AMIRKABIR JOURNAL OF CIVIL ENGINEERING (AMIRKABIR)
Year:2018 | Volume:50 | Issue:1 |Papers Count:20

Tunnel Boring Machine (TBM) is used widely to bore long tunnels in hard rocks. If you choose shield TBMs, precast concrete segments should be installed as permanent tunnel lining. This lining is inherently distinct and therefore in analytical and numerical analyses, the continuity assumption is not acceptable for simplifying. The segmental linings show certain behavior under various loads applied by rock, machine and tunneling processes (such as grouting). In this study, the behavior of segmental lining of Sabzkouh water conveyance tunnel has been compared to full (continuous) lining. In this paper, the behavior of tunnel segmental lining by assigning normal and shear stiffness values for longitudinal and circumferential joints of segments is compared with the continuous lining. The effect of the grouting pressure between rock and segments on the behavior of the tunnel segment is analyzed. Under uniform grouting load, the results of numerical modeling executed by finite difference method show maximum internal forces occur in the joints of segments. With increasing grouting pressure, axial force and bending moment in the joints of the segments is reduced. Moreover, the grouting pressure increases displacements in the segmental lining. In practice, this increase sometimes causes cracking or stepping between segments.

Investigation of development behavior and the dimensions of the embankments behind retaining walls explains the effect of the movement of the wall and its destructing effect. Majority of the natural embankments are layered and are usually in saturated condition. Hence, this research investigates the failure wedge caused by the wall’s rotation around the heel. Physical measurements were performed in order to provide data to use the graphical approach of calculation of lateral pressure of layered embankments in both saturated and non-saturated conditions. Thus, 4 layering models were tested including: 1) two layered (upper layer: clay, bottom layer: sand), 2) two layered (upper layer: sand, bottom layer: clay), 3) three layered (upper layer: sand, middle layer: clay, bottom layer: sand) and 4) a for layered model (upper layer: clay, first middle layer: sand, second middle layer: clay, bottom layer: sand). Elevation of layers in each layering model were determined to be equal. Results indicated that using common theoretical methods will result in a conservative design for walls which increases the construction costs. Absence of the failure wedge at wall toe as well as the 32.75% and 29.25% difference between experimental results to theoretical results of Rankin and Sirnivasa methods are other evidence for the conservative design of walls using common methods.

Dissolved Oxygen (DO) removal can be defined as deaeration or deoxygenation terms in which various methods are used to remove air molecules from water. In this study, sodium metabisulfite and ascorbic acid are experimentally used to deoxygenate Birjand drinking water, Iran and also they are applied for Retention Time (RT), Temperature (T), Hardness (H) and pH variations to measure deoxygenation efficiency. Regarding, findings showed that as RT increased to 100%, DO reduced to almost 60% as well as when T rose about to 10%, has approximately led to 80% reduction of DO concentration. Furthermore, ascorbic acid effects indicated that DO concentration decreased about 40% as T had increased to 10%. In addition, 20% reduction of RT has caused to 25% removal of DO. The effect of pH revealed that alkaline state worked better than acidic state to improve deoxygenation efficiency, as well.

Different and to some extent poor seismic performance of structural systems under various types of near-field earthquake excitation, made re-assess and re-evaluation of “seismic performance factors” used in building codes, an inevitable important task. In this paper, seismic performance of special moment resisting steel frame system (SMRSF) under near-Field (with and without pulse) and far-field record excitation is investigated through FEMA P695 methodology. In order to cover the “design space” of the selected structural system, archetypes consisted of 1, 2, 3, 5, 8 and 15 story buildings with 4 and 8 meters bay are selected and designed based on Iran’s national building codes for a “very high seismic” region. Corresponding non-linear models are built based on most recent advances in structural components modeling using OpenSees software. At first by performing non-linear static analysis, overstrength factor and period-based ductility are evaluated and quality of non-linear models is controlled. Afterwards, incremental dynamic analyses (IDA) are performed using far-field, near-field pulse like and non pulse like records. Finally, by using IDA results, “adjusted collapse margin ratio (ACMR)” of the models are calculated and compared to “allowable collapse margin ratio (ACMRallowable)”. Therefore, seismic performance of the models are evaluated and “response modification coefficient” (R) for the system is investigated and compared with this factor under different types of ground motion records. Results indicated that except for 15 story buildings, proposed “response modification coefficient” and “over-strength factor “for SMRSF system are adequate under far-field records. However under pulse like near field ground motions, it was observed that short period structures are to some extent vulnerable. For long period structures, in contrast with far-field records, seismic performance of structures designed by prescriptive provisions has adequate performance under near-field pulse like motions.

Modeling and analysis of complicated truss arch bridges are very time consuming process. In this paper, for more convenient modeling and reduction of analysis time, the complicated truss arch bridges are simulated to the continuum curved beam elements. As a matter of fact, the three dimensional body of a truss bridge is modeled based on the equations governing the out of plane performance of a curved beam. To this end, a new mixed finite element formulation (stiffness-softness) is presented using weighted residual method. In order to verify the accuracy of the present method, the transverse vibration of three truss arch bridges is investigated under a specific time-history. The results are comparable with those obtained from more exact 3D models simulated with SAP 2000 general purpose software, regarding the acceleration and displacement response. Furthermore, in the proposed method the number of elements is significantly less than complicated 3D models, leading to more suited initial design.

In this paper, the lateral-torsional stability of simply supported thin-walled beams with mono-symmetric section subjected to bending loads has been studied by means of a numerical method based on the finite difference method (FDM). To fulfill this purpose, the equilibrium equations for elastic thin-walled members with linear behavior are derived from the stationary condition of the total potential energy. In the applied energy method, effects of initial stresses and load eccentricities from shear center of cross-sections are also considered. Finite difference method is one of the most powerful numerical techniques for solving differential equations especially with variable coefficients. Between various computational methods to solve the equilibrium equation, finite difference method requires a minimum of computing stages and is therefore very suitable approach for engineering analysis where the exact solution is very difficult to obtain. The main idea of this method is to replace all the derivatives presented in the governing equilibrium equation and boundary condition equations with the corresponding central finite difference expressions. Finally, the critical buckling loads are then derived by solving the eigenvalue problem. In order to present the accuracy of the proposed method, several numerical examples including lateral-torsional behavior of prismatic beams with mono-symmetric sections are considered. In order to illustrate the correctness and performance of FDM, the evaluated results are compared to the finite element simulations and other available methods.

Long-term seismic performance determination of reinforced concrete bridges is one of the effective factors in service life estimation of these structures. Chloride induced corrosion results in deterioration of critical members in the service life of reinforced concrete bridges and therefore leads to degradation of long-term seismic performance of the bridge. Due to seismicity and high rate of corrosion in reinforced concrete structures due to the corrosive environmental condition in Persian Gulf region, evaluation of corrosion-induced degradation on the long-term seismic performance of existing bridges in this region has a high importance. In order to evaluate this problem, at first based on studies done related to Persian Gulf region, corrosion initiation time of columns as critical seismic members of the bridge has been determined. Then effects of corrosion on the reinforced concrete column at specific time intervals (0, 15, 30, 45, 60, 75, 90 years) in bridge service life have been calculated. Effects of corrosion include degradation of cover and core concrete, steel, and bonding between concrete and steel that result in modification of stress-strain relationship of materials. In the next step, at each time interval based on the modified stress-strain relationship of materials, moment-curvature analysis of bridge column conducted and characteristics of plastic hinge have been determined. Finally, based on plastic hinge characteristic at each time interval, pushover analysis of bridge in longitudinal and transverse directions conducted and bridge capacity curves at mentioned time intervals have been compared. Results indicate the time-dependent degradation of bridge capacity under corrosion. According to the obtained results, in order to ensure the long-term seismic performance of reinforced concrete bridges in corrosive environments, value for an increase of design base shear has been proposed.

It is well known that the behavior of concrete is extensively affected by the initiation of cracks and their propagation. Among these cracks, diagonal or shear cracks have more complicated and less known behavior. In spite of extensive research in this field, current codes of practice do not provide a uniform margin of safety against shear failure of reinforced concrete yet. To simulate the non-elastic behavior of concrete in the fracture process zone, the distribution of cohesive forces through the crack sides have been used by researchers. The aim of this study is to evaluate the effect of the crack’s tip cohesive forces on the load-deflection response of reinforced concrete beams using fracture mechanic. In the numerical analysis used in this study, the non-linear behavior of concrete in the compression field is simulated by damage-plasticity model. To simulate the non-linear behavior of concrete in the tension area and simulating the onset and evolution of cracking, non-linear fracture mechanics based on cohesive crack model is used. Using finite element software of ABAQUS, a step by step approach is used. In the presented approach, the probability of possibility of crack evolution in beams is considered. Comparing the calculated load-deflection curves for several reinforced concrete beams with the experimental ones showed a good consistency.

In this paper, lateral behavior of latticed columns is investigated by the finite element method. I-shape rolled sections of IPE120 to IPE200 are used for latticed column specimens in this study. Shell and solid elements are used for plate sections and welds in the finite element model, respectively. The columns considered are under gravity and lateral loads. Variation of gravity load ratio is investigated. Boundary conditions of the FE models are clamped at bottom and rotation restrained at top. Lateral loads are applied to the columns to cause bending about the non-material axis crossing the latticed side of the column. Non-linear characteristics of these columns including lateral elastic and plastic stiffness values, shear yielding and dissipation of energy (hysteretic curves area), are derived under monolithic and cyclic loading. Based on this study, increasing axial gravity loads, decreases initial stiffness considerably. It also decreases lateral capacity of the columns. Initial stiffness and lateral capacity reduction is considerably affected by axial load ratios under 0.2 (i.e., 20 percent of axial capacity of the column) and after that reduction rate decreases. A super-element that is able to consider behavior of these columns with an integrated section is proposed based on results of the nonlinear finite element analysis. This super-element considerably increases the computation speed by substituting an element with only six degrees of freedom in place of a finite element model with a large number of elements.

During two decades ago, it is focused on the use of various sorts of waste in the construction industry and many pieces of research are conducted in this field. With this regard, using wastes not only have benefits for the environment but also cause improvement in the properties of final goods. One sort of the waste using in the construction industry is plastic. Recycled plastics can be used as an aggregate in concrete and some concrete mechanical properties such as resistance to erosion caused by sulfuric acid attack to improve. In this study, the experimental works were conducted on concrete samples containing PET and tire rubber and their resistance against sulfuric acid attack were investigated. The concrete samples immersed in diluted sulfuric acid (pH 1) and some tests such as modulus of elasticity, splitting tensile strength, compressive strength, mass variation and ultrasonic wave velocity in intervals of 20, 40 and 60 days were conducted. The results were analyzed and evaluated. To determine the amount of erosion concrete, we measured variations of the weight and compressive strength and ultrasonic velocity. The results showed that replacement of PET with aggregate positive impact on the strength of concrete is subjected to sulfuric acid.

Concrete, as a main construction material has an alkali nature which makes it vulnerable to attack by acidic solutions. Therefore, investigations on performance of various types of concretes against different kinds of acid attacks are essential to achieve durable concretes in severe environments. Considering the significant effect of durability in sustainability of concrete structures, high performance concrete (HPC) which is characterized by its high compressive strength, low permeability and fine durability in many severe environments, is increasingly utilized in civil and infrastructural constructions. This paper presents an experimental study on durability of HPC and conventional concrete (CC) containing ordinary Portland cement (PC), ground granulated blast furnace slag (GGBFS) and natural pozzolan (NP) under sulfuric acid attack. Compressive strength, ultra-sonic pulse velocity determination, capillary water absorption test and evaluation of electrical resistivity were utilized to investigate mechanical properties and permeability of hardened concrete. The durability properties were studied through measurement of weight and compressive strength loss, ultra-sonic pulse velocity variations and length change of mortar prisms exposed to sulfuric acid. The results indicated that concretes containing less cementitious materials and mineral admixtures were more durable in acidic solutions, and incorporating higher volume of GGBFS and NP could improve performance of concrete against sulfuric acid attack.

In this paper by using the aggregate socioeconomic features of each zone and considering the land use prosperities, the aggregate zonal tours were modeled. For that, classic 4-step modeling database was utilized in which less data collection cost needs. Due heteroscedasticity, appling weighted least square (WLS) method led to multiple weighted regressions by two exogenous independent variables; population and number of employers in zone. Heteroscedasticity affect the efficiency of regression. In comparing of two model, the F test of WLS method growth 27 percent and the amount t students for population reduced from 2.79 to 2.27 that in negligible. On the other hand, the amount of t students for number of employers increases from 2.62 to 3.40 (30 percent). Constant coefficient is negative but in comparison with the maximum number of observed tours (7202 tours) is 0.069 percent and the average number of observed tours (1386 tours) is 0.36 percent that is negligible and the R2 goodness of fit index is 0.927 and acceptable.

In this paper 3D and full tunnel modeling with considering step by step excavation and installation of lining, will be discussed. Full 3D modeling of tunnel by finite element method (FEM) can be ideally represents the behavior of longitudinal and transverse ground settlement by progress of excavation and installation of lining. Results of numerical analysis showed good agreement with empirical formulations for longitudinal settlement. It is also seen that the effect of boundary condition of the model, there are up to five times the diameter of the tunnel and then reaches its maximum and steady-state condition. With increasing the tunnel depth, ground surface settlement decreases before the tunnel face and increases after the tunnel face. Also according to the results, settlement longitudinal curves of different depths intersect in the tunnel face, which means ground surface settlements in the tunnel face are the same for different depths. In the other section of the paper transverse settlement curve obtained by 2D analysis compared with the corresponding trough from 3D analysis, by comparing these two profiles area, can be reached to the stress release factor, that is one of the key parameters in the 2D analysis.

Due to the constructions rate in mega cities, deep excavations have been done in civil engineering projects in the past few years. Strengthening the excavation wall is of great importance and has been pointed out in the seventh issue of national construction rules. There are different ways of achieving the critical strength for the excavations wall, such as Truss method, reciprocal support, sheet piling, piling method, diaphragm wall, anchorage and nailing. The initial design of nailed wall in a condition that deep excavation, surcharge, and soil type are difference can be the major challenge for most designers, employers and administratives. These tables and diagrams can give good and appropriate initial view to construction industry insiders. In this article, with the change of resistance characteristic of the soil (cohesion and angle of internal friction) in the range of common soils and as well as a variety of surcharge (0 to 60 kN/m2) in the brink of the excavation, designs have been made for different deep excavation (maximum for five basements). For each excavation with different characteristics and according to valid codes, several models (on average 50 models) in the limit equilibrium (for calculation safety factor) and finite element software (for calculation displacement and force) reviewed until design have been made economic and finally provided help design tables and diagrams. Nailing system is responsive for a depth of 13 meters in the appropriate lands, but for more depth and surcharge is needed to combined system (For example combined system of nailing and anchorage).

In many cases, natural soil does not have the required strength and needs to be improved. One of these methods is soil improvement with the use of additives. In this method the engineering properties of soil are improved by being mixed with one or more other materials. Nano-silica which is a very active pozzolan can also be considered as a stabilizer to perform cementation reactions. In this study, the effect of cement and nanosilica mixture on Babolsar sandy soil shear strength within 7 and 28 days has been studied. Direct shear tests are performed on specimens containing 4, 6 and 8 percent of dry weight of sand, cement and 10, 30 and 50% of the weight of cement nano-silica with the density of 98%. The results showed that the addition of nano-silica to cement up to a certain percentage increases the shear strength and shear strength decreases with additional amounts. In this study 30 percent increase in nano-silica is followed by the optimized shear strength improvement

This study, tries to suggest a design method based on displacement using experimental and numerical modeling in soil nailed walls. In this case, dynamic loading characteristics, geometrical characteristics of reinforced soil mass and type of the site are considered to introduce the pseudo static coefficient as a function of seismic performance level and dynamic loading characteristics. For this purpose, the influence of dynamic loading characteristics, reinforcement length, height of reinforced system and type of the site are investigated on seismic behavior of soil nailed wall by numerical analysis. Furthermore, the performance levels of this structure were determined by experimental studies of shaking table tests. The results illustrate that the seismic response of this type of wall is highly dependent to cumulative absolute velocity, maximum acceleration, height and reinforcement length. The results also indicate that the use of coefficients in this study leads to most efficient designs in comparison with other methods which are generally suggested in codes that are usually based on limit-equilibrium concept. The outputs show the over-estimation of equilibrium design methods in comparison with proposed displacement based methods here. The pattern of the observed failure mechanisms included a moving block and a parabolic failure surface with certain inflection point. Also, irrespective of different nail lengths, a range of Δx/H = 0.5 % as a transitional level from quasi-elastic to plastic state and based on starting the development of active wedge failure, a range of Δx/H = 3.75% as a transitional level from plastic to failure state were determined.

In general, stable vertical or near-vertical soil embankments, natural and unnatural slopes near the roads can resist existing forces and when the stip loading act on near them, those can be unstable because of tension problem of soils, so increasing of tension resistance of soil is a very important problem in geotechniacal engineering. The use of reinforced soil to design of foundations and soil structures such as retaining walls is an innovation that is considered as the most versatile and most economical problems for soil improvement. Despite numerous studies about the techniques of reinforced soil on lateral displacement of the retaining wall and bearing capacity of strip foundation located on the retaining wall under the soil homogeneity conditions, few studies have been carried out on these walls in the layered soil conditions. In this study small scale laboratory tests conducted to investigate the bearing capacity of strip footing rest on layered soil next to geogrid reinforced retaining walls. The results showed that increasing the number of reinforcement layers ,at appropriate intervals on the multi-layer embankment, decreases the lateral displacement of the wall and increases the bearing capacity of strip foundation and maximum amount of bearing capacity of footing can be achieved at u/B=0.25. Also the results showed that increasing the length of geogrid layer increases the bearing capacity of footing and the optimum length ratio is equal to 4 (L/B=4). Also when the first layer thickness of soil is greater than footing width the bearing capacity of footing depends on only first layer properties.

Urban infrastructure projects are considered the heart of the economy of countries and productivity of these projects is fundamental in development strategy of countries. One of the important determining factors in the success of major projects, especially subway lines construction projects is the managers’ performance in interacting with involving project factors and considering their expectations and demands. In this study, first by offering a theoretical framework, the required processes to model the expectations of key stakeholders is expressed and according to the proposed pattern, project stakeholders are identified initially and by identifying the stakeholder expectations and determining the key stakeholders, the research enters the model designing phase. In the final stage which is modeling the expectations of key stakeholders, the expectations’ model will be designed using the pattern extracted from the QFD approach. The stakeholders’ expectations model shows the expectations of different stakeholder groups from the project. For designing this model, Mashhad Urban Railways (MUR) construction project is studied. The results showed that the definitive stakeholders have the highest expectations level. “Paying attention to the quality standards of project’s implementation methods” and “paying attention to the project’s reporting system” are the most significant expectations; since all the key stakeholders have such expectations. Results also showed that the three types of stakeholders consisting of “dormant, discretionary and demanding” are not among key stakeholders; therefore, in the expectations model of key stakeholders, they don’t have any expectations.