Projects of IL 31

Curved Tension Rods


Introduction

  
As a supplement to the comments made in curved compression rods the following chapter presents constructions which were developed using the "curved tension rods". These structures all belong to the form family of the suspended roofs curvature resembles but because of the flexural rigidity of the free-hangig chain.

Structural Systems

  
Konstruktion
Hanging Curves

Hanging Curves

Vegetal rods which, as a result of their low flexural rigidity but high tensile strengh, are suitable for structures subjected to tensile strebgh produce a caracteristic, asymmetric hangig / bending curve when hung between two bearings.
This form becomes more obvious the greater the load is.
For larger spans and symmetrical roof forms, two or even several rods are combined. Normaly suspended roofs must be stablished by under spanning.
A number of different arch forms are necessary depending on the load situation. Arches, which must bear for example an additional spot load in the centre, are built as suspended pointed arches.
The addition of several hanging / bending curves forms characteristical structures in particular tent-like suspended roofs.
Konstruktion
Tent-like structures

Tent-like structures

DAs the traditional structure in Asia, the umbrella-like tent roof with groins and hoizontal compression struts has probably been developed to become the classic form. In addition to being able to form groins and edge supports as ropes, these elements can also be replaces by flexible rods.
In order to cover large floor plans, it is posible to fan out into a two branch tent with suspended ridge. These structures are formed by combinations of compression and tension elements.

Tensile Cable Structures

  
An-Lan
An-Lan
An-Lan
The An-Lan suspended bridge

Example: The An-Lan suspended bridge

The best known bamboo rope suspension bridge is the An-Lan bridge of Kuanhsien sapnning the river Min. Probably this bridge was erected in the 3rd century A.D. and since then frequently changed and repaired. It is reported that not a single piece of metal has been used in the entire construction of the An-Lan bridge.
The photos taken in 1958 show that the bridge has eight spans. The longest being 61 m and the total length of the bridge is 320 m. The bridge hangs from seven piers. Six out of hardwood, the centre pier out of granite.
For the poduction of rope the bamboo canes are split into fine strips. Because of their lower tensile strenght the strips from the inside of the cane were used for the cable core.Tis core was covered with a densely plaited layer consisting of the very strong bamboo taken from the outer layer of the cane. It is reported that the tensile strenght of such ropes increases by 20 % if the rope is soaked in water.
The anchoring of the bridge cable in the bridgeheads is effected by large wooden winches. The winches are held by huge basket which is filled with stones and by that the bridge cables are re-tensionable.