نشریه مهندسی عمران
سال پنجاه و پنجم شماره 4 (تیر 1402)

Heavy metals are found in high concentrations in industrial wastewater and cause damage to humans and other organisms by entering to water, soil and food chain. Stabilization and solidification is a common process in the treatment of sludge containing heavy metals. In this study, solidification/stabilization of ceramic tile industry sludge was investigated using cement and additives like water, lime, microsilica and ordinary clay.

In this study, by designing the tests by response surface methodology, the effect of different additives on compressive strength and metals concentration after pollution leakage test was investigated. So, hazardousness of wastes after stabilization and solidification and the samples tolerance against the environmental loads was evaluated.

Results showed the highest value compressive strength in high amounts of cement. Decreasing the amount of waste and replacing more lime, clay and microsilica, the compressive strength was increased. In optimal mode, by 5.77% lime, 8.69% clay, 4.35% microsilica and 51.84% cement, the maximum compressive strength was achieved about 116 kg/cm2. The minimum concentration of Cr was 0.0782 mg/L and resulted from 11.23% lime, 21.31% clay, 10.65% microsilica and 27.46% cement. Minimum Pb concentration (0.0043 mg/L) was obtained in 11.23% lime, 21.31% clay, 4.35% microsilica and 33.76% cement.

The more efficiency on compressive strength is related to cement. In addition, applying the lime, clay, microsilica and cement concluded the effective reduction of Cr and Pb concentration in leaching the stabilized samples.

Coarse recycled concrete aggregates have weaker mechanical and physical properties than natural aggregate because of the porous and flimsy cement mortar.Hence, using coarse recycled concrete aggregate in the asphalt mixtures decreases their resistance to different failures. Therefore, in this research, in order to reduce the permeability and increase the resistance of adhered cement mortar, coarse recycled concrete aggregate was modified by two chemical (coating their surfaces using styrene butadiene rubber polymer) and physical (separation of cement mortar using heating) methods. The results of the dynamic creep test also show that employing coarse recycled concrete aggregate increases permanent deformation in the specimens under test because the asphalt mixture stiffness is decreased. But asphalt mixtures containing treated coarse recycled concrete aggregate have less permanent deformation because the styrene butadiene rubber polymer with the penetration into the void of coarse recycled concrete aggregate and reinforcing cement mortar, as well as removing the cement mortar by heat, increases their stability. Also, asphalt mixtures containing coarse recycled concrete aggregate have a lower fatigue life compared to the control mixture, and chemical modification of aggregates has been more effective in increasing the fatigue life of the mixtures containing them compared to the physical method. In addition, the results show that the presence of moisture reduces the resistance of controlled and modified asphalt mixtures against moisture damage, and this reduction is greater in mixtures containing coarse recycled concrete aggregate due to their high absorption.

One of the new processes and technologies that solve many problems of construction projects is Building Information Modeling (BIM). BIM is not widely used in Iran, while in other countries, its culture is settling at a more favorable pace. Ideal modeling so that the micro-models are realistic and have information such as construction time and cost, construction companies, quality, etc, is a time-consuming and costly task, this issue reduces the tendency of stakeholders to implement BIM. What is the role and effect of using databases of materials and equipment in each of the stages of BIM implementation in construction projects? if there is a comprehensive database in the field of BIM, which BIM functions will be facilitated and which stakeholders benefit most from this database, are the questions that this paper seeks to answer. In the present study, after reviewing the literature related to the subject and recognizing the generalities and definitions of the database of materials and equipment, as well as its benefits and effects, semi-structured interviews were conducted with 16 experts in this field, using a qualitative method and then a content analysis. The results show that the use of materials and equipment database is the most used in the detailed design stage and it’s most used in cost estimation, Quantity Take Off and clash detection and also the consultant and employer benefit the most from this database.KEYWORDS

Asphalt mortar and asphalt mixture are viscoelastic materials due to the presence of bitumen in their structures. The master curves of dynamic modulus and phase angle developed through the horizontal shifting of the results using the appropriate shift factors are commonly used to describe the viscoelastic properties of asphalt mortar and asphalt mixture. In this study, constructing master curves of dynamic modulus and phase angle of asphalt mortar and asphalt mixture using the least number of test temperatures and frequencies was investigated. The dynamic modulus test was performed on asphalt concrete and asphalt mortar samples at six temperatures and frequencies. Then, the Laboratoire Central des Ponts et Chaussees method was used to determine the shift factors for constructing master curves. Also, the modified Christensen-Anderson-Marasteanu model was fitted on the master curves to predict their viscoelastic properties at an arbitrary temperature and frequency. In addition, the master curves and the fitted models which are created by using test results at two frequencies and six temperatures, six frequencies and three temperatures, or three frequencies and three temperatures, could provide the same predicted values and patterns as the original fitted model with more than 92% accuracy. So, as a result, it is possible to develop the master curves of the viscoelastic properties of asphalt mixture and asphalt mortar with a lower number of test results that have similar accuracy to the original master curves and reduce the time and cost of experiments up to 50%.

To reduce the seismic response of steel frames, energy dissipation devices can be placed at connections. These connections can be modeled as a rotational spring and damper in parallel. In this paper, an attempt is made to estimate the best distribution of the connections, by time-history analysis and optimization operation. Although in the previous studies, these connections were distributed uniformly, in this research the combination of these connections in rigid frames is proposed. Two 9 and 20-story frames with sections and dimensions based on SAC benchmark structures are studied. Seismic performance of optimized structures with connections equipped with dampers and rigid connections is evaluated and compared with that of the moment frame with uniformly placed such connections. It is observed that performance of hybrid structures, despite having less dampers in connections, is much better than the structure with uniform distribution of this type of connections. On the other hand, linear and nonlinear behavior of elements and connections in structure is developed. Also, in optimal condition, 62 and 68% of the connections in linear and 58 and 61% in nonlinear behavior have been equipped with dampers respectively for 9 and 20-story structures.

Recognizing the nature of risks effective on oil projects is an important issue in the risk management of companies such as Iranian Oil Pipeline and Telecommunication Company. This study aims at identifying risks and extracting the structure of relationships between critical risks of Yazd-Naein oil pipeline construction project using Interpretative Structural Modeling (ISM) to help the pillars of the project. To do this, using different techniques, first the critical risks of the project are identified and prioritized and then using ISM, the reciprocal relationships between risks and their effectiveness on each other are recognized. This study has made attempt to make a more realistic comprehension for confrontation with non-security caused by the risks of Yazd-Naein oil pipeline construction project using ISM. The results showed that sanctions risk on project has to be concentrated by risk management since it has the highest effect on other risks and the least affectability from them. Also, since the opinion of experts have been used in this study, in the case of using in similar projects, it is expected that the implementation of the mentioned structure may positively and significantly influence the achievement of project goals such as cost, time, project scope, quality and sanitation, security and environment.

In the seismic active zones, structures are often exposed to successive earthquakes. Seismic sequence phenomenon refers to the occurrence of repeated earthquakes with significant PGA shortly after the first earthquake. Vulnerability of steel structures with buckling restrained brace (BRB) subjected to successive earthquakes consist of main-shock and critical aftershocks indicates that the effect of consecutive earthquakes, depending on their intensity, has significant effects on structural failure. For this purpose, 2D steel moment and buckling restrained brace frames with 3, 7 and 11-story are designed based on Iranian Standard 2800 (Fourth Edition). In the following, studied frames are implemented in OPENSEES software and analyzed under single and critical successive earthquakes after verification. Based on the results of nonlinear dynamic analysis, the Park-Ang damage index was calculated for all frames and after processing the output results in MATLAB software, the final results were reported. The results show that in all frames, successive earthquakes increased the damage index due to the accumulation of damage in the elements due to stiffness and strength degradation. It has also been observed that the ratio of increased damage in the steel moment frame caused by consecutive to single case was higher compared to the BRB frames. That is, considering the BRB has reduced the ratio of this failure under consecutive earthquakes.

Professor Nooshin and et al defined structural regularity indicators quantitatively three decades ago and used various methods for improving regularity of structures, such as stepping projection, sphere packing concept, recursive techniques, and etc, to create a special category of space structures (domes and flats) and grid shells that were designed in a multifaceted manner, and depending on the type of project, they used one or more of these indicators to analyze and compare the regularity of the structures The regularity studied in this research is related to increase of equal lengths or almost equal lengths, the reduction the count of elements with different lengths, the reduction of the number of length intervals and different shapes of faces while maintaining the geometric form. The aim of this research is to study the previous regularity indicators, investigate and analyze the improving regularity of Delaunay triangulation obtained from the points of the single layer dome of Bidboland Khuzestan with the proposed algorithm: using the circle packing algorithm and genetic optimization (using the minimization of different regularity indicators) to reach a suitable pattern. In order to analysis the improving regularity. we have presented algorithms for calculating the regularity indicators, we have calculated the numerical results of these indices and we have suggested a general definition for regularity degree. we show that each of these indices alone are not criteria for measuring and comparing the regularity of two structures. The results are effective in form finding and optimal design.

Due to spread of automotive industry the worn tires are being consider as a one of the Environmental pollutants in recent decades because of the lack of decomposition in nature. The use of tires crumb with mixed soil is provided as a one of the solutions to prevent environmental hazards caused by tires burial. According to the tires properties, such as elastic behavior, low water absorption and the appropriate cost to use it in the form of crushed, they can be used in arming and improving the properties of earth materials. In this article, the optimal percentage of tires crumb in the sand to increase its shear strength parameters as well as the effects of adding tires crumb on Displacement-load curve by using large-scale direct shear test (box 30x30 cm) has been studied. For this purpose, sand with different percentages of tires crumb and various value of normal stresses in direct shear has been tested and the percentage of optimal tires crumb which the shear strength is maximum for it determined. Since the shear strength of soils is because of angle of internal friction and viscosity, the effect of tires crumb on each of these parameters is studied. Results shows that adding tires crumb cause to increase the capacity of plasticity, viscosity, angle of internal friction and therefore to increase the shear strength of the sand.

Covering spaces has always been one of the main issues in architectural engineering. Barrel vault is one of the cover types used in traditional structures. In this paper, the effect of skewed angle on the bearing capacity of a semicircular brick vault has been examined. The Experimental studies have been performed in two parts: determining the properties of materials and determining the bearing capacity of the vault. Due to laboratory limitations, scaled models of materials and structure are made used. The loading of the specimens is gravitational force with a constant rate in the middle of the span. The finite element model is developed and validated based on the Willam-Warnke failure criterion parameters. Finally, in order to investigate the behavior of skewed semi-circular vaults the different angles and aspect ratios are studied by analytical models. The important behavioral parameters studied in this research are failure load, maximum displacement, and also the behavioral mechanism of skewed vaults in comparison with non-skewed vaults. The results indicate that in all models, the skewed vault has a lower bearing capacity than the non-skewed vault. The maximum drop in bearing capacity due to skew occurs up to skewed angle of 30 degrees and for larger skewed values, the sensitivity of the structural behavioral parameters to skew decreases. So that for the vault with the aspect ratio of 0.5, with increasing the angle of skew from zero to 30 degrees, the bearing capacity of the vault decreases 58% and 18.74 for increase from 30° to 45°.