نشریه مهندسی عمران مدرس
سال سیزدهم شماره 3 (پاییز 1392)

Recently، the study of nano materials in different fields of engineering science has been widely performed. In fact، the study on the behaviour of mixtures of nano material with other materials is among the new horizons in engineering research works. In this paper the impact of nanoclay on consolidation behaviour of bentonite in the presence of heavy metal contaminant is investigated. For this purpose، different percentages of nanoclay were mixed with bentonite and were additionally mixed with different concentrations of copper nitrate. Then، the odometer experiments performed on these prepared homogeneous samples in order to study the consolidation and permeability variations of samples. The results of this study show that the presence of industrial nanoclay causes an increase on the osmotic settlement of samples at the heavy metal concentrations up to 30 cmol/kg-soil of copper nitrate in comparison to the settlement of bentonite. Furthermore، the addition of industrial nano-clay to bentonite causes an increase in permeability of sample in comparison to the permeability of bentonite. This difference is more noticeable at high concentration of heavy metal. In addition، with an increase in external pressure، the permeability of bentonite sample and mixtures of bentonite/nanoclay gets closer to each others. This behaviour has been attributed to the presence of clay particles with nano dimensions in the mixtures of nanoclay-bentonite، the cation exchange capacity (CEC) and specific surface area (SSA) variations of samples due to the presence of nanoclay. In other words، according to the results of this study in the process of settlement of mixtures of bentonite and nano clay in the presence and absence of heavy metals the cation exchange capacity and specific surface area have the significant role. In this regard at the low concentration of heavy metals at the effective stress less than 100 kPa، cation exchange capacity governs the soil behaviour. However، at the effective stress more than 100 kPa، specific surface area is the governing factor which controls soil consolidation performance. Once the concentration of heavy metal increases in which it overcomes the soil buffering capacity، the heavy metals will neutralize negative charge of clay particles. Therefore، the cation exchange capacity of soil will have low effect on the settlement behaviour of soil. In such a case the specific surface area governs soil settlement process. For this reason due to the larger surface area of nano clays، the possibility for the secondary consolidation of soil increases.

Previous investigation has been shown that there are several sample preparation method to model the sand or silty sand behaviors. Methods like Dry Funnel Deposition (DFD)، Water Sedimentation (WS)، Slurry Deposition (SD)، Water Pluviation (WP)، Moist Tamping (MT) and Air Pluviation (AP) are some of the mentioned methods. Each method may be useful to model the behavior of some special deposited soils. For example، DFD is the best method to model the natural deposition of silty sands، while the WS method is suitable for modeling the sands natural deposition in the rivers. MT method is the best method to simulate the behavior of compacted embankments while SD method is suitable to prevent the segregation of particles in respect to other methods like Water Pluviation. Effect of sample preparation methods on the sands and silty sands behavior is investigated to some extent، while the clayey sands are rarely investigated. In order to investigate about the effect of sample preparation method and also clay content on the behavior of sands، some specimens were prepared using air pluviation and moist tamping method and tested under undrain consolidated condition using a monotonic triaxial device. To have uniform specimens with good repetition in sample preparation، a new sample preparation device using air pluviation method was invented by the authors. Specimens of clean and clayey sand mixtures were prepared using different drop height and flow rates. The dry unit weight of all specimens was increased with increase of drop height، while increase of flow rate leads to the decrease of dry unit weight. Also، some specimens were prepared using moist tamping method in order to compare the results. A modified Ladd technique was applied to have the uniform specimens in the moist tamping method. In modified Ladd technique (Under compaction method)، the initial layers are compacted with lower density، while they reach the desired density during the taping of the upper layers. This method prevents the more compacted lower layers، which is usually occurred in the usual moist tamping method. Based on the results، it was concluded that the air pluviated specimens usually behave in strain hardening manner with dilative properties، while moist tamped specimens tends to behave in strain softening manner. In addition، some valuable results are presented about the variation of liquefaction potential. It was seen that the steady state line of sand mixed with 10 percent clay is lower than the steady state line of clean sand in the e-Lnp’ plan، which is the sign of more liquefaction potential in clayey sand mixture. Also، the internal friction angle was found to be lower in clayey sand mixture in respect to clean sand. The interpretation of the results shows that two interaction manner can be distinguished between sand and clay particles; one of them is easy slippage between sand particles due to locating clay particles between them and the other is increasing the friction and cohesion between sand particles due to plasticity of clay particles. The latter will decrease the slippage between sand particles. Effect of each interaction is investigated separately using the obtained results.

Geotechnical designs are commonly based on several assumptions. Regardless of limitations caused by the inherent variability of soil and its unknown behavior، field measurements by the site instrumentation provide opportunities to have a safe and efficient design. Therefore، instrumentation has an important role in geotechnical research and professional studies. With the development of urban construction، excavations adjacent to buildings have increased dramatically. With large changes in stress distribution due to excavation، displacements may occur in the adjoining buildings and the soilmass. In urban excavations، the control of displacements created in soil and adjacent buildingshave always been an important issue due to the risk of damages. An optimum design and safe operation of the supporting system require a full understanding of the load distribution and displacement patterns in it. A simple traditional method in protecting the excavations is the use of inclined struts. This method،commonlyusedinIran،is the use of inclined strutsto support the adjacentbuildings. This method is not merely used in large excavations، but it is very popular for small to medium size excavations because of long-term traditional uses in Iran. Althoughthe mentioned method has practical applications but it is not fully investigated. It is necessary to investigate the presented method to determine itsadvantages and disadvantages as well as the limitations and the appropriate scope of its application. Some theoretical and numerical studies have been conducted in this regard and in fact the primary understanding of the performance mechanism of inclined struts and the loads acting on them are based on numerical studies. Thispaper reports the results of aninstrumentation undertakenon inclined struts during excavation and presentsvaluable informationaboutthe performance of such struts. In addition، a two dimensional numerical modelingwas performedand calibrated in order toverifythe mechanism ofstruts performance observed in thefield monitoring. The results proposethe mechanismof the inclined struts during excavation beside existing buildings as follows: (a) Partofthe load of the adjacent building ispassed to the bottom of the excavation through theinclined strutand consequentlyless pressure is exertedonthesoilbeneath the foundation. Therefore the amount of settlement beneath the foundation decreases. This mechanism suggests that inclined struts act as underpinning. (b) The inclined strutreduces the horizontal displacements of the excavation wall and the neighboring buildings due to the lateral constraintsit creates. As described below، the reduction of horizontal displacement has a significant impact on reduction of damage in neighboring buildings. Moreover، the paper in troduces a set of simpleinstrumentations which are designed in the course of the presented study andcan beusedin common engineering practice for small to medium size excavations. Monitoring is commonly neglected in small or medium projects but the use of proposed set of monitoring tools could play an important roleto increase safety and also in the investigation of excavations in urban areas.

The moment-curvature envelope describes the changes in the force capacity with deformation during a nonlinear analysis. Therefore، the moment-curvature envelopes for columns، beams and shear walls form an essential part of the analysis. The program IDARC now provides an option for users to input their own cross-section properties directly، and the moment-curvature is computed internally. Since IDARC is most practical and well-known software in damage analysis and the value of Park damage index depends strongly on the ultimate curvature، truth of IDARC''s results in section analysis is so highlighted. In IDARC، the moment-curvature analysis is carried out on the cross-section by dividing the concrete area into a number of strips or fibers. The section is subjected to increments of curvature and the strain distribution is obtained from compatibility and equilibrium considerations. In this study، the results of IDARC and OpenSees softwares in determination of moment-curvature curve and ultimate curvature of beams are evaluated. For assessment of the software''s responses، there have been used of the experimental results for 9 reinforced concrete beams with different section properties. The moment-curvature analyses of these beams have been done by use of IDARC، OpenSees and finally the code that has been written in this study. Comparison of the results shows significant differences between the IDARC''s results and other results. In order to control the accuracy of the analytical results two items have been checked، firstly، the strain of the last compressive concrete fiber in ultimate curvature and secondly، satisfying the equilibrium equations of section during the moment-curvature curve path. This study presents some cases that the axial equilibrium doesn''t satisfy in the moment-curvature obtained by IDARC. Also، IDARC doesn''t make attention to the ultimate strain of concrete when calculates the ultimate curvature. This result means that the damage index has been calculated by IDARC is not reliable when software accomplishes section analysis. Afterward، the used algorithm in IDARC for moment-curvature analysis has been revised and by proposing the modified algorithm a code has been written that can apply Chang&Mander and Kent&Park stress-strain concrete models. The effect of confinement on the concrete behavior has been applied based on Mander، Priestley and Park model and also based on Kent&Park model for each beam according to its transverse reinforcement. The results of the proposed algorithm conform exactly to OpenSees results. Although this results doesn''t match exactly with experimental results، but the general form of moment-curvature curves are similar to somewhat that has been obtained in experiments. The main reason of this difference relates to the value assigned to the ultimate compressive strain of concrete. Since the Park model for estimate of ultimate compressive strain of concrete has been applied، and the efficiency of that is not to the point of this study، the mentioned difference is acceptable.

The moment-curvature envelope describes the changes in the force capacity with deformation during a nonlinear analysis. Therefore، the moment-curvature envelopes for columns، beams and shear walls form an essential part of the analysis. The program IDARC now provides an option for users to input their own cross-section properties directly، and the moment-curvature is computed internally. Since IDARC is most practical and well-known software in damage analysis and the value of Park damage index depends strongly on the ultimate curvature، truth of IDARC''s results in section analysis is so highlighted. In IDARC، the moment-curvature analysis is carried out on the cross-section by dividing the concrete area into a number of strips or fibers. The section is subjected to increments of curvature and the strain distribution is obtained from compatibility and equilibrium considerations. In this study، the results of IDARC and OpenSees softwares in determination of moment-curvature curve and ultimate curvature of beams are evaluated. For assessment of the software''s responses، there have been used of the experimental results for 9 reinforced concrete beams with different section properties. The moment-curvature analyses of these beams have been done by use of IDARC، OpenSees and finally the code that has been written in this study. Comparison of the results shows significant differences between the IDARC''s results and other results. In order to control the accuracy of the analytical results two items have been checked، firstly، the strain of the last compressive concrete fiber in ultimate curvature and secondly، satisfying the equilibrium equations of section during the moment-curvature curve path. This study presents some cases that the axial equilibrium doesn''t satisfy in the moment-curvature obtained by IDARC. Also، IDARC doesn''t make attention to the ultimate strain of concrete when calculates the ultimate curvature. This result means that the damage index has been calculated by IDARC is not reliable when software accomplishes section analysis. Afterward، the used algorithm in IDARC for moment-curvature analysis has been revised and by proposing the modified algorithm a code has been written that can apply Chang&Mander and Kent&Park stress-strain concrete models. The effect of confinement on the concrete behavior has been applied based on Mander، Priestley and Park model and also based on Kent&Park model for each beam according to its transverse reinforcement. The results of the proposed algorithm conform exactly to OpenSees results. Although this results doesn''t match exactly with experimental results، but the general form of moment-curvature curves are similar to somewhat that has been obtained in experiments. The main reason of this difference relates to the value assigned to the ultimate compressive strain of concrete. Since the Park model for estimate of ultimate compressive strain of concrete has been applied، and the efficiency of that is not to the point of this study، the mentioned difference is acceptable

One of the important problems in seismic rehabilitation studies of existing structures is opportune decision making about ending or continuance of various stages rehabilitation in order to save time and cost. About that we can use decision maker systems to solve this problem and to give more rational assessment about that problem. This paper presents a procedure based on Fuzzy Logic that classifies structures into qualitative seismic hazard categories. The purpose of this study is to get a model that can speed existing structures seismic rehabilitation primary studies and also to prompt decision making about continuance of study process. In order to account real world data، in addition to expert’s knowledge، groups of school seismic rehabilitation data of different cities of Iran have been used for modeling. In order to reduce the input space and increase generalization ability of the system، a feature selection method has been applied to the data. Among available parameters of data، significant parameters have been selected by Decision Tree Learning method. Then، Fuzzy Membership Functions corresponding to these parameters have been defined. Appropriate defining of these functions، we can insinuate factors such as uncertainty on that parameter in computations also. Afterwards، the Fuzzy System has been designed by conditional regulations. It is worth to say that these regulations are optimizedcompletely. In order to ease the process of risk assessment based on this model، software named “Rapid Seismic Risk Evaluation” (RSRE) has been developed. Thus، we have a model that by inputting 7 entrance parameters of a structure (both structural and geotechnical parameters corresponding to existing structure)، generates its seismic risk level. The proposed procedure has advantages among the rest we can recount the possibility of modeling uncertainties، inputting structural information qualitative and high speed of risk analysis process. It is clear that using Fuzzy Logic not only lead to more simple formation، but also speed the rate of risk analysis process intensely، that this case is one of the most important advantages of the proposed method. In order to scrutiny of the designed model، various controls have been done. These controls have been tested on different data. Outcome results are representative high accuracy of designed model. Finally، in order to survey the efficiency of proposed procedure، the designed model has been applied to some of Tehran and its suburb school structures and outcome results have been compared with main data real results. Outcome results are representative good efficiency of the method. We should notice that using Fuzzy Concluder Systems lead to speed structure risk analysis and so decision making about various stages of structure rehabilitation is performed with more rate than previous. Thus، use of procedure that proposed in this paper، can has suitable applications in rapid seismic risk evaluation of studied structures in first stage of rehabilitation process.

Steel frames with Khorjeeni connections have been widely used in the traditional construction of buildings in Iran during the past decades. In the traditional form of Khorjeeni connections، double section beams are not cut at the intersection with columns، rather they are connected to the column by means of two angles placed over the top and under bottom of the beam flanges. This type of connection offers advantages for frames، which carry gravity loads، but it has deficiencies when the frames are subjected to lateral loads. Like other structural frames، there are masonry infills in many frames with Khorjeeni connections. The behavior of composite frames subject to lateral loads differs from that of bare steel frames. In this paper، positive and negative effects of masonry infills، when strengthed by reinforced shotcrete، are studied on the behavior of steel frames with Khorjeeni connections. Finite element method was used to carry out nonlinear static analysis of subassemblages of this type of frames. Initially، the results of some experiments were utilized to verify the details of the model. Then numerical models of two span or four span frames with different configuration of bracings and masonry infills and characteristics of shotcrete were studied. The results showed that infills increase the stiffness and strength of frames in the absence of bracing considerably. Even when bracings are present، the increase in stiffness and strength is significant. When the infills are strengthened، their effects on stiffness and strength of composite frames increase. However if the steel frames are not strong enough، their strength limit the effects of infills. The masonry infills، however، have some negative effects on the behavior of Khorjeeni frames. Parts of the column in the vicinity of connections are prone to plastic damage، particularly when the infills are relatively strong. The Khorjeeni connections are subjected to vertical forces and tortional moments. Due to limited vertical strength of these connections، top stories of this type of frames may suffer when compressive action of strut is mobilized. For other bays، this action introduces additional moments، which may damage the connections. Therefore، considering these negative effects of infills is very important when seismic behavior of the existing frames is assessed. When the infills are strenghted by shotcrete، these negative effects become even more important and the inter story drift rations need to be limited in order to avoid failure in conections.

Base isolation technique is a new approach in seismic design of structures in which an isolation layer at the bottom of structure helps to reduce earthquake effects on the system. However this powerful technique is less effective in the near-fault regions due to long period pulses of earthquake records. In this work two base isolated structures subjected to pulse type earthquakes were studied. The fixed base natural periods in these structures are chosen far apart (0. 4 and 0. 75 second)، but their isolated periods are chosen equal to each other (2. 5 seconds). The main objective of this study is to investigate on the role of linear and nonlinear viscous dashpots on responses of base isolated buildings subjected to near-fault earthquakes. So that، a number of near-fault records along with some far-fault ones are used in a series of time integration analyses on both structures. The model for base isolation system in this work is a simplified model in which the base isolated building is assumed as a system with only two degrees of freedom. The main structural system and the isolation components are all assumed to behave linear in the analysis procedure. Analyses have been carried out for both structures، equipped with linear and nonlinear viscous dashpots. In case of nonlinear viscosity، velocity exponent is assumed equivalent to 0. 5. Average values of maximum responses، including damper force، super structure drift and base displacement are calculated for both types of earthquakes (near-fault and far-fault records). The results show considerable gains in reducing base displacement and superstructure drift in both structures while using nonlinear viscous dashpots. However، the role of nonlinearity in damping devices on acceleration reduction in super-structure is considered marginal. The results also indicate the existence of an optimum damping value for the system in both cases of using linear and nonlinear damping devices. Providing this amount of damping for the system، minimum value for the selected responses in the structure will follow. In practice، defining an optimum damping value for the system needs a cost benefit study based on the desired structural responses in different dashpot technologies

Squat shear walls are common in low-rise buildings، their seismic rehabilitation، lower stories of high-rise buildings، and nuclear power plants. Wall segments formed by openings also have the same behavior as squat shear walls. Usually walls with aspect ratio less than 1. 5 are known as low-rise or squat shear walls. Shear stresses have significant effect in lateral strength and ductility of such walls. Concrete structures with shear dominant behavior are more complex for Analyzing and their seismic behavior may be poor. Also squat shear walls have various failure modes under lateral loading. In recent years designers have intended to performance based assessment and design of structures. Thus، reliable instruments for nonlinear analysis of squat shear walls are required. Previous efforts to nonlinear modeling of squat shear walls usually were performed by FE codes such as ABAQUS، ADIANA and VecTor2. These codes are not practical for performance based assessment and design of structures. Performance based assessment software programs such as SAP 2000 and PERFORM 3D are more desired to modeling complex structures. Accordingly، there is a need for reliable modeling techniques for nonlinear modeling of squat shear walls using performance based assessment software programs. The purpose of this paper is to finding suitable information for fast and reliable modeling of squat concrete shear walls with widely used building structural software programs. Therefore، by selecting and modeling five test specimens from previous experimental studies using two widely use commercial codes، SAP 2000 and PERFORM 3D، Key parameters for modeling such walls are found and calibrated to bring analytical results near the test results. These software programs employ fiber (layered) model to modeling wall panels. In this model، the member is divided into several segments، and each segment consists of parallel layers. Some layers would represent the concrete material and other layers would represent the steel material. The constitutive laws for concrete and steel materials are defined and assigned to appropriate layer. Different approaches are employed for modeling shear behavior of concrete using this method. In addition to the concrete axial/flexural layer، a shear layer must be implemented; shear constitutive laws are needed for modeling this layer. Also shear behavior of concrete can be modeled using diagonal layers. In these layers shear stresses convert to axial stresses acting on the principal plane of the layer and axial constitutive laws will be used. Results show that، estimated strength and force-displacement curve are in the good agreement with experimental results. concrete diagonal layer characteristics and tension modeling method of concrete are key parameters for modeling squat shear walls using SAP 2000 and concrete shear layer characteristics are key parameter for modeling squat shear walls using PERFORM 3D. It can be said that strength is better estimated than stiffness using this type of analysis.

The main aspect of this research study is investigation on scour phenomenon around marine pipelines with respect to submerged impermeable plates beneath the pipe. So far، numerous investigations have been done but the main difference of this study with them is installation an impermeable base plate under the pipelines. Installing these impermeable plates mainly causes that the developed streamlines under the bed، located under the pipeline، are lengthened and accordingly the pressure gradient reduces across the pipe. Reduction of the pressure gradient may be considered an important issue since one of the most important criteria of establishing and progressing of scour under pipelines is the formation of piping phenomenon under the pipelines. This phenomenon is due to dominance of the pressure gradient on floating weight of the bed materials. For this research study، firstly scour phenomena under the pipelines were investigated both for unprotected pipelines and protected pipelines with submerged impermeable plates، with the piping phenomenon under the pipelines were being considered for both cases. The experiments were carried out in a channel with 10m length، 0. 25m width and 0. 5m depth. P. V. C. pipes with four diameters (i. e.، 2cm، 3cm، 4cm and 5cm) and 0. 5cm thickness were investigated. The bed materials were consisted of sediment particles with median size of 0. 50 mm and geometric standard deviation of 1. 43. The specific gravity of bed materials was 2. 65. All experiments were run at clear water conditions. For each test the steady approach flow was adjusted so that the ratio of velocity to critical velocity was equal to about 0. 85 on the centerline of the flume. A number of rectangular galvanized iron plates with 25cm in length، 0. 7mm thickness and various dimensions of breadths were selected as countermeasure tools for scouring phenomenon. Then، the scour depth beneath two parallel pipelines with side by side arrangements and their interaction on scouring process were investigated. Finally، with installing impermeable base plates under the pipelines، the effect of these plates on scour phenomenon were studied for any arrangements of the parallel pipelines. The experimental results showed that installation a plate under the pipeline could prevent the formation of scour hole to some degrees and protect them from scour hazards. For all test cases of unprotected pipelines، the maximum dimensionless scour depth beneath the pipelines decreased when the pipe diameter increased. For side by side arrangement of two parallel pipelines، the formed scour depth decreased when the distance of pipelines increased. Then، for practical purposes، in order to reduce the maximum scour depth it is recommended that the distance of two parallel pipelines increases as far as possible or a submerged base plate may be used beneath the under pipeline. For all test cases of pipelines with impermeable base plates، the scour process will not further occur unless due to wake vortices.