Search

This research studies and assesses the possibility of employing UHPFRC in exterior beam-column joints (BCJs). Eight specimens with various concrete material characteristics and steel reinforcing details are cast and examined under repeated loads. Normal concrete with seismic reinforcing details is used as a control specimen. For certain specimens, UHPC, UHPFRC with 1% steel fiber, and UHPFRC with 2% steel fiber are poured into all BCJs, and others are poured into the critical zone only. The consequences of removing stirrups from the joint were studied. All specimens' crack patterns, hysteresis and envelope curves, ductility factor, stiffness degradation‎, and energy dissipation are assessed and corresponded to the control sample. The results demonstrate that UHPFRC strengthened the joint, prevented crack development and extension and the shear failure in the joint, and formed the plastic hinge in the beams. UHPFRC outperforms normal concrete with seismic reinforcing details and UHPC without steel fiber in bearing capacity, ductility, stiffness, and energy dissipation. UHPFRC with 1% steel fiber enhanced joint behavior, while UHPFRC with 2% steel fiber was better. Casting the whole sample with UHPFRC achieved very little improvement. The presence of stirrups in the UHPFRC beam-column joint has little effect on its properties. It is more economical to casting UHPFRC in the joint zone only and reduce or eliminate these stirrups in the case of UHPFRC

Vector II slab was tested on a natural scale (a slab with a dimension of 6.30 × 6.30 m) and a strip 6.30 m long and 1.20 m wide. The Vector II slab is built by precast panel 60 cm wide, 4 cm thick and 14-20 cm thick concrete overtopping on the construction site. The main purpose of the slab tests on a natural scale was to observe the “faulting” effect and temporary deflections. During the tests, the displacements in the area of the panel joints in the middle of the slab span were recorded. The maximum difference in displacement between adjacent panels of the slab model was 0.16 mm, and the vertical displacement was 1.9 mm. The strip model had no cracks that could indicate a interface cracks between the precast element and the concrete overlay. After completion of the field tests, the load was left on the slab model to verify long-term effects.

Concrete structures have been widely used for many years to resist impact loads. Steel–concrete composite structures may be considered efficient structures in the emerging modern construction field. Hence, the main objective of this research was to study the impact behavior of steel concrete composite slabs with different shear connectors and compare them with conventional slabs. Seven specimens of dimensions 500 × 500 × 50 mm were cast, which included plain cement concrete slabs, two reinforced cement concrete slabs with steel mesh and steel rebars as reinforcement, and four steel-concrete composite slabs with four different shear connectors: stud, tee, angle, and channel connectors. The composite action was achieved using a steel decking sheet welded with connectors on which the concrete layer was poured at the top. The test setup was fabricated with slots provided for specimens with simply supported end conditions and a mild steel drop weight. The specimens were impacted at the center of the span by dropping a steel mass from a free fall height of 1 m. The number of blows corresponding to the initial cracking and ultimate failure stages was recorded. The parameters that were used to compare the specimens were the impact energy absorbed, crack pattern, crack width, and increase in impact energy from the first blow to the last blow. The experimental results were very close to the analytical results obtained using ANSYS. The experimental and analytical results showed that the composite slabs with channel connectors performed better than the others, and it was proven that the composite slabs performed better under impact loading than conventional slabs.

Degradation and disintegration of concrete depend on the formation of cracks and micro cracks intensively. With increase loading, micro cracks are linked together and form cracks. To solve the problem and to provide the homogenous condition, a series of thin fibers having been spread through the volume of concrete are used in the several last decades and they are called as fibers. In the study, the steel fibers integrated in the different percentages of weight have been investigated. The performance of fibers has been studied how to increase compressive strength, tensile strength, and bending strength. To survey compressive strength, tensile strength, and bending strength in the produced concrete, three plans of mixtures including the different percentages of the steel fibers have been examined. The results show that compressive strength in the concrete reinforced with steel fibers relies mainly on the quality of mortar. The added steel fibers cause the inconsiderable changes in the compressive strength of concrete. The results demonstrate that the concrete reinforced with steel fibers increase tensile strength considerably. The more the volume of steel fibers is, the more tensile strength is. Pozzolanic materials used in the specimens reinforced in steel fibers improve tensile strength. To investigate bending strength of the specimens reinforced with steel fibers, the study has used 4-point loading system. Generally, steel fibers used in the concrete increase bending strength of the concrete. The results indicate the increased steel fibers enhance bending strength in three plans of mixtures. Among the specimen reinforced with steel fibres, the most mechanical properties are related to the plans including 1, 1.5, and 2 percentages of dramix hooked steel fibers in the study. To examine crack pattern of the matrix tensile specimen reinforced with the different percentages of fibers, parameters such as the number of cracks, width of cracks, and distance between them are investigated.

Refined non-linear static or dynamic analyses are increasingly used to assess the behavior of new and existing reinforced concrete structures. To perform these analyses, an adequate knowledge of the force–displacement, bending moment–curvature, and bending moment–rotation curves of relevant parts of structural members is needed, and modeling the bond–slip correlation for steel rebars becomes fundamental. The paper presents the results of an experimental campaign on r.c. specimens under tension, aiming, differently from previous studies, to better reproduce the bond–slip relationship accounting for the local confinement and anchorage conditions of real structural members. Resorting to an original numerical procedure allowing us to predict the relative displacement between steel reinforcement and the surrounding concrete in a reinforced concrete element, once assigned the stress in the naked steel bar and the bond–slip law, the experimental results are compared with the numerical outcomes obtained by adopting codified bond–slip laws. The comparison highlights that experimental values of sliding are well below those that are commonly given in existing bond slip laws, such as that adopted by the CEB-FIP Model Code. A new bond–slip model, which is able to satisfactorily predict actual strain fields and slips along the investigated r.c. elements, is thus proposed with the final aim of extending its implementation into non-linear analyses of r.c. structures.

Diese Arbeit beschäftigt sich mit dem Vergleich diverser Ausbildungsvarianten von Arbeits- bzw. Bewegungsfugen sowie der Erstellung einer Ergebnismatrix für das technisch bestmögliche Abdichtungssystem für diverse Anwendungsbereiche. Da Fugen immer eine Schwachstelle in der ansonsten zumeist wasserundurchlässigen Konstruktion darstellen, ist deren Ausbildung von großer Bedeutung und fordert höchste Sorgfalt bei der Ausführung. Deshalb soll Gegenstand dieser Arbeit sein, diverse Fugenabdichtungssystem zu analysieren und zu vergleichen, um aus den gewonnenen Erkenntnissen eine aussagekräftige Ergebnismatrix erstellen zu können. Um eine solch wissenswerte Analyse zu gewährleisten, werden zu Beginn die Grundbegriffe Arbeitsfuge, Bewegungsfuge sowie Allgemeines zu den Fugen, wie Arten, Beanspruchungen, Zweck etc. näher erläutert und bildhaft dargestellt. Zunächst werden Faktoren, wie Anwendungsbereiche, chemischer Aufbau und Struktur, Eigenschaften, Gewinnung und Herstellung etc. für sämtliche Materialien - von organischen und anorganischen Materialien über Metall bis hin zu Silikonen - verglichen und im Anhang übersichtlich dargestellt. Im nächsten Abschnitt „System und Varianten“ werden zunächst die verschiedenen Prinzipien der Abdichtungsvarianten näher erläutert. Auf Basis dieser Erläuterung erfolgt eine Analyse sämtlicher Systeme (Fugenbänder, -bleche, -profile, Injektionsschläuche und Wannenausbildungen), hinsichtlich dem Abdichtungsprinzip, den verwendeten Materialien, den chemischen Eigenschaften sowie dem Anwendungsbereich des jeweiligen Systems, welche im Anhang wieder übersichtlich dargestellt werden. Abschnitt 5 befasst sich mit Riss- und Schadensbildern. Hierbei werden die Ursachen, Möglichkeiten zur Schadensminimierung bzw. -vermeidung sowie diverse Riss- und Schadensbilder analysiert und Sanierungsmöglichkeiten für diese Schäden angegeben. Anhand der durch die Analyse von Materialien und Systemen gewonnenen Erkenntnisse kann eine detaillierte Ergebnismatrix für diverse horizontale und vertikale Arbeits- und Bewegungsfugen erstellt werden. This thesis deals with the comparison of various design variants of construction and movement joints as well as the creation of a result matrix for the technically best possible sealing system for various areas of application. Since joints always represent a weak point in the otherwise mostly water-impermeable construction, their formation is of great importance and requires the greatest care in execution. The subject of this thesis is to analyze and compare various joint sealing systems in order to create a meaningful result matrix from the knowledge gained. In order to ensure such an analysis that is worth knowing, the basic terms, construction joint, movement joint and general information on the joints, such as types, stresses, purpose etc. are explained in more detail and illustrated. First, factors such as areas of application, chemical composition and structure, properties, extraction and production etc. for all materials – from organic and inorganic materials to metal and silicone – are compared and clearly presented in the appendix. In the next section “systems and variants”, the principles of the sealing variants are explained in more detail. Based on this explanation, an analysis of all systems (joint tapes, water stops, joint profiles, injection hoses and tub seals) is carried out regarding the sealing principle, the materials used, the chemical characteristics and the area of application of the respective systems, which are clearly shown in the appendix. Section 5 deals with crack and damage patterns. The causes, possibilities for minimizing or avoiding damages as well as various crack and damage patterns are analyzed and options for remedying this damage are indicated. Based on the knowledge gained through the analysis of materials and systems, a detailed result matrix can be created for various horizontal and vertical construction and movement joints.

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., Cement and Concrete Research, 162, ISSN:0008-8846

In the present work, thirteen reinforced concrete beams with openings at different locations were tested under four-point bending to investigate the efficiency of strengthening techniques of such openings. Different strengthening techniques around the opening were used before casting as internally reinforced by diagonal or upper and lower additional steel bars or after casting as externally bonded sheets of carbon fiber reinforced polymers (CFRP). The stiffness, mid-span deflection, maximum load, and failure mode of the strengthened beams were discussed. Experimental results showed that the best opening location is in the constant moment region around the neutral axis. The strengthening of such beam by internal reinforcements exhibited a higher ultimate load than that of the beam without opening. At the same time, the strengthening by external bonded CFRP failed to store the strength of such beam. The upper and lower additional steel bars technique is the best technique to restore the beam with the opening in mid-span or beneath the applied load. The worst opening location is in shear span. The beam's strength with the opening in shear span was restored using CFRP, while internal reinforcement�s techniques failed. It can be concluded that the strengthening technique type depends on the opening location.

Textile reinforced concrete (TRC) has gained attention from the construction industry due to its light weight, high tensile strength, design flexibility, corrosion resistance, and remarkably long service life. Some structural applications that utilize TRC components include precast panels, structural repair, waterproofing elements, and façades. TRC is produced by incorporating textile fabrics into thin cementitious concrete panels. Premature debonding between the textile fabric and concrete due to improper cementitious matrix impregnation of the fibers was identified as a failure-governing mechanism. To overcome this performance limitation, in this study, a novel type of TRC is proposed by replacing the cement binder with a polymer resin to produce textile reinforced polymer concrete (TRPC). The new TRPC is created using a fine-graded aggregate, methyl methacrylate polymer resin, and basalt fiber textile fabric. Four different specimen configurations were manufactured by embedding 0, 1, 2, and 3 textile layers in concrete. Flexural performance was analyzed and compared with reference TRC specimens with similar compressive strength and reinforcement configurations. Furthermore, the crack pattern intensity was determined using an image processing technique to quantify the ductility of TRPC compared with conventional TRC. The new TRPC improved the moment capacity compared with TRC by 51%, 58%, 59%, and 158%, the deflection at peak load by 858%, 857%, 3264%, and 3803%, and the toughness by 1909%, 3844%, 2781%, and 4355% for 0, 1, 2, and 3 textile layers, respectively. TRPC showed significantly improved flexural capacity, superior ductility, and substantial plasticity compared with TRC.

Increased urbanization causes traffic and parking issues especially in metropolitan cities like Karachi, London, Shanghai, etc. To accommodate parking issues for the vehicles mainly in urban areas (excavated) underground parking areas under or nearby high rise buildings are preferred. As a result of excavation, ground movements occur that have a major impact on structures, buildings, and utilities. The past research usually oversimplified surface structure as an equivalent elastic beam, which is unable to represent the behavior of a framed building realistically. In this study, the detrimental effects (i.e. crack pattern) on a two-floor RCC framed building founded on piles due to an adjacent excavation-induced ground movement are investigated. Elasto-plastic coupled-consolidation analysis was adopted. The hypoplastic constitutive model was used to capture soil behavior. It is an advanced model which is able to capture the soil unique features which are non-linear behavior, stiffness degradation (with stress, strain & path-dependent), and stress-strain dependent soil dilatancy. The concrete damaged plasticity (CDP) model was used to capture the cracking behavior in the concrete beams, columns and piles. It was revealed that the induced slope and tilting are not equal. Consequently, the frame was distorted. As a result, tension cracks were induced at the inner side of the column.

Under seismic actions, stone masonry buildings are prone to damage. To assess the severity of damaged masonry buildings and their failure modes, engineers connect these problems to surface crack features, such as the crack width and the extent of cracking. We aim to further these assessments in this study, wherein we propose using simple machine learning models to predict: 1) three ratios encoding the degradation of stiffness, strength, and displacement capacity of damaged rubble stone masonry piers as a function of the observed crack features and the applied axial load and shear span ratio; and 2) the pre-peak vs. post-peak regime, based on the crack features. When predicting the stiffness, force, and drift ratios, the prediction error is significantly reduced when the axial load and shear span ratio are included in the feature vector. Furthermore, when predicting the pre-peak vs. post-peak regime, simple machine learning models such as the k-nearest neighbor and the logistic regression result in remarkable accuracy. The obtained results have significant implications on the automated post-earthquake assessment of masonry buildings using image data. It is shown based on documented laboratory test data, that, by selecting proper crack features and incorporating information about the kinematic and static boundary conditions, even simple machine learning models can predict accurately the damage level caused to a rubble masonry pier. The three crack features used in this study are the maximum crack width, length density, and complexity dimension. The pipeline developed in this paper is general enough and is applicable to other masonry typologies and elements upon new evaluation of crack features and image data., Automation in Construction, 140, ISSN:0926-5805

Extrusion-based 3D concrete printing (3DCP) results in deposited materials with complex microstructures that have high porosity and distinct anisotropy. Due to the material heterogeneity and rapid growth of cracks, fracture analysis in these air-void structures is often complex, resulting in a high computational cost. This study proposes a convolutional neural network (CNN)-based methodology for fracture analysis using air-void structures as input. More specifically, the lattice fracture model is used to build a dataset that comprises input air-void structures as well as output fracture information, including the crack patterns and crack-width curves. To establish the relationship between crack morphology and associated microstructures, a U-net convolutional neural network is first presented. With the obtained crack pattern as input, the principal component analysis (PCA) and CNN are then integrated to predict the stress-crack width curves. The predicted results from the CNN model demonstrate a quantitative agreement with lattice numerical analyses, with 0.85 Intersection over Union for crack patterns prediction and 0.75 R2 for the stress-crack width curves prediction. This indicates that CNN models can be used as an alternative to traditional numerical analysis. The feature maps during the convolutional or deconvolutional process are given to explain why the proposed CNN models perform well on fracture analysis of the air-void system. Moreover, the model generalization is discussed using transfer learning with fine-tuning to show the model potential on microstructures expressing varied pore information. In the end, the microstructures cropped from XCT are created to explore the further application of CNN models on fracture analysis of 3D printed materials.

Nowadays plastic is closely linked to the way of our life. The annual consumption of plastics has been increasing gradually. The inadequate disposal of plastic has been resulted in major environmental problems due to the shortage of space for landfilling and low biodegradability. The reuse of plastic wastes as construction materials provides a remarkable future market for waste recycling. This work aims to study the possibility of Evolon ® plastic non-woven sheets in concrete mixtures. For this purpose, an experimental study was conducted to investigate some properties of the ordinary concrete wrapped by non-woven PET plastic sheets. Samples with five various configurations; reference, 1-layer, 2-sides, 3-sides, and full wrapped were considered and prepared. The compressive, flexural, and split tensile strengths and ultrasonic pulse velocity (UPV) were measured. The outcomes of the study highlight that the compressive strength was improved for the wrapped samples, particularly for the cylindrical specimens. In addition, split tensile and flexural strengths of the wrapped samples improved significantly compared to the reference ones at each strengthened configuration. Moreover, it was observed that reference samples were damaged to many parts after mechanical testing, while wrapped specimens were taken by the applied configurations and were not separated into many small fragments. Therefore, non-woven fabrics are recommended to improve certain properties of the concrete.

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

The structural assessment of doubly-curved vaulted masonry structures, such as pavilion vaults, poses challenges specific to their high degree of indeterminacy. Two-dimensional equilibrium analysis methods may provide a lower bound of load or displacement capacity, but they do not accurately describe the three-dimensional (3D) behaviour of these structures, particularly when shear deformation (e.g. sliding) is important. Therefore, discrete element modelling (DEM) methods, which can effectively simulate 3D load re-distribution, have been used to investigate support displacement capacity and corresponding 3D collapse mechanisms. DEM analyses are usually conducted on perfect digital geometries. Meanwhile, both real structures and small-scale physical models have implicit assembly and fabrication imperfections, which may significantly alter their response. The present paper aims to investigate the influence of geometrical and mechanical imperfections by comparing DEM analyses with the results obtained from tests on a scale model. In particular, a new method to simulate imperfections within the DEM framework is proposed, and a DEM parametric analysis is compared to the measured behaviour of a 3D-printed scale model of a pavilion (or cloister) vault on spreading supports. The influence of both mechanical imperfections and geometrical imperfections, due to element geometry deviations or imprecision of the assembly process, have been investigated. Based on these analyses, the three-dimensional behaviour of a pavilion vault subjected to horizontal displacement of the supports is described, and the variability of results due to imperfections is demonstrated. A good agreement between DEM analyses and 3D-printed scale model tests is achieved, in terms of crack patterns and mechanisms. Geometrical imperfections did change the load paths within the vault, as expected, and also influenced the displacement capacity., Engineering Structures, 228, ISSN:0141-0296

Crack width variation along the concrete cover depth has been studied from the past for better understanding of the cracking phenomenon in reinforced concrete (RC) structures. Previous studies have highlighted important cracking behaviors like internal cracks. The behavior of ‘slip’ between the reinforcement and concrete and the formation of a nonuniform crack face along the concrete cover depth are still not very clearly understood. An experimental program has been conducted to study the crack width variation along the cover depth in concrete prisms reinforced with a central ribbed bar and smooth bar, by varying the concrete cover depths. Both in specimens with smooth bars (SS) and specimens with ribbed bars (SR), crack width is larger on the concrete surface than at the steel bar surface. The crack width at the reinforcement is considerably larger in the SS than in the SR. In the SR, the crack width increases from the reinforcement along the cover depth bi-linearly, while, in the SS, it increases linearly. For the SR, the aforementioned behavior is due to the occurrence of internal cracks. In the SS, significant slip has been identified at the reinforcement and concrete interface, whereas negligible slip has been observed in the SR. A surface crack width calculation model has been developed, considering both the strain difference and the effect of the nonuniform crack face along the concrete cover depth. Its predictions showed good agreement with the experimental surface crack widths from the conducted study and with the results from the experiments in literature.

Composites made with inorganic matrix, namely fabric reinforced cementitious mortar (FRCM) composites are becoming widespread as strengthening materials for existing masonry structures. These composites are made of a dry grid of fibres embedded in an inorganic matrix. FRCMs can be considered a valid alternative to traditional organic composites such as fibre reinforced polymers (FRPs) because of their better compatibility with the masonry support. This work presents an experimental study for the tensile characterization of a basalt fabric reinforced cementitious mortar (BFRCM) composite. Tensile tests were carried out on coupons reinforced with one, two or three layers of grid to investigate the influence of the reinforcement on the load–strain and stress–strain response of the composite. The basalt grid and cementitious mortar matrix were also tested in order to compare the mechanical properties of the constituent materials to the response of the composite. The digital image correlation (DIC) technique was used to check in-plane and out-of-plane bending effect, to measure the crack opening and to analyse the crack pattern evolution and failure modes.

The origin of crack patterns in industrial masonry chimneys is investigated. This information is of utmost importance in defining any preservation project, and designing suitable repair interventions. Attention is focused on a 66 m-tall chimney built at the end of the XIX century, which is representative of numerous coeval chimneys of similar geometry. The base and the shaft of the chimney are double-walled: vertical ribs and horizontal diaphragms partially connect the walls of the shaft; the crown is single-walled. Vertical cracks can be observed in the lower part, horizontal cracks in the upper part, and zig-zag cracks in the central part. The structural behaviour of the chimney was investigated by means of finite elements, under gravity loads and thermal variations. Most of the cracks can be explained by thermal effects, if the anisotropic strength of masonry is duly accounted for. Therefore, new cracking phenomena can be excluded, and suitable repair interventions may allow an adequate level of safety to be attained.

This paper aims to experimentally and numerically investigate the flexural behavior of laced reinforced concrete moderately deep beams. The study focuses on the influence of the lacing angle (30, 45, and 60°) and the ratio of the tension reinforcement (0.33, 1.13, and 2.01%). Six beams were fabricated, with a cross-sectional width of 150 mm and a depth of 240 mm, and 1530 mm in length. In five specimens, lacings were employed as shear reinforcement instead of the conventional stirrups. A reference beam was fabricated with conventional vertical stirrups. All beam specimens were subjected to the four-point bending up to failure with effective and shear spans of 1400 and 400 mm, respectively. Compared to the reference beam, laced beams experienced significant stiffness enhancements of up to 43.7%. However, the improvement in the ultimate load did not exceed 10%. The recorded strains in lacings clearly signify the efficiency of lacings in resisting the longitudinal and diagonal tension stresses induced along the flexural and shear spans. Moreover, a nonlinear finite element analysis was performed using ABAQUS, based on which parametric studies were conducted. Parametric studies showed that the ductility was significantly increased with the increase of lacings bar diameter, while the ultimate load capacity was only slightly enhanced.

International audience; In the last few decades, premature deterioration of reinforced concrete (RC) structures has become a serious problem because of severe environmental actions, overloading, design faults, and materials deficiencies. Therefore, repair and strengthening of RC elements in existing structures are very important to extend their service life. There are numerous methods for retrofitting and strengthening of RC structural components such as; steel plate bonding, external pre-stressing, section enlargement, fiber-reinforced polymer (FRP) wrapping, and so on. Although these modifications can successfully improve the load-bearing capacity of the beams, they are still prone to corrosion damage resulting in failure of the strengthened elements. Therefore, many researchers used cementitious materials due to its low-cost, corrosion resistance, and resulted in the improvement of the tensile and fatigue behaviors. Different types of cementitious materials such as; fiber-reinforced concrete (FRC), high performance concrete (HPC), high strength concrete (HSC), ultra-high performance concrete (UHPC), steel fiber-reinforced high strength lightweight self-compacting concrete (SHLSCC), fabrics reinforced cementitious material (FRCM) and so on have been used to strengthen structural elements. This paper summarized previously published research papers concerning the structural behaviors of RC beams strengthened by different cementitious materials. Shear behaviors, flexural characteristics, torsional properties, deflection, cracking propagation, and twisting angle of the strengthened beams are explained in the present paper. Finally, proper methods are proposed for strengthening RC beams under various loading conditions.

This study aims to assess numerically the behavior of a wide range of reinforced concrete (RC) components under bending or combined effect of bending and axial compression. Reference case studies of RC beams with different reinforcement ratios and beam-column joints are modeled using LS-DYNA software. When larger time step is used in modeling with implicit solvers, convergence problems may appear at higher degrees of nonlinearities, as the solution is reached through multiple iterations to reach equilibrium at every time step. To avoid these divergence issues, explicit time integration procedure is another alternative and can be used effectively in simulating dynamic problems. With minimizing inertia effects, this procedure can also be used to solve static and quasi static problems. In this study, explicit time integration procedure is utilized and the acting loads were applied slowly to minimize the inertia effects. Consequently, longer run time for the simulation process is needed with explicit time integration. Selective Mass Scaling (SMS) can be used to control the required run time by increasing the model critical time step by adding artificial mass to a limited number of stiff elements like, the transverse reinforcements. With this procedure, similar results to the reference experimental findings are obtained in terms of load-displacement curves, crack patterns and strains in the reinforcements. Models verification with different added masses are shown using grid convergence index (GCI) method. The main objective of this work, is to assess the accuracy of explicit solvers in modeling RC elements under quasi static loading. So that, they may be used with confidence for modelling different RC elements.

Geogrid is as one of the component materials classified under the geosynthetics used for soil stabilizing and reinforcement. Due to its higher strength-to-weight ratio, ease of handling, and comparatively low costs, geogrid has been gradually explored for possible use in concrete reinforcement. This research aims to assess the feasibility of using geogrids as a possible reinforcement for high-strength self-compacted concrete slabs to provide additional tensile strength and ductility. To enhance the bond between geogrid layers and the cement matrix, two types of geogrid surface modification methods are introduced. Gluing sand to the geogrid surface as a physical surface modification method and immersion in polycarboxylate as a chemical surface modification method are investigated. The effect of geogrid type (uniaxial, biaxial and triaxial) and the number of layers is also introduced. The test results show that the chemical treatment increased the ultimate flexural loading capacity of the tested slab by about 8.5% for one geogrid layer and 13% for two geogrid layers compared to untreated specimens. This work was extended to add two geogrid layers in addition to the slab&rsquo, s steel reinforcement. The results show that adding geogrid decreased the ultimate flexural loading capacity but significantly increased the slab ductility.

Aim of the paper is the evaluation of the bond transfer mechanism and the following cracking behavior for concrete elements reinforced with Glass Fiber Reinforced Polymer (GFRP) bars. At the scope, an experimental survey has been developed on nine 3000 mm long tie-specimens with square cross-section of 150 mm × 150 mm, reinforced with a 4000 mm long GFRP reinforcing bar embedded in the centerline. Besides the reference element, reinforced with conventional steel rebar with diameter equal to 16 mm, nine GFRP bars with the same equivalent diameter and different surface treatments (smooth, sand-coated and helical fiber wrapped surfaces) were taken into account. The specimens were subjected to tensile force and the obtained results have shown how the different surface coating may affect the bond behavior at the concrete – GFRP interface, and the following crack pattern.

The seismic performance assessment of historical masonry structures is still a complex issue in civil engineering. This paper investigates the seismic response of seven masonry churches, which are located in the province of Ferrara (Northern Italy) and suffered extensive damage during the 2012 Emilia earthquake. Different field surveys, which were conducted after the earthquake to collect information on typical damage patterns, provided a preliminary knowledge of utmost importance for developing detailed FE models of the churches and for better understanding the results of advanced numerical simulations. First, modal analyses were performed to have a preliminary insight into the dynamic behavior of the churches. Then, non-linear dynamic analyses with different peak ground accelerations were carried out in order to obtain the damage distribution in the churches and to identify the most vulnerable macro-elements. The results highlighted the influence of morphological and geometrical characteristics on the seismic behavior of the different macro-elements composing the churches.

Recent Italian earthquakes (L’Aquila 2009, Emilia 2012, Central Italy 2016–2017) have shown the high vulnerability of existing and historical masonry constructions to seismic actions. This ...

Contraction of soil during desiccation gives rise to polygon-patterned cracking. This phenomenon was investigated by continuous full-strain measurements on soil sample surfaces using digital image correlation techniques. The results show that desiccation cracking was of the mode I variety and can be reliably predicted through strain field analyses: the observed cracking was restricted mostly to high stretching domains. The observed high stretching stems from either external restraint or internal flaws of the shrinking soil. The cracks redistribute the stress in their vicinity and lead neighboring cracks to intersect them mostly orthogonally. As desiccation proceeds, the surface strain field ceases to provide useful information for predicting crack locations. Further analysis indicates that although drying occurs from exposed material surfaces, late-generation cracks actually initiate in the subsurface and express themselves subsequently at the surface. These observations offer insights into the intrinsic mechanisms of drying-induced crack growth in soils.

External sulfate attack is a progressive degradation process that may cause expansion, cracking, loss of binder cohesion and increased permeability in cementitious materials. Crystallization pressure theory has often been referred to as the most likely mechanism. However, thus far the stress causing the expansion has not been quantified. In this study, small cement paste pipes with a wall thickness of 2.5 mm were prepared and immersed in sodium sulfate solutions with SO42− ion concentrations of 1.5 g/L and 30 g/L. Three types of longitudinal restraints were applied on the specimens before exposure, which were created by a spring, a thin or a thicker stainless steel bar that was centered in the hollow specimens in order to facilitate the non-, low- or high-restraint condition. The free expansion, restrained expansion and generated stress were quantified. The pore size distribution, sulfur distribution and crack pattern were periodically analyzed during the sulfate immersion tests up to 420 days. The generated stresses were found to be as high as 13.1 MPa in high sulfate solution and 8.3 MPa in low sulfate solution under high-restraint condition after 420-day immersion. For the unrestrained specimens immersed in low sulfate solution, an almost uniform sulfur distribution along the diffusion direction was found at 189-day immersion. However, for the unrestrained specimens immersed in high sulfate solution, a layer or several layers of mainly gypsum were formed subparallel to the exposed surface from 133-day immersion.

We all know that steel elements cannot be renewed and their constituent elements take a long time to form. So there is a need for other alternatives which have steellike properties. One alternative is bamboo, bamboo is one material that can be used as a substitute for steel, because bamboo has a high tensile strength close to the strength of steel. In this study an attempt was made to compare the use of reinforcement with bamboo on the outside with the skin and the inside without skin to determine the flexural strength. The flexural strength test results on variations of skin obtained the value of Max P: average: 3400 kg with an average deflection of 9.25 mm while in variations without the skin P Max produced an average of 2400 kg with deflection value of 1.92 mm. Kita ketahui bersama bahawa unsur baja tidak bisa diperbaharui serta unsur penyusunnya yang membutuhkan waktu yang lama untuk terbentuk. Sehingga perlu adanya alternatif lain yang dimana memiliki sifat menyerupai baja. Salah satu alternatifnya adalah bambu, bambu merupakan salah satu bahan dapat digunakan sebagai pengganti baja, karena bambu mempunyai kuat tarik yang tinggi yang mendekati kekuatan baja. Pada penelitian ini dicoba untuk membandingkan penggunaan tulangan dengan bambu bagian luar dengan kulit dan bagian dalam tanpa kulit guna mengetahui kekuatan lentur. Hasil pengujian kuat lentur pada variasi kulit didapatkan nilai P Maks: rata-rata:3400 kg dengan lendutan rata-rata 9.25 mm sedangkan pada variasi tanpa kulit P Maks rata-rata yang dihasilkan 2400 kg dengan nilai lendutan 1.92 mm.

Increased urbanization causes traffic and parking issues especially in metropolitan cities like Karachi, London, Shanghai, etc. To accommodate parking issues for the vehicles mainly in urban areas (excavated) underground parking areas under or nearby high rise buildings are preferred. As a result of excavation, ground movements occur that have major impact on structures, buildings and utilities. The past research usually oversimplified surface structure as an equivalent elastic beam, which is unable to represent the behavior of a framed building realistically. In this study, the detrimental effects (i.e. crack pattern) on a two floor RCC framed building founded on piles due to an adjacent excavation-induced ground movement are investigated. Elasto-plastic coupled-consolidation analysis was adopted. The hypoplastic constitutive model was used to capture soil behavior. It is an advanced model which is able to capture the soil unique features which are non-linear behavior, stiffness degradation (with stress, strain & path dependent), and stressstrain dependent soil dilatancy. The concrete damaged plasticity (CDP) model was used to capture the cracking behavior in the concrete beams, columns and piles. It was revealed that the induced slope and tilting are not equal. Consequently, the frame was distorted. As a result, tension cracks were induced at the inner side of the column.

Three partially pre-stressed interior beam-column sub-assemblages (SI) and two partially pre-stressed exterior beam-column sub-assemblages (SE) made of reactive powder concrete as test specimens were numerically modeled using a finite element program. The objective of this study was to investigate the behavior of the SI and SE numerical models. The numerical model inputs were: material data, details of test specimen dimensions, and test specimen reinforcements. The numerical models were subjected to the same loads as those applied experimentally. The numerical modeling results were hysteretic and backbone curves and stress distribution contours. The numerical model outputs showed good similarity with the experimental results. The stress distribution contours of the numerical models correlated with the crack patterns in the joint zone of the test specimens. The behavior of the SI numerical models differed from the SE numerical models due to various stresses on the beam plastic joints and the joint zones.

On 7th May 1611, the construction of Esfahan Shah mosque started to be a part of the re-modeling of Safavid capital, a building that adopts a glazed bulbous double dome as a hybrid structure of brick and wooden elements. This paper aims to present building techniques, construction process and conservation works of this complex dome through historical evidence and onsite surveying. For these purposes, following a brief history of the building, the paper explores the geometry, morphology and construction sequences. It subsequently addresses the conservation during the last century from Salnameh (1934–36) up to current intervention and their consequences. The paper necessarily illustrates cracks pattern, not only to recognize its causes via their type and geometry but also to address historical performance and structural capacity. According to the objectives, the study of the Shah dome plays an important role to better understand other similar cases. This paper concludes that structural analysis and future conservation could benefit from the achievements derived from historical research, which also allow further understanding of construction techniques., (undefined)

The preservation (in terms of inhibition of failures and collapses) of architectural heritage against horizontal loads (such as earthquakes) requires an accurate assessment of the non-linear response up to failure: to this aim, the use of advanced numerical tools to perform three-dimensional non-linear dynamic analyses is fundamental. This paper investigates the performance (up to the activation of local failures and under horizontal loads) of three historical masonry palaces of the outstanding cultural heritage in Mantua (Northern Italy) after the 2012 Emilia earthquake. Despite the unquestionable importance of the three case studies, until now these palaces have not been studied with advanced numerical simulations; moreover, the recent seismic sequence and the consequent significant cracks patterns observed in the post-earthquake survey phase have pointed out their vulnerability even to small seismic actions. The first part of the study was addressed to an accurate knowledge of the three palaces, focusing especially on the information gathered during on-site surveys, bibliographical and historical research: the data collected were employed to detect the complex three-dimensional geometry of the palaces under study and to define the cracks patterns. In the second part of the study, detailed and representative three-dimensional finite element (FE) models of the structures were developed and non-linear dynamic analyses were carried out to obtain a deep numerical insight into the seismic response of the three palaces, identifying the most vulnerable elements for each structure. The comparison between the numerical results and the damage survey showed that the numerical approach used in this study may be an adequate tool to properly evaluate the seismic response of historical masonry buildings. A comparative assessment of the results obtained for the different palaces was performed in terms of predicted damage distributions, energy density dissipated by tensile damage and maximum displacements registered for the different macro-elements.

This paper investigates the seismic response and partial failure mechanisms of the Castle of St. George, one of the most renowned monumental constructions of the invaluable cultural heritage in Mantua (Northern Italy), which was hit by the 2012 Emilia seismic sequence. The first part of the study is based on historical analysis, documentary research, photographic collection and field surveys to achieve an accurate knowledge of the castle and a proper evaluation of the damage caused by the earthquake. All the collected information is used to create a representative and detailed finite element model of the castle and non-linear dynamic analyses are carried out using a damage plasticity model with different softening behavior in tension and compression for masonry. The finite element simulations provide additional information on the seismic response of the castle, identifying the damage patterns and the most vulnerable parts for different seismic intensity levels. The numerical results indicate that the corner towers and the vaults are the most damaged elements of the castle. The towers exhibit a severe damage concentration in the battlements, near the enlargements of the section in correspondence with the corbels and along the body near the openings. Moreover, the interaction between the tower and the adjacent walls, which are characterized by a different dynamic behavior, causes marked vertical cracks along the walls in correspondence with the connection regions.

This study presents the performance of a combined finite-discrete element method for prediction of the structural response of reinforced concrete beams under impact loading. A combination of finite and discrete element methods enables the modelling of the concrete and the reinforcement before the concrete cracking, as well as a discontinuous nature of the concrete caused by fracture and fragmentation under high impact loading. Discretisation of the concrete with triangular finite elements is coupled with one-dimensional reinforcing bars embedded inside the concrete finite elements. The cracking in the concrete activates the joint elements used to simulate the non-linear behaviour of both concrete and reinforcement. Numerical analysis based on experimental test data has been carried out to simulate the main features of the reinforced concrete beams impacted by free-falling drop-weights. A high level of accuracy was demonstrated in various comparisons between the experimental tests and the analysis results, including peak displacement, crack pattern, damage level and failure modes of reinforced concrete beams.

The architectural heritage was severely damaged by the seismic sequence that occurred in Emilia (Northern Italy) in May 2012. This paper investigates the seismic behavior of three masonry churches that were damaged by the 2012 Emilia earthquake. The analyzed churches are located in the South-East area of the province of Mantua: they are representative of some churches, denoted as “Matildic churches”, belonging to the territorial area between Lombardia, Emilia Romagna and Toscana and built during the Matilde di Canossa domain, between the X and the XI centuries. The study was based on detailed field surveys, in situ tests, visual inspections and existing archives in order to obtain an accurate knowledge of the churches and a proper evaluation of the damage caused by the earthquake. Then, detailed finite element models of the churches were developed and non-linear dynamic analyses with different peak ground accelerations were performed. The numerical simulations provided a deep insight into the seismic behavior of the analyzed churches, identifying the damage patterns and the main collapse mechanisms for different seismic intensity levels. The obtained results appear to be in a good agreement with the damage experienced by the churches during the earthquake. This study can be considered as a first step to assess the seismic vulnerability of the “Matildic churches”, extremely important for their historical and architectural value.

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.

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.

Fibre reinforced concrete (FRC) has been widely used in industrial pavements and non-structural elements such as pipes, culverts, tunnels, and precast elements. The strengthening effect of fibres in the concrete matrix is achieved primarily due to the bridging effect of fibres at the crack interfaces. The workability of the concrete was reduced on addition of high percentages of steel fibres. The optimum percentage of addition of steel fibres varies with its aspect ratio. For this study, 1% addition of steel has resulted to be the optimum percentage for both Hooked and Crimped Steel Fibres and was added to the beam specimens. The fibres restrain efficiently the cracks and take up residual stresses beyond the cracking. In this sense, diagonal cracks are effectively stitched up by fibres crossing it. The failure of beams within the shear failure range changed from shear to flexure in the presence of sufficient steel fibre quantity. The shear strength is increased with the addition of steel fibres and had exceeded the enhancement obtained with the transverse reinforcement. However, such increase is not directly in proportion with the quantity of fibres used. Considering all the clarification made in the present experimental investigation, it is concluded that 1% of crimped steel fibres with an aspect ratio of 50 is the best type of steel fibres for replacement of transverse stirrups in high strength concrete beams when compared to the steel fibres with hooked ends., {"references":["Julia Sauer, Jan Lingemann, Dipl.-Ing., Oliver Fischer, and Konrad Zilch, \"Shear Capacity of Steel Fiber Reinforced Concrete Beams without Stirrups\", 3rd fib International Congress – 2010.","Mohamed Zakaria, Tamon Ueda, Zhimin Wu and Liang Meng, Experimental Investigation on Shear Crack Behaviour in Reinforced Concrete beams with Shear Reinforcement, Journal of Advanced Concrete Technology, Vol. 7, No.1 February 2009, PP. 79-96.","Thomas, J., and Ramaswamy, A., Mechanical Properties of Steel Fiber reinforced Concrete., ASCE Journal of Materials in Civil Engineering,19(5) 2007, PP. 385-392.","Antonie E .Naaman, Engineered Steel Fibers with Optimal Properties for Reinforcement of Cement Composites, Journal of Advanced Concrete Technology, vol.1, No.3, PP 241-252","D. H. Lim, B. H. Oh, Experimental and theoretical investigation on the shear of steel fibre reinforced concrete beams, Eng. Struct. 21 (1999) 37–44.","M. Hamrat, B. Boulekbache, M. Chemrouk, S. Amziane, Shear behaviour of RC beams without stirrups made of normal strength and high strength concretes, Adv. Struct. Eng. 13 (1) (2010) 29–41.","M. K. Johnson, J. A. Ramirez, Minimum shear reinforcement in beams with higher strength concrete, ACI Struct. J. 86 (4) (1989) 376–382.","P. Casanova, P. Rossi, Analysis and design of steel fibre reinforced concrete beams, ACI Struct. J. 94 (5) (1997) 595–602.","R. Narayanan, I. Y. S. Darwish, Use of steel fibres as shear reinforcement, ACI Struct. J. 84 (3) (1987) 216–227.\n[10]\tR. S. Pendyala, P. Mendis, Experimental study on shear strength of high strength concrete beams, ACI Struct. J. 97 (4) (2000) 564–571.\n[11]\tS. Furlan Jr., J.B. de Hanai, Shear behaviour of fibre reinforced concrete beams, Cement Concr. Compos. 19 (1997) 359–366.\n[12]\tS. Shin, S. H. Ghosh, J. Moreno, Flexural ductility of ultra-high strength concrete members, ACI Struct. J. 8 (4) (1989) 394–400."]}

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.

Opisan je numerički i analitički model za predviđanje graničnih stanja uporabljivosti savojnih armiranobetonskih elemenata. Predmetni gredni elementi ispituju se pod kratkotrajnim i dugotrajnim savojnim opterećenjem. Numerički i analitički model provjeren je uporabom postojećih eksperimentalnih podataka. Obje analize daju pouzdanu procjenu progiba tijekom uporabe. Model višesmjerne nepokretne pukotine uključen je u numerički model kako bi se uzelo u obzir nelinearno ponašanje betona nakon stvaranja pukotina (raspucavanja). Za dugoročnu analizu u oba modela primjenjuju se vremenski ovisni učinci betona, puzanja i skupljanja kroz viskoelastično ponašanje betona., A numerical and analytical model for prediction of serviceability limit states of flexural reinforced concrete members is outlined. The considered beam elements are investigated under short-term and long-term bending load. The numerical and analytical model is validated using existing experimental data. Both analyses provide reliable estimation of in-service deflections. A multi-directional fixed crack model is included in the numerical model to account for the non-linear post-cracking behaviour of concrete. For long-term analysis, time-dependent effects of concrete, creep and shrinkage are employed in both models through viscoelastic concrete behaviour.

The various shear-transfer actions due to: aggregate interlock effect, dowel action of the flexural reinforcement, the uncracked concrete in the compressive zone and the direct strut action for the point load close to the support, may provide different crack pattern in the shear span of the concrete beams without stirrups. The aim of this paper is to investigate the shear failure mechanisms in T-shape, single span and simply supported beams exclusively reinforced with longitudinal glass fiber reinforced polymer (GFRP) bars. The research of concrete beams flexurally reinforced with GFRP bars without stirrups indicated the possibility of occurring, besides the conventional shear-compression failure mode, another type of failure governed by the loss of bond between the ordinary reinforcement and concrete. Usually the critical shear crack in RC beams without stirrups develops through the theoretical compression strut preventing a direct transfer of the shear force to the support. The main parameter affecting the crack pattern and the shear strength of the beams is the shear span to depth ratio. However, the test results presented in this paper showed the formation of an arching effect due to the bond losing between the GFRP flexural reinforcement and concrete. This failure mode revealed unexpected critical crack pattern and failure mode. Digital image correlation (DIC) technique was used to better capture and analyse the cracking process up to the formation of the shear failure crack

Reactive Powder Concrete is a new type of concrete that posseses an ultra high compressive strength. The primary component of Reactive Powder Concrete is very fine powder with high silica content to improve the concrete’s chemical reaction and its homogeneity. Reactive Powder Concrete is a mixture of cement, silica fume, 600 μm diameter maximum of quartz, superplasticizer and polypropylene fiber. This research aims to evaluate the behavior of exterior beam-column connections with extended beam longitudinal bars and/ or added reinforcement using reactive powder concrete under lateral cyclic loading. This study consisted of three specimens with reactive powder concrete compressive strength of 135 MPa. The first specimen (BU-1) was detailed as a conventional beam-column connection, the second specimen (BU-2) was detailed by extending beam longitudinal reinforcement bars which are welded to a steel plate as large as beam’s cross section to the far side of column, while the third test specimen (BU-3) was detailed by adding reinforcement to the main reinforcement of the beam in the exterior beam-column connections. The results showed that specimen BU-3 possesed better cyclic behavior compared to the other two specimens in terms of crack pattern, hysteretic curve, energy dissipation, strength and stiffness degradation at each loading cycle.

Strain controlled fatigue tests have been performed on two types of heavily filled epoxy corrosion protection coating sprayed onto a 6 mm steel substrate. Fatigue cycling was performed at R ratios of 0 and −1. The two coatings differed in their formulation and the major differences in mechanical performance were in their static strain to first crack development and their fracture toughness, where Coating A was significantly tougher than coating B. During strain cycling coating crack development was monitored using optical observations and surface replicas. It was found that in both coatings surface crack development began soon after the onset of cycling and proceeded via growth of surface channelling cracks and multiple initiation of new cracks. Detailed studies were made of crack development morphology and its relation to coating type and to the applied strain range. A definition of coating life as the first appearance of a 2 mm surface crack length was used. This represented the end of the life where the coating protected the substrate. Before this life was achieved, crack growth rates of single cracks were invariant with crack length. After this point further crack growth, multiple cracking and crack to crack interactions took place. Cracking in this region could be characterised with a new total crack length parameter shown to be strongly dependent on applied strain range.

International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies, 8, 1, 23-37

Digital Image Correlation (DIC) is a full-field contactless optical method for measuring displacements in experimental testing, based on the correlation of the digital images taken during test execution. It is used in several fields of experimental solid mechanics, but its potential application to the characterization of composite reinforcements has not been fully investigated yet. In this paper DIC is used in tensile and bond tests on composite reinforcements comprising different textiles and matrices. Results obtained by two DIC software programs are validated by comparison with displacement and strain transducers. DIC provides additional information on damage pattern (crack location and width) and composite-to-substrate load transfer mechanism (effective bond length and local stress concentrations). It also offers the advantageous possibility of selecting several measurement points after the test, overcoming some drawbacks of traditional transducers. On the other hand, since only on the outer surface of the specimen is monitored, no information is directly available on the textile embedded in the matrix. The combination of DIC and traditional sensors in laboratory testing allows improving the understanding of the mechanical behaviour of composite reinforcements and the identification of their fundamental properties.

A novel lumped stresses network approach for the analysis of the mechanical behaviour of masonry structures is presented. It is formulated through a network of lumped stresses, making use of polyhedral stress functions and a variational approximation of the continuous equilibrium problem. The proposed method allows for modelling masonry structures as no-tension elements and gives, in the case of curved masonry members, the optimised surface through a predictor-corrector procedure and the stress function describing the membrane stress. The given approach offers a useful tool for predicting the crack pattern of unreinforced masonry structures and the associated stress fields. It is validated against some benchmark case studies dealing with a hemispherical dome, a groin vault, a cloister vault and a masonry beam.

International audience; Surface cracking or heat-checking is investigated at a microscopic scale on a hot work tool steel (X38CrMoV5) tested under thermal fatigue. Thermal fatigue tests are periodically interrupted to observe the surface of the specimens by scanning electron microscopy (SEM). A non destructive and semiautomatic method is developed to assess and evaluate the two-dimensional crack pattern initiated on the oxide scale layer formed on the specimen surface. The crack pattern is characterized by image analysis in terms of density, morphological and topological features. This technique allows to determine the number of cycles to initiate the microscopic heat-checking and to follow its evolution.