Matthias Siemon and Jochen Zehfuß
Incidents like the fire in the Channel Tunnel, where severe concrete spalling was determined, have led to requirements in limiting the spalling depth and involved zone to local…
Abstract
Purpose
Incidents like the fire in the Channel Tunnel, where severe concrete spalling was determined, have led to requirements in limiting the spalling depth and involved zone to local and compatible magnitudes. Because the prevention of critical concrete spalling was also significant for the validity of the load-carrying capacity calculation for an existing railway tunnel, this paper aimed to investigate the spalling behavior of two contemplable concrete mixtures. The large-scale tests should show the load-carrying capacity over the whole duration of the fire exposure respecting all thermal and mechanical loads considered in the calculations.
Design/methodology/approach
In this paper, the fire behavior of two concrete mixtures for an existing railway tunnel are investigated. Small-scale tests prior to the main tests were conducted to identify an appropriate concrete mixture for the large-scale tests. During the large-scale tests, a tunnel segment is loaded with horizontal and vertical loads derived from a calculation taking into account the existing boundary conditions. Resulting restraint forces were calculated using the soil stiffness and tunnel fire design curve as fire scenario and applied via hydraulic jacks. To avoid additional restraint forces during the experiment, thermal strains due to fire exposure were allowed.
Findings
The results of the small-scale tests did not allow for a clear statement whether one concrete mixture would perform better regarding the spalling behavior. The two large-scale tests showed different results regarding the spalling behavior. Over the whole duration of fire exposure, the first test specimen remains nearly undamaged. During the test of the second specimen, spalling started about 3 min after burner activation. Because of the results, a suggestion for the concrete mixture of the first test was made, and this mixture was then used for the redevelopment of the existing railway tunnel.
Originality/value
The test setup was capable of incorporating all relevant boundary conditions for the analysis of an existing railway tunnel as part of an important north – south connection. The results have shown that a fire-proof construction is possible by adding polypropylene fibers to the concrete mixture. Additionally, it was possible to avoid the mounting of expensive and time-consuming fire protection measures like the installation of thermal insulation boards.
Details
Keywords
Sabrina Edeling and Matthias Pilz
The purpose of this paper is to use teaching and learning units specially devised for development of self-competencies and social competencies in the retail sector to explore how…
Abstract
Purpose
The purpose of this paper is to use teaching and learning units specially devised for development of self-competencies and social competencies in the retail sector to explore how learners assess these units in relation to acceptance, quality and self-assessment of improvement in their own performance.
Design/methodology/approach
The study focuses on Poland, Italy and Germany, with a total of 1,020 learners undergoing initial vocational training in the retail sector taking part.
Findings
The findings point to high levels of acceptance by participants and to significant appreciation of the quality of the teaching and learning units. Learners also perceived a marked improvement in their performance after completing the units. Differences in outcomes between individual countries can be explained at least in part by the differing training framework in each country.
Research limitations/implications
The approach did not enable the authors adequately to evaluate the increase in learners’ competencies: participants’ self-assessment is of only limited value for this purpose. Moreover, only three countries were involved in the study. This area in particular will require substantial further research if reliable methods for evaluating competencies are to be developed that improve on the current instruments.
Originality/value
The pedagogical objective of the project was to develop teaching and learning materials that would accelerate the development of self- and social competencies in the retail sector. The aim was that the material should be capable of use right across a range of European countries and be evaluated in a proper way. The findings are based on a very high number of involved students. Also the results are positive and enable teachers in VET-courses to use well tested teaching materials.