Maximum Allowable Crack Research Articles

Adjusting technical requirements for anti-corrosion concrete and reinforced concrete structures in the Vietnam marine environment according to operation standards

Before applying the technical requirements of anti-corrosion for concrete and reinforced concrete structures in the Vietnam marine environment, the reinforcement was corrosived after about 10 years of use. From this standard was promulgated in 2004 (Vietnam Building standard 327: 2004) and replaced (Vietnam standard 9346: 2012), it solved many technical requirements of anti-corrosion for marine environment constructions. When Applying this standards quality assurance concrete, protected reiforcement and the durability of constructions are extended. However, after 20 years the standard is appied, some technical requirements are not suitable for operation standards as: erosion cavitation in marine environment, concrete grade, maximum allowable crack width, construction and acceptance... Therefore, it is necessary to modify some technical requirements in Vietnam standard 9346: 2012, especially the maximum allowable crack width according to operation standards to apply easy, quality inprovement, technical and economic efficiency when project is used.

Safety assessment of allowable through-wall crack angles for pipes subjected to tensile loading

Fully plastic collapse stresses for high toughness ductile pipes with circumferential cracks subjected to tensile loading can be predicted by means of Limit Load Criteria based on the net-section stress approach. The Limit Load Criteria are provided by the ASME Code Section XI. Allowable membrane stresses for part-through cracks were determined by plastic collapse stresses in combination with safety factors. The allowable stresses decrease with increasing angles of the part-through cracks. When crack angles are large, the allowable stresses of the part-through cracks are larger than the collapse stresses of through-wall cracks. For such large cracks, allowable stresses greater than the collapse stresses cause instability, and are thus detrimental to pipe integrity, especially in thin-wall pipes, even though the stresses are allowed. In order to avoid the anxiety associated with this, it is necessary to establish maximum allowable crack angles. This paper proposes maximum allowable crack angles for allowable stresses based on the collapse stresses of through-wall cracks. The maximum allowable crack angles can be expressed by equations for various service level conditions.

Limitations of Flexural Crack Width in Simply Supported One-Way Ribbed Slab

The important consideration in design of multistory concrete buildings is reducing self-weight of the slabs. The system of one-way ribbed slab is one of the many systems chosen in order to reduce self-weight. This reduction occurs in concrete only for what causes high tensile stress in bottom fiber of concrete lead to cracking although the section is reinforced according to design specifications. Limitations of ACI 224R-01 2008 of maximum allowable crack width is 0.3 mm for members’ exposure to humidity, moist air, or soil. The experimental work in this research includes five simply supported reinforced concrete one-way ribbed slab with same dimensions and different in ratio of bottom steel reinforcement. The five specimens have reinforcement ratios of 0.0009, 0.0013, 0.0023, 0.0037, and 0.0059 respectively. The aim of this research is checking experimental crack width at design load with permissible limitations according to ACI 224R-01 2008. The experimental work and the theoretical calculations, for all the specimens, are cracked sections where the first crack appears at load less than design load. At design load the specimens with low and moderate reinforcement ratio 0.0009, 0.0013 and 0.0023 show crack width less than permissible value of 0.3 mm, while the specimens with high reinforcement ratio 0.0037 and 0.0059 show crack width more than permissible value of 0.3 mm, where the increases in width of crack causes reducing in the durability of members. At linear stage, the mid span deflection is decreasing as reinforcement ratio increase at same step of loading for all specimens. Finally, in the design of one-way ribbed slab, the emphasis is on checking the width of cracks according to codes permissible limitation and it is recommended to use low or moderate reinforcement ratio in this system of slabs.

Numerical Failure Analysis and Fatigue Life Prediction of Shield Machine Cutterhead.

This paper presents numerical failure analysis on cracking of shield machine cutterhead structure during a metro-tunnel construction. The stress intensity factors (SIFs) of surface cracks with different shapes and location angles were analyzed by a finite element simulation method based on linear elastic fracture mechanics (LEFM) theory. The ratios of variation in stress intensity factors of cracks with different shapes were analyzed. The maximum allowable crack depth of the cutterhead panel is 50.23 mm by dynamic stress calculation, and the damage tolerance criterion of the cutterhead panel was proposed. The influence of the Paris model parameter values was analyzed based on mathematical methods. It is proven that the location of the cutterhead cracking angle is mainly determined by the mixed-mode SIF. In practice, the crack section basically expanded into the semi-elliptical shape. The cutterhead structure may directly enter the stage of crack propagation due to welding defects during tunneling. The research results provide a theoretical basis and important reference for crack detection in the key parts of the cutterhead, as well as maintenance cycle determination and life prediction of the cutterhead mileage, both of which have important engineering value.

Application of the Failure Assessment Diagram approach for contact fatigue damage evaluation in railway wheel steels

AbstractA Failure Assessment Diagram (FAD), developed for rolling contact, was specifically formulated for railway wheel steels. The FAD allows combining a multiaxial fatigue criterion with the linear elastic fracture mechanics concept; in particular, it was used to assess the fatigue failure in wet contact, related to the pressurization of the fluid entrapped in surface cracks. The approach was applied to the results of previous bi‐disc tests carried out on three railway wheel steels, subjected first to a dry rolling‐sliding contact step, then to a wet contact step. The crack size distribution after the dry contact step was evaluated by a statistical approach; subsequently, the stress intensity factor during the wet contact step was estimated by finite elements. The results of the FAD agreed with the damage observed on the cross section of the specimens at the end of the tests. Furthermore, the FAD was used to determine the maximum allowable crack to prevent rolling contact fatigue, this way showing its potential as a damage tolerant approach.

Improving reliability of high‐strength steel designed against fatigue limit using surface crack nondamaging technology by shot peening

AbstractRecently, surface crack nondamaging technology has been developed to render harmless surface cracks that can reduce the fatigue limit of metals by 20–60%. This is due to the effects of compressive residual stress induced by shot peening. To improve the reliability of high‐strength steel equipment designed against fatigue limit using surface crack nondamaging technology, the following characteristics were determined: (1) the effects of surface crack aspect ratio on maximum harmless crack depth (ahlm) at high‐strength steel for three residual stress distributions; (2) the relationship between the maximum allowable crack depth (acrN) and ahlm assuming the value of safety factor; (3) the relationship between minimum detectable crack depth via nondestructive inspection (aNDI) and ahlm, assuming that nondestructive inspection could detect the crack with sufficient probability; and (4) the relationships between ahlm, aNDI, and acrN.

ANALYSIS OF THE EFFECT OF SLAB THICKNESS ON CRACK WIDTH IN RIGID PAVEMENT SLABS

Cracks that occur in rigid pavements include longitudinal cracks, transverse cracks, and corner cracks. The relatively large crack width not only spoils the aesthetics of the concrete structural elements but can also lead to structural failure. This study aims to determine the crack width of a rigid pavement concrete slab located above the subgrade which is considered a beam on an elastic foundation, so that a minimum rigid pavement concrete slab thickness can be recommended. The specimen will be observed at various thicknesses to obtain the optimum thickness. The load used is a centralized monotonous load, which represents the load of the truck vehicle. The research limitation is using a test object in the form of a concrete plate measuring 2000x600 mm which is placed on the ground with CBR=6 %. The quality of reinforced concrete slabs is fc'=40 MPa and fy=440.31 MPa. The thickness of the concrete slab varies between 100 mm, 150 mm, and 200 mm. The slab placed on the ground is then given a central loading in the form of a centralized monotonic load. The loading range starts from a load of 2–180 kN with a load interval of 2 kN. The experimental results show that the rigid pavement slab has a bending failure so that the crack pattern that occurs begins with the first crack on the underside of the slab. The crack pattern in terms of slab thickness variation has a similar pattern. The initial crack width on the slab is 0.04 mm. The thicker the slab smaller the crack width at the same load. Based on the maximum allowable crack width=0.3 mm. For loads between (80–100) kN (Road Class I, II, and III), a minimum thickness of rigid pavement slabs (70–80) mm is recommended. For loads between (130–140) kN, the minimum thickness of the rigid pavement slab (105–115) mm is recommended

Failure behavior of SA508 Gr.1a LAS and SA312 TP316 SS pipes with a circumferential through-wall crack under large amplitude cyclic loads

This paper presents cyclic fracture test results using small-scale through-wall cracked pipe specimens to investigate the effects of large-amplitude cyclic loads on failure behaviour for different pipe materials. SA508 Gr.1a low-alloy steel (LAS) and SA312 TP316 stainless steel (SS) pipes were used in the experiment. The tests were conducted under quasi-static monotonic, displacement-controlled, and load-controlled cyclic loadings at room temperature (RT). Regardless of the pipe material, displacement-controlled reversed cyclic loading significantly reduced deformation-ability and fracture resistance, promoting crack growth. These effects were more pronounced in the SA312 TP316 SS than in the SA508 Gr.1a LAS specimen. The material-dependence on fracture behaviour was considerable under monotonic load, but was near-negligible under displacement-controlled reversed cyclic loading. Under load-controlled cyclic loading, the number of cycles to failure, the maximum allowable crack extension, and deformation-ability of pipe specimens decreased as the amplitude and compressive level increased. For all load-controlled cyclic loads, the SA312 TP316 SS specimen was less resistant to failure than the SA508 Gr.1a LAS specimen. Regardless of the loading type, a circumferential through-wall crack grew out of the initial crack plane for the SA508 Gr.1a LAS specimen, but propagated in a straight line from the initial crack plane for the SA312 TP316 SS specimen.

The Effect of Periwinkle Shell Ash Mixed with Cement on Water Absorption and Shrinkage of Lateritic Block

Abstract The aim of the study is to examine the effect of periwinkle shell ash (PSA) blended with cement on the water absorption and shrinkage of lateritic blocks. The objectives that would help achieve the stated aim are to investigate the water absorption and shrinkage properties of lateritic blocks blended with periwinkle shell ash/cement. The following methods were used during the research: sedimentation test, standard proctor test, Atterberg’s limit test, smell and Nibble tests. Specific gravity of PSA, bulk density and porosity of PSA were carried out. 5 % of the cement and percentage replacement levels of 0 %, 10 %, 20 %, 30 %, 40 % and 50 % of cement with PSA were used for block production. 21 cm × 10 cm × 10 cm blocks were moulded, cured and subjected to water absorption and shrinkage tests. Data were collected and analysed using graphs, correlation and regression analyses. Result shows that percentage water absorption for replacement levels 0 %, 10 %, 20 %, 30 % were 12.08 %, 16.38 %, 18.21 %, 19.95 %. Again, from 0 % replacement to 30 % replacement of cement with PSA, the linear shrinkage increased from 1.5 mm to 2.8 mm. It implies that up to 30 %, the maximum crack the block could form is 2.8 mm, whereas the maximum allowable crack width for walling materials is 3.0 mm. Therefore, percentage replacement of up to 30 % is recommended for use in lateritic block.

Damage tolerant analysis of corner cracks in small nozzle process penetration of the CAREM-25 reactor pressure vessel

This paper presents a damage tolerant approach assessment of corner cracks in small nozzle process penetrations in the pressure vessel of the small modular reactor CAREM-25 subjected to mechanical and thermal shock loadings during certain operation events. Fracture mechanics analyses were performed following ASME XI guidelines considering a representative geometry and specific loading conditions. Stress distributions in the uncracked component were calculated by finite element techniques, while fracture driving forces were estimated using closed form solutions. Maximum allowable corner crack sizes were calculated using linear elastic fracture mechanics and failure assessment diagram (FAD) approaches. The onset of stable crack growth and crack instability were considered as failure conditions. Additionally, fatigue crack growth estimations during the service life were performed integrating a Paris law up to the maximum allowable crack sizes. The results indicate that it seems unlikely that pre-existing cracks reach allowable sizes during the reactor's service life.

Self-Healing Concrete with Crystalline Admixture—A Review

The scope of the present paper is to understand the effects of crystalline admixture on the self-healing capacity of the cementitious composites. Previous studies were examined and a conclusion was drawn to the effect that different additives to crystalline admixture tend to improve self-healing of concrete for larger cracks. It is recommended that initial treatment with chemical admixture can stimulate and heal further cracks and it has the better repeatability trend in mixing with the concretes and mechanical recovery is possible even under repetitive preloading. Effective self- healing with chemical admixtures even under open-air exposure, leads to study the importance of a service ability design parameter including the maximum allowable crack width by repeatability analysis as a function of the exposure with the concept of sealable crack width.

Shear behavior of large-scale concrete beams reinforced with CFRP bars and handmade strip stirrups

To obviate the premature failure of pultruded FRP stirrups due to low bent portion strength and slippage at overlapping region, this study fabricated handmade strip stirrups with a rectangular cross-section and investigated the shear behavior of concrete beams reinforced with handmade CFRP strip stirrups and CFRP longitudinal bars. Five large-scale concrete beams with the cross-section of 200 mm × 500 mm and the shear span ratio of 2.26 were tested under three-point loading. The effects of stirrups inclination and stirrups spacing were studied. Test results showed that inclined stirrups improved both the shear capacity and the serviceability performance. The beams reinforced with inclined stirrups exhibited 1.19–1.26 times higher shear capacities than the beam reinforced with vertical stirrups. Inclined stirrups not only increased the load corresponding to the maximum allowable crack width to 1.10–1.89 times higher, but also improved the ratio of the load corresponding to allowable crack width to the peak load. Moreover, inclined stirrups are more effective in improving the serviceability performance even compared with vertical stirrups with a halved spacing. The shear provisions in CSA S806-12 produced the most accurate predictions of the experimental shear capacities, while the predictions of ACI440.1R-15 and CSA S6-14 were relatively conservative.

The crack number density theory on air-plasma-sprayed thermal barrier coating

A crack number density (CND) theory model is developed for air-plasma-sprayed thermal barrier coating (TBC), which describes the evolution of crack number and size distribution as function of exposure time. The model is compared in good agreement with experimental measurements from quasi-isothermal-cyclic oxidation tests. Both the CND model and experimental observations indicate that thermally-grown oxides (TGO) are responsible for crack nucleation and growth. The model can be used to define TBC failure (spallation) by coalescence of microcracks into a maximum allowable crack size with a given probability.

Crack sealing capacity in chloride-rich environments of mortars containing different cement substitutes and crystalline admixtures

This paper presents the results of a preliminary study aimed at assessing the crack sealing capacity in chloride environments of different concrete mixtures, incorporating supplementary cementitious materials as well as self-healing enhancing crystalline admixtures. For each addition, also including pulverized fuel ash and silica fume, different contents were taken into consideration. Cylinder specimens were pre-cracked in splitting up to three different crack-opening ranges, simulating different service conditions, and then exposed to different conditioning environments, also containing different concentrations of sodium chloride and including both permanent immersion and wet/dry cycles. Healing conditioning was performed up to three months and crack sealing was visually inspected and quantified via image analysis procedures, monthly. Optimum dosages of each cement substitute/addition were quantified, also considering, besides the healing capacity, also the fresh state performance and compressive strength development. The good performance of mixes with crystalline admixture even under open-air exposure, as well as of other investigated mixes with reference to crack openings and exposure conditions, paves the way to revise the significance of a serviceability design parameter such as the maximum allowable crack width as a function of the exposure with the concept of a sealable crack width.

Safe life approach considering creep-fatigue interaction and Weibull statistics for crack growth evaluation based on field feedback applied to a GT first stage blade

The increased flexibility that the energy market requires makes the service condition of gas turbine (GT) components more and more critical in terms of creep-fatigue interaction. A new lifing strategy has been developed in order to evaluate the expected life of blades and vanes in this demanding service condition taking into consideration creep-fatigue interaction. The developed lifing methodology has been applied to the first stage blade of an Ansaldo Energia F-class GT and the life map has been compared with the available field feedback. With this procedure crack initiation in the base material is considered as the lifing criteria. So, the critical locations have been correctly identified and the number of predicted cycles correspond to service experience. The available field feedback has been treated by using Weibull statistics. The statistical treatment of crack size for the critical locations provides a crack initiation evaluation that is in good agreement with the lifing strategy. Moreover, the available field feedback on the first stage blade allows the correlation of the linear crack size with its depth. This relationship has been used to define the maximum allowable crack length for safe operation of this component.

Coupled effects of crack width, slag content, and conditioning alkalinity on autogenous healing of engineered cementitious composites

Engineered cementitious composite (ECC) is a unique group of fiber-reinforced strain-hardening cementitious composites exhibiting crack self-healing. Due to the absence of coarse aggregates in the ECC mix design, high amount of supplementary cementitious materials (SCM) are generally used to reduce the cement content. The inclusion of slag not only changes the chemical compositionss of the matrix but also alters the crack width of ECC. Both may influence the autogenous healing potential of the slag-based ECC. This paper systematically investigates the influence of the individual factor, i.e. slag content, crack width, and environmental alkalinity, on the autogenous healing efficiency of ECC. Specifically, single-cracked ECC specimens with different slag content and crack width were conditioned under water/dry or NaOH/dry cycles. The autogenous healing performance was evaluated based on crack width reduction, resonant frequency recovery and microstructure analysis. The results show that autogenous healing is determined by a couple effect of physical properties (crack width), chemical compositionss (slag content), and environmental conditions (conditioning alkalinity). At a given slag content and certain alkalinity, there exists a maximum allowable crack width for complete healing, beyond which only partial or no healing would happen. The dominant healing product for the water/dry conditioning is CaCO3 while the NaOH/dry cycles promote slag hydration and results in the formation of CSH and CaCO3 as main healing products. It is concluded that CaCO3 precipitation is more effective to engage autogenous healing than the formation of CSH. The concept to associate allowable crack width and slag content is proposed, which would guides ingredients selection and component tailoring to engage robust autogenous healing in ECC in the future.

Case Study on Aggregate Interlock Capacity for the Shear Assessment of Cracked Reinforced-Concrete Bridge Cross Sections

AbstractA 55-year-old bridge showed large cracking in the approach bridge caused by restraint of deformation and support settlement. After repair, it was uncertain at which crack width the traffic loads on the bridge should be further restricted. The shear capacity was calculated by counting on the aggregate interlock capacity of a supposedly fully cracked cross section. An aggregate interlock relationship between shear capacity and crack width based on an unreinforced section was used to find the maximum allowable crack width. Limits for crack widths at which load restrictions should be imposed were found. The large structural capacity of the cracked concrete section shows that the residual bearing resistance based on the aggregate interlock capacity of reinforced concrete slab bridges with existing cracks is higher than expected. This expected capacity could be calculated with the inclined cracking load from the code provisions. The procedure outlined in this paper can thus be used for the shear assessm...

Development of the indirect ring tension fracture test for hot-mix asphalt

Almost all of the current hot-mix asphalt (HMA) fracture tests are considered to be research tools. This paper describes the development of the indirect ring tension (IRT) fracture test for HMA, which was designed to be an effective and user-friendly test that could be used at the Department of Transportation level. Numerical modelling was utilised to calibrate the stress intensity factor formula of the IRT fracture test for various specimen dimensions. The results of this extensive analysis were encapsulated in a single equation. An experimental plan was developed to optimise the test parameters for HMA specimens. The experiment results revealed that the test is highly repeatable, and capable of capturing the variations in the fracture properties of HMA. Moreover, the data from laboratory tests were utilised to estimate the maximum allowable crack lengths for the pavements based on a viscoelastic model.

Study on the possibility of increasing the maximum allowable stresses in fibre-reinforced plastics

This article presents the results of a study aimed at investigating the possibility of increasing the maximum allowable stresses in fibre-reinforced plastics compared to current practice. The study consisted of a comparison between the maximum allowable stresses of a group of cross-ply laminates, determined by deterministic analyses with safety and model factors as stated in design rules, and their probabilistic responses estimated with a fracture mechanics based model that accounted for material degradation. The results suggest that for the studied cases, the maximum allowable stresses do not provide the desired reliability; thus, their increase cannot be motivated. More importantly, the investigation shows that a better understanding of the effects of matrix cracks, and therefore, the maximum allowable crack density in a composite laminate, would lead to better and safer composite structures.

Leak-Before-Break analysis for Pickering ‘A’ Unit 1 and Unit 4 large diameter main steam line pipes

This paper presents a Leak-Before-Break (LBB) analysis of large diameter main steam line pipes (i.e. NPS 28″ and 30″) running from reactor building to main steam balance header in Pickering nuclear plant Unit 1 and Unit 4. Recent development in LBB technology summarized in U.S. Nuclear Regular Commission report NUREG/CR-6765 was adopted. Based on the tiered approach of LBB philosophy, this LBB analysis belongs to level 2 or level 3 LBB analysis. Detailed fracture tolerance analyses and leakage rate calculations were performed. EPFM (elastic plastic fracture mechanics) theory of J-integral, resistance curve versus ductile crack extension was adopted in carrying out all fracture tolerance analyses. Through-wall cracks in axial and circumferential directions on both straight pipes and elbows were postulated and analyzed. The loads applied on the postulated cracked pipes were obtained from detailed piping stress analysis under deadweight load, design pressure, thermal expansion, seismic design based earthquake (DBE) and thrust load due to the opening of relief valves. J-resistance data were derived from the lowest fracture toughness testing data obtained from Ontario Power Generation's PHT (primary heat transport) LBB material testing programs. A margin of 2 on crack size was chosen in establishing maximum allowable crack sizes. Leakage rates were calculated using SQUIRT Windows Version 1.1 program. The fluid inside the main steam line pipes was assumed single phase steam at 100% quality. One tenth of the calculated leakage rates was proposed as the requirement for minimum leakage detection capability. The paper concludes that the absence of through-wall crack larger than 91.16 mm in length should be maintained in order to ensure the structural integrity of large diameter main steam line pipes. In lieu of this crack size requirement, a reliable leakage detection capability which could quantify mass steam leakage rate of 0.01678 kg per second, or volume leakage rate of 1.01 l/min, should be in place. If both of the above two requirements are met, the Leak-Before-Break of these large diameter main steam line pipes is warranted.