SEMINARON

STRESS RIBBON BRIDGE

KAISER AHMAD MALIKO7-CE-2012

Department of Civil EngineeringCOET,BGSBU.

Motivation IntroductionFinsterwalders bridge theoryForm of structureConstruction procedureComparision with simple suspension bridgeModified stress ribbon bridgesAdvantages and applicationsconclusion

STRUCTURE OF PRESENTATION

‘’Stress ribbon bridge philosphers,thinkers ,intelectuals all appeal please build bridges and not walls between different communities to achieve universal brotherhood’’

MOTIVATION :

Stress ribbon bridges are slender ,concrete deck segments placed on bearing cables in shape of catenary

consists of slightly sagging tensioned cables bedded in a concrete slab that is very thin compared with the slab

It’s a kind of suspension structure where the cables are tensioned so tightly that traffic can be placed on the concrete slab embedding cable

Typically made of concrete reinforced with steel tensioning cables

INTRODUCTION :

Stress Ribbon Bridge

West Golf Cart Bridge

West Golf Cart Bridge

Sacramento River Trail Pedestrian Bridge

Rogue River Pedestrian Bridge

McLoughlin Boulevard Pedestrian

Bridge

Lake Hodges Bridge

Stress Ribbon Bridge uses the theory of a catenary transmitting loads via tension in the deck to abutments which are anchored to the ground. This concept was first introduced by a German engineer Ulrich Finsterwalder.

The stress ribbon itself is a reinforced concrete slab with a thickness of about 10 inches (25.4cm). This reinforcement consists of three to four layers of 1 inch (2.5cm) to 1 ¼ inch (1.2cm) diameter, high strength steel.

FINISTERWALDERS STRESS RIBBON BRIDGE THEORY :

Precast concrete planks with bearing tendons to support them during construction

Joints between planks are sealed with concrete

To reduce dead load and horizontal forces at the abutment deck depth is kept minimum

The prestressing tendons transfer horizontal forces in to the abutments and then to ground using ground anchors

SUPERSTRUCTURES :

Consists of abutments to transfer horizontal forces from deck cables into ground via ground anchors

The ground anchors are tensioned before and after the erection of deck

The soil pressure ,overturning and sliding has to be checked for construction as well as permanent condition

Pedestrains,temperature and wind load can cause large changes in the B.M close to the deck near abutments and accordingly fatigue and crackwidths are to be considered

SUBSTRUCTURES :

Supports:

• Cables are pre-tensioned by anchoring into support structure, hence this region is highly stressed.

• Performance may be improved by construction of: i) flexible saddle

ii) parabolic haunch iii) intermediate arch support

Stress Ribbon Bridge

Rock base is a prerequisite In some cases where the soil conditions do

not permit use of anchors ,piles can also be used

Combination of drilled shafts and anchors can also be used where horizontal deformation is significant

Battered micropiling is another alternative which can resist load from ribbon because of its compression and tension capacity

IDEAL GROUND CONITIONS :

Contrary to simple suspension bridge ,where cables carry loads ,in stress ribbon, by tensioning the cables and the deck between abutments ,the deck shares axial tension forces .

Unlike the simple suspension bridge the ribbon is stressed in compression ,which adds stiffness to the structure

Unlike suspension bridge it does not tend to sway and bounce

COMPARISION WITH A SIMPLE SUSPENSION BRIDGE :

ABUTMENTS ARE BUILT

BEARING CABLES HUNG BETWEEN THEM

PRECAST PLANKS SLID ALONG THE CABLES

CONCRETE PORED BETWEEN PLANK JOINTS ALLOWED TO HARDEN

BRIDGE READY FOR PUBLIC USE

CONSTRUCTION PROCEDURE

Deck: Stress Ribbon Bridge :

Lake Hodges Bridge, USA

Deck:

• Might be pre-fabricated or cast in-situ

• Stressed only by normal forces hence might be reduced by waffles

• Integrated with end and intermediate supporting construction so as to work as a composite structure.

Stress Ribbon Bridge

STRESS –RIBBON BRIDGE

STIFFENED BY ARCH

STRESS-RIBBON BRIDGE

SUSPENDED ON ARCH

The classical stress-ribbon type bridges were insufficient to resist very large horizontal forces at the abutments

It was designed by prof.Strasky Due to dead load ,the horizontal forces both in arch and

in the stress ribbon have same magnitude ,but they act in opposite direction

After post-tensioning the stress-ribbon and arch behave as one structure

Therefore foundation is loaded by only vertical reactions

STRESS-RIBBON BRIDGE STIFFENED BY ARCH :

External bearing cables stiffen the structure both in the vertical and horizontal directions

Horizontal movements caused by live load are eliminated by stoppers which allow only horizontal movement due to temperature changes and creep and shrinkage of concrete

STRESS-RIBBON BRIDGE SUSPENDED ON ARCH

The main advantage is that they can be erected independently from the existing terrain ,hence have minimum environment impact

Economical, aesthetic and ensure visually pleasing end result.

Can be erected without false work or shoring

No bearings or expansion joints used

ADVANTAGES

These bridges are versatile and adaptable structures

They are sustainable structures since not much material is used in the deck

Structurally efficient ,aesthetic, yet cost effective

Easy to assemble and quick to erect Deck slab made of precast concrete so

require no scaffolding

CONCLUSION

THANK YOU