Manfred Curbach

Crack velocity in concrete

Abstract An experimental investigation to determine the crack velocity in concrete is discussed. Apart from the description of the equipment and the measurement technique, main attention is paid to the results and their dependence on strain rate. Finite element calculations which were carried out using a special constitutive model for the descending branch of concrete under tensile loading show that the maximum value of crack velocity is strongly affected by the shape of the stress-strain diagram.

Risk to Historical Bridges Due to Ship Impact on German Inland Waterways

We describe the investigation of two old bridges over inland waterways in Germany under a possible ship impact. Both the numbers of ship impacts against bridges in Germany and the structural description of the bridges have been studied. The investigation is based on probabilistic calculations to take into consideration the uncertainty of a possible impact and the uncertainty of material parameters of the historical bridges. The results for the original bridges and additional strengthening measures are presented in terms of probability of failure and also in terms of risk.

Textile Reinforced Concrete for Flexural Strengthening of RC-Structures-Part 2: Application on a Concrete Shell

The first practical application of the innovative strengthening method using textile reinforced concrete was carried out in October/November 2006 in the retrofit of a reinforced-concrete roof shell structure at the University of Applied Sciences in Schweinfurt, Germany. Since textile-reinforced concrete had not yet been standardized as a construction material, a single “special-case” technical approval was sought from and granted by the appropriate authorities for this particular application of textile reinforced concrete. This strengthening method entailed the layer-by-layer application of three layers of fine-grained concrete and textile fabric comprising 800 tex carbon rovings onto a rough, sandblasted concrete surface. The resulting strengthening layer has a thickness of only 15 mm (0.6 in.) and extended the roof structure’s service life.

Flexural Strengthening of RC Structures with Textile-Reinforced Concrete

Textile-reinforced concrete (TRC) is a high-performance composite in which technical textiles made of high-performance fibers are embedded in a fine-grained concrete matrix. Textile-reinforced concrete extends concrete applications to completely new fields. Besides slender new concrete elements, strengthening of already-existing concrete structures by thin textile-reinforced concrete layers is possible. This type of strengthening noticeably increases both the ultimate load-bearing capacity and serviceability of reinforced concrete structures. This aspect is shown in the present paper using experimental results of TRC-strengthened slabs.

Column Strengthening with TRC: Influences of the Column Geometry onto the Confinement Effect

The increase of the load-carrying capacity of columns being reinforced with Textile Reinforced Concrete (TRC) is partly achieved by the additional concrete cover. But then it is also decisively caused by the confinement effect of the textile reinforcement. The confinement is thereby producing a three-axial state of stress within the concrete core of the column. The effectiveness of such a confinement is especially dependent on the geometry of the concrete column to be strengthened. At rectangular ones with sharp edges without ogees the TRC strengthening can only augment the load-carrying concrete share not create a confinement effect which can be achieved at the round counterparts. Within the study we tested columns with all possible cross-sections from square to circle with different transition radiuses. Thus the influence of the transition radius onto the local-bearing capacity of the reinforcing textile was recorded. Furthermore the impact of different fibre materials and reinforcement degrees of the TRC-strengthening layer has been examined. The first results show a considerable disproportionate increase of the confinement effect with rising transition radius, as well as a growth of the confinement effect with augmenting level of reinforcement in the TRC-strengthening layer.

Load-Bearing Behavior of Textile-Reinforced Concrete

Textile-reinforced concrete (TRC) is a rather new high-performance cementitious composite material. In TRC composites, yarns or rovings from high-performance fibers, such as AR glass and carbon, are processed and oriented in a planar structure. This enables an optimal alignment and arrangement of fibers within structural members and allows for the production of extremely thin concrete components with a high load capacity. This paper gives an overview of some of the most relevant material properties of TRC and the associated mechanisms influencing the mechanical performance of TRC composites.

An attempt to explain strength increase due to high loading rates

Abstract Most materials such as steel, concrete, ceramics, polymers, etc. show an increase of strength due to high loading rates. A number of mathematical equations are available to describe this behaviour. Nevertheless the physical reasons for these observations are still unknown. The common behaviour of a number of materials leads to the assumption that at least some explanations are material independent. Due to this reason the results of the research done at the Institute for Concrete Structures in Karlsruhe are presented in this paper to furnish new ideas for the material research due to dynamic loading.

Strengthening of a Barrel-Shaped Roof using Textile Reinforced Concrete

When reconstructing the Zwickau School of Engineering for use as an IRS Office it became necessary to strengthen a reinforced concrete roof structure more than 100-years of age with textile reinforced concrete (TRC). Compared to other strengthening options, only TRC was able to meet the varied demands of monument and fire protection, the architect, as well as the construction company/contractor, while simultaneously meeting all static standards. The thin TRC layer, made of fine-grained concrete with embedded textile reinforcement, was applied to the roof structure in a total thickness of only 10 to 15 mm.

Textile-Reinforced Concrete for Flexural Strengthening of RC-Structures—Part 1: Structural Behavior and Design Model

The use of technical textiles to reinforce concrete (i.e., textile reinforced concrete [TRC]) extends into entirely new areas of application. The thick concrete covers, as required for steel reinforced concrete, are no longer needed due to the corrosion resistance of textile materials. Slender structural members with thicknesses as small as 10 mm (appr. 4 in.) are possible. Additional characteristic features of textile reinforcement include two-dimensional planar characteristics, as well as ease of deformability and adaptability to complex and curved geometries. This can be exemplified by a pedestrian bridge built of TRC. Various geometric forms, such as slabs, beams, T-beams, shells, and columns can easily be strengthened using TRC. Dimensioning of elements and structures using TRC requires detailed knowledge of the load-bearing behavior of this composite material. Indeed, such behavior resembles that of steel reinforced concrete; however, this behavior is more heavily influenced by the bond between the textile reinforcement and the fine concrete, as well as the bond between filaments within the textile reinforcement. Minimal thicknesses also make it possible to strengthen existing concrete structures using TRC. Such strengthening increases both the ultimate load bearing capacity, as well as the serviceability, of the structure. Experimental results of strengthened slabs and beams, as well as a design model for flexural strengthening, is presented in this paper.

Strain Measurement of Steel Fiber-Reinforced Concrete under Multiaxial Loads with Fiber Bragg Grating

Regarding multiaxial loading tests, conventional measuring methods for the determination of strains are limited in showing the material behavior of specimens, especially in the range of small deformations. As a result, the measured strains are influenced within the entire loading range and a correction might be required. This paper presents a measuring method that uses fiber Bragg gratings to determine strains inside concrete specimens and provides test results as expected, even concerning small strains. By applying six measuring points in a tetrahedron-shaped arrangement, normal and shear strains can be determined. Reference measurements with strain gauges at uniaxial loading tests show that this measuring method produces reliable test results. Regarding multiaxial loading tests with compression-compression tension loads, a realistic determination of the deformation behavior was also possible.