Browsing by Author "Mahrenholtz, Christoph"

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Open Access
Load capacity of shallow embedded anchor channels
(2020) Mahrenholtz, Christoph; Sharma, Akanshu
Anchor channels are cast in concrete and allow the connection of components using channel bolts. In recent years, the design to value resulted in ever thinner concrete elements, which often cannot accommodate the required embedment depth of standard anchor channels. For this reason, channels may be fitted with short anchors. While existing design provisions allow for the calculation of the tension capacity also for shallow embedded anchor channels, tests are required to determine product-specific parameters for the economic shear loads design. The presented study investigated the performance of shallow embedded anchor channels tested in shear. The detailed evaluation of the test data demonstrates that testing of the minimum embedment is conservative and that the load-displacement behavior of channels with welded I-sections is comparable to that of channels with forged headed studs. In addition, a new evaluation approach is proposed.
Open Access
Seismic bond model for concrete reinforcement and the application to column-to-foundation connections
(2012) Mahrenholtz, Christoph; Eligehausen, Rolf (Prof. Dr.-Ing.)
During an earthquake, the bond of anchorages is at risk for two reasons: The seismic excitation of the reinforced concrete structure loads the reinforcement cyclically and, at the same time, generates cracks which open and close cyclically. In joints, the cracks may run parallel along reinforcing bars anchoring adjoining members. The combination of cyclic loads and cyclic cracks leads to a more pronounced bond damage. The damage is secondary for large anchorage lengths with hooks detailed according to conventional design provisions. Large anchorage lengths with hooks are obstructive during construction and preclude post-installation of reinforcing bars. In order to develop an advanced design concept which allows the reduction of the anchorage length for column-to-foundation connections, two core topics were investigated in the course of the doctoral research which are discussed following the introduction (Chapter 1), the presentation of the state of the art (Chapter 2), as well as the explanation of the research approach and background (Chapter 3). First, the bond behaviour under simultaneous load and crack cycling was studied at micro level as existing bond models do not consider the effect of crack cycling. This study allowed extending the applicability of a hysteretic energy model for reinforcing bars subjected to simultaneous load and crack cycling (Chapter 4). In addition, the possibility to simulate the bond damage by means of the finite element method was shown (Chapter 5). Second, column-to-foundation connections were studied at macro level. An anchorage detailing without hooks is advantageous for construction and allows the post-installation of column starter bars in the foundation. Post-installed columns are in particular suitable for the seismic retrofit of soft ground floor stories which failure is one of the most common reasons for total structural collapses during earthquakes. Large scale experimental tests were conducted (Chapter 6) and supplemented by a large number of numerical tests (Chapter 7). The gained knowledge enabled the enhancements of the bonded anchor design provisions (Chapter 8). Based on the enhanced design provisions, a design concept for column to foundation connections is proposed which allows the post-installation of columns (Chapter 9). The design concept was developed in particular for seismic load cases. The thesis concludes in summarising the most significant results and pointing out which open questions in the field of post-installed reinforcing bars should be answered in future (Chapter 10).