bridge plans

8/6/2019 Bridge Plans

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How did I do that?The following detailshow I built some of thestructures seen on myweb site. These arenot plans as such -simply a display ofhow I went aboutbuilding what I have.

Bridges -Things to considerNo single cable, rope, screw, boltor piece of lumber should providetotal support in most applications.A safe and secure rope and plankbridge must be built to carry a loadfar in excess of the expectedmaximum. The anchors or bridgeends should be perpendicular to theline of the bridge to prevent side-to-side sagging. The bridge should sagin the middle to allow for themovement of the tree during high

winds and to reduce strain whenunder load. All lumber should betreated exterior and relatively knotfree. Screws are better than nails.The ideal length of my bridges is 10feet. 15 feet is workable but beyondthat requires very strong and -expensive material.My design is shown below.How high? If I have a choice, 10 to12 feet. High enough to be just a tadscary. How wide? 16" planks. (6 cutfrom 8' piece)

------------- 10--------------1 6 " FINISHED BRIDGEMy bridge design.The bridge is made with 8 vinyl ropes. (244 Ib,test) There are double hand ropes and doubleropes woven between the foot planks. Smaller1/4" vertical ropes are added between each plan

3/4 x 4 x 16" treated lumber.4 notches on each side tohold ropes in place.Notches cut wideenough for 2 ropes.

Loop small vertical ropes around large plank ropes.Take up most but not all slack.Rope tied off and Mark rope here - pull and makesecure PROPER SAG simple knot12" BEFORE PLANKS ARE INSTALLED

SupportboardTree goes here

Do the same for all ropesTree goes here


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THIS WORKS IF THE EYE BOLT IS VERY STRONG ----------PROPER SAG12" BEFORE PLANKS ARE INSTALLED\ Mark rope here - pull and makesimple knotAnchorand supportboard

Eyebolt Do the same for all ropeshimble

INSTALLING THE PLANKS (SIDE VIEW) --------------LAY FIRST PLANK IN CENTER OF BRIDGE

LAY NEXT PLANK AS SHOWN AND PUSH TOGETHER.GAP SHOULD BE ABOUT 1"

FROM THIS POINT ON YOU MAY INSTALL 2 OR 3 PLANKS ON__ ........... _==~O;N!E~S!ID;E~T:H:E:N~KEEP ON ALTERNATING SIDES UNTIL ALL. _ .... ...,.~:::;OF THE PLANKS ARE IN PLACE. ~

..__."K:~_~

Note that one rope enters the support hole ata sharper angle than the other.To fix this, bolt 2 thin strips of hardwood asshown below. Snug - not tight.

Use 4 bolts.

THE LAST STEP IS TO INSTALLTHE VERTICAL ROPES Top view 2


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Bridge AnchorsA bridge may be going from treehouse to tree house, from tree houseto tree or tree to tree.Most bridges from a tree house canbe anchored to the frame of the treehouse. When anchored to a tree aspecial frame is required. Thefollowing shows my solutions to thisproblem. My basic platform provides supportfor the bridge and bridge users. Italso stays level using a design thatlocks it to the tree trunk as weight isapplied to the structure.Here is another of manysolutions for a 2 bridge transfer.I used a similar configurationat the base of my spiral staircasebecause 2 bridges came in atthe bottom.As shown below, iftree locationsare suitable, the step method isan interesting choice.

If there are 3 or 4 bridges going to asingle tree I may build a platform thatcan be left as a simple open transferpoint or enclosed as a tree house.

Board can beangled to beperpendicular tobridge line.

Note: The bridge ropes are tied offat this end. The pull will betransferred to this board and thus tothe tree trunk.Basic frame

Use standard 1" decklumber for floor.Apply as shown formaximum strength.

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Another word about stability. Any platform with a treethrough its middle must be supported vertically andhorizontally. Vertical support

This workswell. Horizontal support(A lag screw heremakes this a verticalsupport also)Verticalsupport

Another fun solution if the trees are fairly close is tomake a solid bridge. I use 2 methods to allow for treetrunk movement. The first is to make a lip on onestructure and a solid anchor on the other. The bridgerests on the lip and slides a bit in the wind.

Solid bridgeslides here.

Horizontalsupport isautomatic inthis type ofstructure.

The secondmethod is tosupport one endloosely withcables.

In this illustration bridgeand platform are onepiece.

Top view

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This is a good place for some details about properlysupporting the items just covered.I use stainless steel cable which is available just abouteverywhere. It is rust free and there is no give. Thesizes I use are as follows: 3/16" = 850 lb. load, 1/4" =1,400 lb. load.A cable can be secured with cable clamps or tumbucklesrated to match the cable load. It can be fixed to a treeby a lag screw in the trunk or by looping it over a sturdylimb. Shown below are 2 methods of securing thecable to the load.

Use thimblesto ease thebend of the.>

Iron pipe easesbend of cable anddistributes load onbeam.

This is one way to support a bridge using a lip. I usethis about 12 feet up where trunk movement is minimaLag bolts on to

Hole drilled and bolt, washerand nut used.2 boards here. Thcarry all the weight

ridge beams rest onthese surfaces.Add 1" thick '------h'lr-.if"""TT"""-----,,.,...,,-.I\ ,

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