The historic quay walls of Amsterdam

Abstract

The city of Amsterdam contains about 1600 bridges and 600 kilometres of quay walls. Of these walls, about 200 kilometres are of masonry walls placed on a timber floor and founded on timber piles. These quay walls are sometimes over 100 years old. Due to the increasing loads in the past century and the degrading of material properties in the masonry wall and timber elements, the quay walls are in bad shape. When designing a quay wall, a cross-sectional analysis is used to calculate the desired dimensions to withstand the loads. When this calculation is performed on a quay wall over a 100 years old, containing a failing pile foundation, the quay wall should fail. However, many of the quay walls under the condition of a partly failing foundation, are deforming, but still standing. During recent years, at 16 locations in Amsterdam, the risk of collapse appeared imminent, and emergency structures are put into place. Possible practical measures are removing trees on the quay walls, traffic limitations in the city centre and placing temporary struts and sheet piles to provide stability. Since the scale of the problem in Amsterdam is large, the time to renovate all the quay walls is lengthy. Therefore, there is a need for knowledge on the state of quay walls at the end of their life phase when partly failing. Different failure mechanisms occur, and various measures are developed to control those and provide (temporary) stability. This research answers the question: How can 2D analyses of quay walls, in multiple directions, under the condition of a partly failing foundation, provide insight into the hidden structural capacity within the masonry work? The study focuses on the severeness and scale of the foundation defects in the quay wall's cross-sectional and longitudinal direction. For the longitudinal models, the effects of the masonry material qualities are studied by using different material properties. Also examined is the effect of the failing foundation pile's post-peak behaviour, modelled as brittle and checked for plastic behaviour. Finally, the relevancy of the timber floor is studied for a stiff continuous floor and most notable, the full removal of the floor. To study this, two 2D regular plane stress, nonlinear elastic, finite element models are created in Diana FEA. The foundation piles are modelled as nonlinear elastic springs via a force-displacement diagram. The foundation piles' defects are modelled by assuming a smaller pile diameter, resulting in a weaker force-displacement diagram and larger displacements in the quay wall system. The foundation defects can be scaled over a small or big area by adapting multiple foundation piles over the length of the quay wall. The masonry's behaviour is researched by using a macro material model using smeared material properties for the brick and mortar, resulting in a continuous material. The material model used is the Total Strain Rotating Crack Model, which can be used in a 3D analysis of the quay wall system in future research. Finally, the interface between the timber floor and masonry is modelled using a coulomb friction interface criterion. This simulates the effects of the mortar layer connecting the timber floor and masonry work in a quay wall. The results conclude that analysing a foundation defect in the cross-sectional direction of the quay wall results in instability of the wall without further horizontal and vertical constraints to keep the quay wall in place. Modelling the pile foundation defects using a reduced pile diameter and consequently, a decreased force-displacement diagram as spring input provides the model with temporary stability. Ultimately, the cross-sectional analyses contribute little knowledge on residual strength and hidden structural capacity. Separately, the longitudinal model implements a vertical constraint in the masonry by using the bending capacities of the material. The results present an expected correlation between the scale of the foundation defects and the vertical displacements. Similar to the cross-sectional analyses, the reduced pile capacity of the foundation piles provides the model residual strength compared to the situation where the total failure of a timber pile is used. The timber foundation pile's failure mechanism needs to be researched in-depth since the results present a notable difference for crack patterns and force-displacement curvatures when modelled brittle or plastically. For brittle failure, a horizontal crack forms at the tip of the central, vertical crack, due to the abrupt enlargement in vertical displacement of the quay wall. The functionality of the timber floor in the longitudinal analyses presents itself when the crack patterns are analysed. The presence of the timber floor results in multiple smaller cracks instead of a single large crack when foundation defects of the quay wall system are analysed without a timber floor. It can be concluded that the masonry quality, most notably the tensile strength, affect the results significantly in terms of maximum values in the force-displacement diagrams and crack development. The material properties are based on Groningen masonry experiments, and it is recommended to perform experiments to the masonry quality of Amsterdam quay walls. Finally, the observed displacements related to the intervention points of the municipality conclude that foundation defects result in cracks for displacements below the marking points of 20 and 25 millimetres. For weaker masonry, the quay wall fails before the indication values. It is recommended to perform more measurements to the quay walls in Amsterdam and study the reliability of the intervention points.