User's Manual

Cast Beam Structures Set ME-7009

Reinforced Concrete

Reinforced concrete has reinforcement bars (“rebar”), grids, plates or fibers incorporated to increase the tensile strength of the con-

crete. Since steel is a material that has high strength in tension, it is commonly placed in concrete to add strength and to help the

concrete resist tension. Reinforced concrete is sometimes described as precast concrete.

Typical reinforced concrete uses reinforcing bars that are round in cross-section and corrugated to improve the bond between the

concrete and the steel. The coefficient of thermal expansion for concrete is similar to that of steel, so the concrete conforms to the

surface details of the steel, and the concrete’s alkaline chemical environment produces a film on the surface of the steel that makes

it more corrosion-resistant.

Prestressed Concrete

Prestressed concrete is an important method for overcoming the concrete’s natural weakness in tension. The method can be used to

produce beams, floors, or bridges with a longer span than is practical with reinforced concrete. One type of prestressed concrete is

pre-tensioned or pre-loaded concrete.

Pre-tensioned concrete is cast around already tensioned tendons (generally of high tensile steel cable or rod). The bond between the

tendon and the concrete protects the tendon and allows for direct transfer of tension. However, pre-tensioned concrete requires

stout anchoring points for the tendons so the tendons are usually in a straight line. Most pre-tensioned concrete elements are prefab-

ricated and then transported, which limits their size.

Making a Pre-tensioned Cast Beam

Assemble the Mold

• Assemble the rebar member and the mold. One way to do

this is to hold the mold in one hand and the rebar member in

the other.

• First, slide one end of the rebar into one end of the mold

until the tabs of the mold make contact with the notches on

the rebar member.

• Then rotate the rebar member down into the mold so that the

tabs on the mold click into place on the rebar member.

Assemble a Tension Fixture

One way to stretch the rebar member is to build a tension fixture

with Structure Set members (see the next page), attach one end

of the rebar member to the tension fixture, and then pull the

other end of the rebar member (for example, with weights hang-

ing on the end of a cord suspended over a pulley). You can use

the ME-7009 Cast Beam Structures Set or the ME-6992A

Advanced Structures Set.

Caution: Do not stretch the rebar member with more than 100 N of force (the hanging weight of about 10 kg of mass).

Ta b

Tab

Rebar

Member

Mold

Assembled Rebar

Member and Mold

1. Slide the rebar into

one end of the mold.

2. Rotate the rebar into

the other end of the mold.