نشریه مهندسی عمران
سال پنجاه و پنجم شماره 1 (فروردین 1402)

The bearing capacity and settlement of shallow foundations located on the pipe are usually not acceptable in sandy soils. Therefore, in order to improve the performance of strip foundations, various methods are proposed, as a cost-effective alternative is to add skirts to the edges of the shallow foundation. the addition of the skirt to the edges of the shallow foundation increases the effective depth of the foundation and soil trapped within the skirts, and loads of the structure are transferred to the bottom depth at the level of the skirt tip. In recent years, performance assessment of skirted foundations has become one of the desired topics for civil engineers. In this article, the effect of the burial depth and horizontal distance from the center of the pipe to a single load have been evaluated using numerical and experimental tests. Therefore, the skirted foundations located on the buried pipe with skirts B and 2B (B is the width of the foundation) have been used. The results of the laboratory tests show that by using the skirted foundation with skirts of 2B, the bearing capacity can be increased by more than 300% compared to the strip foundation. A numerical comparison of the skirted foundation with semi-deep and embedded strip foundation shows that the bearing capacity of the skirted foundation was less than 10% different from the semi-deep foundation. Civil engineers can be led towards more economical and accurate designs by using the skirted foundation.

Harmful materials penetrate the concrete and reduce its durability. Therefore, knowing the permeability of concrete is essential. Today, concrete penetration-reducing additives are widely used to construct various concrete structures such as water storage tanks. This paper discusses the effect of factors such as the amount of cement, water-to-cement ratio, penetration-reducing materials, concrete age, and the relation between surface strength, compressive strength, and surface water penetration into the concrete. Concrete cube samples are prepared with the strength of 25, 30, 35, and 40 MPa and ages of 7, 28, and 90 days. Permeation reducers such as waterproof, micro silica, and mezocret have been used in the samples. Using the torsion method with a cylindrical chamber device and a concrete breaker jack, the surface strength, permeability, and compressive strength of concrete specimens have been measured, and their relation with each other has been investigated. Also, the volume percentage of permeable pores was calculated according to ASTM C642-06. This standard was used as a criterion for measuring permeability. The results show that the highest permeability reduction is for waterproof, micro silica, mezocret, and without additive concrete samples, respectively, and its amount varies from 5 to 20 ml. Despite the complex structure of penetration-reducing materials, it is possible to predict the water penetrating volume into the concrete specimens with appropriate accuracy by obtaining the compressive and surface strength of concrete specimens and using the proposed regression equations.

Soil improvement has long played an important role in civil sciences, especially in geotechnics. However, with the passage of time and the lack of resilient lands for the construction of more advanced construction structures, engineers in this field decided to use new methods to stabilize and reinforce problematic soils. Also in recent years, environmental problems such as the increase of waste and industrial waste and their release into the living environment have created problems for the life of living Creatures. In these circumstances, geotechnical engineers have tried to use these materials in construction projects to protect the environment and, also, due to the very low cost of waste materials, reduce the economic costs of soil improvement projects. As a result of this study, granular soil is reinforced in two loose and semi-dense states using Polymeric industrial waste material called full ethylene-vinyl acetate (EVA). The experiments were performed at different weight percentages of EVA (0, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 3 and 4), without adding moisture and using the CBR device. The results show that soil CBR has increased significantly with the use of these additives, and its effect on the soil increases with the reduction of the specific weight of the soil.

The existence of underground cavities such as aqueducts and water supply pipelines causes changes in the estimated seismic response on the ground. Since the characteristics of an earthquake are different near and far from the seismogenic source and the corresponding regulations have not considered near- and far-field effects on loading, it is necessary to study and compare such effects. This study has used the finite element method and the two-dimensional Plaxis software to investigate seismic responses on the ground while there are underground circular cavities. To this end, a set of near- and far-field accelerograms belonging to Bam, Landers and Loma Prieta were selected. Those recordings were different in terms of frequency. To examine the effect of soil type, four types with different mechanical characteristics were selected, and the seismic responses on the surface of the ground were studied in the presence and absence of an underground cavity. The effect of the buried depth of the cavity was evaluated with regard to two different buried depths (H/R = 1, 3). The results showed that the presence of an underground cavity leads to an amplified response of the ground. For instance, the amplification index of the displacement on the ground with and without cavities in the most critical conditions (Landers earthquake) was found to be 4.8 and 6 as recorded in near-field and far-field accelerograms, respectively. Moreover, the farther from the cavity center (X/R > 4), the less amplification was clearly observed on the ground under different loadings. The selected parameters also proved to have significant effects on the acceleration and displacement on the surface of the ground. To gain more insight about these effects, further research is needed.

One of the recycling approaches for waste materials like tires and glass is to use them in concrete. In this paper, the effect of the simultaneous use of waste rubber as partial substitution of fine aggregate and glass powder as partial substitution of cement, on workability and mechanical properties, in ambient temperature and after exposure to temperature of 600 °C, is investigated. In order to evaluate the effect of rubber particle size on workability and mechanical properties, two different rubber particle sizes of 0.15-1mm and 3-5mm were used. In total, 13 mixtures were prepared. Except for the reference mixture, the rest contained a combination of rubber particles replacing fine aggregate with the percentages of 5% and 10% by volume and glass powder replacing cement with percentages of 10%, 15% and 20%. First of all, the slump test was carried out. Moreover, compressive strength and tensile strength, before and after thermal exposure, were investigated. In order to have an understanding of waste material's behavior, scanning electron microscopy and energy-dispersive X-ray spectroscopy tests were conducted. the results indicated that 5% for rubber particles, 10% for glass powder and also rubber particle size of 3-5 mm presented the best results among mixtures containing rubber and glass powder, in terms of compressive and tensile strengths.

There are many cases in which the foundation, in addition to static load, is exposed to cyclic loading, such as earthquakes, traffic loads, and machine vibrations. In this laboratory study, the effect of foundation width, sandy soil density, number of loading cycles, static and cyclic overhead intensity on cyclic strip foundation settlement has been investigated. The soil material used in this research is poorly graded medium sand (SP). The foundation model has a width of 5, 7.5 and 10 cm and its length is 34 cm. In medium and dense sandy soils, the average amount of foundation settlement in the first loading cycle is about 46 and 51% of the total cyclic settlement, respectively. Medium-density sandy soils below the foundation have failed at a settlement of 22 to 27% of the foundation width. The dense sandy soil beneath the foundation has failed at a settlement of 33 to 43% of the width of the foundation. The lower the total overhead entering the soil, the more loading cycles the soil can withstand to fail; That is, with increasing static and cyclic overhead, the soil is failed in a smaller number of cycles. Due to the creation of permanent settlements under the effect of cyclic loads, in the design of foundations under the effect of this type of load, the amount of predicted settlement must be less than the allowable amount.

One of the simple and cheap ways for flow measurement in canals is to use flumes. In this study, the efficiency of trapezoidal flumes with prismatic piers for flow measurement in trapezoidal canals was investigated. Laboratory investigations on four prismatic piers installed in the trapezoidal canal floor with an adjustable side slope were conducted. Based on the results of conducting several experiments, in the first analysis, a relationship and graph to calculate the discharge for each side slop and a relationship for all of the investigated side slopes were separately presented using dimensional analysis. In the second analysis the relationship and graph to calculate the discharge coefficient for each side slope and a single relationship for all of the investigated side slopes were separately obtained through the simultaneous use of the concept of energy principle and dimensional analysis. To investigate the accuracy of the obtained relationships, the statistical parameter of Mean Absolute Relative Error (MARE) was used. In the first analysis the mean value of the relative error to estimate the discharge in the investigated side slopes (z=0.268, 0.4663, 0.7 and 1) were 8.8, 10, 7.7 and 8.3 percent, respectively. Also in the second analysis, the value of this statistical parameter to estimate the discharge in the investigated slopes were 6.5, 10, 1.8 and 3.4 percent respectively and based on the single relationship for all of the investigated side slopes was 9%. Therefore, to calculate the discharge, the second analysis was recognized to be more appropriate than the first.

In order to reduce the negative environmental effects of Portland cement production, lightweight alkali-activated slag concrete can be considered as a new building material in the construction industry. According to the studies conducted by the authors, there is no research about drying shrinkage of one-part lightweight alkali-activated slag concrete. In the present study, the effect of slag content, the dosage of one-part alkali-activator and aggregate combination on the compressive strength and drying shrinkage of lightweight one-part alkali-activated slag concrete were considered. Also, two types of curing methods i.e. water curing and plastic cover curing were selected to investigate the effect of curing conditions on drying shrinkage and compressive strength. To make lightweight concrete, lightweight aggregate (Leca) was used in combination with natural aggregates and two aggregate combinations, one containing lightweight fine aggregate and normal weight coarse aggregate and one other containing both lightweight fine and coarse aggregates, were considered for conducting the experimental tests. A Portland cement mix was also used to make a reference mix of concrete. Compressive strength of the samples was measured at the ages of 7, 28 and 90 days and the drying shrinkage up to the age of 180 days. According to the results, slump and setting time decreased with increasing slag and activator content, while compressive strength and drying shrinkage increased. Examination of the curing condition of lightweight one-part alkali-activated slag concrete showed that drying shrinkage increased and compressive strength decreased with plastic cover curing.

The probabilistic analysis could effectively apply the effects of uncertainty in the structural analysis, where fragility curves are a well-established technique for the probabilistic evaluation of the structural performance. Notably, incremental dynamic analysis (IDA) is one of the most common analytical methods for obtaining fragility curves. In this study, the statistical and probabilistic seismic performance of 3- and 9-story steel buildings are investigated under 22 pairs of far-fault records introduced in FEMA P695. The seismic performance of both uncontrolled and controlled buildings with LRB is studied using IDA. Then, a general mathematical equation corresponding to each structure will be determined for all damage states known as the probabilistic seismic demand model (PSDM) of the structures. Using this equation, the collapse fragility curve of the structures will be determined for both uncontrolled and controlled structures with LRB. To evaluate the possible impact of different levels of seismic intensities on the performance of the isolated structure, the collapse fragility curves for three different levels of intensities of the benchmark records are presented. According to the collapse fragility curves, in addition to the effect of different levels of seismic intensity on the seismic performance of the structure, it is possible to see the positive effect of the LRB in reducing the probability of collapse. Also, the collapse margin ratio (CMR) in the 3- and 9-story buildings has increased by 100% and 81%, respectively, which indicates the better performance of the LRB isolators in low-rise structures.

In this paper, the role of effective factors on the instability of tunnels and underground excavations was explored through statistical analysis. To reach this goal, the effective factors (including 25 different factors) on the tunnel instability were recognized based on the deep literature survey and expert judgment. Then, a database of previous tunnel instabilities was established based on the type of tunnels and the main factor of instabilities. The effective factors were classified into six main groups and utilized for statistical analysis based on the relative frequency of tunnel instability. The results of this paper show that the geomechanical factors, design-investigation issues, and geological-geographic conditions of the site are the main three reasons for tunnel instability, where these main factors control more than 70% of civil-utility tunnels through all case studies. In addition, the design-investigation issues and geological-geographic conditions show the lowest and highest dependency on the tunnel utility, respectively. The “weak zones”, “inadequate redesign during construction”, and “the groundwater level and conditions” are the main three effective factors in tunnel instability, where the relative frequency of instability due to these factors reaches up to 40% for most of the case studies. Based on the main effective factors of instability, the freeway and highway tunnels show the highest consistency with all other utilities for tunnels in the statistical population. Therefore, freeway and highway tunnels can be considered as the most representative of overall utilities. The outcome of this paper can be applied to risk assessment of tunnel instabilities and technical management.

Permanent deformation after an earthquake increases the cost of the retrofit and even the implementation of the rehabilitation plan. A resisting system to control the lateral forces due to earthquakes is to use shear walls with good energy dissipation capability. Permanent deformation and cracking in the border and critical areas of the wall after relatively strong earthquakes leads to a decrease in the seismic performance of the wall. In this research, the responses and cyclic behavior of concrete shear walls under the cyclic loading protocol are investigated. For this purpose, using OPENSEES software platform, concrete shear wall modeling based on SFI-ΜVLEM method or wall modeling using multiple vertical elements based on the macro fiber method has been studied. The main models analyzed in this study include 2 concrete walls with steel rebars and memory alloy (SMA) with different dimensions and arrangement of reinforcements and innovative concrete wall with separate border elements in the form of concrete columns made of engineered concrete (ECC) and SMA rebars.  Validation of the models was based on previous studies. After validation of the initial models, the parametric study of the models was performed in order to investigate the effects of the dimensions of the boundary areas, the type and arrangement of the reinforcements and the amount of gravitational forces on the shear walls in the models. The results obtained from the outputs show that the use of SMA materials in the boundary areas of the wall has a significant effect on the self-centering behavior of the wall and the energy dissipation of the shear wall is reduced by using SMA materials.

The use of reinforced concrete wall of the coupling causes better control of lateral displacement and also more energy dissipation due to the earthquake. This paper examines the types of energy demands in coupling walls in which two reinforced concrete walls are coupled by reinforced concrete beams. First, the structures are designed using the spectral analysis method according to valid regulations and then by preparing a nonlinear model of the wall with fiber elements in PERFORM-3D software and performing time history analysis due to near and near earthquakes faults, input energy, kinetic energy, energy Damping and inelastic energy are investigated and the contribution of reinforced concrete beam and wall to energy dissipation is studied. Two approaches, single plastic hinge (SPH) and extended plastic hinge (EPH), are considered for reinforced concrete walls. In the SPH approach, the plastic joint is traditionally allowed only at the foot of the reinforced concrete wall, and the rest of the wall is modeled elastically. In the EPH approach, the entire wall has the ability to expand plasticity. The results showed that in all structures, the share of coupling beams in inelastic energy dissipation is higher than the share of reinforced concrete walls. On average, in the EPH approach, the share of beam beams is about 60% and the share of reinforced concrete walls is about 40% of inelastic energy, and these numbers in the SPH approach are about 77% and 23%, respectively. The reason for the increase in the share of coupling beams from inelastic energy in the SPH model is that the wall is elastic at 90% of its height and the share of the wall decreases, and therefore the share of coupling beams in inelastic energy will increase.