نشریه مهندسی سازه و ساخت
سال دهم شماره 7 (پیاپی 72، مهر 1402)

The main objective of the present numerical study is to investigate the seismic vulnerability of the caisson-type gravity quay walls with improved backfill soil located on a non-liquefiable dense seabed soil layer. In this regard, the effects of different improvement patterns applied to the liquefiable backfill on the seismic response of the wall are evaluated and compared. For this purpose, the Lagrangian explicit finite difference method and the UBCSAND constitutive model are utilized. First, a basic two-dimensional numerical model of the caisson quay wall is created and its response is validated against the corresponding experimental observations. Afterward, by performing non-linear time history dynamic analysis under the effect of various seismic events with different risk levels, 11 series of probabilistic seismic fragility curves are developed within the performance-based design framework for the caisson quay walls with 10 different backfill improvement patterns and also for the caisson quay wall without improvement. According to the damage probability of the wall with various improvement patterns at different seismic levels as well as the area of the improved zone behind the wall, the effectiveness and efficiency of the proposed improvement patterns on enhancing the seismic performance of the system are evaluated and discussed. The results show that the backfill replacement and modification improve the seismic performance of the wall and reduce its vulnerability in all seismic levels. By applying different backfill improvement patterns, the permanent horizontal displacement at the top of the wall after earthquake decreases on average between 40% and 73% compared to the wall without improvement. The triangle and trapezoidal geometrical patterns with the base at the bottom have the most positive effect on reducing both the horizontal displacement of the wall and the possibility of its seismic damage.

Tires and waste glass are long-lasting pollutants in nature. One of the ways to recycle waste glass and rubber is to use it in concrete, which will result in minimal extraction of natural minerals. Many engineering structures are exposed to fire hazards, and therefore it is necessary to know the mechanical properties of concrete materials at high temperatures. In this research, waste glass and rubber were used as a substitute for a part of natural fine grain (sand). The size of glass particles is between 0.2-0.85 mm and with percentages of 5%, 10% and 15% and the size of rubber particles is between 3-5 mm by volume and with percentages of 5% and 10%, replacying fine aggregates. In total, 12 mixing plans were made, and from each mixing plan, 3 cubic and cylindrical specimens were made with different percentages of glass and rubber. The compressive and tensile strength, workability, weight loss, ratio of residual compressive and tensile strength of the specimens were measured at ambient temperature and at 600 °C and the average values were evaluated. In terms of appearance, after applying heat, the color of the specimens became darker and hairline cracks were widely visible on the concrete surfaces. As expected, with increasing the rubber, the compressive strength of the speciemns decreased. After applying heat, the resistance drop of all specimens was higher than the ambient temperature state. With the increase in the rubber, the resistance decreased more, which can be attributed to the burning and destruction of rubber particles and the appearance of small holes and porosity in concrete. With increasing glass percentage, the trend of compressive strength was slightly improved. The results showed that the combined design of 5% glass and 5% rubber is the optimal design and has a more appropriate performance than other designs.

In RC structures, it is possible to move the shear wall due to architectural factors such as creating entrances for parking, creating openings, changing uses and other factors, which leads to in-plane discontinuity. According to recent studies, this irregularity can lead to weakness in the seismic response of RC buildings. In this type of irregularity, the beam above the transferred shear wall will be the focus of failure. In this study, a 9-story RC frame shear wall structure is modeled nonlinearly. Then, by applying different scenarios of in-plane discontinuity irregularity and strengthening the beam above the transferred shear wall with a concrete jacket, the seismic fragility curve of regular and irregular frames have been developed based on the results of incremental dynamic analysis. The near and far-field ground motion records used in the time history analysis of the frames are selected based on the conditional spectrum. Also, to consider the effect of irregularity on the damage limit states, the pushover analysis of the frames has been done. Results indicate that by strengthening the beam above the transferred shear wall, the seismic fragility of the irregular frames has decreased in most cases compared to the regular frame. Also, results show that in irregular frames, the median peak ground acceleration in the two-story shear wall transfer case for different damage limit states is 19% higher than the one-story transfer case to the side spans. Also, the median peak ground acceleration in the state of transition of the shear wall to the adjacent span for different damage limit states is 15% higher than the state of transition to the far span.

This paper experimentally examines the effect of geotextile layers on the undrained behavior of cement-stabilized clay specimens using unconfined compressive strength (UCS) tests. Accordingly, the low-plasticity clay specimens were remolded in three different moisture contents, including optimum moisture content and two other ones corresponding to 90% relative compaction. The clay specimens were also stabilized by cement with various percentages equal to 3, 5, and 7% of the dry weight of the soil. The stabilized clay specimens were then cured in 7, 14, and 21 days prior to performing the unconfined compressive tests. In order to investigate the effect of reinforcement type, the stabilized clay specimens were reinforced with two types of non-woven geotextiles with different values of tensile stiffness. Results of experiments showed that reinforcing cemented-clay specimens with geotextile sheets improves the mechanical properties such as maximum compressive strength, residual strength, and rupture strain of reinforced specimens compared to unreinforced ones. The greatest increase in compressive strength occurred in specimens reinforced with three geotextile layers, which had an average 37% increase in strength compared to non-reinforced specimens. The comparison between reinforced specimens with two different geotextiles showed that increasing the tensile strength of the geotextile increases the compressive strength, rupture strain, and residual stress of the reinforced specimens.

The high cost and the accumulation phenomenon of graphene in the cement matrix are the main obstacles to its use in the concrete industry. In this study, both of the above challenges were solved by producing graphene through the combination of graphite and polycarboxylate ether-based superplasticizer by exfoliation method. In this regard, mechanical properties and permeability, as well as comprehensive microstructural studies, were investigated for the feasibility of using graphene produced based on superplasticizer in cement composites. The SEM and TEM analyses revealed that the multilayer graphene sheets produced with a polycarboxylate ether-based superplasticizer are of high quality and have few defects. According to the results of this research, the sample containing graphene based on the combination of 5 grams per liter of graphite and superplasticizer at the rate of 0.1% of the cement used, the compressive and bending strength was increased by 82.05% and 33.56%, respectively, compared to the control sample at the age of 3 days. On the other hand, the porosity in the graphene-containing mixture is reduced by 50% compared to the control sample. Besides, the results demonstrated that graphene has an effective influence on capillarity absorption due to increased twisting and modification of cement matrix pores. Also, the XRD results showed that using solution containing graphene led to the consumption of C3S and C2S at the age of 3 days and more CH, CSH phases were formed in the cement structure. These results together with TGA and FESEM characterization results showed that the effect of graphene nucleation is more evident at early ages.

Megacities recently are experiencing a shortage of green spaces basically due to an increase in both urbanization demand and residential complexes. In order to solve this problem and create sustainable urban development, green roofs have been suggested as one of the useful options. Therefore, it is necessary to pay special attention to its use so that we can witness the creation of urban facilities and welfare along with the preservation of citizens' health. The purpose of this research is to evaluate and prioritize effective criteria in the development of green roof. For doing so, by using library studies and experts' opinions, the criteria were extracted and classified into three environmental, economic and social groups, consisting of thirteen sub-criteria. After checking and confirming validity and reliability and collecting questionnaires distributed among experts, data analysis has been done using the best-worst method. The results shows that economic indicator attract the highest priority among others. Additionally, the most important sub-criteria in environmental, economic, and social groups was air quality, roof longevity, and public health, respectively. Finally, the respective highest and lowest scores were assigned to roof longevity and biodiversity when all criteria were considered. However these results may change in other countries .

Poor time performance is a common problem in gas transmission line projects, which had many direct and indirect negative consequences. accordingly. The aim of this study is identifying and evaluating the causes of delays in the mentioned projects. In this regard, first, based on literature review, an initial causes of delays list was prepared, and then, to refine the causes extracted from literature, and also their ranking, the data was collected with the help of a questionnaire from the target community who were experts involved in the target projects and was analyzed using the combined technique of qualitative risk analysis and the best-worst method. The results showed that the five most important causes of delays in this study were: the client's delay in paying contractor, the financial instability of the market, the contractor's weakness in cash flow management, the delay in fulfilling obligations from the suppliers and subcontractor’s delays. Finally, each of the mentioned causes were described and the solutions to overcoming them were explained. Also, the evaluation within the seven groups showed that in the group of causes originating from the project contract documents, the short duration of the initial project contract; In the group of causes originating from interactions and communications among the project parties, the difficulty of coordination among them; In the group of causes originating from the client, the client’s delay in paying the contractor; In the group of causes originating from the contractor, the contractor's weakness in cash flow management; In the group of causes originating from the consultant, the bureaucracy of the consultant in the process of approval; In the group of causes originating from labor, the shortage of labor; And in the group of causes originating from environment, the financial instability of the markets was ranked first among the causes of their family.

The main idea of developing green buildings is based on the construction of environmentally friendly buildings and energy conservation and sustainable development. Although the concept of green building alone can open the way to achieve such goals, a mechanism for its implementation must also be provided. Therefore, identifying and evaluating the necessary incentives for the development of green buildings has a key role. The main goal of this paper is to evaluate the effectiveness of the incentive measures (policies) influenced on the promotion of green buildings. By reviewing and summarizing the results of the research literature to identify relevant policies in the field of green construction based on different phases of the project's life cycle, a database consisting of 6 major goals and 42 incentive actions (policies) effective on the promotion of green buildings was identified. By developing the comprehensive fuzzy evaluation method and forming the policy-action matrix, policies and policies were evaluated in the direction of further development of green buildings. The results showed that regulatory measures play an important role in all five phases of the life cycle of green buildings. However, it should not be overlooked that due to the obstacles created by regulatory policies for the future green building market, these policies may not be the best approach for green building development. Incentive measures such as financial incentives for the decision-making stage of development, improvement of technical standards and evaluation system, and conversion to an integrated design model in the market and technology are ranked higher than regulatory policies. The results of the present research provide a clear understanding of the adoption of effective incentive policies on the promotion of green buildings.

In this research, a method based on the optimal neural network and pattern search optimization algorithm is presented to solve reliability-based design optimization problems. The main idea is to find a surrogate model that does not suffer from the phenomenon of overfitting and therefore has a good generalization accuracy. In the first stage, using the program written using the SM toolbox, a data set of inputs and outputs of the problem is created by running Sap2000. Then an optimization problem is solved to obtain the best performance of the neural network. The design variables in the neural network training stage, are the number of layers, the number of neurons in each layer and the type of transfer. The objective function is the performance ratio, which is defined as the ratio of the number of parameters in the neural network to the number of members of the data set used in the training process. Subsequently. The pattern search algorithm is used to optimize the examples using the developed optimal ANN as a surrogate model. To demonstrate the effectiveness of the presented method, two numerical examples are considered. In the first example, a ten-bar plane truss and in the second example, a two-layered 832-membered barrel vault have been investigated. In the first example, the proposed method has worked about 32 times faster in the vase of continuous variables and 25 times faster in the case of discrete variables. (Compared to solving the problem with the original SAP 2000 model and the Latin hypercube sampling method). In both examples, the surrogate model obtained from the proposed method has provided the desired performance in both the validation and the test data.

Due to its desirable properties, polymer concrete is used for repairing or building structures that require both mechanical strength and high durability in a short period of time. On the other hand, reducing the weight of polymer concrete by using light aggregates can double the benefits of using this type of concrete in practical cases in order to make it easier to repair damaged concrete or use it in special conditions. Since the increase in concrete strength usually results in a decrease in ductility, therefore, the use of fibers in the concrete matrix can largely compensate for the problem of the decrease in ductility. The aim of this research is to investigate the mechanical properties of lightweight optimized polyester polymer concrete (with and without fibers) and compare it with the mechanical properties of lightweight concrete. To check the mechanical properties of polymer concrete, compressive strength, tensile strength, flexural strength, impact resistance and abrasion resistance tests were used. Also, electron microscope (SEM) images were used to investigate the effect of fibers on the microstructure of polymer concrete samples. The results showed that in line with the remarkable improvement of the mechanical resistance of polymer concrete compared to light concrete, the addition of fibers can improve the mechanical properties of polymer concrete. In this study, the use of 0.25 percent by volume of composite fibers in the mixing design of polymer concrete increases the compressive, tensile, flexural, and abrasion resistance by 9.1, 8.8, 6.2, and 6.3 percent, respectively, compared to polymer concrete without It is fiber. The analysis of SEM indicates the continuity and cohesion of polypropylene fibers and polymer concrete matrix, which can be considered as a good justification for improving the mechanical properties of polymer concrete containing fibers.

With the population growth, technological advancement, and the increase in heavy metal pollutants, besides the location of a quarter of the earth's surface in cold regions, it is necessary to study the effect of freeze-thaw cycles on clay and predict its behavior over time. The effect of freeze-thaw cycles on the behavior of clay contaminated with heavy metals has been less studied. In addition, low plasticity clay and shale sedimentary rock are frequent in Iran. As an innovation in this article, the effect of the freeze-thaw cycles on the compressibility behavior of shale-clay soil in the presence of lead and zinc heavy metal pollutants is investigated. The combination of low plasticity clay with 40 and 60% crushed shale was investigated. For this purpose, 60 one-dimensional and Atterberg limit tests were conducted on the samples in the presence of 0, 5 and 25 cmol/kgsoil of lead nitrate and zinc nitrate pollutants. According to the obtained results, the most changes in liquid limit are related to the samples contaminated with 25 cmol of lead nitrate after 12 cycles of freeze-thaw cycles with a 43% reduction. And the lowest changes in liquid limit are related to the combination of 40% kaolinite with 25 cmol of zinc nitrate pollutant. Also, the results obtained from the consolidation test indicate that the compressibility of the samples was affected by the concentration of lead and zinc heavy metal pollutants and the freeze-thaw cycles. The increase of heavy metal pollutants led to a decrease in the initial void ratio and compressibility index of the samples compared to freeze-thaw cycle, which led to an increase in these ratios. The maximum changes were made in the first four cycles of the freeze-thaw cycle, and the changes were insignificant until the 12th cycle.

Most of the methods for estimating the strength are either destructive or have expensive and imported equipment. Some of them also indirectly measure the strength. Therefore, a test that has cheap, simple and available equipment, with high accuracy, can be applied in all conditions, has minor damage and can be performed both in the laboratory and on the project site, it is required. Therefore, in this article, the compressive and tensile strength of different mortars and stones have been measured using a in-situ method with cheap and available equipment called "friction transfer" test. In this test, first a partial core with a diameter of 50 mm is created on the surface of the sample, and then the friction transfer device is fixed on the core and using a normal torque meter, a torsional anchor is applied to the core until it fails. be made Then, by determining the surface resistance obtained from the friction transfer test and comparing the obtained results with standard tests, the equations obtained to convert the results from the "friction transfer" test into the uniaxial compressive strength of the materials are presented. Tests were performed on seven different types of stone and cement mortars that are used in normal repair works. The obtained results show the high accuracy of the friction transfer test in measuring the strength of stones and mortars. The coefficient of determination between the results of the friction transfer test and the uniaxial compressive strength of the stones was found to be 93.2%, and according to the calibration curve, by using the friction transfer test, the compressive strength of the stones can be determined using the equation y=1.67x+90.8 measured. Also, by using the friction transfer test, the compressive and tensile strength of mortars can be measured with an accuracy of about 94%.