Inspection and Assessment of Masonry Arch Bridges: Ivanjica Case Study

The importance of masonry arch bridges as a traffic network element calls for a thorough analysis focused on both structural stability and loading capacity of these historical structures, considering the usage of these bridges in contemporary traffic conditions. This paper focuses on the analysis of longitudinal cracks in a single span masonry arch bridge to evaluate its influence on structural behaviour of the system. As longitudinal cracks do not necessarily present an inevitable collapse mechanism, analysis of the causes is crucial for evaluating the serviceability and functionality of the bridge investigated. The methodology is based on the following: literature review, observation of the stone bridge in Ivanjica, geological testing of the site, geophysical testing of the bridge, laboratory testing of mechanical characteristics of stone used for the bridge construction and biological analysis of the samples of implemented materials on the bridge. Finite element analysis of the bridge was conducted to define the causes of the longitudinal cracks. The 3D simulation model was based on the data collected through observation and experimental analysis. This paper provides extensive research on a single span masonry bridge, examining how different deterioration mechanisms, in conjunction, can lead to the appearance of cracks in masonry arch bridges and provide remedial measures accordingly.

Case Study: Road Embankment Foundation on Weak Organic Soils

The paper presents the problem of embankment foundation during reconstruction and extension of regional road 110 on the section Witomierz - Grądy. On this section the road crosses the valley of meltwater formed during the last Weichselian glaciation. It is a watershed area between the streams Stuchowska Struga and Otoczka Reska. In the Holocene a 961 ha fen peat called Wielki Smogorze has been formed. There are favorable conditions in the area for the formation of fen peats. The thickness of the peats is over 4 m, reaching almost 8.0 m in its peak. Since 1964 the Przybiernówko-Grądy II deposit (402 ha) is continuously exploited. Currently, the deposit is being used by a company called "Lasland". Extraction is conducted on the basis of a relevant concession within a designated mining area of 242.9 ha. The mining concession is valid until the end of 2030. The pits are deep and are located on both sides of the regional road no. 110. Peat is transported by narrow-gauge railroad to the nearby processing plant, where it is sieved, sorted and packed. Based on the analysis of available archival materials, the road as found today was functioning already in the middle of the 19th century. In the 1970s the road was widened to 6.0m In 2003 due to the bad condition of the surface the asphalt layer was renovated by applying a grid and new asphalt layers. During the renovation longitudinal cracks have been reported and there were problems with the compaction of the mix. The direct cause was the shallow layer of peat located just 1.1 - 1.3 m under the road. Conducted renovation did not bring expected results, so in 2019 the documentation for the reconstruction of the road was prepared. Different methods of road foundation were analyzed, from soil replacement through the use of piles. In the end the decision was made to directly settle the embankment with the use of geosynthetics. This study presents a selected solution and shows the results of calculations. Changes during the execution of the reconstruction were discussed. The applied solution allowed for simultaneous functioning of the mining plant and reconstruction of the regional road on the section of 1.2 km. geotextiles and geonets were used. The main argument for such solution was relatively low cost of reconstruction and time of execution. During construction there were problems with obtaining the parameters on the substructure for asphalt layers. Two alternative solutions were proposed, one of which required increasing the thickness of embankment reinforced with geo-mesh and an additional layer of CBGM mix substructure. The solution allowed to meet the design requirements and complete the reconstruction according to the plan without any problems.

INFLUENCE OF CONCRETE CORROSION FROM THE INTERACTION OF ALKALIS OF CEMENT WITH REACTIVE AGGREGATES ON DAMAGE TO REINFORCED CONCRETE SLEEPERS IN A TRACK

The article analyses the causes of cracks and other damage in reinforced concretesleepers. The effect of concrete corrosion, which is caused by the interaction of cement alkalis withreactive aggregates, on damage to sleepers has been established. The significance of each of thereasons has been established. Corrosion of concrete sleepers, which is caused by the reactionbetween alkalis and silicic acid - Alkali-Silica Reaction (ASR), in Ukraine was initially caused by ahaphazard change in suppliers of aggregates and cement. Also it influenced by the modernization ofthe production of cement plants, which led to an increase in the content of alkalis in cement by morethan 0.6%. Of all concrete structures, corrosion from ASR proceeds faster precisely in the railwaytrack structures - its signs appear on average after 2.8 years of operation, and the foundations ofoverhead catenaries - after 3 years. For other structures, these signs appear later - for bridgestructures after 3.7 years, for road surfaces - after 6.9 years. This is due to the peculiarities of thedesign and operating conditions of the sleepers, including, possibly, the effect of leakage currentsadditional to the water cut. The corrosion rate from ASR in structures in Ukraine is much higher(signs of corrosion appear on average after 2.2 years) than in the countries of North America, Central and Northern Europe (6.1 and 6.4 years, respectively). This is due to the wider use of additives inconcrete, a better regulatory framework and a culture of compliance in these countries. ASR directlycauses 15.5 % of defects, contributes to the formation and development of 32.8% of defects to thegreatest extent, does not affect 30.9 % of defects at all, and to a limited extent contributes to theemergence and development of other 20.8 % of defects. The effect of corrosion of concrete from ASRon the occurrence of damage (defects) in sleepers is explained by the fact that as a result of ASRtensile stresses arise in concrete, which lead to the formation of a spatial network of microcracks anda decrease in the tensile strength of concrete. Since the prestressing of the reinforcement has createdtensile stresses in the transverse direction, predominantly longitudinal cracks occur in the sleepers.Prestressed reinforced concrete structures are more vulnerable to damage caused by ASR concretecorrosion than conventional reinforced concrete or concrete structures.

Enhanced the Efficiency of Enzymatic Hydrolysis on Wheat Straw via Freeze-thawing Pretreatment

This research was investigated to enhance the efficiency of enzymatic hydrolysis on wheat straw via freeze-thawing pretreatment, and to find the physicochemical structural changes after this pretreatment. Results show that, this pretreatment enhances the enzymatic hydrolysis efficiency of cellulose and hemicellulose, and hemicellulose is more susceptible to this pretreatment. The highest enzymatic hydrolysis efficiency of cellulose and hemicellulose was 57.06% and 70.66% occurred on -80℃, 24 h and -10℃, 24 h pretreated samples, with an improvement of 2.23 and 3.13 folds of control. SEM images exhibited that transverse cracks appeared before longitudinal cracks as pretreated conditions aggravated, and holes can be found on every sample after this pretreatment. FTIR and XRD analysis implied that freeze-thawing pretreatment had effect both on the crystalline and amorphous regions, and disrupted the hydrogen bonds among them. This study provided a physical pretreatment method to improve the efficiency of enzymatic hydrolysis on wheat straw.

Experimental and Numerical Analyses of the Thermal Regime of a Traditional Embankment in Permafrost Regions

Traditional embankment is widely used in the permafrost regions along the Qinghai-Tibet Railway (QTR) because of its simple construction and lower cost. However, this form of embankment has insufficient ability to resist external thermal disturbance. To clarify the thermal characteristics of traditional embankment under climate warming, the ground temperature change process of section K1068 + 750 of the QTR was analysed in this study. Based on the field monitoring data from 2006 to 2019 and the established heat transfer model, the past and future changes of permafrost thermal regime under the embankment were analysed. The results show that the degradation of permafrost under the embankment is faster than that under the undisturbed site due to the combined of embankment construction and climate warming. The sunny-shady slope effect related to embankment orientation makes the distribution of permafrost temperature under embankment asymmetric. In the long term, permafrost degrades both under the undisturbed site and embankment. The continuous degradation of permafrost causes the settlement and deformation of embankment, especially the asymmetric degradation of permafrost on sunny side and shady side will cause longitudinal cracks on the embankment. Therefore, timely application of strengthening measures which can slow down the degradation of permafrost and adjust the uneven ground temperature on the sunny and shady sides under the embankment is of great significance to the safety of the traditional embankment.

In-Plane Shear Strength of Single-Lap Co-Cured Joints of Self-Reinforced Polyethylene Composites

The present study introduces the analysis of single-lap co-cured joints of thermoplastic self-reinforced composites made with reprocessed low-density polyethylene (LDPE) and reinforced by ultra-high-molecular-weight polyethylene (UHMWPE) fibers, along with a micromechanical analysis of its constituents. A set of optimal processing conditions for manufacturing these joints by hot-press is proposed through a design of experiment using the response surface method to maximize their in-plane shear strength by carrying tensile tests on co-cured tapes. Optimal processing conditions were found at 1 bar, 115 °C, and 300 s, yielding joints with 6.88 MPa of shear strength. The shear failure is generally preceded by multiple debonding-induced longitudinal cracks both inside and outside the joint due to accumulated transversal stress. This composite demonstrated to be an interesting structural material to be more widely applied in industry, possessing extremely elevated specific mechanical properties, progressive damage of co-cured joints (thus avoiding unannounced catastrophic failures) and ultimate recyclability.

Pixel-Level Recognition of Pavement Distresses Based on U-Net

This study develops and tests an automatic pixel-level image recognition model to reduce the amount of manual labor required to collect data for road maintenance. Firstly, images of six kinds of pavement distresses, namely, transverse cracks, longitudinal cracks, alligator cracks, block cracks, potholes, and patches, are collected from four asphalt highways in three provinces in China to build a labeled pixel-level dataset containing 10,097 images. Secondly, the U-net model, one of the most advanced deep neural networks for image segmentation, is combined with the ResNet neural network as the basic classification network to recognize distressed areas in the images. Data augmentation, batch normalization, momentum, transfer learning, and discriminative learning rates are used to train the model. Thirdly, the trained models are validated on the test dataset, and the results of experiments show the following: if the types of pavement distresses are not distinguished, the pixel accuracy (PA) values of the recognition models using ResNet-34 and ResNet-50 as basic classification networks are 97.336% and 95.772%, respectively, on the validation set. When the types of distresses are distinguished, the PA values of models using the two classification networks are 66.103% and 44.953%, respectively. For the model using ResNet-34, the category pixel accuracy (CPA) and intersection over union (IoU) of the identification of areas with no distress are 99.276% and 99.059%, respectively. For areas featuring distresses in the images, the CPA and IoU of the model are the highest for the identification of patches, at 82.774% and 73.778%, and are the lowest for alligator cracks, at 14.077% and 12.581%, respectively.

IMPLEMENTATION OF ROOT CAUSE ANALYSIS METHOD TO INVESTIGATE FAILURE OF FRONT WALL TUBE BOILER

Root cause analysis is a method that observes on all of possible causes that can make the system or components fail. This research is implemented such method to investigate failed front wall tube on the boiler. The purpose of this research is to find out the main cause of failure on front wall tube in order to avoid similar problem in the future.  With considering all aspects that have potential to be the main cause of failure therefore, many tests and examinations are done including visual test, fractography, metallography, chemical analysis, hardness test, SEM and EDS analysis.  Examination result on the fracture surface shows two bulges on a tube and some longitudinal cracks spread on bulges outside surface area. While thick scale is also found on inside surface of these bulges. Moreover microstructure and hardness changes are also found on this area.  From all of tests result that obtained it is concluded that the main cause of failure is the presence of scale that reduce heat transfer, so that local over heating occurred. Consequently, its tensile strength in this area is decreased and finally tube could not support operational pressure and deformed to make bulge.     Root cause analysis is a method that observes on all of possible causes that can make the system or components fail. This research is implemented such method to investigate failed front wall tube on the boiler. The purpose of this research is to find out the main cause of failure on front wall tube in order to avoid similar problem in the future.  With considering all aspects that have potential to be the main cause of failure therefore, many tests and examinations are done including visual test, fractography, metallography, chemical analysis, hardness test, SEM and EDS analysis.  Examination result on the fracture surface shows two bulges on a tube and some longitudinal cracks spread on bulges outside surface area. While thick scale is also found on inside surface of these bulges. Moreover microstructure and hardness changes are also found on this area.  From all of tests result that obtained it is concluded that the main cause of failure is the presence of scale that reduce heat transfer, so that local over heating occurred. Consequently, its tensile strength in this area is decreased and finally tube could not support operational pressure and deformed to make bulge.    Â

Fracture analysis of a nonhomogeneous beam with two concentric cylindrical longitudinal cracks

This paper is concerned with the analysis of the fracture behaviour of a nohomogeneous cantilever beam with two concentric longitudinal cracks. The beam has a circular cross-section with linearly varying radius along the beam length. Moreover, the beam exhibits continuously varying material inhomogeneity in the radial direction. The fracture is analyzed in terms of strain energy release rate assuming nonlinear mechanical behaviour of the material. For this purpose, solutions for the strain energy release rate are derived by considering the energy balance. Two cantilever beam configurations with different lengths of longitudinal cracks are analysed. Moreover, the two cracks are arranged arbitrarily in the radial direction. The longitudinal fracture behaviour of the beam is also analysed by considering the complementary strain energy for verification. The strain energy release rate solutions are used to investigate the influence of varying radius of the cross section along the length of the beam on the longitudinal fracture behaviour. The effects of crack lengths and the location of the two concentric cracks in the radial direction on fracture are also studied. The influences of the loading conditions of the beam and the inhomogeneity of the material in the radial direction on the fracture behaviour are also evaluated.

Evaluation of Premature Cracking in Urban Concrete Pavement

This study investigated the causes for premature, transverse cracking on urban jointed plain concrete pavements in Illinois. A field survey of 67 sections throughout Illinois coupled with ultrasonic evaluation was completed to synthesize the extent of premature cracking on urban JPCP. The visual survey showed some transverse and longitudinal cracks were a result of improper slab geometry (excessive slab length and width). Ultrasonic tests over the contraction joints determined some notched joints had not activated and adjacent transverse cracks were likely formed as a result. Three-dimensional finite-element analyses confirmed that cracking would not develop as a result of normal environmental factors and slab-base frictional restraint. The concrete mixture also did not appear to be a contributing factor to the premature cracks. Finally, the lack of lubrication on dowel bars was determined to potentially be a primary mechanism that could restrain the transverse contraction joints, produce excessive tensile stresses in the slab, and cause premature transverse cracks to develop.