Main Body Floating Bridge

8/16/2019 Main Body Floating Bridge

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1. INTRODUCTION

A pontoon bridge (or ponton bridge), also known as a floating bridge,

uses floats or shallow-draft boats to support a continuous deck for pedestrian and vehicle travel.

The buoyancy of the supports limits the maximum load they can carry. ost pontoon bridges are

temporary, used in wartime and civil emergencies. !ermanent floating bridges are useful for

sheltered water-crossings where it is not considered economically feasible to suspend a bridge

from anchored piers. "uch bridges can re#uire a section that is elevated, or can be raised or

removed, to allow waterborne traffic to pass. !ontoon bridges have been in use since ancient

times and have been used to great advantage in many battles throughout history, among them

the $attle of %arigliano, and the crossing of the &hine during 'orld 'ar . A pontoon bridge is

a collection of specialied, shallow draft boats or floats, connected together to cross a river or

canal, with a track or deck attached on top. The water buoyancy supports the boats, limiting the

maximum load to the total and point buoyancy of the pontoons or boats. The supporting boats or

floats can be open or closed, temporary or permanent in installation, and made of rubber, metal,

wood, or concrete. The decking may be temporary or permanent, and constructed out of wood,

modular metal, or asphalt or concrete over a metal frame.

Fig. 1.1* Typical example of a !ontoon $ridge+


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[1] mage courtesy* www.weiku.com

n the /01s, the 2rench devised the copper pontoon3 after this point, rivers and

canals ceased to present significant obstacles. The early modern period in pontoon use was

dominated by the wars of the 4th and 5th centuries during which the art and science of

pontoon bridging barely changed. This however did not stop all innovation, in 014 a "wedish

army used a leather pontoon bridge to cross a river before the $attle of 6olowcyn. 7uring

the !eninsular 'ar the $ritish army transported 8tin pontoons8 that were lightweight and could

be #uickly turned into a floating bridge.

9t :ol :harles !asley of the &oyal "chool of ilitary ;ngineering at

:hatham ;ngland developed a new form of pontoon which was adopted in 40 by the $ritish

Army. ;ach pontoon was split into two halves, and the two pointed ends could be connected

together in locations with tidal flow. ;ach half was enclosed, reducing the risk of swamping, and

the sections bore multiple lashing points. The 8!alsey !ontoon8 lasted until 4 foot centres, heavy cannon could

cross. The canoes could also be lashed together to form rafts. ?ne cart pulled by two horse

carried two half canoes and stores. A comparison of pontoons used by each nations army shows

=


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(a

)

(

b

)

(c

)

(

d

)

that almost all were open boats coming in one, two or even three pieces, mainly wood, some with

canvas and rubber protection, $elgium used an iron boat. America used cylinders split into three.

Fig. 1.2*(a) ughal ;mperor Akbar using boats as pontoons to build a bridge for elephants,(b)A

@" army boat as pontoon,(c)!ontoon bridge across ames &iver, @". (d) !ontoon bridge across

&avi &iver, ndia. +=


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+= mage :ourtesy* .= (a), (b), (c), (d) B 'ikipedia

2. NEED FOR THE RE!ENT !TUD"

The development of continuous floating bridges has been accomplished largely in the

'orld3 the development of analytical and design methods has not, therefore, involved studies from all

over the professional world. The associated reliance on local studies and the incidence of failure places a

maCor responsibility on the bridge engineers. The understanding of the behavior of existing bridges

under extreme environmental conditionsand conDdence in predictive schemes in the design of new

bridges re#uires methods that are both accurate and precise.

This report reviews the significant studies on floating bridges made over the last => years

and reveals expert analytical schemes that examine the various aspects of the wind- wave-force behavior

and wind-force behavior systems. They involve uncertainties in modeling of both the wind-wave-force

and the structural systems, the assignment of parameters (especially the damping of the structural

system), and the expected local wind characteristics to be considered. 6owever, these reductionist

schemes produce an understanding of the various features that influence the behavior of floating bridges.

"uch accuracy can be obtained by re#uiring that these integrated results be constrained by relations

between measured wind characteristics and measured kinematic behavior.

The review found that these measurements had only been completed in the special study of

draw span fatigue maintenance problems. t is suggested that these wind-kinematic behavior relations be

obtained for the existing bridges and that they be used as accuracy constraints on the reductionist studies.

!ersistence in these studies will improve the understanding of floating bridge behavior and the precision

E


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of the analytical results. The availability of the wind-kinematic behavior relations will ensure that such

integrated studies are accurate.

Availability of the relations between the initial environmental feature, wind, and the

conse#uent structural behavior, bridge kinematics, for existing bridges will display performance changes

for the different structural arrangements. These results can be applied to a new bridge design if the wind

conditions at the site are available.

#. RE$IE% OF &ITER'TURE

+ Hart et al. (1*+,) The study of forces on continuous floating bridges has been of continual

interest to the 'ashington "tate 7epartment of Transportation since the early design

considerations of the 9acey F. urrow $ridge in 5E1>. The first of urrowGs four concerns

was the determination of such forces (!acific $uilder and ;ngineer 500)."ubse#uently, 6art

and his colleagues studied the short crested wave interaction with the structure with the intention

of understanding the applied forces. The idea was to replicate the confused seas associated with a

mixture of incident and reflected waves by these choppy waves. The final work (%eorgiadis

54l3 6art* and %eorgiadis 54* 6art* and %eorgiadis 54=) consisted of a finite element

modeling of floating bridge behavior in short crested waves. This work was an outcome of

empirical studies on the 6ood :anal $ridge, where wave characteristics, wave forces on the

bridge, and the bridge response were measured (6art and &ichey l501* 6art and ukheiCi

503 ukherCi 50=). n none of these studies were ade#uate wind measurements obtained to

develop wind-wave-force relations. A conse#uence of the modeling reported was the necessity to

reduce the determined forces by an attenuation function in order to obtain reasonable agreement

between the measured and predicted values. The design work of Tokoia, ;arl, and 'right (505)

>


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on the replacement of the western part of the 6ood :anal $ridge was based on the assumed

superposition of long crested waves.

+= -loten 'ociate Report (1**1) the 55 reports of the %losten Associates provide a

sophisticated finite element method for the analysis of floating bridges. The behavior is predicted

by perturbation about the steady displaced shape. n this way the non-linearity in the governing

e#uations are dealt with in two steps* the determination of the static state associated with the

mean environmental situation, in itself a non-linear problem, and the dynamic state about that

mean.

+


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for a proposed solution, a floating bridge were presented. These aspects included environmental

loads, structure and the mooring system. They also concluded that the proposed floating bridge

may cost less than half the price of a fixed bridge.

. O45ECTI$E! OF THE !TUD"

$ased on the literature review presented above, the salient obCectives of the present

study have been identified as follows*

. To understand how the floating bridges actually work, the challenges put forward by such a

ega "tructure.

=. To study the worldGs 9ongest floating bridge in the world the E6ergreen oint Floating

4ridge also known as "&>=1 .

. To understand the creep of concrete and the mix design for floating bridges pontoonGs.

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,. 'N'&"!I! OF ' F&O'TIN- 4RID-E

A. Research Approach:

The integration of the reductionist studies gives an estimation of bridge

behavior. The accuracy of this estimate is evaluated from a system theoretic approach in which

the input is the wind character and the output the kinematics of the bridge and derived internal

forces. The relationship between input and output provides a transfer function. The form of the

function is that given by a mathematical match, and little physical insight is evident. A transfer

function is also the end product of the integrated reductionist analysis, but here physical insight

exists at each step. The intention is to deal with accuracy by the input-output match. The various

steps of the reductionist analysis will provide the precision in modeling, together with physical

insight, and the integrated effects will be restrained by the input-output match. Thus, any

sharpening of the various steps, either by improved modeling or by better parameter estimation,

must not reduce the accuracy.

The 5


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where y is the strain, x the mean wind speed, and the wind direction relative to the normal of

the bridge.

&egression constants c, m, n are obtained by the regression fit3 the goodness of fit was defined

by the following*

R 7 8 (9:)2.(9c)

;2 (2)

'here ym is the actual strain measurement and yc the value computed from e#uation (). The

process involved measurements of x, ym and 3 the computation of yc by e#uation ()3 and an

evaluation of the process closeness of all yc to ym from e#uation (=).

This approach would determine the reaction of a floating bridge to winds without

the evaluation of the separate wind-wave ,wave-force-kinematics, wind-force-kinematics, and

structural behavior characteristics.

B. Elastic Analysis Approach:

. ;nvironmental loading study using :omputational 2luid 7ynamics (:27),

=. $ridge structure analysis using the 2inite ;lement ethod (2;),


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(a)

(c)

(b)

2igure >.* 2loating bridge design and analysis algorithm

2igure >.=* (a) "treamlines around the bridge body3 (b) Felocity :ontours3 (c) 6ydrostatic

!ressure and static pressure by :27.

1


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(a)

(b)

2igure >.


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1 meters (>,>41 ft). ts =,41 ft) floating section was the longest floating bridge in the world until April , =1/, when

its replacement exceeded it by


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(a)

(b)

2igure /.* (a) Aerial Fiew, (b) "chematic Fiew of "& >=1

2igure /.= :ross section of old and new bridge


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CONCRETE FOR THE 4RID-E=

'"7?T went through a J=.4 million test to find the ideal mixture for the water tight

concrete. The one its engineers chose uses fly ash and micro silica to combat the corroding

effects of salt water. The issue with concrete is that it cracks due to either shrinkage or creep. n

floating bridge, cracks e#ual water leaks. A crack, even Cust one-six thousandth of an inch wide is

considered a structural flaw for a pontoon because it allows water to get inside and compromise

the structural integrity of the entire pontoon. ?ne way to reduce this problem is by installing

piping within the keel slab- the bottom of the pontoon, to which the walls are attached. Kow

when it comes time to pour the walls, engineers heat the keel slab to the same temperature,

between =1 and E1 degrees as the fresh pour. Then, both the keel slab and walls cool at the

same time, shrinking together and virtually eliminating cracks.

E


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2igure /.


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[1] !mage courtesy" wwwwei#ucom

$%& !mage 'ourtesy" % (a) (b) (c) (d) * +i#ipedia

$,& -ccuracy and precision in the analysis and design of .loating /ridges

by 'olin / /rown 0rofessor Emeritus Department of 'i1il Engineering

2ni1ersity of +ashington (+345-')

$6& Elastic 5esponse -nalysis for .loating /ridges in +a1es by 3hunzo 7#a

et al Mitsubishi hea1y industries ltd 4echnical 5e1iew 8olume",9 :an

%;;;

$>wwwwsdotwago1>0ro@ects>35-bout>/ridge.actshtm

$A& http">>wwwpopularmechanicscom>technology>infrastructure>g===>how?to?build?the?worlds?longest?oating?bridge>BslideC

$& /rown '/ 'hristensen D5 ea1ner :+ Fandy M- and 8asu 5(A) G.loating /ridge Drawspan MaintenanceG :ournal of the

3tructural Di1ision -3'E 8ol ;9 34 ll$;& 'astenada ,


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Main Body Floating Bridge

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