نشریه مهندسی عمران مدرس
سال سیزدهم شماره 1 (بهار 1392)

This experimental study is intended to evaluate the effectiveness of a Near Surface Mounted (NSM) technique using bars made of carbon fabrics (BMCF) for strengthening of RC beams. When the amount of NSM reinforcement in strengthening of RC beams is low، the failure is likely to be due to debonding of individual reinforcing rod and in this case improved bond properties as well as proper anchoring of the BMCF rods are likely to delay the failure of the beam. BMCF provide a larger perimeter to cross sectional area ratio with respect to conventional rods for the same amount of fibre used، providing potentially higher bond strength. In addition، the circular shape of BMCF is not only convenient for production but also suitable for NSM strengthening as noted by previous researchers. Another key advantage of introducing the BMCF is that it allows the incorporation of a different anchor system that can be used to improve the performance of NSM BMCF reinforcement for strengthening of RC beams in applications with low strengthening reinforcement percentage. A distinguished benefit of the proposed anchor system is that it only requires the access to the beam sides for installation. This means that the proposed anchorage system can be conveniently applied to beams whose top and/or bottom face is inaccessible. A set of deficient beam specimens were designed. All specimens had the same internal reinforcement arrangements. They were 300 mm wide، 350 mm high and 2050 mm long. One half of each beam was designed to be weak in load bearing as the test span while the other half was designed as the strong span. Only the test span was strengthened in with NSM BMCF. The amount of steel reinforcement in the two sides was designed to ensure that shear failure would occur in the test span. All beams were simply supported at the ends and tested under a concentrated monotonic load applied at the mid-span. Test results presented in this paper have confirmed that the use of BMCF is an effective technique for improving the shear capacity of RC beams. The increase in the shear capacity was between 18 to 55% for beams strengthened with BMCF، compared with the reference beam. The load–deflection response of beams is presented. The capacity of specimens for energy absorption are also presented and discussed in this paper. In order to predict the contribution of NSM-BMCF strengthening method، an analytical study is presented in this paper. The analytical procedure is evaluated by experimental findings. It is concluded that the analytical formulation can reasonably estimates the contribution of NSM-BMCF strengthening reinforcement and as a safe design point of view; it is advisable for engineering application aims.

In this paper، the results of a statistical study on inelastic displacement ratio for structures subjected to pulse like near fault ground motions are presented. This study is important because the results can be used for evaluating inelastic displacement demand of structures with known lateral stiffness and strength subjected to near fault ground motions. Inelastic displacement ratio is computed from the response of single-degree-of-freedom systems having 6 level of strength reduction factor subjected to 61- pulselike near fault records. The influence of period of vibration normalized by period of peak spectral displacement، strength reduction factor، period associated with velocity pulse TP، earthquake magnitude and distance to the source، post-yield stiffness and hysteresis behavior of a structure on inelastic displacement ratiois investigated. For more study on the strength and the stiffness degradation effects on inelastic displacement، three type of hysteresis behavior have been considered. The first type iselasto-plastic behavior. Elasto-plastic behavior is generally used to represent the non-degrading hysteretic behavior. Second and the third typesarethe stiffness degrading and the strength-stiffness degrading hysteretic behavior. Results indicate that strength and stiffness degrading in short period region increases inelastic displacement demands. Further the period associated with velocity pulse plays a main role in inelastic displacement and has a significant effect on it. It is found that strain hardening can reduce inelastic displacement relative to system with perfectly elasto-plastic hysteresis behavior. Magnitude and source to site distance have little effects on inelastic displacement. Finally، a simple equation is proposed for estimating the mean inelastic displacement ratio for structures subjected to pulse like near fault ground motions.

Cemented sandy soils can be found in different parts of nature. Slopes and natural cuts are observed to be stable for long periods of time. Indeed the stability is related to the cementation and bonding between soil grains which induces an equivalent cohesion for coarse grained soil. Several experimental and theoretical studies have been performed to investigate the mechanical behavior of this category of geomaterials. In present research، a constitutive model is proposed for simulating the mechanical behavior of cemented sandy soils. The model is based on separating the mechanical behavior of cemented soil to two different parts; firstly the uncemented soil matrix and secondly the cemented bonds. The generalized plasticity model developed by Manzanal et al. (2011) is used for predicting the mechanical behavior of the uncemented soil matrix. The model is based on critical state concepts and is able to simulate the behavior of sandy soil in a wide range of confining pressures. It contains sixteen parameters which can be determined using ordinary geotechnical tests for the base soil. Also the elastic-plastic damage bond model proposed by Haeri and Hamidi (2009) is used for cemented bonds. The model has two additional parameters and is able to predict the brittle behavior of cemented bonds besides their degradation with increase in shear strain. Peak shear resistance of cemented bonds increases with confining pressure، however، the axial strain associated to the peak shear strength decreases with enhancement of confining stress. Also cement content is considered in this bond model which is its advantage in comparison with similar ones. Both components have been combined together based on deformation consistency and energy equilibrium equations. Deviatoric stress-shear strain curves besides volumetric strain-shear strain ones have been compared with the results of consolidated drained triaxial tests on a gypsum cemented sand to verify the proposed model. Also deviatoric stress-axial strain besides deviatoric stress-mean effective stress curves of model are compared with results of tests in consolidated undrained state. Results of verification indicate good performance of developed model in a wide range of cement contents and confining pressures. The proposed model has two distinct advantages. At first it considers the effect of cement content as a model parameter and shows variation of the results with this parameter. Secondly، it simulates the soil behavior in a wide range of confining pressures which enables using it in the boundary value problem in geotechnical engineering. However، it should be noted that the model predicts the mechanical behavior of cemented sand in cement contents less than floating limit. Increasing the cement content from the floating threshold changes its role from effective bonding between soil grains to a filler of voids. In this condition، the model can not predict the behavior of cemented soil due to the limitations in the elastic-plastic damage bond model applied in present constitutive model.

Ballasted railway track are of the most common types of railway in our country. The aim of this paper is study of three-dimensional suitable model for railway ballasted track and Dynamic analysis of that using numerical Runge-Kutta 4th Order Method. After the dynamic analysis is performed the responses related to railway components are determined. To analyze the effect of passing railway train on track، a function of time variant moving load on the railway line is applied and the effect of dynamic response under loading is evaluated. Previous researchers in the field of this activity have worked on modeling and analyzing of railway track system and train-track interaction problems on the two-dimensional models and the dynamic time domain problem for 3D models has not completely examined before. But this study is trying to consider the extra transverse nodes on previous models and come in three-dimensional dynamic analysis by numerical method. In other words، a new perspective in this article، is considering the nodes for transverse model of railway track and also numerical analysis of that. In this article، a 3D analytical model of Moving Load‐Track interaction is organized by elements of mass، spring and dashpot. Since، railway track structure can innovatively be simulated with a continuous model of mass‐spring system. Then by using the principles of structural dynamics and finite element method، equations that governing the motion of components of this model are identified and final equations are extracted. Brief description of the numerical method is use of solving algorithm to solve the track- moving load interaction. In this research، simulation and modeling for rails، tie، connections and railway superstructure layers، is considered as elements of lump masses، springs and dampers. Traditional methods used for design of rail elements، have been based on static loading and quasi-dynamic analysis، but in this paper، according to the structural dynamics phenomena in relation to rail component vibrations and study of dynamic loading effects on track components، are the issues to more realistic analysis. Responses obtained from dynamic analysis can be utilized as inputs for designing concepts and optimizing the track components.

Recent damaging earthquakes in Iran and around the world have induced great death and damage providing serious reminders of seismic vulnerability of existing structures. It is more crucial in Iran، where many structures have been built when seismic codes were not effective enough، especially considering the fact that construction has not been perfectly consistent with design specifications and drawings. Many of existing building، therefore، have inadequate strength when subjected to earthquake. To prevent such damage and tragic event، efficient ways are necessary for seismic upgrading of these buildings. One of useful extensively used methods is passive control. By reducing seismic demand and increasing ductility، these control ways can reduce rate of seismic damage. One of the most effective mechanisms available for dissipating seismic energy through inelastic deformations of metallic substances is use of shear panels. Use of such yielding dampers has been increased recently for their high capability in energy dissipation. Despite eccentrically braced frames، EBFs، these pieces are not embedded in floor and can be exchanged easily with little cost after earthquakes. The basic role of shear panel system is to absorb a major portion of input seismic energy، thus reducing energy dissipation demand on structural members and minimizing probable structural damage. Due to recent advances in these passive control methods specifically significant improvements in earthquake energy dissipation and prevention of damage in the main parts of the structures، this paper provides a new hysteretic damping system، especially beneficial to retrofitting steel structures having Eccentrically Braced Frames، EBFs. This research studies the seismic performance of EBFs with double shear panels. Five specimens have been evaluated using nonlinear finite element analysis under cyclic and monotonic loading. The findings present the proper performance of proposed revision for EBFs، the rise in energy dissipation and the elimination of damage to the main parts of structure (column، bracing، main beam) and its concentration in shear panels reducing displacement of horizontal link (main beam) of EBFs. The analytical results showed the shear panel shear distortion capacity of 0. 08 - 0. 15rad (displacement of horizontal link of 0. 5 - 1. 25cm). The response modification factor of this system was also obtained in the range of 8. 7-9. 8. Based on the results obtained in this paper، using double SPS in addition to dissipating more than 70% of imposed energy and increasing the structural ductility، can reduce lateral displacements due to decreasing seismic demand. Finally، using shear panel is highly recommended as an effective and efficient way for seismic design of new steel building structure and also for seismic retrofit of existing steel buildings.

An attempt in this paper has been made to experimentally investigate the behavior of rock like pre-cracked samples under uniaxial loading. To reach that aim، several physical models made up mixture of cement، gypsum and water with 5×10×20 cm of dimensions which contained open and closed joints with rough and smooth surface. Open and closed joints with rough and smooth surfaces were located in the center of samples. Open and closed joints with 4، 5 and 6 cm of lengths and 30، 45 and 60 degree of angles relative to loading direction were located in the center of samples. Saw cut profiles were used to make a roughness in the specimens. Experimentally results illustrate that depend on length and angle of closed or open joints، two types of cracks (wing and secondary cracks) propagated from the tips of pre-existing joints. Secondary cracks propagated after than wing cracks. With increasing internal stress due to loading، tensile stress concentration were happened earlier than shear stress concentration at the tips of pre-existing open cracks. Propagation of cracks from the tips of joint proved stress concentration was larger than another part of joints. In fact stress concentration in the central part of joint is more than joint tips. Location of crack propagation changed into the central part of joint with decreasing of closed joints angle relative to horizontal direction so stress concentration in the center more than another part of closed joints. Crack initiation stress depends on length، dip and closed or open state of joints. Wing crack initiation stress proportional to joint angle relative to loading axis and inversely proportional to joint length. In the Similar circumstances Initiation stress for closed joints more than open joints. In this research، effective parameters on secondary crack propagation were investigated. The experimental results reveal that secondary crack propagation depends on joint dip and distance between crack tips and sample sides. If minimum distance between crack tips and sample sides called (s) and width sample called (b) then for the specimens with 30 degree of dip angle and ratio secondary cracks propagated from crack tips to sample sides.

The importance of non-structural components in seismic Performance Based Design of buildings is well known nowadays. In this research calculation of absolute acceleration applied on non-structural components located on floors of moment-resisting، eccentric braced and concentric braced frames subjected to earthquake ground motions has been studied. The results of nonlinear time-history analyses of 3، 5 and 7-story steel frames with 8 different periods and 5 reduction factors subject to 15 records of near-field earthquakes and 15 records of far-field earthquakes has been used to investigate the effects of different parameters on absolute acceleration induced in each floor of the structures. The effect of inelastic behavior of system، natural periods of primary and secondary systems، structural system type and near-field ground motions have been studied with use of modified shear-building models of steel frames. The shear building models are set to have an equivalent lateral force-deformation behavior in each story to the one’s of given steel frames. Reliability of these models to estimate the maximum roof displacement and the maximum inter-story drift of steel frames has been investigated elsewhere through probabilistic analysis of the results obtained from comprehensive incremental dynamic analyses. The relationships that are presented in building codes to calculate the force applied on non-structural components has been usually expressed as a ratio of peak ground acceleration. This method of calculating of input acceleration to non-structural elements ignores the effect of frequency content of design ground motion. The results of the present study have been used to introduce a new method for calculation the force applied on non-structural components based on ground acceleration spectrum. In this method the input acceleration to non-structural components has been expressed as a ratio of earthquake response spectrum (instead of the peak ground acceleration). For this ratio which is entitled as “spectral amplification factor” two different expressions have been proposed for use in structures with linear and nonlinear behavior. This approach explicitly accounts for the frequency content of design earthquake in calculation of peak floor acceleration. The results of this study show that Euro-code 8 and ASCE 7-2010 recommendations need to modify specially for the precise location of the non-structural element and inelastic behavior of the structure. It has been demonstrated that structural system type does not significantly affect the amount of induced acceleration on each floor of steel frames.

Liquefaction is one of the most important phenomena that occurs during earthquakes. Loose granular soils along with a high ground water level make soil deposits susceptible to liquefaction. Liquefaction occurs due to an increase in excess pore water pressure and decreases in effective stress in the soil deposit. Thus، pore water pressure generation has significant affects on the shear strength، stability، and settlement characteristics of a soil deposit، even if it does not cause full liquefaction in the soil. Most natural sands and artificial soil deposits like hydraulic fills contain some plastic and non-plastic fines، which make their behavior different from clean sands. The generation of pore water pressure in a saturated soil beneath level ground during an earthquake is generally assumed to be due to the cyclic shear strains. This study presents the results of strain-controlled cyclic triaxial tests on silty sands to evaluate pore pressure generation characteristics of these material sands under cyclic loading. Strain-controlled testing allows for a more fundamental assessment of pore pressure generation because of the strong relationship between shear deformation and pore pressure generation. The cyclic triaxial tests were performed on the specimens including mixtures of Monterey #0/30 sand and 0%، 10%، 20%، and 30% of Sil-Co-Sil 52 non-plastic silt. To prepare the specimens، wet tamping Undercompaction technique was used. In this method، each layer is compacted to a lower density than the final desired value by a predetermined amount، which is defined as the percent of undercompaction. The advantages of this method are minimizing particle segregation، preparing specimens in wide ranges of density، and making uniform specimens. In addition، all of the specimens were prepared at an initial relative density =50%. The specimens were subjected to 50 at cycles of axial strain at loading rate of 0. 1 Hz. Axial strain was measured by a miniature LVDT and this value converted to shear strain using elasticity theory and a Poisson’s ratio of 0. 5 for undrained condition (=1. 5.). The specimens were subjected to various levels of shear strains ranging from 0. 003% to 0. 3%. The results show that overall void ratio decreases during the saturation and consolidation process، this effect increasing with increasing silt content. Also، excess pore water pressure decreases with increasing silt content up to 10%. At silt contents greater than 10% up to 30%، excess pore pressure increased because، the sand skeleton void ratio is greater than the maximum void ratio of the clean sand، thus the sand grain-to-grain contact is removed and the response is controlled by the silt matrix.

Some of the structures founded on clay soils in the desert area of the country، especially in Yazd، have suffered damages، most probably due to swelling of the soil. The ambiguity in the interpretation of the mechanisms and causes of these damages has necessitated studying swelling characteristics of these soils. Thirty soil samples، taken from 1. 5m to 3. 0m below the ground surface، were tested. Tests included: (a) physical tests including determination of Atterberg Limits، hydrometer method gradation، natural dry density، water content، and swelling pressure/percentage; (b) chemical tests for determining chemical substances and cations of the samples and (c) XRD tests to determine the soil mineralogy. According to the indirect methods of swelling assessment، most of the samples lie in the medium to low swelling potential catgories. The direct oedometer test support this notion. The prevailing minerals present in the soil samples are illite and calcium montmorillonite. The paper also presents the relationships between the swelling potential and the Atterberg Limits، clay fraction، sodium and calcium contents of the soil.

Using structural and nonstructural measures for flood damage reduction is a long-standing problem in water resources planning and management. In present study، an algorithm is presented to optimal design of flood mitigation measures in the watershed scale by simulation based optimization approach. To do so، the numerical model of MIKE-11 was used to calculate the risk of death and the physical damages of flood scenarios under different combinations of structural and non-structural flood mitigation measures. The numberdeath depends on the flood characteristics (the intensity of hazard) obtained by run of numerical model in each round، the vulnerability of population and the vulnerability of properties in flood-prone areas. Each of flood mitigation measures changes one of these three factors and affects on the number of death in flood events. As likewise، each measure may affect on physical damages by altering the magnitude of floods or vulnerability of land uses. In fact for a flood scenario، the physical damages in each combined option are computed using the change of geometry of rivers in model and its boundary conditions or modifying the damage-elevation curves or both. The numerical model was coupled with the NSGA-II multi-objective optimization model to provide the optimal Pareto front solutions considering two conflict objectives of minimizing the investment costs and the potential flood damages in the watershed. Finally، the presented model was applied for a small watershed in the center of Iran as a case study and the optimal trade-off solutions were calculated for different flood scenarios. Results showed by application of presented approach the investment costs may decrease several times and at the same time potential flood damages are minimized. Using a numerical model in the structure of proposed framework provides a flexible tool to consider the interaction of different measures in different reaches of watershed. For example model can dynamically predict in which rivers there is a need to build dam and what is the optimal height of dams in various branches to prevent the synchronizing the flood peaks of branches or detention dams with which measures must be applied to minimize the total cost and flood damages. For the study area، flood wall option just proposed by flood warning option in obtained optimal designs. This shows “flood wall” option to reduce damages on properties with “flood warning” option to reduce the loss of lives is an effective flood mitigation strategy for the study area. Also، if the investment level is low، the application of two non-structural measures of “waterproofing” and “watershed management measures” have a priority than the other measures for the study area. Using the obtained trade-offs، for each level of funding، decision makers can assign the optimal combined option considering the decision criteria.