Fort, vesting en -onderdelen, Vestingwerken bij 1 T 1 Naarden (Gooise meren 27)

English translation

The text above is the record as published by the Rijksdienst voor het Cultureel Erfgoed, in Dutch. The English below is a machine translation made by TreeAlive, not by the Rijksdienst voor het Cultureel Erfgoed; it has not been checked by a person. Where the two differ, the original is the record. Report a translation error: privacy@treealive.com

Description

Cluster 7. Bridge with crane bridge.

NEW HOLLANDIC WATERLINE

Introduction

BRIDGE WITH CRANE BRIDGE as part of Fort Ronduit, of which the crane bridge represents a bridge type that is rare on a national scale. Fort Ronduit is located in the northern part of the New Hollandic Waterline, between the Fortification Naarden and the former Zuiderzee, now IJsselmeer. The fort is physically connected to the Fortification Naarden by means of a defensive rampart on its south side. Fort Ronduit served to defend the lands outside the dike on the north side of the fortification, the sea dike and the Naarder Trekvaart. Naarden was of very great military-strategic importance as a defence of the direct access to Amsterdam. The fort was intended to prevent the Fortification Naarden from being bypassed on the north side.

The raising or removal / destruction of bridges has since antiquity been a proven means of keeping out intruders. Not only did this impede or delay passage or crossing over a watercourse, a dry or wet ditch or terrain depression, but the attacker also had to provide the means to take the barrier if necessary. Wooden bridges were relatively quick to destroy, if need be by setting them on fire. Stone and concrete bridges required a larger and more time-consuming intervention, although a explosive charge could sometimes quickly achieve the desired effect. With the advent of iron bridges - applied on a large scale in the course of the 19th century in many different variants - the second option remained possible, but the first disappeared. Blowing up bridges was capital destruction and only happened in the utmost necessity. One way in which iron bridges could be closed off was by removing or rendering inaccessible (small) parts of them.

On the west side of Fort Ronduit there is an access road with a bridge over the fort ditch. The bridge was restored in 2006 according to a specification from 1878. The bridge was renewed using components of the first fort bridge from 1874. This had been severely damaged when two consecutive storms in 1877 knocked away two bridge piers. When rebuilding, a crane bridge was chosen, an invention of railway engineer F.W. Conrad from 1837-1847. Conrad called his invention 'rotating track' or 'rotating track bridge', but because the components on which the bridge rotates resemble (hoisting) cranes, this bridge type is particularly known as 'crane bridge'. The crane bridge was indeed invented for railway bridges, but had the great advantage for military purposes that the bridge deck rotated sideways and did not stand upright and was therefore less vulnerable to enemy fire. The principle of the crane bridge is as follows: the bridge has a number of crane girders, which rotate around a vertical axis, called the back-axle. The back-axles are attached to the abutment. When opening the bridge, the crane girders swing around the back-axles towards the abutment. Before the bridge can be opened, the wooden girders on the rotating part of the bridge deck must be removed. When the crane bridge at Fort Ronduit was rebuilt in 1878, by contractor C. Verheul from Hardinxveld, the length of the span was shortened by almost 8 metres compared to the bridge from 1874. As much material as possible from the old bridge was used. Thus the western abutment, the westernmost bridge pier, part of the hardstone bearings and part of the railings of the bridge from 1874 were preserved. To prevent undermining, the ditch was provided with a rip-rap bed and the embankments had to be repaired. Initially, the barrier (access gate) made of wood and wrought iron from 1874 was also preserved. However, this was replaced by an iron version in the early 20th century. The crane bridge itself was adapted or repaired several times over the years. Among other things, extra girders were added beneath the bridge in the mid-20th century and the double bridge deck was replaced by a single bridge deck. The latter after a lorry carrying Naarden's lifeboat had sunk through the bridge deck. Because of the rarity of the bridge type, of which it is believed only three remain in the Netherlands, the 2006 restoration went back as much as possible to the situation of 1878. Where possible, authentic or original material was used. Sometimes a visual solution was chosen, such as in the reuse of the side flanges of the old girders against modern steel beams. The double bridge deck of wooden girders respectively was also restored. It was decided to maintain the 20th-century iron barrier and not to restore it back to the situation of 1878. Colour research into the original paint layer was carried out during the restoration. From this, the colour combination dark grey and green emerged as the most plausible.

Description

The BRIDGE WITH CRANE BRIDGE from 1878 was built using components of the first fort bridge from 1874. The bridge was restored in 2006 to the original situation according to the specification from 1878. The bridge consists of a fixed (approx. 4.00 m) and a horizontally rotating (approx. 8.00 m) section. The rotating section is located on the east side (fort side). It has four crane girders, which rotate around a back-axle (vertical axis). The crane girders and back-axles are attached to an extended part of the eastern abutment. The girders are of unequal length because the abutment is bevelled. This is necessary to create space for the rotated crane girders when the bridge is open. The crane girders are supported by braces and are interconnected by means of coupling rods. The crane bridge is opened by a rack (a toothed iron band) which is attached to a winding mechanism in a hardstone block on the eastern abutment. Mechanical devices are attached to this bridge to secure the bridge in its open state. Before the bridge can be opened, the bridge deck must be removed. For this purpose, iron rings are fitted to the sides of the wooden girders. The bridge deck consists of an oak underdeck and a pine topdeck. The bearings and girders for the fixed and rotating parts of the bridge are different. Both bridge sections are fitted with the original T-shaped iron railings dating from 1874 and lattice work of crossing bars, which are fitted with cast-iron rosettes. On the western bridgehead stands an iron barrier (access gate) from the early 20th century.

Valuation

The BRIDGE WITH CRANE BRIDGE from 1878 with early-20th-century barrier is of general importance because of:

* Cultural-historical values as part of the New Hollandic Waterline as designed by C.R.T. Kraijenhoff and initially realised from 1815 by him, Jan Blanken and major-engineer Willem Offerhaus and subsequently strengthened and improved by others for approximately 125 years.

* Architectural-historical values, in particular as an expression of military-strategic building, which is based on the system of inundation and access defence (19th century).

The complex component from 1878 with building components from 1874 and the early 20th century is an example of a historical hydraulic engineering expression related to military-strategic building and in particular as a bridge and crane bridge.

* Ensemble value and situational values as part of the New Hollandic Waterline and also because of the functional and physical coherence with the other components of the complex.

* The component is extremely rare because only three crane bridges remain in the Netherlands, the birthplace of this bridge type.

* The component is reasonably well preserved, in that a major restoration of the bridge took place in 2006 based on authentic and original material.