02 Fakultät Bau- und Umweltingenieurwissenschaften
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/3
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Item Open Access Computer simulation: splitting tests of concrete thick-walled rings(1992) Pukl, Radomir; Schlottke, Bernd; Ozbolt, Josko; Eligehausen, RolfTwo non-linear program systems are used for a computer simulation of splitting failure of thick-walled concrete rings under internal radial pressure. Results of the numerical analyses for plane stress models, axisymmetrical model and 3D model are compared with available experimental data and empirical formulas. It is shown, that the behavior observed in experiments can be simulated, using advanced material models, namely the non local microplane model and SBETA material model based on the crack hand theory. With increasing outer radius of the ring, a size effect can be observed.Item Open Access Fracture size effect: review of evidence for concrete structures(1994) Bazant, Zdenek P.; Ozbolt, Josko; Eligehausen, RolfThe paper reviews experimental evidence on the size effect caused by energy release due to fracture growth during brittle failures of concrete structures. The experimental evidence has by now become quite extensive. The size effect is verified for diagonal shear failure and torsional failure of longitudinally reinforced beams without stirrups, punching shear failure of slabs, pull-out failures of deformed bars and of headed anchors, failure of short and slender tied columns, double-punch compression failure and for part of the range also the splitting failure of concrete cylinders in the Brazilian test. Although much of this experimental evidence has been obtained with smaller laboratory specimens and concrete of reduced aggregate size, some significant evidence now also exists for normal-size structures made with normal-size aggregate. There is also extensive and multifaceted theoretical support. A nonlocal finite element code based on the microplane model is shown to be capable of correctly simulating the existing experimental data on the size effect. More experimental data for large structures with normal-size aggregate are needed to strengthen the existing verification and improve the calibration of the theory.Item Open Access Numerical analysis of headed studs embedded in large plain concrete blocks(1990) Ozbolt, Josko; Eligehausen, RolfAnchoring elements such as headed studs, expansion, grouted or undercut anchors are used for local transfer of loads into concrete members. Parameter study of the behavior of headed stud anchors with embedment depth h v= 130 mm and failing by pulling out a concrete cone, is performed through numerical analysis. Compression and tension strength, fracture energy and the head diameter are varied. Numerical analysis is performed using nonlocal microplane model and axisymmetric finite elements. Results of the analysis are compared with experimental results.Item Open Access Fastening elements in concrete structures - numerical simulations(1993) Ozbolt, Josko; Eligehausen, RolfAnchoring elements such as headed and expansion studs and grouted or undercut anchors, are often used for local transfer of loads into concrete members. In order to better understand the failure mechanism, a large number of experiments have been carried out in the past. However, due to the complicated three-dimensional load transfer a very few or no numerical studies have been performed for a number of different fastening situations i.e. influence of the embedment depth, crack-width inftuence (fastening in cracked concrete), influence of the edge distance etc. Therefore, in the present study some results of the axisymmetric and three-dimensional numerical analysis of the headed studs embedded in plane concrete block are presented. Influence of different geometrical and material parameters have been studied employing finite element method and nonlocal microplane model. Comparison between experimental and numerical results indicate reasonable good agreement. Generally it has been observed that the failure mechanism is governed by fracture energy rather than by tensile strength of concrete. As a consequence, the size effect is strong and close to linear elastic fracture mechanics.Item Open Access Simulation of cycling bond-slip behavior(1992) Ozbolt, Josko; Eligehausen, RolfIn the present paper results of a numerical analysis for a deformed steel bar embedded in a concrete cylinder and pulled out by monotonic and cyclic loading are shown and discussed. The analysis is performed by the use of axisymmetric finite elements and an improved 3D general microplane model for concrete, instead of the classical interface element approach, a more general approach with spatial discretization modeling the ribs of a deformed steel bar is employed. The pull-out failure mechanism is analyzed. Comparison between numerical results and test results indicate good agreement. The present approach is able to correctly predict the monotonic as well as cyclic behavior including friction and degradation of pull-out resistance due to the previous damage.Item Open Access Influence of crack width on the concrete cone failure load(1992) Ozbolt, Josko; Eligehausen, RolfIn the present paper the influence of the crack width on the concrete cone failure load of headed anchors embedded in concrete is analyzed. The analysis is carried out on a reinforced concrete thick plate specimen using three-dimensional finite elements and the non local microplane model. In order to introduce precracking into the specimen before loading the headed anchor, the specimen is loaded in longitudinal direction by applying tension forces through reinforcement. At different crack levels pull-out of the fastening element is performed. Results of the analysis show that the concrete cone failure load is decreasing with increasing crack width up to ω ~ 0.15 mm to approximately 70 % of the failure load obtained for non-cracked concrete. Further increase of the crack width does not cause further decrease of the failure load. Comparison between numerical and experimental results indicates good agreement.Item Open Access Analysis of reinforced concrete beams without shear reinforcement using non-local microplane model(1991) Ozbolt, Josko; Eligehausen, RolfThe shear resistance of reinforced concrete beams without shear reinforcement is studied using the non-local microplane model and plane stress finite elements. The main objective of the present work is the study of the size effect. Calculated failure loads for geometrically similar specimens of four different sizes are compared with test data and the recently proposed size effect law. Results of the analysis as well as test results exhibit significant size effect. Observed failure is of the brittle type and is due to failure in tension-compression. Further studies with variations of the mesh size and load path demonstrated that results of the calculations using a non-local continuum are not influenced by the above parameters. However, the calculated failure loads depend on the characteristic length over which the strains are measured. In contrast to that, the calculated failure loads are inobjective when a local continuum is used and depend on mesh size, load path and convergence criteria. This is due to the stability of the numerical analysis, which may lead to an overriding of the critical failure mode and activating to a more stable one. In order to correctly predict failure load using local analysis and crack band approach it is necessary to check the stability of the numerical procedure.Item Open Access Nonlocal fracture analysis - identification of material model parameters(1994) Ozbolt, Josko; Petrangeli, Mario; Eligehausen, RolfIn the present paper a short description of the nonlocal microcrack interaction approach is presented. The physical meaning of this approach when used in the smeared finite element code is discussed. The present nonlocal "averaging" consists of a long-range interaction (crack interaction function) and local averaging. The first controls the crack propagation and the second is responsible for the correct energy consumption due to cracking. It is demonstrated that the nonlocal material model parameters may be identified by usual concrete fracture properties such as tensile strength, concrete fracture energy and maximum aggregate size. The nonlocal microcrack interaction approach is compared with the nonlocal strain approach and a possible simplification is considered.Item Open Access The size effect in concrete structures(1994) Ozbolt, Josko; Eligehausen, Rolf; Petrangeli, MarioIn the present paper the results of a size effect study on plain concrete unnotched and notched beams loaded in three-point bending are shown and compared with experimental results and Bazant's size effect law. The numerical results, obtained using the nonlocal microplane finite element code, confirm a strong size effect for smaller beam sizes. However, for larger unnotched beams the nominal strength tends to a constant value related to the uniaxial tensile strength. These results are in good agreement with what has been observed in experiments. The reason why the nominal strength of large unnotched beams should approach a limit value different from zero is investigated and the range of applicability of the size effect law is discussed. It has been concluded that the applicability of the size effect law is dependent on the problem type i.e. if the crack propagation before peak load is very stable the size effect law may be used in a rather broad size range. However, if this is not the case, the validity of the size effect law is limited to a smaller size range. Therefore, before extrapolating the size effect from tests with a small size range to a very large size range experimental data from a large size range should be available.Item Open Access Size effect in concrete structures(1992) Eligehausen, Rolf; Ozbolt, JoskoThe size effect for notched-tension specimens, three-point bend specimens, pull-out headed anchor specimens and beams loaded in torsion are calculated using a 2D and 3D finite element program. The program is based on the nonlocal microplane model. The calculated failure loads are compared with previously obtained experimental results. Test results and calculated data are compared with the recently proposed size effect law. Results of tests and analysis exhibit significant size effect that should be taken into account in design practice. It is demonstrated that the nonlocal microplane model used in a 2D and 3D finite element code can correctly predict failure loads for similar specimens of different sizes.