•The full-range behavior of CFRP-steel joints is analytically studied.•A trilinear cohesive material law is used to solve the bond differential equation.•CFRP-steel joints with a rubber-toughened ...adhesive are tested.•CFRP-steel joints with short and long bonded lengths are studied.
Fiber-reinforced polymer (FRP) composites represent an effective solution to strengthen and retrofit existing steel members. Namely, bonded or unbonded carbon FRP (CFRP) plates have been employed to improve the strength, fatigue behavior, and durability of steel bridges. In bonded solutions, the effectiveness of the CFRP reinforcement strongly depends on the adhesive employed to bond the plate, as failure usually occurs due to debonding. Within this framework, the use of toughened adhesives is particularly attractive since they may improve the load carrying capacity of the CFRP-steel interface, also providing a certain ductility. Debonding in CFRP-steel joints was previously studied using a cohesive approach. However, solutions able to describe the full-range behavior of joints with toughened adhesives and finite bonded length are not available in the literature. In this paper, a trapezoidal (trilinear) cohesive material law (CML) is employed to model the bond behavior of pultruded carbon FRP-steel joints made with a rubber-toughened epoxy adhesive, which showed cohesive debonding within the adhesive layer. The analytical solution provided is employed to study the experimental response of nine CFRP-steel joints tested using a single-lap direct shear set-up. Comparisons of analytical and experimental results of joints with three different bonded lengths confirm the effectiveness of the solution proposed.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The application of composite materials to strengthen existing structural elements is a valid alternative to traditional strengthening techniques. Fiber reinforced cementitious matrix (FRCM) ...composites have been successfully employed to strengthen existing reinforced concrete (RC) and masonry structures in bending, shear, torsion, and to confine axially loaded elements. Although failure of FRCM strengthened elements depends on different parameters, such as the composite and substrate geometrical and mechanical properties, debonding at the matrix-fiber interface is generally the failure mechanism. Therefore, the study of the bond behavior of FRCM composites is a key topic to develop reliable design procedures. Numerous experimental campaigns were carried out recently to study the bond behavior of different FRCM composites. An analytical model is employed in this paper to describe the bond behavior of FRCM-concrete joints and different trilinear cohesive material laws are defined based on the experimental results. The experimental and corresponding analytical load response, strain profile, slip profile, and shear stress profile along the bonded length are compared. An analytical formulation of the bonded length needed to fully develop the stress-transfer mechanism at the matrix-fiber interface, i.e. the effective bond length, is provided for the trilinear cohesive material law employed.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•Direct shear tests of FRCM composites provide the CML of the fiber–matrix interface.•Tensile tests are performed to determine the tensile properties of FRCM composites.•An analytical model combining ...results of tensile and direct shear tests is proposed.•The model shows that clevis-grip tensile test is a fiber–matrix bond test.
Fiber-reinforced cementitious matrix (FRCM) composites are usually mechanically characterized by means of tensile and bond tests. The former, in the clevis-grip version, is referred to by the American guidelines ACI 549.4R (2013) to determine the tensile properties of the FRCM composite. The latter, in the single-lap version, is used in the Italian guidelines CNR-DT 215 (2018) to determine the effective strain. The effective strain is the strain at which debonding occurs and therefore composite action is lost. In this paper, the poliparafenilene benzobisoxazole (PBO) fiber–matrix stress transfer law, also known as cohesive material law (CML), is employed in an analytical model that describes clevis-grip tensile tests of PBO-FRCM composites. The CML was previously obtained by the authors from single-lap shear tests. The load responses provided by the model are compared with the results of tensile tests herein presented in addition to selected tests from the literature. The experimental cracking process, tensile strength, and deformation capacity can be accurately predicted by the analytical model. The comparison indicates that the knowledge of the CML of the fiber–matrix interface allows for an accurate prediction of the main tensile properties of the PBO-FRCM coupon.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Fiber-reinforced polymer (FRP) composites have been largely used for strengthening and retrofitting reinforced concrete members in the last few decades. However, limited information is available ...regarding their performance after prolonged exposure to different environmental conditions. In this paper, the effect of wet-dry cycles on the bond behavior of carbon FRP-concrete joints tested using a single-lap direct shear test set-up is investigated. Specimens were exposed to 50 wet-dry cycles, each comprised of 6 h of immersion in water at 25 °C followed by 18 h of drying at 50 °C. The digital image correlation technique was used to obtain the displacement field of the composite and determine the cohesive material law and fracture energy of the FRP-concrete interface. A finite element model was then used to reproduce the load response and reinforcement strain profile observed experimentally. The results show that wet-dry cycles affect the FRP-concrete bond properties and change the failure mode from a cohesive debonding within the concrete substrate to an adhesive debonding within the interface.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The cohesive material law (CML), i.e., relationship between the interfacial shear stress and slip between a fiber reinforced composite and the substrate, is a fundamental tool to model the structural ...behavior of composite-strengthened elements. A crucial problem that researchers working in the field of strengthening applications with fiber reinforced cementitious matrix (FRCM) composites face is how to obtain the CML. A direct method to determine the CML could be applied if the longitudinal strain is measured along the bonded length. However, since the critical interface for some FRCM composites appears to be the interface between the fibers and matrix, measuring the fiber strain in FRCM composites is a difficult task due to the presence of the matrix that embeds the fiber textile. To overcome this difficulty, an indirect method is proposed in this paper. The parameters of the CML are determined by fitting experimental data in terms of peak load measured for different composite bonded lengths. The procedure is applied to single-lap shear test results previously published by the authors. The CML obtained shows good correlation with the CML obtained from direct calibration of strain profiles measured along the bonded length and is able to predict the experimental load responses.
Display omitted
•The proposed indirect method to calibrate the cohesive material law of FRCM-concrete joints does not require strain measurements.•Indirect calibration of the CML is performed simply by employing peak load versus bonded length plot.•Peak strain and corresponding slip versus bonded length and analytical load responses compare well with experimental data.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Externally bonded reinforcement (EBR) represents a valid solution for strengthening and retrofitting existing structures. Among possible reinforcements, fiber-reinforced composites gained large ...popularity in the construction industry mainly due to their high strength-to-weight ratio and durability. Due to their high strength, failure of externally bonded fiber-reinforced composites is usually due to debonding, which makes understanding the bond behavior of these materials of paramount importance for the effectiveness of the strengthening application. Within this framework, bond tests are generally employed to obtain information on the stress-transfer mechanism between the composite and the substrate. The results of these bond tests can be employed to derive the interface cohesive material law (CML), which describes the relationship between the shear stress and corresponding slip at the interface where debonding occurs.
In this paper, a rigid-trilinear CML is proposed to describe the stress-transfer mechanism of externally bonded composites that show the presence of frictional stresses at the debonding interface. The analytical solution of the full range behavior of composite-substrate joints with long and short bonded lengths and with free and fixed far end is provided using the proposed CML. Then, the results of thirty-five single-lap direct shear tests of PBO fiber-reinforced cementitious matrix- (FRCM-) concrete joints are presented and employed to calibrate the CML. Good agreement is found between the analytical and corresponding experimental direct shear test load responses.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Based on the excellent mechanical properties and piezoresistive effect of carbon fiber, carbon fiber reinforced cementitious matrix (CFRCM) has been used in the strengthening and self-monitoring ...research of reinforced concrete (RC) structures. In this study, the assumptions of the telescopic layered model theory of CFRCM were refined. The factors influencing the piezoresistive effect of carbon fibers were subsequently analyzed. Simultaneously, the resistance calculation theory for the pull-out process of CFRCM bundles was established by combining the parallel circuit theory. Based on the above theories, a pull-out equivalent telescopic layered failure model of carbon fiber bundles in the cementitious matrix was developed, considering the trilinear cohesive material law (CML) and the piezoresistive effect. Pull-out tests on carbon fiber bundles in both freshwater standard sand and seawater sea-sand matrices were conducted. This model was successfully used to simulate the piezoresistive effect during the pull-out process of CFRCM bundles with two matrices and different embedded lengths. The number of fiber filaments in each layer, the rupture damage of the fiber filaments during the loading process, and the degree of matrix infiltration into the carbon fibers were calculated. This work lays the foundation for advancing the development of structural strengthening and structural health monitoring.
•The telescopic layered failure model has been modified.•The resistance calculation theory of CFRCM has been proposed.•A full process failure analysis of CFRCM based on the piezoresistive effect has been achieved.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Solving three-dimensional boundary-value engineering problems numerically requires material laws. However, it is difficult to build the material laws in three dimension, since the material behaviors ...are usually measured by one-dimensional uniaxial tension/compression experiments. In this way, the material behavior in the three-dimension is ‘compressed’ into one-dimensional data. Here we propose a new method, coined MAP123 (map data from one-dimension to three-dimension), to decompress the one-dimensional data into three dimension for nonlinear elastic material modeling without the construction of analytic mathematical function for the material law. The decomposition of stress and strain into deviatoric and spherical parts for isotropic nonlinear elastic materials at finite deformation makes this data-driven approach work quite well. Several examples are used to demonstrate the capability of MAP123, such as a rectangular plate with a circular hole under uniaxial tension. Corresponding experiments are also carried out to further verify the MAP123 method. Based on the proposed approach, uniaxial experiment is suggested to measure the deformation in three directions not only the force and extension along the loading direction. Limitation of the proposed MAP123 approach is also discussed.
•MAP123 can decompress 1D data into 3D to solve BVP problem without material laws.•MAP123 is implemented and employed to solve BVP problems by 1D data.•MAP123 demonstrates a way to express 3D material law through two sets of 1D experimental data.•MAP123 can analyze the mechanical response under finite deformation.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•SRG-masonry joints exhibit a scattered behavior associated with nature of matrix.•Direct measurement of strain in the fibers to obtain CML is difficult in FRCMs.•An indirect calibration of CML is ...proposed that employs the experimental responses.•Fracture properties are independent of CML shape if debonding load is used.
Fiber reinforced cementitious matrix (FRCM) composites, also known as textile reinforced matrix (TRM) composites, are a suitable alternative to fiber reinforced polymer (FRP) composites to strengthen reinforced concrete and masonry structures. In the toolbox of FRCMs, a recently-developed composite that employs high-strength steel fibers embedded in a hydraulic mortar is particular appealing for applications on historical masonry constructions. This type of composite is known as steel reinforced grout (SRG). In this paper, an extensive experimental work is presented. Single-lap shear tests are performed to study the debonding of SRG strips from a masonry substrate, which is the critical failure mode for strengthening applications. For SRGs, debonding typically occurs at the fiber-matrix interface. A large scatter of the experimental results is observed, which is related to the variability of hydraulic mortars and their ability to impregnate the fibers. Although strain gauges can be applied directly to the fibers to obtain the experimental strain profile along the fibers, because of the presence of the matrix these measurements are complex and in some cases not reliable. Thus, indirect method based on the global response of the test is proposed to obtain the interfacial properties.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
10.
Data-Driven games in computational mechanics Weinberg, K.; Stainier, L.; Conti, S. ...
Computer methods in applied mechanics and engineering,
12/2023, Volume:
417, Issue:
Part A
Journal Article
Peer reviewed
Open access
We resort to game theory in order to formulate Data-Driven methods for solid mechanics in which stress and strain players pursue different objectives. The objective of the stress player is to ...minimize the discrepancy to a material data set, whereas the objective of the strain player is to ensure the admissibility of the mechanical state, in the sense of compatibility and equilibrium. We show that, unlike the cooperative Data-Driven games proposed in the past, the new non-cooperative Data-Driven games identify an effective material law from the data and reduce to conventional displacement boundary-value problems, which facilitates their practical implementation. However, unlike supervised machine learning methods, the proposed non-cooperative Data-Driven games are unsupervised, ansatz–free and parameter–free. In particular, the effective material law is learned from the data directly, without recourse to regression to a parameterized class of functions such as neural networks. We present analysis that elucidates sufficient conditions for convergence of the Data-Driven solutions with respect to the data. We also present selected examples of implementation and application that demonstrate the range and versatility of the approach.
•We resort to game theory in order to formulate a new Data-Driven method for solid mechanics in which stress and strain players pursue different objectives.•The non-cooperative Data-Driven games identify an effective material law from the data and reduce to conventional displacement boundary-value problems.•The games are unsupervised, ansatz-free, parameter-free and strive to effect a direct connection between data and prediction.•Selected examples of implementation and application that demonstrate the range and versatility of the approach are presented.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
PDF
