Page 4 - June-Month

TECHNICAL PAPER

STRENGTHENING OF BRIDGE-

DECK OVERHANGS FOR SOUND

WALL ADDITION USING NSM

FRP COMPOSITES ANNA PRIDMORE,

VISTASP M. KARBHARI*

Abstract However, there are many instances where roads already exist,
and traffic volumes have increased substantially, or there are
Increasing urban sprawl is resulting in buildings and inhabited no reasonable options for placement in order to enable the
areas being located closer to highways resulting in complaints effectiveness of commerce. In such cases, mechanisms to reduce
regarding noise from traffic. Sound walls and noise barriers are the level and transmission of noise become extremely important.
often used to decrease noise. In the case of elevated bridges, Ohiduzzaman et al. have reviewed a range of techniques to
[2]
the barriers have to be added to existing decks resulting in the reduce noise and hence these will not be repeated here. Among
need for substantial addition of overhang steel reinforcement the more popular techniques is the placement of noise barriers
to carry the additional load. In many cases related to older or sound walls constructed along the roadway to mitigate
box-girder bridges, this either is not feasible structurally or
requires substantial demolition of the existing structure with noise from vehicles as well as from the interaction between
[3]
the consequent extensive disruption of traffic. The use of near tires and the road surfaces . These are structural elements
surface mounted (NSM) fiber-reinforced composite (FRP) strips placed between the road/highway and the area that needs to
as additional reinforcement on the overhang region is shown be shielded from the noise with the goal of the barrier being to
to be an effective strategy enabling efficient and cost-effective reduce the overall levels to between 7 dB and 10 dB at locations
[4]
rehabilitation of box-girder type bridge decks without extensive closest to the roadway through both absorption of the noise
modification of the existing structure and much less disruption by the barrier and reflecting it back onto the roadway itself.
of traffic. Sound waves can, however, carry over and around obstacles
such as barriers and hence their viability can be constrained by
Keywords: Bridges, Fiber-reinforced composite, Near surface distance . Effective barriers are able to reduce the level of noise
[5]
mounted, Noise barrier, Overhang, Strengthening, Sound walls.
by as much as 50% with a barrier capable of effecting a 10 dB
reduction reducing the sound level of a tractor-trailer to that of
1. INTRODUCTION a car . Aspects such as materials used in the barrier, its height,
[6]
and details of placement all impact effectiveness [4,7] . A historical
The increase in population and commerce in cities has resulted
in increasing traffic. In the past, major roads carrying large perspective of noise control on highways as well mechanisms for
amounts of traffic were away from residential areas as well as attenuation of its effect and various forms of barriers have been
[8]
areas of business. However, urban sprawl and expansion through discussed by Ekici and Bougdah .
flyovers and elevated roadways has resulted in major highways While noise attenuation mechanisms can be affected through
and traffic routes carrying heavy traffic being situated in
residential areas, next to schools, hospitals, and parks, causing changes in road surfacing and placement of walls/barriers/
significant disruption due to noise emanating from traffic. The berms during the construction of new roads and highways, the
noise is not only annoying but can result in other issues that modification of existing roadways continues to be a growing
affects the quality of life and can also be the cause of issues concern. In these cases the placement of sound/noise barriers
[1]
that affect human wellness. Noise pollution from traffic increases can be complicated by issues such as space limitations and
as the volume of traffic increases and has become an aspect of presence of K-rails, and in the case of elevated roadways, the
significant concern globally resulting in it now being treated as lack of sufficient reinforcement in the existing overhang regions
an environmental issue of importance in planning. Increasingly, can cause further difficulties. As with a number of agencies, the
the level of noise and its effects are treated as important criteria California Department of Transportation has been retrofitting
in the placement of new roads and cities and have ordinances select roadways with sound barriers placing these on top of
and policies associated with these. existing K-rails where necessary following their “memo to

8 THE INDIAN CONCRETE JOURNAL | JUNE 2021
*Corresponding author : Vistasp M. Karbhari, Email: vkarbhari@uta.edu