Shiraz University
Iranian Journal of Science and Technology Transactions of Civil Engineering
2228-6160
39
C1
2015
02
01
FINITE ELEMENT ANALYSIS USING MIXED FORCE-DISPLACEMENT METHOD VIA SINGULAR VALUE DECOMPOSITION
1
19
EN
10.22099/ijstc.2015.2736
The present approach is a combination of the force method and displacement approach<br />to achieve the analysis using the substructuring technique. In this method, the inverse of the<br />stiffness matrices of the substructures are constructed for the formation of the flexibility matrices.<br />This part of the solution is equivalent to the stiffness approach. In the subsequent stage, the results<br />of the analysis are assembled using the singular value decomposition (SVD) and the solution for<br />the entire structure is obtained. In fact, for assembling the structure, we need the flexibility<br />matrices of the substructures which are obtained by the stiffness method.<br />In this paper, a mixed force-displacement method is applied to finite element models for<br />increasing the speed of their solution. Each substructure is analyzed independently by singular<br />value decomposition of the corresponding equilibrium matrix. Methods are then utilized for<br />transforming the substructures into regular forms whenever it is possible. The application of this<br />method in finite element models with different substructures improves the process of analysis, and<br />makes the use of the existing solution techniques possible for regular systems.
Mixed force-displacement method,substructuring,singular value decomposition of equilibrium matrix,regular forms,finite element analysis
http://ijstc.shirazu.ac.ir/article_2736.html
http://ijstc.shirazu.ac.ir/article_2736_dba1f230f6da4cb9e929543cb2c58801.pdf
Shiraz University
Iranian Journal of Science and Technology Transactions of Civil Engineering
2228-6160
39
C1
2015
02
01
OPTIMUM PARAMETERS OF TUNED MASS DAMPERS FOR SEISMIC APPLICATIONS USING CHARGED SYSTEM SEARCH
21
40
EN
10.22099/ijstc.2015.2739
In this paper, optimum parameters of Tuned Mass Dampers (TMD) are determined<br />to minimize the dynamic response of multi-story building systems under seismic excitations.<br />Charged System Search (CSS), as an efficient optimization algorithm, is revised and applied for<br />tuning passive mass dampers. A MATLAB program is developed for numerical optimization and<br />time domain simulation. Optimization criteria are the peak values of the first story displacement<br />with and without TMD, and the transfer function from input ground acceleration to the first story<br />acceleration response. An alternative formulation is also presented for solving state space<br />equations. Compared to other population-based meta-heuristics, the charged system search has a<br />number of advantages distinguishing this algorithm from the others. However, for improving<br />exploitation (the fine search around a local optimum), it is hybridized with HS that utilizes charged<br />memory (CM) to speed up its convergence. To ensure good performance of this approach, some<br />numerical considerations are conducted to verify the effectiveness and feasibility of the presented<br />approach.
Tuned mass damper,charged system search,structural control,state space equations of motion
http://ijstc.shirazu.ac.ir/article_2739.html
http://ijstc.shirazu.ac.ir/article_2739_dcb0574550239b0e5d13c4f3c01dc086.pdf
Shiraz University
Iranian Journal of Science and Technology Transactions of Civil Engineering
2228-6160
39
C1
2015
02
01
PERFORMANCE OF RC BEAMS STRENGTHENED FOR SHEAR AND FLEXURE USING DIFFERENT SCHEMES OF U-SHAPED CFRP ANCHORAGES AND/OR STRIPS
41
51
EN
10.22099/ijstc.2015.2741
Deficiencies of RC structures can be overcome by strengthening/retrofitting using<br />different strengthening methodologies. This paper emphasises the effectiveness of externally<br />applied U-shaped CFRP anchorages/strips on the performance of RC beams of relatively low<br />compressive strengths (approximately 21 MPa). Three types of the beams were cast based on the<br />shear reinforcement detailed as containing “no shear reinforcement”, “minimum shear<br />reinforcement” and “adequate shear reinforcements” as suggested in ACI 318-08. All beams were<br />provided adequate flexural reinforcement as recommended by ACI 318 to fail the beams in<br />flexure. U-shaped CFRP anchorages and strips were bonded to the beams in the predominant shear<br />and flexural loading regions and tested under four-point bending condition by varying shear spanto-<br />depth ratio (a/d) as 2.46 and 3.38. Different strengthening schemes (including CFRP anchorage<br />alone and in combination with CFRP strips) as well as the effect of U-shaped CFRP anchorages<br />applied over full and partial applied beam depth was also the parameter of investigation in the<br />current study. Results showed that externally bonded U-shaped anchorages applied along the beam<br />span and at the ends together with CFRP strips improved the deformability, strength and<br />performance of RC beams by transforming failure manner from brittle to ductile. Moreover, use of<br />partial depth anchorage is beneficial to attain higher load in comparison to the full depth<br />anchorages, particularly anchorage height equal to 3/4 of the beam depth is found to be most<br />suitable.
Carbon fibre reinforced polymer,Reinforced concrete beams,Shear span to depth ratio
http://ijstc.shirazu.ac.ir/article_2741.html
http://ijstc.shirazu.ac.ir/article_2741_2ff0a5cf7b25b46bec2dd557e7cd8f6e.pdf
Shiraz University
Iranian Journal of Science and Technology Transactions of Civil Engineering
2228-6160
39
C1
2015
02
01
SHEAR STRENGTH OF REINFORCED CONCRETE BEAMS–RELATIONAL DATA BASE
53
63
EN
10.22099/ijstc.2015.2750
Shear capacity of concrete (Vc) in reinforced concrete members depends on a number<br />of influencing parameters including compressive strength of concrete (ƒ), ratio of tension<br />reinforcement (), shear span to depth ratio (<br />), size effect or depth factor (ξ), size of the aggregate<br />in relation to the minimum size of the member (aggregate interlock aspects). Over the last several<br />decades, researchers have tested reinforced concrete beams (without web reinforcement) to study<br />these parameters over a range limited by the breadth and depth of their experimental investigations<br />and, on the basis of their experimental results, proposed empirical equations for predicting the<br />shear capacity of concrete in reinforced concrete beams.<br />In this paper a relational database using ACCESS software is developed. The database<br />contains experimental results of 2145 shear critical reinforced concrete beams without web<br />reinforcement.<br />Using the ACCESS shear database developed in this study, an evaluation was conducted to<br />assess the predictive accuracy of shear design equation of Euro Code EC2. The results indicate<br />that the Euro Code EC2 design equations are found to be adequately conservative to predict the<br />shear capacity of reinforced concrete beams over the range of variables considered in this study.
Shear strength,concrete compressive strength,shear span to depth ratio empirical equations,database
http://ijstc.shirazu.ac.ir/article_2750.html
http://ijstc.shirazu.ac.ir/article_2750_c433a77a5b07e64be3046219313f6d0a.pdf
Shiraz University
Iranian Journal of Science and Technology Transactions of Civil Engineering
2228-6160
39
C1
2015
02
01
EVALUATING TOPOLOGY DESIGN OF MATERIAL LAYOUT IN STEEL PLATE STRUCTURES WITH HIGH STIFFNESS AND EIGENFREQUENCY
65
79
EN
10.22099/ijstc.2015.2751
This study presents optimal distributions of steel materials in steel thin plate structures<br />determined by using a classical element-wise and the present node-wise topology optimization<br />design methods for a dynamic problem. More specifically, the present article describes an<br />application of a node-wise topology optimization technique to the problem of maximizing<br />fundamental frequency for plane structure. The terms element-and node-wise indicate the use of<br />element and node densities, respectively, as design parameters on a given design space. For a<br />dynamic free vibration problem, the objective function in general is to achieve maximum<br />eigenfrequency with first-order eigenmode subject to a given limited material, since structures<br />with a high fundamental frequency have a tendency to be reasonably stiff. For both static and<br />dynamic problems SIMP (Solid Isotropic Microstructure with Penalization for Intermediate<br />Density) material artificially penalizing the relation between density and stiffness is used in this<br />study, and an implemented optimization technique is the method of moving asymptotes usually<br />used for topology optimization. Numerical applications topologically maximizing the first-order<br />eigenfrequency and depending on element or node densities as design parameters and varied<br />boundary conditions to verify the present optimization design method provide appropriate<br />manufacturing information for optimally form-finding of steel materials with Poisson’s ratio of 0.3<br />into thin plates.
Topology optimization,material layout,stiffness,eigenfrequency,Plate,SIMP
http://ijstc.shirazu.ac.ir/article_2751.html
http://ijstc.shirazu.ac.ir/article_2751_222e076399e5c646d72d5c3723f025ff.pdf
Shiraz University
Iranian Journal of Science and Technology Transactions of Civil Engineering
2228-6160
39
C1
2015
02
01
DETERMINATION OF MODAL DAMPING RATIOS FOR NON-CLASSICALLY DAMPED REHABILITATED STEEL STRUCTURES
81
92
EN
10.22099/ijstc.2015.2754
There are many reasons for rehabilitation of existing buildings. Adding stories is one of<br />the most common reasons. When a steel building is retrofitted by concrete jacketing for adding<br />stories, this system contains several structural systems. These systems are composite concrete and<br />steel systems in initial stories, welded steel system in middle stories and cold-formed steel frames<br />in upper stories. Dynamic analysis of hybrid structures is usually a complex procedure due to<br />various dynamic characteristics of each part, i.e. stiffness, mass and especially damping.<br />Availability of different damping factors causes a higher degree of complication for evaluating<br />seismic responses of hybrid systems. Due to using several structural systems, an existing building<br />is changed to hybrid system. Damping matrix of these structures is non-classical. Also, the<br />nonlinear software is not able to analyze these structures precisely. In this study, a method and<br />graphs have been proposed to determine the equivalent modal damping ratios for rehabilitated<br />existing steel buildings for adding stories.
Hybrid buildings,damping ratio,rehabilitation,non-classical damping,nonlinear analysis
http://ijstc.shirazu.ac.ir/article_2754.html
http://ijstc.shirazu.ac.ir/article_2754_a25a4e7247e516eb333597d6657463d2.pdf
Shiraz University
Iranian Journal of Science and Technology Transactions of Civil Engineering
2228-6160
39
C1
2015
02
01
STRENGTH AND FRACTURE PROPERTIES OF HYBRID FIBRE REINFORCED CONCRETE
93
102
EN
10.22099/ijstc.2015.2756
This paper investigated the shear, impact and fracture strengths of high-strength<br />concrete reinforced with two different industrial waste fibres. Locally available steel lathe waste<br />and nylon waste were used at different volume fractions as fibre cocktails in concrete. Steel lathe<br />wastes were used as-received lengths and nylon fibres were chopped into 40 mm lengths in this<br />investigation. In total, 12 hybrid mixes were casted and tested at four different volume fractions<br />(0.5%, 1.0%, 1.5% and 2.0%). The experimental programme was used the slump test and the air<br />content test on the fresh concrete. The hardened concrete was tested for its shear and impact<br />strength. A flexural test on notched beams under three-point bending was also carried out<br />according to the RILEM 50-FMC committee recommendations. Load vs. mid-span deflection and<br />load vs. crack mouth opening displacement were obtained and the fracture energy was evaluated.<br />The best performance was obtained in hybrid which was enhanced due to the hybrid nature of the<br />fibre cocktails of all the mixes, 2% volume fraction with a combination of steel ½ + nylon ½ fibres<br />gives the best performance. The steel lathe waste fibres mainly contributed to limiting the crack<br />initiation and lightweight non-metallic nylon fibres restricted the crack propagation. The combined<br />advantages of these fibres provide high mechanical and fracture strength. Hence this hybrid fibre<br />reinforced concrete with industrial waste fibres is doubly advantageous as it provides a superior<br />performance without increasing the cost of the concrete.
Fibre reinforcement,high-strength concrete,Mechanical properties,fracture energy,industrial waste
http://ijstc.shirazu.ac.ir/article_2756.html
http://ijstc.shirazu.ac.ir/article_2756_2f2e2dde60aa3b5420df3768272c642b.pdf
Shiraz University
Iranian Journal of Science and Technology Transactions of Civil Engineering
2228-6160
39
C1
2015
02
01
SEISMIC PERFORMANCE OF RC FRAMES RETROFITTED BY FRP AT JOINTS USING A FLANGE-BONDED SCHEME
103
123
EN
10.22099/ijstc.2015.2757
A new, FRP flange-bonded scheme, with practical application to 3D RC frames and<br />with the aim of relocating plastic hinges away from the joints is presented and its performance is<br />compared with that of the web-bonded scheme. For this purpose, nonlinear pushover analyses of<br />detailed Finite Element (FE) models of retrofitted joints of a benchmark RC frame are carried out.<br />The optimal thicknesses of the Fibre Reinforced Polymer (FRP) sheets for relocating the plastic<br />hinges are first determined. The moment-rotation curves of the joints are then utilised to create a<br />representing model for the RC frame. Further, nonlinear pushover analyses are carried out on the<br />retrofitted and the original frame to evaluate their capacity curves and seismic performance<br />parameters such as ductility, behaviour factor and performance points in relation to a specified<br />demand earthquake. The results are then compared with those of the same frame when retrofitted<br />with the web-bonded scheme as well as with steel bracing. Results point to the marked superiority<br />of the flange-bonded scheme compared to the web-bonded scheme in different aspects including,<br />capacity, ductility and the performance level and cost. The performance of the FRP flange-bonded<br />scheme also compares well with that of the steel bracing method.
Seismic retrofitting,RC frames,FRP,joint,nonlinear static (pushover) analysis,performance level,web-bonded,flange-bonded,steel bracing
http://ijstc.shirazu.ac.ir/article_2757.html
http://ijstc.shirazu.ac.ir/article_2757_bf4b8957b91c6824cdd58121934838f0.pdf
Shiraz University
Iranian Journal of Science and Technology Transactions of Civil Engineering
2228-6160
39
C1
2015
02
01
A COMPARATIVE NUMERICAL STUDY OF A GEOSYNTHETICREINFORCED SOIL WALL USING THREE DIFFERENT CONSTITUTIVE SOIL MODELS
125
141
EN
10.22099/ijstc.2015.2761
In this paper, three different soil constitutive models for granular soils were<br />implemented in the numerical simulation of a full-scale reinforced soil segmental wall in order to<br />predict the wall response during construction. The soil constitutive models in the order of<br />complexity are: linear elastic-perfectly plastic Mohr-Coulomb, Duncan-Chang hyperbolic, and a<br />nonlinear elastic-plastic hardening model. The latter, which can be regarded as a modified version<br />of the Mohr-Coulomb model, captures the nonlinear stress-dependent soil response. The nonlinear<br />model can consider soil dilative behavior. In this regard, it keeps the simplicity in the formulation<br />together with the accuracy in the prediction of soil response. By comparing the results, in general,<br />there is good and acceptable accordance between numerical simulations and field measurements. It<br />is seen that using a simple soil model can acceptably predict the performance of reinforced walls.<br />However, the disadvantage relates to poorness in the prediction of wall facing displacement, which<br />is sensitive to proper consideration of deformation parameters in a soil model. The accuracy of the<br />prediction can be augmented by adopting reasonable functions for elastic (stiffness) and plastic<br />(dilatancy) parameters with respect to the stress condition within the soil backfill.
Soil constitutive models,reinforced soil wall,response prediction,numerical analysis,geosynthetic
reinforcements,soil dilatancy
http://ijstc.shirazu.ac.ir/article_2761.html
http://ijstc.shirazu.ac.ir/article_2761_80cefdcd8fc825e65ec0a32d821761c1.pdf
Shiraz University
Iranian Journal of Science and Technology Transactions of Civil Engineering
2228-6160
39
C1
2015
02
01
PREDICTION OF SOIL-WATER CHARACTERISTIC CURVE USING GENE EXPRESSION PROGRAMMING
143
165
EN
10.22099/ijstc.2015.2763
Soil–Water Characteristic Curve (SWCC) is one of the most important parts of any<br />model that describes unsaturated soil behavior as it explains the variation of soil suction with<br />changes in water content. In this research, Gene Expression Programming (GEP) is employed as<br />an artificial intelligence method for modelling of this curve. The principal advantage of the GEP<br />approach is its ability to generate powerful predictive equations without any prior assumption on<br />the possible form of the functional relationship. GEP can operate on large quantities of data in<br />order to capture nonlinear and complex relationships between variables of the system. The selected<br />inputs for modelling are the initial void ratio, initial gravimetric water content, logarithm of<br />suction normalized with respect to atmospheric air pressure, clay content, and silt content. The<br />model output is the gravimetric water content corresponding to the assigned input suction.<br />Sensitivity and parametric analyses are conducted to verify the results. It is also shown that clay<br />content is the most influential parameter in the soil–water characteristic curve. The results<br />illustrate that the advantages of the proposed approach are highlighted.
Unsaturated soil,soil–water characteristic curve,artificial intelligence,gene expression programming
http://ijstc.shirazu.ac.ir/article_2763.html
http://ijstc.shirazu.ac.ir/article_2763_494883c8b9200888befd765acbc03c25.pdf
Shiraz University
Iranian Journal of Science and Technology Transactions of Civil Engineering
2228-6160
39
C1
2015
02
01
ANALYTICAL SOLUTION FOR CALCULATION OF BEARING CAPACITY OF SHALLOW FOUNDATIONS ON GEOGRID-REINFORCED SAND SLOPE
167
182
EN
10.22099/ijstc.2015.2765
The bearing capacity of foundations resting on slopes is commonly calculated using<br />empirical equations. In recent years, it has been demonstrated that geosynthetic reinforced soil can<br />enhance the foundation bearing capacity. In this paper, an analytical method for determination of<br />the ultimate bearing capacity of surface strip footing on a sand slope reinforced with geogrid layers<br />is presented. The angle of the slope with the horizontal direction is varied within 20o to 40o. In this<br />study, the Coulomb-type lateral earth pressure theory has been used to compute the foundation<br />bearing capacity. It is assumed that geogrid layers act such that the active earth pressures are<br />reduced. The results obtained from the proposed method are compared with experimental and<br />numerical results. Parametric studies have also been performed to show the effects of contributing<br />parameters such as number of geogrid layers, locations of reinforcement layers, soil properties and<br />the slope angle on the bearing capacity of strip foundations resting on the reinforced sand. The<br />results indicate that the magnitude of bearing capacity of strip footings on the sand slope can be<br />significantly increased by using geogrid layers.
Geogrid-reinforced slope,strip footing,Bearing capacity,shallow foundation
http://ijstc.shirazu.ac.ir/article_2765.html
http://ijstc.shirazu.ac.ir/article_2765_6bec4957a09a26cb8ace6ec0156088a4.pdf
Shiraz University
Iranian Journal of Science and Technology Transactions of Civil Engineering
2228-6160
39
C1
2015
02
01
THE PROPERTIES OF SCALE EFFECT ON THE DENSITY OF ROCKFILL MATERIALS BASED ON FRACTAL THEORY
183
200
EN
10.22099/ijstc.2015.2767
To study the scale effect on the density of rockfill materials, the relative density tests<br />were carried out by physical tests and numerical tests. Fractal theory was drawn into the grading of<br />rockfill materials. Then, the fractal properties of scale effect on the density were studied by<br />physical tests and numerical tests. There are close relations between fractal dimension D and<br />densities of rockfill materials. The densities are largest when D is the critical value Dc. Further, Dc<br />is independent of the relative density Dr and the maximum diameter dmax. Truncation error is one<br />of the main factors of scale effect of densities of rockfill materials. The existing four scale methods<br />in the standard can all be explained with fractal theory, and a unified formula was suggested. The<br />achievements in the paper lay a good foundation for further studying scale effect of rockfill<br />materials with fractal theory.
Scale effect,density,rockfill material,fractal theory,PFC2D (Particle Flow Code in 2 dimension)
http://ijstc.shirazu.ac.ir/article_2767.html
http://ijstc.shirazu.ac.ir/article_2767_5295643772c4d53b8d317a6b2dd581b5.pdf