Quantcast Chapter 4. Inspection of Glulam Arches

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CHAPTER 4. INSPECTION OF GLULAM ARCHES
Section 1. SIGNS OF DISTRESS
Elements of a typical glulam arch are shown in Figure 4-1. Any of the follow-
ing signs of distress (Figs. 4-2 - 4-6) indicate a need for more detailed investiga-
tion as described under PROCEDURES in Chapter 2.
4.1.1 DEFLECTION. Arches should maintain their original shape without
noticeable change unless there is a problem such as delamination. loose connec-
tors. or some type of wood failure. Excessive deflection at the crown can usually
be detected visually by the flat appearance instead of the continuation of the curve.
There may also be evidence of crushing or splitting at connectors. In extreme
cases there will be a downward deflection at the crown joint. Such a deflection
will often result in roof leaks and be accompanied by water stains. The amount
of deflection is difficult to assess since there is no reference point unless
measurements from the crown to the floor were recorded at the time of con-
struction. In some cases an estimate of the deflection can be made by comparing
the crown-to-floor distance with that of an arch that appears in good condition.
Any flattening of the crown should receive a rating of 60. A slightly downward
deflection should be rated 20 (Figs. 4-6B and 4-5C).
Because of the outward thrust at the ends of the arch. some outward displace-
ment may occur. Such displacement may be evident as a slight offset at the con-
nector (Fig. 4-6B). Either of these conditions is serious enough to require a 20
rating.
4.1.2 DELAMINATION.  Delamination of arches fabricated prior to the
late 1940's is often an indication of a water problem since the adhesives before
that time were not waterproof. Delamination also may result from poor bonding
techniques coupled with seasonal cycling of moisture content. Three factors that
affect the degree of strength reduction caused by delaminations are size. loca-
tion, and frequency. The most serious delaminations extend completely through
the cross section of the member. This makes the member in that area act as two
smaller members. Single complete delaminations near the top or bottom of the
cross section may be rated at 80 (Fig. 4-3A). If these delaminations are 3 feet
or more in length, or located near the center of the cross section, the rating should
be 60. More than one delamination in the same cross section or any delamina-
tion near a connector should result in a 40 rating (Fig. 4-5A). Numerous delamina-
tions or any delamination directly through a connector should be rated 20. At
the lowest rating there should also be signs of deflection or displacement. Where
delaminations do not extend through the member. their depth should be measured
with a thickness guage and noted under comments.
4-1





 


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