KẾT CẤU MỚI TENSILE SPACE STRUCTURES

SPACE FRAMES The traditional MERO System, the Ball Node System (KK) is the first prefabricated space frame system developed by Dr. Ing. Max Mengeringhausen during the second worldwar. Loads are applied via the nodes, the members distribute the compression and tension forces. The original idea was to build a space frame with uniform length of members and regular nodes with 18 holes with angels of 45 and 60 degrees. Nowadays the angles between the members may be freely chosen and also the length and diameter of the members is not uniform. The members are round hollow sections, because they have the best resistance against buckling. Diameters from 30355 mm with different wall thickness are standard. The length differs i.g. 1,55,0 m but is not fixed. The nodes are to give a free choice for the connections holes. The standard ball nodes have diameters from 49,5350 mm.

A B S T R A C T

With the rapid advance of technology in engineering, the

creation of sound yet innovative construction has

evolved into a sophisticated global challenge For more

than fifty years MERO has been a part of world-wide

architectural success, in its creation of ingenious modular

construction systems, paying particular attention to steel,

aluminium and glass structures

MERO's path led from structures made of their classic

spaceframe of tubes and nodes to structures of profiles in

combination with tensile cables, integrating the cladding

as supporting element In the following this path is

described

S P A C E F R A M E S

The traditional MERO System, the Ball Node System (KK) is the first prefabricated space frame system developed by Dr Ing Max Mengeringhausen during the second world-war Loads are applied via the nodes, the members distribute the compression and tension forces The original idea was to build a space frame with uniform length of members and regular nodes with 18 holes with angels of 45 and 60 degrees

Nowadays the angles between the members may be freely chosen and also the length and diameter of the members is not uniform The members are round hollow sections, because they have the best resistance against buckling Diameters from 30-355 mm with different wall thickness are standard The length differs i.g 1,5-5,0 m but is not fixed The nodes are to give a free choice for the connections holes The standard ball nodes have diameters from 49,5-350 mm

I Krolsliohiprofii (KHP)

2 Kegel

3 Gevnndebolzen

A Scnliisseliriutte

5 Knebelkerb&lill

3 Threaded boll

5 Dowoipin

To connect several members to a relatively small node the members have conical ends T h e member is connected to the node via a high tensile bolt The bolt has

a dowel pin and is screwed into the node via a sleeve Compression force is transmitted via the sleeve, tensions via the bolt (fig.3)

With this system single and multilayer space frames can

be designed Examples for Ball Node system ( KK ) are the Split Stadium cover and the Music Pavilion in the

Fig 4 Fig 7

The MERO Bowl Node System (NK) is a further

development of the M E R O space frame system developed from the KK-Ball Node-System

The advantage is that cladding or glazing can directly be fixed on the top chord without additional purlins Thus a higher transparency of glazed structures is achieved The standard bowl nodes have diameter from 160 to 200m The members of the top grid are rectangular hollow profiles The members are pin jointed to the nodes The screws are fixed invisible via the bolt insertion hole Members and nodes are flush fitting and torsion proof The nodes and the members of the bottom grid such as the diagonals correspond to the KK-system

The biaxial load transfer of space frames often leads to

a very low dead weight They are therefore specially

suited for wide span constructions Loads from cladding

or suspended loads should be applied via nodes

Membranes are directly fixed to the nodes, while sheets

are fixed to a purlin system These purlins are fixed on

stools of different height to achieve a sloped roof on a

horizontal spaceframe

NK Knoten / node / noeud

f •¥

Fig 10

The pyramid shaped greenhouses in Essen (fig 9) with a

lateral length up to 30 m are a perfect example for this

system These new glasshouses were designed as a

replacement for the former ones Three fully glazed

pyramid structures of different sizes together with a shed

hall and other flat connecting buildings form a square

around a totally enclosed garden courtyard The loads

from the glazing are applied directly to the rectangular

hollow profiles of the top chord These members and the

circular hollow section diagonals are interconnected via

bowl nodes The steel weight of the structure is 15

Also the largest hemisphere in the world, the Stockholm

Globe Arena, was built with the MERO bowl node

system (fig 11) The Arena designed as a

multipurpose-hall for international events is in the center of the

developing district of Hovet 5.000 to 16.000 seats can

be offered according to the different events The

geometrical optimization resulted in a dome with 96

meridians and 19 horizontal rings Thus a very

reasonable wide-meshed net with max field sizes of 3.6

x 4.4m was produced For reasons of stability a double

layered space frame construction with a max depth of

2.1 m had to be chosen For cladding an Alucopan®

Sandwichpanel was chosen Due to the requirements of steam tightness a perimeter support of each panel was needed

Thus the MERO Bowl Node System with rectangular hollow profiles in the top grid was used together with an extra secondary member by which the surface was now divided into max sized panels of 3.6 x 2.2 m This size was ideal for manufacturing and transport of the panels With a construction height of 85 m and a globe diameter

of 110 m the steel structure has a self-weight of only 32 kg/sqm surface area Because of their dimensions such large projects are not only a challenge in view of their huge space but also acoustic aspects have to be considered However the globe shape itself is rather advantageous It has the highest volume compared with the surface and provides an optimal distribution of temperature as far as the athletes and/or spectators level

is concerned and thus creates a comfortable atmosphere

The standard nodes have diameter of 200 mm, the

member sections are from 100x60 - 160x80 mm The

members are screwed invisible

ZK Knaten / node / noeud

Fig 13

Fig 14

Fig 16

TK Knoten / node / noeud

Fig 17

development

Fig 21

The glazed barrel vault is 244m long with a span of 80 m The characteristics of the design are (fig.21):

• clear hierarchy glass, point fixing devices, single layer barrel vault structure, trussed arches

• welded nodes, axial member connection through hidden bolts,

• separation of front walls (fig23) and barrel vault,

• single-layer shell consisting of bending resistant square grid, without wind bracings,

• stress free, point-fixed suspended glazing, two safety glass panes with a thickness of 8mm each laminated with 1.5mm PVB foil were used for the glazing

• surface flush sealing, the glass panes are sealed with extremely elastic silicon strips which are glued to the

consist of laminated safety glass The general layout of the roof is elliptical in shape This made the geometry of the connecting details a particularly tricky and daunting task

Fig 25

To cover the foyer area and the winter garden of the Musee des Beaux Arts in Montreal the Bowl Node system is combined with stainless steel rods and cables (fig.26+27)

The top chord consists of rectangular hollow sections with bending resistant connections to bowl nodes Rafters divide the grid into dimensions of approx 1.5 x 3.0 m Diagonal and bottom chord members are of high tensile stainless steel rods 16-20mm, directly screwed into the nodes Struts of circular hollow section 88.9 mm connect the bowl node with the bottom chord ball node Fig 22

Fig 27

Stainless steel cables act as tie down cables against wind

uplift forces The double glazing is fixed on the top chord

as "Structural glazing"

supported by stainless steel cables and stainless steel fittings

Fig 30

The innovative design is based on a tennis raquet, with

glass panels supported by pre-stressed cables The glass

is connected to the cables by double hinged connectors

which allows movement and rotation in all directions,

without breakage to the glass or ruptures to the sealant

An example for a counteracting biaxial curved tensile

structure is the cable net structure for the Rhon Klinikum

medical facility covering two promenades connecting

different buildings This allows the visitors and patients

to move and communicate protected from weather

influences The cladding of the cable net consists of glass

shingles connected to the cable net with special clamps

(fig.29+30)

Fig 32

The roof is designed to cover a ground plan of approx

The primary steel structure, the MERO space frame, consists of the main trussed arch with a span of about 118 metres and 6 smaller curved trussed girders with variable spans from 34 metres up to 46 meters which are connected to the main arch (fig.32)

The trussed girders are rigidly connected with the main arch and pin jointed at the foundation; the main arch is pin jointed at the base points

The membrane roof consists of 7 individual membrane panels spanning between the curved girder trusses The

Fig 34

The cable net facade is tensioned between the main arch

and the existing building with nearly no curvature The

cable net is covered with glass shingles to protect the

stage area from rain but to allow a view as transparent as

possible (fig.33)

The shapes of the membranes are designed by means of

a form-finding process, considering structural and

aesthetical aspects, as well as the boundary conditions

The curvature of the membranes is anticlastic (fig 35)

with the main load carrying directions following the lines

of principal curvature In this case the wind suction loads

are carried by the hogging traverses (fig 35 A-A) and

wind pressure and/or snow loads in the sagging direction

(fig 35-B-B)

All membranes are pretensioned with tension rods to the

Mero nodes of the upper chords of the trussed girders

(fig.36)

The design of the space frame components, tubular

members and spherical nodes, was performed by means

of a specialized design program, based on the general

approval for the MERO space frame system

This program is covers all design steps - beginning with

the geometry of the structural model, the analysis and the

evaluation of section sizes and diameters of the spherical

nodes - and continuing with the evaluation of parts lists

of 300mm diameter with up to 90mm diameter high strength bolts and max node diameters of 350mm

(fig.37)

A further challenge in terms of membrane structures is the Eden Project near St Austell in Cornwall, designed

by Nicholas Grimshaw & Partners The buildings will contain different climatic conditions to support a diverse range of plant life The buildings consist of a number of hemispherical domes which are set against the quarry walls The diameters of the domes vary from 40 m to 120m and are constructed from two layer reticulated steel members The domes will be covered with inflated three layer ET -foil-cushions which are hexagonal in plan and the edge lengths vary from 2.1m to 5.3 m The cushions themselves are held with aluminium frames

C O N C L U S I O N

Using the advance of technology in engineering and the development of innovative materials it is possible to create new sophisticated high tech quality solutions The integration of cladding materials such as aluminium and/or titanium sheet metal, glass and membranes covers

a very wide spectrum So it becomes more and more important to consider the structure and the cladding as one package