FRP composites in Civil Infrastructure – Series 1

Fibre reinforced polymer (FRP) composites are an emerging new technologies find its way to replace steel and other corrosive material in civil infrastructure as FRP material demonstrates excellent durability compared to steel. The main intension of this article is to disseminate the knowledge in this area. The article will have three main series and several sub sections as it will be discussed in wide array of occasions where FRP is widely used.

Courtesy: Shinsung Basic Materials, Korea

The problem

Concrete considered one of the most durable material man to invent. However, the corrosion of steel in reinforced concrete often raise concerns over the durability of concrete structures. Structures exposed to corrosive conditions such as roads and highways, coastal structures, underground structural elements and water retaining structures requires frequent repair and maintenance due to corrosion damages.

Repair and maintenance of steel reinforced concrete structures is an additional expense which results in huge burden on the authorities which maintain those structures. In the United Kingdom, repair cost due of concrete infrastructure exceeds £500 million/year (Broomfield et al. 2002) and much higher in the United States and Canada (Bedard 1992). Even sometimes the repair and maintenance costs have exceeded the original cost of the bridges. Due to these concerns, there were considerations either to protect steel from corrosion or replace it with non corrosive materials.

Better quality concrete, steel protection methods such as epoxy coating, galvanizing have been practiced in the last decades in an effort to prevent the corrosion in steel reinforced structures (Clarke 1999). However, the efficiency of these methods raised concerns when corrosion was detected on epoxy coated steel reinforcement (Keesler & Powers 1988).

Rock-Fiber Rebar Gets First Big Test – ENR.com

Researchers in Northern Ireland report promising results from a demonstration project that used rods made with basalt fibers to reinforce a 22-meter-long concrete-deck section of a $1.5-million replacement bridge in County Fermanagh. The mineral material, which resists corrosion and has twice the tensile strength of steel, is not yet accredited for structural use in the U.K.

Photo: Courtesy of MagmaTech

Northern Ireland Road Service worked with researchers to test basalt-fiber rebar.

In addition to testing the basalt-fiber-reinforced polymer (BFRP), the project is a demonstration of compressive membrane analysis in deck design, says Susan Taylor, a senior structural-engineering lecturer at Queen’s University, Belfast, which secured a $160,000 grant from the U.K. Dept. for Transport for the demonstration. The method takes into account the arching behavior within restrained slabs, which enhances load capacity beyond that predicted using conventional flexural theory, she says.

Taylor champions the deck design method to enhance sustainability by improving concrete durability and making more efficient use of materials. Although compressive membrane design analysis was accepted by U.K. regulators eight years ago, “a lot of consultants are only using [it] for assessments of [existing bridges] while using conventional methods for new designs,” Taylor says.

For the demo, Taylor directed the Thompson’s Bridge structural engineer, AECOM Ltd., Glasgow, to design the middle two-thirds of the bridge span using compressive membrane action and self-compacting concrete, obviating the need for vibrators. The section was built with basalt rebar, while the 5-m-long ends of the deck were conventionally reinforced and designed.

The 10.9-m-wide deck was cast in place over four longitudinal, precast-concrete, flat-bottomed U-shaped beams. The 16-centimeter-thick deck typically spans 1.6 m between the beams.

After the bridge’s structural completion in August, Taylor’s team tested the deck by applying a simulated wheel load up to 40 tonnes—nearly three times the European Union’s maximum vehicle axle load, Taylor says.

Subcontractor Sengenia Ltd., Belfast, monitored the test by fitting strain gauges to sets of both the BFRP and the steel rebar, using fiber Bragg grating written on optical cables. The firm’s founder, Simon Grattan, claims the optical cable technique is better than using more cumbersome metal wires still common in the U.K.

Taylor says the tests recorded maximum strains of the BFRP rebar as “very, very low,” at 11.7% of the maximum capacity. The BFRP-reinforced deck deflected around 0.8 millimeters, which was less than half the deflection recorded on the equivalent steel-reinforced section. But because of other variables in the concrete, Taylor says she is reluctant to claim that BFRP reinforced sections demonstrated much better performance than the steel samples, beyond saying the BFRP section of deck “was behaving well under service loads and was slightly better” than steel.

Members of the team, working for the project’s design-build contractor McLaughlin & Harvey Ltd., Mallusk, Northern Ireland, say they saw little difference between detailing the areas with either BFRP or steel bars. One drawback, however, is the inability to bend BFRP bars on-site. “It’s got to be ordered in … shape,” says one designer.

The material is sourced from a manufacturer in Cheboksary, Chuvash Republic, Russia, which constrained the researchers’ ability to make last-minute detailing changes.

BFRP has twice the tensile strength—at about 1,200 megapascals—of steel, while weighing 75% less and is more resistant to the alkali concrete environment than glass fiber, says Ben Williams, managing director of the start-up supplier MagmaTech Ltd., London, which supplied the “RockBar” reinforcing rods for the project. He says the cost of BFRP rebar is similar to that of glass fiber, 30% to 40% cheaper than stainless steel and roughly three times more expensive than common steel rebar.

In construction, wall tiles fabricated with the material have been used as an alternative to stainless steel when low thermal conductivity is required, but Williams says the Thompson’s Bridge project is the first significant structural use of BFRP rebar. He calls the project “a great step forward.”

Williams is targeting high-corrosion-risk projects in which repairs would be difficult. In these conditions, BFRP would be less costly than stainless steel and, he claims, perform better than a glass-fiber product.

BFRP production is “very simple,” Williams adds. Unlike glass, he says, “Basalt is mined, melted and extruded into fibers with no purification steps or additives.”

The bridge’s owner, the Northern Ireland Road Service, says it’s interested in BFRP’s potential to eliminate bridge corrosion; at a more mundane level, they say, it’s pleasing to get most of their bridge’s rebar paid for by the Queens researchers.

Using BFRP rebar in U.S. highways “will take some time,” believes Mohsen Issa, professor of Structural and Materials Engineering at the University of Illinois at Chicago. His department has tested beams reinforced with the material and he is talking with various agencies about its possible use. “We are working with the industry to try using BFRP in a pilot project like a concrete slab or a bridge deck,” he adds. “The industry is very excited about the BFRP rebar due to its strength and durability properties.”

by: Reter Reina Follow up

Researchers in Northern Ireland report promising results from a demonstration project that used rods made with basalt fibers to reinforce a 22-meter-long concrete-deck section of a $1.5-million replacement bridge in County Fermanagh. The mineral material, which resists corrosion and has twice the tensile strength of steel, is not yet accredited for structural use in the U.K.

Slide Show

Photo: Courtesy of MagmaTech

Northern Ireland Road Service worked with researchers to test basalt-fiber rebar.

Related Links:

Beating Corrosion With Basalt Rebar

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In addition to testing the basalt-fiber-reinforced polymer (BFRP), the project is a demonstration of compressive membrane analysis in deck design, says Susan Taylor, a senior structural-engineering lecturer at Queen’s University, Belfast, which secured a $160,000 grant from the U.K. Dept. for Transport for the demonstration. The method takes into account the arching behavior within restrained slabs, which enhances load capacity beyond that predicted using conventional flexural theory, she says.

Taylor champions the deck design method to enhance sustainability by improving concrete durability and making more efficient use of materials. Although compressive membrane design analysis was accepted by U.K. regulators eight years ago, “a lot of consultants are only using [it] for assessments of [existing bridges] while using conventional methods for new designs,” Taylor says.

For the demo, Taylor directed the Thompson’s Bridge structural engineer, AECOM Ltd., Glasgow, to design the middle two-thirds of the bridge span using compressive membrane action and self-compacting concrete, obviating the need for vibrators. The section was built with basalt rebar, while the 5-m-long ends of the deck were conventionally reinforced and designed.

The 10.9-m-wide deck was cast in place over four longitudinal, precast-concrete, flat-bottomed U-shaped beams. The 16-centimeter-thick deck typically spans 1.6 m between the beams.

After the bridge’s structural completion in August, Taylor’s team tested the deck by applying a simulated wheel load up to 40 tonnes—nearly three times the European Union’s maximum vehicle axle load, Taylor says.

Subcontractor Sengenia Ltd., Belfast, monitored the test by fitting strain gauges to sets of both the BFRP and the steel rebar, using fiber Bragg grating written on optical cables. The firm’s founder, Simon Grattan, claims the optical cable technique is better than using more cumbersome metal wires still common in the U.K.

Taylor says the tests recorded maximum strains of the BFRP rebar as “very, very low,” at 11.7% of the maximum capacity. The BFRP-reinforced deck deflected around 0.8 millimeters, which was less than half the deflection recorded on the equivalent steel-reinforced section. But because of other variables in the concrete, Taylor says she is reluctant to claim that BFRP reinforced sections demonstrated much better performance than the steel samples, beyond saying the BFRP section of deck “was behaving well under service loads and was slightly better” than steel.

Members of the team, working for the project’s design-build contractor McLaughlin & Harvey Ltd., Mallusk, Northern Ireland, say they saw little difference between detailing the areas with either BFRP or steel bars. One drawback, however, is the inability to bend BFRP bars on-site. “It’s got to be ordered in … shape,” says one designer.

The material is sourced from a manufacturer in Cheboksary, Chuvash Republic, Russia, which constrained the researchers’ ability to make last-minute detailing changes.

BFRP has twice the tensile strength—at about 1,200 megapascals—of steel, while weighing 75% less and is more resistant to the alkali concrete environment than glass fiber, says Ben Williams, managing director of the start-up supplier MagmaTech Ltd., London, which supplied the “RockBar” reinforcing rods for the project. He says the cost of BFRP rebar is similar to that of glass fiber, 30% to 40% cheaper than stainless steel and roughly three times more expensive than common steel rebar.

In construction, wall tiles fabricated with the material have been used as an alternative to stainless steel when low thermal conductivity is required, but Williams says the Thompson’s Bridge project is the first significant structural use of BFRP rebar. He calls the project “a great step forward.”

Williams is targeting high-corrosion-risk projects in which repairs would be difficult. In these conditions, BFRP would be less costly than stainless steel and, he claims, perform better than a glass-fiber product.

BFRP production is “very simple,” Williams adds. Unlike glass, he says, “Basalt is mined, melted and extruded into fibers with no purification steps or additives.”

The bridge’s owner, the Northern Ireland Road Service, says it’s interested in BFRP’s potential to eliminate bridge corrosion; at a more mundane level, they say, it’s pleasing to get most of their bridge’s rebar paid for by the Queens researchers.

Using BFRP rebar in U.S. highways “will take some time,” believes Mohsen Issa, professor of Structural and Materials Engineering at the University of Illinois at Chicago. His department has tested beams reinforced with the material and he is talking with various agencies about its possible use. “We are working with the industry to try using BFRP in a pilot project like a concrete slab or a bridge deck,” he adds. “The industry is very excited about the BFRP rebar due to its strength and durability properties.”

Types of Concrete Bridges – cbdg.org.uk

ARCH BRIDGE

Arch bridges derive their strength from the fact that vertical loads on the arch generate compressive forces in the arch ring, which is constructed of materials well able to withstand these forces.

The compressive forces in the arch ring result in inclined thrusts at the abutments, and it is essential that arch abutments are well founded or buttressed to resist the vertical and horizontal components of these thrusts. If the supports spread apart the arch falls down. The Romans knew all about this.

Traditionally, arch bridges were constructed of stone, brick or mass concrete since these materials are very strong in compression and the arch could be configured so that tensile stresses did not develop.

Modern concrete arch bridges utilise prestressing or reinforcing to resist the tensile stresses which can develop in slender arch rings.

The shape attracted the attention of many of the early pioneers of concrete construction. In 1930, Freyssinet was responsible for a spectacular arched bridge at Plougastel in France and three years later, Swiss engineer, Robert Maillart created the famously elegant Schwandbach bridge in which slender cross-walls tie the arch to the horizontally curved roadway.

REINFORCED SLAB BRIDGE

For short spans, a solid reinforced concrete slab, generally cast in-situ rather than precast, is the simplest design. It is also cost-effective, since the flat, level soffit means that falsework and formwork are also simple. Reinforcement, too, is uncomplicated. With larger spans, the reinforced slab has to be thicker to carry the extra stresses under load. This extra weight of the slab itself then becomes a problem, which can be solved in one of two ways. The first is to use prestressing techniques and the second is to reduce the deadweight of the slab by including ‘voids’, often expanded polystyrene cylinders. Up to about 25m span, such voided slabs are more economical than prestressed slabs.

BEAM AND SLAB BRIDGES

Beam and slab bridges are probably the most common form of concrete bridge in the UK today, thanks to the success of standard precast prestressed concrete beams developed originally by the Prestressed Concrete Development Group (Cement & Concrete Association) supplemented later by alternative designs by others, culminating in the Y-beam introduced by the Prestressed Concrete Association in the late 1980s.

They have the virtue of simplicity, economy, wide availability of the standard sections, and speed of erection.

The precast beams are placed on the supporting piers or abutments, usually on rubber bearings which are maintenance free. An in-situ reinforced concrete deck slab is then cast on permanent shuttering which spans between the beams.

The precast beams can be joined together at the supports to form continuous beams which are structurally more efficient. However, this is not normally done because the costs involved are not justified by the increased efficiency.

Simply supported concrete beams and slab bridges are now giving way to integral bridges which offer the advantages of less cost and lower maintenance due to the elimination of expansion joints and bearings.

BOX GIRDER BRIDGE

For spans greater than around 45 metres, prestressed concrete box girders are the most common method of concrete bridge construction. The main spans are hollow and the shape of the ‘box’ will vary from bridge to bridge and along the span, being deeper in cross-section at the abutments and piers and shallower at midspan.

Techniques of construction vary according to the actual design and situation of the bridge, there being three main types:

i.e.  incrementally launched
span-by-span
balanced cantilever

Incrementally launched

As the name suggests, the incrementally launched technique creates the bridge section by section, pushing the structure outwards from the abutment towards the pier. The practical limit on span for the technique is around 75m.

Span-by-span

The span-by-span method is used for multi-span viaducts, where the individual span can be up to 60m.

These bridges are usually constructed in-situ with the falsework moved forward span by span, but can be built of precast sections, put together as single spans and dropped into place, span by span.

Balanced cantilever

In the early 1950s, the German engineer Ulrich Finsterwalder developed a way of erecting prestressed concrete cantilevers segment by segment with each additional unit being prestressed to those already in position. This avoids the need for falsework and the system has since been developed.

Whether created in-situ or using precast segments, the balanced cantilever is one of the most dramatic ways of building a bridge. Work starts with the construction of the abutments and piers. Then, from each pier, the bridge is constructed in both directions simultaneously. In this way, each pier remains stable – hence ‘balanced’ – until finally the individual structural elements meet and are connected together. In every case, the segments are progressively tied back to the piers by means of prestressing tendons or bars threaded through each unit.

INTEGRAL BRIDGES

One of the difficulties in designing any structure is deciding where to put the joints. These are necessary to allow movement as the structure expands under the heat of the summer sun and contracts during the cold of winter.

Expansion joints in bridges are notoriously prone to leakage. Water laden with road salts can then reach the tops of the piers and the abutments, and this can result in corrosion of all reinforcement. The expansive effects of rust can split concrete apart.

In addition, expansion joints and bearings are an additional cost so more and more bridges are being built without either. Such structures, called ‘integral bridges’, can be constructed with all types of concrete deck. They are constructed with their decks connected directly to the supporting piers and abutments and with no provision in the form of bearings or expansion joints for thermal movement. Thermal movement of the deck is accommodated by flexure of the supporting piers and horizontal movements of the abutments, with elastic compression of the surrounding soil.

Already used for lengths up to 60m, the integral bridge is becoming increasingly popular as engineers and designers find other ways of dealing with thermal movement.

CABLE-STAYED BRIDGES

For really large spans, one solution is the cable-stayed bridge. As typified by the Dee Crossing where all elements are concrete, the design consists of supporting towers carrying cables which support the bridge from both sides of the tower.

Most cable-stayed bridges are built using a form of cantilever construction which can be either in-situ or precast.

SUSPENSION BRIDGES

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Concrete plays an important part in the construction of a suspension bridge. There will be massive foundations, usually embedded in the ground, that support the weight and cable anchorages. There will also be the abutments, again probably in mass concrete, providing the vital strength and ability to resist the enormous forces, and in addition, the slender superstructures carrying the upper ends of the supporting cables are also generally made from reinforced concrete.

Source : http://www.cbdg.org.uk/bridge_types.html