نشریه مهندسی عمران
سال پنجاه و چهارم شماره 2 (اردیبهشت 1401)

The need for high viscosity in self-compacting concrete (SCC) in order to maintain uniformity and to avoid segregation of particles, has paved the way for the use of waste powder substances in the mix of SCC. The production of nearly 50% of powder waste from marble and granite stones in different stages of quarrying and the need to bury these wastes also raises environmental concerns. On the other hand, today, researchers with environmental as well as economic concerns are pursuing the method for using as little cement as possible in the concrete mix and thus reducing carbon dioxide emissions. Burial of red mud waste (containing oxides of silica, alumina and iron), known as aluminum plant wastes, is associated with the detrimental environmental impacts on the soil, the climate around the landfills. In this research, the effect of using red mud as cement replacement in SCC mix is questioned. Also, the wastes of stone-cutting factories (marble and granite powders) have been used as a filler in these mixes. The workability, mechanical properties and durability of self-compacting concrete are measured using appropriate tests. Although dry red mud has a slight pozzolanic activity, the fineness of its particles has caused the concrete matrix to condense at low replacement percentages (up to 5%). On the other hand, it is shown that the use of granite powders instead of limestone powders in SCC will not be a problem in terms of workability, strength and durability.

Due to inadequate public financial status and increasing demand on infrastructure facilities, many governments worldwide are exploring new arrangements through Public Private Partnerships (PPP). However, PPP tenders are not feasible at all, but investors and developer may pay a lot of time and money for preparation for a tender that may not pay him back. Therefore private investors are seek a model to support them to decision whether bid or no bid in a PPP tender. This paper, present a decision support system based on MADM decision making models to evaluate Cost Opportunity of tenders. Utilizing the proposed model, private investors can rank the PPP tenders and select most tender with least cost opportunity. Deploying the proposed model in 11 Iranian PPP project in the field of water and power plant, prove that private investor decide to bid in a tender not only for fiscal attracters of project , but also they consider how public authority is organized and committed to government’s responsibilities. Public party can improve the success chance of PPP tenders by offering some incentive and advocate de-risking mechanisms.

The construction industry is a large part of Iran's economy. A considerable amount of national resources, including energy and materials, are consumed in this sector. Therefore, the efficiency of this industry has an essential role in the sustainable development of the country. Cost overruns of construction projects or deviating from the budget is one of the most influential factors in reducing the efficiency of this industry and the occurrence of numerous problems in it. Therefore, accurate knowledge of the reasons for the deviation of costs from the planned budget is a significant factor in managing the cost of construction projects. In this paper, a review of similar research conducted and a long list of reasons for cost deviation was prepared. Then, based on the ecology of Iran's construction industry, this list was modified, completed, and categorized. The list has been distributed as a questionnaire among 230 experts, and the severity and frequency of each factor were asked. Based on the obtained data, statistical analyzes such as ANOVA were performed. According to the results, inflation, project prolongation, slow administrative processes, inadequate resource planning, and low efficiency and reprocessing due to incorrect or non-integrated design in various fields are among the most critical factors causing increased costs and deviation from the budget plan.

With the increasing development of military weapons around the world and the variety of explosives, terrorist attacks are a growing threat. The science of vibration control is well developed against natural loads. Although blast loads are different than natural loads, this science can also be used to reduce explosive load responses. For this purpose, passive and semi-active method included tuned mass damper (TMD) and magneto-rheological (MR) damper have been used to reduce the vibrations caused by the blast load in the base-isolated structure. In this study, a type-2 fuzzy system has been used to determine the appropriate voltage of the MR damper so that the existing uncertainties do not adversely affect its performance. The numerical simulation of two explosives with distance of 15m from a system of 5 degrees of freedom, has been performed by theoretical and empirical equations. The use of the proposed control tools along with the base isolation system showed that not only these methods can maintain the proper performance of the base isolated system, but limit the displacement and possible damages at larger excitations. The comparison results showed that the use of MR damper along with the base isolation system can have the best performance against blast and seismic loads. The use of this system on average reduced the maximum drift of the stories to about 36% in blast loads, 68% in far-field earthquakes and 46% in near-field earthquakes, while the drift of the base significantly has been limited than the base-isolated system with a TMD.

Plastic shrinkage cracking is one of the most common distress in concrete pavements, which reduces the durability and level of service. Using different admixtures in the optimal amount can reduce these cracks. This study investigates the effect of air-entraining agent content in creating intentional air in air-entrained concrete pavements, in controlling or reducing the severity of plastic shrinkage cracking. For this purpose, the effect of adding air-entraining agent in the amount of 0.04, 0.07, and 0.10% by weight of cement on the severity of plastic shrinkage cracking in concrete pavement mixture with water to cement ratios of 0.40, 0.45 and 0.49 was investigated by using ASTM C1579 method. The results showed that the addition of air-entraining agent reduced the severity of plastic shrinkage cracking in air-entrained concrete compared to the conventional one. It was seen that with more addition of air-entraining agent than a certain amount, the severity of cracking has increased, which is a specific and optimal amount of 0.07% in this study. The results showed that increasing the water to cement ratio at lower change intervals has a greater effect on the severity of cracking. Also, the percentage of entrained air due to the addition of the optimal amount of air-entraining agent is less than the maximum percentage of allowed entrained air in concrete pavements. Therefore, with the use of this admixture in the optimal amount, the severity of plastic shrinkage cracking in concrete pavements can be reduced.

In the present study, global stability, soil-nail pullout failure and nail tensile failure are chosen to study. Cohesion, unit weight and angle of internal friction of soil and ultimate bond strength along the soil nail and yield strength of nail are modeled as random variables. Computations of reliability are performed using Matlab and RT software. For better understanding, a case of soil nail wall constructed to support a vertical excavation in Tehran is considered for the study and its stability is evaluated for three failure modes. The purpose of this research is to firstly analyze the reliability of nailing walls and validate it using the Monte Carlo simulation method. In addition, the effect of correlation between soil parameters and distribution of random variables on reliability index was investigated. By sensitivity analysis, the importance of variables in reliability index was investigated. Then, the reliability index changes were evaluated with respect to the safety factors. Finally, changes in the reliability index were studied by changing the length of nails and the diameter of the nails. According to the assumptions, the correlation between the soil resistance parameters does not have much effect on the pullout mode, if the general failure and pulling modes of the nails have a significant effect and should be taken into account in analyzes as well as the type of distribution of variables affects the reliability index and the choice of distribution type is important.

Considering the statistical and probabilistic characteristics of construction conditions, the investigation of dynamic overloads' effects on the urban excavation wall is of great importance. In the present study, the performance of nailed and braced excavations under two vibrational dynamic excitations, traffic and near-field earthquake loads, have been investigated in four regions of Ahvaz. Critical boreholes with the lowest static bearing capacity have been selected by analyzing the layers' strength parameters in each region. Numerical models have been designed to limit the seismic waves' reflection at the excavation boundaries with 20 x 100 meters and with absorbing walls. Also, the damping ratio was assumed to be 2%. A harmonic wave at different speeds has simulated the excitation caused by the traffic passage. Resonant frequencies due to traffic induced vibration have been recorded in the speed range of 56 to 72 km/hr. Due to the traffic load, the bracing and the nailing systems showed less vertical and lateral displacements, respectively. Moreover, the excavations have been analyzed under ten acceleration with compatible near field characteristics of the Ahwaz plan acceleration (0.25g). The Kiyanpars region showed the highest vertical displacement difference between the two systems in the range of 0.032 m to 0.006 m. Due to earthquake loads, the bracing system showed less vertical displacement. The error of the analytical models' results in vertical displacement was 10% and 26% and in lateral displacement was 5% and 20% less than a nailed excavation located in the Kiyanpars region under traffic passage.

Determining the dynamic properties of soils is an important issue in solving seismic geotechnical engineering problems. In this respect, several types of field and laboratory methods are available with different advantages and limitations regarding solving different problems. The difference between the results of in-site and laboratory tests is one of the engineers’ difficulties. Some reasons for the difference between the values of dynamic parameters which achieved from field and laboratory tests, are remolding effect of samples, difference in stress conditions and loss of cementation; negligence to these facts in soil dynamic properties may lead to serious damage due to unrealistic soil analysis. Among the laboratory methods, the resonant column test is one of the methods which determines the dynamic properties of soils at small strains. In this research, Young’s modulus and damping ratio of cored and reconstituted earth materials have been studied by performing resonant column test in flexural mode. The effects of consolidation stress and anisotropic consolidated stress was studied by using the Young’s modulus and damping ratio versus shear strain diagrams. The results of the study indicate that reconstituting reduces the Young’s modulus, but the variation of damping ratio versus shear strain for cored and reconstituted samples is negligible. Increase in the consolidation stress and anisotropic consolidated stress, result in the increase of Young’s modulus. Comparing the damping ratio results with the two methods of free vibration decay and half power bandwidth, indicates that the damping ratio values obtained from the half power bandwidth method are higher.

Excavating tunnels in urban areas could have a profound effect on the site characteristics and could change the free-field motion due to many different reasons. Although the previous earthquake events have ascertained that the response of the above-ground buildings close to the tunnel will also change, this effect is not well-addressed in the national and international design building codes. In this paper, considering a fully coupled system of tunnel-soil building interaction, the presence of a tunnel on the seismic response of a two dimensional 15-story scaled benchmark building under two far- and two near-field benchmark earthquake records has been investigated. Additionally, non-linear dynamic analyses considering the material and geometric nonlinearity have been applied, and to obtain nonlinear behavior of the soil, Mohr-Coulomb failure criterion and the equivalent linear method are implemented. The interface between structural foundation and soil is simulated by normal and shear springs and, the interaction between tunnel and soil is modeled using Coulomb Friction. As a parametric study, the effect of tunnel shape, cross-sectional area, the burial depth of the tunnel, and the effect of site soil material on the seismic response of the building is evaluated by evaluating the ratio of the structural responses with the presence of the tunnel to the structural responses without the presence of the tunnel. The results showed that the maximum relative displacements of the building for soils with 320 and 150 m/s in the presence of the tunnel decrease at most 10 percent under both far- and near-field earthquake records.

Sequential earthquakes have severe destruction on structures, including the accumulative structural and non-structural damage, compared to single earthquakes and due to the lack of sufficient opportunity to repair of the structure, the possibility of structural damage increases. In this research, the effect of seismic sequence on the relatively new system of reinforced concrete frames equipped with steel plate shear walls has been investigated. Based on this, four system of 4, 8,12and 24 stories, which represent short, intermediate, tall, are modeled in finite element software and subject to four sets of single and sequential earthquake and with a variety of application methods. Sequential earthquakes, including real, repetitive and randomized methods, are subjected to nonlinear dynamic dynamic analysis under four sets of single and sequential acceleration. The seismic scenarios used include sequential recorded critical earthquakes. The analysis showed that the predominant period of the aftershock significantly influences the post-mainshock response. Real seismic sequence increases the tatio of peak interstory drift by an average of 2 times the similar demand in a single earthquake and increases the ratio of maximum ductility demand by 1.52 times in the structure.In artificial sequence, the ratio of peak maximum interstory drift demand increase is in 100%, 150% and 200% aftershocks, In the iteration method, it is equal to 1.2, 2.0 and 2.6 times the single earthquake. Aftershocks may change the direction and magnitude of residual displacement in real and artificial seismic sequences. Continuation of the equation to calculate the demand for seismic sequence ductility was extracted.

Unknown situations or factors in design of a structure such as underlying soil characteristics and presence of adjacent structures can affect the reliability, and consequently, the cost of the project. Therefore, the effects of soil-structure interaction as well as the simultaneous effects of this interaction in the presence of adjacent structures on the seismic response of 3, 9 and 20-story benchmark steel moment resisting frame structures are investigated, including six different adjacency cases of the structures in three different distances. The effect of soil-structure interaction is considered by using a hybrid method, in which the stiffness matrix of soil system is obtained through analysis of a two-dimensional model in Abaqus considering a plain strain condition. Then, the matrix is added to the nonlinear 2D model of the structure by using a set of pre-defined and a new developed element in OpenSEES. The results obtained from the time history analysis under ten far-field earthquake records show that the effect of soil-structure interaction on the response of a 20-storey high-rise structure is more significant than the other two structures and leads to a maximum increase of 9 percent in the maximum average drift ratio and decrease of 6.99 percent in the average base shear in this structure compared to fixed base. In addition, the presence of high-rise and mid-rise adjacent structures increase the maximum average drift ratio of low-rise structures by 10.44 and 9.36 percent and the average base shear in this structure by 2.87 and 3.93 percent, respectively.

Reduced adhesion between aggregate particles and bitumen binders, and reduced cohesion within the bitumen of mixes, will result in stripping and segregation distresses. These distresses will ultimately result in pothole formation and other distresses in pavements. For repairing these distresses, major maintenance works will be required, including reconstruction of the pavement. In this research, with the aim of determination of adhesion and cohesion properties between aggregate particles and bitumen binders, pull off testing method was adopted. Samples were consisted of two cationic bitumen emulsions of rapid and medium breaking types that were also modified with a latex liquid rubber. Aggregates were consisted of two different types of granite and dolomite origin. Their mineralogy was determined, carrying out XRF testing and analysis. In performing the research the role of parameters such as curing time and curing temperature were also investigated. Testing results showed that modification of the bitumen emulsions with the application of 3% latex provided increased adhesion properties and increased durability between bitumen emulsion and the aggregate particles. It was also shown that the interaction between aggregate particles and the bitumen emulsions were great. Comparing behavior of the two aggregate types, it was concluded that the dolomite aggregates provided better adhesion properties. In addition, it resulted that the role of curing time and temperature were dominant in providing adequate adhesion between bitumen and aggregate particles. The increase was more dominant in samples containing latex modified binders.

Due to the suitability of the eccentric bracing system in terms of optimal performance and ductility on the other hand, as well as the effect of reversible materials such as shaped memory alloy in reducing the residual displacement at the end of the earthquake and seismic evaluation of structures with the different number of stories, structures with eccentric bracing dual steel bending frame system within 5, 10 and 15 stories equipped by shaped memory alloy rods, were subjected to the nonlinear dynamic analysis of time history. Maximum absolute displacement of the roof and relative displacement of stories, the maximum residual displacement of the roof, maximum base shear, and roof acceleration in the desired frames were evaluated and compared. Survey results showed that the absolute and relative inter-story drift in all three models due to the lower elastic modulus of shape memory alloy has been greater than models that have not been equipped with shape memory alloys. On the other hand, the residual displacement values of structural models due to the super-elastic property of the shape memory alloy materials and the shear stories and acceleration of the roof of structural frames due to the increase in period time and structural softness have shown a sudden sharp drop compared to models that have not been equipped with shape memory alloys. Comparison of structural responses in different models also showed a further reduction effect on the plastic displacement of the 5-stories model and base shear and roof acceleration of 10 and 15-stories structures.

In building design codes, no attention has been paid to the interaction effect of underground structures and the building, which can change the amount of applied forces on the building. Therefore, in the present study, by using numerical modeling with FLAC 2D software, the effect of tunnel and building interaction on the seismic response of building stories has been investigated in order to have more accurate assessments of seismic forces on the building when we want to design it. In this study, the model was first stimulated in the case of presence of building alone (SF model) by harmonic shear SV waves and the real earthquake waves. Then, by adding a tunnel to the model (STF model), the system was analyzed. By comparing the result of the maximum acceleration of buildings floors in case of STF to the SF model, the effect of tunnel and building interaction on stories acceleration have been investigated. In low frequencies, the negative effect of tunnel on the acceleration response of the building stories was observed. In high frequencies, the positive effect of tunnel on the acceleration of the stories was observed. It was also concluded that the harmonic waves with the frequency equal to the dominant frequency of the real motions, applied to the models, have created more amplification in acceleration response of buildings.

Concrete pavements are widely used by pavement engineers due to their advantages over flexible pavements such as longer lifetime, good performance and durability, etc. However, concrete pavements represent some drawbacks such as shrinkage that increases the tensile stress in concrete, which may lead to cracking, warping, etc. Drying shrinkage is the most important type of shrinkage in concrete pavements. polypropylene fibers can be used to control or reduce width of cracking by bridging both sides of crack. In this study, the effect of Emboss fiber on the behavior of concrete pavement was investigated. Slump, compressive strength, third-point flexural strength, electrical resistance, skid resistance, free shrinkage and restrained shrinkage by ring test were performed. Two water-cement ratios of 0.35 & 0.4 were used for mix design and the percentage of polypropylene fiber used in mixtures was respectively 0.44% by concrete volume. The results showed that the use of Emboss Fiber reduced the workability of concrete. Also, these reinforcements had different effects on compressive and flexural strength and electrical resistance depend on homogeneity of Emboss fiber reinforced concrete. Furthermore, toughness indices and energy absorption of concrete were significantly increased by using Emboss fiber reinforced concrete. In addition, using fiber indicated a slight reduction in the amount of free and restrained shrinkage and occurrence of first-crack. polypropylene fibers had a key role in controlling crack width by bridging both sides of crack. Finally, no certain relationship was observed between using SRA and changing the skid resistance of concrete pavement.

In this study, the VMD algorithm was used to identify the modal characteristics of the structure using the decomposition of the acceleration responses recorded by the sensors. This algorithm has advantages over other signal decomposition methods that is resistant to the noise and sampling frequency. Also, the VMD algorithm extracts the natural frequencies of the structure concurrently. The damping ratios of the structure were estimated by fitting a linear function to the logarithmic diagram of the modal response in the decaying amplitude and calculating the slope of this line. The efficiency and accuracy of this algorithm were investigated by decomposing the acceleration responses obtained from the sensors installed on a prestressed concrete bridge that is located under the load of passing vehicles. The VMD algorithm was used for signal processing in MATLAB to estimate the natural frequencies, damping ratios and mode shapes of the bridge and ARTeMIS was utilized for verifying the results. The finite element modeling and modal analysis of the bridge were performed in ABAQUS and the natural frequencies and mode shapes of the bridge were obtained. The results showed that the mode shapes estimated by the VMD algorithm was in good agreement with the finite element model and ARTeMIS. Also, the damping ratios estimated by this algorithm were obtained close to the damping value of the prestressed concrete bridge. The difference between the frequencies calculated by the VMD algorithm and ARTeMIS was about 1%, and the difference with the finite element model frequencies was close to 5%.

Although Buckling-Restrained Braces (BRBs) can dissipate a large amount of the seismic input energy. However, they need to be repaired or replaced due to large permanent deformation after a severe earthquake. To overcome this issue, the use of Shape Memory Alloys (SMAs) in the braces has recently received attention. These alloys are able to return to their original state after loading. The present study aims to analyze the fragility curves and to investigate the sidesway collapse of the BRB frames equipped with SMA during near-field earthquakes in comparison with those given for the case without SMA. For the purposes, two 5 and 15-story BRB and BRB-SMA frames subjected to 7-pair of near-fault earthquake records are studied. Nonlinear Incremental Dynamic Analyses (IDAs) are carried out using OpenSees software. On average, the simulation results showed that collapse capacity and collapse duration of the BRB-SMA frames are about 30% and 35% more than those given for the BRB frames, respectively. For an instance, a collapse probability of 38% for the 5-story BRB-SMA frame and a collapse probability of 60% for the BRB frame is given for 3g spectral acceleration. Furthermore, at the performance level of 50% for the 15-story frame, the collapse duration of the BRB-SMA frame is obtained 25.6 seconds, while it is given about 10 seconds for the BRB frame. In addition, the use of a memory alloy for spectral accelerations of 1 to 4 g resulted in a reduction of 50% to reach the collapse performance level of the frames.

The increasing number of rubber wastes and their depots is a significant environmental problem. These wastes can be used to improve soils. On the other hand, cement production causes environmental pollution. If natural cementitious materials such as zeolite, which have abundant resources in Iran, are used, it will be economical and help the environment. In this research, the use of rubber granule and zeolite as additives in the stabilization of sandy soils with cement is evaluated. For this purpose, uniaxial compressive strength test on samples with different amounts of cement 6, 8 and 10% relative to the dry weight of the sample and replacement percentages of 0, 10, 30, 50, 70 and 90 of zeolite relative to cement and replacement percentages 0, 2.5, 5, 7.5, 10 and 12.5 of rubber granules were carried out. The results show that rubber granules and zeolites increase the final strength and strainability of the samples. SEM imaging of the samples showed the cohesion and integrity of the stabilization due to the addition of zeolite and rubber granule. The best mixing composition in the present study is 7.5% rubber granule and 30% zeolite as a cement substitute.

With the expansion of the global application of building information modeling (BIM), its application in many countries, including Iran, is facing many obstacles. Therefore, studying the implementation barriers is necessary. In this paper, the research background was first examined and barriers to BIM implementation were identified and categorized. Then, using a questionnaire, the importance of obstacles and challenges from the perspective of experts was assessed. Analysis of collected data with the help of Kendall ranking showed that the most important challenges and obstacles facing the adoption and implementation of BIM in the Iranian AEC industry are: Lack of policy and roadmap in the organization, lack of knowledge and support of senior management, lack of readiness of the manufacturing industry, lack of attention to various aspects of BIM in current contracts and lack of guidelines and application standards. Also, those in charge of overcoming these obstacles and challenges were identified at four levels of decision-making: (1) government, (2) professional institutions and associations, (3) organization, and (4) inter-organizational. In the mentioned questionnaire, the level of responsibility of each level in front of removing obstacles was also evaluated and using risk analysis method, prioritization of obstacles and challenges for different levels of decision making was determined. Accordingly, the barriers of "BIM implementation requires changes in legal procedures", "lack of guidelines and application standards", "lack of knowledge and support of senior management" and "poor partnership between consultant and contractor" are the most important barriers for the decision making levels.

In engineering designs, structural analysis is generally performed assuming a rigid base. While introducing the effect of structural substrate flexibility on the response and dynamic properties of structures is important. Introducing different solutions to reduce the response of the structure against dynamic forces is another important issue in engineering designs. In this paper, the passive Pall friction damper system has been used for this purpose. In the researches that have been done so far, various optimization methods have been used for the optimal design of friction dampers, but in most of these methods, the effect of soil-structure interaction has not been considered for friction dampers, while in earthquake soil-structure interactions is important. One of the main objectives of this study is to investigate the effect of soil-structure interaction on the optimization of friction dampers. The actual forces and displacements of a structure due to free-surface seismic movements can be determined by considering the effects of soil-structure interaction. In this regard, in this paper, two-dimensional frames of 4, 8, and 12 floors equipped with dampers were analyzed in nonlinear structural analysis software under seven accelerometers using nonlinear time history method once, considering the effect of soil-structure interaction and introducing 3 Different lateral loading patterns and again without this effect. The results show that considering this issue in terms of cumulative triangular slip load pattern has increased the loss of earthquake input energy.