Josef Hegger

Punching Strength of Reinforced Concrete Footings

This study investigates the punching shear behavior of reinforced concrete footings. Punching tests were conducted on 17 reinforced concrete footings were tested to study the parameters assumed to affect the punching shear strength of footings. These parameters included shear span-depth ratio (a/d), concrete strength, and punching shear reinforcement. The (a/d) ranged between 1.25 and 2.0, while the concrete strength ranged between 20 and 40 MPa (2.9 and 5.8 ksi). To study the effect of soil-structure interaction, five footings were realistically supported on sand. The remaining specimens were supported on a column stub and a uniform surface load was applied. The present experimental investigations indicated that the angle of the failure shear crack is steeper in punching tests on compact footings than observed in tests on more slender slabs. Furthermore, the (a/d) significantly affects the punching shear capacity. The provisions of ACI and Eurocode 2 are evaluated by comparing them with experimental results. Modifications are proposed to overcome the deficiencies of these codes.

Experimental Investigations on Punching Behavior of Reinforced Concrete Footings

This article reports on a study of 5 reinforced concrete footings that were tested to investigate the punching shear failure of footings. Contrary to most of the research in this area, in which footings are supported on springs or on a column slab, this study used concrete column footings realistically supported on sand. The tested specimens had different slab thicknesses and reinforcement ratios. The consistency of the sand was also varied as a test parameter (dense and loose). Four footings had no shear reinforcement, whereas the fifth one included shear reinforcement (vertical bars mechanically anchored at top and bottom by welded anchor plates). Results showed that the angle of the failure shear crack is steeper than that observed by punching tests of flat slabs. In addition, the shear slenderness seems to significantly affect the punching shear capacity. The consistency of the sand has no other influence on the soil pressure distribution underneath the footing. The authors report on their study and review other tests from the literature, developing a test data bank. They also compare ACI and Eurocode 2 provisions and rules for the design of footings with their present test results as well as the information from the test data bank.

The effect of anchorage on the effectiveness of the shear reinforcement in the punching zone

Abstract All building codes require well anchored shear systems in the punching zone. The enforced experimental investigation of 10 symmetric punching tests with conventional stirrups and stirrups made of fabric reinforcement shows, that the effectiveness of the shear reinforcement depends on the quality of the anchorage. This result could be confirmed by tests from the literature too. In addition, the punching design approach of DIN 1045-1, 2001 [Tragwerke aus Beton, Stahlbeton und Spannbeton, Teil1: Bemessung und Konstruktion. Beuth Verlag, Juli 2001] is presented.

Recommendation of RILEM TC 232-TDT: test methods and design of textile reinforced concrete: Uniaxial tensile test: test method to determine the load bearing behavior of tensile specimens made of textile reinforced concrete

Textile reinforced concrete (TRC) is a high performance cementitious composite using straight and parallel aligned fibers of suitable materials, e.g. ARglass and carbon, as continuous reinforcement in form of textiles. Textile reinforced concrete is usually used for thin concrete elements or as strengthening layers for concrete structures. Textile reinforced concrete shows a multi linear stress-strain-behavior with three distinct stages (uncracked, multiple cracking, cracking completed). The crack formation in textile reinforced concrete is significantly finer than in customary reinforced concrete. Therefore, not only the tensile strength of the concrete but also the total tensile load bearing behavior of the composite material textile reinforced concrete is of importance. The uniaxial tensile test presented here is a test method to determine the load bearing behavior of tensile specimens made of TRC. Bond characteristics of textile reinforcement can not be derived from this tensile test since this information could only be derived indirectly from cracking patterns. However, in textile reinforced concrete cracking is mainly controlled by transverse fibers which are typically present in textile reinforcement. For bond properties reference is given to the RILEM recommendation TDT A.2 (pull-out).

INVESTIGATION OF PRE-AND POSTCRACKING SHEAR BEHAVIOR OF PRESTRESSED CONCRETE BEAMS USING INNOVATIVE MEASURING TECHNIQUES

At present, no unified theory exists that is capable of fully describing the complex behavior of reinforced concrete (RC) elements subjected to shear, with recent research results tending to contradict each other. Using innovative measuring techniques, the pre-and postcracking shear behavior of concrete beams was studied giving insight to the shear resistance mechanism of RC beams. Laser interferometry was used to study the precracking behavior. It is shown that nonlinear stress distributions occur before the formation of visible cracks, thereby influencing the cracking angle. Photogrammetry was applied to study postcracking behavior. The measured displacement components of the crack edges were used to estimate the shear transferred across the cracks by shear friction. It is shown in this paper that for beams with low or high shear reinforcement ratios, the amount of shear force transferred across cracks by shear friction is negligible.

NONLINEAR FINITE ELEMENT ANALYSIS OF REINFORCED CONCRETE BEAM-COLUMN CONNECTIONS

A nonlinear finite element analysis is used to investigate the behavior of exterior and interior beam-column joints. The model was calibrated using results of the third authors tests. The behavior of exterior beam-column joints turned out to be different from that of interior connections. The parameters influencing the shear strength are not the same for both types of connections. The main parameters influencing the shear strength of exterior beam-column connections such as joint slenderness, the column reinforcement ratio, concrete compressive strength, efficiency of the beam reinforcement anchorage, and the amount and the efficiency of the shear reinforcement are investigated. For interior beam-column joints, the main factor affecting the shear strength turned out to be concrete compressive strength. A comparison is also done with proposed shear strength equations.

High-strength concrete for a 186 m high office building in Frankfurt, Germany

Abstract In Germany, high-strength concrete was used for the first time for the construction of the 186 m high office building ‘Trianon’ in Frankfurt. As the German standard for reinforced concrete does not cover a strength of 85 MPa, special approval by the relevant state building authority was required. The paper reports on the chosen mix design, design assumptions, fire tests, experience on site, quality control and economic aspects.

Realization of TRC Façades with Impregnated AR-Glass Textiles

In the last 30 years, façade-panels made of steel-reinforced concrete have become less attractive for architects and clients. Due to the metallic reinforcement, the insufficient concrete covers of former design code generations and hence the material-dependent corrosion, many cases of damage occurred. Using technical textiles for a new composite material, Textile Reinforced Concrete (TRC), it is possible to produce concrete structures which are not vulnerable to corrosion. The presented ventilated large-sized façade elements and self-supporting sandwich panels exemplify the capability of TRC. In the paper, applied materials are characterized and the production process of tailor-made textile reinforcements as well as the load-bearing behavior of the members is described.

Structural Assessment of Concrete Bridges in Germany : Shear Resistance under Static and Fatigue Loading

Abstract The demands on the load-carrying capacity of bridges have increased over the last few decades because of the higher traffic volumes and weights. In the future, an even greater increase is expected. Since a large part of the existing bridges in Germany was built in the 1960s and 1970s, the assessment of these structures is deemed crucial. Therefore, the German Ministry of Transport introduced guidelines in 2011 allowing for a more accurate determination of the bearing capacity compared to the current German bridge design code. Nevertheless, many concrete bridges show deficits in shear and fatigue resistance. Consequently, a supplement to the guideline was published in 2015 to incorporate new research results. This paper describes the approaches for static and fatigue shear verification that consider the provided shear reinforcement. These methods refer to a truss model with variable compression strut inclination. Further, an application to a typical box-girder bridge in the road network is presented, demonstrating the potential for increasing the design value of the bearing capacity.

Project Life INSUSHELL: Reducing the Carbon Footprint in Concrete Construction

Within the Life INSU–SHELL project (Environmentally Friendly Facade Elements made of thermal insulated Textile Reinforced Concrete) RWTH Aachen University together with industrial partners developed and implemented an innovative and eco friendly modular system for sandwich facades. The thin–walled, light–weight sandwich structure combines Textile Reinforced Concrete (TRC) and a PUR–rigid–foam–insulation. With the use of TRC a large quantity of concrete material and therefore CO2–output can be avoided. The lower amount of concrete used in the new elements results in a reduction of CO2–output of about 70% in comparison to a similar element of ferroconcrete. The lower weight saves energy and fuel. Moreover it reduces the pollutant emission in transport and application. The employment of the innovative elements at the new INNOTEX building (ITA: Institut fuer Textiltechnik of RWTH Aachen University) with a facade size of about 590 m2 saved large quantities of CO2–output in comparison to conventional building t...