Abstract: This study introduces an eddy current thermography technique that can be used to detect and evaluate steel corrosion in a reinforced concrete structure. The rate of surface temperature changes in reinforced concrete is proposed as a means to characterize the degree of steel bar corrosion. The rate of surface temperature changes increased gradually with an increase in the corrosion degree. The influence of structural parameters on the rate of the temperature change was analyzed in detail. The results indicated that the rate of surface temperature change increased with a decrease in the concrete cover depth and with an increase in the humidity of the concrete, and this was affected by the diameter of the internal steel bar. Concrete cover was the most significant factor that affected the rate of the surface temperature change, except for the corrosion degree. The variations in the surface temperature of reinforced concrete can be explained using the law of electromagnetic induction and the electrochemical property change of corroded steel bar. This research provides a reliable basis for real-world applications and is helpful to understand the application scope of eddy current thermography technology for the quantitative detection of steel corrosion. PubDate: Mon, 24 Feb 2020 15:20:00 +000

Abstract: The paper presents a framework for the seismic analysis of the coupled high-speed train-bridge with the isolation of friction pendulum bearing (FPB). Taking the rail irregularities as system’s self-excitation with the seismic as external excitation, the equation of motion of the train-bridge coupled system under earthquake is built up. A five-span simple-supported railway bridge is taken as an example, and the computer simulation method is used to establish the dynamic model of the train-bridge system with the isolation of FPB under earthquake. A train composed of eight 4-axle coaches of 35 degrees-of-freedom (DOF) is considered, and FPB is simulated by a force element which includes both nonlinear spring and damper characteristics and a hysteresis function. Backward differentiation formula and the mode superposition method are adopted in the calculation of coupling vibration of the train-bridge system. The dynamic responses of the train running on the bridge with the isolation of FPB and with the common spherical bearing (CSB) under earthquake are studied. The results show that FPB with a friction coefficient no less than 0.05, instead of CSB, can reduce the dynamic response of the train greatly; the faster the train speed and the higher the pier, the greater the effect of FPB. However, FPB may increase the dynamic response of the train when the seismic intensity exceeds 0.14 g. PubDate: Mon, 24 Feb 2020 12:50:00 +000

Abstract: The horizontal differential layer element method was used to study the active earth pressure of the finite-width soil formed by the rigid retaining wall for the embankment or adjacent foundation pits. The cohesionless soil was taken as the research object, and the soil arch theory was introduced based on the translation mode of rigid retaining wall and the linear sliding fracture surface. The minor principal stress line was assumed as circular, considering the deflected principal stress as soil arching effect. The shear stress between level soil layers in the failure wedge was calculated, and the differential level layer method was modified. Then, the theoretical formula of the active earth pressure, the resultant earth pressure, and the point of application of resultant earth pressure were obtained using this revised method. The predictions by the proposed formula were compared with the existing methods combined with the cases. It is shown that the resultant finite pressure increases gradually and approaches to Coulomb active earth pressure values when the soil is infinite, with the increase of the ratios of the backfill width to height. Moreover, the horizontal pressure for limited soils is distributed nonlinearly along the wall height. Considering the shear stress between level soil layers and the soil arching effect, the position of application point of the resultant active earth pressure by the proposed formulation is higher than that of Coulomb’s solution. The wall is rougher, and the resultant pressure will be smaller. The application point distance from the bottom of the wall will increase. Finally, an experiment was conducted to verify the distribution of the active earth pressure for finite soil against rigid retaining wall, and the research results agree well with those of the experimented observations. PubDate: Mon, 24 Feb 2020 12:35:00 +000

Abstract: The carbonation behavior of lime-stabilized expansive soil is important for assessing the stabilization efficiency from the perspective of durability. In this study, the accelerated carbonation tests, measurement of pH value distribution, and the free swell ratio tests were conducted to investigate the evolutions of carbonation depth, carbonation extent, and expansive potential of lime-stabilized expansive soil. XRD, MIP, and SEM techniques were adopted as supplements to reveal the carbonation mechanism. Results demonstrated that the carbonation depth of lime-stabilized expansive soil increased significantly as time elapsed; however, the rate of increase reduced when the carbonation time increased. Higher carbonation depth was obtained at higher temperature and CO2 concentration and lower relative humidity, which was described by an empirical model. Fully, partly, and noncarbonated zones were subsequently presented with an increase in the depth of the soil. The expansive potential of lime-stabilized expansive soil was partially recovered during carbonation. The obtained linear relationships between the free swell ratio and pH value were adopted to describe the evolution of expansive behavior with carbonation time and depth. In microstructural analysis, the conversion of portlandite into calcium carbonate was significant, which resulted in changes in microstructure and controlled the carbonation behavior. PubDate: Mon, 24 Feb 2020 05:20:01 +000

Abstract: As porous, heterogeneous, and anisotropic material, the microscopic structure of the rock has a significant influence on its mechanical properties. Rare studies were devoted to this area using pore scale modeling and simulations. In this paper, different types of sandstones are imaged using micro-CT technology. The rock porosity is obtained by filtering, binarization, and threshold segmentation. The texture coefficient (TC) and the tortuosity of the rock skeleton are calculated by open source program, where the tortuosity of the rock skeleton is firstly used to characterize the microscopic structure of the rock. Combining with the rock mechanics parameters obtained in the laboratory, the simulation of uniaxial compression is performed on the reconstructed pore scale rock finite element mesh model by ANSYS software. Young’s modulus, compressive strength, yield strength, shear modulus, and other related parameters obtained by numerical simulation are adopted to determine the optimal representative volume element (RVE) size. Moreover, the effects of microscopic structure characteristics on the mechanical properties of the rock are studied quantitatively. The results indicate that the averaged von Mises stress distribution, displacement field, and plastic strain field of rocks show anisotropy and heterogeneity. The stress concentration and the X-shaped conjugate plastic shear zone are investigated. The samples of S1∼S4 reach the elastic limit and enters the plastic yield state, when the strain is about 0.5%. And the critical yield strain of samples S5300-1∼S5400-2 is about 1%. Then, the quantitative relationships between porosity, TC, tortuosity of rock skeleton and rock mechanics parameters of digital rock samples are established and analyzed. The tortuosity of the rock skeleton is highly correlated with the mechanical parameters of the rock, i.e., Young’s modulus (R2 = 0.95), compressive strength (R2 = 0.94), yield strength (R2 = 0.92), and shear modulus (R2 = 0.94), which is believed to be more feasible to reveal the impacts of the microstructure of the rock on its mechanical properties. PubDate: Mon, 24 Feb 2020 03:20:01 +000

Abstract: Concrete creep plays a significant role in the long-term performance of the prestressed concrete structure. However, most of the existing prediction models cannot accurately reflect the in-site concrete creep in a bridge construction environment. To improve the prediction accuracy of creep effects in concrete structures, an innovative creep analysis method is developed in this study. Parameters in the creep model in fib MC 2010 have been calibrated with respect to the long-term loading test results of the prestressed concrete beam. The measured strains of concrete and the midspan deflections of the test beam are compared with the predicted results using the creep model in fib MC 2010. It indicates that the results predicted by the calibrated creep model are in good agreement with the test results. However, the results predicted by the creep model in fib MC 2010 significantly deviate from the test results. This proposed creep analysis method can provide a new thought to improve the predicted effect of the creep effects on creep-sensitive structures. PubDate: Mon, 24 Feb 2020 03:05:01 +000

Abstract: Urban rail transit is an effective way to deal with the problem of traffic congestion in major cities. Trains travel through dense residential and commercial areas, providing convenient transportation while also result in vibration problems in the surrounding environment. Long-lasting vibrations result in disturbance to people’s sleep, malfunction of sensitive equipment, and even damage to heritage buildings. Compared with elevated and tunnel sections, ground surface urban railway generates vibrations and propagates to the surroundings via a more direct path in the form of surface waves, which makes the environmental problem more prominent. Due to the complexity of the train-track-ground system, the characteristics of the vibration propagation and attenuation are yet to be revealed. In this paper, we investigate the vibration of the ground and the subgrade next to the Beijing Urban Rail Line 13 by a field measurement combined with a mathematical model. The duration of ground vibration is divided into two parts: the train passing time and the Doppler effect-related tailing part. Through a regression analysis of the duration, the train passing time is identified and the train traveling speed is estimated. The attenuation relationship of ground vibration intensity is expressed by a piecewise function. In the subgrade, the vibration intensity of particle decays with increasing depth and the stress decay rate is faster than that of the acceleration. The dynamic wheel/rail interaction behaves stationary and periodic, and the magnitude fluctuates up and down with the quasi-static axle weight. The intensity attenuation relationship fitted in this paper provides a basis for designing new lines and renewing old lines and can be used as a reference for the development of vibration-reduction technology. The simulated time history of the wheel-rail force provides an excitation sample for further model experiments and numerical simulation. The proposed train speed identification method may be useful for parameter identification of moving sources such as ships, automobiles, and airplanes. PubDate: Mon, 24 Feb 2020 02:35:01 +000

Abstract: Rebound hammer tests and postinstalled pull-out tests are commonly used for evaluating the compressive strength of ordinary concrete, and the strength of concrete is estimated by strength curves. However, using these strength curves to predict the compressive strength of carbon fiber-reinforced concrete (CFRC), polypropylene fiber-reinforced concrete (PFRC), and carbon-polypropylene hybrid fiber-reinforced concrete (HFRC) may lead to considerable uncertainties. Therefore, this study revises the strength curves derived from rebound hammer tests and postinstalled pull-out tests for ordinary concrete. 480 specimens of fiber-reinforced concrete (FRC) of six strength grades are examined. Standard cube compressive strength tests are used as a reference, and the results of various regression models are compared. The linear model is determined as the most accurate model for postinstalled pull-out tests, whereas the power model is the most accurate for rebound hammer tests. The proposed strength curves have important applications for FRC engineering of the postinstalled pull-out tests and rebound hammer tests. PubDate: Mon, 24 Feb 2020 02:20:01 +000

Abstract: Rutting is a major distress occurring in the service life of the asphalt pavement, especially in hot weather areas. A laboratory-produced specimen is widely used for rutting performance evaluation which may not be completely represented by the field situation. The objective of this study is to evaluate the rutting performance of field specimens from the Chongqing highway by utilizing the Hamburg wheel-tracking test (HWTT) and dynamic modulus test. Different test conditions were conducted on the HWTT by investigation of the actual local weather condition. The results showed that rutting depth was different under different test conditions, and 10000 loading cycles were recommended as the maximum loading cycles. Particularly, several factors that influence the rutting depth were investigated, and the specimen height of 6 cm is more appropriate for the HWTT. Additionally, different test conditions were proposed as the HWTT test condition for different asphalt concrete (AC) layers in the Chongqing area. Rutting contribution of each AC layer to the pavement structure was analyzed. Moreover, the dynamic modulus at 54.4°C, 5 Hz and 54.4°C, 1 Hz could effectively represent the rutting performance of the asphalt mixture, and the dynamic modulus test is recommended for the rutting performance evaluation of the full-thickness AC layer. PubDate: Mon, 24 Feb 2020 02:05:03 +000

Abstract: Floods are seen in countries in tropical climatic zones, both in terms of quantity and harm. The non-tropical climate countries such as Turkey are also affected by the floods. The geographical structure of Turkey is extremely complex and varies even at short distance. Therefore, the shape and effects of the floods vary from region to region. Considering the peculiar state of nature, floods, which are the greatest disasters after the earthquake, are unlikely to occur. But floods are becoming more risky for human beings day by day because of the population growth, need of water and settlements, wrong zoning plan, and unplanned engineering practices. Regulation comes at the beginning of measures to be taken to minimize the damages that occur from the floods. To do these studies, it must be specified the changes which bridges on the rivers and hydraulics structures like regulator cause in cross sections and the effects of the changes to water surface profile due to the natural state of the land. In order to determine water surface profiles, many software packages have been developed for facilitating the analysis and calculation. HEC-RAS is one of them. In this study, the floodplain analysis was handled between Diyarbakır-Silvan Highway and historical Ten-Eyed Bridge. There are three bridges, and one of which are historical bridges, as well as fertile agricultural lands, facilities, and hospitals in the Dicle University campus, the Hevsel Gardens on the UNESCO World Cultural Heritage List, and some residential areas on the route under study. The aim of the study we have done in this much important route is to evaluate the flood areas and create a flood hazard map which can predict risky areas. And also contributing to the Tigris River Rehabilitation Project is one of the aims. About methodology, the 1/1000 maps of the study area were digitized using the AutoCAD Civil 3D program and cross sections were made by obtaining the digital elevation models of the region. The obtained cross sections were defined in the HEC-RAS software, and the hydraulic characteristics of the flood bed and the water surface profiles of the Q25, Q50, Q100, and Q500 flood recurring and one-dimensional floodplain analysis of the Tigris River were determined. PubDate: Mon, 24 Feb 2020 02:05:02 +000

Abstract: During the thermal recovery of heavy oil when using cyclic steam injection technology, a microannulus tends to form at the cementing interface subjected to high temperature and pressure during steam injection, and large temperature and pressure differences after injection can lead to wellbore integrity failure. In this study, a thermomechanical coupled finite element casing-cement-formation model of a thermal recovery wellbore is established. The deformation of the wellbore during both the steam injection stage and the steam shutdown stage is analyzed. The microannulus formation mechanism at the cementing interface of the wellbore is studied. During steam injection, under the large thermomechanical coupling load, the wellbore generates a high stress that leads to elastic-plastic deformation. In the steam shutdown stage, with the load on the wellbore decreasing, elastic deformation recovers mostly, while plastic deformation continues. If the plastic deformation is large enough, a microannulus will form at the cementing interface. Increasing the elastic moduli of the casing, cement, and the formation can enlarge their plastic deformation during steam injection. The increase of plastic deformation of the cement or formation can enlarge the microannulus of the casing-cement interface or the cement-formation interface correspondingly in the steam shutdown stage. PubDate: Sat, 22 Feb 2020 12:20:02 +000

Abstract: This study aimed to investigate the influence of loosely bound water (LBW) on the compressibility of compacted fine-grained soils and accurately determine the soil’s compression index. Four fine-grained soils (i.e., heavy clay, heavy silt, lean clay, and lean silt) and a coarse-grained soil were examined. The volumetric flask method was used to measure the LBW contents of the five soils. X-ray diffraction (XRD) analysis was then performed to test the mineral compositions and help explain the reason why the LBW content varied between different soils. A concept of modified void ratio was proposed by assuming that LBW is a part of the solid phase in soil. Subsequently, consolidation tests and permeability tests were conducted on saturated compacted specimens. The results show that the compression indexes or permeability coefficients tend to be the same for the soils with identical initial modified void ratios. Consolidation tests were also carried out on the unsaturated compacted heavy silt of four different dry densities prepared at a water content higher than the optimum. They show that the compression of unsaturated soil occurs if pore air is discharged when the water content is less than the LBW content. This confirms the previous assumption that LBW can be regarded as a part of the soil solid phase. A modified compression index was deduced and implemented to predict the settlement of a road embankment. The result suggests that the modified compression index is capable of calculating the compression of fine-grained soils, whose water contents are higher than their LBW contents. PubDate: Sat, 22 Feb 2020 08:05:02 +000

Abstract: This paper aims to evaluate the resistance performance of the vinyl acetate ethylene polymer cement (VAEPC) composite and the polyvinyl alcohol fiber-reinforced cement (PAFRC) composite against a low-velocity impact in varying temperature. Their impact resistance performances are analyzed and compared with plain mortar after 28 days of age. Low-velocity impact tests were carried out under the various room temperatures of −70°C, 70°C, and 140°C. Also, an INSTRON CEAST 9350 drop-tower system has been used to get the impact load, fracture energy, and displacement of the specimens while loading low-velocity impacts. From these tests, the failure pattern, shape, and strength of each test specimen were evaluated for the VAEPC, the PAFRC composite, and the plain mortar. Those test results showed that the flexural strength of both the VAEPC and the PAFRC composites has increased compared to that of the plain mortar. However, the compressive strength of the PAFRC composite decreased slightly after 28 days, while its flexural strength increased by 24.4% compared to that of the plain mortar. In addition, the drop test results show that PAFRC composite specimens have the highest impact fracture energy compared to other specimens at −70°C, 70°C, and 140°C, whereas plain mortar specimens have their lowest. This is because the PVA fiber included in the PAFRC acts as a bridge to suppress crack propagation and to improve energy absorption performance, which helps it resist relatively better against impact. It is also known that while the VAEPC composite and the plain mortar were destroyed in a form of being perforated, the specimens of PAFRC composite were observed to some extent to suppress the perforation failures. Therefore, under a load of low-velocity impact, the resistance performance of the VAEPC composite and the plain mortar was proven to show brittle fracture behavior, while the PAFRC showed ductile fracture behavior in virtue of PVA fiber reinforcement which improved its flexural performance. According to the SEM observation which followed the tests, the PAFRC composite as a fiber-reinforced material of the hydrophilic material was found to show the most excellent interfacial bond adhesion compared to the other composite and the plain mortar. The PAFRC composite manufactured in the study has been proven to be very useful as a reinforcement material in both high and low temperature environments. PubDate: Sat, 22 Feb 2020 08:05:01 +000

Abstract: Settlement simulating in cohesion materials is a crucial issue due to complexity of cohesion soil texture. This research emphasis on the implementation of newly developed machine learning models called hybridized Adaptive Neuro-Fuzzy Inference System (ANFIS) with Particle Swarm Optimization (PSO) algorithm, Ant Colony optimizer (ACO), Differential Evolution (DE), and Genetic Algorithm (GA) as efficient approaches to predict settlement of shallow foundation over cohesion soil properties. The width of footing (B), pressure of footing (qa), geometry of footing (L/B), count of SPT blow (N), and ratio of footing embedment (Df/B) are considered as predictive variables. Nonhomogeneity and inconsistency of employed dataset is a major concern during prediction modeling. Hence, two different modeling scenarios (i) preprocessed dataset (PP) and (ii) nonprocessed (initial) dataset (NP) were inspected. To assess the accuracy of the applied hybrid models and standalone one, multiple statistical metrics were computed and analyzed over the training and testing phases. Results indicated ANFIS-PSO model exhibited an accurate and reliable prediction data intelligent and had the highest predictability performance against all employed models. In addition, results demonstrated that data preprocessing is highly essential to be performed prior to building the predictive models. Overall, ANFIS-PSO model showed a robust machine learning for settlement prediction. PubDate: Sat, 22 Feb 2020 08:05:00 +000

Abstract: The Bohai Sea is the sea area with the worst ice condition in China, and the ice loads significantly threaten the safety of structures in the sea. The intense vibrations of the pile-supported bridge under stochastic ice loads will increase the fatigue damage of a bridge structure and reduce the fatigue life of a bridge structure. In the present study, a comprehensive analysis model is presented to study fatigue damage for pile-supported bridges under ice loads in Bohai Sea. On the basis of measured statistical data of ice parameters and stochastic ice loads spectrum of Bohai Sea, the time histories of the stochastic ice loads of Bohai Sea are simulated. Fatigue damage analysis is carried out in time domain utilizing the finite element method considering soil and bridge structure interaction. The effect of soil conditions and water depth on the cumulative fatigue damage of the pile-supported bridges is studied. Numerical results indicate that in comparison with stiff soil conditions, pile-supported bridges in soft oil conditions can increase the cumulative fatigue damage substantially; pile-supported bridges in deep water also can increase the cumulative fatigue damage obviously. The study presented the first danger position of cumulative damage of the pile cross section under stochastic ice loads. The findings of this study can be used to fatigue damage evaluation and bridge construction in the ice-covered sea area. PubDate: Fri, 21 Feb 2020 13:35:00 +000

Abstract: To study the influence of the debris accumulation caused by the continuous collapse of the postearthquake building structure on the avoidance distance of the road red line, taking the typical masonry structures of three stories, five stories, and seven stories as examples, this study simulates the process of sloughing collapse and the positive and negative collapse along the Z axis of the building structure under 28 different seismic conditions in details. Taking “the flying stones” into consideration, this study divides the influence distance of the collapsed building structure under earthquakes into (a) the safety distance during earthquakes and (b) the main influence distance of the debris accumulation after the earthquake. In this study, two types of movement laws of flying stones are analyzed statistically first. Then, the statistical analysis and hypothesis testing are carried out on the main influence distance of all the debris accumulation using the influence width coefficient, and the main influence distance distribution probability models of the debris accumulation of the collapsed building structure under earthquake excitation are established. The distribution models include the gamma distribution and the extreme value type III along the Z axis and the normal distribution probability model along the X axis. Finally, a simplified calculation table of the influence distance of collapsed building structures is established. It provides a scientific basis for the safe control distance of buildings to avoid the road red line and for the minimum distance between the buildings and people after a destructive earthquake. PubDate: Fri, 21 Feb 2020 07:20:01 +000

Abstract: Ballasted railway track is an important factor that forms railway transportation over the world, which may face severe damage during operation due to the deterioration of the track ballast geometry. A practical method of evaluating train moving load-induced vertical superimposed stress in substructure by incorporating the effects of ballast characteristics and multilayered substructure is presented. The proposed method is validated by comparing with the field measurements compiled from the literature with the calculated value. It is found that the prediction accuracy of the proposed method is within ±10%, in comparison with field measurements. Meanwhile, it should be emphasized that the predicted value by traditional methods was 1.4–5.0 times field measurements. Also, key factors affecting the predicted accuracy are identified through parameter analysis by using the proposed and the traditional methods. PubDate: Fri, 21 Feb 2020 06:05:00 +000

Abstract: “Covering effects” dominated by water vapor migration in arid and semiarid areas threaten the stability of engineering entities. To explore the “covering effects” dominated by water vapor migration under the influence of diurnal temperature variations, a series of one-side evaporation experiments were conducted. Characteristics of water vapor migration between the unsaturated loess soil column with and without a lid were compared in detail to illustrate the “covering effects” on water vapor migration, as were the effects of test time. Further, the characteristics of “covering effects” in loess and sand soil columns were compared. The results show that the “covering effects” formed in the loess soil column with a lid by cycling day and night temperature differences led water vapor to accumulate and condense beneath the lid. However, unlike the “covering effects” during freezing conditions that lead to a significant increase in the moisture content in the top layer, in this study, the moisture content in the top layer (0–8 cm) decreased. Although “soil lid” and the “soil covering effects” exist in both loess soil columns with and without lids, the “soil covering effects” for the former are much more obvious, and the moisture content in the upper part of the loess soil column (8–45 cm) shows a significant increase. By cycling day and night temperature differences, the “covering effects” or “soil covering effects” grew as the test time increased. Compared to the loess soil column, the “covering effects” in the sand soil column were extremely weak, and the moisture migration in the sand soil column was dominated by the downward movement liquid water. This paper illustrates the “covering effects” under the influence of diurnal temperature variations and reveals the mechanism of water vapor migration in subgrade soils in arid and semiarid areas. PubDate: Fri, 21 Feb 2020 05:05:00 +000

Abstract: This study presents a finite element model to investigate the bidirectional seismic behavior of masonry infill walls. The test data are utilized to verify the numerical model. The comparison between the analytical and the experimental results indicates that the finite element model can successfully predict the failure mode, stiffness, and strength of the masonry infill wall. Based on the model, the effects of aspect ratio (height to length), slenderness ratio (height to thickness), and masonry strength on the out-of-plane (OOP) response of infill wall with in-plane (IP) damage are explored. Considering the aspect ratio, slenderness ratio, and masonry strength of infill wall, the OOP behavior of infill wall with and without IP damage is studied. Finally the reduction of the stiffness and strength in the OOP direction, due to the IP damage, is discussed. PubDate: Fri, 21 Feb 2020 04:05:02 +000

Abstract: Bridge washouts connected to flood events are deemed one of the main reasons for structural collapse. Compared to traditional continuous jointed bridges, integral abutment and jointless bridges (IAJBs) have better lateral stability because there are no expansion devices. The mechanical performance of Shangban IAJ bridge, located in Fujian, China, is thoroughly investigated by Finite Element Analysis (FEA). The numerical model is created and validated based on experimental results obtained from static load tests performed on the bridge. A detailed parametric analysis is carried out to assess the correlation between the flood-resistant performance and a number of parameters: skew angle, water-blocking area, span number, pile section geometry, and abutment height. Except for the abutment height, other parameters significantly affect the bridge performance. Furthermore, the change in the span number has a meaningful impact only when fewer than four spans are modeled. Finally, pushover analyses estimate the maximum transverse displacement and the sequence of plastic hinge creation as well as the mechanical behaviour of the structure under lateral flood loads. The analysis results show that IAJBs have better flooding-resistant performance than conventional jointed bridges. PubDate: Fri, 21 Feb 2020 04:05:01 +000

Abstract: This article is the second part of the series of the comprehensive review which is related to the outrigger and belt-truss system design for tall buildings. In this part, by presenting and analyzing as much relevant excellent resources as possible, a guideline for optimum topology and size design of the outrigger system is provided. This guideline will give an explanation and description for the used theories, assumptions, concepts, and methods in the reviewed articles for optimum topology and size design. Finally, this part ended up with a summary for the findings of the reviewed studies, which is useful to understand how different parameters influence the optimum topology and size design of a tall building with outrigger and belt-truss system. PubDate: Fri, 21 Feb 2020 04:05:00 +000

Abstract: The traditional source-site-structure model for the calculation of seismic response of underground structures at near-source sites is restricted by the grid scale and the size of the structure. As a result, an excessive number of elements in the model make the numerical solving process difficult. To solve problems such as an inefficient computation and challenging nonlinear simulation, a multiscale analysis method for the calculation of the seismic response of underground structures at near-source sites is developed. The generalized free-field seismic response of the near-source region is obtained by establishing a large-scale calculation model of the source site and is used to simulate the fracture mechanism of faults and the process of seismic wave propagation. Then, using the method of seismic wave input based on artificial boundary substructures, the free-field motion of the wave is transformed into the equivalent seismic load, which is the seismic wave input data for the small-scale region of interest. Finally, with the help of local elements with special shapes to realize the grid transition of different scales, a small-scale model with reasonable soil-underground structure interaction is established, and the seismic response of the overall model can be effectively solved. The calculation and analysis of the seismic response of underground structures in irregular terrain are carried out. Compared with the results obtained directly from the source-site-structure model, the multiscale method has satisfactory accuracy and meets the needs of engineering design. Since the number of elements is fewer and the calculation time is much shorter than those required by the traditional model, the advantages in computational efficiency of the new method are highlighted. In addition, the reflected waves are too weak to have a considerable impact on structures because of the great energy loss at the reflection interface, which further proves the feasibility of the closed artificial boundary substructure method. PubDate: Thu, 20 Feb 2020 05:50:02 +000

Abstract: The effects of Reynolds number (Re) and surface roughness on the wind pressure coefficient on a MAN type dry gas tank were analyzed in detail by wind tunnel tests. A wind load calculation model was then established, which is suitable for the wind resistant design of the gas tanks. The test results revealed that in the range of 7 × 105 PubDate: Thu, 20 Feb 2020 03:20:00 +000

Abstract: To calculate the required strength of a cemented backfill with high aspect ratio, the confirmation of lateral pressure is fundamental and needs to be determined first. As for the backfill with a high aspect ratio of height to length, the shape of the slip surface is not straight when in the active state due to the limited space, which is different from the general backfill. For this reason, a formulation of the slip surface with a curved shape and a lateral pressure calculation method based on this curved slip surface were proposed. The proposed equation of the slip surface is affected by the geometry parameters of the backfill, internal friction angle of the backfill, and the friction angle of the backfill-rock interface. Then, by the combination of the minor principal stress trajectory method and the horizontal slice method, an ordinary differential equation of stresses was established and then solved numerically. Finally, the method based on Mitchell’s three-dimensional limit equilibrium model was used to calculate the required strength of the cemented backfill. The calculated results were compared with previous studies and validated with numerical models. The results showed good consistency for the backfills with high aspect ratios. PubDate: Wed, 19 Feb 2020 14:05:03 +000

Abstract: Creep generally showed a great impact on the temperature stress of concrete structure. At present, little research has been done on the creep law of cemented sand and gravel (CSG), and the calculation of creep temperature stress mainly adopts a set of relevant parameters. In this context, experimental compressive creep tests were carried out on the specimens of large-sized cylinders with different cementing agent contents; the creep temperature stress of CSG was also calculated. The results showed that the creep of CSG increased with the increase of cementing agent content, but the specific creep was not obvious. In addition, the creep model of CSG with high accuracy was also obtained, which could provide a basis for the numerical simulation of CSG dam. Furthermore, the results of numerical simulation showed that creep has a great influence on the stress of CSG dam, and the thermal stress energy was less than 37%. At the same time, it was necessary to determine whether temperature control should be considered according to different cementing agent content and external climate conditions, which cannot be generalized. PubDate: Wed, 19 Feb 2020 09:50:00 +000

Abstract: Over the past two decades, project governance has attracted increasing attention from researchers and practitioners worldwide and has become an important research area of project management. However, an inclusive quantitative and systematic analysis of the state-of-the-art recently available research in this field is still missing. This study attempts to map the global research on project governance through a state-of-the-art review. A total of 285 bibliographic records were retrieved from the Web of Science Core Collection database and analyzed by the visual analytic tool—CiteSpace. The results indicated that there has been an increasing research interest in project governance. The most productive and the most highly cited author in the area of project governance is Müller R., and most of the existing project governance research achievements are from Australia, China, USA, and Norway. By synthetically analyzing the keywords, future research might focus on governance of megaprojects and project success. Additionally, 9 knowledge domains of project governance were identified, including conceptual framework, public projects, governance structure, governance context, megaproject governance, contractual and relational governance, sustainability, portfolio governance, and project success. This study contributes to the body of knowledge by mapping the existing project governance research. It is particularly helpful to new and early-stage researchers who plan to do research on project governance, as it can provide them an overview of project governance research, including key authors, main institutions, hot topics, and knowledge domains. Moreover, the findings from the study are beneficial to industry practitioners as well, as they can help industry practitioners understand the latest development of governance theory and practice and thereby help them locate the best governance strategies for project management. PubDate: Wed, 19 Feb 2020 08:20:01 +000

Abstract: Slope evaluation is a basic geotechnical engineering issue. The rationality of index weight greatly affects the accuracy of evaluation results in the evaluation system. Furthermore, in practical engineering, some indexes can be considered random variables obeying a certain distribution. Traditional evaluation methods of slope stability ignore the effect of this index uncertainty. Therefore, it is necessary to obtain the evaluation results of slope stability reasonably by modifying the previous weighting methods and considering the uncertainty values of the indexes. A new method has been introduced to solve the problem mentioned previously based on TOPSIS (Technique for Order Preference by Similarity to Ideal Solution) and Monte Carlo simulation (MCS). TOPSIS is used as a basic model for evaluating slope stability. TOPSIS and MCS are coupled to establish multiobjective optimization simulation model, which can search the more optimal and reliable weight. The optimal weight is then substituted into the TOPSIS basic model to calculate the status of slope stability. In this calculation process, MCS is introduced into the TOPSIS basic model to consider the uncertainty value of index. The new method of evaluating slope stability was demonstrated by taking a practical project as an example. Compared with other weighting methods, the coupled TOPSIS and MCS model can obtain the most reliable weight, and the reliability is 48.7%. Then, the evaluation of slope stability was examined with the certainty and uncertainty cases, respectively. The results demonstrate that the proposed new evaluation method is more realistic than the traditional methods for evaluating the slope stability. The new method has high accuracy and is easy to use. PubDate: Wed, 19 Feb 2020 08:20:00 +000

Abstract: A new type of explosion-resistant biomimetic layered honeycomb structure was designed based on the natural mechanism and biological inspiration, which was mainly composed of a sacrificial layer and a bearing layer. The shock tube device was adopted to analyze the dynamic response of the biomimetic layered honeycomb structure under the action of explosion load in order to obtain the deformation modality, deflection data, and strain time-history curve of the structure. It turns out that the maximum deformation deflection of the back panel of the structure is only 28 mm. Compared with the structure of single-layer honeycomb, the independent sacrificial layer, and bearing layer, the biomimetic layered honeycomb structure has good explosion-resistant performance and can repeatedly bear multiple explosion loads. Besides, equivalent homogenization theory was employed to carry out numerical simulation. The results show that the numerical simulation results are perfectly in line with the results of experiments, and the numerical simulation method is proven to be feasible and effective. Under the action of explosion load, the biomimetic layered honeycomb structure absorbs energy mainly by sacrificial layers that are in layered and staggered arrangement. In addition, the sharp rangeability of the kinetic energy of bearing layer structure indicates that it has the feature of large mass, which can be used as the bearing part of the biomimetic layered honeycomb structure. PubDate: Wed, 19 Feb 2020 07:50:01 +000

Abstract: In order to improve the accuracy of shield tunneling parameter matching under the limited data, the matching model based on support vector machine (SVM) and exponential adjustment inertia weight immune particle swarm optimization (EAIW-IPSO) is proposed. The nonlinear relationship model between the tunneling parameters and the ground settlement is constructed by SVM and trained with the actual engineering sample data. Based on the trained model, EAIW-IPSO is used to optimize the tunneling parameters. At the same time, UI interface was developed based on the tunneling parameter matching model. The matching model based on BP neural network and PSO algorithm is compared in simulation experiments and engineering case. It is verified that the matching model based on SVM and EAIW-IPSO still maintains great accuracy and stability as the number of samples continues to decrease. The paper provides a better solution for the matching of tunneling parameters in actual engineering. PubDate: Tue, 18 Feb 2020 13:05:00 +000

Abstract: Frost damage in permafrost tunnels is very common, and this can have a negative influence on traffic. The most serious frost damage typically occurs at a certain length from the tunnel opening. Thus the antifreeze measures of the lining structure in this area need to be strengthened. In this study, the antifreeze disease fortification length for permafrost tunnels is determined from heat transfer and mathematical physics equations by the theoretical analysis method. The temperature distribution characteristics of the lining along the tunnel axis under the influence of the tunnel depth, the tunnel radius, the wind velocity at the tunnel opening, and the thermal conductivity of the insulation layer are analysed. The results show that the longitudinal temperature characteristics in the tunnel axis are influenced by many factors. The proposed antifreeze disease length of the permafrost tunnel was found to be approximately 31 times of the tunnel diameter, which agrees with the results of the numerical simulation. It verifies the rationality of the theoretical calculation. This value, 31 times of the tunnel diameter, can be used as a reference for the design of the tunnel antifreeze disease fortification length. PubDate: Tue, 18 Feb 2020 08:05:00 +000