نشریه مهندسی سازه و ساخت
سال دهم شماره 2 (پیاپی 67، اردیبهشت 1402)

The use of wastewater outflowing from the municipal wastewater treatment plants for irrigation of agricultural lands is one of the important and fundamental issues for reuse of the plants’ effluent. In recent years, the artificial neural networks (ANN) have received considerable attention for modeling the sewage treatment process. Accordingly, the ANN models, fuzzy logic (FL) and adaptive neuro fuzzy inference system (ANFIS) have been utilized in this paper to predict quality of the effluent running out of the treatment plant. For this purpose, first, three scenarios were chosen and their inputs were reduced using the principal component analysis (PCA) method. Finally, the process of modeling was conducted with and without this method and then, the results were compared. Evaluating the results obtained from the predictions using the statistical indicators revealed that the ANFIS model with mean error reduction value of 13.92% compared to that of the FL model and a reduction value of 8.22% in contrast to the ANN model, benefits from a higher accuracy and this trend has been held true with and without PCA. Moreover, calculating the percentage of pollutant removal efficiency indicated that the maximum removal efficiency is obtained when total suspended solids (TSS) are removed which is equal to 96.68%. It bears to mention that the rest of the pollutants had values approximately equal to that of TSS. Based on the results, as a simple, accurate, efficient and reliable approach, the ANN models can be applied to predict quality of the effluents.

One of the crises facing humanity is damage to the environment. Inadequate management and attention to greenhouse gas emissions threaten human life on Earth. Given the CO2 emissions from cement production, finding a way to reduce cement consumption in concrete as the most widely used building material is a priority. In this paper, a natural pozzolan from Iran with suitable physical and chemical properties for replacing part of cement in concrete was introduced and its engineering properties were investigated. To strengthen its strength, steel and polypropylene fibers were used separately and hybrids with new mineral pozzolans were used in concrete. According to previous studies and optimizations, mineral pozzolan with a weight fraction of 15% cement in concrete was used. A comparison of the strength of local mineral pozzolan samples with other famous pozzolanic concretes showed that concrete with local pozzolan is more resistant than ordinary cement concrete. Also, concrete containing steel fibers and local pozzolan has higher compressive strength than other samples. Pozzolanic concrete samples containing a combination of steel fibers and polypropylene had better performance in flexural strength than other samples and the impact toughness of these samples was better than other samples. Investigations showed that the impact resistance of samples containing local mineral pozzolans was 3.75 and 8.33% higher than conventional cement concrete at 28 and 90 days, respectively. The test results generally indicate that the local mineral pozzolans studied can be a good option to replace part of the cement in concrete and while improving the engineering properties of concrete, not only greatly reduce cement consumption but also a valuable finding for environmental protection. Biology, construction, and production of green concrete.

Bridges play a key role in transportation networks, and damage to them during an earthquake may delay emergency rescues and first-aid efforts. Thus, the development of structures with low damage and reduced downtime after extreme earthquake events is necessary. Post-tensioned self-centering (SC) systems improve the serviceability of bridges by eliminating residual displacements after severe earthquakes. In these systems, post-tensioned tendons have a critical role in self-centering piers so that they return the structure to its initial position and remain their functionality. In this study, the seismic performance of post-tensioned rocking bridge piers was investigated and compared with monolithic reinforced piers through time history analysis. Demand and capacity of bridges in models with different heights were investigated using incremental dynamic analysis (IDA). The probability of failure of each bridge has been investigated by studying the fragility analyses based on the maximum drift ratio and the stress of the tendons. According to the results, the collapse probability of bridges with conventional piers is higher than their corresponding bridge models with SC piers. Adding dampers to the SC piers increases the lateral load capacity of the model and decreases the probability of failure under an earthquake record with specific peak ground acceleration (PGA). On the other hand, using dampers in SC piers improves the energy dissipation capacity of the system and reduces the possibility of tendon yield by reducing the maximum displacement.

Most of the bridges in the world are generally designed and built according to the old criteria and regulations, These bridges should be subjected to seismic improvement studies and strengthen with appropriate method if needed. One of the practical methods for assessing the performance of a structure under different levels of seismic hazard is the fragility models, which are presented as fragility curves. The fragility curve expresses the conditional probability of reaching or exceeding a limit state as a function of ground motion parameters and the probabilistic method is also used to consider the different states and uncertainties that affect structures and earthquakes.Boxed cross-section arch bridges have good mechanism for bearing vertical loads due to stability and proper distribution of gravity loads. LRB seismic isolation systems are used to improve the seismic performance of the bridge. This study investigates the seismic behavior of the Nanin Bridge Arc Case in Switzerland, which has a cross-section overpass deck with a LRB Then, by evaluating the structural response states and the capacity of the members. Examination of the results of the seismic response of this structure as well as the probability functions of the frailty curve in different situations showed that the use of this system resulted in a significant reduction in the amount of earthquake damage at all levels of failure in foundation. With the use of Rubber lead seismic isolator, displacement of the structural base, the likelihood of base failure and base shear has been greatly reduced and due to the use of maximum member capacity and reduced member dimensions as well as a significant reduction in the amount of financial damage the system has also benefited.

Uncertainty of design parameters is one of the most important variables in determining the reliability of structures. In the design and analysis of steel frames, buckling-restrained brace (BRB) equipped with intelligent materials such as shape memory alloy (SMA), there are various variables such as gravity loads, lateral loads, material properties, and geometrical specifications that the uncertainty of each of which can have a significant effect on the safety of the structure. In this research, considering the existing uncertainties in material properties, loading and geometry of members, the reliability of steel BRB frames equipped with intelligent materials has been investigated. Evaluation of sensitivity and reliability analyses based on kriging meta-model of BRB frames with and without SMAs under artificial near-fault earthquakes are conducted. For this purpose, two frames 5 and 15-story with BRB with and without SMA have been studied under 9 artificial near-fault earthquakes. Nonlinear dynamic analyses were performed using OpenSees software and reliability analyses were performed by linking MATLAB software on frames. The results of this research showed that in the studied frames, the random variables of the length of SMA and the cross-sectional area of the BRB were the most effective variables in calculating the probability of failure in BRB frames with and without intelligent materials, respectively. Also, by increasing the height of the frames, the reliability index has decreased. For example, the reliability index of a 5-story BRB frame with SMA has decreased by approximately 17% compared to a 15-story frame. Meanwhile, the maximum values of the reliability index using SMA in 5 and 15-story frames have increased by 10 and 6%, respectively.

There are many factors involved in the lifecycle of construction industry projects, among them, resources and consequently human relations are the main criteria of activity development, so the conflict of interest between stakeholders in projects in this industry is an obvious and challenging issue. Claims are one of the most important factors influencing the failure to meet the project objectives. The most important result of claims are delays and overflows in construction industry projects. Therefore, in this research, an attempt has been made to improve the performance of projects by ranking the causes of claims and analyzing their effects on key performance indicators. In this research, first, the factors that create claims in Water and Sewage projects and also the key factors of success in projects have been identified. Then, by distributing the questionnaire among the experts, the importance coefficient of key success factors was calculated by the fuzzy SWARA method. The weighting results showed that among the 10 key factors of success, scheduling factors, safety and health, and cost have the first to third important factors. The causes of claim creation were ranked based on the key success factors and fuzzy TOPSIS method. The results showed that the factors of delays, changes, expediting orders, overtime, changing workshop conditions and finally, ambiguity in contractual terms have the first to sixth important ranks. The results of this research can guarantee the grounds for preventing the loss of human and physical capital, as well as ensuring timely and high-quality project completion, by considering all the effective factors in the occurrence of claims.

The high costs of base-isolation systems is one of the obstacles for their application in developing countries. In this research, a low-cost base-isolation system for low-to-medium-rise building has been proposed. For this purpose, a soil layer with plain sand or sand-rubber mixture is applied under building base. To provide lateral movement, a gap is created around the soil layer and filled with flexible materials. This gap let the layer have shear deformations and thus the amplitude of the structural response will be potentially decreased. To evaluate the performance of the proposed base-isolation system, several models have been developed in OpenSees software, with the aim to study the effective factors: the type of layer material, gap width and layer thickness. In these models, a 9-story structure of steel moment frame system including soil layer with the prescribed factors has been analysed by nonlinear time-history analysis procedure with appropriate ground motion records. To evaluate the performance of the proposed base-isolation system, the responses of peak story drift, peak story displacement, maximum axial force of the column and maximum rotation of the plastic hinge of the beam in different models have been compared. The results show that the proposed system, have been very effective in reducing the structural seismic responses. The base-isolation with sand-rubber mixture and layer thickness of 0.5 m and gap width of 10 cm, showed the best performance.

Calcium aluminate cement is one of the special cements that performs much better than Portland cement in severe environmental conditions. Engineers, on the other hand, have been critical of this unique cement due to the loss of long-term strength and durability caused by the conversion phenomena. The goal of this study is to improve the durability of calcium aluminate mortar by replacing the cement with pumice powder. In this study, pumice was used as cement substitutes in proportions of 0, 5,15,25, 40, and 60%, and a total of 6 mortar mixes were developed and it was examined in terms of durability properties. The results showed that the plain mixture reached a compressive strength of 33 MPa at the age of 1 day, and 44MPa at the age of 28 days but at 90 days, due to the conversion phenomenon, its strength had decreased by 45%. Pumice had a considerable effect on the strength and, more significantly, the durability properties of mixtures by influencing the conversion phenomena. At the age of 90days, Compressive strength, chloride ion migration coefficient, and electrical resistance, for example, have improved 47%, 78%, and 400% in the ideal mixture (P40) compared to the plain mix. According to the review of the literature, the effect of replacing pumice with CAC cement has not been considered significantly and the effect of pumice on the durability of this type of cement has not been investigated, which can be considered an innovation of this study.

Nowadays, the need to move towards sustainable development emphasizes the need to investigate the behavior of environmentally friendly concrete. So far, several studies have investigated the mechanical properties of this type of concrete, but their impact properties have rarely been investigated. In this research, impact performance of environmentally friendly fiber reinforced concrete was investigated under drop weight impact, according to the method proposed by ACI C544. In order to achieve environmentally friendly concrete, natural aggregates (NA) was replaced by recycled concrete aggregate (RCA) with amounts of 0, 50, and 100%, and ordinary Portland cement (OPC) was replaced by ground granulated blast furnace slag (GGBFS) with amounts of 0, 15, and 30%. Moreover, specimens made in this study were reinforced by 0, 0.5, and 1% hooked-end steel fibers. The results of this test include the number of impacts to create the first visible crack, the number of impacts to create ultimate destruction, and impact energy absorption. The results of investigations showed a 20.1% and 3.6% reduction in ultimate impact resistance due to the use of 100% RCA and 30% GGBFS, respectively, while the addition of 1% steel fibers increased this parameter by 8 times. Finally, statistical analysis on the results of impact tests showed that two-parameter Weibull distribution is a suitable statistical distribution for the statistical investigation of the impact resistance of concrete containing RCA and GGBFS.

This paper investigates the dynamic response of the vertical arch bridge due to the moving vehicle. These responses include the record of vertical, horizontal displacements, and the rotation of various points of a single-span arch bridge. Moreover, the reference points were positioned at one-quarter, half, and three-quarters of the bridge span length. Considering the complicated behavior of these structures, field experiments are essential to assess their behavior. However, it is impossible to perform field experiments for every type of these structures due to their diversity. Therefore, accurate simulation seems essential to study their behavior. Accordingly, the Finite Element Method (FEM) has been employed to model the bridge structure. Primarily, the modeling was coded using FEM in MATLAB software, furthermore, the bridge-vehicle interaction model was applied, then the effect of arch radius modifications on bridge parameters was examined. Validation was carried out in two methods. The first included the modeling of the bridge in finite element software and a comparison of the modes shape and frequency of the first three modes with the results of the modeling and The second, compared the time history responses of displacement in the middle of the bridge and the degree of freedom of vehicle in the present study with previous prominent studies. The results of validation showed appropriate consistency, which confirmed the modeling. According to the results of the present study, by increasing the curvature radius of the beams, the vertical displacement in the middle of their spans increases. Furthermore, by reducing the curvature radius of the beams, the horizontal displacement of the middle of its span increases, which shows the reverse result compared to the vertical displacement. Moreover, the advantages of the presented study include simplicity, appropriate accuracy, and practicality in the monitoring of bridge health.

One of the most important hazards that threaten earth dams is hydraulic failure. This phenomenon often occurs during the first flooding of the dam, when the water pressure rises suddenly. There are several ways to study hydraulic fracture and damage in a dam core. In this paper, the phenomenon of hydraulic fracture and seepage in Hajilerchai dam body in Tabriz has been investigated. For this purpose, first, using Geo-Studio, which is a program based on finite element, investigates the phenomenon of hydraulic failure in the two middle sections of the core and the upstream side of the dam core for two types of clay with low and high plasticity. The phenomenon has been identified. In modeling, layer-by-layer construction of the dam is also considered and the weight of the layers is taken into account in calculating stresses and deformations. As a result of these evaluations, high plasticity clay was selected as the selected soil and low plasticity clay was selected as the critical soil for use in the dam core. Also, Fukushima criteria and Ghanbari criteria had the most optimistic and conservative data, respectively, and the possibility of hydraulic failure in parts of the dam core was identified as possible.

Due to the large number of fire and the resulting financial and human costs, it is necessary to prevent the roof from collapsing as one of the key members of the building during a fire. Because concrete has an inherent weakness in tensile stress, cracking in the tensile area of slabs is inevitable. On the other hand, in a system of prestressed concrete joist slab system, the tensile area of the concrete is usually completely eliminated or effectively reduced, and the performance of the floor can be expected to improve under fire conditions. The critical temperature was obtained and compared in 9 samples that differed in the amount of prestressing force, strength and concrete cover as well as the span length. The thermal load was applied to the studied samples according to the ISO 834-1 standard protocol. The temperature distribution across the slab was applied uniformly and incrementally and the failure states in the model were predicted and verified with laboratory results. The results showed that the prestressing force has the greatest effect and the span length has the least effect on decreasing or increasing the critical temperature index. Changing the prestressing parameter from zero to 600 and 1120 MPa, increases the critical temperature index by 20 and 43% and changing the beam length parameter from the initial value of 4.5 m to 6 and 7.5 m, decreasing the critical temperature index by 1 and 2%, respectively. Changing the parameter of concrete cover from 20 mm to 10 and 30 mm has caused a decrease and increase of critical temperature index by 11 and 9%, respectively. Also, in all samples, the same failure mode occurred in the middle of the joist in a bending manner.