Wood Handbook, Wood as an Engineering Material

General Technical Report FPL–GTR– 190

the header differs depending on whether the joist hanger is
a face mount or top mount. Face-mount hangers transmit
loads through lateral loading of dowel-type fasteners; top-
mount hangers transmit loads by bearing on the top of the
header and lateral loading of the dowel type fasteners. De-
sign of the joist hanger varies from manufacturer to manu-
facturer. Examples of such plates are shown in Figure 8–28.

Design loads are limited to the lowest values determined by
experiment or by calculations. By experiment, design loads
for joist hangers are determined from tests in which a joist
is loaded at midspan and supported by two joist hangers
attached to headers, following ASTM D 7147 procedures.
The smallest value as determined by two different means
is the test design load for normal duration of load: (1) the
average load at 3.2-mm (0.125-in.) deformation between the
joist and header of at least six specimens and (2) the average
ultimate load of at least six specimens divided by 3.0 or the
least ultimate load for lower than six replicates divided by
3.0. Design loads for calculations are also highlighted in
ASTM D 7147.

Fastener Head Embedment

The bearing strength of wood under fastener heads is im-
portant in such applications as the anchorage of building
framework to foundation structures. When pressure tends
to pull the framing member away from the foundation, the
fastening loads could cause tensile failure of the fastenings,
withdrawal of the fastenings from the framing member, or

embedment of the fastener heads in the member. The fas-

tener head could even be pulled completely through.

The maximum load for fastener head embedment is related

to the fastener head perimeter, whereas loads at low embed-

ments (1.27 mm (0.05 in.)) are related to the fastener

head bearing area. These relations for several species at

10% moisture content are shown in Figures 8–29 and 8–30.

When annularly threaded nails are used for withdrawal ap-

plications, fastener head embedment or pull-through can be

a limiting condition and should be considered in design.

Figure 8–27. Typical load–slip curves for two types of
metal plate connectors loaded in tension.

Figure 8–28. Typical joist hanger connectors.

Figure 8–29. Relation between maximum embed-

ment load and fastener perimeter for several spe-

cies of wood.

Figure 8–30. Relation between load at 1.27-mm (0.05-

in.) embedment and fastener bearing area for sev-

eral species.