What Kind of Bridge is That - Joe Spadafino '76

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WHAT KIND OF BRIDGE IS THAT?

WHAT KIND OF BRIDGE . IS THAT? written by

Joseph F. Spadafino photographs taken by Eric Paul

To Lourie. H., With Love. ,..,..

�ople. ore. lonely be.cause. -they bu·11d wolfs instead of brid3e.s. · .:r°"� r. Ne.ti,,.

CONTENTS Introduction Stationary Bridges

Beam Arch

Truss

Cantilever-

Suspension Movable Bridges Pontoon Bascule Draw Swing .

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4 8

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20 22 27 29

Vertical Lift

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Natural

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Other lnterestin9 Brid9es

Covered

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42 Foot 44 Bridge-Tunnels How Much Did You Learn?46

-Bridges are very im­ portant. The� help you and me to 90 from one place to another safely.

There ar-e many t�pes of brtd9es. This swing bridge helps people cross the Passaic Riven

r ve o o g s e Some bridg s e k a t d ri b s i h T 9f! roads. one road over another.

GARDEN SfltTE PA-R�WA't .. ftl..OOIMPIEI.D NJ'.

Br id9es that take one road over another road are called VIADUCTS. 2.

Sti II other brid9es 90 over rail roads.

WILLIAtil SON ST· 8ll0GE. - 81.�&LP, NT.

Now· let'-s learn about the different types of !

brid9es.

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o t d e s u n rna Early at h t s g o l n o s cross str�am . m e h t s s o r c a n e \ l ia ad h d a h n a m r e t f a Later on, s a w e h , ls o o t d invente n w o is h n w o d u+ c able to \09s and put a bridge wherever he wanted one.

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These log bridges are cal led SIMPLE BEAM BRIDGES. Today we make brl�es out ot concrete and steel. These th\n9s are called bvilding MATERIALS. Here is a modern sR01toir. ... simple beatn bridge ..CLIFTON ,N -� ii

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Man soon found that some r-ivers were too wide tt, cross with Just one log. He.hadtomake bridges with bri9er SPANS. lhe span is th-e. length of 1h6 bridge or 'the. \e.ngth of anďż˝ section of a bridge.

Some of the ear-l lJ n,en tried 1o build lon<3er bridges. These men were the first¡ CIVIL ENGINEERS. 6

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Engineers made brid9es l0T1<3e.r by ualng PIERS. Piers are pUas of rocks or logs or conerete put in ihe middle of the r-lver to ho\d up th-e. ends of each becun. Now the brid<3 e is not a simple. . e g id b-eam ' but a beam ---br ---�---- ··-

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1he ARCH bridg� was first made out of s-tone..

In the arch bridge the weight of an�thlng goinq over the bridge is passecJ from stone to stone unt,\ i't reaches the �round.

The top stone is called the k9ystone. Cqn you find \t? �

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Today, engineers use stone and concrete or steel when bvildin9 arc.h bridges. They also change the design; like they did in this steel crch.

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To make brid�s stron9er engineers desi9ned the TRUSS bridge.

A truss is a beam -th-it

is 91ven extra st ren9th by braces.

To show how braces help, let 1 s tr,bthis:

1) Take two six-inch strips of cardboard and pin them together with a paper fastener, as shown.

2) If the Colrdboard was the span of a bridge,

t would happen if ethin9 wen1 over tt?

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Pull down on th e. fastener to find out-.

3) Now take three mor-.a strips of cardboard, one five-inches long and the others eight inchesâ&#x20AC;˘

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Now fasten all five strips together like in the picture. After you have done this, iry pul lin9 down on the center

See, it doQsn't collapse.

Thisis how braces help tnake truss brid9es stronqer.

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This picture shows the braces in a truss bridge, lookinq up.

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The CANTILEVER is a new bridge. The first one was built in 1867.

The cantilever has two arms that reach out fr¡om

shore and meet over the middle of the r, ver. The arms rest on piers.

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Another ne¼' type of bridge is the SUSPENSION brid

Suspension brid9es are a\so -the world's mos-t beautiful bridges.

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Tall towers are built in the river and big cables-are strung between them. TI.e ends of the cables are. fastened to the shore.

Smaller cables are hung off of the larger cables and the roadway is SUS­ PENDED by these small ·cables. Suspended means hung from.

Could you see the different cables: ,and the tower-s in the p;cture?

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The bridges we have seen so far do not move.

They are called fixed or stationary bridges.

Engineers also build bridges that move. Let's see some of these now.

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Pontoon brtdse. built- durin<J the. G,vcl Wo.r, f�oto�t1l�e, vy h\Qitbe.W 8rocly • Todo.y, instead� Ult"9 woocle.al _.t�, Qr-mies use. �..t-oons at mdol or p\asnc..

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The simplest type of movable bridge is the , PONTOON bridge. It is also' the oldest type. Ancient Greeks and Romans put small boats, or PONTOON S1 in rivers with planks on top of them so their armies could cross thca rivers.

When the bridge was not needed, i+ could be taken apart easily .

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The BASCUL E bridge is s i t a h t e g d i r a truss b d n a d n e e n o t a d e pinn free at the other. The span is free to be raised when ¡a ship has to 90 under it.

In the picture of the bascule bridge . the big . concrete block is a COUNTERWEIGHT. This block wei9hs almost as much as the truss. When· the brldgekeeper has to raise the bridge onfy, a· small motor is needed -to raise that whole bridge.

This is because of -� LEVERAGE. Let's learn about levera'3e. Try this:

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2) Now take a big pen eraser and put ft on the short end. Try to balance the. ruler and eraser. The eraser is a counterweight".

'3) The last step is placing a penny on the 25

eraser ·so the long Sid� raises. The weight of the penny is like tha pull of the small motor.

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The motor ( penny) f s small, but it can raise the bridge (ruler) because of the levera9e of the counterweight (eraser).

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A OOAWBRIOGE ts a typ ,f basovl e bridqe. A drawbridge has its counterweights hidden underneath, in the piers.

Can yov see any coun1'arwei9his on this dosed drawbridge?

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Her-e is a picture of the counterweights on that drawbridge.

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An interesting movable bridge is the swing bridge.

A whole section of bridge swings out to let ships by.

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TWE' WOl(L"D'� LAR6E(T SWING s�u,c.E TuE GaEO«<iE' V. Cc>Le-M.\N �M.8ltlf�E' OV•ll THE 'fOlltc. Rnl&'ll IN YOltKTt> Wf.l I VA, l P1(1'U16 Of OPEN BftlOGe- "" NliXT f'A-GO

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VERTICAL LIFT brid9es have two towers with large gears on · top. There is a truss section with chains attached on each end .

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The chains pass over the 9ears. There are. counterweights on the

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Mother Nature made this natural bridge in Virginia. Man built a hK3hway, U.S. Route 11, over it.

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The Humpback Brid,9e of Virginia is a covered ¡ arch bridge . It \s not used anymore, but it is the main at-traction of a peaceful picnic area.

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AMI SH BtlO�Ci .. VtNClrSTER PA. 1Nlet10ft

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e g d i r B h s This Ami e. <3 d i br' s s u r t d e r e is a cov ­ n n e P n i s i e g d i r b T hi s y b d e n w o s i t I . a i s':tlvan ou y d n a , t n a r u sta e a r h rt.

'3 u o r h t e v i r d \ \ i t s ca n

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This is the onlďż˝ covered bridge in New Jersey. It is a covered beam brid9e.

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f:OOTIIIIMai OVER 61,,rr FALLS' 1 PMatON ,N..f. t FOOTSRl�li OV8f RAIUOAO Yltl.P I NDJll1t,C,N°r. ♦

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Some bridges are for people on foot or bike.

These foo1bridges are designed like heavy-traffic bridges. The bridge on the top of page 42' is an arch. Below it is a truss bridge; and, on this pa9e 1 there is a beam brid

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ESAPWE B� IDGE ·TUNN

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Somettmes bridges are. vsed with tunnels to cross large bodies of water.

Br id<Je�unnels are a new idea and a good one. be.- · cause no traffic.. is held up . . These prctures are of bridge­ tvnnels on Chesapeake Bay 0

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Do youthlnk you could tell whai 'kinds of bridges are in these pictures?

The answers are on pa9e 50.

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Answers: n Suspension 6) Bascule 2>Arch 7)8eam 8)Truss 3)Truss 9) Arch 4)A rch 5)Vertical Lift

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