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Challenges Made For Construction Of Bridge In Hilly Areas”

INTRODUCTION

A bridge is a structure build to span a valley, road, river, body of water, or any other physical obstacle.

The first bridges were made by nature itself-as simple as a log fallen across a stream or stones in the river.

The first bridges made by humans were probably spans of cut wooden logs or planks and eventually stones, using a simple support and cross beam arrangement.

Hilly region pose unique problem for bridge construction. In restricted hilly area itself climatic conditions, geological features and hydrological parameters vary considerably.

Keeping in view the bridge site and various constraints , type of bridge and method of construction are to selected carefully for safe, economical and successful completion of bridge construction.

BRIDGE CONSTRUCTION OVERVIEW

Why the particular site was selected for the bridge.

Why particular type of bridge is proposed.

Site data.

Proposal for preparation drawing.

Soil strata in the form of bore log.

Model study detail if already done for scour assessment.

Salient features of the bridge and quantities of each items involved.

Upto date approved structural drawings.

CHALLENGES IN HILLY AREA BRIDGES CONSTRUCTION

Construction of bridge across the gorges;

Construction of bridge on rivers with boundary beds;

Construction of bridges in extreme temperature zones;

Construction of bridges on sharp turn on highways;

Landslides or debris flow.

BRIDGE FOUNDATION AND SUBSTRUCTURE

Foundation construction for any large bridge takes time.

Problems encountered during construction of foundation depend upon type of foundation, soil strata encountered, equipment/plant deployed and logistic problems.

In case of well foundation, the various types of soils are encountered and it becomes difficult to give any clear time shedule about the sinking of wells unless the soil details are very clear and the anticipated profile matched with actual encountered.

In case of bouldary and clayey soil the rate of sinking shedule is likely to be slow when compared with the sandy soil.

Also there may be requirement of pneumatic sinking technique subsequent to open grabbing due to difficulties in siking of well.

SUPER STRUCTURE

For particular site there are numerous structural arrangements possible.

Final proposal be made based on the grater examination of site condition may be technical, aesthetic and construction methodology.

Special care need to be taken in case of deep gorge where there is sizable difference between soffit level and bed level. This may pose difficulties for staging and shuttering.

Proposal recommended for site should be well read in advance.

The quantities of each items involved and execution method are listed. Basically method statement should be kept ready for overall execution including job estimate.

MANAGEMENT OF CONSTRUCTION ACTIVITIES

Management of bridge construction demands that construction manager to re-orient all the resources in such a way that the projects are completed without any time/cost overrun.

Output of the work depend upon how best the activities are managed which will vary from site to site based on many factors.

Based on the experience, various aspects are identified for efficient construction management.

Latest software management tool can be used for this in case of a major bridge project.

PLANT MANAGEMENT Requirement of equipment/plant be assessed systematically.

Time available for work execution ;

Details of equipment and also minimum requirement as per job position;

Rated capacity of equipment /plant;

Assessed capacity ;

Scheduled of maintenance

Inventory of spare parts required;

Repaired cover to equipment/plant.

MATERIAL MANAGEMENT

Material management is a parallel activity along with start of the project.

This cover procurement of camp material, office equipment, major purchase items, such as aggregates, sand, cement, steel, structural steel, shuttering consumables, electrical fittings.

Forecasting of quantities and cost of various items on monthly basis must be done at least 3-6 months in advance which should be regularly reviewed.

 

QUALITY MANAGEMENT Quality of work at site is most important activity and

manager should always grapple to improve the same.

Training to staff should be provided to update the quality control measure and it should become part of the work culture.

At site laboratory be established to check the quality of concrete.

Tests are analyzed at site based on the size of job.

Latest guidelines issued by IRC and MORT&H are followed for systematic quality assurance.

FINANCE MANAGEMENT

No project and implementation or project and implementation management can be meaningful without this.

In case government work the manager should gate his budget fixed on monthly basis, on the basis of work done, on minimum to be fed site, on the decision of higher authorities.

Key measure financial planning lies in taking all above action and taking suitable measures at appropriate time to ensure that individual inputs are achieved to the maximum and capital investment kept at lowest level.

SAFETY MANAGEMENT

Safety of employees at site should be observed very seriously.

All the workers are given briefing about the safety requirements based on the site hazards.

when the simply supported structure is attempted on deep gorge, suitable arrangement should be made to avoid any accident at site during insitu casting of superstructure.

In case of foundation if the deep excavation is involved, the quality of surrounded soil be kept in view.

There are incidents where few workers got buried in deep excavation due to sudden slide, this should be taken care.

TYPES OF HILLY AREA BRIDGES

BEAM BRIDGESTRUSS BRIDGECANTILEVER BRIDGEARCH BRIDGE;TIDE ARCH BRIDGE;SUSPENSION BRIDGE;CABLE-STAYED BRIDGE

BEAM BRIDGE

Beam bridges are the simplest structural forms for bridge spans supported by an abutment or pier at each end.

No moments are transferred throughout the support, hence their structural type is known as simply supported.

The simplest beam bridge could be a stone slab or a wood plank laid across a stream.

Bridges design for modes infrastructure will usually be constructed of steel or reinforced concrete, or a combination of both.

BEAM BRIDGE

TRUSS BRIDGE A truss bridge is a bridge whose load-bearing

superstructure is composed of a truss , a structure of connected elements forming triangular units.

The connected elements may be stressed for tension, compression or sometimes both in response to dynamic loads.

Truss bridges are one of the oldest types of mordern bridges.

A truss bridge is economical to construct because it uses some materials efficiently.

 

TRUSS BRIDGE COMPONENTS

CANTILEVER BRIDGE

A cantilever bridge is a bridge built using cantilevers, structures that project horizontally into space, supported only one end.

For small footbridges, the cantilevers may be simple beam; however, large cantilever bridges designed to handle road or rail traffic use trusses built for structural steel, or box girders built from pre-stressed concrete.

A simple cantilever span is formed by two cantilever arms extending from opposite sides of an obstacle nto be crossed, meeting at the centre.

 

Cantilever bridge components

HOWRAH BRIDGE

ARCH BRIDGE

An arch bridge is a bridge with abutments at each end shaped as a curved arch.

Arch bridges work by transferring the weight of the bridge and its load partially into a horizontal thrust restrained by the abutments at either side.

A long bridge may be made from a series of arches, although other more economical structures are typically used today.

ARCH BRIDGE

TIDE ARCH BRIDGE

A tied-arch bridge is an arch bridge in which the outward-directed horizontal force of the arch, or top chord, are borne as tension by the bottom chord, rather than by the ground or bridge foundations.

Thrusts downward on such a bridge’s deck are translated, as tensions, by vertical ties of the deck to the curved top chord , tending to flatten it and thereby to push its tips outward into the abutment, like other arch bridges.

However, in a tied-arch or bowstring bridge, these movements are restrained not by the abutments but the bottom chord, which ties these tips together, taking the thrust as tension, rather like the string of a bow that is being flattened. Therefore, the design is often called a bowstring -arch or bowstring-dirder bridge.

TIED ARCH BRIDGES

SUSPENSION BRIDGE

A suspension bridge is a type of bridge in which the deck (the load-bearing portion) is hung below suspension cables on vertical suspenders.

The bridges without vertical suspenders have a long history in many mountainous part of the world.

this type of the bridges has cables suspended between towers, plus vertical suspenders cables that carry the weight of the deck below, upon which traffic crosses.

This arrangement allows the deck to be leveled or to arc upward for additional clearance.

SUSPENSION BRIDGE

CABLE-STAYED BRIDGE

A Cable-stayed bridge has one or more towers (or pylons), from which cables support the bridge decks.

There are two major classes of Cable-stayed bridges: harp and fan.

In the harp or a parallel design, the cable are nearly parallel so that the height of their attachment to the tower is proportional to the distance from the tower to their mounting on the deck.

In the fan design, the cables all connect to or pass over the top of the towers. The fan design is structurally superior with minimum moment applied to the towers but for practical reasons the modified fan is preferred as specially where many cables are necessary

Cable-stayed bridge is optimal for span longer than cantilever bridges, and shorter than suspension bridges.

CABLE-STAYED BRIDGE OVER COOPER RIVER

CONCLUSION

All bridges held generally the same amount of weight. The arch bridge held a little more than the other bridges. They were in the1400-1500 gram range. The other bridges were in the1000-1200 gram range.

The bridges would not stand up on their own, so a support at each end had to be constructed, balancing the weights on the bridges required patience. Clamps were used to hold the bridges during gluing.

The bridges supported different amount of weights because each type has different construction. The arch bridges supported the most weight because of the great natural strength of the arch. The pier bridges supported the least weight because the supporting pier broke during construction.

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you…….