PASSERELLE PEDONALI FORMA E STRUTTURA

Transcription

1 Lunedì 23 Maggio 2011 Presso lo Spazio Viterbi della Provincia di Bergamo PASSERELLE PEDONALI FORMA E STRUTTURA Prof. Ing. Bruno Briseghella University of Fuzhou (PRC) Prof. Ing. Enzo Siviero Università IUAV di Venezia Prof. Ing. Tobia Zordan Tongji University (PRC) NUOVE TENDENZE PASSERELLE STRALLATE PASSERELLE A NASTRO TESO

2 Footbridges can be special objects

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5 What is the usual practice for bridge engineers?

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7 Disappointing! How can we improve our skills in bridge design?

8 What are bridges and footbridges? Are they just crossing devices?

9 Are they just the result of the application of codes requirements? Are they just the result of the checking process of repeated standard solutions?

10 Hopefully not. Proficiency in any art or science is not attained until its history is known. History is very fully taught in schools of architecture, but up to the present, very little time or thought has been given in the engineering school to history of engineering, which is certainly quite as worthy of attention - History of Bridge, H.G.Tyrrell

11 So what are bridges and footbridges? A FOOTBRIDGE CAN BE

12 A FOOTBRIDGE CAN BE A FOOTBRIDGE CAN BE

13 A FOOTBRIDGE CAN BE THE MOST ENJOYABLE GAME FOR ENGINEERS! BUY CAN ALSO REPRESENT A PROBLEM FOR HUMANS AND LANDSCAPE

14 What makes you feel a bridge is beautiful or ugly? Bridges are naked constructions Bridges combine form with function. Bridges are sincere constructions. When Conceptual Design is wrong, the bridge will be a bad one and designer and owner will have no chance to disguise it! Generally bridges seem aesthetically more pleasing if they are simple in form, the deck is thinner (as a proportion of its span), the lines of the structure are continuous and the shapes of the structural members reflect the forces acting on them.

15 "... a good looking bridge is one which responds most gracefully to the structural requirements that it must meet." David P. Billington How do we sense bridges?

16 How can we deal with perception?

17 Footbridge or handle

18 Turbine or footbridge VISUAL PERCEPTION BRIDGE AND SOURROUNDINGS Shaping parameters Ratio elevation/background Neighbouring objects Rooting on the ground Verticality vs horizontal Trasparence vs Presence Dynamic continuity Lighting Colors Material Historical tradition other

19 VISUAL PERCEPTION BRIDGE AND SOURROUNDINGS Shaping parameters Ratio elevation/background Neighbouring objects Rooting on the ground Verticality vs horizontal Trasparence vs Presence Dynamic continuity Lighting Colors Material Historical tradition other VISUAL PERCEPTION BRIDGE AND SOURROUNDINGS Shaping parameters Ratio elevation/background Neighbouring objects Rooting on the ground Verticality vs horizontal Trasparence vs Presence Dynamic continuity Lighting Colors Material Historical tradition other

20 VISUAL PERCEPTION BRIDGE AND SOURROUNDINGS Shaping parameters Ratio elevation/background Neighbouring objects Rooting on the ground Verticality vs horizontality Trasparence vs Presence Dynamic continuity Lighting Colors Material Historical tradition other VISUAL PERCEPTION BRIDGE AND SOURROUNDINGS Shaping parameters Ratio elevation/background Neighbouring objects Rooting on the ground Verticality vs horizontal Trasparence vs Presence Dynamic continuity Lighting Colors Material Historical tradition other

21 VISUAL PERCEPTION BRIDGE AND SOURROUNDINGS Shaping parameters Ratio elevation/background Neighbouring objects Rooting on the ground Verticality vs horizontal Trasparence vs Presence Dynamic continuity Lighting Colors Material Historical tradition other VISUAL PERCEPTION BRIDGE AND SOURROUNDINGS Shaping parameters Ratio elevation/background Neighbouring objects Rooting on the ground Verticality vs horizontal Trasparence vs Presence Dynamic continuity Lighting Colors Material Historical tradition other

22 Girder cross seciton The shadow created by the overhang reduces the dominance of the girder. The deck overhang should be proportional to the girder depth. Girder cross seciton Different girder cross sections can have different aesthetic effects. The cross sectional shape of the girder should be considered in accordance with the following principles. A right angled (90 ) connection can catch the light and a double line may be visible. Maximizing the overhang will increase the shadow.

23 Girder cross seciton An angled connection would minimize this effect Girder cross seciton A very acute angle provides a deep shadow nearly all of the time.

24 Girder cross seciton A curved soffit will provide a gradation of tone and minimize a sharp line at the base of the beam. VISUAL PERCEPTION BRIDGE AND SOURROUNDINGS Shaping parameters Ratio elevation/background Neighbouring objects Rooting on the ground Verticality vs horizontal Trasparence vs Presence Dynamic continuity Lighting Colors Material Historical tradition other

25 VISUAL PERCEPTION BRIDGE AND SOURROUNDINGS Shaping parameters Ratio elevation/background Neighbouring objects Rooting on the ground Verticality vs horizontal Trasparence vs Presence Dynamic continuity Lighting Colors Material Historical tradition other Some useful principles to approach design

26 Understand context Understand the natural, built and community context of that would influence the design. - Topography, water bodies and water courses. - Other bridges in the area and along the road corridor. - Soils and geology. - Biodiversity. - Views to and from the bridge location. - Landscape and built character. - History, tradition and culture of the place Setting consistent design objectives and goals - Unobtrusive or landmark? - Integration (preferable) with landscape / Denial of surroundings. - Proportions: symmetrical / non-symmetrical - slender / stocky. - Simple / refined. - Conform / not conform to suite of bridges along corridor.

27 Explore different possibilities Understand and channel force flows Topological Optimization for Bridge Tower and Anchor Y MX Z X Y MX Z X

28 Understand and channel force flows Topological Optimization for Three-hinged Arch Y MX Z X MN Y MX Z X MN Y MX Z X MN Sometimes a structure is magnificently shaped by the flow of forces under specified boundary conditions and constraints so that each single component fulfill his task

29 J. Schlaich Proposal for a pedestrian bridge Sometimes this does not occur

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31 But when this is the case an observer might feel more comfortable and harmony it s introduced in the design

32 Girder bridges Truss bridges Arch bridges Cable stayed bridges Suspension bridges More variety can be found in footbridges

33 Stress ribbon Arch + Stress ribbon Suspension / Stress ribbon And even more MEMORIAL BRIDGE IN RIJEKA Croatia, 2003

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37 Trusses Footbridge Alveiro University, Portugal

38 J. Da Fonseca Aveiro bridge, Portugal Last trends: new forms

39 BRIDGE AT THE ROYAL VICTORIA DOCK London, UK, 1998

40 Pedestrian bridges Cost per unit surface

41 New forms Stess ribbon

42 Sacramento J. Strasky River Bridge, stress Redding, ribbon California, footbridge USA

43 Grants Pass Bridge, Oregon, USA

44 Sacramento River Bridge, Redding, California, USA

45 Grants Pass Bridge, Oregon, USA J. Schlaich Northbridge, Rostock

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47 J. Schlaich In den Enzauen, Knoll J.Conzett - Suransuns footbridge, 40m span, pre-stressed natural stone deck (h=6cm) Switzerland

48 Stainless steel structural components, pre-stressed stone, and dry joints are used for the deck

49 Stess ribbon supported by arch

50 Expressway R3508, Czech Republic Expressway R3508, Czech Republic

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52 Erection of footbridge: arch segments and deck segments Possible different arrangements of partially or fully self-anchored systems with the use of an arch Arch fixed at the anchor blocks of the prestressed concrete deck (tied arch) The deck below the arch work as a saddle for the stress ribbon scheme of the side spans (tied arch with side spans) Side spans are stiffened by thicker sections Two spans stress ribbon suspended on arch

53 PASSERELLE SIMONE DE BEAUVOIR Paris, France, 2007

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62 Self anchored supported by lower suspension

63 J. Strasky - Johnson Creek Bridge, Portland, Oregon USA Johnson Creek Bridge, Portland, Oregon, USA Johnson Creek Bridge, Portland, Oregon, USA

64 Curved suspension or cable stayed decks

65 Different layouts of curved cable stayed decks outer suspended and their implications

66 Different layouts of curved cable stayed decks centrally suspended and their implications Radial uniformly distributed load Radial uniformly distributed force H on the edge The principle is that highlighted by Boyle-Mariotte for a circular ring subjected to a uniform pressure distribution. The tensile force in each parallel (including that corresponding to the restraints) equals to: N = H r a

67 J. Schlaich footbridge in Kelheim over Danube

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69 J. Schlaich footbridge in Deutsche museum in Munich

70 J. Schlaich Reedy river bridge, Greenville - USA

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73 Structural Study J. Strasky proposal for a pedestrian bridge

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