drawings-en (1).pdf

Student Research Project

Membrane constructions - solutions for corner details

Student Research Project 2011-2012 Budapest University of Technology and Economics Faculty of Architecture Department of Mechanics, Materials and Structures, Füzes Bálint Péter Advisor: Dr. Hegyi Dezső, PHD Assistant Professor

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Table of contents

1.

Abstrakt

2.

Membrane constructions and their main detaillings

3.

Main typologies of tensile surface structures

4.

Statical behaviour of tensile surface structures

5.

Simple connections

6.

Solutions with webbing

7.

Solutions with metal plates

8.

Solutions with membrane kept away from the corner

9.

Solutions with continuous ropes

10.

Solutions connected to flexible edging

11.

Solution with two layers

12.

Sources

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I. Abstract

Scientific research (Student Research Project) performed as part of my extracurricular studies, was to investigate a special type of structure in the field of membrane structures (more commonly referred to as canvas or awning structure). My aim is to compile an engineering guide which clearly shows the corner nodes and the operation of the nodal points of this type of structure. My long term plan is to create ’structural descriptions’ which deals with the complete positioning of all membranes of the awning and offer wide ranging solutions for them i.e. the anchorages and cable connections, the corner details, the stiff and flexible edge details, the awning edges and mast details. Amongst these types of connections I found many examples, however at the 2011 Student Research Project Forum only the corner details were fully developed. Within the scope of Hungarian reference literature, you are still unable to find a collection of technical drawings showing these structural nodes, for which these solutions are specifically outlined. Therefore my Student Research Project paper fills a structural engineering niche, which I hope will be useful for everyone who is either simply interested , or who is researching the topic for a specific project whether it be a simple shade, or covering public areas or stadiums. Regarding the construction and design of the manual, I used graphical illustrations to explain the behavioural characteristics of the structure. In the introduction , firstly the geometric characteristics of the structure will be explained then briefly we will discuss the main structural components (awnings, keders, cables, webbings) materials and functional properties, design characteristics. These do not need to be discussed in detail as there are plenty of reference books regarding these. The introduction also describes the main types of nodes, and detail the behaviour of the membranes with a specific given power, which is based on Mariotte’s formula. The formula shows, how an „infinitely small” piece of the canvas, through internal or external pressures on the surface keeps an even balance. Next, the canvas corner nodes particular behaviour will be described - the tensions at the corner connections form an extremely complicated system, a detailed discussion of which could be the basis of a doctoral

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thesis, however we explain the main effects, which serves as a basis to introduce the engineering categories and variations. Fundamentally the paper deals with the corner connections, predominantly foreign examples are used. Along with the technical drawings, explanatory dimensional and functional diagrams are included. The examples (circa 50) are divided into groups, such as the unbroken rope connections, the fixed canvas on metal plate connections, flexible edge connections, etc..

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II.

Main details of the membrane structures

First of all about membranes. These building constructions do have the smallest dead load in comparison with the span. Around the 1 kg/m 2. They are building constructions and frames in themselves. Their specialty is that in the surface there is only tension, no bending, no compressive forces and no trimming.

We can see the main typical detaillings of the structure on this tent.

1.

Anchorages

2.

Stiff edges

3.

Flexible edges

4.

Corner details

5.

High-points

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Student Research Project Down here we can see the main types of the membranes based on how we produce the tensioned forces which are responsible for the stability of the constructions. In the first cell you can see the category of the tensioned structures. We tension all the edge fittings, plates and constructions around and in the membrane. In the middle you see the category of pneumatic membranes. The surface is loaded with inner atmospheric pressure. At the last cell there is a group of holders and sacs. The inner pressure here is ensured by water, stored materials or other fluids. We are going to run on the first category.

Tensioned surfaces

Pneumatic structures

One-layer tents

Pneumatic tubes

Pillows

Tensegrity structures

Holders, sacks

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At next we can the main geometric typologies of the tensile surface structures it is getting clear, how much possible spots are there of detaillings discussed later. The architecture of this type of structure is getting always developed, this is only an insight.

Most generic symmetrical membrane, supported with an inner mast - high pointed membrane. Most generic symmetrical membrane over a poligon, supported with an inner mast Most generic symmetrical membrane, supported with an inner mast.

Generic, high pointed structure with multiple mast support, with flexible edges.

Membrane supported from outside , with flexible and stiff edges.

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Structure tensiled on an arch, combined with flexible edges.

Combined geometry with sruface tensiled on arch, with flexible and stiff linear edges.

Membrane tensiled over an ellipsis on an arch, combined with stiff edges. Hard to erect.

Membrane tensiled over an ellipsis on an arch, combined with flexible edges.

Membrane tensiled over an ellipsis on two arches, combined with flexible edges and stiff corners. Hyperbolic paraboloid membrane tensiled by the cornerings. It is used quite commonly, often at smaller constructions.

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III.

Constructional elements



Technical membrane



KEder cord



Wire rope



Webbing

First of all: technical membranes. We transfer forces in them. They have the goal to share spaces and bear loads. Their first group is the group of the solid films, often made of PVC, which have proportional less strenght and are often transparent. In the other group you can see the coated fabrics, that have UV protection. There is a perpendicular system of strands, and this fabric is coated with different materials, like PVC. Technical materials do have their own literature. The keder cords are linear load-bearing elements - this is practically a plastic, or rarely metal rope with the diameter of circa 1 centimeter. This cord-shaped element ensures a linear surface to the clamping plates and other tensioning elements to hold the membrane at its proper place. It is mostly welded on the membrane.

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Student Research Project Wire ropes are also linear load-bearing elements. They mostly transfer great forces of the building. They have a different elongation from that of the surfaces, which can be an important problem at complex detaillings, as we will see it later. They also have an own literature. The fittings, forces are transferred with, are going to be important at the corners.

III-1. ábra

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Webbings are also linear load-bearing elements.They are available to strenghten the membrane at the edges. They are also available to collect forces, as we ill see it later. They can be glued, welded or seamed on the surface. They have to be placed on the UV-protected side of the surface or do have to be coated with a slice of membrane.

.

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IV. Statics of tensioned surface structures The stresses, the forces occöring here could serve as the subject of a phd thesis, my point here was the engineering collection, but will touch the main force-systems too. The typical of the tensioned surface structures is that in every point of the surface there are two different stress-systems present. First the so called meridian forcesystem, which connects the mast and the anchorage in the case of this membrane and does not allow the construction to lift. The other stress-system is the ring-system, which connects the horizontal stress-components of the neighboring elements. We can see, that without these stresses the awning would elongate in the meridian direction and would split. These two systems are always there in every point, but this changes in the corner: the ring-stresses are hitting the wire ropes and the meridian forces are having another angle to the ropes than ninety degree.

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gy 

pR t

The fact, that we can balance stresses with pulling forces at the endings of the curved ropes, bases on the formula of Mariotte. This expresses, how a tube loaded with inner pressure can stay balanced.

m 

pR 2t

With developing this formula you can explain the membrane stresses in the surface even in three-dimensional cases. ( a bq  P) Q  q b

b  r  Q  2  g  (sin( / 2))

r q 

2  g  (sin( / 2))



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If the piece of the surface is infinite small, is kicsi  is also getting infinite small sin( )   ,

q

g r

N 2   2  a1

N1   1  a2

P

N1 N 2 ,  R1 R 2

The goal at these type of structures is to ensure stability without the loads, however at these formulas we can understand the statical behaviour of the surface.

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On the left side you can see the meridian-force-system alone. When we split it into components, we can see a force-system paralell to the axis of the rope, which tries to pull up the membrane from the corner, so it would split in the middle. And we can see the other stress system perpendicular to the axis, which tries to pull the membrane together and causing creases and excess in the surface. Important is, that according to the Mariotte formula, the forces perpendicular to the rope can be supported in the form of pulling forces. The paralell forces must be supported with other fittings. Even a small skin friction is working here, but we can not base the designing on it.

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The ring-stresses can be also split into components, with a similar behavior - they must be also anchoraged.

Important is, that these forces are always present, so to a proper positioning of a corner we need to handle these forces at the same time. Our goal is not to allow the membrane to split or to allow creasess to evolve.

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V.

Simple connections

In this section I collected the simple connections. One of their most important characteristic is that they are economically developed. These solutions are used at smaller constructions, where there are no greater forces to transfer, like at the case of smaller awnings, roofs in gardens, etc. In the most cases there is only a webbing glued, seamed or welded on a membrane, which is transfering the paralell and the perpendicular forces to the anchorages. The disadvantage of these solutions is, that they can easily fold, and that there is no possibility of more precise installation. Foldings can be reduced by adjusting the anchorage systems.

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Student Research Project Simple connections – 1-2. solutions

At the first solution the membrane is not clamped to anywhere. This can only work properly, when the angle of the wire rope is close to 180 degrees. If not, the membrane would be pulled up from the corner. At the second solution there is a ring which does not allow the membrane to be pulled up.

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Student Research Project Simple connections – 3. solution

At the drawned solution we can see three webbings welded on a membrane to strengthen the membrane at the corner. The solution you can see in the middle of the pictures, does have got webbings along the edge continuously, this is why it is more aestethic and does not have bigger foldings in the surface.

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Student Research Project Simple connections – 4-5. solutions

We can see this solution on simple shading awnings in gardens. The membrane is simply clipped with a ring.

The difference here is that you can see a webbing welded on a membrane along the load-bearing wire rope.

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Student Research Project Simple connections – 6. solution At this solution you can see three webbings on the surface connected to a forcetransfering ring-element. The difference of the anchoraging bolts can be properly installed. This solution can be for example connected to a reinforced concrete construction.

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Student Research Project Simple connections – 7. solution

The functioning of the corner is similar to the first solution shown in this section. The forces perepndicular to the wire rope are not collected, this detailling only works properly by smaller forces and at the case of an angle close to 180 degrees. It is interesting in a way that it shows you that an anchoraging column can greet multiple clamping plates in three dimenions.

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VI. Solutions with webbings At the solutions collected in this section there are webbings used to transfer paralell forces to the anchorages. The webbing transfers the paralell forces, the wire rope collects the perpendicular forces. The membrane mostly does not reach the corner fitting. There are examples collected here to introduce how the metal plate can solve the problems of the corners. There is no possiblity at the most solutions to change the lenght of the webbing. The webbing has got the second function to block the foldings to come up along the edge.

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Student Research Project Solutions with webbings - Detail 1.

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Student Research Project Solutions with webbings - Detail 5-6.

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Student Research Project Solutions with webbings - Detail 7

Hosszmetszet

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VII.

Solutions with metal plates

These are the most commonly used solutions. The main point here is the metal plate, which collects the forces and transfers them to the anchorages. The plate is able to greet the wire ropes with a socket and to collect the forces perepndicular to the rope, and it is available to collect the paralell forces - it has a proper space for the membrane to clamp it on.

At too great forces the membrane can be split up at the clamping plates: there are great forces foceused here and the surface is weakened here by the clamping bolts.

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Student Research Project Solutions with metal plates - Detail 1.

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VIII.

Solutions with membranes kept away from the corner

At these solutions the collected forces are transferred to the anchorages by a metal plate again. The reason why these detaillings are discussed separate, is that the membrane is not fixed on the metal plate. At the first solution we coat the membrane around a metal plate. At a proper spot we make a cut in the surface and we fix this metal plate to the central plate with adjustable bolts. At the second and third solutions we will see that keder cords can be useful even here. With clamping metal plates we can keep the membrane away from the corner with a distance that can be adjusted with bolts.

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Student Research Project Solutions with membranes kept away from the corner - 1. solution

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Student Research Project Solutions with membranes kept away from the corner - 2. solution

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Student Research Project Solutions with membranes kept away from the corner - 3. solution .

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IX. Solutions with continuous ropes The next category of the collected detailings is the group of solutions with continuous ropes. The significant problem here is the same. We have to design a fitting that is available to connect the forces paralell and perpendicular to the axis. Here we can see three type of ways how we can collect the forces.

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Student Research Project Solutions with continuous ropes - Detail 1.

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Hosszmetszet

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X. Solutions connected to flexible edging The next category is the group of solutions where the corner is connected to flexible edging. The forces to transfer are quite great here, the different elongation of the membrane and the rope can not be ignored here. The force collected in the rope would cause creases in the membrane, when the membrane would only be wrapped on the wire rope. That's why we make the wire rope run in sleeves along the edge. The flexible edges do have their own solutions, we can see here the typical section ot the mostly used detailling. There is a keder cord welded to the membrane, and so the membrane is properly ensured against sliding out of the plates, which are clamped here along the edge. With sheet metal loops we hang the array of the clampings on the load-bearing wire rope.

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Student Research Project Solutions connected to flexible edging - Detail 1.

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Hosszmetszet

Függesztő szerelvény metszete

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Függesztő szerelvény metszete

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XI. Solution with two layers At last we can see a solution with two layers. There can be a need of producing a tensile surface structure because of different reasons. You may want to build a membrane where the lower layer is connected to an inner stiff edge, for example to a wall made of reinforced concrete. Even the ventillation between the two layers can have an advantageous affect on the thermostatic behavior of the construction.

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Student Research Project Solution with two layers - Detail of the upper layer

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Student Research Project Solution with two layers - Detail of the lower layer

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XII.

Sources

Michael Seidel: Tensile Surface Structures: A practical guide to cable and membrane construction (Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. HG Berlin, Germany - 2009)

Kollár Lajos: Ponyvaszerkezetek (Műszaki Könyvkiadó, Budapest, 1987)

Kollár Lajos: Ponyvaszerkezetek Tervezési Segédlet Statika (ÉVM megbízásából, Tervezési és Technikai Építészeti Intézet – 1988)

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XIII.

Collection of Hungarian terms

Állítható csavar

Adjustable bolt

Csavar

Bolt

Csomólemez

Metal plate

Ellenmenetes csavar

Screw-bolt

Fa gerenda hátszerkezet

Wooden beam construction

Fém csiga

Metal pulley

Fém csomólemez

Metal plate

Feszítőelem

Tensioning element

Feszítőszerelvény

Tensioning fitting

Foglalat

Socket

Függesztőfül

Hanging element - sheet metal loop

Fül

Loop

Hajtűcsavar

Bolt

Hátszerkezet

Anchorage

Heveder

Webbing

Hosszmetszet

Longitudinal section

Kéder

Keder (cord)

Kengyel

Stirrup

Kötél

Wire rope

Kötélhüvely

Socket of the wire rope

Membrán

Membrane / Surface

Merev rögzítés

Stiff clamping

Metszet (A-A metszet)

Section (A-A Section)

Nézet

View

Oszlop

Column

Ponyva

Membrane / Surface

Rögzítés a hátszerkezethez

Fixing to the anchorage

Rögzítőelem

Clamping/fixing element

Rögzítőlemez

Clamping/fixing plate

Szorítólapka

Clamping sheet

Szorítólemez

Clamping plate

Visszahajlított ponyva

Membrane bolt back

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drawings-en (1).pdf

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