Figure 7-30.-Welded wire mesh fabric.
braces, walers, ties, and shebolts should be properly
secured before placing concrete.
Splicing Reinforcing Bar
Because rebar is available only in certain lengths,
it must be spliced together for longer runs. Where
splices are not dimensioned on the drawings, the bars
should be lapped not less than 30 times the bar
diameter, or not less than 12 inches.
The stress in a tension bar can be transmitted
through the concrete and into another adjoining bar by
a lap splice of proper length. The lap is expressed as
the number of bar diameters. If the bar is No. 2, make
the lap at least 12 inches. Tie the bars together with a
snap tie (figure 7-31).
CONCRETE CONSTRUCTION JOINTS
LEARNING OBJECTIVE: Upon completing
this section, you should be able to determine
the location of construction joints.
Concrete structures are subjected to a variety of
stresses. These stresses are the result of shrinkage and
differential movement. Shrinkage occurs during
hydration, and differential movement is caused by
temperature changes and different loading conditions.
These stresses can cause cracking, spalling, and
scaling of concrete surfaces and, in extreme cases, can
result in failure of the structure.
TYPES OF JOINTS
Stresses in concrete can be controlled by the
proper placement of joints in the structure. Well
discuss three basic types of joints: isolation joints,
control joints, and construction joints.
Isolation joints are used to separate (isolate)
adjacent structural members. An example is the joint
that separates the floor slab from a column. An
isolation joint allows for differential movement in the
vertical plane due to loading conditions or uneven
Isolation joints are sometimes called
expansion or contraction joints. In this context, they
allow for differential movement as a result of
temperature changes (as in two adjacent slabs). All
isolation joints (expansion or contraction) extend
completely through the member and have no load
Figure 7-31.-Bars spliced by lapping.