Journal of Civil Engineering
Volume:5 Issue: 1, Winter 2021

Assessment of existing structures is an essential topic for engineers working in the field of construction in most industrial countries. Evaluation of compressive strength is one of the most critical factors for concrete structures. Non-Destructive Testing (NDT) techniques are the most extensively used techniques for the prediction of compressive strength in the existing concrete structures. Among NDTs, ultrasonic pulse velocity and rebound hammer are more common to predict the compressive strength of the concrete. This study also investigates surface electrical resistivity as an NDT.  In many studies, concrete specimens are constructed in cubic or cylindrical shapes, but the role of conversion factor has been overlooked that may change the NDT results from cubic to cylindrical specimens and vice versa. Hence, in the present paper, an experimental study was conducted on concrete specimens based on NDTs. In this experimental process, cubic and real cylindrical specimens were assessed in the same mix designs at the ages of 7, 28, and 90 days. Herein, some accurate equations were also proposed to convert NDTs and compressive strength of cubic concrete specimens to cylindrical specimens based on experimental data and response surface methodology. Results showed that the proposed equations perform sufficient accuracy for the conversion intended.

Functionally graded materials (FGM) are some kind of composite materials that due to the continuity of mixture of constituent materials, have more effective mechanical properties than composites which leads to eliminating interlayer stress concentration. The most application of these materials is in thin structures such as plates and shells. This research presents a Tamura-Tomota-Ozawa based model to obtain the elastoplastic behavior of Functionality graded materials under impact loads. Also, based on this model, the ceramic phase of FGM was considered as an isotropic elastic material and the metal phase was considered as an elastoplastic material.Several parametric studies have been conducted to assess different aspects of such material behavior. The results show thatthe maximum displacement of the shell has increased by increasing the volume fraction index and the thickness ratio, and it has decreased  by increasing the aspect ratio. It was also observed that the thickness ratio(32%), volume fraction index(30%), aspect ratios(23%) and shell curvature (16%) parameters affect the maximum displacement of the shell. The elasto-plastic response of FGM shells is similar to homogeneous shells and the TTO model can describe the mechanical behavior of FGM shells beyond the elastic range where the FGM response is mainly governed by the plastic region of the metal phase.

Following the principles of low-cost, energy-saving, low polluting, and sufficient thermal, humidity and acoustic insulation of soil blocks as a construction material, there is an increasing interest to study clay adobe elements. This study presents a mathematical model for predicting the relationship between uniaxial compressive stress and corresponding strain which can be useful for simulating the structural behavior of plain and short fiber reinforced adobes with concrete damage plasticity model in ABAQUS.  In this direction, the compressive properties of four different plain and short fiber reinforced adobes weremeasured in experimental tests. From the obtained results, the essential parameters of the stress-strain curves for all various mix design specimens were extracted for numerical modeling.  By a statistical study on the various results of compressive tests as available in the related literature, the proposed equations were developed for predicting the necessary parameters when the only needed experimentally determined parameter is the peak compressive stress. The suggested model is compatible with the behavior of different adobes with different compositions, compacting, curing, and testing condition. The recommended model and formulations are to some extent more successful in predicting the linear and nonlinear behavior of different adobes according to other models.Finally, a mathematical model is developed for predicting the inelastic range of the compressive stress-strain curve.

Analyzing how safety culture influences the drivers’ behavior is extremely important from the public-health point of view. It allows experts and researchers to propose preventive measures based on a multidisciplinary approach. In this regard, several studies have investigated the importance of safety culture and its effect on traffic safety. However, only a few studies have evaluated this issue in the drivers of heavy vehicles which carry chemical hazardous materials (HAZMAT). Thus, the main objective of this research is to obtain the effective parameters affecting the safety culture of HAZMAT drivers. The ultimate goal is to determine the priority of parameters and weigh them to provide insights into the factors leading to accidents in this type of vehicle. To address this goal, 339 questionnaires were obtained from the drivers whose jobs were carrying this type of material; subsequently, the results of the survey were analyzed using the Analytical Hierarchy Process (AHP). The weights were calculated in order to define a global score for each of contributing factors. The results showed that the priorities of the predefined contributing factors are social, psychological, legislation and law enforcement, public education, and economic respectively. The first and second factors are human-related. In a conclusion, human-related factors, are the most important factors in safety culture. Therefore, to improve safety, focusing on human-related factors is essential.

The moment frame system is used as a lateral load resisting system against seismic loads. So far, a large body of research has been conducted on steel connections and various types of connections including Reduced Beam Section (RBS) and Drilled Flange Connection (DFC). Using RBS results in the formation of inelastic deformation in a part of the beam far from the column flange. They have studied the seismic performance of the recently developed DFC as a simple and efficient alternative to mostly used conventional RBS. In this research, the beam flange is drilled in different patterns in terms of the hole diameter. After simulating the models in Abaqus, the moment-rotation curves are extracted and analyzed numerically. Having obtained the results of the current research regarding the moment connection where beam flanges are drilled, it is evident that drilling holes in the beam flange with a clock pattern can better satisfy the flexibility expectations. Moreover, this pattern has the higher capability for plastic hinge transfer from the column face compared to the direct pattern. Additionally, this pattern can reduce the bending stress in the penetration weld of the direct beam to column connection. Thus, the clock pattern of beam flange holes performs better than the straight one.

Waste tires are widely used for geotechnical applications as backfill material that is either a substitute for natural soils or combined with them. This paper determines the shear strength parameters of tire chip-sand-geotextile mixtures using a triaxial test apparatus. For this purpose, tire chip–sand mixtures with mixing ratios of 0:100, 15:85, 25:75, 35:65, and 100:0 by volume were used as fill materials. Also, for the reinforcement of these mixtures, the layer of geotextile is used. In all tests, the strain rate has been kept the same. Three confining pressures have been applied in all experiments. The influences of the tire chip content, number of geotextile layers, and confining pressure at the strain levels of 3%, 6%, 9%, 12%, 15%, and 18% on the sample were studied and described. This paper focuses on the stress-strain behavior of different mixtures. The results show that the imposed strain level on the samples plays an essential role to increase the strength of the tire chip-sand mixtures compared with sand alone. It implies that the beneficial effect of tire chip content to enhance the strength of samples appears in high strain, especially for reinforced samples with geotextile, while in low strain, tire chip does not have a beneficial effect. Hence, it is necessary to consider the strength of tire chip-sand mixtures compared with sand alone at the imposed strain level.

Oil and its derivatives can be distributed through various transportation modes. Although the fact that the pipeline is considered the most prevalent mode of transporting oil products, policymakers confront several parameters in making a straightforward decision about how to transport such products. Other modes of transportation may be used in many regions due to higher flexibility and affordability. Therefore, competition between pipelines and other modes of transportation exists due to economic concerns. Therefore, a study clarifying this competition is essential. In this study, a game-theoretic framework in a duopolistic supply chain is developed for modeling the competition of two oil products transportation systems, including road and intermodal pipeline-road. These are considered the most prevalent modes of transporting oil and refinery products in many countries. Transportation prices of the two rival systems, in addition to the availability of tanker truck fleet are the main variables considered in this study. Flexible and inflexible schemes are introduced and based on them, the effects of four different policies on the degree of competence in the oil transportation market are analyzed. Moreover, some useful managerial insights are provided including transfer from flexible scheme to inflexible scheme, fuel price increase, employment of modern trucks with low fuel consumption, and decrease of peripheral costs in the intermodal system.

The hanger systems of the footbridges are used in two vertical and inclined forms. Both systems have their advantages and disadvantages. The inclined hangers are more prone to slackness and fatigue phenomenon, and are stressed too much. There is no much slackness, fatigue phenomenon and overstress in the vertical system, but this system is more prone to vertical vibration at low frequencies than inclined ones. In recent years, a new modification has been made to eliminate deficiencies in the inclined hanger system. In the modified system, the slackness phenomenon has been removed completely and the force variations of two adjacent hangers have been reduced significantly. In this study, modeling and analysis of the footbridge were performed with CSI Bridge software and the disadvantages of the old modified hanger system are eliminated by proposing a new modified hanger system. A modal analysis was also carried out to compare the dynamic characteristic such as natural modes and frequencies on a footbridge with the vertical, inclined, old modified, and new modified hanger systems. Results showed that the new modified hanger system was improved compared with the old one in the terms of vertical vibration mode so that the new system had no vertical frequency in the pedestrian vertical frequency range.

Compared with normal-weight concrete, lightweight aggregate concrete (LWAC) has a lower compressive strength. However, its plus points, including preferable fire resistance, appropriate durability, and dead-load decline lead to the LWAC’s application in the construction industry. A practical method to overcome its drawback could be adding nano-silica (NS) to the mixes. For this purpose, the current experimental work aimed at researching to explore the compressive response of LWAC containing different dosages of nano-silica. Therefore, cylindrical specimens of size 150 × 300 mm improved by nano-silica were subjected to compressive cyclic and monotonic loading; six dosages of NS, including 0, 1, 2, 3, 4, and 5 weight percent of cement were added to mixes as cement replacement. Experimental stress-strain curves were investigated to determine the stress-strain relationships. The results show that the addition of up to 3 wt % nano-silica improves the properties of LWAC, as it was found to enhance compressive strength and modulus of elasticity during monotonic loading, shift up the common point coordinate, and reduce the stiffness degradation of the reloading paths in cyclic loading. However, larger dosages of nano-silica (4% and 5%) were found to have diminishing returns, considering the improved properties of LWAC. Furthermore, stress-strain models for the nano-silica-incorporated LWAC were proposed in compression. The experimental findings were also compared with the proposed model. There was an acceptable concurrence between the proposed model data and experimental findings.

In this study, traffic and geometric factors affecting accidents occurring in road segments are investigated across different transportation modes (vehicle, motorcycle, and pedestrian) using micro and macro levels variables simultaneously while accounting for the effect of intra-zone correlation due to the same independent variables for accidents occurring within a zone. The data relating to 14903 accidents that had occurred in 96 Traffic Analysis Zones (TAZ) in Tehran were collected and imported into Geographic Information System (GIS) application. Negative Binomial models and multilevel models were adopted to predict the number of traffic accidents. Due to considering the multilevel structure of the data in multilevel models, it showed a better performance in explaining the factors affecting accidents. Moreover, based on the results obtained from analyzing the sensitivity analysis of variables for final models, the effect size of one variable in accidents varies across different modes of transport. This discloses the necessity of investigating accidents across modes of transport. According to the results, variables like the high intensity of intersection in one TAZ and the length of the road segment increase the number of traffic accidents in all three modes of transport. Variable of the ratio of the principal arterial length to total roads available in one zone has almost 3.2 times stronger effect on motorcycle accident than vehicle and pedestrian accidents. So that adding 1 unit to this variable increases the number of vehicle and pedestrian accidents by a factor of 1.7, whereas, this variable increases motorcycle accidents by a weight of 5.4.

The Marshall test method is widely used for the design and control of hot mix asphalt (HMA). The Marshall and modified Marshall mix design methods are most widely used in Iran. Determining Marshall test results (Marshall stability, flow, and Marshall quotient (MQ)) are time-consuming. Therefore, using new and advanced methods to determine the results of Marshall testing is essential. In this study, the genetic programming method based on artificial intelligence was used for the prediction of Marshall test results. Input variables in the genetic programming models use the volumetric properties of standard Marshall specimens such as air voids, voids in mineral aggregate (VMA), and voids filled with asphalt (VFA). Also, multiple linear regression models were used as the base model to evaluate the models presented by the genetic programming method. The results indicated that the proposed methods are more efficient than the laboratory costly method and the performance of the genetic programming model is completely satisfactory in comparison to the base model and has been able to predict the results of Marshall testing based on the input parameters. The GP models have a higher coefficient of determination and fewer errors than MLR models. The presented models will also help further researchers willing to perform similar studies, without carrying out destructive tests.

One of the methods to improve the quality of dispersive clays to reduce its washout tendency is to add lime with a proportion of 4% in construction projects. Besides, adding lime will lead to the stabilization of the soil furthermore. Therefore, if the stability of soil is of concern, some portion of soil may be replaced by lime. In this paper, the incinerated sewage sludge ash (ISSA), mixed with hydrated lime by appropriate proportions and about the duration of the curing process, was used to improve specifications and parameters of dispersive clay. Afterward, the effect of this mixture on unconfined compressive strength relying on the dispersive properties of soil and the curing process of the combination was investigated at different periods. This research aims is to investigate the cementation process of dispersive clay with the addition of ISSA and I.L mixturet to curing durations. Both mixtures were added to dispersive clay in 2, 4, 8, and 16 percent by weight. Also, the proportion of ISSA to hydrated lime is 4: 1 in weight.  Results of the tests showed that the unconfined compressive strength of the test specimens was increased by more than three times compared to the pure clay by adding hydrated lime and ISSA, indicating numerous potential applications of the mixture for soil improvement and administrative affairs in geotechnical engineering as well as practical applications in environmental engineering.