C.B.M. Blom

New Design Method for the Production Tolerances of Concrete Tunnel Segments

Some damages observed in tunnels constructed with tunnel-boring machines are caused by contact deficiencies between segments, which are the result of the sum and accumulation of several types of tolerances. Because the relation among the tolerances, the contact deficiencies, and the structural damage is not quite clear, the segmented lining is usually designed to meet very tight tolerances. The existing tolerance recommendations consist mostly of extrapolation of tolerances applied to other types of concrete structures with different characteristics. This explains the wide variation of production tolerances found in the literature, with different repercussions on the cost of molds and on the performance of the structure. The first part of this study shows the relation between structural damage and contact deficiencies. The second part of the study explains how the contact deficiencies found in practice are generated by the tolerances. Finally, a general design method is proposed for the estimation of the production tolerances. Based on this, general recommendations are derived for the maximum admissible production tolerance used to limit the incidence of structural damage.

UHPC Pedestrian Bridges and Measured Human Induced Vibrations

The use of high strength materials in the design of pedestrian bridges leads to slender structures with decreased mass and low stiffness. The resulting low Eigen frequency makes the bridge more susceptible to human induced vibrations. As a consequence, user comfort may decrease significantly. In some designs it has been found that the geometry has been adapted to fulfil user comfort requirements (e.g. increased height, more mass, tuned mass damping), which has a negative effect on costs and use of resources but which is unnecessary from the point of view of ultimate limit states.

Repair Strategy of the Deteriorated Immersed Maastunnel

The first immersed concrete tunnel in the world is heavily deteriorated due to reinforcement corrosion. Beside its great historical importance, the tunnel is situated in the heart of Rotterdam and is one of the most important city connections. Therefore, upon discovering structural damage, a major task has been to prove that the structural safety is at a reliable and acceptable level (Blom 2013). Consequently a repair plan has been worked out to preserve this tunnel for the future and to minimise disturbance of traffic in the city centre during repair closure. This paper shows the dilemma’s and choices in realising the repair strategy.