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Cracks are one of the major characteristics of soil structure failure. Successfully performed numerical simulation of the soil crack evolution process is conducive to the prediction of potential dangers. In recent years, crack evolution simulation has been greatly facilitated in the field of fracture mechanics by the development of the extended finite-element method (XFEM). However, it is rarely used to simulate crack evolution in earth structures, because in most cases soil cannot be regarded as a quasi-brittle material. Based on the characteristics of stress concentration and redistribution at the tip of a soil crack revealed by numerical tests, this paper proposes a discriminating method for crack propagation that can reflect the influence of the stress field at the soil crack tip on the crack propagation direction, which is then coded to an XFEM program. Compared with existing methods, this new method is found to be more accurate and effective. [ABSTRACT FROM AUTHOR]

Cracking is a common failure mode in asphalt concrete (AC) pavements. Many tests have been developed to characterize the fracture behavior of AC. Accurate crack detection during testing is crucial to describe AC fracture behavior. This paper proposes a framework to detect surface cracks in AC specimens using two-dimensional digital image correlation (DIC). Two significant drawbacks in previous research in this field were addressed. First, a multiseed incremental reliability-guided DIC was proposed to solve the decorrelation issue due to large deformation and discontinuities. The method was validated using synthetic deformed images. A correctly implemented analysis could accurately measure strains up to 450%, even with significant discontinuities (cracks) present in the deformed image. Second, a robust method was developed to detect cracks based on displacement fields. The proposed method uses critical crack tip opening displacement (δc) to define the onset of cleavage fracture. The proposed method relies on well-developed fracture mechanics theory. The proposed threshold δc has a physical meaning and can be easily determined from DIC measurement. The method was validated using an extended finite-element model. The framework was implemented to measure the crack-propagation rate while conducting the Illinois-flexibility index test on two AC mixes. The calculated rates could distinguish mixes based on their cracking potential. The proposed framework could be applied to characterize AC cracking phenomenon, evaluate its fracture properties, assess asphalt mixture testing protocols, and develop theoretical models. [ABSTRACT FROM AUTHOR]

Line contact usually causes stress concentration, resulting in the wear and failure of materials and structures. The characterization of the contact phenomenon thus plays an important role in the safety evaluation of materials and structures. In this paper, an inverse method is developed that can identify the principal parameters in contact by employing the experimentally measured displacements and mathematical optimization. Basing on the contact theory, the relationship between the contact parameters and displacements on the interface is modeled. The parameters are then inversed by matching the modeled displacements to the experimentally measured data through optimization. Only the displacements on the surface of the contact member are required in this method, which can be easily measured by a segmentation-aided digital image correlation approach. By utilizing the proposed method, the contact between a cylinder and a plate is characterized and the variations of the contact parameters associated with the applied loads and cylinder's radius are discussed. Error estimation is carried out by implementing the proposed method with the finite element simulated data. Results show that the proposed method can provide reliable identification results under the influence of different kinds of disturbances. [ABSTRACT FROM AUTHOR]

This paper presents a three-dimensional (3D) image-based microstructural computational modeling framework to predict the thermoviscoelastic, thermoviscoplastic, and thermoviscodamage response of asphalt concrete. X-ray computed tomography is used to scan dense-graded asphalt concrete (DGA) to obtain slices and planar images, from which the 3D microstructure is reconstructed. Image processing techniques are used to enhance the quality of images in terms of phase identification and separation of particles. This microstructure is divided into two phases: aggregate and matrix. The aggregate phase is modeled as an elastic material and the matrix phase is modeled as a thermoviscoelastic, thermoviscoplastic, and thermodamage material. Stress-strain response, damage propagation, and the distributions of the viscoelastic and viscoplastic strains are predicted by performing virtual uniaxial and repeated creep-recovery tests of the developed 3D model of asphalt concrete. The effects of loading rate, temperature, and loading type on the thermomechanical response of asphalt concrete are investigated. In addition, the microscopic and macroscopic responses of DGA are compared with those of stone matrix asphalt (SMA). The results demonstrate that SMA can sustain higher strain levels at the microscopic level and higher macroscopic ultimate strength. The damage in SMA is more localized than in DGA. The microstructure-based framework presented in this paper can be used to offer insight on the influence of the distribution and properties of microscopic constituents on the macroscopic behavior of asphalt concrete. [ABSTRACT FROM AUTHOR]

Crack growth in rocks with preexisting flaws is of real concern for many rock engineering applications. The present paper considers the flaw that has a narrow gap that eventually gets closed on loading. Crack growth behavior leads to different failure modes, and corresponding strength characteristics were studied with respect to flaw angle. An experimental study was carried out with gypsum specimens replicating rock, that considered single and double flaws subjected to uniaxial compression. Crack growth and stress behaviors were analyzed and compared. The study was later extended to include numerical analyses using ABAQUS that adopted the extended finite element method with a cohesive zone model to capture crack growth behavior. The numerical model successfully mimicked wing crack propagation similar to the experimental results. The appearance of shear cracks and their growth upon loading was also predicted and crack initiation stress with respect to wing- and shear cracks was investigated. No significant differences were observed for single flaw specimens. However, in the case of multiple flaws with nonparallel configurations, the effect of shielding had a significant impact on coalescence behavior. [ABSTRACT FROM AUTHOR]

This paper presents a computational investigation of the response of steel beam-column assemblies with moment connections under monotonic loading conditions simulating a column removal scenario. Two beam-column assemblies are analyzed, which incorporate (1) welded unreinforced flange bolted web connections, and (2) reduced beam section connections. Detailed models of the assemblies are developed, which use highly refined solid and shell elements to represent nonlinear material behavior and fracture. Reduced models are also developed, which use a much smaller number of beam and spring elements and are intended for use in future studies to assess the vulnerability of complete structural systems to disproportionate collapse. The two modeling approaches are described, and computational results are compared with the results of the full-scale tests described in the companion paper. Good agreement is observed, demonstrating that both the detailed and reduced models are capable of capturing the predominant response characteristics and failure modes of the assemblies, including the development of tensile forces associated with catenary action and the ultimate failure of the moment connections under combined bending and axial stresses. [ABSTRACT FROM AUTHOR]

The development of corrosion as a result of tendon exposure to moisture or corrosive media often leads to wire fractures. Such fractures in unbonded tendons are expected to induce global strand and anchor response through the progression of prestress loss from the break to the end anchors. Radial pressure, interwire friction, and lateral confinement, however, affect the magnitude of prestress loss carried to the anchors and have important implications on breakage detectability by tendon monitoring methods that rely on anchor response. This paper presents an experimental investigation of tendon behavior after successive wire cuts in confined and unconfined conditions and demonstrates the effects of confinement on stress recovery. In addition to analysis of strand prestress loss and axial strain along individual wires, the strand's dynamic postbreakage response was examined. Moreover, the effects of deviators on stress recovery were tested with a multistrand tendon specimen. A finite-element model of a seven-wire strand was developed and experimentally validated. Both experimental and numerical results showed significant prestress loss even at distant locations from wire breaks and confirm a correlation between wire breakage and modal properties, which can be a useful damage indicator. [ABSTRACT FROM AUTHOR]

We extend the applicability of the embedded unit cell (EUC) method to three-dimensional (3D) fracture problems, which are modeled by the extended finite element method (XFEM). The EUC method is a concurrent multiscale method based on the computational homogenization theory for nonperiodic domains. Herein, we show that this method can accurately estimate fracture parameters and, in particular, stress intensity factors using the J-integral method. Additionally, the method is shown to capture crack propagation within the microscale domain, as well as cracks initiating at the microscale and propagating outwards onto the macroscale through the internal subdomain boundaries. To demonstrate the accuracy, robustness, and computational efficiency of the proposed method, several 3D numerical benchmark examples, including planar cracks with single and mixed-mode fractures, are considered. In particular, we analyze horizontal, inclined, square, and penny-shaped cracks embedded in a homogeneous material. The results are verified against full FEM models and known analytical solutions if available. Practical Applications: The insights of this research offer practical application for engineers and scientists in designing more resilient and durable structures. By extending the EUC method to 3D fracture problems, the study addresses the ability to forecast and access fracture phenomena in materials. This method is shown to be an effective approach for exploring the interaction between local microscopic discontinuities and cross-scale crack propagation, crucial for evaluating the durability of engineering structures. The EUC approach, integrated with XFEM, provides a comprehensive methodology for analyzing different fracture scenarios, including stationary mixed-mode cracks and crack-propagation examples. Its ability to accurately transition from microscale to macroscale analysis without remeshing introduces a valuable computational advantage, making it a more cost-efficient solution in fracture analysis. This research's application offers tangible benefits in industrial context, especially in aerospace, automotive, and construction industries, where precise evaluation of structure and material failure can lead to more cost-efficient and safer designs by reducing the maintenance costs and failure risks. [ABSTRACT FROM AUTHOR]

The extended finite-element method (XFEM) was proposed to simulate the problem of crack growth without any remeshing. In this paper, the penalty function method is introduced to deal with the contact constraints, and the trial-and-error method is employed to investigate the converged contact state. The monitoring points seed on the interface to detect the contact states of the cracks and to interpolate the displacement of the grid node. The formulations of the dynamic frictional contact problem for crack slip are established based on the multidimensional space method. In this proposed method, the implicit Newmark time integration scheme is applied to deal with the problems of dynamic frictional contact. Moreover, a numerical case is illustrated to verify the precision and robustness of the proposed method. It is found that the numerical results obtained from proposed method agree well with those obtained from the standard finite-element method. [ABSTRACT FROM AUTHOR]

In the present paper, stress intensity factor (SIF) analyses and fatigue-crack-growth simulations of corner cracks emanating from loaded pinholes of attachment lugs in structural assemblies are carried out for different load cases. A three-dimensional (3D) symmetric Galerkin boundary-element method (SGBEM) and FEM alternating method is developed to analyze the nonplanar growth of these surface cracks under general fatigue. The 3D SGBEM-FEM alternating method involves two very simple and coarse meshes that are independent of each other: (1) a very coarse FEM mesh to analyze the uncracked lug, and (2) a very coarse SGBEM mesh to model only the growing crack surface. By using the SGBEM-FEM alternating method, the nonplanar growth of cracks in 3D (surfaces of discontinuity) up to the failure of structures are efficiently simulated, and accurate estimations of fatigue lives are made. The accuracy and reliability of the SGBEM-FEM alternating method are verified by comparing them to other FEM solutions, as well as experimental data for fatigue-crack growth available in the open literature. The SIF calculations, crack surface evolutions, and fatigue-life estimations are all in good agreement with other detailed FEM solutions and experimental observations. It is noted that for fracture and fatigue analyses of complex 3D structures such as attachment lugs, a pure FEM requires several hundreds of thousands or even millions of elements, whereas the present 3D SGBEM-FEM alternating method requires only up to 1,000 FEM elements and SGBEM elements. It thus demonstrates that the present SGBEM-FEM alternating method, among the many Schwartz-Neumann-type alternating methods developed in the past 20-30 years are suitable for analyzing fracture and fatigue-crack propagation in complex 3D structures in a very computationally efficient manner, as well as with very low human labor costs. [ABSTRACT FROM AUTHOR]

The epoxy-bonded fiber-reinforced polymer (FRP) technique has been attracting more attention for repairing steel structures. In this paper, cracked steel plates repaired with FRP laminates were investigated with the finite element (FE) method. Three different FRP configurations designed with equivalent tensile stiffnesses were employed to repair cracked steel plates to determine the best FRP configuration for extending the crack growth life. The stress intensity factor () and the crack growth life of FRP-repaired specimens were compared, and the parameters influencing the repair effectiveness were analyzed. The results showed that FRP configurations have an obvious effect on and the crack growth life. Configuration 1 was more effective than Configuration 2. The superiority of Configuration 1 over Configuration 2 was more evident with an increase of FRP thickness and/or initial crack length, but the superiority decreased with a thicker adhesive thickness and/or a larger local debond size. However, a comparison between Configuration 1 and Configuration 3 was highly dependent on FRP thickness, initial crack length, FRP width arranged in Configuration 3, and local debond size. Based on limited analyses of the three FRP configurations, FRP Configuration 1 is recommended for practical engineering applications when the fatigue cracks of steel members are similar to the center crack. Finally, two additional investigations were recommended for future study. [ABSTRACT FROM AUTHOR]

A new three-dimensional finite-element model of two-dimensional, triaxially braided composites is presented in this paper. This mesoscale modeling technique is used to examine and predict the deformation and damage observed in tests of straight-sided specimens. A unit cell-based approach is used to consider the braiding architecture and the mechanical properties of the fiber tows, the matrix, and the fiber tow-matrix interface. A 0°/±60° braiding configuration has been investigated by conducting static finite-element analyses. Failure initiation and progressive degradation has been simulated in the fiber tows by using the Hashin failure criteria and a damage evolution law. The fiber tow-matrix interface was modeled by using a cohesive zone approach to capture any fiber-matrix debonding. By comparing the analytical results with those obtained experimentally, the applicability of the developed model was assessed and the failure process was investigated. [ABSTRACT FROM AUTHOR]

Web holes are often made in wood I-joists to allow passage of services. Design properties of wood I-joists with a web hole are commonly developed through testing which leads to empirical design information. This paper describes a mechanics-based method to predict the strengths of wood I-joists with a circular web hole that is suitable for implementation as a design tool. Curved beam theory is used to compute stresses around a hole. Peak tensile stresses obtained from curved beam analysis agree well with those predicted using the finite-element method. Failure load is attained by the application of fracture mechanics based finite area method. The method developed is used to predict failure loads of wood I-joists of different depths with different web hole sizes. Simplification of the method leads to the development of a simple expression that can be used for engineering design. It is found that the predicted strengths are in a good agreement with the corresponding test results. The calculation method developed can potentially replace the testing approach generally adopted by the wood I-joist industry. [ABSTRACT FROM AUTHOR]

Asphalt paving layers, particularly the surface course, exhibit vertically graded material properties. This grading is caused primarily by temperature gradients and aging related stiffness gradients. Most conventional existing analysis models do not directly account for the continuous grading of properties in flexible pavement layers. As a result, conventional analysis methods may lead to inaccurate prediction of pavement responses and distress under traffic and environmental loading. In this paper, a theoretical formulation for the graded finite element method is provided followed by an implementation using the user material subroutine (UMAT) capability of the finite element software ABAQUS. Numerical examples using the UMAT are provided to illustrate the benefits of using graded elements in pavement analysis. [ABSTRACT FROM AUTHOR]

Thin bonded cement-based overlays include surface repairs, toppings, and linings, especially on slabs, slabs on soil, concrete pavements, and tunnel walls. The aim of this paper is to show that, contrary to a widely held belief, debonding of cement-based overlays is governed not by the shear stress along the overlaybase interface but by the built-in tensile stress perpendicular to this interface. After a brief comparison with laminated composite materials and with beams reinforced by bonded strips (made of metal or of composite), the specific case of thin cement-based overlays is presented. Different conditions of debonding of an overlay are investigated. In all cases, the tensile stress perpendicular to the base-overlay interface is confirmed as the designing parameter. In terms of fracture mechanics, debonding of cement-based overlays is governed by a mixed mode in which mode I is widely dominant. There is a lack of appropriate tests to accurately characterize the mechanical behavior of the interface. Nevertheless, finite-element calculation relying on the mean values of the shear and tensile strength of the interfacial bond (calculation was performed with CESAR code) provides a good approximation of debonding initiation and propagation. [ABSTRACT FROM AUTHOR]

Model-based crack identification in beam-like structures has been a classic problem. The authors have recently developed a framework to identify crack damage in beams based on a cracked beam element model, which stems from the local flexibility and fracture mechanics principles. This paper presents an experimental study on the cracked beam element model for crack damage identification in a physical testing environment. Five solid beam specimens were prepared with different numbers of cracks, and they were subjected to a modal testing and analysis procedure to extract the natural frequencies and mode shapes. The extracted modal data were then compared with the predicted counterparts using the cracked beam element model to verify the accuracy of the model. The extracted modal data were also employed to inversely identify the cracks with the cracked beam element model through a model updating procedure. Results indicate that all the cracks can be identified correctly with accurate crack depth and location information. To enhance the modal dataset for finite-element (FE) model updating, the artificial boundary condition (ABC) technique has also been applied on the test beams, and the incorporation of such frequencies proves to enhance the identification of cracks from the FE model updating. [ABSTRACT FROM AUTHOR]

Extensive damage to light gauge steel roofing systems caused by high wind events such as cyclones and storms has been a concern to the communities living in cyclone/storm prone areas over many years. In recent times, pull-through failures of roof battens occurring in their bottom flange to rafter or truss connection have become the main reason for severe roof failures. Therefore, a detailed experimental study was first undertaken using full-scale and small-scale tests to investigate the pull-through failures of roof battens subject to high wind uplift loads. However, since experimental tests can be expensive and time consuming, the ability to successfully use numerical models is imperative. Hence a detailed numerical study was undertaken by developing suitable finite-element models with the inclusion of a suitable failure criterion to predict the initiation of critical pull-through failures of roof battens that are associated with a tearing fracture around the screw fastener head edge. The overall load versus deformation behavior, ultimate failure loads, and failure modes were compared with the experimental results to validate the developed finite-element models. The ability of the validated finite-element models to accurately predict the pull-through failure loads of roof battens for other cases was evaluated by comparing relevant experimental results. This paper presents the details of this numerical study and the results. [ABSTRACT FROM AUTHOR]

In cantilever-erected concrete box-girder bridges, a great number of longitudinal posttensioning tendons curve twice in the top flange to fit their anchor position. The radial force attributable to the curved tendons produces transverse bursting stresses, resulting in tension in the concrete of the top flange. In practice, longitudinal cracking is sometimes observed in the convex side of the horizontally curved tendons. Thus, it can be inferred that the transverse bursting stresses induced by horizontally curved tendons are partially responsible for the cracking. To seek an analytical solution to such scenarios, this study used a semi-infinite slab model with proper boundary conditions. By introducing the Airy stress function and its derivative on the boundary, an analytical formula for transverse tensile stresses was developed, and this formula was verified to have good accuracy as compared with finite-element analysis. Analysis revealed that the transverse bursting stresses were predominately affected by the curved angle and the distance of the two inflection points. Finally, this paper proposes countermeasures to control this unfavorable effect. [ABSTRACT FROM AUTHOR]

The behavior of materials and structures is strongly influenced by the loading rate. Compared with quasi-static loading structures loaded by high loading rate and impact acts in a different way. First, there is a strain-rate influence on strength, stiffness, and ductility, and, second, there are inertia effects activated. Both influences are clearly shown in experiments. Although steel does not exhibit significant strain rate sensitivity, the dynamic fracture of steel is highly sensitive on loading rates. In this paper, the static and dynamic fracture of steel is numerically studied on a compact tension specimen (CTS), which is loaded under loading rates up to 100 m/s. First, the proposed microplane model for steel is discussed and verified for monotonic and cyclic quasi-static loading. Subsequently, three-dimensional (3D) finite element dynamic fracture analysis is carried out. It is shown that the resistance of steel (apparent strength and toughness) increases progressively after the critical strain rate (approximately 100/s) is reached. Moreover, the crack branching phenomena and significant decrease of ductility are observed. The phenomena that are also well known from experimental evidence are attributed to the effect of structural inertia and inertia related to the high nonlinear behavior of steel at the crack tip and in the plastification zone. The numerical results indicate that maximum crack velocity of steel is much lower than the Rayleigh wave velocity, and for the investigated steel, it reaches approximately 400 m/s. [ABSTRACT FROM AUTHOR]

This paper outlines a general methodology used to design digital data streams of electronic sensors attached to critical components of a structure to be processed by a structural impairment detection system (SIDS). The methodology begins by evaluating a specific structure, establishing a baseline behavior profile, and identifying specific structural impairments that are likely to occur. Finite-element modeling of a specific test bed is presented as a tool with which to design and create diagnostic data streams. Establishing a list probable impairments is critical to designing diagnostic data streams with which to implement a SIDS capable of indicating and, more importantly, identifying digital data signatures that may indicate specific structural impairments. Once a set of impairment scenarios is defined, finite-element models representing those impairments are created and several locations sensitive to modeled impairments are identified. A matrix of different locations and measurement types determines the instrumentation schedule. Through experimental observation and iterative structural analysis, diagnostic data streams are created that serve as (1) patterns for training neural diagnostic algorithms and (2) patterns to be interrogated to evaluate a testbed structure. [ABSTRACT FROM AUTHOR]

In this paper, the propagation behavior of an induced hydraulic fracture in the presence of a natural fracture is described. A complex meshing and finite-element technique are employed to couple a poroelastic formation, a hydraulic fracture, and an arbitrarily oriented natural fracture. Possibilities of fracture deviation, arrest, and crossing for various angles of approach are investigated under different scenarios of in situ stress contrast, rock strength, and natural fracture geometry (length). Results of this study show that orientation of natural fracture and its length have a profound effect on induced hydraulic fracture propagation. It has been observed that, in most cases, the induced hydraulic fracture crosses short natural fractures (). As the induced hydraulic fracture approaches the natural fracture, fluid leak off increases, and consequently, the width of the induced fracture at the wellbore (fracture mouth) decreases. Once the induced hydraulic fracture breaks out of the natural fracture, the fluid leak off decreases, thus increasing the width of the induced fracture. It has been also observed that propagation of induced fracture is blocked or diverted by the presence of a long natural fracture (). With an increase in the injection rate, however, the induced fracture is likely to cross a long natural fracture (). The new understandings derived from the fully coupled poroelastic model have many beneficial applications, including design and optimization of hydraulic fracture treatments in naturally fractured reservoirs (tight gas and shale gas reservoirs) and permeability enhancement by fluid-induced shear displacement of fracture surfaces [enhanced geothermal systems (EGS)]. [ABSTRACT FROM AUTHOR]

In the field of nondestructive testing of structural components, active thermography methods are increasingly in demand. The most experience is available in testing of carbon-fiber-reinforced plastic (CFRP) or similar types of composite material. One of the emerging techniques is ultrasound excited thermography, which has not been fully transferred to massive steel members used in constructional steelwork thus far. The idea of ultrasound excitation is to generate elastic waves that propagate inside the investigated structure. In case of internal flaws, such as cracks, the boundary faces move relative to each other. The resulting rubbing and clapping of crack faces generate frictional heat, which is detected by means of an infrared camera. This paper demonstrates the usage of high-frequency mechanical excitation to detect cracks in hot-rolled girders and reduced plate specimens. The ultrasonic lock-in and the ultrasonic sweep thermography approaches are presented. Localized heating of the crack regions and distributed heating patterns caused by material damping can be observed. The influences of the tuned frequency and the crack depth as well as effects of prestressing and repeated excitation are discussed. In addition to experimental results, a finite-element simulation of the thermostructural problem is conducted. The model can be easily adjusted to match the experimental results of a performed ultrasonic sweep thermography. [ABSTRACT FROM AUTHOR]

The catastrophic earthquake that struck the city of L'Aquila in early April 2009 caused extensive damage to buildings at the University of L'Aquila. Among these edifices are those of the Engineering Faculty, which, in particular, suffered large structural displacements and accelerations that resulted in failures of nonstructural elements (infills, false ceilings, door and window frames), the breakage of wiring and piping systems, and the destruction of furniture and machinery. Of these buildings, the so-called Edifice A presents the most critical damage scenario, requiring a significant rehabilitating intervention. The structural behavior of this building, composed of seven independent RC substructures, is the object of intensive investigation; this is in part because irregularities among these substructures, in terms of geometry, stiffness, and weight distribution, provide a rich case study for interpreting different structural and nonstructural damage scenarios. The paper interprets the observed damage through use of incremental analyses for evaluation of the threshold between linear and nonlinear structural behavior. For this purpose, several finite-element (FE) models are developed with increasing complexity in the geometry and the shear-wall modeling. Capacity curves obtained by the nonlinear pushover analyses are afterward compared with the perceived seismic demands of the structures including site effects. Moreover, based on simplified analyses, numerical evaluations of acceleration-producing failures in the infill walls and the split-face brick walls were performed to achieve an overall description of the structural and nonstructural damage. [ABSTRACT FROM AUTHOR]

The paper reports the results of a research aimed at analyzing and interpreting the cracking pattern on the Cappella dei Principi (Prince's Chapel, the Medici's mausoleum) in the Basilica of San Lorenzo (Florence, Italy). The research was motivated by the sudden collapse of a keystone of an internal barrel vault sustaining one of the lateral apses. After a brief description of the geometry of the structure, the principal results obtained from in situ surveys (flat-jack tests and cored samples) are described; then the numerical analyses developed both to obtain the static identification of the monument and to assess the possible causes leading to the observed failure are illustrated. The numerical modeling operation has been performed step by step, from linear and quite simple models built with plane elements up to a nonlinear model with three-dimensional elements. The nonlinear FEM, which has been tuned by utilizing the results of the in situ measures, is allowed to both qualitatively and quantitatively reproduce the behavior of the structure and its static problems in the area of the barrel vault over the side apses, allowing for justification of the manifested damage. The comprehension of the structural behavior allows identification of a proper retrofitting strategy. [ABSTRACT FROM AUTHOR]

The method of testing asphalt mixtures including initial cracks appearing in pavements is presented in this paper. The main aim of the study was a determination of the durability of asphalt mixtures in regard to crack sizes. For this purpose, the four-point bending test was performed according to the technical standard PN-EN 12697-24. The test was conducted with selected asphalt mixtures under the controlled strain and with the application of different crack sizes. Specimens with cracks were analyzed. Moreover, a model based on finite-element method (FEM) calculations was worked out, which allowed for the verification of conditions of the asphalt mixtures' response to strains and the assessment of the state of stresses and strains at the crack tip. The wide range of studied conditions helped to determine the fatigue criterion for the 'cracked' beam in the fatigue tests. The presented fatigue condition is very useful in the estimation of fatigue durability of asphalt mixtures. The results of analyses clearly showed the influence of cracks on the decrease in stiffness modulus. This effect has a nonlinear behaviour in the case of larger cracks. The proposed FEM model of beam including cracks is very useful in studies of stresses and tensile strains concentrated at the crack tip. [ABSTRACT FROM AUTHOR]

The objective of this paper is to evaluate the deformation behavior of clay-based landfill covers subjected to differential settlements through centrifuge model studies and finite-element analyses (FEA). A series of centrifuge tests were performed on model soil barriers subjected to continuous differential settlements through a motor-based differential settlement simulator by varying the thickness of the soil barrier with and without overburden equivalent to that of landfill coves at 40 gravities. In addition, a parametric study was carried out numerically by varying the thickness of the soil barrier and overburden pressure by using PLAXIS, a geotechnical finite-element code. The modeling considerations adopted in FEA were developed such that they are close to the centrifuge model tests in prototype dimensions. Differential settlements in FEA were assigned by using predefined displacement profiles. Results from centrifuge model tests deduce that both 0.6 and 1.2 m thick soil barriers were observed to experience full-depth cracks at the zone of maximum curvature and fail to serve the basic purpose of an effective hydraulic barrier. The results from FEA indicate the development of higher values of tensile stresses and strain extending throughout the thickness of the soil barrier at the zone of maximum curvature, which indirectly advocate the possibility of formation of tension cracking when the generated tensile stresses caused by deformation exceed the permissible tensile strength of the soil barrier material. The magnitude of the horizontal tensile stress along the top surface of the soil barrier at the zone of maximum curvature was found to be suppressed with an increase in the value of overburden pressure. When the soil barrier was subjected to an overburden pressure in the range of 50-75 kPa, there exists a complete transformation of tensile stresses to compressive stresses, which indirectly suggests that there can be no prospects of development of tension cracks even at a distortion level of 0.125. [ABSTRACT FROM AUTHOR]

Displacement coefficients and profiles have been proposed as objective indexes for bridge structural condition evaluation by many researchers. In this paper, experimental data of the following type were collected for structural identification (St-Id) of a deteriorated bridge: (1) static displacement and strain measurements taken under proof-load level and (2) multireference impact testing (MRIT) data from one of the spans of a three-span, cast-in-place reinforced concrete T-beam bridge (Smithers Bridge). The MRIT was used to generate the modal data for computation of the modal flexibility and displacement profiles. Several significant obstacles were encountered during the St-Id of the Smithers Bridge including high damping level (which led to difficulties in identifying and selecting the poles), finite-element (FE) model updating challenges, and correlation of the MRIT results with truck load test measurements. The first challenge was addressed through the use of the complex mode indicator function method of modal identification, which is capable of identifying highly damped modes. Then the updating of the FE model was accomplished using the Strand7 FE analysis package coupled with the MATLAB application programming interface. Finally, to allow for direct comparison of the MRIT and truck load results, two strategies were employed. The first involved the redistribution of truck load force to the MRIT degrees of freedom and the second utilized interpolation functions for modal expansion of the MRIT results to include the truck tire locations. The St-Id procedure used during this application was designed to mitigate blatant human error and epistemic uncertainty in the data interpretation process. Successful results from the MRIT demonstrated the reliability of the applications for bridge condition assessment based on impact testing. [ABSTRACT FROM AUTHOR]

A critical aspect in the design of tubular bridges is the fatigue performance of the structural joints. The estimation of a fatigue crack life using the linear elastic fracture mechanics (LEFM) theory involves the calculation of stress intensity factors (SIF) at a number of discrete crack depths. The most direct way is to carry out modeling by either the finite-element method (FEM) or the boundary-element method (BEM). For tubular joints commonly found in tubular bridges and off-shore structures, due to the complicated geometry resulting from the tube intersections and welding, the construction of the numerical model often becomes a complex process. This paper presents two different model construction techniques that have been developed independently at the Swiss Federal Institute of Technology (EPFL) and the Nanyang Technological University (NTU), Singapore, that are based in the BEM and the FEM, respectively. The SIF values obtained by these two methods are compared. It is found that as long as consistent geometric models are employed, compatible SIF values can be obtained by both approaches. The best and the most consistent values are obtained for the deepest point along the crack front and should be used for fatigue-life computations. [ABSTRACT FROM AUTHOR]

Intermediate crack-induced debonding (IC debonding) is a common failure mode of RC beams strengthened with externally bonded fiber-reinforced polymer (FRP) reinforcement. Although extensive research has been carried out on IC debonding, much work is still needed to develop a better understanding of the failure mode and a more reliable strength model. This paper presents an advanced finite-element (FE) model on the basis of the smeared-crack approach for predicting IC debonding failure. Existing FE models of the same type are generally deficient in capturing localized cracks (both their pattern and widths). This deficiency is overcome in the proposed FE model through the accurate modeling of interfaces between the concrete and both the internal steel and the external FRP reinforcements. The capability and accuracy of the proposed model are demonstrated through comparisons of its predictions with selected test results. The importance of accurate modeling of localized cracking is also explained using numerical results obtained from the FE model. [ABSTRACT FROM AUTHOR]

This paper demonstrates the size effect on the shear strength of reinforced concrete (RC) beams with stirrups and does so in two separate and independent ways: (1) by fracture mechanics, based on finite-element analysis calibrated by a large beam test; and (2) by purely statistical analysis in which a newly assembled database of 234 tests is filtered to eliminate spurious size effects caused by nonuniformity of secondary influencing parameters. Both ways show that stirrups, whether minimum or heavier, cannot suppress the size effect completely, although they can mitigate it significantly for beam depth d<1 m (39.4 in.). The effect of stirrups is to push the size effect curve in logarithmic scale into sizes larger by about one order of magnitude. For beam depths d<0.5 m, 1, 2, and 6 m (19.7, 39.4, 78.7, and 236.2 in.), the percentages of beams whose shear strength is below the code limit are calculated as 3.5, 6.5, 15.7, and 55.1%, respectively. The corresponding failure probabilities are 10-6, 10-5, 10-4, and 10-3, whereas 10-6 is the generally accepted standard for a tolerable maximum in risk analysis. It follows that, for beams with stirrups having depth >1 m (39.4 in.), the size effect cannot be neglected. [ABSTRACT FROM AUTHOR]

A combined experimental and numerical program was conducted to study the in-plane shear behavior of clay brick masonry walls strengthened with near surface mounting carbon-fiber-reinforced polymer (CFRP) strips. This paper is focused on the numerical program. A two-dimensional finite-element (FE) model was used to simulate the behavior of FRP-strengthened wall tests. The masonry was modeled using the micromodeling approach. The FRP was attached to the masonry mesh using the shear bond-slip relationships determined from experimental pull tests. The model was designed in a way so that FRP crossing a sliding crack (perpendicularly) would prevent crack opening, normal to the direction of sliding (dilation), and increase sliding resistance. This sliding resisting mechanism was observed in the experimental tests. The FE model reproduced the key behaviors observed in the experiments, including the load-displacement response, crack development, and FRP reinforcement contribution. The FE model did not include masonry cracking adjacent to the FRP and through the wall thickness (as observed in some experiments). This type of cracking resulted in premature FRP debonding in the experiments. Debonding did not occur in the FE model because this type of masonry cracking was not modeled. [ABSTRACT FROM AUTHOR]

Over the past years, with increasing traffic volumes and higher wheel loads, fatigue damage in steel parts of typical orthotropic steel bridge decks has been experienced on heavily trafficked routes. A demand exists to find a durable system to increase the fatigue safety of orthotropic steel bridge decks. A solution might be to enhance the stiffness of the traditional orthotropic bridge deck by using a cement-based overlay. In this paper, an orthotropic steel bridge deck stiffened with a cement-based overlay is analyzed. The analysis is based on nonlinear fracture mechanics, and utilizes the finite-element method. The stiffness of the steel deck reinforced with an overlay depends highly on the composite action. The composite action is closely related to cracking of the overlay and interfacial cracking between the overlay and underlying steel plate (debonding). As an example, a real size structure, the Faro\ bridges located in Denmark, are analyzed. The steel box girders of the Faro\ bridges spans 80 m, and have a depth of 3.5 m, and a width of 19.5 m. The focus of the present study is the top part of the steel box girders, which is constructed as an orthotropic deck plate. Numerous factors can influence the cracking behavior of the cement-based overlay system. Both mechanical and environmental loading have to be considered, and effects such as shrinkage, temperature gradients, and traffic loading are taken into account. The performance of four overlay materials are investigated in terms of crack widths. Furthermore, the analysis shows that debonding is initiated for a certain crack width in the overlay. The load level where cracking and debonding is initiated depends on the stress-crack opening relationship of the material. [ABSTRACT FROM AUTHOR]

This is a practical paper which consists of investigating fracture behavior in asphalt concrete using an intrinsic cohesive zone model (CZM). The separation and traction response along the cohesive zone ahead of a crack tip is governed by an exponential cohesive law specifically tailored to describe cracking in asphalt pavement materials by means of softening associated with the cohesive law. Finite-element implementation of the CZM is accomplished by means of a user subroutine using the user element capability of the ABAQUS software, which is verified by simulation of the double cantilever beam test and by comparison to closed-form solutions. The cohesive parameters of finite material strength and cohesive fracture energy are calibrated in conjunction with the single-edge notched beam [SE(B)] test. The CZM is then extended to simulate mixed-mode crack propagation in the SE(B) test. Cohesive elements are inserted over an area to allow cracks to propagate in any direction. It is shown that the simulated crack trajectory compares favorably with that of experimental results. [ABSTRACT FROM AUTHOR]

This paper presents finite-element and fracture mechanics studies of plate girders with corrugated webs. The failure mode of this type of girder under fatigue loading is distinguished by its location in the tension flange and is discussed in detail. A comprehensive nonlinear finite-element analysis was conducted to study the effects of the different geometrical parameters of this type of girder on the stress concentration at different locations, and to explain findings of an earlier experimental study. Different parameters, such as the radius of curvature between the web folds, the inclined fold angle of inclination, and the use of sinusoidal corrugation were investigated. Two sources of stress concentration leading to fatigue cracking were isolated; one is dependent on the radius of curvature between the web folds and the other depends on the inclination angle of the inclined fold. An analytical technique based on fracture mechanics is proposed to determine the fatigue life of the girders. The technique enables designers to evaluate the fatigue life of structures built using corrugated web steel girders and subjected to fatigue-type loading, such as bridges or industrial facilities subjected to dynamic loading. [ABSTRACT FROM AUTHOR]

A damage detection and assessment method has been developed in this paper using the concepts of inverse method and fracture mechanics. The objectives are to detect, locate, and quantify any damage that has occurred within a beam during its service using displacement measurements taken at arbitrary points along it. Grobner bases are used to check the compatibility among the measured displacement data. Any incompatibility among those measured values indicates some damage. The curvatures are computed using the finite-difference technique. These curvatures show abrupt change at damaged locations. The damage is quantified in terms of crack length, and an analytical model is developed using a cracked-beam finite element. [ABSTRACT FROM AUTHOR]

Finite element analysis (FEA), combined with on-site and laboratory tests, might be an effective and versatile tool for studying existing structures, providing useful insights on structural resisting resources and failure mechanisms. When adopted in structural rehabilitation studies, FEA might help the engineer in defining the retrofitting strategies, and in testing their effectiveness. This paper presents an application of nonlinear FEA to the diagnostic study of the wooden dome of Palazzo della Loggia (Brescia, Italy, 1914), in order to assess the feasibility of its preservation, and to aid in planning its strengthening. The FEA demonstrated the influence of local mechanisms, such as clearances and splitting failures at joints, on the large existing crown deflection. Small scale tests were then carried out to study local phenomena and to assess the efficiency of some retrofitting techniques aimed at reinforcing the joints. The numerical model was then used to simulate the strengthening works. The results proved that the wooden roof could be preserved by repairing a few critical joints only, thus considerably limiting the impact of the retrofitting works. [ABSTRACT FROM AUTHOR]

Two types of steel, 20MnCr5 and S275JR, are compared in this paper based on numerical prediction of their fracture behavior. The comparison was made using the numerically determined -integral, an important fracture mechanics parameter. For that reason, a numerical algorithm that calculates the -integral as a measure of crack driving force was developed. As an input, the algorithm uses results from the finite element analysis conducted on numerical models of two types of specimens usually used in experimental fracture investigations, single-edge notched bend (SENB) and disc compact type (DCT). The -integral results obtained are plotted versus specimen crack growth size () for a range of specimens' initial crack sizes (, 0.5, 0.75). [ABSTRACT FROM AUTHOR]

An illustrative fracture mechanics-based design paradigm is proposed for unbonded concrete overlays (UBCOs), an increasingly popular pavement rehabilitation system, with the ultimate goal of establishing a more rational design procedure than those currently available. To illustrate the advantages of the fracture mechanics-based approach to design, specific attention is paid to one type of failure associated with pavement structures, reflection cracking. The design formulas derived from the results of a large number of crack propagation simulations of both the UBCO composite and a reference single-layer new pavement quantify the dependence of the required overlay thickness and load-carrying capacity on all relevant material and geometric parameters. Preliminary comparisons of the results with field observations suggest that the fracture mechanics paradigm offers a promising procedure for improved design of UBCOs. [ABSTRACT FROM AUTHOR]

Two methods of upper bound solutions were used to calculate the needed support pressure σT for shallow tunnel stability in cohesive-frictional ground. One uses a proposed rigid blocks failure mechanism for shallow rectangular tunnel of upper bound solution, and another uses a finite-element upper bound solution with linear program. In the rigid blocks failure mechanism, the velocity discontinuities in the side wall of the shallow rectangular tunnel occurred in both radial and tangent directions, so as to increase its flexibility. The main formulas for calculating support pressure σT were deduced for the above two methods; thereafter, the corresponding calculating programs were compiled. The needed support pressure σT for shallow tunnel stability and its parametric influences were obtained. The results show that both methods can be used effectively to analyze the stability problems of shallow rectangular tunnel using upper bound solutions. [ABSTRACT FROM AUTHOR]

A numerical study on the fracture behavior of steel fiber-reinforced concrete (SFRC) slabs on grade for industrial pavements is presented. Finite element analyses have been carried out by using a commercial finite element code where user subroutines based on nonlinear fracture mechanics have been implemented to describe the progressive cracking behavior of SFRC. The model is capable of simulating both primary and secondary cracks when they occur in concrete and it has been validated by comparing numerical predictions with experimental observations of full-scale tests on slabs on elastic subgrade under point loads in different positions. A real pavement with contraction or construction joints has been numerically simulated to investigate the stress and the strain fields for the most significant positions of point loads. [ABSTRACT FROM AUTHOR]

Tests and finite-element analyses of blunt notch and dogbone specimens are presented to demonstrate the application and validation of the cyclic void growth model (CVGM) to evaluate the initiation of ductile fracture under cyclic loading in steel structures. Modeling concepts and procedures for characterizing the CVGM material parameters using notched bar tests are described. Accuracy of the model is validated through a series of cyclic tests of 14 blunt notch compact fracture specimens and four dogbone specimens. Four types of moderate to high strength structural steels are investigated (two types of A572-Grade 50, A514-Grade 110, HPS70W). The test specimens reflect stress and strain conditions encountered in structural steel components and provide sufficiently strong stress and strain gradients to validate the characteristic length assumptions in the model. Detailed finite-element analyses that employ the CVGM criterion are shown to predict fracture with good accuracy across the specimen geometries, steel types, and loading histories. [ABSTRACT FROM AUTHOR]

Micromechanics-based models that capture interactions of stress and strain provide accurate criteria to predict ductile fracture in finite-element simulations of structural steel components. Two such models—the void growth model and the stress modified critical strain model are applied to a series of twelve pull-plate tests that represent reduced (or net) section conditions in bolted and reduced beam section connections. Two steel varieties, A572 Grade 50 and a high-performance Grade 70 bridge steel are investigated. The models are observed to predict fracture much more accurately than basic longitudinal strain criteria, by capturing stress–strain interactions that lead to fracture. The flat stress and strain gradients in these pull plates allow the use of relatively coarse finite-element meshes providing economy of computation while capturing fundamental material behavior and offering insights into localized ductile fracture effects. [ABSTRACT FROM AUTHOR]

Conventional fracture mechanics approaches have limited capabilities to accurately predict fracture under conditions of large scale yielding or in complex geometries where there are no significant pre-existing flaws. Such conditions are found, for example, in welded steel moment connections that meet stringent detailing and quality assurance requirements for seismic design that have been imposed in response to damage caused by the Northridge earthquake. The stress modified critical strain (SMCS) criterion provides an alternative approach for modeling ductile crack initiation by relating the fundamental process of void initiation, growth, and coalescence to macroscopic stresses and strains, obtained using detailed finite element models. The material-specific parameters of the SMCS model are calibrated for mild A572 Grade 50 steel using a series of notched tensile tests and fractographic data. Accuracy of the SMCS criterion is demonstrated for specimens with a range of triaxial constraint conditions, including both sharp-crack fracture specimens and blunt-notch specimens, the latter being examples of cases where conventional fracture mechanics approaches would not apply. The SMCS model is then applied in a practical demonstration to relate data from idealized pull-plate tests to the fracture resistance of beam–column moment connections. [ABSTRACT FROM AUTHOR]

A singular hybrid finite element with seven nodes and triangular shape is used to determine the stress intensity factors for the splitting tension test. For different types of marble the finite-element simulations were used to compute the fracture toughness values. The small-grained marble types exhibit a high fracture toughness and stable crack growth. The smallest toughness was obtained for the coarse grained Georgia marble. [ABSTRACT FROM AUTHOR]

Presents information on a study which described a finite-element-based linear elastic fracture mechanics analysis of the pullout of headed anchors. Modeling of the cracking that develops during the pullout of headed anchors using the finite-element program; Results and discussion.

Presents information on a study which investigated the laminating effect of laminated beams using finite-element method. Influence of stiffness variation on stress distribution; Laminating effect as predicted by fracture mechanics; Conclusions.

Since the smeared crack concept has proved to be very attractive when used in the finite-element fracture analysis, many different material models have been put forward. The majority of these models, usually known as a single or multiple crack models, are based on a linear elastic material constitutive law coupled in series with a softening crack-bridging law. The crack-bridging law on the plane where tensile fracture occurs, although defined in terms of stresses and strains, is basically the same vectorial relation used in the discrete crack approach. These models yield some problems due to the nonconsistency of the basic hypothesis and sharp discontinuities in the resulting material behavior. In this paper some of these problems are analyzed and compared with concepts and results coming from the nonlocal microplane material model. Numerical studies on the material and finite-element level using both approaches are reported. [ABSTRACT FROM AUTHOR]

This paper presents an energy-based approach for the finite-element modeling of mixed-mode cohesive crack propagation. This approach predicts the propagation of a quasistatic cohesive crack based on the principle of energy conservation. The crack propagation direction is assumed to be perpendicular to the direction of the maximum tensile principal stress at the cohesive crack tip. A generalized virtual crack-extension technique including the cohesive crack model is used to efficiently evaluate the crack propagation condition. The energy-based approach is both theoretically more fundamental and numerically more accurate than the commonly used strength-based cohesive crack modeling approach. A two-dimensional automatic mixed-mode discrete crack propagation modeling program has been developed that is capable of modeling both nonlinear and linear elastic crack propagation problems. The numerical efficiency and convergence behavior of the present approach are demonstrated through two example problems: a three-point bend beam and a single edge-notched shear beam. [ABSTRACT FROM AUTHOR]

This study presents a simple yet efficient phenomenological hysteretic model for hollow circular steel (HCS) braces without a middle connection in concentrically braced frames (CBFs). The model is calibrated on the basis of the available experimental results and on a series of numerical simulations by finite-element (FE) models, which are validated by existing experiments. The Miner linear cumulative damage theory based on the Coffin-Manson expression is used to represent the low-cycle fatigue deterioration of a brace subjected to cyclic loading. Furthermore, the cumulative yielding strength degradation is considered by a simplified formulation, which is defined as the cumulative fatigue damage. Comparisons of the hysteretic responses obtained by the proposed model with the results of the FE models show that this model can capture several failure modes of a brace during inelastic cyclic behaviors, such as yielding, inelastic postbuckling, strength degradation, and fracture due to low-cycle fatigue, as well as the fracture point. The cumulative dissipated energy of a brace is well-predicted by the model. In addition, this model takes much less computing time than the FE model and is therefore suitable for structural analyses. The model should be further examined to more precisely consider the effect of the local buckling of a brace with different cross-sectional geometries. [ABSTRACT FROM AUTHOR]

A new damage model, based on continuum damage mechanics and simulating the opening, closing, and reopening of cracks in concrete using only one surface of discontinuity, is proposed in this article. The model complies with the thermodynamics principles of nonreversible, isothermal, and adiabatic processes. Two scalar internal variables have been defined: a tensile damage variable d+ and a compressive damage variable d-; the threshold of damage is controlled by only one surface of discontinuity and a new parameter controlling the damage variable that should be activated. This new parameter represents the ratio of tensile stress to compressive stress in the damaged material. The continuity of response under complex loads, which is one of the aims of this work, is ensured. An adequate response under different types of loads leads to the conclusion that the proposed model provides a powerful tool to numerically analyze reinforced concrete structures. Validation and illustrative examples are included in the article. [ABSTRACT FROM AUTHOR]