid Neuro-Genetic Approach to Short-Term Traffic Volume Prediction
Afandizadeh
Shahriar
Kianfar
Jalil
1
3
2009
7
1
41
48
10
05
2009
11
01
2014
This paper presents a hybrid approach to developing a short-term traffic flow prediction model. In thisapproach a primary model is synthesized based on Neural Networks and then the model structure is optimized throughGenetic Algorithm. The proposed approach is applied to a rural highway, Ghazvin-Rasht Road in Iran. The obtainedresults are acceptable and indicate that the proposed approach can improve model accuracy while reducing modelstructure complexity. Minimum achieved prediction r2 is 0.73 and number of connection links at least reduced 20%as a result of optimization.
195
In-Plane Behavior of Confined Masonry Walls with and without Opening
Eshghi
Sassan
Pourazin
Khashaiar
1
3
2009
7
1
49
60
10
05
2009
11
01
2014
Confined masonry buildings are used in rural and urban areas of Iran. They performed almost satisfactoryduring past moderate earthquakes of Iran. There is not a methodology in Iranian Seismic Code (Standard 2800-3rdedition) to estimate their capacities quantitatively. In line with removing this constraint, an attempt is made to studyin-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 aredeveloped and a pushover analysis is carried out. To model the non-linear behavior of the confined masonry walls, thefollowing criteria are used: (1) The Rankine-Hill yield criterion with low orthotropic factor to model the masonrypanel (2) The Rankine yield criterion to model reinforced concrete bond-beams and tie-columns (3) The Coulombfriction criterion with tension cutoff mode to model the interface zone between the masonry panel and reinforcedconcrete members. For this purpose, the unknown parameters are determined by testing of masonry and concretesamples and by finite element analysis. Comparing the results show that the initial stiffness, the maximum lateralstrength and the ductility factor of walls with and without opening are different. Also, the severe compressed zones ofthe masonry panels within the confining elements are found different from what are reported for the masonry panelsof infilled frames by other researchers. This study shows that a further investigation is needed for estimating capacityof confined masonry walls with and without opening analytically and experimentally. Also where openings, withmedium size are existed, the confining elements should be added around them. These issues can be considered in thenext revisions of Iranian Seismic Code.
196
Effect of Particle Crushing on Shear Strength and Dilation Characteristics of Sand-Gravel Mixtures
Hamidi
A.
Alizadeh
M.
Soleimani
S.M.
1
3
2009
7
1
61
71
10
05
2009
11
01
2014
There are limitations in experimental studies on sand-gravel mixtures due to the small size of testingspecimens. Due to this problem, many researchers have worked on prediction of the shear strength of mixture by testingthe sandy fraction of soil alone and developed empirical relationships. Most of the previous relationships have beendetermined for low surcharge pressures in which particle breakage does not affect the shear strength parameters.However, the particle breakage affects the relationships in higher confinements. At the present study, the results oflarge scale direct shear tests on sand and sand-gravel mixtures was used to investigate the shear behavior anddilatancy characteristics in a wider range of surcharge pressures. The gravel content, relative density, surchargepressure and gravel grain size were considered as variables in testing program. The relationships between shearstrength characteristics of sand and sand-gravel mixtures were determined considering dilation characteristics of thesoil. In this regard, the minimum void ratio was found as a useful indirect index that relates uniquely to the criticalstate friction angle independent of soil gradation. The relations between critical state or peak friction angles of themixture with minimum void ratio were determined as a function of surcharge pressure. The correlations could be usefulfor determination of the strength parameters of sand-gravel composites by testing sandy fraction of mixture.