Possible Modes Of Failure Research Articles

Remaining fatigue life assessment of in-service road bridge decks based upon artificial neural networks

By using a multi-scale simulation together with the pseudo-cracking method, the remaining fatigue life of real RC bridge decks is estimated based upon their site-inspected surface crack patterns of a wide variety, and it is confirmed that the crack location and its orientation are primary factors on the remaining life together with crack width. For quick diagnosis for the remaining fatigue life at the site, an artificial neural network (ANN) to correlate the fatigue life with observed cracks is built up based upon large numbers of assessed fatigue life related to wide range of crack patterns and their widths. Artificially created crack patterns associated with the firm coupling of shear and flexure are also included in training dataset to cope with indeterminate crack events which may arise in future and to assure a robust and reliable artificial neural network model. It is recognized by conducting the cross-validations that the training data-set for ANN shall include crack patterns rooted in mechanically possible modes of failure. Otherwise, the risk of wrong assessment due to overlearning will arise.

Addressing technical barriers for reliable, safe removal of fluoride from drinking water using minimally processed bauxite ores

Throughout the developing world, over 200 million people drink groundwater containing fluoride concentrations surpassing the World Health Organization's maximum recommended contaminant level (WHO-MCL) of 1.5 mg F−/L, resulting in adverse health effects ranging from mottled tooth enamel to debilitating skeletal fluorosis.Existing technologies to remove fluoride from water, such as reverse osmosis and filtration with activated alumina, are expensive and are not accessible for low-income communities. Our group and others have demonstrated that minimally-processed bauxite ores can remove fluoride to safe levels at a fraction of the cost of activated alumina. We report results from testing for some technical challenges that may arise in field deployment of this technology at large scale, particularly in a sufficiently robust manner for application in development contexts. Anticipating possible modes of failure and addressing these challenges in advance in the laboratory is particularly important for technologies for vulnerable communities where the opportunity to re-launch pilot projects is limited and small failures can keep solutions from the people that need them most.This work addresses three potential technical barriers to reliable removal of fluoride from drinking water with bauxite ore from Visakhapatnam, Andhra Pradesh, India. We evaluate competition from co-occurring ions, adsorption reversibility, and potability of the product water with regards to leaching of undesirable ions during treatment with various adsorbent materials including raw and thermally activated bauxite, and synthetic gibbsite (a simple model system). Under the conditions tested, the presence of phosphate significantly impacts fluoride adsorption capacity on all adsorbents. Sulfate impacts fluoride adsorption on gibbsite, but not on either bauxite adsorbent. Nitrate and silicate (as silicic acid), tested only with gibbsite, do not affect fluoride adsorption capacity. Both thermally activated bauxite and gibbsite show non-reversible adsorption of fluoride at a pH of 6. Raw bauxite leached arsenic and manganese in a TCLP leaching test at levels indicating the need for ongoing monitoring of treated water, but not precluding safe deployment of bauxite as a fluoride remediation technology. Understanding these phenomena is crucial to ensure field deployment over large diverse geographical areas with aquifers varying in groundwater composition, and for ensuring that the appropriate engineering processes are designed for field implementation of this innovation.

Reliability Analysis of Possible Modes of Failures in the Counterfort Retaining Wall

Reliability Analysis of Possible Modes of Failures in the Counterfort Retaining Wall

Towards innovative FRP fabric reinforcement in concrete beams: concrete–CFRP bond

The paper reports results of an experimental investigation into load response and failure behaviour of rectangular prismatic concrete beams reinforced with a combined flexural and shear reinforcement system made from carbon-fibre-reinforced polymer (CFRP) fabric. It is shown that CFRP U-channels with aggregate coating and an anchorage system consisting of a lipped channel section with intermittent closed loops were found to provide improved composite action between the CFRP reinforcement and concrete. These CFRP channels also ensured adequate strength and ductility before failure. Possible modes of failure of the beams are discussed, as is the effect of the design parameters on the failure mode and the failure load. It is anticipated that the findings of this paper could be effectively used in other applications such as non-prismatic concrete geometries and as permanent formwork/reinforcement in thin concrete members where the flexible characteristics of dry CFRP fabrics are most useful.

An engineering approach to the fracture assessment of hopper wagons

A hopper wagon is a type of railroad freight car used to transport many types of materials such as coal, ore, grain, ballast and minerals and bulk cargo. It is a complicated welded structure. When performing a safety assessment of cracks in a hopper wagon, it is necessary to consider fatigue crack propagation and fracture among the possible modes of failure. In any such analysis the stress intensity factors at crack tips are important parameters for estimating both residual life and criticality (residual strength). The purpose of this paper is to present engineering fracture analysis method for calculating the stress intensities for cracks in a hopper wagon. The advantage of the present approach is that it negates the need to explicitly model cracks. A crack of any size can be analysed using the original (un-cracked) finite element model. Furthermore, as cracks are not modelled explicitly a coarse mesh can be used to minimise the number of degrees of freedom, thereby reducing the analysis time. As such solutions for the stress-intensity factors can then be obtained quickly and easily for a variety of cracks and crack lengths using the original uncracked finite element analysis. The interaction between neighbouring cracks growing towards each other have been considered in this paper. Comparing the values of stress intensity factors computed using traditional finite element, the results obtained by new method presented in this paper suggest an agreement of within 3.5%. Therefore, this approach is sufficiently satisfactory to enable engineering estimates for residual strength (safety) and residual life. The method used in this paper is approximately ten times faster than computationally expensive methods.

Root cause analysis of the degradation in a unitized regenerative fuel cell

Abstract The present study emphasizes the possible modes of failure of a unitized regenerative fuel cell (URFC) when operated in fuel cell as well as in electrolysis mode at different temperatures viz. 30 °C and 60 °C. The carbon based catalyst (Pt/C) and diffusion layers are used to characterize the degradation of the URFCs. The electrolysis mode of operation is found to dominate the root cause of failure with increase in temperature. Agglomeration and loss of catalyst along with delamination of electrode from membrane are observed. Membrane degradation owing to it's structural as well as chemical damage is seen to be prominent at higher temperature. Characterization techniques such as SEM, TEM and ICP-AES confirm the study showcasing the effect.

Wrinkling in Sandwich Structures With a Functionally Graded Core

This paper illustrates the effectiveness of a functionally graded core in preventing wrinkling in sandwich structures. The problem is solved for piecewise and continuous through-the-thickness core stiffness variations. The analysis is extended to account for the effect of temperature on wrinkling of a sandwich beam with a functionally graded core. The applicability of the developed theory is demonstrated for foam cores where the stiffness is an analytical function of the mass density. In this case, a desirable variation of the stiffness can be achieved by varying the mass density through the thickness of the core. Numerical examples demonstrate that wrinkling stability of a facing can significantly be increased using a piecewise graded core. The best results are achieved locating the layers with a higher mass density adjacent to the facing. A significant increase in the wrinkling stress can eliminate wrinkling as a possible mode of failure, without noticeably increasing the weight of the structure. In the case of a uniform temperature applied in addition to compression, wrinkling in a sandwich beam with a functionally graded core is affected both by its grading as well as by the effect of temperature on the facing and core properties. Although even a moderately elevated temperature may significantly lower the wrinkling stress, the advantage of a graded core over the homogeneous counterpart is conserved.

Nonsway Model for Lateral Torsional Buckling of Wooden Beams under Wind Uplift

AbstractSimply supported wooden beams nailed to deck boards subjected to wind uplift forces are subjected to compressive stresses at their bottom fibers. Because the restraining action provided by decking is at the top fibers, it is unclear to what extent such restraints are effective in controlling lateral torsional buckling as a possible mode of failure under wind uplift. Present design standards do not have provisions for such cases. Thus, the present study aims to quantify the effect of restraints provided by the deck boards on the lateral torsional buckling capacity of twin-beam-deck systems under wind uplift. Toward this goal, a series of analytical and numerical models were formulated. All models capture the continuous rigid lateral restraint and partial twisting restraint provided by the deck boards. The effects of load type and load position were investigated. The bending stiffness of deck boards was observed to have a significant influence on the lateral torsional buckling capacity of twin-beam-...

A simple method for calculating the stress intensity factors for complex 3D cracks at a notch

When performing a safety/durability assessment of structural components it is often necessary to consider both fatigue crack propagation and failure by fast fracture among the possible modes of failure. In this context the stress intensity factors at crack tips are important parameters for estimating residual life and criticality. The purpose of this paper is to present a simple method for calculating the mode I stress intensity factors (K) for through-the-thickness flaws with an oblique (part) elliptical crack front. A range of examples are presented to demonstrate the accuracy of this method.

Effects of Increasing the Base on Concrete Dam Stability

The concrete dam is one of the most important hydraulic infrastructures which play a vital role in providing a wide range of water services and helps prevent many potential disasters such as floods. The concrete dam subjected to many kinds of static and hydrodynamic forces which almost needs taking into account of design under different circumstances to satisfy the safety requirements. The shape of dam is pertinent to the stability of dam regarding the major forces and stresses. One of the most common ways which is necessary to solve the problems in design due to the cases of unsafely for any mode of failures is to add mass to the dam upstream face. In this work, a parametric study is made to investigate the effects of the increase in the base of dam on the principal and shear stresses developed in the dam. In all cases, all the relevant factors of safety are satisfied. The stability analysis for all possible modes of failures is carried out to check the performance of the initial section of dam due several loading conditions. Parameters of importance are studied, discussed and conclusions are drawn.

The Chalkboard: Lithium Batteries as Electrochemical Sources of Energy

The operating principle of an electrochemical battery is introduced on the example of a lithium chemistry cell. The concept of introducing first the classical zinc-copper system is deliberately avoided. Both primary and secondary lithium, or lithium-ion battery is introduced, with advantages, disadvantages, typical capacities, available energy and power and possible mode of failure.

Novel anchor-jointed precast shear wall: testing and validation

Precast concrete shear walls are used to resist lateral loads in low- to medium-rise buildings. This paper introduces an innovated joining technique for these precast walls that will reduce the possibility of concrete damage and capital loss during earthquake events. The proposed technique consists of precast panels joined together and to the base using threaded steel anchor bolts, which in turn makes the construction process easier and faster. An experimental programme is conducted to validate this system and characterise its behaviour under lateral loads. Four reduced-scale wall specimens are tested under monotonic in-plane horizontal load. The lateral strength, ductility and possible modes of failure are used to evaluate the connection performance. The joined precast shear wall exhibits a high non-linear deformation without any signs of panel damage, which can be attributed to the gap opening and steel yielding at the connection plane. This indicates that the steel anchor bolts at the connection can be designed to act as structural ductile fuses.

Optimization Method and Experimental Study on the Shear Strength of Externally Prestressed Concrete Beams

This paper presents a performance-based evolutionary topology optimization method for externally prestressed concrete(EPC) beams in automatically generating optimal strut-and-tie models using the finite element method. The concrete and steel bar elements with least contribution to the stiffness of the EPC beam are removed by calculating the element virtual strain energy. Load transfer mechanism of EPC beam is characterized by remaining elements. The optimal strut-and-tie model is determined from the topology history. A theoretical formula of the shear strength is derived from optimal strut-and-tie model for EPC beams. The model predicts possible modes of failure, which may be broadly classified into shear-type failure and flexural-type failure. 9 EPC beams were casted in place to evaluate the validation of the proposed method. The predictions of the method are compared with the 9 specimen and other available test results of EPC beams from literatures. Case studies are conducted and compared with the results of the ACI 318–11 Code and AASHTO specification equations to evaluate the accuracy of the proposed method. It is shown that the proposed method can be used in practice, especially in the design of complex externally prestressed concrete members where no previous experience is available.

Probabilistic pseudostatic analysis of pile in laterally spreading ground: Two layer soil profile

Coupling the finite element model of pile under lateral spread with the Monte Carlo Simulation is frequently prohibited by excessive lengthily computations. In the present paper, a simplified pseudostatic method is integrated with an improved response surface scheme to evaluate the reliability of pile subjected to lateral spread. The pseudostatic model takes both geometric and soil nonlinearities into account, while, the response surface formulation takes; load, geometry, material and model uncertainties into consideration. First; the improved response surface scheme is suggested and validated with the help of a simple example. Then, the pseudostatic model of a full size pile under lateral spread is integrated with the improved response surface scheme in order to assess the pile reliability. In the considered example, for both operational and structural possible modes of failure, it has been found that the most influential random variables are lateral displacement, and pile radius, respectively.

Analytical Design Model for Reinforced-Concrete Beams Strengthened in Shear Using L-Shaped CFRP Plates

AbstractThis paper presents the results of an analytical study on reinforced concrete (RC) T-beams strengthened in shear with L-shaped fiber-reinforced polymer (FRP) plates. The main objective of this study is to develop design equations for RC beams retrofitted in shear using L-shaped FRP plates, considering all possible modes of failure in ultimate limit states. Unlike RC beams strengthened with externally bonded (EB) FRP plates and fabrics, prefabricated L-shaped plates feature unconventional failure modes because of their special shape and anchorage. The possible failure modes for RC beams strengthened with L-shaped FRP plates are (1) concrete breakout at the embedded part of the FRP plate in the flange; (2) FRP pull-off at the epoxy/FRP interface; (3) FRP pull-off at the concrete/epoxy interface; and (4) FRP overlap failure at the beam soffit. These failure modes do not occur in RC beams shear-strengthened with EB FRP fabrics and plates. Therefore, the existing design models for EB FRP fabrics and pl...

Local facesheet pulse buckling in a curved, composite sandwich panel

Local facesheet buckling of a curved sandwich panel subjected to external pressure pulse loading was investigated in this paper. Equations of motion for the facesheet transient deformations in the sandwich shell were derived from Lagrange’s equations of motion, and solutions using this approach compared well with FEA results from ABAQUS Standard. Both facesheet fracture during stable deformation response and local dynamic pulse buckling of facesheets were considered as possible modes of failure in the curved sandwich panel. Parametric studies indicated that local facesheets buckling is more likely to occur than facesheet fracture in thin and deep curved sandwich panels. The facesheet laminate layup can also be adjusted to improve the local buckling resistance of the curve panel.

Analytical and experimental investigations on seismic performance of exterior beam–column subassemblages of existing RC‐framed building

SUMMARYSeismic performance of exterior beam–column subassemblages of reinforced concrete structure designed and detailed on the basis of the provisions of Eurocode and Indian Standards at different stages of their evolution is evaluated. Performance of the subassemblages designed and detailed according to the three different stages of codal evolution (gravity load design, ‘Nonductile’, and ‘Ductile’) is evaluated through analytical formulations and experimental investigations. In the ‘NonDuctile’ specimens, it has been observed that the shear distortion and degradation in stiffness and strength are significantly high. Performance of the ‘Ductile’ specimens based on Eurocode and Indian Standards is almost similar in terms of strength and stiffness degradation. Nevertheless, the specimen designed on the basis of Indian Standard shows higher energy dissipation at a given drift ratio. In the analytical study, shear and flexural failure of members of subassemblage and shear failure of the joint are considered as possible modes of failure of the beam–column subassemblage. For evaluating the shear strength of the joint region, a soften strut‐and‐tie model is used. Analytically obtained strengths based on the failure criteria of different components of the specimens have been first validated with experimental results and then used to determine the strength of the specimens. The investigation could indicate even the mode of failure at local level. It is utmost important to mention here that even the ductile specimens dissipate most of the energy through the development of damage in the joint region, which is neither desirable nor safe for the stability of whole structure. Copyright © 2013 John Wiley & Sons, Ltd.

Masonry Infill RC Frames with Openings: Review of In-plane Lateral Load Behaviour and Modeling Approaches

Un-reinforced masonry walls are commonly used as infills in reinforced concrete (RC) buildings. These build- ings have high in-plane stiffness and strength, and therefore, the lateral load behaviour of such RC frames is different than that of the frames without infill walls. Openings in walls significantly reduce the lateral strength and stiffness of RC frames, and alter their failure modes. Past researchers have tried to find out experimentally and analytically the influence of several parameters, like opening size and location, aspect ratio of openings, connection between frame and infill wall, ductile detailing in frame members, material properties, failure modes, etc. on behavior of masonry infill RC frames. Ac- cordingly, several analytical models have been proposed in the literature and seismic codes of some countries to model the stiffness and strength properties of infill walls. Most of the past studies and seismic codes recommend modeling the infills as equivalent diagonal struts, and cross-sectional area of the struts are reduced appropriately to account for openings in the walls. Analytical methods have also been proposed to estimate the possible mode of failure and lateral load carrying ca- pacity of infill frames with and without openings. The current article is intended to review and compare past relevant stud- ies and seismic codes of different countries on in-plane lateral load behaviour and modeling approaches for masonry infill RC frames with openings. The comparative study may help designers and code developers in selecting and recommending suitable analytical models for estimating strength, stiffness, failure modes, and other properties of infill RC frames with openings.

Analytical Model for RC Beams with Externally Bonded Laminates Using Strut-and-Tie Method

An analytical model for RC beam strengthened with externally bonded laminates based on the strut-and-tie method is reported herein for predicting the strength and mode of failure of the strengthened RC beam. From the proposed model, four inequality equations were derived corresponding to four possible modes of failure. These four inequality equations define a safe domain. When the loading path up to the ultimate flexural limit state of a beam is plotted on the same diagram, the mode of failure and strength of the beam can be identified. The possible modes of failure consist of both flexure-type and shear-type failures. Flexure-type failure is due to the yielding of internal longitudinal reinforcement or the yielding of externally bonded laminates, whereas shear-type failure is due to the crushing of the diagonal compressive concrete strut or the yielding of the shear reinforcement. The failure mode initiated by one flexure-type followed by another is possible. Mode of failure initiated by one flexure-type followed by a shear-type is also possible but not otherwise. In short, this model describes the mode of failure and the corresponding strength of an RC beam strengthened with externally bonded laminates, which can be used to verify the adequacy of design for beam strengthening.

Cyclic Performance of Composite Bracing Members

In seismic regions, steel tubular bracing members have widely been used in steel structures. Although there are some shortages with such systems, due to their economical advantages, they are being used in many structures. The steel hollow brace members exhibit stable hysteretic behavior up to the point of first local buckling, and subsequently they exhibit significant degradation in strength and ductility. Comparing composite braces with steel braces, the presence of concrete infill has shown to influence the possible mode of failure in the specimens. It is also found that the infill supplies the extra compression resistance of the brace after several load reversals; consequently improves ductility capacity of the system. In this research, using the finite element method, the seismic behavior of the composite bracing system with and/or without the infill is simulated. Analytical models with the capability of displaying the cyclic behavior are utilized for concrete filled tubular bracing members. The analysis has been implemented numerically by employing the general purpose finite element software. Overall, it is shown that the difference in improvement gained by concrete infilling was attributed to pertinent variables such as the width to thickness ratio, shape of the section and concrete compressive strength, yield stress of the steel tube and the axial load level on the stiffness, strength and ductility of concrete-filled steel tube braces. In addition, this paper provides information on key response parameters, including tensile and compressive strength and post-buckling capacity, as well as, ductility and energy dissipation capabilities. Particular attention is given to the influence of member slenderness. The analytical findings are compared with the recommendations of a number of international codes of practice; and areas of agreement or discrepancy are highlighted. Finally, special considerations for enhancing the seismic performance goals are discussed.