Major Crack Research Articles

Contesting crack modes modeling of reinforced concrete structure threatened by the progressive rust expansion in rebars in the presence of external load

Disastrous concrete cracks as initiated by rebars pit corrosion and the resulted rust expansion have continually threatened the vitality of the reinforced concrete structures. In investigating the effects attributed to the rust expansion, existing scholastic works have, however, either focused only on examining one type of major crack or disregarded the influence of the external loading. Therefore, various contesting crack modes of the reinforced concrete structure due to rust progressive expansion from the rebars pit corrosion under external load are analytically modeled in this paper. To begin, such a multi-factors incident has been formulated under the premise of a thick cylindrical section with plane strain conditions and the new consideration of external loading. Considered major contesting crack modes include those of vertical, diagonal, and horizontal. Furthermore, a novel experimentally complying expansion ratio relating the rust expansion with the corrosion penetration depth is introduced into the model. Concrete cover thicknesses are categorized via the fracture mechanics process zone length, LFPZ, in determining the crack mode. In conclusion, thin covers are dominated by the vertical crack whereas thicker covers may crack diagonally or horizontally, depending on LFPZ and the crack tip deformation state. The rust expansion reduces both the moment capacity and the critical crack time to reach the concrete cover surface. tcr, while the critical corrosion penetration depth increases with the concrete cover thickness. However, the horizontal crack when dominating can offset this concrete cover effect by significantly reducing tcr. Additionally, the rust expansion affects the concrete cracking more than the external load.

Evaluation of structural defects and the dynamic of stress and strain on a building along Oluwole Area, Southwestern Nigeria

This research was carried out within the Basement Complex terrain along Oluwole, off Akure High School, Akure, Ondo State, Nigeria, with the aim to ascertain the reasons for the major cracks and sign of apparent failures observed in a building few years after its construction and usage. The geophysical investigation involved two electrical resistivity techniques; Vertical Electrical Sounding (VES) using the Schlumberger configuration and 2-D electrical imaging using Dipole-dipole electrode configuration. Three traverses were established E–W direction cutting across geologic strike with a distance of 100 m and of varying inter-traverse spacing. Six (6) VES stations were occupied covering the entire study area for layer stratification and geoelectric parameters. The results were qualitatively and quantitatively interpreted and are presented as sounding curves and geoelectric sections. The 2-D imaging gave information on the subsurface characteristic in the area with generally low apparent resistivity indicating low competence material. The results obtained from the VES delineated four to five geoelectric units which comprise of the topsoil, moderately clayey sand layer, the partially weathered layer, resistive partially fractured basement and fresh basement. The results from the VES were used to determine the second order parameters. The entire results correlate well with one another showing that all the techniques used were complemented. This study has further justified the inevitability of geophysical site investigation for necessary foundation evaluation before embarking on any construction of any kind.

Seismic performance of shear-critical prefabricated reinforced masonry shear walls with innovative vertical joint connections

The in-plane seismic behavior was investigated for five single-story reinforced masonry shear walls (RMSWs) (four prefabricated and one cast-in-place) subjected to an axial compressive load and reverse lateral excitation. An innovative vertical joint connection method for the prefabricated RMSWs was developed. The variables under study were the level of axial compressive stress, horizontal reinforcement ratio, and construction method. The experimental results showed that all walls had a similar failure mode with diagonal cracking. However, the crack distribution depended strongly on the construction method. The bearing capacity of the walls increased with the applied axial compressive stress and amount of horizontal reinforcement. The prefabricated walls showed better post-cracking performance than the cast-in-place wall. The wall secant stiffness decreased rapidly to approximately 60% of the initial stiffness when the first major diagonal crack occurred. The idealized equivalent elastic–plastic system indicated that the prefabricated RMSWs had greater displacement ductility of 2.6–4.7 than the cast-in-place RMSW. The equivalent viscous damping for the walls was 0.10–0.20 at 0.32% drift, which indicates that RMSW buildings can be expected to provide a high level of damping to reduce the seismic demand.

Fire resistance of stiffened CFDST columns after earthquake-induced damages

Abstract Despite the awareness about the hazard gained through the past evidence, fire following an earthquake remains a predominant agent of damage to buildings and life-line structures. Often the damage caused by the subsequent fire can be more severe than the damage caused by the ground motion itself. Concrete filled double skin tube (CFDST) columns as a special composite structure are particularly prone to the inadequate steel-concrete interface bonding and subsequent local buckling during separate fire conditions and seismic action. To establish a favorable interface interaction between steel and concrete as well as to postpone overall buckling under post-earthquake fire, the effectiveness of stiffening CFDST columns with longitudinal steel stiffeners are investigated. The analyses on CFDST columns with different patterns of stiffeners embedded in the interior or exterior surfaces of the inner or outer tubes are conducted with a sequentially coupled approach, starting with a heat transfer analysis and followed by a stress/deformation solution. In the finite element modeling, the confinement provided by both the inner and outer tubes on the compressive strength of concrete is accounted for. The effect of concrete fracture is incorporated by inserting a horizontal discrete crack model at the location of the major tensile crack. The results showed that stiffeners on the exterior surface of the inner tubes are among the most effective of various patterns studied in enhancing the fire endurance of the columns up to 64%. For stiffened CFDST columns contrary to the unstiffened ones, the fire-resistance reduction to seismic damage is usually less than 5% of the initial value. The fire-resistance rating reduction obtained for hollow ratios of 0.5 is 58%, with respect to the hollow ratio of 0.25.

Fracture Properties and Restrained Shrinkage Cracking Resistance of Cement Mortar Reinforced by Recycled Steel Fiber from Scrap Tires

Thanks to better processing technology, quality recycled steel fiber (RSF) is routinely extracted from scrap tires, offering opportunities to reinforce cementitious materials in a more economical and sustainable manner. In this study, a detailed experimental program on cement mortar reinforced by up to 2 vol. % RSF was carried out. The work involved conventional tests to characterize cement mortar mechanical properties including compressive strength, elastic modulus, and splitting tensile strength. It also featured an innovative semi-circular bending (SCB) fracture test to characterize fracture-related properties, and a customized ring test to study the cracking resistance under restrained drying shrinkage of the studied mortars. The combined use of the fracture and ring tests is believed to lead to a better assessment of concrete structure behaviors in the field. Based on the test results, the addition of up to 2% RSF shows noticeable improvement on the splitting tensile strength, but it has marginal effects on the cement mortar compressive strength and elastic modulus. The improved fracture properties of the cement mortar reinforced by 2% RSF from the SCB fracture test demonstrate that the RSF-reinforced mortar not only has a better resistance to the initiation of major cracks but also exhibits an enhanced post-cracking performance. Based on the ring test results, the longer cracking time and higher residual strain level of the 2% RSF mortar samples clearly reveal that the RSF could effectively delay and bridge cracks.

Recommendations for rehabilitation and corrosion protection of a 100-year-old steel bridge (Durgadee) across heavily polluted river near Mumbai, India

This paper describes the rehabilitation proposal, methodology of evaluation of distress and likely remedial measures for 100 years old steel bridge on Ulhas river, near Mumbai. The bridge is constructed in year 1914 during British era apparently now heritage bridge as it was constructed with unique structural arrangement of jack arch decking and warren truss girder with verticals. After structural audit in 2000, it revealed the deterioration of steel parts and concrete initiated long back because of humid atmosphere and pollution in the area. Durgadee bridge showed various signs of bridge distress like major cracks in masonry abutments, heavy corrosion of Mild Steel (MS) structural members, non -functioning of expansion joints and bearings, failure of jack arch roof plates, de-bonding of concrete and exposed reinforcement etc. Paper discusses recommendations for rehabilitation and corrosion protection.

OPTICAL SENSOR PREPARATION USING THE SOL-GEL TECHNOLOGY FOR DISSOLVED AMMONIA DETECTION

The sol-gel route was utilized to prepare an optical sensor for the detection of low concentration of dissolved aqueous solution of ammonia. Several alcohols were tested to find a good solvent for dopant immobilization. Thus isobutyl alcohol was shown to be a suitable choice. The materials were characterized using the light microscopy and powder XRD techniques and no major cracks and deteriorations detected. Prepared films show a linear relationship to the concentration of ammonia in a wide range.

A Robust Automated Vision Based Filamentous Steel Strip Crack Detection System Based on Neuron Model Segmentation

Crack detection has always been a dominant requirement for steel industries to ensure quality production and seamless infrastructure maintenance. However, application complexities and defect morphological differences make existing approaches confined. Steel-strip surface often undergoes scratch, crack and fatigue conditions during production. Manual crack detection schemes are no longer effective in current day complex environment. Amongst major steel strip crack detection approaches vision based techniques have found potential; Filamentous crack which is caused due to fatigue or strain is fine-grained and thin and hence highly difficult to be detected by classical morphology and static threshold based schemes. In the present work steel strip surface (filamentous) crack detection system has been developed which employs Varying-Morphological Segmentation (VMS) also called Neuron-Model Segmentation (NMS) in conjunction with local directive filtering and active contour propagation. The proposed method can be stated as an augmented variational framework that employs multi-directional filters for local crack-region identification followed by automated multi-directional region growing and iterative contour evolution which performs level set energy minimization to achieve accurate crack detection even under topological non-linearity and varying illumination conditions Simulation results with standard benchmark data has confirmed that the proposed method exhibits satisfactory performance for steel strip surface cracks.

Anchorage of naturally corroded, plain reinforcement bars in flexural members

Reinforced concrete structures are often damaged by corrosion, which affects the interaction between reinforcement bars and concrete. Earlier studies mostly applied artificial corrosion to test the bond between deformed bars and concrete. However, there is a lack of knowledge on the effects of natural corrosion on plain bars. In this paper, 20 beams with naturally corroded plain bars and varying amount of damage were taken from an 80-year-old bridge and tested in three-point bending. All but three of the specimens anchored the yield force of the bars after the opening of one or two major bending cracks. At large deflections, the load-carrying mechanism changed from beam to arch action. Eventually, end-slip of the reinforcement bars was observed. The bars were extracted, cleaned, three-dimensionally scanned, and tested in tension. The average bond strength in the unyielded zone was found to be equal to 7.39 MPa, with a standard deviation of 3.33 MPa. The casting position was identified as an important factor: when uncorroded, bottom-cast bars had a higher bond strength than that of top-cast bars. However, they were more prone to splitting cracks and, consequently, loss of bond strength for small corrosion levels. Top-cast bars had increasing bond strength with increasing corrosion levels, owing to the absence of external cracks. These differences were likely related to a denser concrete surrounding the bottom-cast bars. The remaining bond capacity in the yielded zones was evaluated to be approximately 1.0 MPa.

Axial compressive behavior of engineered cementitious composite confined by fiber-reinforced polymer

A novel hybrid member made from two kinds of composite materials, ductile engineered cementitious composite (ECC) as the core material and linear elastic fiber-reinforced polymer (FRP) as the confining material was proposed for application. A series of axial compressive experiments on FRP-confined ECC cylinders were carried out. The test results indicated that FRP-confined ECC specimens exhibited similar compression hardening behavior in the axial stress-strain curve to FRP-confined normal concrete specimens. Moreover, the “self-confinement” effect of ECC and the confinement stiffness of FRP had significant influence on the stress-strain response and failure mode. Based on the FRP strain distribution, a failure mechanism was proposed for FRP-confined cement-based materials under compression. FRP-confined ECC cylinders underwent three distinct stages under compression: formation of microcracks, formation of multiple cracks, and formation and propagation of major cracks. A qualitative model for FRP confined ECC was developed, which illustrates the effects of different tensile properties of cement-based materials on the failure mode and explains why the hoop rupture strain is lower than the ultimate tensile strain of FRP. In addition, fitting equations were proposed for predicting the compressive strength and ultimate strain of FRP-confined ECC cylinders at the ultimate state.

Damage and fracture of gun barrel under wear-fatigue interaction

Gun, projectile and propellant are three fundamental components of a launching system. Generally, a barrel has to be condemned after a number of rounds have been fired. During the total useful life of gun barrel, it bears severe damage induced from erosion by high pressure and high temperature propellant combustion gas, and wear due to high speed friction between projectile and gun bore. Meanwhile, the gun barrel undergoes a dynamic loading of gas pressure, mechanical stress and thermal stress when firing a round. Thousands of firing cycles lead to gun barrel fatigue. Interaction of wear, including erosion, and fatigue damages the gun barrel and eventually the gun will become inaccurate because of wearing away gun bore materials. However, a gun barrel will fracture in a sudden manner because of fatigue. It is found that microcracks form on the bore surface after only a few rounds have been fired, which lays the foundation for growth and propagation of cracks under fatigue loading. In this paper, laboratory hydraulic fatigue tests were carried out on a tube with pre-machined crack on its inner surface by using an MTS 809. Strain gauges were adhered to the outer surface of the tube to monitor strain during testing process. The hydraulic oil pressure was measured by a pressure sensor. The experimental results show that there are three stages of outer surface strain variation, namely stable increase, fast increase and abrupt increase, which corresponds to the history of crack evolution. Crack grew stably in the initial stage under cycle of loading and a major crack is gradually formed. When the major crack size reaches a certain value, the propagation velocity of crack is accelerated fast and the critical size is reached in a short time. Eventually the tube fractured suddenly. The experimental findings will help us to gain new insight into the physical mechanism of fatigue and fracture of gun barrel and provide a possible method to evaluate health of gun barrel in service.

A study on the ultimate strength of ship plate with coupled corrosion and crack damage

Under fatigue loading, crack damage shaped by stress concentration of pitting corrosion in the steel plate adversely affects the strength of ship structure. A nonlinear finite element study is carried out in this paper to investigate how coupled corrosion and crack damage influences the ultimate strength of ship plate. The parameters such as the length, angle and transverse position of cracks, corrosion density and depth and the plate slenderness ratio are taken into account in the present study. It is presumed that the crack is through-thickness and symmetrically distributed inside and on both sides of the corrosion pits, and no contact of crack faces occurs at the ultimate limit state. Reasonable crack gap and a shape of semicircular tip are employed based on numerical results. The crack propagation is not considered in this paper. It is found that the major crack impacts on the ultimate strength depend on the interactions between the length and location as well as the plate slenderness ratio. In addition, the effect of different corrosion factors can be attributed to the corrosion volume. When the crack and corrosion exist together in the plate, their reduction for the ultimate strength is less than their superposition when they exist alone. Moreover, the difference of these two reductions becomes larger as the crack angle increases. Based on numerical results, two mathematical formulas for predicting the residual ultimate strength of steel unstiffened plates with coupled corrosion and crack damage are proposed for longitudinal cracks, transverse and inclined cracks, respectively.

A Damage-Based Approach to Determine the Dynamic Increase Factor for Concrete

The failure strength of cementitious materials is often observed to increase significantly under dynamic loading conditions. A physical mechanism believed to be a significant driver of this rate sensitivity is the cracking and fragmentation process in these brittle or quasi-brittle materials. While high-speed photography can be used to make in-situ observations of specimens under dynamic loading, this optical technique is incapable of identifying the onset of strain localization and major unstable crack growth within opaque materials. In this study, the non-destructive high-resolution 3D imaging capabilities of X-Ray micro-computed tomography are implemented to analyze the state of damage within concrete specimens subjected to controlled high strain-rate loading. A modified Kolsky compression bar coupled with a momentum trapping technique was used to achieve dynamic constant strain-rate deformation before rapid unloading at a predetermined stress level allowing recovery of specimens for internal damage analysis. Results from this novel experimental technique reveal that, for the two materials studied here, a total of 38% to 68% of the dynamic strength increase occurs after the onset of major crack propagation. This result indicates that the dynamic increase factor calculated using the dynamic peak failure strength in these materials may include significant contributions from the fragmentation process, which is not representative of the intrinsic material properties. In light of these experimental results, a new logistic regression-based method is proposed to obtain the dynamic damage initiation stress for high-strength concrete and a more accurate definition of the dynamic increase factor is proposed.

Empirical Models for Lateral Stiffness and Strength of Masonry-Infilled RC Frames Considering the Influence of Openings

Lateral load behavior of reinforced concrete (RC) frames infilled with fly-ash brick masonry having various sizes of central openings was investigated experimentally. Results showed that the infilled frames with openings exhibited significantly different lateral load behavior than the corresponding infilled frames without openings. The drift limit states corresponding to commencement of major events during the lateral loading (initiation of major cracks in frame members, peak load, and 80% of postpeak load) were found to improve significantly due to the presence of openings when designed in accordance with current earthquake standards. The presence of openings in masonry infills modifies two of the most important design parameters, lateral stiffness and strength, for which nonlinear prediction models were developed by carrying out statistical analyses of the experimental results. Empirical models were used to estimate the stiffness and strength of frames tested in past studies and were found to be more accurate and consistent compared with several existing predictive relations. A normalized lateral load–drift relationship for different performance levels of such frames was also propounded based on the observed damage events. The empirical equations can be used very conveniently to simulate the variations of stiffness and strength (global response) of the infilled frames with openings under lateral loads.

The Effect of Stress Wave Interaction and Delay Timing on Blast-Induced Rock Damage and Fragmentation

Rock fragmentation by blasting is the most efficient way of rock breakage in hard rock mining applications. Fragmentation, as well as the properties of the fragments generated by the explosion, are of significant concern as the energy consumption at the mill is greatly affected by them. Dynamic loading of blasting generates a countless number of microcracks in the host rock, which despite the major cracks forming the fragments could not get enough time to coalesce and create macrocracks. These microstructures eventually impact the integrity of the intact rock and reduce its strength. Damage is considered as a scalar parameter, which accounts for the creation of flaws and microstructures in the rock, deteriorating its elasticity modulus. The stress waves and their interactions are the parameters that control damage around blastholes. In this study, using LS-DYNA numerical code, the effect of initiation timing on blast-induced rock damage and fragmentation is investigated. The results of the numerical models reveal the importance of the delays in damage as well as fragment size distribution. Delayed initiation provides enough timing for the cracks to grow, which preconditions the surrounding rock for the neighboring blasthole. The interaction between the stress waves resulting from the detonation of neighboring blastholes plays an important role in damage and fragmentation analysis. The optimum delay time can be obtained by considering the rise time and the duration of the stress pulse, the P and S wave travel times in the host rock, and the crack propagation time within the rock burden.

Joining of stainless steel (SS304) and OFE copper by vacuum brazing

This paper describes the vacuum brazing process for joining OFE copper with stainless steel (SS 304) using silver based filler material (68Ag27Cu5Pd). Vacuum brazing of SS304 and OFE copper was carried out in a vacuum furnace at a vacuum level of 10−6 mbar. The peak brazing temperature was kept as 920 °C with a soaking time of 10 min. This combination is often used in bi-metallic joints for high vacuum applications. Optimization of brazing parameters was done to produce defect free joints. Micro structural analysis of the brazed joint was carried out using optical and scanning electron microscope. The flow of filler material and diffusion of its elements into substrates was observed. The brazed joint was found to be of good quality and free from any major cracks. The micro hardness was evaluated across the interface and it was observed that hardness decreases towards the interface. The hermeticity of the joint was investigated using helium spray method.

Highly Robust and Automated Vision based Filamentous Steel Strip Crack Detection System

Crack detection has always been a dominant requirement for steel industries to ensure quality production and seamless infrastructure maintenance. However, application complexities and defect morphological differences make existing approaches confined. Steel-strip surface often undergoes scratch, crack and fatigue conditions during production. Manual crack detection schemes are no longer effective in current day complex environment. Amongst major steel strip crack detection approaches vision based techniques have found potential; Filamentous crack which is caused due to fatigue or strain is fine-grained and thin and hence highly difficult to be detected by classical morphology and static threshold based schemes. In the present work steel strip surface (filamentous) crack detection system is developed which employs Varying-Morphological Segmentation (VMS) also called Neuron-Model Segmentation (NMS) in conjunction with local directive filtering and active contour propagation. The proposed method can be stated as an augmented vibrational framework that employs multi-directional filters for local crack-region identification followed by automated multi-directional region growing and iterative contour evolution which performs level set energy minimization to achieve accurate crack detection even under topological non-linearity and varying illumination conditions Simulation results with standard benchmark data has confirmed that the proposed method exhibits satisfactory performance for steel strip surface cracks.

Effect of Intermetallic Compound Layer on Peel Strength and Crack Propagation Behavior in Cu/Al/Cu Clad Composites

The effects of interfacial modification in tri-layered Cu/Al/Cu composites by heat treatment on interface stability and crack propagation were investigated. In order to investigate the crack path during the peel test, the intermetallic compound layer with the propagating crack was examined using electron backscatter diffraction (EBSD) analyses. The increase of peel strength from 7.8 to 9.1 N/mm in the tri-layered Cu/Al/Cu composite in the presence of thin discontinuous intermetallic compounds with heat treatment at 200–300 °C was accompanied by the increase of electrical conductivity from 65.3% IACS (International Annealed Copper Standard) to 66.8% IACS. Continuous intermetallic layers consisting of Al2Cu, AlCu, and Al4Cu9 were found in Cu/Al/Cu heat-treated at temperatures above 350 °C and its thickness increased rapidly and reached up to 35.2 μm at 500 °C. The peel strength drastically decreased to 5.75 N/mm after heat treatment at 400 °C, and it gradually increased as the heat treatment temperature was increased to 450 °C (5.91 N/mm) and 500 °C (6.16 N/mm). The increased peel strengths after heat treatment at 450 and 500 °C were accompanied by pronounced serrations of the peel strength–displacement curves. The amplitude of serration increased substantially with increasing annealing temperature from 400 to 500 °C. The major crack along the interface propagated, mostly along the Al2Cu/AlCu boundary with some inclined cracks, propagated through the AlCu and Al4Cu9 intermetallic compound layers. The repetition of crack propagation along the interface and crack deflection through the intermetallic layer as an inclined crack induced the serrated surface on the peeled-off Cu plate, enhancing the interface toughening.

Elevated temperature corrosion resistance of additive manufactured single phase AlCoFeNiTiV0.9Sm0.1 and AlCoFeNiV0.9Sm0.1 HEAs in a simulated syngas atmosphere

High entropy alloys have attracted great interest due to their great stability and exceptional mechanical properties. Due to growing demand of novel engineering materials, which can endure harsh corrosive atmospheres, HEAs have been studied extensively to meet the demands of challenging industrial environments. Current manufacturing techniques of HEAs include arc-melting or spark plasma sintering, which are limited by factors such as high energy, grain refinement, alloying, and size limitations. In this study we report elevated temperature corrosion behavior of two new HEAs AlCoFeNiTiV0.9Sm0.1 and AlCoFeNiV0.9Sm0.1, produced by laser-based additive manufacturing, which offers high freedom of design, fast prototyping, and rapid quenching rates that are ideal for many industrial applications. These alloys were tested in corrosive syngas atmosphere at elevated temperatures to explore their applicability in such harsh environments. Phase analysis results indicated the presence of a single FCC phase in these HEAs with no major surface cracks after enduring such corrosive atmospheres. These alloys exhibited good corrosion resistance as revealed by electrochemical testing methods. CALPHAD and DFT simulations were also performed to reveal the phase stability and crystal structures to further corroborate our experimental results.

Strain-based Evaluation of Bridge Monitoring using Numerical Model Analysis

According to visual inspection on the bridge site, the target bridge has major cracks in RC deck in the center span. This certain type of damage could affect structural performance and should be monitored. The structural health monitoring system was set up on the target bridge and the strain-based evaluation could be used to quantitatively determine bridge condition. The FE model of the bridge was modeled with various types of RC cracking pattern to represent the severity of bridge damage. The relationship between damage level and strain measurement is generated, As a result, Bridge monitoring curve based on strain index has been established.