CC BY
24
RESEARCH PAPER / НАУЧНАЯ СТАТЬЯ
УДК 539.3:625.84:625.717.2
DOI: 10.22227/1997-0935.2022.9.1206-1217
A parametric study of concrete runway pavement layers depression
under impact load
Hayder Abbas Ashour AlAraza1,2, Kharun Mahmud1,3
1 Peoples' Friendship University of Russia (RUDN); Moscow, Russian Federation; 2 University of Kerbala; Kerbala, Iraq; 3 Moscow State University of Civil Engineering (National Research University) (MGSU);
Moscow, Russian Federation
ABSTRACT
Introduction. Airport runway pavement is always subjected to considerable impact loads as a result of aircraft landing heavily on the concrete surface. As a result, runway pavements must have adequate strength and durability capability to avoid damage caused by a hard impact, such as surface deflection downward or penetration, because repair works are inconvenient within the operating conditions of the airport and increase the service life cost of the pavement structure. 3DFE research is carried out to identify some beneficial elements in influencing the concrete and base layers deformation of the runway pavement.
Materials and methods. The research developed 3D finite element model from the previews study by using the Explicit
Dynamics model using the Ansys workbench. The concrete characteristics such as slab thickness, concrete density, modulus
of elasticity, flexural tensile strength, and compressive strength of the runway pavement are tested, while the impactor
weight and velocity are chosen and investigated too.
H H Results. The results included the effect of 4-7 different values for each factor. The depression of the concrete and base N N
O O layers is presented.
Conclusions. The main conclusion that can be drawn from this work is that flexural tensile strength, compressive strength,
® ® and slab thickness have a significant effect on the concrete depression of the runway pavement as well as the impactor
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- — KEYWORDS: concrete runway pavement, impact load, concrete deformation, concrete depression, rigid pavement,
tQ N explicit dynamics model, Ansys Workbench, 3D finite element model . r
t- £ FOR CITATION: Hayder Abbas Ashour AlAraza, Kharun Mahmud. A parametric study of concrete runway pavement layers
2 § depression under impact load. Vestnik MGSU [Monthly Journal on Construction and Architecture]. 2022; 17(9):1206-1217.
£ 75 DOI: 10.22227/1997-0935.2022.9.1206-1217 (rus.).
'v ^ Corresponding author: Hayder Abbas Ashour AlAraza, Hayder@uokerbala.edu.iq, hayder3a@gmail.com.
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Параметрическое исследование прогиба слоев бетонного покрытия взлетно-посадочной полосы при ударной нагрузке
и Хайдер Аббас Ашур АлАраза1,2, Харун Махмуд1,3
— 1 Российский университет дружбы народов (РУДН); г. Москва, Россия;
.Е о 2 Университет Кербелы; г. Кербела, Ирак;
?Ь с 3 Национальный исследовательский Московский государственный строительный университет
й ^ (НИУ МГСУ); г. Москва, Россия
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Введение. Покрытие взлетно-посадочной полосы (ВПП) аэропорта всегда подвергается значительным ударным наел грузкам в результате тяжелой посадки самолетов на бетонную поверхность. В связи с этим покрытия ВПП должны — ^ обладать достаточной прочностью и долговечностью, чтобы избежать повреждений, вызванных сильным ударом, ^ • таких как прогиб поверхности или пробивание, поскольку ремонтные работы в условиях эксплуатации аэропорта О jj затруднительны и имеют немалую стоимость. Исследование проводится для выявления параметров, влияющих
О на деформацию бетона и базовых слоев покрытия ВПП.
^ Е Материалы и методы. Разработана Эй-модель конечных элементов на основе предварительных исследований с по-
S мощью модели Explicit Dynamics и использования рабочей среды Ansys. Рассматривались характеристики бетона,
__ такие как толщина плиты, плотность бетона, модуль упругости, прочность на изгиб и прочность на сжатие покрытия
¡^ jj ВПП, а также вес и скорость ударного элемента.
U > Результаты. Результаты включали влияние 4-7 различных значений для каждого фактора. Представлена депрессия
бетонного и базового слоев.
1206 © Hayder Abbas Ashour AlAraza, Kharun Mahmud, 2022
Распространяется на основании Creative Commons Attribution Non-Commercial (CC BY-NC)
Выводы. Основной вывод, который можно сделать, заключается в том, что прочность на изгиб при растяжении, прочность на сжатие и толщина плиты оказывают существенное влияние на депрессию бетона покрытия ВПП, а также на вес и скорость ударного элемента.
КЛЮЧЕВЫЕ СЛОВА: бетонное покрытие взлетно-посадочной полосы, ударная нагрузка, деформация бетона, углубление в бетоне, жесткое покрытие, явная динамическая модель, Ansys Workbench, Эй-модель конечных элементов
ДЛЯ ЦИТИРОВАНИЯ: HayderAbbas AshourAlAraza, Kharun Mahmud. A parametric study of concrete runway pavement layers depression under impact load // Вестник МГСУ. 2022. Т. 17. Вып. 9. С. 1206-1217. DOI: 10.22227/1997-09Э5.2022.9.1206-1217
Автор, ответственный за переписку: Хайдер Аббас Ашур АлАраза, Hayder@uokerbala.edu.iq, hayder3a@gmail.com.
INTRODUCTION
During a big aircraft landing, the airport runway surface is subjected to significant impact loading [1]. Extremely big and heavy aircraft have also been developed to accommodate travel demand, which may impose a significant impact force on runway pavement. As a result of such an impact, some neighboring regions of the top surface layer of runway pavement are penetrated or depressed. The level of damage can vary depending on parameters such as aircraft weight, velocity, and landing angle, as well as material properties and runway pavement thickness.
A few experimental, infield, and finite element-based research investigations were done to better understand the behavior of concrete/rigid runway pavement. The consequences of impact loads caused by forceful landings of big aircraft on airport runways have been studied by Ku et al. [2]. The flexible pavement on a runway at Cagliari-Elmas Airport in Italy was studied in situ for its responsiveness to aircraft operations was investigated by Al-Qadi et al. [3]. Rufino et al. conducted a comprehensive infield experiment at Denver International Airport to investigate slab-Base interaction. Gap analysis from deflection data, interface analysis from paired strain data, and comparison of predicted and observed strains were the three aspects of this technique. The gap investigation demonstrated that there are gaps between the slab and the foundation, depending on the temperature differential and slab location. Based on temperature fluctuations and slab location, a gap analysis between the slab and the Base was conducted. During the gap analysis, an effective built-in temperature difference was also identified. Despite the presence of gaps beneath the slab, the paired strain data analysis indicated contact friction or bonding action under wheel loads. The maximum contact friction was found in the slab interior, followed by doweled transverse joints and transverse dummy joints, while tied longitudinal joints showed an unexpected full-slip state. According to a comparison of observed and predicted strain, contact friction is formed when airplane gear is loaded [4]. Buonsanti et al. developed a finite elements (FE) technique to evaluate contact stresses in a flexible pavement under landing aircraft weights [5].
A comprehensive study has been conducted to evaluate runway pavement degradation and to provide
improvements, specifically for such pavement under moving aircraft loads. Kim and Tutumluer [6] used a finite element (FE) analysis to investigate the impacts of multiple wheel load interaction on the flexible runway pavement rather than a single wheel load condition under moving aircraft load.
Maitra et al. investigated the influence of contact friction on concrete pavement response. The interface friction of ordinary concrete pavements was measured using a series of push-off tests. For this purpose, concrete slabs were placed over several types of bases with smooth and rough interface conditions. The influence of various interface conditions on the critical responses of pavement
subjected to the combined action of axle load and ^ ™
temperature fluctuation was explored using parametric & t
analytical investigation and the FE technique. A negative k |
temperature gradient creates substantially higher tensile ^
stresses at the slab top when the contact between the slab S r
and the base is rough. The tensions grow considerably C y
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Caliendo and Parisi propose two specific § t 3-dimensional FE models for assessing maximum
stresses at critical sites in concrete slabs (i.e., at the interior i n
and edge) that outperform approximation approaches. § m
Research on square-shaped slabs on concrete airport § g
pavements is now underway. A homogeneous, isotropic > 6
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model to explore the influence of change in Young's c §
modulus, in contrast to Winkler's response modulus. r §
The effects of two planes (the A380 and the B747), as • C
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airplanes. The results of the FE software are also utilized 2 2 to develop a more straightforward method for determining
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maximum stresses. This predictive approach is useful for calculating stresses in the preliminary design phase more rapidly. Revisions to Westergaard's load stress model and Eisenmann's temperature stress model, as well as unique load and t actions, are required in the proposed equations. Because the method uses dimensionless variables, it may be used for a wide range of square slab dimensions [8].
An impact is an alternative method of creating a short-term dynamic reaction in a structure, similar to the loading induced by a blast event in certain ways. The layer type of the target is important in this study since the runway pavement is a layering system. When a layered-type target material is affected, stresses and strains are created. When the layer of particles in the target is squeezed, compressive stress is formed. As a result of this process, which is analogous to, stress waves are created. Only a few studies have looked into the post-cracking performance of BF HPC. This is troublesome because, in many actual applications, initial crack strength is not enhanced. The inclusion of fibers, on the other hand, helps the post-cracking reaction the most. Chopped BF and MiniBars BF have both been shown to increase the flexural toughness of concrete. However, establishing the relative worth of each product is difficult because the findings are based on different test procedures. According to the ACI Committee 544 proposed to drop weight test for impact resistance, BF can considerably enhance performance after cracking. The outcome, on the other hand, is based on data from four or six instances per concrete mix. This testing process, which demands around 40 specimens for each combination, is prone to large variations. The test process is notorious for its large variations, necessitating roughly 40 specimens per mix to keep the percent error of recorded mean values below 10 %. Li and Xu [9] observed that BF may significantly increase the energy absorption capacity of geopolymer concrete during impact loading using a Split-Hopkinson pressure bar technique. However, nothing is known regarding the impact performance of Basalt Fiber Reinforced Concrete (BFRC) in general. Because the results of impact testing obtained using various test methodologies are seldom comparable, the results of a basic test method may serve as a more practical standard against which future comparisons may be made. Because BFRC is a newer organization, this is extremely crucial.
In research by Wu et al., an intriguing technique combines a constructed multilayer pavement runway and evaluates it under blast stress. There are two sorts of slabs. A series of field explosion tests were conducted to assess the new multilayer pavement's performance in the field. Two 275 mm thick slabs of pavement were cast and tested. The initial slab, which had an Asphalt Concrete layer of 75 mm thickness, was reinforced with Geogrid, then the High Strength Concrete layer of 100 mm thickness, and lastly the Engineered Cementitious Composites layer (100 mm thickness). The second slab
was a 275 mm thick ordinary concrete pavement. The novel multilayer pavement outperformed the standard pavement system, according to the study. In addition, using 3D FE numerical modeling, the dynamic behavior of the two slabs subjected to blast stress is studied [10].
The behavior of thin slabs of High Strength-High Ductility Concrete after many moderate-velocity hits is evaluated using drop weight impact tests. High Strength-High Ductility Concrete is a fiber-reinforced cementitious composite that combines compressive strength (more than 150 MPa) and tensile ductility in a single material (more than 3 percent). Deformation processes, cracking patterns, and impact load resistance of high strength-high ductility concrete slabs are researched and compared to slabs made of Cor-Tuf, a fiber-reinforced ultra-HPC with a compressive strength of around 200 MPa. The ductile flexural behavior of the High Strength-High Ductility Concrete slabs is characterized by many tiny cracks that are equally distributed, whereas the quasi-brittle flexural and shear failures of the Cor-Tuf slabs are characterized by large, localized fractures and severe spalling. According to a FE investigation of their responses, the observed difference in structural behavior of High Strength-High Ductility Concrete and Cor-Tuf slabs is a direct result of the differential in tensile ductility of these two materials [11].
Damage such as surface penetration depth happens as a result of an airplane's landing. As a consequence, a three-dimensional FE analysis (three-dimensional FE analysis) is conducted to identify some relevant criteria for regulating the top surface penetration depth of runway pavement. The mass, velocity, impact angle, and boundary conditions of the impactor are determined as exterior factors, whereas the thickness, compressive strength, and density of materials used in the runway pavement are chosen as internal characteristics. The impact angle has a significant influence on the top surface deflection for both types of runway pavement, according to the study. When the impact angle is adjusted from 30 to 60 degrees, surface penetration of runway pavement rises by around 78 percent, whereas it increases by about 42 percent when the impact angle is changed from 60 to 90 degrees. Surface penetration improves significantly with increases in concrete compressive strength up to the normal strength concrete range (30 to 50 MPa). Again, utilizing enough high-strength concrete has been shown to help reduce surface depression [12].
Yan et al. investigated the interlayer bond quality of a double layer runway pavement using a splitting tensile test with a double layer Beam configuration. For the splitting tensile test, a 150 x 150 x 150 mm cube specimen was created, with half of the specimen made of new cement concrete and the other half made of aged cement concrete. A fiber grid was laid down on the bottom of the old cube, and the new cube was then linked to the old overlay cube. The loading velocity for the splitting tensile test was 0.08 MPa/s. The researchers found that adding fiber to concrete increases its splitting tensile
strength by up to 32 %, with 5 mm BF being the most effective. They also took strain readings in the Beam's top and bottom layers. The strain distribution in the two-layer Beam was found to be essentially linear across its depth. The lower Beam was discovered to carry the tensile load, while the higher Beam absorbed compressive stress. Horizontal friction between the interfaces of double-layer beams also lowered tensions between the top and bottom layers by 44 to 98 percent, according to the researchers. The size of the coarse aggregate, on the other hand, did not influence a concrete material component [13].
Cao studied BFRC's static and impact behaviors. Compressive, flexural, splitting tensile, and impact test properties were all included in the investigation. In addition, the effects of fiber mixing amount on concrete mechanical properties were investigated, and the appropriate fiber mixing amount was identified. The research looked at five different BF concrete mixtures as well as a control mix. According to the findings, the static and impact test behaviors of BFRC were considerably improved, and strengthening and toughening effects were accomplished. The ideal BF percentage was reported to be between 1.5 and 2 kg/m3 [14].
Fu et al. investigated the impact analysis and modeling of mineral admixture basalt polypropylene fiber reinforced concrete [15]. The impact load test was carried out with a 75 mm Split-Hopkinson pressure bar. According to the findings, the dynamic compressive strength, dynamic elastic modulus, and critical strain of basalt polypropylene fiber reinforced concrete all increased as the strain rate rose. The addition of basalt fiber (BF) and polypropylene fiber (PF) to concrete improved the strain rate effect of dynamic compressive strength and dynamic elastic modulus, as well as the deformation capacity of the concrete. PF had a greater influence on the strain rate effect of dynamic compressive strength of concrete than BF. However, there was no difference in the impacts of BF and PF on the strain rate effect on the dynamic elastic modulus of concrete. The strain rate effect of BPFRC's dynamic compressive mechanical behavior revealed a significant positive relationship with fiber hybrid volume. The proposed viscoelastic damage constitutive models from this work might be used to accurately reflect BPFRC's dynamic mechanical behavior [15]. The strain-rate influence of the dynamic compressive strength, dynamic elastic modulus, critical strain, specific energy absorption, and characteristic length of HBPRC was fully investigated. The findings demonstrated that when the strain rate grew, so did all of the HBPRC's mechanical indices. The dynamic growth factors of compressive strength and elastic modulus rose linearly as the decimal logarithm of the strain rate grew, but the critical strain and characteristic length increased linearly as the strain rate increased [16].
In response to environmental parameters, Wei et al. investigated nonlinear strain distribution in a field-instrumented concrete pavement slab. When measuring the curling and warping of a concrete pavement slab,
the strain is generally considered to be distributed linearly across the slab depth, and a plane section is expected to keep its plane after deformation. The strain distribution in a concrete slab, on the other hand, may not be linear due to the material's viscoelastic nature. This study examined the temperature and strain development at various depths in a field-instrumented concrete pavement slab starting 12 hours after construction. The nonlinear distribution characteristics of temperature and strain along the slab depth were explored at the slab corner and center. According to the measurements, temperature and strain were determined to be nonlinearly distributed together with slab thickness. The nonlinear distribution, particularly the strain, was more severe at the slab corner than at the slab center. This work presents a method for determining the slab depth and the amount of drying shrinkage induced by external drying [17].
Curling stresses of continuously reinforced concrete pavements as a function of foundation parameters were studied by Zhang [18]. A realistic evaluation of the curling Stresses of Continuously Reinforced Concrete Pavements (CRCP) under various types of bases is necessary for the reasonable design of concrete pavements. The effects of six common bases on curling stresses of CRCP subjected to temperature changes are investigated in this paper using a 2D FE technique. When establishing Base characteristics, both the factional bond-slip stiffness and the Base stiffness are taken into consideration. When compared to the vertical stiffness of the underlying Base, a stiffer foundation is shown to be desirable for CRCP in terms of concrete stress, whereas the bond-slip relationship between slab and Base (with no interface treatment) does not influence concrete stresses. The variation in steel stress between six standard bases is not significant. Due to the CRCP slab fracture, the steel is in a tensile state at the longitudinal site, and even with a small temperature differential, the maximum curling stress can be rather high [18].
The investigation by Tian et al. established a method for evaluating cumulative damage factors based on Miner's law to improve airport runway stiff pavement design [19]. This approach makes use of data from measured aircraft wheel drifts as well as built-in influence surfaces. We built an aircraft wheel wander measuring system and measured actual aircraft wheel loading locations at Shanghai Hongqiao International Airport (SHA). To generate influence surfaces, we employed finite element analysis (FEA) and multivariate interpolation. Researchers utilized FEA on a nine-slab model to simulate load transfer effects. Based on the observed wheel wander distribution and the created influence surface, a cumulative damage surface construction approach for estimating cumulative damage factors is proposed. The proposed cumulative damage surface technique offers the following preliminary benefits: (1) each load repetition's damage is addressed independently for the computation of the cumulative damage factor, and (2) the load transfer impact is considered using FEA simulations. Furthermore, the field
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data we collected at SHA reveals that the extreme value distribution better reflects aircraft wheel drift than a normal (uniform) distribution. When the maximum cumulative damage factors calculated using the extreme value distribution are compared to those estimated using the normal distribution, the maximum cumulative damage factors projected using the extreme value distribution are 210 percent higher. According to the different cases analyzed in this study, the recommended cumulative damage surface methodology gives lower cumulative damage factors values than the normal Civil Aviation Administration of China method [19].
Park et al. [20] suggest enhanced criteria for material quality and mix proportions of concrete slabs to improve the performance of concrete pavements at Incheon International Airport in the Republic of Korea. Two comparable airports were chosen for comparison with Incheon IA based on their facilities status and annual flight processing capacities. Both other airports, after Incheon International Airport, have the second and third greatest annual numbers of flights per unit area of the runway. Because of the poor quality of the aggregates used and the frequent freeze-thaw cycles, standards for aggregate and mix proportions were established to improve crack durability. When compared to the other airports, the concrete slab mix requirements at Incheon IA revealed smaller amounts of cement and liquid admixture, a higher abrasion rate of coarse aggregate, and a larger proportion of fines in the aggregate. New criteria were devised based on the comparison of outcomes. Using the updated criteria, the performance of the concrete pavement was evaluated by measuring the air content and freeze-thaw resistance of 12 mixes with varying amounts of cement, liquid admixture, and particles in the aggregate. Increases in cement and liquid admixture concentration, as well as a decrease in fines content in the aggregate, were found to improve air content and freeze-thaw resistance of the concrete runway, according to the study [20].
Studying the individual factors' implications on the infrastructures' dynamic reaction during impact via
full-scale experiments is usually out of reach. To estimate the dynamic reaction of infrastructure subjected to impact loadings with varying parameters, numerical simulation is typically used. As a result, a thorough numerical analysis was performed to investigate the important determining parameters accountable for runway concrete pavement layer and base layer deformation under the impact load. This research will begin with the verification of the numerical model on the concrete pavement by applying experimental results from previous research [21]. To accomplish this, a 3D FE model is developed using Ansys Workbench 2022R1. Following validation, a thorough parametric analysis is performed to assess the influence of various factors on the performance of runway pavement under impact loading, particularly the surface penetration depth of concrete runway pavement and base layer. These factors include impactor and concrete properties. The impactor properties used included the velocity of the impactor, impactor mass, and impactor density. While the runway concrete properties include slab thickness, concrete density, modulus of elasticity, flexural tensile strength, and compressive strength.
MATERIALS AND METHODS
In this part of the study, a methodology for developing a FE model to simulate HPC under the impact load is presented, followed by a validation of the FE model using literature data. Wu's (2018) drop weight experimental approach on a normal concrete pavement was used for validation [21]. Furthermore, the impact resistance of several different BF HPC was examined using a rigid pavement FE model that has been established. A parametric study was also conducted to investigate the impact of various parameters on the impact resistance of the validated FE models. An Explicit Dynamics analysis is used to estimate the dynamic response of a structure due to stress wave propagation, impact, or rapidly changing time-dependent loads. Momentum exchange and inertial effects between moving objects
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are typically important aspects of the studies that are conducted. This type of analysis may also be used to model mechanical processes that are exceedingly nonlinear. Materials, contact, and geometric deformation can all induce nonlinearity. This type of research can successfully duplicate events that happen in fractions of a second (typically on the order of 1 millisecond). For longer-duration events, consider using a transient analysis system1.
To confirm the experimental impact load, a 3D FE simulation was performed in Ansys Workbench Explicit Dynamic [21]. A 3D FE simulation in Ansys Workbench Explicit Dynamic was used to corroborate the experimental impact load. The study uses explicit materials since they include data that is particular to an Explicit Dynamics analysis. On top of the subgrade, a 275 mm thick concrete slab was used to construct the model. There are two strata to the subgrade. Geocell reinforced sand is found in the top sand layer, whereas compacted sand is found in the bottom layer. As indicated in Fig. 1, each subgrade layer measured 1,000 x 1,000 x 300 mm, whereas the concrete slab utilized in the experiment was 900 x 900 x 275 mm. Fig. 2 shows the drop weight apparatus that was used. The impact load of 1,181 kg was applied at the mid-point of the top surface of the concrete slab using a 100 mm hemispherical drop mass. The test used a drop height of 1.5 m with an impact velocity of 5,133 m/s. The mechanical properties of the materials used in the FE model analysis are given in Table 1-3.
Table 1. Mechanicalproperties ofconcrete slab
Fig. 2. Drop weight test machine
Parameters Value
Young's modulus E, GPa 33
Poisson's ratio v 0.2
Density p, kg/m3 2,400
Compressive strength fc, MPa 54
Flexural Tensile strength ft, MPa 2.7
Table 2. Mechanical properties of subgrade
Parameters Geocell reinforced sand Sand
Young's modulus E, MPa 103.5 40
Poisson's ratio v 0.3 0.3
Density p, kg/m3 1,600 1,600
Friction angle p, degrees 40 40
Cohesion c, kPa 89 13.8
Table 3. Mechanical properties of the Impactor
Parameters Impactor
Young's modulus E, GPa 207
Poisson's ratio v 0.3
Density p, kg/m3 118,000
Yield strength fy, MPa 500
1 ANSYS I. Mechanical User's Guide 2021-R2. Ansys. 2021; 15317(July):1028.
Element Selection and Material Modeling
Concrete Slab
The concrete model in explicit materials provided in Ansys Workbench was used to model a concrete slab. Table 1 was used to alter the parameters of the concrete slab. The elastic parameters were chosen in accordance with Wu [21], and the plastic characteristics were taken into account following Riedel et al. [22].
Subgrade
The subgrade was also modeled using the Ansys Workbench's sandstone material attributes. The elastic-plastic behavior of subgrade soil was simulated using the Drucker - Prager plasticity model. The properties of geocell reinforced and ordinary subgrade sand are listed in Table 2.
Drop Mass
In the experiment, a drop mass of 1,181 kg was employed, as indicated in Fig. 1. The impactor was modeled using explicit materials in Ansys Workbench, with the mechanical characteristics changed to match the impactor used in the experiment. In addition, to match the overall weight, a point mass was placed on the top of the impactor.
Wu's (2018) cylindrical-shaped hemispherical impactor's detailed specifications are shown in Table 3. The impactor's Stiffness Behavior is set to stiff.
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FE Meshing and Contact Modelling
The quantity and precision of meshes required for element meshing define the mesh size. Choosing the right mesh size for the FE model was crucial for accurate analytical findings and, more importantly, for high strain loading. A tiny mesh size was used for the whole model to achieve a better outcome. The concrete slab was chosen with a finer mesh size than the subgrade because it was immediately subjected to impact load. A mesh size of 5 mm for the concrete slab and 8 mm for the subgrade was chosen based on the convergence study. With linear element order, explicit mesh types are employed. The aspect ratio (Explicit) approach was utilized to create a high-quality mesh. Fig. 3 shows the Symmetric FE meshing of concrete pavement specimens.
the concrete slab. However, because the normal friction coefficient maintains within the range of 0.4-0.55 under impact loading, a dynamic friction coefficient of 0.45 was chosen at the point of contact between neighboring surfaces. Boundary Conditions and Loadings.
The fixed support condition was applied on the Subbase bottom. Two sides of the Subbase, two sides of the Base, and two sides of the concrete pavement were believed to have symmetric support. On the other two sides, there was no restriction on the use of the concrete pavement. On the other two sides of the Base and Subbase, the displacement boundary condition is utilized. The impactor's other vertical sides were kept from moving to the side. For all bodies, the standard Earth Gravity is specified.
Validation of FE Model
The outcomes of Wu's drop weight impact tests were compared with the results obtained from the Developed FE model of concrete pavement specimens. The Researcher found the greatest vertical deflections at three sites on the top surface of the concrete pavement specimen [23] (see Fig. 4).
Fig. 3. Symmetric FE meshing of concrete pavement specimens
A generic contact algorithm was used to characterize the interaction between a hemispherical impactor and a concrete pavement specimen. By linking together, the contact surfaces of the concrete slab and the subgrade, the surface-to-surface interaction between the concrete slab and the subgrade was calculated. The hard contact formula was used to characterize normal stress behavior in both the general and surface-to-surface contact approaches, while the penalty frictional formulation was used to define tangential stress behavior at contact surfaces. A similar modeling approach was utilized to simulate the interaction between the textile belt and
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Fig. 4. Selected locations to measure deflections by Wu (2018)
As a consequence, the symmetric FE model was confirmed at the three sites with the maximum vertical deflections. The highest downward deflections observed in the impact test and computed using FE analysis at these three specified locations of the concrete pavement specimen exposed to a single impact force at a velocity of 5,133 m/s are shown in Table 4. The experimental and FE models were found to accord rather well. The FE result was found to be about 1.03, 0.99, and 0.99 for the P1, P2, and P3 sites, respectively, with Coefficients of Variation of 0.0245, 0.0065, and 0.0343.
Table 4. Maximum deflections ofconcrete slab under the impact load
Location Maximum deflection in FE analysis, mm Maximum deflection in experimental investigation of Wu (2018), mm FE result/experimental result Coefficient of variation, CoV
P1 26,992 26.07 1.03 0.0245
P2 26,811 27.06 0.99 0.0065
P3 26,654 27.98 0.99 0.0343
In the FE analysis, penetration in the region of the impact loading application directed the failure of a concrete slab, which was determined to be the same as Wu's experimental test. Based on Wu's impact test, Fig. 2. 16 displays the concrete pavement failure mechanisms. As a consequence, the constructed FE model properly anticipated the behavior of the concrete pavement specimen, and the confirmed FE model was used in the parametric analysis described in the following sections.
RESULTS OF THE RESEARCH
The effects of various factors on the behavior of a concrete slab (900, 900 and 275 mm thick) to impact loads were studied using parametric research. More importantly, parametric research was conducted to assess the influence of various factors on the concrete slab's deflection. The impact load's influence on the deformation of both concrete and sand layers was determined using parametric research. There were three types of parametric studies in the research. Concrete and impactor characteristics were among these. The slab thickness, concrete density, modulus of elasticity, and compressive and flexural tensile strength were among the concrete parameters. The velocity and weight of the impactor were among the impactor attributes. The investigation also discovered that the concrete's Poisson ratio had no effect.
Slab Thickness
A thicker pavement slab would enhance the structure's bending resistance and provide greater protection for the base and subbase layers when subjected to static or dynamic stresses. On the other hand, the thickness of the pavement slab cannot be extended forever. In rigid pavement design, the slab thickness was commonly specified at 200 to 300 mm [24].
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225
300
250 275
Slab Thickness, mm
Total Sand A Concrete
Fig. 5. Slab thickness effect on the deformation
Four different thicknesses of concrete slabs were chosen to explore the effect of slab thickness on modifying the deflection of concrete slabs under impact loading: 225, 250, 275, and 300 mm. The compressive strength of the concrete was maintained at 54 MPa. Variation in concrete slab deflection as a function of concrete slab thickness is shown in Fig. 5. As the slab thickness grows, the deflection of the concrete slab decreases within the prescribed values, as shown in Fig. 5. The deflection in the Sand layer and concrete slab layer was reduced by 3.75 and 6.4 percent, respectively, when the slab thickness was raised from 225 to 250 mm. When the thickness of the Sand and Concrete layer was extended to 300 mm, the decrease climbed to 11 and 18.3 percent, respectively. As a result, the slab thickness is expected to have a significant influence on impact deflection.
Concrete Density
The density of the concrete used for the concrete slab was chosen as 2,300, 2,350, 2,400 and 2,400 kg/m3, with a constant concrete slab thickness of 275 mm and concrete compressive strength of 54 MPa, to investigate the influence of concrete density on the deflection of the concrete slab under the impact load. Fig. 6 shows how the deflections of a concrete slab and sand layer vary as the concrete's density varies. The deflection of the concrete slab was reduced by 3.7 percent and the deflection of the sand layer was reduced by 1.3 percent when the concrete density was increased to between 2,300 and 2,350 kg/m3. The amount of sand deflected reduced by 0.6 to 1.8 percent. Furthermore, the concrete deflection fell from 0.65 to 3.7 percent. The deflection was marginally reduced by the concrete density.
Modulus of Elasticity
To investigate the effects of the modulus of elasticity on the deflection of the concrete slab under the impact
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load, the modulus of elasticity of the concrete used for the concrete slab was chosen as 33,000, 36,000, 40,000 and 45,000 MPa, with a constant concrete slab thickness of275 mm and concrete compressive strength of 54 MPa. Fig. 8 demonstrates how the deflections of a concrete slab and sand layer change as the modulus of elasticity changes.
Fig. 7 shows that increasing the modulus of elasticity from 30 GPA to 33,000 MPa reduced the deflection of the concrete slab by 0.5 percent while increasing the deflection of the sand layer by 0.4 percent. As the modulus of elasticity increased from 36,000 to 40,000 MPa, the sand deflection reduced from 1.6 to 1.74 percent, respectively. The concrete deflection, on the other hand, increased from 0.53 to 0.41 percent. When the modulus of elasticity is between 45,000 and 50 MPa, the concrete deflection decreases by 1.3 to 3.0 percent. Furthermore, the sand deflection rose from 1.74 to 2.3 percent.
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strength was increased to 10 MPa. The concrete deflection reached 38.1 percent when the flexural tensile strength reached 15 MPa. As a result, the concrete slab's deflection was greatly reduced by the flexural tensile strength.
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Fig. 7. Modulus of elasticity effect on the deformation
Flexure Tensile Strength
To investigate the impact of concrete flexure tensile strength on the deflection of concrete slabs under impact loading, four different flexure tensile strength values for the concrete slab were chosen: 2.7, 5.0, 10 and 15 MPa. The concrete slab's thickness was set at 275 mm. Fig. 8 shows how the deflection of the concrete slab changes with the concrete's Flexure Tensile.
The distortion of the sand layer dropped by 2.4 percent as the flexural tensile strength increased from 2.7 to 5 MPa, and by 4.7 percent when the flexural tensile strength reached 10 MPa, before progressively increasing. Furthermore, an increase in flexural tensile strength only results in a considerable reduction in concrete slab deformation. The deformation was reduced by 8.3 percent when the flexural tensile strength was increased from 2.7 to 5 MPa, and by 24.5 percent when the flexural tensile
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Flexural tensile strength, MPa Total Sand A Concrete
Fig. 8. Flexural tensile strength effect on the deformation of concrete slabs
Compressive Strength
To investigate the influence of concrete compressive strength on the deflection of concrete slabs under impact loading, four different compressive strength values for the concrete slab were chosen: 50, 54, 60 and 65 MPa. The concrete slab's thickness was set at 275 mm. The deflection of the concrete slab changes with the compressive strength of the concrete, as illustrated in Fig. 9.
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Compressive strength, MPa Total Sand A Concrete
Fig. 9. Compressive strength effect on the deformation of concrete slabs
The sand layer deformed by 6.2 percent when the compressive strength climbed from 50 to 54 MPa, by 4.9 percent when the compressive strength reached 60 MPa, and by 2.3 percent when the compressive strength reached 65 MPa. Furthermore, increasing compressive strength only leads to a significant decrease in concrete slab deformation. When the compressive strength was increased from 50 to 54 MPa, the deformation was decreased by 4.7 percent, and by 8.3 percent when the compressive strength was increased to 60 MPa. When the compressive strength reached 65 MPa, the concrete deflection fell by 15.7 %. As a result, the concrete slab's compressive strength greatly reduced slab deflection.
Impact Velocity
To test how impact velocity influenced the deflection of the slab under the impact load, the impactor's impact velocity was adjusted to 4,000, 5,000, 6,000 and 7,000 mm/s for a concrete slab with a constant weight of 1,181 kg. The consistent impact weight of181,000 kg indicates that the impactor's weight was constant regardless of impact velocity. The impactor was cylindrical and featured a hemispherical drop head. The impactor was 100 mm in diameter. Fig. 10 depicts the variation in deflection as a function of impact velocity.
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to 5,000 mm/s, 57.2 percent when the velocity reached 6,000 mm/s, and 86.9 percent when the velocity reached 7,000 mm/s. Furthermore, increasing velocity only resulted in a considerable increase in concrete slab deformation. The deformation rose by 41.3 percent when the velocity was increased from 4,000 to 5,000 mm/s, and by 78.8 % when the velocity was increased to 6,000 mm/s. When the velocity of the concrete reached 7,000, the deflection increased by 137.8 %. As a result, the velocity of the impactor greatly increased slab deflection.
Impactor Weight
The influence of impact weight on deflection was studied using a hemispherical drop head impactor with an impact mass of 1,181 kg. The impact weights of the impactor were set at 800, 1,000, 1,200 and 1,400 kg. The impactor's velocity and other factors were held constant. The impactor's impact weights were set to produce sufficient deflection on the top surface of the concrete slab. Because the FE model of the concrete slab was validated using an impact test, the impact weight values were chosen to be close to the original impactor weight. Fig. 11 shows how the deflection varies with different impact weights.
Fig. 11 shows that as the weight of the impactor increased, so did the deflection of the concrete slab and Sand layer. When the impactor weight was increased to 1,000, 1,200 and 1,400 kg, the deformation in the sand layer rose by 9.7, 16.2 and 23.3 percent, respectively, compared to the initial position. As a result, the distortion of the concrete slab rose dramatically as compared to the starting position (800 kg). When the impactor weight was raised from 800 to 1,000 kg, 1,200 and 1,400 kg, the deformation rose by 26.3, 56.6 and 86.2 percent, respectively. This section of the paper should demonstrate the author's methodical analytical and statistical content.
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Total Sand ö Concrete
Fig. 10. Velocity effect on the deformation of concrete slabs
Fig. 10 shows that as the impact velocity increased, the deflection of the concrete slab increased in a nonlinear fashion. The four impact velocities were chosen because the range was considered to be large enough to generate significant deflection. It is obvious that the low velocity has no significant deflection, however choosing a larger velocity resulted in damage to the selected specimen. The deformation of the sand layer increased by 27.6 percent when the velocity climbed from 4,000
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Fig. 11. Impactor weight effect on the deformation of concrete slabs
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CONCLUSION AND DISCUSSION
Ansys Explicit dynamics were used to do a finite element analysis to validate the concrete pavement model under impact loads using test findings from the literature. Following validation, parametric experiments were carried out to assess the impact of several factors on the deflection of the concrete pavement under the impact load. The following are the important conclusions from the impact research of concrete pavement:
• as the thickness of the concrete slab increased, the deflection of the slab was reduced. With each mm increase in slab thickness;
• the concrete density and the modulus of elasticity have an insignificant effect on the deflection of the slab within the range used;
• the flexural tensile strength increased the deformation of the concrete slab decreased significantly;
• increasing the compressive strength of the concrete leads to a decrease in the deformation of the slab;
• the impact velocity and impactor weight were shown to have a substantial influence on the deflection of the concrete slab's top surface.
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Received June 6, 2022.
Adopted in revised form on June 24, 2022.
Approved for publication on September 14, 2022.
B i on ot e s : Hayder Abbas Ashour AlAraza — postgraduate student of the Department of Construction; Peoples' Friendship University of Russia (RUDN); 3 Ordzhonikidze st., Moscow, 115419, Russian Federation; PhD Candidate at Civil Engineering Department, Department of Civil Engineering; University of Kerbala; Kerbala, Iraq; hayder@ uokerbala.edu.iq;
Kharun Mahmud — Professor of the Department of Civil Engineering; Peoples' Friendship University of Russia (RUDN); 3 Ordzhonikidze st., Moscow, 115419, Russian Federation; Doctor of Technical Sciences, Professor [ е of the Department of Reinforced Concrete & Stone Structures; Moscow State University of Civil Engineering (National n H Research University) (MGSU); 26 Yaroslavskoe shosse, Moscow, 129337, Russian Federation; miharun@mail.ru. k и
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Принята в доработанном виде 24 июня 2022 г. J 9
Одобрена для публикации 14 сентября 2022 г. ° —
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Об авторах : Хайдер Аббас Ашур АлАраза — аспирант кафедры строительства; Российский университет дружбы народов (РУДН); 115419, г. Москва, ул. Орджоникидзе, д. 3; кандидат технических наук, инженерно- О 3 строительный факультет; Университет Кербелы; г. Кербела, Ирак; hayder@uokerbala.edu.iq; t I
Харун Махмуд—профессор кафедры строительства; Российский университет дружбы народов (РУДН); С S 115419, г. Москва, ул. Орджоникидзе, д. 3; доктор технических наук, профессор кафедры железобетонных и каменных конструкций; Национальный исследовательский Московский государственный строительный университет (НИУ МГСУ); 129337, г Москва, Ярославское шоссе, д. 26; miharun@mail.ru.
Вклад авторов: все авторы сделали эквивалентный вклад в подготовку публикации. Авторы заявляют об отсутствии конфликта интересов.
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