Tag Archives: SIngle A-Frame Bridge

Single A-Frame Bridge Pictorial

The Single A-Frame Bridge is made up of three subassemblies. Please refer to Bridge Walkways as a point of reference for two of the three of these subassemblies. The following photos will enliven the text and instructions featured in Adolph Peschke’s informative, older pioneering merit badge pamphlet. Click on the photos for larger views:

Lashing the top of the legs with a two pole shear lashing. Lashing on the ledger to the bottom of the legs. Lashing on the transom at the desired distance from the butt ends of the legs. All square lashings are lashed tightly, especially on the transom.
Captured from the 2013 Jamboree Pioneering Area
Carry the assembled A-Frame to the creek or ravine. Standup the A-Frame in the desired position. Carry over the walkways and place them on the A-Frame’s transom. Connect the underspars of the walkways to  the transom with three strop lashings.
Captured from the 2013 Jamboree Pioneering Area

Single A-Frame Bridge Materials and Instructions

Single A-Frame Bridges at the Jamboree

Single A-Frame Bridges at the Jamboree

A triumphant success—posing on their Single A-Frame Bridge
A Triumphant Success—posing on their Single A-Frame Bridge

In the Pioneering Area of the 2013 national jamboree, we put together a couple of Single A-Frame Bridge kits, so Scouts and Venturers could build this simple crossing bridge during their visit to Garden Ground Mountain. Each kit included:

  • two pre-constructed walkways
  • two 12-foot leg spars (shear legs)
  • one  5-foot transom spar
  • one 6-foot ledger spar
  • two pre-positioned anchors
  • four pioneering stakes
  • two guylines
  • five lashing ropes

Whenever a crew wanted to build a bridge, we provided an overview of the design and gave them a quick introduction to tying a rope tackle and the Japanese Mark II Square LashingWhat follows are some photo montages of the Single A-Frame bridges built from the kits during the jamboree. For larger and largest views, click on the photos once, and then once again:

Positioning their A-Frame in the ditch while preparing the guylines, and lashing the walkways to the transom.
Positioning their A-Frame in the ditch while preparing the guylines, and lashing the walkways to the transom.
Lashing the ledger tightly to the legs and putting tension  on a guyline.
Lashing the transom to the legs and putting tension on a guyline.
Positioning their A-Frame and hammering stakes in the corners of the walkways.
Lashing on the Transom
Lashing on the transom to the legs.
Lashing on the ledger and holding the A-Frame up while adjusting the height of the transom.
Lashing on the ledger and holding the A-Frame up while adjusting the height of the transom.
The shear lashing at the top of the legs, and lashing the ledger at the bottom.
The Shear Lashing at the top of the legs, and lashing the ledger at the bottom.
Lashing the A-Frame legs with a shear lashing, and lashing on the ledger.
Lashing the A-Frame legs with a Shear Lashing, and lashing on the transom.
Carrying their A-Frame to the ditch and placing the walkways on the transom.
Carrying their A-Frame to the ditch and placing the walkways on the transom.
Lashing on the transom and attaching the walkways.
Lashing on the transom and attaching the walkways.
Tightly frapping a square lashing for the transom and working together to join the walkways to the A-Frame.
Tightly frapping a Square Lashing for the transom and working together to join the walkways to the A-Frame.
Strop lashing the walkways to their A-Frame.
Strop lashing the walkways to their A-Frame.

On occasion, a pair of Scouts wanted to build a bridge, and with persistence, and the help of staff or friendly Scouter, they were able to get it done.

Dynamic Duos!
Dynamic Duos!

JAMBOREE PIONEERING AREA: BRIDGES

JAMBOREE PIONEERING AREA: MAIN PAGE

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Single A-Frame Bridge

Two A-Frame Bridges in the  Early Morning Fog on Garden Ground Mountain at the Summit Bechtel Reserve
Two Single A-Frame Bridges in the Early Morning Fog on Garden Ground Mountain at the Summit Bechtel Reserve

The simplest of all crossing bridges is the Single A-Frame Bridge. The design was featured at the 2013 National Jamboree which afforded Scouts an opportunity to construct the bridge right on the spot.

Single A-Frame Bridges at the Jamboree

Single A-Frame Bridge Pictorial

Link to: Older Pamphlet InfoThe following text is by Adolph E. Peschke as presented in the 1998 printing of the 1993 edition of the Pioneering Merit Badge Pamphlet:

Building this bridge is quite simple because there are very few lashings needed for the center A-frame. The A-frame is a triangular shape that resists racking and provides strength for the structure.

A-frame. Start this project by determining the depth of the creek or ravine to be spanned. You have to add 8 feet to that measurement to get the total height of the legs for the A-frame. For example, to span a creek 4 feet deep, the legs of the A-frame should be about 12 feet or longer.

This total length allows for the distance from the butt ends of the A-frame legs up to the transom that supports the walkways. The transom should be about 1 foot higher than the banks of the creek. It also allows for the height from the walkways up to the tops of the legs to permit free passage for a person along the walkways.

Lay the A-frame subassembly out on the ground to check if the spars are long enough when lashed together for the two requirements mentioned above.

A-frame Legs. When you’ve determined the length of the spars for the legs of the A-frame, lash them together at the top with a shear lashing, not a diagonal lashing. This lashing should be made somewhat loose so that you can spread the spar legs apart to form the A-frame. As you spread the spar legs, the Shear Lashing will tighten. A little practice will show you how loose to make the shear lashing initially in order for it to be tight when the A-frame is formed.

View of A-frame and Attachment of Walkways
View of A-frame and Attachment of Walkways

Ledger and transom. To complete the A-frame, use square lashings to lash the bottom ledger across the legs about 1 foot from the bottom of the legs. Then lash a transom spar to support the walkways at the proper height in relation to the banks of the creek.

Walkways. The two 10-foot walkway sections are made as separate subassemblies. (Refer to “Bridge Walkways.”)

Assembly. After the walkways are made, take them to the assembly site along with the A-frame. Place the A-frame in the center of the creek and heel in the legs about 4 to 6 inches deep. As the legs are being heeled in, level the transom to accept the walkways in a level position.

Single A-Frame Bridge
Single A-Frame Bridge

When the A-frame is upright and the transom is level, lash both underspars on the walkways to the transom with strop lashings at three points. Finally, lash the cross spars at the ends of the walkways to stakes on the banks of the creek with Strop Lashings.

For safety, it’s best to add a light 1/4-inch guyline from the top of the A-frame to both sides of the creek to prevent it from tipping over.

List of Materials for a A-Frame Bridge

  • two 3-inch x 12-foot A-frame legs
  • one 2-inch x 6-foot bottom ledger
  • one 3-inch x 6-foot transom
  • four 3-inch x 10-foot walkway lateral spars
  • twelve 2-inch x 3-foot walkway cross spars
  • four 2-1/2-foot  walkway cross spars
  • two 2-inch x 10-foot walkway planks
  • four stakes

Single Trestle Bridge

Single Lock Bridge

Introduction to Pioneering

Link to: Older Pamphlet Info.The following text is by Adolph E. Peschke as presented in the 1998 printing of the 1993 edition of the Pioneering Merit Badge Pamphlet:

Pioneering is the knowledge and skill of using simple materials to build structures that are used in a wide range of Scouting activities. These skills are sometimes referred to as “backwoods engineering.”

Down through the ages, people have used ropes, spars, and simple hardware to build bridges, towers, and even their own shelters. In the early development of our country, pioneering methods were used in mining and transportation, to clear the wilderness, and to build roads and bridges. So it is understandable that the term “backwoods engineering” was applied.

The same skills can be used by Scouts to build pioneering projects ranging in complexity from a simple camp gadget to a signal tower.

Whatever the project, the same applied principles of physics, geometry, and math are used to build pioneering projects and structures. But, keep in mind that all the information (in this pamphlet*) is eventually used for a practical, hands-on application—that is, to build something.

Pioneering is a good foundation for many Scouting activities. You must learn, and then use, such disciplines as planning ahead and teamwork. You can also put to use the basic skills learned in rank advancement, such as knot tying.

But most of all, pioneering provides a practical way to experience the joy of accomplishment when you’ve built something that is needed for yourself or others; it can be something that makes living in camp easier and more comfortable. Pioneering can be both fun and challenging when you use your skill and knowledge to choose the right materials (ropes and spars) and build a usable structure.

The basics of pioneering, such as tying knots, making lashings, using rope tackle, constructing anchors, and basic rope knowledge can be done at home. The projects and structures (shown in this pamphlet**) can usually be constructed with materials available at summer camp or at council camping events.

* SAFE PIONEERING

* ROPE-TOSS-LOG-LIFT CHALLENGE

ROPE FOR PIONEERING AND CAMP USE

KNOT-TYING TERMINOLOGY

TIMBER HITCH

ROUNDTURN WITH TWO HALF HITCHES

ROLLING HITCH

BUTTERFLY KNOT

CARRICK BEND

CONSTRICTOR KNOT

WATER KNOT

PIPE HITCH

PRUSIK

SPLICING ROPE

* MAKING ROPE

WHIPPING

ANCHORING PIONEERING PROJECTS

ROPE TACKLE

LASHING

JAPANESE MARK II SQUARE LASHING

MAKING A TRESTLE

BRIDGE WALKWAYS

PIONEERING PROJECTS

** SINGLE TRESTLE BRIDGE

** SINGLE LOCK BRIDGE

** SINGLE A-FRAME BRIDGE

** 14′ DOUBLE LADDER SIGNAL TOWER

** DOUBLE A-FRAME MONKEY BRIDGE

PIONEERING KIT