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DIAPHRAGM WALLS, CUT-OFF WALLS AND SLURRY WALLS

Diaphragm Walls

Diaphragm walls are concrete or reinforced concrete wallsconstructed in slurry-supported, open trenches below existingground. Concrete is placed using the Tremie installation method orby installing pre-cast concrete panels (known as a pre-castdiaphragm wall).

1 : Diaphragm wall excavation

2: Excavation pit retained by tiedback diaphragm wall and partiallybraced by cast-in-place buildingfloor slab.

3: Excavation pit retained bydiaphragm wall and bracing

Diaphragm walls can be constructed to depths of100 meters and to widths of 0.45 to 1.50 meters.Diaphragm wall construction methods are relatively quiet and causelittle or no vibration. Therefore, they are especially suitable for civilengineering projects in densely-populated inner city areas.Due to their ability to keep deformation low and provide low waterpermeability, diaphragm walls are also used to retain excavation pits in the direct vicinity of existing structures.

If there is a deep excavation pit at the edge of an existing structureand groundwater is present, diaphragm walls are often used as themost technically and economically favorable option. They can beused for temporary support or as load-bearing elements of the final building. Diaphragm walls can be combined with any anchor and bracing system.Diaphragm wall panels are also used in deep, load-bearing soillayers as foundation elements to carry concentrated structural loadin the same way as large drilled piles do. These foundation elements are known as “Barrettes”.

1: Diaphragm wall excavation usinghydraulic cutter disk and grabexcavation

2: Guide wal

3: Diaphragm wall chisel

If diaphragm are socketed into impermeable soil layers of sufficientthickness or if they are combined with seal slabs (grout injection ortremie concrete slabs) almost waterproof excavation pits are created.

After reducing the initial groundwater level within theexcavation, only small amounts of residual water will penetrate.

Diaphragm Wall construction using grab excavation and removable Stop-End Pipes

• Preliminary excavation to 1.0 – 1.5 meters below groundelevation to install guide walls

• Prior to diaphragm wall excavation, cast-in-place or pre-cast concrete guide walls are placed.

These braced guide wallsstabilize the soil in the upper diaphragm level and provide a stableguide-way for the grab. In addition, they also support thediaphragm wall reinforcement and provide sufficient bearing forthe hydraulic jacking system to remove the Stop-End Pipes.

Thespace between both guide walls serves as a storage space for thestabilizing fluid.

• Lamella excavation Using hydraulic grabs with clam shell sizesof 2.8, 3.4 or 4.2 meters, single diaphragm panels can beexcavated down to tip elevation. To avoid collapsing ground,trixotropic stabilizing fluids (Bentonite slurry = clay/water slurry)are pumped into the excavated panel. Depending on groundcondition and geotechnical design, several single panels can becombined to one large lamella. Hard soil, rock or obstructions canbe removed using chisels in addition.

1: Diaphragm wall reinforcing cagewith block-out

2: Stop-end pipe with hydraulic pipeextractors

3: Flat steel joint element

• Stop End Pipe Installation. To separate the single concretingphases, stop-end pipes are installed at both panel fronts. Thesehave the same diameter as the panel’s wall thickness and areremoved after initial concrete setting. The remaining semicircularjoint provides a very good interlock between the individualconcrete panels.

• Slurry Refreshing.

• Placing of Rebar Cage

• Concrete Placing by Tremie Method. Simultaneously withplacing concrete, slurry is pumped from the panel to be refreshedand re-used in the next panel excavation. Since the slurry isreplaced by concrete, this method is called “Double-PhaseMethod”.

• Removal of Stop -End Pipes after concrete setting usinghydraulic pipe extractors.Diaphragm Wall Joint Design• There are three (3) types of joint design used for diaphragm wallsconstructed by the grab excavation method• Steel stop-end pipes, which are removed before the concrete hasset completely (as mentioned before). Concrete seeped aroundthe stop-end pipes can be safely removed by the use of chisels.

• Pre-cast reinforced concrete panels, which remain in the panelsas permanent stop-ends (high weight, twice the number of joints).Seeping concrete can not be removed safely.• Steel joint element. This flat steel panel element contains one ortwo elastic joint tapes, which remain in the setting concrete afterthe joint element has been removed. Removal of the element canonly take place after the adjacent panel was completelyexcavated

If diaphragm walls are constructed using the hydro-cuttertechnique, stop- end pipes do not need to be installed. After theprimary panel set sufficiently, the secondary panel excavation willslightly cut into the fresh concrete to ensure a tight overlap duringthe concrete placement.

Excavation

Double rope grabs as well as grabs guided by telescoping Kellybars are commonly used for excavation in soils. Hydro-cutters canbe employed for rock as well as soft soil excavations.

They continuously cut into one panel by sucking the soil-bentonite slurryat the cutter head while replacing it with fresh bentonite at thepanel’s top.

Construction sequence

Two different construction techniques, the alternating method (orPilgrim) and the continuous method can be distinguished forexcavation. During the alternating method, only primary panels willbe placed leaving out the following secondary panels. Following thefirst primary panels, gaps will be closed by the adjacent secondarypanels. Primary and secondary panels will have different sizes dueto the use of stop end pipes.During the continuous excavation method (Endless Panel), all thepanels are excavated in one continuous process. Therefore they allhave the same size.

Cut-off Walls

1: Cut-off wall applications

2: Cut-off wall Rostock,Warnowquerung

3: Cut-off wall site set up

Cut-off walls are vertical slurry walls with very low waterpermeability to minimize the ground water flow.In contrast to the known load-bearing, impermeable retaining wallssuch as:

• Concrete secant pile walls

• Reinforced two-phase diaphragm walls

• Sheet pile wallsare cut-off walls mostly without any load-bearing function.

The following cut-off wall types can be distinguished:

• Cut-off walls constructed using diaphragm wall techniques

• Secant pile walls from concrete of slurry

• Thin slurry walls• Injection walls• Jet-Grouting walls

• Freezing walls

They can be used as:

• Cut-off walls underneath water dams with core seals in areas ofpermeable soils to socket into lower impermeable layers toprevent undercurrent

• Cut-off walls for “watertight” excavation pits outside of theload-bearing retaining structure to minimize water inflow into thepit

• Cut-off walls to enclose brown fields and contaminated areas withpenetration into lower impermeable soil layers

Cut-off walls constructed using diaphragm wall techniques

If slurry walls are intended to act as cut-off walls without any loadbearing function, a mixture of water, bentonite, cement and maybefiller can be used.This slurry remains in the excavated panel and hydrates.

It alsoremains as a plastic seal, so that the wall can follow smalldisplacements in the soil without cracking. Since the slurry remainsin the panel, this is called the Single-Phase technique. After completion of the guide wall, the excavation proceeds with:

• One long-boom excavator (max. depth of 10m)

• Or by the use of slurry wall grabs or hydro-cutters Using the single-phase technique, panel depth is limited due to therelatively short time from placing and setting of the suspension.In deeper panels, the Two-Phase technique is used to construct aslurry wall. Construction is similar to the cast in-situ diaphragm wallinstallation. After completion of the panel’s excavation, the actualsealant slurry will replace the stabilizing bentonite fluid.

This sealanthas to be placed using the slurry-displacement or tremie methodand needs to have a 0.75 to/m³ higher unit weight than the bentonite slurry to replace it.To improve permeability and contaminant resistance, combinationcut-off walls can be installed using the Single-Phase system. Sheetpiles or plastic liner sheets can be installed within abentonite-cement-slurry wall.

Cut-off walls with embedded sheet piles or structural beams beingconstructed using the single phase method can also be used as”water- tight” excavation pits.In the process the sheet piles or beams act as load transferringelements and will extend to required depth below the excavation pit.

The Cut-off wall as sealing element will only penetrate the artificialseal slab or reach down to the natural impermeable soil layer.Sheet pile or beam walls can be tied back

Thin Slurry Walls

1: Construction of a vibrated thinslurry wall, Doemitz

2: Vibro-beam

3: Thin vibro slurry wall

Thin slurry walls also can act as vertical cut-off walls to retainhorizontal groundwater flow.In contrast to cut-off walls constructed using the diaphragm walltechnique (replacing the soil by slurry sealant), thin slurry wallsdisplace the soils using a vibrated steel profile.

During the extraction process, sealants are injected into the created cavities.Drivable soils, such as sands and gravels, are required for thisinstallation method. The created slurry wall thickness depends onthe shape of the steel profile used and the soil conditions.

Thickness varies between 5 cm in sands and 20 cm in gravel. Incombination with high-pressure jet grouting, wall thickness of up to30 cm can be achieved.A continuous wall is created by overlapping single penetrationelements installed one after another by the vibrated steel profile.

A guide plate attached at the beam`s flange is running down thealready completed web of the previous panel. This ensures thecorrect overlap to the previous panel.

Source : spezialtiefbau.implenia.com

Top 10 Civil Engineering Blogs

Entering the keyword Civil Engineering Best Website into any search engine will return millions and millions of websites.

Finding a perfect site has became a herculean task these days. Same as others, Civil Engineering has also got plenty of blogs and websites in which only few are worth considering to bookmark.

Here is the list of such top resources for Civil Engineering.

1. The Engineerinig Community

The Engineerinig Community is designed for Civil Engineering Professionals, Undergraduates to update them selves with latest versions of civil engineering software, spreadsheets, E-books, software training videos & Manuals.

2. CAD Templates

CAD Templates is an exclusive forum that connects the creative community of innovative Auto cad designers, firms and organizations.

3. Managementproject.net

Managementproject.net is the best free platform to everyone want to learn management for free.

4.The Constructor

The Constructor is a valuable informational resource for civil engineers, related professionals, and students. Information, Articles and Guides are categorized into sections. Practical Guide deals with testing methods and practical applications at site.

5. ASCE (American Society of Civil Engineers)

ASCE is dedicated to the advancement of the individual civil engineer and the advancement of the science and profession of civil engineering through education. ASCE represents more than 150,000 civil engineers worldwide dedicated to designing & building infrastructure that protects the public health, safety, & welfare.

6. CEP (Civil Engineering Portal)

The biggest civil engineering portal on the internet. This site is made for educational purpose so as to help the fellow civil engineering students and to spread the knowledge about the latest civil engineering projects and software.

7. Civil Digital

Website for Civil Engineers and Students. CivilDigital.com – Civil Engineering Site civil forum, engineers forum, civil doubts, civil engineering notes, civil engineering ppts, civil engineering seminars, structural engineering ppts, interview questons, multiple choice, objective, GATE preparation, IES coaching.

8. ENR News (Engineering News Record)

ENR is a stand-by construction magazine that has been around since 1874. Always offering the latest construction industry data, analysis, news and commentary, it’s a must for all construction professionals—from contractors to suppliers to regulators.

9. C S Engineer Mag

Civil Structural Engineering is a home of the magazine and website for all your civil and structural engineering news, stories, updates and education.

10. iamcivilengineer

Iamcivilengineer is a blog for civil engineers having huge number of books, software and excel sheets to download. Frequently updates, news and views.

Asphalt paver, how it works?

A paver (paver finisher, asphalt finisher, paving machine) is a piece of construction equipment used to lay asphalt on roads, bridges, parking lots and other such places. It lays the asphalt flat and provides minor compaction before it is compacted by a roller.

All machines consist of two basic units; the tractor unit and the screed unit.

1. Tractor Unit

1.1 General:

The tractor unit provides moving power for the paver wheels or tracks and for all powered machinery on the paver. The tractor unit includes the receiving hopper, feed conveyor, flow control gates, distributing augers (or spreading screws), power plant (engine), transmissions, dual controls, operator’s seat, and wheels or tracks.

When in operation, the tractor unit power plant (engine) propels the paver, pulls the screed (leveling) unit, and provides power to the other components through transmissions. Hot mix is deposited in the hopper from where it is carried by the feed conveyor through the flow control gates to the distributing augers (spreading screws).

The augers distribute the mix evenly across the full width of the paver for uniform placement onto the roadway surface. These operations are controlled by the paver operator by means of dual controls within easy reach of the operator’s seat. Refer to Figure 1. Many pavers have hydrostatic drive systems that permit an unlimited number of speeds within the operating range and once set, will automatically maintain the desired speed.

1.2 Pneumatic Tires and Crawler Tracks:

The tractor unit may be equipped with either rubber tires or steel tracks. If the paver is equipped with pneumatic tires, tire condition and air pressure must be checked. It is particularly important for the pressure to be the same in tires on both sides of the paver.

If the paver moves on tracks (crawlers), the tracks should be checked to be certain they are snug but not tight, and the drive sprockets should be checked for excessive wear. Low tire pressure or loose crawlers can cause unnecessary movement of the paver, which when transmitted to the screed unit results in an uneven pavement surface. There should be no build-up of material on tires or on tracks. Excessively worn parts should be replaced.

1.3 Governor :

The governor on the engine must be checked to be sure there is no periodic surge in the engine RPM. If it is not working properly, there can be a lag in power when the engine is loaded. Such a lag causes temporary failure of the vibrators or tamping bars in the screed unit, resulting in a stretch of pavement that is less dense or contains slightly less material than the immediately adjacent area. After rolling, such an area shows up as a transverse ripple in the pavement. A power lag can also interfere with the smooth and consistent operation of electronic screed controls.

1.4 Hopper, Flow Gates and Augers :

The hopper, the slats on the feed conveyor, the glow gates, and the augers should be checked for excessive wear and observed to be certain they are operating properly. Necessary adjustments should be made by the contractor to ensure these components are functioning as designed and are able to deliver a smooth flow of mixture from the hopper to the roadway.

All of the machines have adjustable flow control gates, which regulate the amount of the paving mixture, which is carried on the slat feeders from the receiving hopper to the distributing augers. The slat feeders should be operating most of the time (80% to 90%) and the flow control gates should be set to keep the augers at least two-thirds covered with material. It is very important that the level of the material in front of the screed be kept fairly constant.

If the level of material is allowed to intermittently rise and fall and thereby flood or starve the screed, a rough mat, segregation of the material, and imperfections in the surface will result. Some pavers are equipped with automatic controls to maintain a uniform depth of material ahead of the screed; the adjustment of the sensing device and the flow gates should be coordinated so the slat feeders operate most of the time as stated above.

Quarter-line cracking or raveling of the mat is believed to be caused by worn interior augers, paddles, and baffles that tend to starve the screed near the center of the paver. Such equipment should be regularly inspected, and if excessively worn, should be replaced or rebuilt to original dimensions.

Feeders, gates, and augers should be checked for excessive wear. They should be observed while operating without mixture to be assured they are functioning properly and in synchronism with each other.

2. Screed Unit

2.1 General:

The screed unit strikes off the mix, controls thickness, imparts smoothness, and provides initial compaction of the mixture. A typical screed unit is comprised of the following: screed tow arms, screed plate, hearing unit, tamping bars or vibratory attachments, and controls.

The screed unit is towed by long arms attached to pivot points located forward on the tractor unit, permitting the screed to operate on a floating principle which tends to compensate or dampen irregularities in the base that affect the tractor unit. Mat thickness is adjusted manually by tilting the screed up or down around a pivot pin just above the screed.

When operating an automatic grade control the screed compensates for irregularities in the base by adjusting the screed arm at or near the pivot point of the screed arms. As the manual thickness controls are adjusted, the screed seeks a new level, up or down, as the machine moves forward, but the total effect of the change may not be realized until the machine has moved several feet. Consequently, the machine should be allowed to move 50 feet before any further adjustments are made.

The sensitivity of the controls differs between makes of machines and consequently the maximum amount of adjustment that should be made at any time differs with the machine. The amount of change in thickness produced by any given adjustment on the controls depends on the mixture being placed, so it is impossible to state that a particular adjustment will change the mat thickness by a definite amount.

Refer to Figure 1. Screeds with tamping bars or vibratory mechanisms are designed to strike off and then compact the mixture slightly as it is placed. There are two purposes to this screed action. It achieves maximum leveling of the mat surface, and it ensures minimum distortion of the mat surface, and it ensures that minimum distortion of the mat surface will occur with subsequent rolling. Because the different screed compaction systems function differently, they are discussed separately below.

2.2 Tamping Bar Type:

Tamping bar type screed compactors compact the mix, strike off the excess thickness, and tuck the material under the screed plate for leveling. The tamper bar has two faces; a beveled face on the front that compacts the material as the screed is pulled forward and a horizontal face that imparts some compaction. The horizontal face primarily strikes off excess material so the screed can ride smoothly over the mat being laid.

The adjustment that limits the range of downward travel of the tamping bar is the single most important adjustment affecting the appearance of the finished mat. At the bottom of its stroke, the horizontal face should extend 0.016″ – about the thickness of a fingernail – below the level of the screed plate. If the bar extends down too far, mix builds up on the screed face that tends to scuff the surface of the mix being placed.

In addition, the tamping bar will lift the screed lightly on each downward stroke, often causing a rippling of the mat surface. If the horizontal face of the tamping bar is adjusted too high (either by poor adjustment or due to wear of the bottom of the horizontal face), the bar does not strike off excess mix from the mat. Consequently, the screed plate begins to strike off the material, which results in surface pitting of the mix being placed as the leading edge of the screed plate drags the larger rocks forward.

Therefore, the tamper bar should always be checked before operating the paver. If necessary, the contractor should adjust it, and before it approaches knife-edge thinness it should be replaced. Refer to Figure 2. Clearance between the rear of the tamper bar and the leading edge of the screed frequently is overlooked.

Properly adjusted, there should be just enough clearance to allow free movement of the tampers – approximately 0.010″ to 0.020″. Refer to Figure 2. Screed plates will wear out first about 4″ to 6″ in from the trailing edge. The first indications will be either an indentation or an actual ripple in the surface of the screed plate. These should be checked periodically and replaced as needed.

2.3 Vibratory Type:

he operation of vibratory screeds is similar to that of tamping screeds, except that the compactive force is generated not by a tamping bar, but by either electric vibrators, rotating shafts with eccentric weights, or hydraulic motors that vibrate the screed plate.

On some pavers, both the frequency (number of vibrations per minute) and the amplitude (range of motion) of the vibrators can be adjusted. On others, the frequency remains constant and only the amplitude can be adjusted. Frequency and amplitude are set in accord with the type of pavers, speed of the paver, thickness of the mat, and the characteristics of the mixture. Once set, frequency and amplitude do not normally need adjustment until mat thickness or mixture change.

Some pavers have a “pre-strike-off unit” or a curved strike-off blade at the leading edge of the screed for use with “critical” material. It is attached to and receives vibration from the screed plate itself. It meters the amount of material going under the screed plate and can be adjusted vertically. Some other pavers have a round-nose strike-off bolted directly to the screed frames and welded to the screed plate so no adjustment can be made.

In these, the screed shield assembly is the only part of the screed that is adjustable. It can be moved up for normal material flow or down for dense mixes and thin lifts. As with tamping screeds, the screed plates will begin to wear first about 4″ to 6″ in from the trailing edge. Those with excessive wear should be replaced.

2.4 Oscillating Type:

Some pavers are equipped with both an oscillating screed and a vibrating compactor. The oscillating screed, beveled for initial compaction, operates at 600 strokes per minute, with 1/4″ transverse strokes, striking off the material for the desired depth. The vibrating compactor, mounted to the rear of the oscillating screed, supports the screed unit, imparts additional compaction, and irons out the surface of the mat.

The most critical adjustment is positioning the oscillating screed relative to the vibrating compactor. The bottom rear edges of the oscillating screed and the bottom rear edges of the vibrating compactor must be parallel. The compactor should be sloped or tilted so that a projection of the plane of the bottom will intersect at a point 0.4″ above the bottom of the screed. Minor adjustments in this differential may be necessary to obtain a uniform appearance in the mat. Refer to Figure 3.

2.5 Crown Adjustment :

All machines have provision for adjustment of crown in the screed. Usually it is desirable to provide a slight amount of crown in the screed to avoid the appearance of the mat being low in the center of the lanes.

The usual crown allowed per lane on rural-type pavements is 0.10″; however, urban cross sections may require special adjustment. Also, the amount of crown at the front edge of the screed is generally increased somewhat from that required at the back, with at least a 0.08″ increase usually being recommended.

The amount of this differential may be varied with the particular material being used, and is sometimes helpful in reducing and eliminating non-uniformity of the surface texture across the paved width. Too much crown in the leading edge of the screed will crease an open texture along the edges. Too little crown in the leading edge will create an open texture down the center of the mat.

2.6 Automatic Screed Controls:

The paver shall be equipped with an approved automatic control system, which controls longitudinal grade and transfer slope, except when paving miscellaneous areas or when the engineer finds the use of this system impractical.

The specifications require the use of such longitudinal control, unless the engineer permits its omission on the final surface course. Exceptional conditions could arise, however, where omission of the longitudinal grade control in the interest of a smoother ride can be permitted.

The engineer may discontinue use of the automatic equipment and require manual control when it appears better results may be obtained thereby. Such might be the case on work which includes sections with an urban-type cross section with non-uniform crown, or on intersections, interchanges, or similar areas.

Pavers not equipped with automatic controls may be used when the engineer determines the use of such controls is impracticable, as on small specialized projects, jobs entirely urban with variable crown, or jobs having frequent intersections or other features which are not adaptable to such use.

When the automatic grade control fails, the paver can be operated under manual control for only the remainder of the working day on which the automatic control system broke down. The automatic control systems use electronic sensors to control grade and to control transverse slope. Refer to Figure 3. The sensor gets its information from a sensing device riding on a fixed stringline, a mobile stringline, or a traveling straightedge.

The specific type of sensing device used on the initial lane of a layer or course is subject to the engineer’s approval. For paving subsequent lanes of the course or layer, the paver may use a shoe or straightedge riding on the adjacent lane as a sensor.

There are several grade sensor types and transverse slope sensor types. Some systems make screed adjustments by raising or lowering the pull arm pivot points with hydraulic rams activated through solenoids. Some make adjustments by varying the angle of hinged pull arms through electrically driven screws. Others adjust the thickness control screws with electric servomotors.

In operation, once the screed is set for the desired depth of spread, the automatic system takes over to produce a smooth mat. Transverse slope is controlled by a pendulum that acts through switches to activate the appropriate piston. The sensitivity of the controls is critical to the smoothness of the mat. The sensors should be properly nulled as provided in the manufacturer’s instructions.

2.7 Heaters :

The screed assembly is equipped with heaters to prevent the mix from sticking to the screed plate. They are used to heat the screed plate at the start of paving operations or on a cool, windy day. Heaters should never be used to heat mix being delivered to the paver. Heaters should be observed while lit to assure they produce sufficient heat.

2.8 Screed Extensions:

Extensions should be attached properly to the main section of the screed. They should be, as their name implies, an extension of the plane of the tamper bar and the screed section if uniform compaction behind the paver is to be attained.

Pavers with a vibratory main screed and vibratory side extensions should be checked by the inspector for satisfactory frequency. Use of a vibrating reed tachometer held against the main screed unit and each extension will give quick, reliable, and measurable results to be compared against manufacturer’s authentic data.

The accuracy of variable vibratory frequency control supplied on some models could also be checked with the tachometer.

2.9 Maintenance :

An important item of paver operation, often overlooked, is proper clean up of the paver at the end of the working day. While the machine is still warm from its day’s operations, the hopper, feeder augers, tamper bars, and screed plates should all be cleaned and sprayed with a light oil to assure smooth start-up the next day of use.

What is better steel or concrete?

Construction projects require many decisions. A key decision is to find the most effective option, as well as determining which process could produce ideal results.

Take a look at this breakdown. This example weighs the pros and cons of Structural Steel versus Concrete.

Costs

Structural Steel: A large majority of all steel manufactured today comes from recycled materials; A992 steel. This recycling usage makes the material much cheaper when compared to other materials. Although the price of steel can fluctuate, it typically remains a less expensive option compared to reinforced concrete.

Concrete: A large cost benefit to concrete is the fact that its price remains relatively consistent. On the other hand, concrete also requires ongoing maintenance and repairs, meaning added costs throughout its lifetime. Supply-and-demand may also impact the availability of concrete. Even though it can be poured and worked with directly onsite, the process to completion can be lengthy and could accrue higher labor costs.

Strength

Structural Steel: Structural steel is extremely strong, stiff, tough, and ductile; making it one of the leading materials used in commercial and industrial building construction.

Concrete: Concrete is a composite material consisting of cement, sand, gravel and water. It has a relatively high compressive strength, but lacks tensile strength. Concrete must be reinforced with steel rebar to increase a structure’s tensile capacity, ductility and elasticity.

Fire Resistance

Structural Steel: Steel is inherently a non-combustible material. However, when heated to extreme temperatures, it’s strength can be significantly compromised. Therefore, the IBC requires steel to be covered in additional fire resistant materials to improve safety.

Concrete: The composition of concrete makes it naturally fire resistant and in line with all International Building Codes (IBC). When concrete is used for building construction, many of the other components used in construction are not fire resistant. Professionals should adhere to all safety codes when in the building process to prevent complications within the overall structure.

Sustainability

Structural Steel: Structural steel is nearly 100% recyclable as well as 90% of all Structural Steel used today is created from recycled steel. Due to its long lifespan, steel can be used as well as adapted multiple times with little to no compromise to its structural integrity. When manufactured, fabricated and treated properly, structural steel will have a minimal impact on the environment.

Concrete: The elements within concrete are natural to our environment, reducing the harm to our world. Concrete may be crushed and used in future mixtures. This type of recycling can reduce a presence of concrete in landfills.

Versatility

Structural Steel: Steel is a flexible material that can be fabricated into a wide array of designs for endless applications. The strength-to-weight ratio of steel is much higher when compared to other affordable building materials. Steel also offers many different aesthetic options that different materials, such as concrete, cannot compete with.

Concrete: Although concrete can be molded into many different shapes, it does face some limitations when it comes to floor-to-floor construction heights and long, open spans.

Corrosion

Structural Steel: Steel may corrode when it comes into contact with water. If left without proper care, it could affect the safety and security of a structure. Professionals should care for the steel with such processes such as water-resistant seals and paint care. Fire-resistant features may be included when water-resisting seals are applied.

Concrete: With proper construction and care, reinforced concrete is water resistant and will not corrode. However, it’s important to note that the steel reinforcement inside should never be exposed. If exposed, the steel becomes compromised and can easily corrode, compromising the strength of the structure.

Reference : blog.swantonweld.com

Concrete calculator formula

What is concrete?

Concrete is one of the most commonly used building materials.

Concrete is a composite materialmade from several readily available constituents(aggregates, sand, cement, water).

Concrete is a versatile material that can easily be mixedto meet a variety of special needs and formed to virtually any shape.

What you should know Before Estimating :

Density of Cement = 1440 kg/m3
Sand Density = 1450-1500 kg/m3
Density of Aggregate = 1450-1550 kg/m3

How many KG in 1 bag of cement = 50 kg
Cement quantity in litres in 1 bag of cement = 34.7 litres
1 Bag of cement in cubic metres = 0.0347 cubic meter
How many CFT (Cubic Feet) = 1.226 CFT
Numbers of Bags in 1 cubic metre cement = 28.8 Bags

Specific gravity of cement = 3.15
Grade of cement = 33, 43, 53
Where 33, 43, 53 compressive strength of cement in N/mm2

M-20 = 1 : 1.5 : 3 = 5.5, (Cement : Sand : Aggregate)
Some of Mix is – 5.5

Where, M = Mix
20 = Characteristic Compressive strength

Consider volume of concrete = 1m3

Dry Volume of Concrete = 1 x 1.54 = 1.54 m3 (For Dry Volume Multiply By 1.54)

Calculation for Cement, Sand and Aggregate quality in 1 cubic meter concrete:

CALCULATION FOR CEMENT QUANTITY

Cement= (1/5.5) x 1.54 = 0.28 m³∴ 1 is a part of cement, 5.5 is sum of ratio
Density of Cement is 1440/m³

= 0.28 x 1440 = 403.2 kg

We know each bag of cement is 50 kg
For Numbers of Bags = 403.2/50 = 8 Bags

We Know in one bag of cement = 1.226 CFT

For Calculate in CFT (Cubic Feet) = 8 x 1.225 = 9.8 Cubic Feet

CALCULATION FOR SAND QUANTITY

Consider volume of concrete = 1m³

Dry Volume of Concrete = 1 x 1.54 = 1.54 m³

Sand= (1.5/5.5) x 1.54 = 0.42 m³∴ 1.5 is a part of Sand, 5.5 is sum of ratio

Density of Sand is 1450/m³

For KG = 0.42 x 1450 = 609 kg

As we know that 1m³ = 35.31 CFT

For Calculation in Cubic Feet = 0.42 x 35.31 = 14.83 Cubic Feet

CALCULATION FOR AGGREGATE QUANTITY

Consider volume of concrete = 1m³

Dry Volume of Concrete = 1 x 1.54 = 1.54 m³

Aggregate = (3/5.5) x 1.54 = 0.84 m³∴ 3 is a part of cement, 5.5 is sum of ratio

Density of Aggregate is 1500/m³

Calculation for KG = 0.84 x 1500 = 1260 kg

As we know that 1 m3 = 35.31 CFT

Calculation for CFT = 0.84 x 35.31 = 29.66 Cubic Feet

Concrete Quality calculation sheet download

Calculation for Cement, Sand quality in mortar for Plaster:

Area of brick wall for plaster = 3m x 3m =9m²

Plaster Thickness = 12mm (Outer-20mm, Inner 12mm)

Volume of mortar = 9m² 0.012m = 0.108m³

Ratio for Plaster Taken is = 1 : 6

Sum of ratio is = 7

Calculation for Cement Volume

Dry Volume of Mortar = 0.108 1.35 = 0.1458 m³

Cement= (1/7) = 0.0208 m³

Density of Cement is 1440/m³

= 0 1440 = 29.99 kg

We know each bag of cement is 50 kg

= (29.99/50) = 0.599 Bags

Calculation for Sand Volume

Sand = (6/7) x 0.1458 = 0.124m³

Density of Sand is 1450/m³

= 0 1450 = 181.2 kg

Now we find how many CFT (Cubic feet) Required

As we know that 1m³ = 35.31 CFT

= 0.124*35.31

= 4.37 CFT (Cubic Feet)

Plaster calculation sheet download

Reference : tutorialstipscivil.com

How intelligent scheduling is changing construction management process

Introduction to Programming BIM 4D

In recent decades, we have witnessed an intense progress of technology and computer applications. This progress is very noticeable in all aspects of the construction industry and especially in the development of BIM software. In a recent market survey with the Virtual Construction Software programming BIM 4D are reported as a huge support tool for all involved in major construction projects: construction managers, prime contractors and their customers.

In the small group of specialized software for programming BIM 4D, BEXEL Manager stands out for its unique features and capabilities directed toward management, programming (BIM 4D), cost estimation (BIM 5D) and even, facilities management (BIM 6D) of construction projects. I will try to briefly introduce its main features related to construction scheduling, which are a real game changer for future programming processes BIM construction.

Benefits of BIM 4D programming

Traditional programming process begins when planners and project managers often create construction schedules containing thousands of tasks to the level of each work item. Sort these tasks, connect and create dependencies and relationships allocation and balance a lot of resources can be extremely challenging and slow, even for more experienced managers project.

The main objective of the program is to improve 4D BIM planning processes and communication between all parties involved, allowing all participants to visually provide the entire process of building a very understandable and natural. Visual real-time simulations revolutionize complete planning processes, leveling traditional Gantt planning a 4D virtual presentation of the whole project implementation on the screen long before you start building.

The obvious and most significant benefits of BIM 4D programming process are:

Increased savings in time and cost, which can be variable, but reaching up to 500% in terms of the time required for program implementation.
Improving coordination and communication with stakeholders and the general quality of the work schedule.
Greater speed in creating offerings and optimizing budgets.
Improved site design and planning security.
Additional benefits that are not expressed through saving time and costs, but also greatly influence and augment the planning and construction process are the 4D visualizations.

Programming processes and estimation based on the model help the entire team to identify and optimize every detail designed. The efficiency and accuracy of visualization created BIM 4D allows experts project to identify and mitigate risk in the initial stages of the project, long before its construction. It also allows planning teams run different scenarios built to generate the best possible solutions while verifying their impact on costs. All schedule changes and variations made the Gantt chart are immediately updated and viewed in 3D view programming.

BIM 4D programming is much more than just visualization 4D

Today, many software solutions are advertised or used incorrectly as “4D BIM software,” however, there is a clear and obvious difference between viewing BIM 4D and 4D BIM software programming. The “4D BIM software” in general, can produce virtual construction simulation (visualization of construction process).

However, 4D BIM software programming as BEXEL Manager allows users to view the construction process and also virtually plan (create schedule) construction project. Our programming software BIM 4D allows you to create and change tasks / planned activities, change their duration and predecessor / successor tasks as well as optimize and validate the sequence of these activities, all within the software itself, while almost simultaneously, has updated the display changes in the view of 3D programming software.

The intelligent programming concept BEXEL 4D BIM Manager

On the other hand, the scheduling engine BEXEL Manager implements advanced programming algorithms, specially designed to provide the functionality to create fully automated construction schedules, simplifying manual sequencing unpleasant 4D. That’s where the real power of BEXEL Manager.

Unlike other solutions BIM 4D market, where it is necessary to create the schedule activities manually or semi-automatically depending on the elements of the BIM model available, our complete solution BIM 4D-5D-6D uses a visionary concept that allows planners and managers to easily apply their engineering experience.Its engine unique and intelligent programming allows the creation of construction methods and construction activity groups such as planners think and anticipate the processes running on your mind. Similarly, groups can be created different levels of activities of tasks based on the phases of construction, buildings, activities and anticipated elements. The next step is to create logical relationships and dependencies of these groups of activities and methodologies. In the same way most experts are accustomed to the softwares traditional programming, here you can select types of relationships between elements (for example, from end to beginning from start to start, end to end, etc.) and the duration or delay the created relationship.

A brief introduction to BIM 5D and cost management

Additionally, the next logical step in the process construction management BIM is assigned labor, equipment, material resources and costs to tasks and reach the next dimension BIM, ie 5D. Our solution allows multiple custom implement cost classification systems for different versions of costs within the same model, this is feasible in the BIM 5D Cost module named Editor (Editor Cost).

In addition, the user can manage, view and export graphs and reports cost, labor, materials and equipment. Keep track of planned and actual costs, and once construction begins, track and update progress on schedule, and analyze actual versus planned progress, hypothetical scenarios and mitigation strategies.It is very valuable that a user is enabled to handle and manage practically all dimensions BIM (3D, 4D, 5D and 6D) within an integrated software platform.

Automatic generation of 4D BIM schedules based on predefined construction methodologies

In addition, all created methodologies are saved in the software so that the user can store multiple templates to automatically create schedules using pre-defined methodologies and their variations. Once created the methodology of construction, scheduling engine CPM (Critical Path Method) with all its features, is used to find an optimal solution in terms of cost and minimum construction time and the balance of resources, providing fully detailed construction schedules in seconds, even for the most complex projects containing thousands of tasks and respective elements. All methodologies and previously saved templates can be reused for any other similar project,

Visualization and optimization of schedules BIM 4D

BIM 4D initial schedules generated automatically and can be tuned further by the user by placing a specific order of steps and activities with BIM model elements linked in temporal and spatial sense.

The amounts of resources can also be defined and modified for any task or phase subcontractor company. A user can change and improve visual sequences built using custom color schemes for items, tasks and resources. Changes can be made and additional exceptions by implementing custom calendars for tasks and subcontractors.

Management, optimization and classification of a lot of work by any standard model are extremely easy and intuitive programming using built-in filters.Planning teams can also compare visually and within the Gantt chart, different versions of the schedule and planning methodologies directly in the solution, easily switching between different versions cost for any of the scheduling options.

perfect interoperability

Finally, the duration of the entire activity of a task can be changed manually, before finalizing the schedule BIM 4D and video simulation construction. All programs created can be exported from BEXEL Manager to traditional software programming and most commonly used, such as Oracle Primavera or Microsoft Project ™ ™ or Microsoft Excel ™. All activities, durations, links and dependencies of the schedule originally created in BEXEL Manager will be retained and stored in the exported files, enabling seamless interoperability.

Mentioning interoperability, taking into account that the solution also allows the import of schedules traditionally derived from the aforementioned programming tools. As all tasks, duration, links and dependencies created originally explained also they are kept in BEXEL Manager.

Semiautomatic generation BIM 4D simulation based on imported schedule

Unlike most software BIM 4D market, where the process of linking programming tasks imported with the respective elements of the model is mostly done manually, BEXEL Manager uses an intelligent engine for semiautomatic linking elements activities using predefined rules, name / identification of activities and level of hierarchy. With comfortable views of each set of selection of model elements and cross-checking with categories, families, properties of each element, and improved search capabilities based on their properties and other criteria, bind errors are eliminated almost completely.

Once programming is imported, you can make additional adjustments, modifications and verification tasks within the Schedule Editor (Editor Programming) of BEXEL Manager. When all activities are linked, the software generates a video simulation of 4D construction, suitable for real-time review by project stakeholders. The created virtual simulation of 4D construction can also be exported as a video file.

conclusion

Once all stakeholders, mainly planners and project managers embrace the full potential and benefits of smart processes 4D programming, the entire industry will benefit and evolve, leading to a very accessible and tangible future of building BIM, where the 3D parametric design, construction simulations in real time and exchange of information are part of impeccable business every day.
By: Mileta Pejovic, BEXEL Consulting

By: Mileta Pejovic, BEXEL Consulting

Source : www.bimcommunity.com

WHAT YOU MUST KNOW BEFORE BUYING A 3D LASER SCANNER

In emergent tech sectors it’s common to find start-up companies which are not in command of the core skills required to do their work.

That’s certainly true in the scanning sector.

Like many new industries the sector infrastructure barely exists and for customers, finding a credible service provider can be challenging.

New sectors are like Wild West towns in the 1870s – there may or may not be a sheriff, a marshal, or a judge, and they may or may not have a grip on local law enforcement; they may or may not be well-versed in the law and they’re operating a long way from established civil society.

For customers, it can be a bit of nightmare, so here are a few of the things to look out for.

1. Tech manufacturers need to sell their tech and software, and their key messages often emphasise ease of use and application. Most tech-competent people can get up and running at an extremely basic level, but not with the performance requirements of a company offering professional services for a fee.

It’s only easy to use if you already have high-level intuitive tech skills (we have in-house tech staff who have developed our own training and operational hubs and can do everything, including adapting software and writing code)!

2. There are no generic, industry-wide, approved training courses. Manufacturers (Leica, Z+F, Faro etc) operate differently, manufacture different types of equipment, generating different outputs. Inexperienced companies get confused by this and overwhelmed by the need to learn different systems.

3. People are learning scanning in all sorts of ways – from YouTube and other online sources, and by trial and error (we train scanning operators and those doing post-production in-house, and we’re developing clear training protocols).

4. There’s a divide in the industry, between tech-led firms that have little understanding of BIM / FM / construction / design and build / project management etc; and firms led by people who have all these skills, but whose tech skills are deficient (we have employees with extensive skills and experience in both areas).

5. The entry level costs are peanuts by the standards of many industries; but for the individual sole-trader start-up entrepreneurs who so often pioneer new markets, they’re horrendous! No qualifications are required and most customers have little experience of the tech and haven’t yet acquired the skills to differentiate between a credible and non-credible offer.

Capital apart, the barriers to entry are, therefore, low, and many of the bottom-feeders are people with low-level business skills. (We have a successful, profitable, 17-year old company with great credit references and access to capital).

6. If you’re an individual sole-trader entrepreneurbuying all the equipment and software you need to run a scanning company, you’ll need a fair number of customers – very quickly – to pay-back your start-up costs, so you need to have the skills to grow a business to scale fast.

Why fast? Because the tech is developing so fast that within months / a year or so you’ll need to invest heavily again, to keep pace – and you can’t do that if you haven’t paid-down your initial investment or you can’t raise the capital (we were doing scanning projects across France, Germany and UK within weeks of starting our own operation; we have access to capital, we have a healthy income stream, and we invested in our second generation of technology before even launching a dedicated scanning company).

7. New entrants sometimes fail to realise that one day of scanning could require multiple days of post-production in order to produce something that is useable by most clients.

If you don’t do that, you’ll give the client an output which is clunky, data-heavy, difficult to use and awkward. They won’t get the most out of it, they won’t use it, they’ll consider the money wasted, and they won’t come back for a second bite (we have skilled in-house staff who can process scanned data quickly and make it very easy for customers to use).

8. The software that ‘comes in the box’ with a scanner isn’t sufficient for a professional operation. You need to apply other software, and probably adapt or write software for your specific requirements.

Writing code is simply beyond many of the people who go in to the business (Xmo Strata has always been an IT-literate company and we have introduced numerous IT-led customer solutions; writing code is second nature to our IT staff).

9. Scanning is essentially a professional services operation. Some of the companies in the field simply don’t have the customer-facing communications skills required; their founders have come out of corporates who are used to being on the ‘client’ side of the table and the cultural shift is beyond them (we have run a professional Business-To-Business service company for 17 years).

10. The initial cost of a basic scanner and everything you need to set-up is below six figures, if you do it on the cheap. But some of those in the sector have no experience of running an SME (Small to Medium Sized Enterprise) and think that they can set-up for the cost of the equipment alone.

Undercapitalised companies don’t last very long. If they haven’t provided customers with useable outputs (which is frequently the case) all the work disappears when they go out of business (we have extensive business experience covering not only our own companies but major brands).

The truth is that providing 3D digital scanning and digital modelling as a professional service is not for amateurs; but a generation of amateurs may have to come, and go, along with their customers’ money and much of the work customers have paid for, before that lesson is properly understood.

By Steve Martin, Managing Director, Xmo Strata and ManagingDirector, SpectisGB

THE 10 KEYS THAT DETERMINE HOW LONG A (3D) LASER SCAN TAKES!

How long does it take to do a scan and provide a client with the output they want?

Like so many services … it depends.

A room that is a simple box can be scanned and processed quickly and easily, but room (of the same size or volume) that is not a simple box, and which contains internal walls and pillars, permanent fixtures and fittings, equipment etc may take longer.

Complexity takes time (but is often the reason why scanning is so important).

Here are some of the things that will affect the timing:

1. The size of the area to be scanned.

2. The shape and dimensions of the architecture / interior design / equipment being scanned.

3. Whether a building has to be scanned both inside and out.

4. Are colour scans required – or is black and white sufficient?

5. The number of floors, rooms, corridors, staircases and internal spaces.

6. Whether the roof has to be scanned; how that will be done; and whether the roof is a simple shape or a complex one.

7. Whether ceiling voids have to be scanned, and whether they can be scanned from a single location (internal ‘shaped’ ceilings, around dormer windows or with recesses, may require additional locations).

8. The number of different scan locations the technician has to use in order to cover the requirement.

9. The precise output required.

10. The distance between locations, if there is more than one.

Remember that the scanning is only one part of the operation.

In order to make the scans useable for a client, post-production work is required – and again, how long that takes will depend on the variables of the project (perhaps as little as a day or so, perhaps as much as five days for every day of scanning).

Your service provider will be able to give more information once they have a full brief.

By Steve Martin, Managing Director, Xmo Strata and ManagingDirector, SpectisGB

BRIDGE REHABILITATION TECHNIQUES

1. Introduction

Modern bridge infrastructure comprises of primarily concrete (reinforced or pre-stressed) and steel structures. Over the service life of a bridge, its constituent materials are continually subjected to fatigue and wear-tear due to dynamic vehicular loads. Overloading due to increase in wheel loads and regular exposure to aggressive external environment may aggravate the situation further.

Post-tensioned concrete bridges may also exhibit loss in pre-stress overtime, resulting in drop in load carrying capacities of the affected members. Poor quality of construction and lack of regular maintenance could potentially lead to major retrofit in a bridge structure. Furthermore, components facilitating expansion/ contraction of bridge and load transfer to the sub-structure, such as expansion joints & bearings, may also require rehabilitation or replacement over time.

Defects in the constituent materials may be manifested in the form of cracking – spalling of concrete, excessive deflection of structure, corrosion of steel components/ reinforcement etc. It is evident that rehabilitation of bridges involves addressing a myriad of problems and no single technique or retrofit method could offer a complete solution. Therefore, answer lies in being able to address each individual problem with an appropriate technique to result in a durable retrofit. This article aims at providing an overview of a variety of structural retrofit techniques available to rehabilitate bridges.

2. Reinforced / Pre-stressed Concrete Bridges

Most of the structural repair and retrofitting techniques used for ordinary reinforced concrete are applicable to reinforced concrete bridges as well. Structural repair techniques include crack injection with low viscosity epoxy and patch repair using an approved material such as polymer modified mortar or non-shrink grout. Strengthening techniques include concrete jacketing, steel plate or FRP (fibre reinforced polymer) bonding on the external surface of the member to be retrofitted.

For strengthening of pre-stressed concrete structures, external post-tensioning or FRP retrofit may be appropriate.

Concrete jacketing

Involves increasing size of the existing reinforced concrete section by adding more reinforcement and concrete. It could be accomplished by either of the following methods:

1. Conventional Concrete – Pouring concrete around the member to be strengthened with additional steel reinforcement properly anchored to the existing section. Ordinary concrete jacketing requires formwork and is time consuming due to long curing time. Furthermore, it is difficult to achieve a dense mix in constrained conditions. Adhesion is also an issue, especially for overhead applications.

2. Sprayed Concrete (Shotcrete) – Pneumatically projecting concrete on to the reinforced (usually with wire mesh) and prepared surface of the member being strengthened with a spray gun. A variety of additives and admixtures are also introduced to expedite strength gain, reduce rebound, reduce water requirement, curb shrinkage and improve adhesion.

The grading of aggregates is critical in sprayed concrete due to the absence of external vibration and the reduction in the quantity of coarse aggregates as a result of rebound. Shotcrete does not require formwork and is useful to retrofit large areas in a relatively short period of time. But, the operation is very messy with enormous loss of sprayed materials, resulting not only wastage of materials but an unsightly-rough surface finish too. It is not economical for small areas of retrofit due to high setup and machinery costs.

3. Pre-Packed Aggregate Grouting – Pumping of cementitious grout into washed/ graded coarse aggregates placed with properly anchored reinforcement around the member to be strengthened in a tightly sealed formwork. It is one of the better ways of jacketing a concrete member as it results in a dense mix with good surface finish.

Regardless of the method deployed, jacketing results in increase in dimensions as well as dead weight of the retrofitted member.

Steel Plate Bonding

This technique involves enhancing strength (shear, flexure, compression) or improving stiffness of deficient reinforced concrete members by bonding steel plates of calculated thickness with adhesives and anchors to the existing sections.

Steel plate not only acts as externally bonded reinforcement to the concrete section but it also improves the moment of inertia (stiffness) of the composite (concrete-steel) section. This technique is useful for the flexural and shear strengthening of bending elements such as beams and slabs and for compression capacity enhancement of columns.

Steel plate bonding is a cumbersome process requiring extensive hacking & drilling in the existing section. Steel plates are hard to lift and need to be tailor made to suit to the as-built dimensions of the members. Resulting surface finish is unsightly and steel plate retrofit is prone to corrosion over time.

FRP Strengthening

A Fibre Reinforced Polymer (FRP) typically consists of high tensile continuous fibres oriented in a desired direction in a speciality resin matrix. These continuous fibres are bonded to the external surface of the member to be strengthened in the direction of tensile force or as confining reinforcement normal to its axis. FRP can enhance shear, flexural, compression capacity and ductility of the deficient member.

Aramid, carbon, and glass fibres are the most common types of fibres used in the majority of commercially available FRPs. FRP systems, commonly used for structural applications, come in many forms including wet lay-up (fibre sheets or fabrics saturated at site), pre-preg (pre-impregnated fibre sheets of fabrics off site) and pre-cured (composite sheets and shapes manufactured off-site).

The properties of an FRP system shall be characterized as a composite, recognizing not just the material properties of the individual fibres, but also the efficiency of the fibre-resin system and fabric architecture.

FRP strengthening is a quick, neat, effective, and aesthetically pleasing technique to rehabilitate reinforced and pre-stressed concrete structures. Unlike steel plates, FRP systems possess high strength to self-weight ratio and do not corrode. But, it is imperative to be aware of the performance characteristics of various FRP systems under different circumstances to select a durable and suitable system for a particular application.

It should be ensured that the FRP system selected for structural strengthening has undergone durability testing consistent with the application environment and structural testing in accordance with the anticipated service conditions. Suitably designed protective coatings may also be applied on an FRP system to protect it from exposure to adverse environmental conditions (acids, saltwater, UV exposure, impact, temperature, fire etc.).

External Post-Tensioning

Over the service life of a pre-stressed concrete member, loss in pres-stress may occur due to a variety of reasons. Post-tensioned bridges can be effectively rehabilitated by external post-tensioning technique to compensate for loss in pre-stress or increase in wheel loads.

In this technique, pre-stressing tendons or bars are located according to pre-determined profile on the external surface of the member to be strengthened according to design. Anchor heads are positioned at the ends of these tendons/ bars to post-tension the member using hydraulic jacks.

Although, this method is quite effective but it requires sufficient strength in the existing concrete to transfer the stress and exposed tendons & anchorages need to be protected against corrosion and vandalism.

3. Steel/ Composite Bridges

Components of a steel bridge need to be continually protected against environmental corrosion. Proper care needs to be exercised to maintain critical elements such as piles, piers, decks, suspension cables etc.

Piles and piers may be rehabilitated using bonded steel plates or FRP strengthening/ protection. Steel bridges are generally covered with a concrete decking, which gets worn off over time due to cyclic dynamic loads. It is a time consuming and cumbersome process to retrofit reinforced concrete decks with conventional methods. The following techniques are useful to rehabilitate a steel bridge deck:

Bridge Deck Replacement

Exodermic™Bridge Deck (www.dsbrown.com) is a modular deck replacement system consisting of a reinforced concrete slab composite with an unfilled steel grid. This arrangement maximizes the use of the compressive strength of concrete and the tensile strength of steel. Top portions of the main bars of the steel grid are specially designed with perforations that get embedded into the concrete to effectively transfer horizontal shear. The concrete component can be precast before the panels are installed on the bridge, or cast-in-place.

Overall thickness of the system ranges between 150mm and 250mm. The system is designed to speed up the construction process while reducing the dead load. A typical application weighs 35 to 50 percent less than a reinforced concrete deck that would be specified for the same span. It not only helps reduce dead load on the sub-structure but also enables bridge structure to sustain higher live loads.

The panelized nature of the Exodermic™ design is well suited for rapid, even overnight, redecking projects.

Bridge Cable Protection

Cableguard™ Elastomeric Wrap system (www.dsbrown.com) is a corrosion protection system exclusively developed to protect bridge cables, applicable during construction or rehabilitation of cable-stayed and suspension bridges.

The patented wrap material is based on cross-linking a chlorosulfonated polyethylene polymer that is manufactured into a three ply (polymer-fabric reinforcement-polymer) laminated construction. It comes in a wide variety of colours and hence, does not require painting.

Cableguard™ Elastomeric wrap is applied directly over existing cable coating using a Skewmaster™ automatic wrapping device to encapsulate the entire cable. Wrap is heated to fuse its overlapped portion and shrink it snuggly to the cable surface to result in an impermeable barrier against intrusion of moisture into the cable.

Although, the Cableguard™ wrap shrinks securely on the cable, it does not fuse or bond to the cable. Therefore, partial removal for inspection of the internal strands is not impaired. Application does not require sandblasting, high-pressure washing or any type of solvent cleaning, eliminating need for containment and disposal of hazardous materials.

Cableguard™ Elastomeric Wrap system presents a watertight sealing mechanism to protect bridge cables from corrosion and premature failure.

4. Rehabilitation of Expansion Joints and Bearings

Expansion Joints

Bridge expansion joints allow movement (expansion and contraction) resulting from temperature changes, shrinkage and creep etc. in the bridge structure, while maintaining its watertight integrity. Like bridge deck, they are continually subjected to dynamic vehicular wheel loads, wear & tear, and fatigue during their service lives.

Depending upon their movement capacities and make, expansion joints may fall into the categories of bituminous, rubberized or mechanical joints. They may also be categorized as bolted-down or positively anchored on the basis of their mode of anchorage with the bridge deck.

Generally, rubberized and finger bolt-down joints tend to loosen over time with the application of wheel loads. Upon loosening, dynamic forces are accentuated further that hamper proper functioning of the system as well as riding quality.

Sealing elements may also get damaged overtime due to wear and tear. Large movement joints such as modular expansion joint assemblies may also require replacement of their elastomeric components during their service lives.

Rehabilitation of bridge expansion joints poses the challenge of replacing the components or complete joint without disrupting traffic flow.

Generally, replacement is carried out lane by lane during off-peak hours to allow the traffic flow while work is underway. To accomplish, replacement of expansion joint with in a short period of time, it is important that the system proposed meets the following criteria:

1. Joint can be installed in a shallow box-out to limit cutting & hacking

2. Joint can be installed lane by lane

3. Nosing material is elastic and bonds well with the deck concrete and expansion joint mechanical elements

4. Nosing material sets quickly (less than an hour or so) without special curing requirements

5. System provides a water-tight integrity Delcrete™ Strip Seal Expansion joint systems (www.dsbrowm.com) meet all above-mentioned criteria and present an ideal solution to rehabilitate bridge expansion joints. Delcrete™ is a pour- in-place, free flowing, two-part polyurethane-based elastomeric concrete.

It has been compounded to bond to a variety of surfaces including steel and concrete. It is non-brittle over extreme temperature ranges, resistant to nearly all chemicals and has one-hour cure time.

Bridge Bearings

Bridge bearings primarily carry out the following functions:

1. Create a desired support system for the bridge superstructure

2. Transfer loads from the super-structure to the sub-structure

3. Allow movement and rotation of the superstructure Like expansion joints, bridge bearings also come in various types, makes and materials.

They fall into two broad categories of elastomeric and mechanical bearings. Elastomeric bearings are generally composed of neoprene or natural rubber, with or without steel plate reinforcement.

Mechanical bearings may be categorized into mechanical pot, roller, rocker, knuckle, or disc bearings. Defects in elastomeric bearings may be manifested in the form of cracking or tearing of elastomeric material, slip of steel reinforcing layer or the bearing itself, excessive shear movement in the bearing etc.

Mechanical bearings may also exhibit signs of distress during their service lives in the form of excessive movement/ rotation, bearing failure at sub-structure or super-structure, dislodging of components such as sliding surfaces/ materials, failure of anchorage systems etc. In most of these situations, it is advisable to replace the complete bearing assembly with a new one.

Therefore, provisions must be made at the design stage itself to ensure easy replaceability of structural bearings at a future date. To replace existing bridge bearing, it is necessary to make alternative arrangements for load transfer from the superstructure to the sub-structure during the duration of replacement.

Normally, hydraulic jacks are used to lift the bridge superstructure for replacement of the affected bearing. If the bridge sub-structure has sufficient space in the vicinity of the bearing to be replaced, then the hydraulic jacks can be placed on the substructure itself, otherwise supporting frame is erected from ground or friction gripped to the bridge pier to support the jacking arrangement. Bearing replacement exercise involves careful consideration of bearing pressures, effective load transfer mechanisms, ensuring balanced-gradual lifting and stability of superstructure, and speed of replacement.

What is RIBA plan of work?

The RIBA Plan of Work is published by the Royal Institute of British Architects (RIBA). The latest version is also is endorsed by the Chartered Institute of Architectural Technologists, the Construction Industry Council, the Royal Incorporation of Architects in Scotland, the Royal Society of Architects in Wales and the Royal Society of Ulster Architects.

It was originally launched in 1963 as a fold out sheet that illustrated the roles of participants in design and construction in a simple matrix format. The first detailed plan of work was published in 1964 (ref. Introduction, RIBA Plan of Work 2007).

Split into a number of key project stages, the RIBA Plan of Work provides a shared framework for design and construction that offers both a process map and a management tool. Whilst it has never been clear that architects actually follow the detail of the plan in their day to day activities, the work stages have been used as a means of designating stage payments and identifying team members responsibilities when assessing insurance liabilities, and they commonly appear in contracts and appointment documents.

The Plan of Work has evolved through its history to reflect the increasing complexity of projects, to incorporate increasing and changing regulatory requirements and to reflect the demands of industry and government reports criticising the industry. It has moved from a simple matrix representing just the traditional procurement route, to include multiple procurement routes, more diverse roles, multi-disciplinary teams, government gateways and to add stages before and after design and construction. It is supported by other RIBA publications such as the RIBA Job Book.

The Plan of Work has been criticised for being too architect focused, for missing many of the client tasks undertaken at the beginning of a project, and for condensing construction into a single stage.

The latest version, published in 2013, has moved online and has undergone a radical overhaul. It is now more flexible, with stages such as planning permission and procurement being moveable, it reflects increasing requirements for sustainability and Building Information Modelling (BIM) and it allows simple, project-specific plans to be created. In addition, the work stages have been re-structured and re-named.:

0 – Strategic definition.
1 – Preparation and brief.
2 – Concept design.
3 – Developed design.
4 – Technical design.
5 – Construction.
6 – Handover and close out.
7 – In use.

There is also a BIM overlay and a sustainability overlay for the plan, but these do not seem to have been updated to reflect the 2013 work stage definitions.

The 2013 Plan of Work has come under some criticism as it is significantly less detailed than the previous 2007 edition, its flexibility and customisability is very limited and the definition and naming of work stages does not reflect the terminology that is used by the industry.