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This paper presents a model of random tessellations that reflect several features of crack pattern. There are already several theoretical results derivedwhich indicate that thismodel can be an appropriate referencemodel. Some potential applications are presented in a tentative statistical study.

Recently (Nagel and Weiss, 2005), the class of homogeneous random tessellations that are stable under the operation of iteration (STIT) was introduced. In the present paper this model is reviewed and new results for the mean values of essential geometric features of STIT tessellations in two and three dimensions are provided and proved. For the isotropic model, these mean values are compared with those ones of the Poisson-Voronoi and of the Poisson plane tessellations, respectively.

The presence of the largest part of World Heritage sites in a seismically-prone area, like Italy, demands always greater measures to protect the most important built heritage, as well as the minor architecture. This requires a constant improvement of the current protocol from the damage survey and the provisional safety measures to the final intervention. This procedure is summarized, briefly, here and additional practical suggestions are given to improve the activities, based on the experience of on-site volunteers during the damage survey after the earthquake that struck Italy in 2016. Basic issues on the recurrent characteristics of historic masonry buildings, that make them often complex constructions with unexpected behaviour, are fundamental in the preparation of the volunteers in surveying damage. This helps in reducing evaluation mistakes and in designing the provisional safety structures aimed at the preservation of built heritage to the extent possible. Some examples of incorrect interpretation of the damage in historic buildings are reported here. In conclusion, only the awareness that it is necessary that a correct understanding of the recurrent or, on the contrary, peculiar, characteristics of a historic building plays a key role in the damage evaluation and in its subsequent protection from further damage.

• Alternative cyclic loading and unloading tests were performed on deeply buried rock. • Energy conversion and mesoscopic crack pattern are all impacted by the prior fatigue damage. • The relationships between strain energy and confining pressure were established. • Post-test CT scanning suggests that the consumed energy is not proportional to the crack scale. Rock failure subjected to respective cyclic loading or unloading have been well investigated, however, the energy mechanism of deeply buried rock under alternative cyclic loading and unloading are not well understood. This work aims to reveal the effect of prior fatigue damage on rock fracture and energy evolution characteristics subjected to triaxial alternative cyclic loads and unloading confining pressure. Testing results show that rock stress strain responses, deformation, energy dissipation, and mesoscopic crack pattern are all impacted by the prior fatigue damage. The incremental radial and volumetric strain at the unloading confining pressure stage (UCPS) is larger than the cyclic loading stage (CLS), and their relationships and the confining pressure are revealed. The total energy, elastic energy, and radial strain energy increases and dissipated energy decreases with the increase of disturbed cycles. The relationship between strain energy and confining stress was established at both the UCPS and CLS, it is found that dissipated energy at the UCPS is larger than at the CLS. A series of post-test CT images reveal the internal failure modes and confirm the effect of the number of disturbed cycles on energy release and dissipation. It is suggested that the consumed energy is not proportional to the crack scale, the formation of shear cracks consumes much more energy than those of tensile cracks. [ABSTRACT FROM AUTHOR]

• Historical mosques with a square plan and a single dome are examined. • 3D detailed finite element models of historical mosques are created and material properties are defined. • The collapse mechanisms of historical mosques are presented under strong ground motions. • V-shape and Ʌ-shape collapse mechanisms have been obtained for investigated mosques. The protection of historical masonry mosques against earthquakes can be achieved by an accurate assessment of nonlinear behavior, such as heavy damage and collapse. To this end, nonlinear analysis of 3D finite element models of structures is a common and reliable approach. This article examines the seismic performance of four historical mosques, which are defined as cultural assets by the Ministry of Tourism and Culture of the Republic of Turkey, under the influence of earthquake ground motion. Three of these mosques have not been studied before using any advanced numerical simulation method. In addition, no studies have been conducted to determine the damage propagation and collapse mechanisms of these mosques. Detailed finite element models were developed by defining the architectural features of mosques. In order to obtain the seismic behavior and collapse mechanisms of the mosques, nonlinear dynamic analyses were performed using the ground motion records from 1992 Erzincan, 1992 Cape Mendocino and 1995 Kobe earthquakes. An evaluation has been made for mosques in terms of mode shapes, maximum principal strains, maximum displacements, damage distributions and failure mechanisms. It has been determined that the crack distribution and damage mechanism can be generalized in historical masonry domed mosques with square plan. [ABSTRACT FROM AUTHOR]

Finite-element analyses (FEA) of reinforced concrete slab-column connections with shear reinforcement are presented and discussed. Ultimate loads and crack patterns are shown and compared to the experimental findings. The damaged plasticity model in ABAQUS, previously calibrated and validated on tested slabs without shear reinforcement, is adopted to properly simulate the behavior of slab-column connections with shear reinforcement. Four interior slab-column specimens were tested under vertical loading applied through the column. One slab specimen was without shear reinforcement, while the other three differed in the amount of the shear bolts. The objective of this paper is to propose a novel numerical modeling strategy for simulating and analyzing shear reinforced slabs with shear bolts. For that purpose, in the numerical analyses, four different approaches for modeling the shear bolt are introduced and described. Discussion and comparison on the predicted failure loads from the design codes and models in conjunction with the experimental and numerical data, are presented. Finally, a parametric numerical study is conducted, where the rectangular and the radial shear reinforcement arrangements are compared. [ABSTRACT FROM AUTHOR]

This paper presents the experimental study of concrete beams in bending, externally strengthened with Textile Reinforced Cementitious materials (TRC) with varying contact area with the concrete. In order to study the pure influence of the TRC on the concrete substrate, only non-internally-reinforced concrete beams are considered. The crack pattern evolution is monitored with Digital Image Correlation, and the influence of the contact width between the concrete substrate and the external reinforcement is investigated. The results show that the TRC reinforcement has an important crack bridging capacity, and consequently that its application over the full beam width is beneficial for the loadbearing capacity and the limitation of the crack widths of the concrete beam. [ABSTRACT FROM AUTHOR]

An experimental investigation has been conducted to collect fundamental data and to develop more understanding of the dynamic response of ultra-high-performance fiber-reinforced concrete (UHP-FRC) plates. Six reinforced plates with identical dimensions are tested using multi-impact technique by dropping a 475.00 kg (1047.20 lb) steel weight from a clear height of 4.15 m (13.60 ft). Three parameters are investigated: concrete type, fiber volume content, and steel reinforcement ratio. The results of this investigation confirmed that UHP-FRC plates exhibited superior damage control characteristics compared to high-strength concrete (HSC) plates. Increasing the fiber content was shown to improve the dynamic performance of the UHP-FRC plates, resulting in reduced peak and residual displacements at the same impact loads and an increase in the specimen’s ability to sustain increased impact energy capacity before failure. The test results showed that steel reinforcement played an important role in specimens’ overall behavior and increasing impact capacity. [ABSTRACT FROM AUTHOR]

Ultra-high performance concrete (UHPC) is one of the most promising construction materials because it exhibits high performance, such as through high strength, high durability, and proper rheological properties. However, it has low tensile ductility compared with other normal strength grade high ductile fiber-reinforced cementitious composites. This paper presents an experimental study on the tensile behavior, including tensile ductility and crack patterns, of UHPC reinforced by hybrid steel and polyethylene fibers and incorporating plastic beads which have a very weak bond with a cementitious matrix. These beads behave as an artificial flaw under tensile loading. A series of experiments including density, compressive strength, and uniaxial tension tests were performed. Test results showed that the tensile behavior including tensile strain capacity and cracking pattern of UHPC investigated in this study can be controlled by fiber hybridization and artificial flaws. [ABSTRACT FROM AUTHOR]

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This study aims to investigate the effects of corrosion distribution, specifically non-uniform and localized corrosion, on cracks propagation in concrete. Different corrosion distributions along rebar length were simulated using a sodium chloride pond with various sizes set on the concrete cover, and a direct current was applied to accelerate the corrosion process. The test results showed that the crack pattern is more influenced by corrosion distribution than by concrete cover thickness. The cracking mechanism was analyzed using the Rigid Body Spring Method with a corrosion-expansion model, which utilized a set of experimental data relating to corrosion distribution. The crack patterns are simulated reasonably well. The analysis also indicated that the internal crack pattern is closely related to concrete surface deformation. [ABSTRACT FROM AUTHOR]

One of the main difficulties, when dealing with landslide structural vulnerability, is the diagnosis of the causes of the crack pattern. This is also due to the excessive complexity of models based on classical structural mechanics that makes them inappropriate especially when there is the necessity to perform a rapid vulnerability assessment at the territorial scale. This is why in this article a new approach for the rapid diagnosis of crack patterns of masonry buildings subjected to landslide-induced settlements is proposed. This approach is based on the Load Path Method, recently applied to the interpretation of the behavior of masonry buildings subjected to landslide-induced settlements. [ABSTRACT FROM AUTHOR]

Masonry domes represent an important part of the architectural heritage. However, the literature about domes analysis seems less consistent than that referred to other masonry structures. The collapses that have happened in recent years as a consequence of seismic actions or lack of maintenance show the need for detailed studies. Here a limit analysis to evaluate the masonry domes behavior is presented. An algorithm based on the kinematic approach has been developed to evaluate the geometric position of the hinges that determine the minimum collapse load multiplier. The proposed procedure is validated by a comparison with some meaningful cases—the collapse of Anime Sante Church in L’Aquila, the collapse of San Nicolò Cathedral in Noto, the crack pattern of San Carlo Alle Quattro Fontane Church in Rome, and the analysis developed on Hagia Sofia in Istanbul. The comparison with real cases shows a good agreement between the model results and the phenomenological crack patterns. [ABSTRACT FROM PUBLISHER]

This paper presents the shrinkage cracking characteristics of cement treated demolition waste as a road base layer, which was produced by using recycled crushed concrete and masonry aggregates from construction and demolition waste (CDW). The developed method to estimate the crack pattern was based on the structural properties of cement treated demolition waste measured in the laboratory and the average climatic conditions recorded in the Netherlands. The influences of four mixture variables (masonry content, moisture content, cement content and degree of compaction) on the crack pattern were investigated. Results show that the proposed estimation model can predict the crack pattern of cement treated demolition waste comparable to the crack spacing observed in the field. The masonry variation in CDW is a key factor to determine its shrinkage cracking characteristics. [ABSTRACT FROM AUTHOR]

An experimental study was conducted to investigate the effect of web opening dimension on the behavior of reinforced concrete hybrid deep T-beam subjected to pure torsion. Four reinforced concrete hybrid deep T-beams were tested under pure torsion, where the three beams with different dimension of circular web opening and the other beam without opening as a reference beam. The testing program and experimental results are presented. The results show that dimension of circular web opening with diameter more than 100 mm significantly reduces the cracking and ultimate torque. It is also shown that the angle of crack inclination with respect to the longitudinal axis of the beam increases with the increase of web opening dimension.

In this paper, we present a novel finite element model to simulate alkali-silica reaction in a realistic concrete meso-structure. Application of the internal ASR loading leads to the evolution of multiple deviated cracks and corresponding macroscopic expansion. A particular crack-extension algorithm and a solution scheme provide numerical stability and allow to model complicated crack patterns while preserving the physics. The predictive validity of the model is demonstrated by matching an analytical solution of a loaded penny-shaped crack. The model is applied to the experimental dataset comprising the time-evolving X-ray tomograms of the ASR-affected concrete. Similar to the tomography data, the model results in an expanded concrete sample with a developed crack network. Two hypotheses on the crack loading and extension mechanisms are tested by comparing the crack statistics. Simulations with varying number of ASR sites and application of the uniaxial loading bring interesting insights. The latter concerns the role of the ASR-sites number, the individual loading amplitude and the difference in crack patterns. [ABSTRACT FROM AUTHOR]

• The aggregate compression method for modeling the elliptical geometry of recycled aggregate was established. • The BFEM on complementary energy principle was applied to analyze the damage problem of non-homogeneity materials. • The effects of initial internal defects characteristics on the properties of RAC were explored and analyzed. • The projection length of the initial defect in the loading direction has a significant effect on the properties of RAC. To study the effect of the initial defect on the mechanical properties and failure pattern of recycled aggregate concrete (RAC), several numerical models containing the initial defects were established and simulated under uniaxial compression. The recycled aggregate was simulated as an ellipse geometry, which can be constructed by compressing the circular geometry. The base force element method on the complementary energy principle was applied for the loading condition analysis. In addition, the stress–strain curves, deformation, and crack extension patterns of RAC were explored. Moreover, the maximum principal stress distribution and stress concentration were also investigated. The results demonstrate that the angle and length of the initial defect have a significant effect on the mechanical properties of the RAC. The initial defect interrupts the loading transfer path, forcing it into other continuous regions and forming a new transfer path. In addition, the longer the projection length of the initial defect in the loading direction, the most substantial influence on the mechanical properties, stress transfer, and damage mode. [ABSTRACT FROM AUTHOR]

This paper presents the results of simple and double indentation tests conducted on three hard rocks: granite, limestone and sandstone. The main objective is to analyze the rock behavior under indentation test in relation with the physical and microstructural properties. First, the experimental set-up used during the tests is described as well as the sample preparation. Then, an image analysis based technique is applied on thick sections made from the tested samples in order to evaluate the size of indentation-induced cracked zone and to assess the crack types (vertical or sub-horizontal) below the indenter. The interpretation of the results was made on two levels. First, several physical parameters (energies and displacements) have been derived from the so obtained experimental indentation curves. Very high correlations were found between the loading, indentation and specific energies versus the plastic displacement. Second, cracked zone radius was estimated showing a very high correlation to the specific energy and governed by the physical and mineralogical properties of the tested rocks. Finally, the analysis of double indentation tests proved that changing the distance between two adjacent inserts allows the determination of the optimal spacing producing overlay of cracked zones and causing rock damage and large chip departure. [ABSTRACT FROM AUTHOR]

The measurement of steel strains in reinforced concrete structures is often critical to characterise the stresses along the member. In this scope, this manuscript describes the development of a method to assess steel strains inside concrete members using solely surface measurements. These measurements were obtained using photogrammetry and image processing. The technique was validated using two concrete ties monitored with strain gauges placed inside the steel bars. The experimental results showed that one of the most important parameters affecting the accuracy of the technique is the measurement of crack widths. In comparison, the concrete strain has little effect on the final results. The technique is particularly advantageous since it is non-contact and does not impact on the bond conditions. It also does not require accessing the reinforcements. As a main conclusion, this work showed the feasibility of estimating strains inside the structure using surface measurements. This technique will benefit in the near future from further improvements namely in what concerns the camera resolution. [ABSTRACT FROM AUTHOR]

The cohesive finite element method together with Monte Carlo simulation for nanostructured metallic alloys with random fracture properties is developed to study the 3D fatigue crack propagation and torsional fatigue life. Three-parameter Weibull distribution is used to characterize the spatially random cohesive strength and fracture energy. The proposed model also considers the effects of thickness and different treatment of the nanograined layer (NGL) on the fatigue life. It is shown that the model can predict realistic crack patterns and reasonable fatigue life. The simulated fatigue cracks are mainly circumferential or oblique at an angle and they are in good agreement with the experimentally observed fracture patterns. Both different random fields and loads have significant effects on the crack initiation, crack pattern, and fatigue life. It is found that this layer plays a very important role in improving the fatigue life. As the layer thickness increases, the torsional fatigue life of the nanostructured metal also increases. The increase is particularly pronounced at high stress levels. We find that the major source of this increase is due to the increased probability for fatigue cracks to initiate from the interior surface of the tubular specimen and then propagate toward the exterior surface. This process has a profound beneficial effect on the fatigue life. [ABSTRACT FROM AUTHOR]

This paper presents characteristics of interfacial crack-induced (IC) debonding behavior of RC beams externally strengthened with sprayed FPR laminates. From four-point loading tests, crack patterns and failure modes of the beams were observed. The control beams displayed sudden and brittle shear failure mode, whereas strengthened specimens exhibited three different mixed modes. From the load–displacement ( p – u ) curves and the corresponding load–strain ( p – ɛ ) curves, crack loads, IC debonding loads, ultimate loads, and energy absorption capacities over the control beams were evaluated. A higher volume fraction of fibers and greater thickness can be more effective to enhance the strengthening performance in terms of crack load, ultimate load, and energy absorption capacity. With respect to the theoretical approach to interfacial crack-induced debonding behavior at FRP-to-concrete joints, four different IC debonding models were used in this study. The strain values at interfacial debonding of the sprayed FRP laminate were calculated and compared with experimental data. The prediction results according to four different IC debonding models are distributed around the line of ɛ db , i / ɛ db , ex = 1.0 ( i = 1, 2, 3), although a large scatter is presented in a range of 44–50%. [ABSTRACT FROM AUTHOR]

Seven full-scale steel fiber reinforced self-consolidating concrete (SFRSCC) beams were tested to study the effects of macro steel fibers on the flexural behavior of reinforced self-consolidating concrete beams. The major test variables are fiber contents and longitudinal reinforcement ratios. The ultimate load, midspan deflections, steel reinforcement strains, crack width and crack spacing were investigated. The enhanced ultimate flexural capacity and reduced midspan deflection due to the addition of steel fibers were observed. With the increasing of fiber contents, the strain in longitudinal reinforcement, crack width and crack spacing decreased significantly. The possibility of using steel fibers for partial replacement of the conventional longitudinal reinforcement is estimated, which is meaningful for extending the structural application of SFRSCC. A method incorporating fiber contribution to the post-cracking tensile strength of concrete in the flexural analysis of SFRSCC beam is also suggested. Comparisons are made between the suggested model and the fib Model Code 2010 model with experimental data. The results showed that the suggested model can estimate ultimate flexural capacity accurately. [ABSTRACT FROM AUTHOR]

Underground Coal Gasification (UCG) is considered to be a clean coal technology primarily intended to utilize deep underground (>300 m) coal deposits. In this process, a mixture of reactant gases like air/oxygen and steam are injected directly to an ignited portion of underground coal seam. UCG involves complex interactions of different processes like drying, pyrolysis, chemical reactions and spalling. Spalling is detachment of small coal particles from the coal seam due to interconnection of cracks developed in it. It plays an important role by offering higher surface area to give improved performance. The mechanism of spalling and its characterization are not well understood. Furthermore, there are no well established experimental techniques to measure the spalling rates. This paper studies spalling behavior of a lignite coal, which is characterized by high moisture and volatile matter, and suggests a possible underlying mechanism. The rate of spalling was measured using an experimental setup under the UCG-like conditions. In this setup, a reacting coal block was attached to a load cell and suspended in a UCG-like environment. When the experiments were repeated under similar conditions with different blocks of same coal, it was found that there were variations in the rates of spalling. This might be due to the heterogeneity in coal blocks in the form of originally present fissures or weak regions. A UCG process model was used to explain these experimental results and also to investigate the effect of spalling rate on product gas calorific value. We believe that spalling happens due to formation and extension of cracks. Hence a microscopic crack pattern on a heated coal monolith was examined in different stages of heating to understand the mechanism of spalling. It is concluded that cracks are first formed during the initial stage of drying due to the capillary stresses developed due to removal of moisture from the pores and were further extended due to shrinkage of coal during pyrolysis. The detachment of coal particles happens due to horizontal linking of vertical cracks, which might result out of either horizontal cracks, if any, or available fissures and weak regions or relatively weak interlayer bonding at the bedding planes. [ABSTRACT FROM AUTHOR]

In every electronic assembly line where ceramic capacitors are used and printed circuit boards are depaneled the quality risk “flex cracks” is widely known. Unfortunately flex cracks in “cercaps” always extend under the metal terminations of the capacitors and electrical tests only reveal about 1% of the affected parts. With a new method—etching away the terminations and looking at the otherwise hidden cracks—it is possible to identify all sources of mechanical bending and warping. In the course of failure analysis it is helpful to know that most of the time not only the failed ceramic capacitor shows a crack pattern but all the surrounding cercaps as well. Well-founded knowledge of different crack patterns and failure modes also allows us to discover unsafe bending and warping lines on the PCB. This gives us a guideline on how to place the ceramic capacitors in optimal orientation not only to depaneling lines but also in the vicinity of mounting and screw openings. Finally we will review the different kinds of cercaps with internal layouts that prevent boards from failing even if flex cracks should show up. [ABSTRACT FROM AUTHOR]

In order to study the crack pattern of Beishan granite under a single normal and inclined disc cutter, a series of linear cutting experiments were conducted. During the tests, a constant cross-section disc cutter with a diameter of 17 in. was used and a block of Beishan granite with the size of 1000 × 1000 × 600 mm (Length × Width × Height) was adopted. After the experiments, it is found that in the rock sample, there is a broken area beneath the cutting groove with variable degrees of fragmentation. Based on the crack pattern and crack density, the rock sample is divided into the re-compacted zone, the crushed and crack zone, and the intact rock zone. Meanwhile, the size and area of these zones were analyzed and the corresponding ultrasonic velocities were measured. It is shown that the crack patterns for normal and inclined cuttings at the same penetration depth are greatly different due to different included angles and cutting forces in the two scenarios. As the penetration of inclined cutting increases, the size and area of various zones expand significantly. In addition, the ultrasonic test reveals that the ultrasonic velocity of each zone agrees well with the degree of fragmentation and the velocities of corresponding zones for different scenarios are similar. [ABSTRACT FROM AUTHOR]

To generate enough thrust for a Tunnel Boring Machine (TBM) to excavate a soil and advance, several jacks are typically used to apply force to the last installed ring that acts as a reaction frame. These loads generate bursting stresses that might cause cracks in the longitudinal direction of the segments. Many studies dedicated to evaluate this phenomenon focus mainly on elements with similar height-to-length ratios. To cover the wide variety of dimensions and load application patterns, additional experimental assessments are required. The objectives of the present paper are to extend the study of with different height-to-length ratios subjected to concentrated loads and to validate analytical formulations for the verification of concrete segments in SLS and ULS. To accomplish this, an experimental program was carried out using small-scale specimens with and without fibre reinforcement. The results obtained were used to validate the formulations derived from a struts-and-ties model. Finally, an application of the formulation proposed to the case study of Line 9 in Barcelona is presented. This study represents a contribution towards the development of engineered approaches for the design of segmented linings. [ABSTRACT FROM AUTHOR]

This paper presented a experimental investigation into the advantage of RC member with shear strengthening using strain hardening cementitious composites (SHCC), focused on the crack pattern of SHCC strengthening layer and its obvious advantage for increasing the shear load carrying capacity of the strengthened RC member. Especially, the shear failed SHCC member was also adopted to reflect the reduced multiple fine crack distribution in SHCC strengthening layer. Moreover, the contributions of matrix and reinforcing fiber for shear load carrying capacity of SHCC strengthening layer were also calibrated respectively, and the shear load carrying capacity of SHCC strengthening layer was assumed as the sum of load carried by matrix and reinforcing fiber. This work provided experimental foundations for RC member with shear strengthening using SHCC. [ABSTRACT FROM AUTHOR]

In this study, experimental testing was performed on cast-in-place and precast barriers subjected to quasi-static loading and anchored to 6 m long bridge decks with a 1 m overhang. The three selected bridge barrier configurations include an ordinary concrete cast-in-place barrier, and two high performance fibre reinforced concrete precast barriers, one with and one without barrier-to-barrier connections. An experimental setup dedicated to testing the large-scale barrier-deck slab overhang specimens to failure was designed. The structural behavior of the three barrier configurations were analyzed and compared. The tests demonstrated that all three test configurations exceeded the design criteria in CSA-S6-06 and AASHTO LRFD, that the durability of the slab overhang is not adversely affected when using precast barriers, and that the shear key designed to connect the precast barriers provides adequate barrier longitudinal continuity. [ABSTRACT FROM AUTHOR]