TERM PAPER

Course Code:-CIV101

Course Name:-Elements Of R.C.C

TOPIC:- DOWEL BARS

-: SUBMITTED TO:- -: MADE BY:-

MR. AMIT DHIR ASHISH SINGLA (03),

ACKNOWLEDGEMENT

This is a humble effort to express our sincere gratitude

towards those who have guided and helped us to complete

this project.

A project reported is

major milestone during the study period of a student. We

could have faced many problems but our well wisher’s kind

response to our needs and requirement, their patient

approach and their positive criticism helped us in making

our project. Very warm thanks to our project-in-charge

“Mr. Amit Dhir” with his support we finished our project .

THANK YOU

CONTENTS 1. DOWEL.

2. DOWEL BARS.

3. PLACING OF DOWEL BARS.

4. GFRP

-BENEFITS.

-PHYSICAL PROPERTIES.

-FIELD TRIALS.

-PERFORMANCE.

5. DOWEL BAR RETROFIT

-DEFINITION.

-CASE STUDY 1

-PROBLEM.

6. EXAMPLES OF DOWEL BARS.

1. DOWEL

A dowel is a solid cylindrical rod, usually made of wood, plastic or metal. In its original

manufactured form, dowel is called dowel rod.

Dowel rod is employed in numerous, diverse applications. It is used to form axles in toys, as

detents on gymnastics grips, as knitting needles and as structural reinforcement in cabinet

making. Dowel rod is often cut into short lengths called dowel pins, which are used in various

ways:

As shelf supports in furniture.

As moveable pieces (i.e., pegs) in games.

As supports for hanging items such as key rings and tools.

To secure two objects together with precise alignment in a dowel joint: a hole is bored in

both objects and the dowel pin is inserted into the aligned holes.

Stone masonry

Steel dowels are commonly used in masonry to pin stone components together. Holes are

bored in the stone and the steel dowels inserted to secure the components.

2. DOWEL BAR

Dowel bars are short steel bars that provide a mechanical connection between slabs without

restricting horizontal joint movement .It is a device made from steel or fiber-reinforced plastic in

bar form, used for carrying shear force across a joint in highway pavement and in airport

runways and taxiways.

It increase load transfer efficiency by allowing the leave slab to assume some of the load before

the load is actually over it. This reduces joint deflection and stress in the approach and leave

slabs.

It is to transfer the load from one slab to another whilst permitting axial thermal expansion along

the axis of the dowel.

Dowel bars are typically 32 to 38 mm (1.25 to 1.5 inches) in diameter, 460 mm (18 inches) long

and spaced 305 mm (12 inches) apart. Specific locations and numbers vary by state, however a

typical arrangement might look like Figure 1.

In order to prevent corrosion, dowel bars are either coated with stainless steel (Figure 2) or

epoxy (Figure 3). Dowel bars are usually inserted at mid-slab depth and coated with a bond-

breaking substance to prevent bonding to the PCC. Thus, the dowels help transfer load but allow

adjacent slabs to expand and contract independent of one another. Figure 3 shows typical dowel

bar locations at a transverse construction joint.

Figure 2. Stainless steel-clad dowel bars/

(Epoxy Coating on Ends Only)

Figure 3. Dowel bars in place at a construction

joint- the green color is from the epoxy coating.

3. PLACING OF DOWEL BARS. The present invention

relates generally to an apparatus for slip forming of concrete, using a pan which initially begins

the concrete forming process ..Of such a machine or an apparatus for inserting dowel bars for a

concrete slip forming machine.

More particularly to such a method and apparatus which inserts dowel bars directly between

spaced apart portions of the pan of such machine, instead of utilizing a separate dowel bar

insertion device disposed behind the pan, which has been the custom of the prior art.

In concrete slip, forming machines used for building roads , it is customary to form joints therein

at predetermined intervals. One of the reasons for these joints is to hold adjacent sections of

concrete together while at the same time allowing for them to shift to some extent, which occurs

during freezing and thawing cycles. These dowel bars are typically inserted all the way across

the pavement being formed and generally are aligned with the forward movement of the

machine. These joints can be perpendicular to the slab and to the direction of forward movement

of the machine or they can extend across the strip of concrete being formed at an angle thereto,

which is commonplace in present day road construction so that each set of tires of a vehicle does

not hit the joint at precisely the same time, thereby lessening the thumping problem that often

occurs when the concrete joints are perpendicular to the direction of the movement of the vehicle

traveling thereon.

The aforementioned concrete slip forming machines have for many years used dowel bar

insertion mechanisms thereon,

The need to have this dowel bar inserting apparatus and accompanying trowel mechanism makes

it necessary to lengthen the machine by a considerable amount. This additional length creates

many problems such a making the machine more difficult to move and requiring much more

time to assemble and disassemble as these machines are moved from one job site to the other.

Additionally, on roads that have sharp vertical curves up or down, if the paver is too long, it can

extend completely across such a low spot and not be capable of reaching low enough to correctly

pave the surface there under or it can extend completely across the high spot leaving only a thin

layer of concrete. Furthermore, a machine which has a conventional dowel bar inserting thereon

and a follow-up trowel mechanism almost always needs to be a four-track machine, which

increases the costs of manufacture and use over that of a two-track machine, and also causes the

aforementioned problem relating to the difficulty of being able to pave roads which have sharp

vertical curves up and down.

The present invention is an improvement thereto since it has been determined that it is better to

form a wide space in the pan than to merely have openings which extend there through for

inserting dowel bars.

Consequently, there is a need for a method and apparatus for inserting dowel bars on a concrete

slip forming machine which will overcome the aforementioned disadvantages of the prior art.

4. ONE OF THE BEST TYPES OF DOWEL BARS

Glass Fiber Reinforced Polymer (GFRP) Dowel Bars have a number of advantages when used

as load transfer devices for extended life pavement. The Achilles Heel of concrete pavement is

the joint. Joint failure is often the result of corrosion of the steel dowel bar. Aslan 600 Dowels

will not rust or corrode, locking a concrete joint together or causing spilling of the surrounding

concrete. In addition, while providing the necessary shear capacity at the joint, the lower

stiffness of the GFRP Dowel bars may reduce fatigue stresses in the concrete surrounding the

dowel.

Aslan 600 GFRP Dowel Bars are also electromagnetically transparent and frequently used in toll

collection areas near inductance loops embedded in paving. Typically Aslan 100 GFRP Tie Bars

are also use for longitudinal joints in conjunction with Aslan 600 Dowels.

SHEAR STRENGTH

The shear strength of the GFRP Dowels is measured in two ways, shear in bending and pure

shear. The bending shear test used is a standard ASTM test placing the dowel bar in a three-point

loading fixture. Also known as a short beam shear test.

In case of pure shear, a special test fixture is used to shear the dowel in two planes. The shear

strength is determined from the double shear test.

Field Trials

In 1983, the Ohio Department of Transportation (ODOT) installed several alternative dowel bars

for long-term durability performance studies in sections of Interstate 77 in Guernsey County and

Ohio State Route 7 in Belmont County. These dowel bars were produced with the same

constituent materials as in the Aslan 600 GFRP Dowels. In 1998, the Market Development

Alliance (MDA) of the composites industry organized the extraction and testing of samples of

these dowel bars to determine their durability performance after 15 years of in pavement service.

These results show that the GFRP Dowel Bars were virtually unaffected by approximately 15

years of field service and exposure.

GFRP Dowel Bars have been installed in Illinois, Iowa, Kansas, Minnesota, Ohio, Wisconsin,

Colorado, New York, New Jersey, Texas, Florida, California, Arizona, Hawaii, and Manitoba

and many countries outside North America.

PERFORMANCE OF GFRP DOWELS

(According to research centre)

The three design elements for dowels are spacing, length and diameter. Due to flexibility of the

sub grade,

the load is not transferred by a single dowel but by a group of dowels.(Tests performed at the

University of Manitoba in Winnipeg Canada show the joint effectiveness of GFRP Dowels to be

in the range of 86% to 100% effectiveness using a weak sub grade and 90% to 97% using a stiff

sub grade). An ACPA criterion for successful joint load transfer is 75%. The research concludes,

"GFRP dowels are a viable, corrosion free alternative to steel dowels." (ACI Structural Journal

Vol. 98 No. 2, March-April 2001, Glass Fiber Reinforced Polymer Dowels for Concrete

Pavements, D. Eddie, A. Shelby and S. Rizkalla.)

LOOSE OR BASKET

Aslan 600 GFRP Dowels are generally furnished loose. When supplied loose they may be used

by dowel bar insertion machines or as part of a dowel bar retrofit system

Aslan 600 Dowels may also be furnished in a 100% non-metallic basket assembly, the DBB1500

series. The completely metal free basket allows for free flow of concrete between the dowels

which helps maintain alignment during the pour. The basket has been tested for a vertical load in

excess of 1500 lbs.

The DBB1500 series is very light weight. Individual support chairs are snap fit into #3 fiberglass

rebar runners and the 1-1/2" x 18" smooth round GFRP Dowel Bars snapped into place. Basket

assemblies are generally field assembled.

With GFRP Dowel Bars, there is no need to grease the dowels as the bond strength to concrete is

sufficiently low to allow longitudinal movement of the concrete.

DOWEL BAR RETROFIT (DBR):-

It is a method of reinforcing cracks in highway pavement by inserting steel dowel bars in slots

cut across the cracks. It is a technique several states have successfully used to address faulting in

older jointed plain concrete pavements. The typical approach is to saw cut and jackhammer out

the slots for the dowels. Following dowel placement, the slots are then typically backfilled with a

non-shrink concrete mixture (grout) and the pavement is diamond-ground to restore smoothness.

CASE STUDY .1.

For more than ten years, Washington State Department of Transportation (WSDOT) has been

rehabilitating its aged concrete pavements by retrofitting the transverse joints with dowel bars.

WSDOT has found that this procedure is a cost effective option for rehabilitating concrete

pavements, however, there are many unknown design aspects. For example, what pavements are

most appropriate for dowel bar retrofit: What is the long-term performance (extension of

pavement life)? Once a pavement has been dowel bar retrofitted, what is the most likely method

of failure? This research will develop a complete design package for dowel bar retrofit projects

that would include the proper selection of suitable candidates for rehabilitation and a prediction

of expected pavement life extension as a result of the retrofit.

PROBLEM

Dowel bar retrofits have occasionally been plagued with problems. These problems are usually

due to poor workmanship and can be avoided by careful following of specifications and close

supervision of workers. Use of heavy jackhammers (heaver than 14 kg class) tends to cause

cracking of the concrete all around the slots. Lack of caulk or voids in the caulk put in the joints

or cracks leads to cracks around the joints. Voids in the grout (especially below the dowel bar)

can cause failure of the grout

….. EXAMPLES OF DOWEL BARS…..

-:REFRENCES:-

1. R.C.C DESIGN-RAMAMRUTHAM.

2. REINFORCED CONCRETE DESIGN-PILLAI & MENON .

3. WIKIANSWERS.COM.-what is dowel bars.

4. EN.WIKIPEDIA.ORG/WIKI/DOWEL BAR RETROFIT.

5. PAVEMENTINTERACTIVE.ORG/INDEX.PHP?TITLE=DOWEL BARS.

6. WWW.IGGA.NET