Modares Civil Engineering journal
Year:2017 | Volume:17 | Issue:1 |Papers Count:22

Dry-joint construction method is among the oldest techniques adopted in most of the ancient and historical masonry buildings. Historical structures constructed using this method are highly vulnerable today. In addition, the strength of mortar is strongly affected–in most cases- by the passage of time and corrosion. Thus, the structure behavior would most likely be dependent on the dry-joint characteristics. Therefore, non-destructive dynamic-based methods are attractive tools to assess the existing damages of masonry walls, as they are capable of capturing the global structural behavior. In this paper, micro-modeling approach is adopted for the evaluation of masonry walls. The approach is based on the application of Distinct Element Method (DEM) as assemblies of units consist of block and mortar. Idealization of discontinuous nature governing the nonlinear mechanical behavior of the mentioned units is considered trough the modeling approach. Due to the heterogeneous and complex behavior of the interface between blocks and mortar, DEM seems to be the best-adapted approach for modeling this kind of structures, in particular for reproducing complex nonlinear post-elastic behavior. At the first step, micro-modeling strategy is used for masonry walls by DEM, and particularly post-elastic behavior is verified with valid experimental data. However, DEM does not directly obtain natural frequencies and mode shapes of the wall via a classic vibrational analysis. Therefore, the second objective of this study is to propose a technique to indirectly identify dynamic characteristics of masonry walls using DEM. The aim of this part is to check the capability of dynamic identification procedure, in the extraction of the dynamic characteristics of the masonry wall in the used DEM software. For this purpose, the dynamic behavior at low vibration levels of an existing masonry building subjected to forced hammer impact test, was investigated. By transforming the collected data of the dynamic response of wall from time domain to frequency domain -using Fast Fourier Transform (FFT) - natural frequencies can be found from Fourier amplitude spectrum. The proposed technique is then validated by comparison with the results of modal analysis which was carried out using Finite Element Method (FEM). The dynamic characteristics of walls (i.e., natural frequencies and mode shapes) may change when different levels of damage are induced to the wall. The proper knowledge of these variations is a key issue in order to study the seismic demand and seismic performance of structures. Aiming at finding adequate correspondence between dynamic behavior and internal crack growth, several numerical simulations are performed; progressive damage is induced in the wall; and sequential structural frequency identification analysis is then performed at each damage stage. In this paper, frequency and drift are selected as dynamic behavior and crack growth indices, respectively. Quantifying the relative frequency drop shows that although the shape does not vary significantly with increasing damage, there is a relation between frequency drop and damage variations -based on analyzed data. These properties are firstly modified in the elastic range, and then are developed in the inelastic range with increasing damages. It is also observed that while the failure mode of the wall is the diagonal cracking, the in-plane vibration mode shapes are much affected by the initiation of crack. On the other hand, modal properties of out-of-plane mode shapes are affected less by the diagonal crack.

Drict discharge of domestic wastewater (sewage) to the environment or into absorbing wells has caused many problems including surface and groundwater pollution. To reduce such problems, the number of wastewater treatment plants has increased significantly in Iran during the last two decades. During wastewater treatment, a significant amount of sludge, composed of organic and mineral material, is produced. This sludge, if not handled and disposed properly, can create serious environmental and health issues. One environmentally attractive way of dealing with such wastes is to use them in different types of applications. In this regard, many economical and beneficial methods have been developed to reuse sludge. Incineration of sludge for energy recovery or the use of sludge ash in cement-based construction materials are among these methods. Sludge incineration produces considerable amount of ash which should be disposed. However the ash can be used as cement substitude in procuction of cement-based material. The subject of using sludge ash as cement substitude has been investigated by a few researcher with the conclusion that the usage of ash can affect the final cement-based product quality. Based on their experimental results, the use of sludge ash tends to decrease the workability of fresh mortar or concrete, and to increase the cement setting time. Also a decrease in compressive strength of mortar or concrete was reported. However, it should be mentioned that no research has yet been done to investigatethe the effects of sludge ash replacement on mechanical and durability properties of concrete. The main aim of this study was to investigate the effects of sludge ash usage as cement substitude on physical, mechanical and durability properties of concrete. For this purpose, the effects of three key parameters: replacement level (0-20%, by weight), curing times (7, 28, 91 and 180 days) and water-cementitious material ratio (0.35, 0.45 and 0.55) were investigated. The sludge used in this research was obtained from one of the local wastewater treatment plants, which subsequently was dried and then was incinerated at 800oC to produce ash, The ash was in general, made up of irregular grains which were aggregates of smaller particles. Also, the ash was composed mainly of calcium, silica and aluminium oxides. The results showed that increasing the amount of sludge ash induced higher mortar setting times as compared to the control samples, using Vicat test. The effect of ash content on mechanical properties of concrete samples was carried out by compressive strength tests. Results indicated that for 7 and 28 days curing time, concrete samples containing a mixture of sludge ash and cement yielded lower compressive strength values than those samples using only cement (without any ash content). However, for curing times greater than 28 days, the increase in ash content of concrete samples (in the range of 0-15% by weight) led to an increase in compressive strength. Water absorption and electrical resistivity tests were conducted to determine the durability of concrete containing sewage sludge ash. As blending percentages of ash content increased fom 5% to 20% (by weight), electrical resistivity of concrete samples decreased for regardless of the applied curing times. This phenomenon might be the result of increased porosity and material ionization.

Shear strength is one of the most important features in mechanical behavior of soils. The shear strength of unsaturated soils is still a controversial discussion among the researchers in this field. The methods of determining unsaturated shear strength are classified into two major categories. First, two independent stress variables known by matric suction and net stress are employed. Further, saturated and unsaturated strength parameters are considered to be independent. In other words, as soon as the pore water pressure becomes negative, the saturated effective friction angle and cohesion become invalid. This approach became significantly dominant since the validity of effective stress in unsaturated soils was questioned, as it was not clear how the collapse phenomenon can be described through effective stress concept. In the late 90s, some researchers referred back to effective stress concept and some ambiguity in explaining collapse was resolved. In this approach, effective stress is the main stress variable. Net stress and suction are combined into effective stress. The saturated and unsaturated shear strength parameters are assumed to be independent, and there is a smooth transition between saturated and unsaturated soil modeling. In this research these two approaches are compared by means of unsaturated direct shear experiments and some relevant experimental data from literature. The advantages and shortcomings of the mentioned methods are analyzed. In the direct shear experiments, a wide range of soil suction was applied to the samples. Therefore, it is possible to compare the effective stress and independent stress approaches in a wide range of suctions. The suctions of samples were measured by filter paper method. By plotting the failure envelopes in two approaches, the advantage of effective stress approach over the approach of independent stress variables is obvious. This advantage is especially drastic at higher suctions. The experimental data from literature similarly revealed this result. Thus, it can be stated that effective stress approach is simpler and less time consuming since the failure envelope is an identical unique line for all suctions and strength parameters of a soil at saturated and unsaturated states. Contrary to independent stress variable approach, it is not required to measure the strength parameters at various suctions. In other words, if the effective stress is properly estimated, the unsaturated shear strength can be predicted straightforwardly. Effective stress parameter is the key factor for appropriate evaluation of effective stress in unsaturated soils. One of the highly cited proposed equations for effective stress parameter is verified by experimental data. The values of predicted effective stress parameter and the values measured from experiment are plotted versus suction. There is a good agreement between the effective stress parameters calculated by the equation and those measured from experimental data. Therefore, it can be concluded that the empirical equation can accurately predict the effective stress parameter. It is worth mentioning that by normalizing the suction through dividing it into air entry suction, the effective stress parameter versus normalized suction becomes a unique line, regardless of soil type. Thus, the effect of soil type and its structure is normalized by means of using suction ratio.

Earthquake loads induce significant damages and cause widespread failures into buildings. Having appropriate system against seismic loads is a minimum necessary requirement for a structure. Moment Resisting Frame Systems (MRFS) are one of the common seismic resisting systems against lateral seismic loads. Ductility is the most important properties of these kinds of systems; but increase in ductility leads to decrease stiffness and increase lateral deflections and hence induces damages to nonstructural components. Although stiffness can be magnified through increasing section sizes of members, but it would not be economical. To compensate this deficiency, the combination of these systems with reinforced concrete (RC) shear walls may be useful.Although in general, this combination (RC shear walls and MRFS) decreases the section size and increase stiffness; but in low rise structures using this combined system cause decrease in ductility and dissipation of energy under moderate/strong earthquake. This deficiency can be improved by using vertical slits in RC shear walls of low to moderate height. These slits invert shear behavior of RC shear wall into flexural behavior of several columns and are able to increase ductility. So, for the first time in this paper, a study was conducted on introducing behavior factor (R) for Steel Moment Frame (SMF) with reinforced concrete slit shear wall system at two levels of demand and supply.In view of existing concerns about precise of behavior factors in seismic design codes, due to developing these factors based on engineering judgment from observing seismic performance of structures subjected to past earthquakes besides the lake of these information in current seismic design codes causes the seismic design of RC slit shear wall system needs more research works. The behavior factors are used to reduce the linear elastic design spectrum to account for the energy dissipation capacity, over-strength and redundancy of the structure.The most distinctive feature of this study respecting to similar studies is multi-level definition of behavior factors and their extraction with respect to seismic intensity, and accepted damage level as expected performance levels in designing RC slit shear wall structural system. Hence, the demand/supply behavior factors are determined with a more accurate attitude involving the effective parameters such as ductility, overstrength, redundancy, seismic hazard level, performance levels, etc.In this study, to determine the appropriate behavior factor, static pushover analysis along with Incremental Dynamic Analysis (IDA), are used. The behavior factors in two levels of demand and supply are obtained with two procedures: At the first, the pushover analysis was applied on case study structures and then(R, m, T) relationship for SDOF system of Newmark and Hall, Nassar and Krawinkler, and Miranda to evaluate behavior factor for MDOF structures were used. At the second stage both pushover and incremental dynamic analysis were used to achieve directly the behavior factor for MDOF structures.In this paper, two 5 and 10-story steel moment resisting frame with RC slit and ordinary shear wall systems were designed by ETABS software. These structures were designed in which their behavior factors were the same values. Then the pushover and IDA were conducted on sample structures using nonlinear analysis software PERFORM. Results show that, although initial elastic stiffness has not been considerably changed in slit RC shear wall systems, but they show higher behavior factor relative to regular RC shear wall systems.Converting the shear behavior of RC ordinary shear wall to ductile flexural behavior of a series of wall pieces as columns by providing slits in shear wall may be considered as the reason for achieving more ductility and dissipating high seismic energy in this innovative systems.

The main goal of seismic design is to provide required safety level during earthquake, and to make a structure remain repairable. According to the available reports of recent earthquakes, structures designed using force based design procedures are not precise enough in eliminating the damage of structures. Therefore, a new generation of design codes based on the performance level design procedure is introduced. In order to estimate the amount of damage in structural elements, related criteria are defined as damage indices. Damage indices are functions of damage variables and indicate the effect of thevariables on the element’s damage. Park-Ang damage index is among the most important damage indices, which shows the damage of reinforced concrete elements as a linear combination of maximum deformations and absorbed cyclic energy. The analytical value for this damage index is set to be zero if there is no damage, and 1.0 for the collapse of the element. The Park-Ang damage index in non-negative and shows the reduction of element’s resistance in cyclic loading. It also specifies energy dissipation and the strength damage of the elements. This factor has been used for calibrating damage index. It has been found that the damage index is merged with one in the failure point. Applying this model in structural systems requires determination of an overall member’s deformation. Since inelastic behavior is limited to plastic zones adjacent to the ends of a member, it is difficult to define the relationship between overall member deformation, local plastic rotations and the damage index. Therefore, a modified version of this model has been developed by Kunnath et al.The most important difference between Kunnath model and Park-Ang model is representing the equation based on the moment-curvature diagram and replacing the non-dimensional factor with the strength deterioration factor in a hysteretic model. Supposing this factor as a constant will increase the diversion of the damage index in collapse prevention performance level. In this paper, the Park-Ang damage index and its improved relations has been evaluated for the various performance levels, including immediate occupancy, life safety and the collapse prevention levels. For this purpose, three reinforced concrete frames with different numbers of stories, was each designed for three performanc levels. Nonlinear dynamic analysis has been carried out with seven earthquake acceleration records. Finally, the damage analysis has been performed. The damage index has been derived for all of the nine frames and the values of damage indices have been evaluated. The beam damage indices are related directly to the rotation which happens in the plastic hinges. In components with immediate occupancy level, this linear characteistic is more clear; however, by increase in the rotation of the componenets or in the collapse prevention level, damage indices will diverge more. It has been shown that this damage index needs to be investigated at the collapse prevention level and the second part of the damage index (strength damage) shall be determinedby the element’s type and level of performance. The sensitivity of damage index to the column damages is little and the damage caused by the weak story is low and needs to be evaluated.

As a conventional method, the finite element model is used for static and dynamic analysis of structures such as dams and bridges. Nevertheless, these models are not able to describe the accurate behavior of structures against dynamic loads, because of some simplifications used in numerical modeling process, including loading, boundary conditions etc. Nowadays, modal testing is used to solve these problems. The dynamic tests, including forced, free and environmental vibration tests, are used in system identification of civil structures. Considering either unknown nature of inputs or unsuccessful steps of measuring them, some methods have been developed to analyze the results of dynamic tests which are based on measuring only output data and are known as operational modal analysis. Some of such methods are Peak Picking (PP), Frequency Domain Decomposition (FDD) and stochastic subspace methods. However, unknown nature of applied forces, the presence of environmental noise and measurement errors may result in some uncertainties within the results of these tests. In this article, a modal analysis is presented within a stochastic subspace which is among the most robust and accurate system identification techniques. In contrast to the previous methodologies, this analysis identifies dynamic properties in optimized space -instead of data space- by extracting ortho-normal vector of data space. Given the optimum nature of the proposed method, more accuracy may be served in detection and removal of unstable poles as well as high-speed analysis. In order to evaluate the proposed method in terms of civil systems detection, seismic and steady-state sinusoidal excitations were used. The former is selected from the most real and strong environmental vibrations and the latter is from the most precise forced vibration tests. In the first step, 2001 San Fernando earthquake data were analyzed using SSI-CCA and SSI-data methods. Data processing rate in the SSI-CCA method is almost twice as much as that in SSI-data method, and it is just because of processing in an optimum space while lowering the use of least squares method to compute system vector. Furthermore, there is one unstable pole in the results of the proposed method while 4 noisy characteristics were recognized in the results of SSI-Data method. Estimated damping ratio comprised the major difference observed in the results presented by above-mentioned methods. Modal damping ratio -estimated by the proposed method- were 60% closer to the previous results compared to those of the previous subspace method. Mode shapes of both subspace methods with MAC value of 92% and 75% for the first and the second modes, respectively, are well correlated with each other.Due to the lack of access to the mode shape vectors of Alves’s method, it was not feasible to calculate the corresponding MAC value. In the following, forced vibration test results of Shahid-Rajaee Dam conducted by steady sinusoidal excitation in 2000 and analyzed by a method known as four spectral, are re-processed using the SSI-CCA method. As results indicate, by using the proposed method the first three modes, which were not on the preliminary results, are obtained. In addition, other modes are in good agreement with the results of the finite element method.

The increasing demand for engineered cut and fill slopes on construction goals has increased the need of understanding the analytical methods, investigation tools and the most important stabilization methods to solve slope stability problems. The first step to maintain the stability of soil slope is performing excavation in the slope crest or/and filling the slope toe. This is the cheapest method for stabilization of soil slopes. If the method cannot provide the required factor of safety, it is necessary to use other stabilization methods. Numerical and laboratory approaches are useful for modeling soil slopes stabilization. Modeling the stability of earth slopes using numerical methods is a common practice in geotechnical engineering. Moreover, stabilization of soil slopes using piles has been practiced by many researchers in numerical and analytical approaches. Although numerical and analytical methods have special capabilities, laboratory modeling is more reliable. Stability slope analysis has attracted lots of researchers around the world and it shows the significance of this matter. When suspicious about stability of soil slopes, immediate actions and preventative steps should be used for suppression of instability occurrence. Many projects intersect with valleys and rides, which can be prone to slope stability problems. Natural slopes that have been stable for many years may suddenly fail because of many reasons; therefore, finding useful techniques for stabilizing them is a great concern for geotechnical engineers. In all soil slopes, the primary way for stabilization is the excavation in slope crest and/or filling slope toes. If this would not increase safety factor, other procedures should be applied. Three common styles of stabilization methods are; vertical reinforcement (such as stone columns and piles), horizontal reinforcement (like Geo-grids), oblique reinforcement (such as nailing). One of the common methods that is used to increase the safety factor of slopes is stone columns. All of the experimental tests were modeled and compared using the limit equilibrium (LE) and finite element (FE) methods, which are compliant with each other. Understanding soil properties is crucial for analysis of soil slopes. In this study, the effect of cohesion in embankment is investigated. This is carried out by performing laboratory tests and using finite element method software (PLAXIS2D) and finite difference method software (FLAC3D). A sand slope is reinforced with a stone column at the middle of slope. It is then saturated by precipitation and loaded up to the failure. Experimental studies in this article have the potential to give valuable information about the effects of embankment cohesion and penetration depth of stone column into the stiffer layer, in stability of stone column reinforced soil slopes.

Side weir is one of the most important structures in flood control projects. The structure can be designed based on classic design procedure, provided the main channel bed is rigid. However, in the most practical cases, the main channel bed is movable; Consequently the changes in bed can produce wavelike patterns as bed forms. Additional effects of side weir on bed forms may also be produced due to an aggradation of sediment deposits in front of the weir. This causes additional bed resistance and increase in flow depth in comparison with the situation with no structure. Thus, the present research studies the effect of side weir hydraulic and geometric properties -including Froude Numbers, diversion discharge ratios and flow depths- on bed forms and its effect on design conditions. A set of experimental program -with 9 individual tests- was conducted in a flume with dimensions of 0.85 m width, 0.40 m height and 10 m length. The flume is located on a mobile bed, having median sediment particle size of 0.23 mm, running with side weirs with crest lengths of 20, 40 and 60 cm. Furthermore, 3 experiments were conducted without using any weir, as bench mark runs. The sediment bed level at the end of each run was recorded using the automatic bed profiler in a distance of 220 cm of main channel, so that the weir is located in the middle of the reach. These measurements were carried out in a net of points with incremental distance of 5 and 3 cm in longitudinal and transverse directions, respectively. The dimensions of bed forms including wave length and height were then determined using the well-known crest-through method. Dimensional analysis is undertaken for dependent and independent variables involved in the process of the phenomenon including properties of fluid, sediment particles, channel and weir geometry. Non-dimensional parameters are also introduced. Results indicate that the effect of flow depth, discharge, and diversion ratio on bed form dimensions are significant, and increase in these parameters will cause increase in both length and depth of bed forms. In addition, a number of four equations are suggested for the prediction of bed form dimensions in terms of characteristic parameters for both cases with and without using the weir. The parameters of the equations were calibrated using randomly selected 80% of all experimental data and the equations are then verified using the remaining 20%. Verification results revealed that the relation may predict bed form dimensions within the error values of 50 and 30 percent for the cases of using weir or not, respectively. Analyzing these relations showed an important influence of applying side weirs on lateral variation of bed form dimensions in the main channel. Thus, in comparison with the case with no side weir, an increase of up to 70% and 2% of channel width may occur in bed form length and height, respectively, near the side weir.

Beam theory is used in the analysis and design of a wide range of structures, from buildings to bridges to the load-bearing bones of the human body. Beams resting on elastic foundation is vastly applied in many branches of engineering problems namely geo-technics, road, railroad, marine engineering and bio-mechanics. Foundation is often a rather complex medium, e.g. a rubberlike fuel binder, snow, or granular soil. The key issue in the analysis is modelling the contact between the structural elements and the elastic bed. Herein, the response of the foundation at the contact area is of interest, and not the stresses or displacements inside the foundation material. In most cases, the contact is presented by replacing elastic foundation with simple models, usually spring elements. The most frequently used foundation model in the analysis of beam on elastic foundation problems is the Winkler foundation model. In the Winkler model, the elastic bed is modeled as uniformly distributed, mutually independent, and linear elastic vertical springs, which produce distributed reactions in the direction of the deflection of the beam. However, since the model does not take either continuity or cohesion of the bed into account, it may be considered as a rather crude representation of the elastic foundation. In order to find a physically close and mathematically simple foundation model, Pasternak proposed a so-called two-parameter foundation model with shear interactions. The first foundation parameter is the same as the Winkler foundation model and the second one is the stiffness of the shearing layer in the Pasternak foundation model. Dynamic analysis is an important part of structural investigation and the results of free vibration analysis are useful in this context. Vibration problems of beams on elastic foundation occupy an important place in many fields of structural and foundation engineering. With increase in thickness, the existence of simplifying hypotheses in beam theories such as the ignorance of rotational inertial and transverse shear deformation in classic theory, the application of determination coefficient in first-order shear theory and the expression of one or few unknown functions based on other functions in higher-order shear theories are accompanied by reduction in the accuracy of these theories. This represents the necessity of precise and analytical solutions for beam problems with the least number of simplifying hypotheses and for different thicknesses.In the present study, the analytical solution for free vibration of homogeneous prismatic simply supported beam with rectangular solid sections and desired thickness resting on Pasternak elastic foundation is provided for completely isotropic behaviors under two-dimensional theory of elasticity and functions of displacement potentials. Characteristic equations of natural vibration are defined by solving partial differential equations of fourth order through the separation of variables and the application of boundary conditions. The major characteristics of present study include lack of limitations for thickness and its validity for beams of low, medium and large thicknesses is quite reliable. To verify, the results of present study were compared with those of other studies. Results show that increases in foundation parameters are associated with increases in natural frequency. The intensity is reduced considerably by increase in the ratio of thickness to length, for the values larger than 0.2 and in the higher modes of vibration.

Jack arch masonry slab, developed in the 19th century in Britain has been used widely in floors and roofs of industrial and residential masonry buildings in many parts of the world. It is still in use in parts of Europe, the Middle East and Indian subcontinent. Taking into account the widespread use of the jack arch flooring and its ease of constructing as compared to the more modern concrete-based slabs, it should be pointed out that such slabs are built in traditional ways and little control is applied to their method of construction.Collapse of a large number of these composite slabs during past earthquakes pointed out the weakness of this type of flooring to seismic loads. It has also highlighted the need for developing appropriate retrofitting schemes, since a large number of buildings in Iran are roofed with masonry slabs. As an illustration, the statistics have shown that around half of the slabs used in traditional buildings of Iran are jack arch roofs. Due to their poor construction style and lack of appropriate retrofitting, these slabs cannot tolerate high seismic demands and fail to meet the seismic performance required in areas with high seismic activities (especially the slant types which have been widely used in the buildings of northern areas of Iran). Therefore, rehabilitation of these roofs must be considered. One of the effective methods is to add a thin layer of reinforced concrete over the slab. The retrofitting procedure includes three main steps: (1) Removing the top flooring finish, (2) Installing a mesh of reinforcement bars over the slab and (3) Covering the bars with a layer of concrete. To further investigate the seismic behavior of these roofs, response modification factor can be utilized as a well-known seismic parameter.This study investigates the seismic performance of masonry buildings with slant jack arch slabs retrofitted by the method of adding a layer of reinforced concrete. Two groups of one story masonry buildings with jack arch masonry slabs are designed including roofs with slopes of 0, 10, 15 and 20 degrees with and without concrete layer for roof retrofitting. Static nonlinear (pushover) analysis is carried out. Nonlinear analysisprogram “ANSYS” is employed for the analyses. The load–displacement curves for both types of models are obtained and variations of strength, ductility factor, stiffness and rigidity of roofs on both types of models are investigated. Response modification factors of two groups are calculated and results are compared. Results show that according to standard No.2800 criterion, slant jack arch masonry slabs are classified as semi-rigid roofs and by retrofitting them, their rigidity can be enhanced. Also increasing the Slope of roofs inversely affects the Response modification factor (R), strength and elastic stiffness of structure. Finally For the consideration of economic factors, a cost analysis based on the tariffs of the Iranian Management and Programming Organization is carried out on three conventional methods of roof retrofitting (method of adding a concrete layer on the roof, steel grid method and tie-bracing method recommended by standard No.2800). The obtained results indicate that method of adding a concrete layer is the most cost-effective method for jack arch retrofitting.

The experience of previous earthquakes shows that the inelastic response of structure is related to the intensity and content of ground motion. In this case, the evaluation of nonlinear response of structure demonstrates the reduction in the base shear force. This reduction which leads to inelastic base shear is defined by Behavior Factor (strength reduction factor) in seismic codes. One of the important parts in R factor is ductility reduction factor Rm. While Rm is related to the type of earthquake, it seems that for near fault motions there would be a different value in comparison to ordinary earthquakes. For the near fault earthquakes, due to the direction of fault rupture from the site, the directivity effect becomes an important parameter. Previous researches show that for forward directivity effect, there would be two components for earthquakes. One is normal strike and the other is parallel strike. In this paper, these components are regarded as SN and SP. Also, in the concept of performance-based design, the ratio between inelastic and elastic response of structure is an important index in calculating the target displacement. This ratio is called CR, hereafter. It is good to mention that CR factor is defined as C1 coefficient in FEMA440. In previous researches, the evaluation of CR for near and far fault motions has less been considered.To evaluate Rm and CR, the extended number of SDOF systems (from 0.2 to 4 Sec.) are considered for four levels of target ductility (2, 3, 4 and 5). Accordingly, Rm and CR are calculated for near field (normal and parallel component) and far fault earthquakes. The normal strike component is traced by a sensitivity analysis, changing the strain hardening ratio and inherent damping. To perform the analysis, the nonlinear time history analysis was selected in Opensees. The steel material was also defined to be bilinear. To set the required ductility with the prescribed target ductility -during trial and error procedure- the yield strength of SDOF was changed, since the target ductility was achieved. To solve the inelastic equation of motion, the Newmark-Beta method was selected. The inelasticity in Opensees was modeled with distributed plasticity using the fiber element. Finally, to calculate Rm and CR for near and far field motions, approximately 84000 nonlinear time history analyses were carried out. In addition, to study the sensitivity of Rm and CR to damping and strain hardening ratio for the normal strike earthquake, approximately 22400 nonlinear time history analyses were carried out.The results show that for all three sets of earthquake, the Rm increases up to a specific value and after that, becomes constant while the fundamental period (T) increases. For small values of ductility (m), increase in T may lead to convergence of Rm to target ductility. In the near field, when the values of T and μ are increased, Rm becomes almost greater than μ. However, for small values of T, Rm is not dependent on demand m. The study shows that: using far field value of Rm for near field motions may lead to a non-conservative value. Furthermore, while T increases, the CR value converges to the unit. In the short period, CR depends on m and T, severely. Using CR of far field against SN component leads to Non-conservative result. For a constant value of m and T, increase in damping may increase CR. Using C1 for near field motions is non-conservative for near field motions. Also, for short periods and high ductility demand, CR, corresponding to SN component is about 40% greater than C1. Evaluation of the ratio of displacement modification factor to behavior factor shows that the Cd/R ratio for T -greater than 1 Sec.- converged to the unit. For small period values, this ratio is significantly dependent on the duration. Also, using Cd/R of far field for near field motions may lead to inaccurate results.

Cracking is one of the major modes of failure in asphaltic pavements. Structural cracks occur in two forms of top-down and bottom-up cracking. Bottom-up cracking occurs due to the fatigue of asphaltic materials under repetition of tensile strain at the bottom of asphaltic layer. Top-down cracking (TDC) is among the major forms of asphaltic pavement distresses that significantly affects the serviceability and development of structural failure. Interaction of tire and pavement plays a key role in the initiation of TDC. This study utilizes viscoelastic analysis -using finite element modeling- to evaluate the influence of axle loads and tire configuration on the top-down and bottom-up cracking (BUC) in typical unreinforced and reinforced asphaltic pavement structures. Reinforcing by glass-grid geogrid is selected for the reinforced structure.The highest vertical tensile strain at the surface and the highest horizontal tensile stress at the bottom of asphaltic layer are related to the TDC and BUC, respectively. Viscoelastic behavior is assumed for the asphaltic layer and linear elastic behavior is assumed for the base, sub-base and sub-grade. Prony series is used for characterizing the viscoelastic behavior of asphaltic layer. Using the tire pressure of 600kPa, effects of three axle load levels of 5, 8.2 and 15 ton and two tire configurations (conventional dual tire assembly and super single tire) on TDC and BUC have been investigated. Results show that the highest tensile strain at the surface occurs at the edge of super single tire and dual tires, with a higher values for the single tire. However, the location of the highest tensile strain shifts to the central region of dual tire with increasing axle load level. The results also show that under axle load of 5 and 8.2 ton, top-down cracking initially occurs at the inner edges of the tires, while under axle load of 15 ton its occurrence between the tires is more probable than in the other zones. For the pavement without reinforcement, the highest tensile strain at the surface is higher than that at the bottom under dual tires; however, under super single tire, the critical tensile strain at the surface is lower than that at the bottom of asphaltic layer. The results show that geogrid reinforcement is more effective in reducing the critical tensile strain at the bottom of asphaltic layer than that at the surface. This indicates that the reinforcement of pavement using geogrid at the bottom of asphalt layer is more effective on the bottom up cracking than on the top down cracking. In addition, geogrid reinforcement is more effective in reducing the critical strains under single tire than under dual tires. The rate of increase in the critical tensile strain at the surface with increasing axle load is more than that of the critical tensile strain at the bottom of asphaltic layer. Among bottom-up cracking (BUC) and TDC, BUC is more sensitive to the variations of tire type. By comparison, the super single tire created more TDC damage ratio than the dual tires assembly, in both reinforced and unreinforced pavements. However, the damage ratio due to the super single tire in unreinforced pavement is more than in reinforced pavement.

Adhesion of bitumen to Aggregates is the basis of the strength of the asphalt pavements. The term "stripping" is used for hot mix asphalt (HMA) mixtures to show the separation of asphalt binder film from aggregate surfaces, due primarily to the action of moisture and/or vapor. If this phenomenon is eliminated for any reason, stripping will be occurred. This problem not only is as a distinct distress but also can cause other asphalt distresses which are finally resulted in the overthrow of road. Mainly because this distress either results from or is dominated by moisture, it is usually called“moisture damage” or “moisture susceptibility”.The main goal in this research is to study stripping in asphalt mixtures. The key factors which must be considered in this research are aggregates and selecting the suitable approach for controlling and assessment of this distress in laboratory conditions. the most recent approach introduced is the rehabilitation and modification of asphalt mixtures against stripping, whether asphalt concrete or surface treatment. Thus, in this study on "Zanjan-Qazvin" freeway where this distress have usually been observed, the aggregates for constructing the asphalt was selected from sections of the aggregate the stripping intensity of which is higher than the others. First, the sensitivity of stripping was specified by XRF & XRD analysis. There is a requisite to do a realistic laboratory test method to predict moisture susceptibility of HMA mixtures. It was observed in the case histories that the asphalt pavements were saturated with water (55-80% saturated as specified in ASTM D4867 or AASHTO T283). Thereafter, in order to calculate the tensile strength ratio, it is required to consider unsaturated specimens some of which remained with no conditions. A laboratory test procedure that simulates such conditions will be more realistic. The cylindrical asphalt concrete specimens are constructed by marshal method. Thus, their durability is evaluated according to AASHTO-T283. In this method, those stabilities are measured by indirect tensile test; the amount of their stripping was previously estimated by boiling test. Results showed that according to literature boiling test method is not reliable enough to be accurate. On the other hand, the result of laboratory test of AASHTO-T283 is quantitative and much more technical. Also, using hydrated lime 3% for this material can be useful to reduce the adverse effect of stripping, and it can be used as a suitable anti-stripping. Based on the probabilistic analysis, all the specimens result either in Indirect Tensile Test, or in the TSR results. This showed the improvement of the strength. Also, the rate of increasing is close to that of the parabolic curve.WTAT test was carried out over the surface treatment specimens constructed using these aggregates. Hydrated lime was utilized as the most important anti-stripping additive for prevention and rehabilitation of this distress in all of the experiments.

The U-shaped channels are applied as a transition cross-section from rectangular to circular in manholes.Also the U-shaped channels along the side weirs are used in the sewage networks, irrigation-drainage systems, flood protection and etc. The flow in the main channel along the side weir can be the supercritical conditions. In this study, the free surface flow in the supercritical regime has been simulated by FLOW-3D software, RNG k-e model and volume of fluid (VOF) scheme in a U-shaped channel along the side weir.The comparison between the numerical and experimental results showed that the numerical simulation predicted the free surface flow with the reasonable accuracy. Generally, the flow depth decreases with distance from the upstream end of the side weir towards the downstream end in the U-shaped channel. The APE and RMSE of the water surface profile along the side weir have been computed 1.7% and 0.213%, respectively. Also, the APE and RMSE were respectively 3.8% and 0.0177% for the discharges over the side weir. In continue, the effects of the upstream Froude number on the flow pattern in the main channel were investigated. For all Froude numbers, because of entrance effects, a free surface drop occurred at the upstream end of the side weir and the water depth gradually reduced toward the downstream end. Then, a surface jump happened at the last fourth of the side weir length in the vicinity of the inner bank. Unlike the potential energy, the kinetic energy increases along the surface jump. Also, a stagnation point is created at the end of the surface jump. The height of this stagnation point increases with increasing the Froude numbers. In addition, the dividing stream surface and stagnation zone were respectively produced near the inner and outer bank in the main channel along a side weir. The dividing stream surface reduces from channel bottom toward the side weir crest then increases to the flow surface. Also, the dimensions of the dividing stream surface and stagnation zone increased with increasing Froude number. The maximum lateral flow in the U-shaped channel occurs almost at the downstream end of the side weir. The transverse velocity increases at each cross-section of the main channel with increasing Froude number. The angle of the spilling jet (j) was close to 90o at the upstream and downstream of the side weir crest and the pattern of spilling jet angle is similar for all Froude numbers. The minimum angle of the spilling happens approximately at the downstream of the side weir crest however, the minimum j decreases with increasing Froude number. The pattern of the bed shear stress can be used to prediction of the areas of the scour and sedimentation in the alluvial channels. In the U-shaped channel along a side weir, the bed shear stress increases along the main channel axis form the beginning of the side weir toward the middle then decreases toward the downstream end. Generally, with increasing Froude number, the bed shear stress increases in the main channel along the side weir.

Evolutionary structural optimization (ESO) is based on the simple concept of systematically removing inefficient elements from the structure after each finite element analysis, so that the obtained design is gradually evolved to an optimum. The bidirectional evolutionary structural optimization (BESO) method is a new version of the ESO method in which simultaneous removing and adding elements is allowed. The procedures of removing and adding elements are performed using various criteria. Due to the importance of nonlinear structural analysis, in this study the BESO approach is used. The nonlinearity is assumed for the geometry, material, and for both geometry and material. In the first example, the BESO is applied to maximize the stiffness of a cantilever beam with a time dependent loading. The complementary work for the optimized shapes are compared. It is concluded that using BESO results in a more optimized shape. Optimized shapes for this case were obtained from linear and nonlinear analysis using BESO, and nonlinear analysis using Solid Isotropic Material, with Penalization for intermediate densities (SIMP). In the next example, BESO is applied to optimize the stiffness of a plate with the material nonlinearity. The results show that the nonlinear analysis leads to a much stiffer design. In the third example, a cantilever beam with both material and geometry nonlinearity is considered. The beam is also to be optimized for stiffness. The optimized shapes are compared for linear and nonlinear analysis against the SIMP. The nonlinear analysis with BESO also results in a stiffer design.Furthermore, the effectiveness of ESO is proved by applying them to some shape optimization problems. The aim is to find the best circular hole so that it possesses a lower stress concentration factor. Design boundary has been set with some control points, and optimization process is only applied to these points. A square plate with a circular hole at its center is optimized for minimizing the stress concentration. The obtained results for linear and nonlinear analysis using ESO are compared with the results obtained using the biological growth method. It is concluded that using ESO, the maximum stress concentration around the boundary of the hole can be significantly decreased with linear analysis and the ESO is a powerful alternative for the biological growth method. Results show that ESO has a superior capability for shape optimization of holes in nonlinear structures, and in this case maximum stress is reduced by 28%.

The rapid boost of wastewater volumes produced in the world is opening a new market for membranes, which have a significant potential to take the role as the main technology for these applications. today, an increasing number of wastewater treatment facilities are using membrane technologies, and this number is growing year by year. Membranes processes have high selectivity values required to achieve high water and wastewater quality standards, are more cost-effective than other conventional processes, require less area, and can replace several unit treatment processes with a single one.In the past years, microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) membranes, as well as membrane bioreactors (MBRs), have been increasingly implemented in water and wastewater treatment processes such as groundwater, desalination of brackish water and seawater, and decontamination of wastewater of diverse nature and sources, e.g., including urban wastewater, coking, carwash, nuclear power, power engineering, steel industry, textile and tannery, pulp and paper, pharmaceutical, and agro-food industries, such as dairy, beverage, winery, tomato and olive oil, among others. Other membrane processes, such as electrodialysis (ED), membrane distillation (MD) and forward osmosis (FO) are also being explored.Produced water is the largest waste stream generated in oil and gas industries. It is a mixture of many organic and inorganic compounds. Because of the increasing volume of waste all over the world in the recent decade, the outcome and effect of discharging produced water on the environment has lately become a significant issue of environmental concern. Produced water is conventionally treated through different physical, chemical, and biological methods. In offshore platforms because of space constraints, compact physical and chemical systems are used. However, current technologies cannot remove small-suspended oil particles and dissolved elements. Besides, many chemical treatments, whose initial and/or running costs are high produce hazardous sludge. As high salt concentration and variations of effective characteristics have direct influence on the turbidity of the effluent, it is appropriate to incorporate a physical treatment, e.g., membrane to refine the final effluent. For these reasons, major research efforts in the future could focus on the optimization of current technologies and use of combined physico-chemical and/or biological treatment of produced water in order to comply with reuse and discharge limits.The objective of this study was to evaluate the feasibility of treating desalting plant produced water to meet the applicable flow rate limits and injection to well standard consistently using single and hybrid membrane processes to reduce the risk of clogging of the injection well. The treated effluents of two sand filtration units from Aghajari maroon were used as feed. A Pilot scale hybrid membrane unit with a spun polypropylene of 0.45 μ pore size microfilter and a hollow fiber polypropylene of 0.1 to 0.01 μ pore size ultrafilter membrane were used in this study. Trials on different membrane fluxes were conducted for two processes: microfiltration, and hybrid micro and ultrafiltration processes. Results show that flow rate of 32 LPM was more applicable. The optimal flux was 120 LMH. The average removal percentages of Turbidity, Oil and grease, TSS and particle size were 98.53, 98.81, 98.23 and 99.93, respectively. The results showed that the quality of the product consistently met the requirements for well injection. It is concluded that it is feasible to treat the produced water using micro and ultra filters.

One of the most important goals of optimal control of structures is achieving the desired reduction in responses using minimal control forces. Regarding many researches conducted in the field of active control, several control algorithms have been presented over the past few decades. Most of these researches calculate the required control forces by optimizing a second-order performance index. There exist simplifying assumptions in formulation of these classic algorithms and constraints in mathematical optimization techniques that have been used in optimizing the performance index. For example, because of unknown nature of earthquakes, the LQR classic controller cannot consider the external forces -as earthquake excitation- in calculation of control signal. This may make difficulties in finding the optimal solution for optimization problem. Metaheuristic optimization methods, such as differential evolution, are modern algorithms and because of their special capabilities in finding global optima are powerful tools that can be used in solving complex problems. Despite of many advantages, these methods has not been used extensively for solving civil engineering problems, especially in the field of active control of structures. In this paper active control of structures is considered as an optimization problem and a controller is proposed. The controller uses the differential evolution metaheuristic algorithm for finding gain matrix elements of active control problem. The gain matrix elements are globally searched by differential evolution algorithm to minimize the LQR performance index. The proposed method is repetitive and does not need to solve the Riccati differential equation. Therefore, it is possible to consider the effect of external excitation in finding the gain matrix and calculation of control signal. The controller is applied on sample 2DOF and 10DOF structures. Responses of these structures under several excitations from the historical earthquake records are obtained by MATLAB programming. In addition to the performance index, the maximum control force, maximum displacement and 9 benchmark indexes -previously measured in controlled structures- are calculated in this study. These indexes represent the reduction of controlled maximum and average responses of structure in comparison with uncontrolled responses. In order to evaluate the effectiveness of the proposed controller, these 9 performance indexes are calculated for 2DOF and 10DOF examples against 7 historical earthquakes and are compared for proposed and LQR controller. The simulation results indicate that the proposed method is effective in keeping the controlled responses of structures in desired range. This is also efficient in reducing the vibrations of structures with lower need to control the amount of energy in comparison with LQR algorithm. Because of the great capabilities of DE algorithm in searching large spaces and due to the iterative nature of controller, it considers the effects of external forces in control process. Numerical simulation shows that performance of the presented control algorithm is better than the LQR controller in finding the optimal displacements and control forces. Therefore, metaheuristic algorithms such as differential evolution can be used in active control of structures to achieve more efficient results in comparison with classic controllers.

Adding steel fibers to reinforced concrete improves the active mechanisms on crack surface including tension and shear transfer mechanisms. In Steel Fiber Reinforced Concrete (SFRC), tensile stresses are developed in fibers and deformed reinforcing bars just after crack initiation. With this beneficial effect, concrete tensile strength is improved and crack spacing decreases. In this research, SFRC member behavior is analytically investigated under pure tension and in order to verify the model, the results are compared with some recent experimental results. From the viewpoint of constitutive modeling of RC elements, there are two main approaches, discrete crack and continuum level models. The major disadvantage that adheres to discrete crack models is the fact that these models focus on the local crack behavior and seek to detect the crack paths, which of course requires a high computational cost. By contrast, continuum level models take advantage of the spatially averaged models between two primary transverse cracks. In a process of developing average constitutive models, it is important to model local mechanisms, these mechanisms in a reinforced concrete domain are related to initiation and propagation of cracks.In this article, the tension stiffening model is developed considering all effective local stress transfer mechanisms including tension behavior of deformed bar, fibers pullout, tension softening of plain concrete and bond slip-stress between the reinforcing bar and concrete matrix. Straight and end hooked fibers have different mechanisms during pullout such as debonding, friction and mechanical anchorage of end hooked fibers. To predict the fiber tensile behaviors, it is necessary to define fiber stress transfer mechanism on the crack surface. The most important parameters that affect fibers behavior are material properties, size and geometry, distribution and orientation of fibers. The model used in this research considers a uniform random distribution forfiber’s geometrical location and inclination angle. In this model, the slip occurred in the fiber is considered on both sides of fiber embedded in concrete. The bond slip- stress behavior of straight fiber is defined as linear before the bond stress reaches to the bond strength, then the bond stress is considered constant until the complete pullout. In end-hooked fibers, in addition to debonding and friction, the end mechanical anchorage of the fiber has also an important effect on the bearing capacity. In fact, in the process of fiber pullout, hooked part of fiber most have plastic deformation. To simulate it, a parabolic model is used. In order to solve the algorithm, an iterative analysis method is applied to calculate tension stress-elongation of specimen. To increase the accuracy of the model, the local yielding of reinforcing bars and matrix damage at the crack surface are also numerically simulated. Model verification is carried out by comparing the computational predictions with available experimental results. The results show good agreement with the test results. The proposed model is also shown to be useful in considering the effect of various percentages of fibers on average stress-strain behavior of deformed bar, total load elongation of specimen, crack spacing and concrete tension stiffening. By increasing fiber percentage, crack spacing will decrease so the average stress- strain behavior of deformed rebar becomes more similar to the bare bar.

Despite the success and versatility of mesh based methods --finite element method in particular- there has been a growing demand in last decades towards the development and adoption of methods which can eliminate using the mesh, i.e. the so called meshless or mesh-free methods. Difficulties in the generation of high quality meshes, in terms of computational cost, technical problems such as serial nature of the meshgeneration process and the urge of parallel processing for today’s huge problems have been the main motivation for the implementation of new researches. Apart from these, the human required expertise can never be completely omitted from the analysis process. However, the problem is much more pronounced in 3D problems. To this end, many meshless methods have been developed in recent years among which SPH, EFG, MLPG, RKPM, FPM and RBF-based methods could be named. The exponential basis functions method (EBF) is one of these methods which has been successfully employed in various engineering problems, ranging from heat transfer and various plate theories to classical and non-local elasticity and fluid dynamics. The method uses a linear combination of exponential basis functions to approximate the field variables. It is shown that these functions have very good approximation capabilities and their application guarantees a high convergence rate. These exponential bases are chosen such that they satisfy the homogenous form of the differential equation. This leads to an algebraic characteristic equation in terms of exponents of basic functions. From this point of view, this method may be categorized as an extension to the well-known Trefftz family of methods. These methods rely on a set of the so called T-complete bases for their approximation of the field variables. These bases should satisfy the homogenous form of the governing equation. They have been used with various degrees of success in a wide range of problems. The main drawback of these methods –however- lies in the determination of the basis, which should be found for every problem. This problem has been reduced to the solution of the algebraic characteristic equation in the exponential basis functions method. The method is readily applicable to linear, constant coefficient operators, and has been recently extended to more general cases of linear and also non-linear problems with variable coefficients. The relative performance of usual programming languages such as C++in comparison with mathematical software packages -like Mathematica and/or Matlab- is one of the major questions when using such packages to develop new numerical methods. This can affect the interpretation of the performance of newly developed methods compared to established ones. In this paper, the implementation of the exponential basis functions method on various software platforms has been discussed. C++and Mathematica programming have been examined as a representative of different software platforms. The exponential basis function method is implemented in each platform, using various options available. Results show that with a proper implementation, the numerical error of the method can be decreased considerably. Regarding the results of this research, optimal implementations of C++and Mathematica platforms, error ratio is between 2.5 and 6, respectively.

Design and construction of a concrete arch dam needs two essential conditions: these are good rock foundation and convenient topography. When these two conditions are satisfied, arch dams would be the most desirable and the most economical types of dams. Sometimes the geometry of the valley is good, but the rock foundation is not appropriate or the rock has good material but the geometry of valley is poor. One important factor in safe design of an arch dam is the rock foundation stability problem when a large part of the external loads is transferred to the foundation by the arches. In arch dams, these forces are much larger than similar forces as compared with other dams. Moreover, the stability of an arch dam also depends on bearing capacity of the rock foundation. The idea of construction of arch dams with perimetral joint and pulvino was introduced by Italian engineers in the 40s to improve stress conditions. It was gradually expanded in the following decades. Pulvino is a thick concrete pad built between the arch dam body and the rock foundation as a strip foundation. Use of this structural component, reduces the uncertainties of the rock foundation, enabling a thinner body for the dam. Thus providing perimetral joints between the pulvino and the dam body; ensures more symmetrical distribution of stresses within the dam body. It also reduces potential tensile stresses at the boundaries of the dam body. In this study, the effect of pulvino is investigated on the behavior of a concrete arch dam body built in a valley with weak rock layers. The results are compared with the case of a conventional concrete arch dam (Control Dam); i.e., without pulvino in the same valley conditions. In order to maintain the same concrete design properties, the volume of the Control Dam had to increase by 40% in respect to the total volume of the dam with pulvino. The foundation has a weak layer in different situations identically for both dams. The only nonlinearity accounted for, corresponds to the perimetral joints. Applied loads include the weight and the hydrostatic pressure load. The dam weight is applied step by step to simulate the staged-construction of a concrete arch dam. The ANSYS 12.1 program is used to create the finite element models of the objective arch dam and its foundation. Results of this study show that use of pulvino causes symmetric and uniform distribution of stresses in the dam body even if the rock layers are weak and asymmetric. Contrary to the Control Dam case, higher tensile stresses occur only inside the pulvino and thus the main body of the dam is protected against such stresses. As pulvino is usually reinforced, the dam with pulvino and its perimetral joint remain acceptable. Thus, despite a rather expensive and harder construction job for such dams with pulvino and perimetral joints, their considerably lower concrete volume may well compensate the problem. Thus this type of concrete arch dams remains still economic and competitive for the future designs.

New techniques in seismic design of structural systems are based on flexibility and energy dissipation approach. In this approach, the role of energy dissipaters is quite important. The behaviors of these devices and the way they dissipate energy have always been a concern for many researchers to improve the efficiency of these important parts of the structural systems. There has been a large number of investigations on behavioral aspects of energy dissipating devices capable of using in seismic design of structural systems.The concept of adding dissipating supplemental devices to a structure assumes that much of the energy imposed to the structure from a transient will be absorbed, not by the structure itself, but rather by supplemental damping elements. Among them, viscous devices have received considerable attention. The behavior of these energy dissipaters are dependent, not only on the relative velocity, but also on a large number of other parameters including relative displacement, compressibility of fluid, internal friction etc.The behavior of viscous devices are also dependent on the frequency of excitation and their thermal conditions. Determination of mechanical characteristics of these devices is usually based on experimental studies including cyclic tests in different amplitudes and frequencies.In this study, a new type of viscous dashpot in which the main body of the device has been made of contractible steel bellows (developed in IIEES) is chosen for experimental studies. The viscous device has the capacity of 500 kN and axial deformability of ±150mm. The tests have been carried out using an actuator capable of providing axial forces up to 300 kN in cyclic tests with displacement range of ±120mm. Axial forces on dashpot and resulted deformations on the device during experiments have been used to find the relationships between applied forces and induced relative displacement and velocity on the device.According to the results, the dashpot shows a dominant viscous behavior. It also represents a small frictional behavior in order of 10 kN (on average). The device also shows a frictional feature that is proportional to its internal fluid pressure. This feature is due to a small asymmetry in manufacturing some parts of the device, but it can be used later to improve the behavior of contractible dashpots. To be able to develop a model for this device, the test results are used in the form of cyclic behavior and time series. The time series results show the fact that there is not a linear proportionality between forces and velocity experienced by the dashpot in all the range of excitation frequencies. In addition, according to the test results, damping constants for this device is also dependent on the excitation frequency. Different types of behavioral models have been examined for the device. The proper model is proposed based on the three element type Maxwell model. The model can be further improved to represent the pressure dependent frictional forces in this dashpot.

According to the observations after the recent near-field earthquakes, structural damages are mostly attributed to the vertical component of the ground motion, i.e. concentration of the damages in column members leading to progressive structural collapse. This is whyinvestigation of ground motion’s vertical component effect has been widely regarded in recent studies. In seismic design, this component is considered less than other components of earthquake. However, in near fault earthquakes, large vertical acceleration components cause extensive damages compared to the ones with horizontal acceleration. Failure and damage in concrete columns is among the examples of the negative effects of vertical component. Vertical component of earthquake is considered in the design of specific members on the recommendation of seismic codes such as EC-8 and FEMA 356. The design is intended to use the scaled horizontal component, where this can result in incorrect answers due to lack of stimulation because of the specific characteristics of vertical component of earthquake and structural properties in the vertical direction. Also, the vertical component of earthquake is less studied in seismic risk analyses. In this study, the effects of vertical earthquake excitations on medium-rise concrete moment frames are investigated in two separate stages including near field and far field records.In this research, various structural models, representative of real structures and designed in accordance to seismic codes and under actual gravitational loads have been subjected, simultaneously, to horizontal and vertical components of near- and far-field ground motion records at two stages. Nonlinear time history and progressive dynamic analyses have been performed in this regard. Furthermore, the effect of elevation orreduction of initial gravitational forces as well as columns’ initial axial forces have been investigated by applying differing gravitational loading coefficients. Structural response parameters including tensional and compressional axial loads of the columns as fluctuating forces, columns’ uplift forces at various plan positions and under various gravitational coefficients, the interactive axial-flexural forces of the columns at different gravitational coefficients, shear demand-to-capacity of columns, axial deformation of the columns in presence and absence of vertical component of the earthquake, have been comparatively investigated and the effect of vertical ground motion component has been assessed, separately, for far- and near-field acceleration records and for external and internal columns placed at different stories.The obtained results reveal that tensional uplift forces are more critical in external columns than the internal ones. This is mainly true for lower stories, while at the upper stories the tensional forces experienced by internal columns are seen to be more critical. The existence of vertical component of earthquake leads the minimum compression forces to increase and change toward tension range. The amount of this reduction has been witnessed to reach to 84% in the more extreme case. It was also seen that for smaller gravitationalcoefficients, tensional axial forces are more frequently observed. The presence of earthquake’s vertical component has been shown to amplify the columns’ shear demand by the values reaching to 31% at the most extreme cases.