Static structures (e.g. – buildings) – Processes – Column – mast – etc. – construction
Reexamination Certificate
1995-09-27
2001-03-13
Chilcot, Richard (Department: 3635)
Static structures (e.g., buildings)
Processes
Column, mast, etc., construction
C052S218000, C052S219000, C052S745210
Reexamination Certificate
active
06199345
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to a chimney. More particularly, the invention relates to seismic upgrades of pre-existing household chimneys in order to meet earthquake standards.
BACKGROUND OF THE INVENTION
In older existing homes built in areas prone to earthquakes, brick chimneys may crack or be completely destroyed during an earthquake. If a brick chimney is significantly damaged during an earthquake it may cause bricks to fall to the ground possibly injuring persons or property nearby. To avoid this in certain cities and counties, earthquake standards for new chimney construction have been introduced. The Uniform Building Code sets minimum standards while cities may impose higher standards for new chimney construction. Furthermore certain cities have required that preexisting chimneys be brought up to code when any work is to be performed upon the masonry unit of a chimney or fireplace. Also, real estate sales contracts were written which required a seller to repair the fire, safety, and structural defects of older pre-existing chimneys upon the transfer of title to a home. Previously to meet building codes it required the removal of all or portions of the old chimney and then construction of a new chimney that would meet the building codes.
In older homes and geographic areas without earthquakes, chimneys may be non-reinforced.
FIG. 1A
represents a cutaway view of a non-reinforced chimney
112
A resting upon a fireplace
110
. The outer facade of the fireplace
110
and chimney
112
, also referred to as the brick masonry unit
128
, is made up of brick
160
and mortar
162
. Within chimney
112
A there is an airspace
103
and a chimney liner
104
. Many older homes may not have the chimney liner
104
and rely on the brick masonry unit
128
to direct heat and smoke up through the chimney and out into the atmosphere.
Chimneys may be designed into a home in three broad categorical groupings. One group of chimneys may be designed and constructed such that the fireplace and chimney are external to a home and the back face of the chimney adjoins a homes wall for a significant portion of the chimney height. This first group will be referred to as “external wall chimney”. A second group of chimneys may designed and constructed such that the fireplace and chimney are external to a home and the chimney is freestanding above the roof-line for a significant portion of the chimney height. This second group will be referred to as “external roof chimney”. A third group of chimneys may be designed and constructed such that the fireplace is completely internal to the home and the chimney only rises above the roof for a short portion of the chimney. This third group of chimneys will be referred to as “internal chimneys”. The construction codes for a given city will vary depending upon the above type of chimney that is designed and constructed in a home. For example, pre-existing internal chimneys require no horizontal reinforcement or anchorage because there is little danger that an internal chimney will fall on persons or property.
As earthquakes caused damage to chimneys in geographic areas prone to earthquakes, real estate sales contracts were written which required a seller to repair the fire, safety, and structural defects of older pre-existing chimneys upon the transfer of title to a home. Initially only a horizontal tie or anchorage at the roof-line or plating was installed.
FIG. 1B
represents early attempts to satisfy the horizontal reinforcement requirements for pre-existing external wall chimneys that were flush to a house wall. In
FIG. 1B
, chimney
112
B has an external strap
120
attached to an external wall
125
by use of bolts
121
. This is similar to a brace illustrated in U.S. Pat. No. Des. 285,411 invented by Nathaniel J. Mahoney having a filing date of Nov. 30, 1983. One disadvantage to the use of the external strap
120
is that chimney
112
B may break or crack just above the external strap
120
. Another disadvantage to the use of the external strap
120
is that the bolts
121
may break free from the wall
125
because of the pulling force exerted by the weight of the chimney is so large that the wall can not bear it. Generally the bolts
121
are inserted into holes in the wall
125
that have been drilled through cement. Another disadvantage to the use of the external strap
120
is that it does not satisfy the Uniform Building Code requirements for horizontal reinforcement and anchorage of preexisting chimneys. It is desirable that an external strap or anchor for a preexisting chimney be bolted to the internal frame of a house and meet current building code requirements.
As stronger earthquakes occurred, it became known that a horizontal anchorage such as illustrated by
FIG. 1B
was not enough to prevent parts of a chimney from falling in the case of the external wall or external roof chimney types. Vertical reinforcement was introduced into the pre-existing chimney.
FIG. 1C
illustrates an early attempt at providing the vertical reinforcement of a preexisting chimney in order to meet these initial codes. Chimney
112
C rests upon a fireplace
110
. A mortar cap
114
completes the top of the chimney
112
C while a spark arrestor
116
is attached to either a chimney liner
104
or the mortar cap
114
.
In order to reinforce the chimney and meet the initial codes, the mortar cap
114
was removed and a hole
106
was drilled into the mortar of the firebox at each corner of the chimney. A mortar cement
105
was placed in each hole
106
and steel rebar
100
of one-half inch or five-eights inch diameter extending the length of the chimney
112
C was inserted into each hole
106
. A mortar cement
102
was poured into the void between the brick chimney and the chimney liner
104
to further solidify the chimney. To reinforce the mortar cap, a bond beam
108
of two wraps of a No. 2 pencil steel rod was placed around the four steel rebars
100
. While this technique met the earlier code for vertical reinforcement of pre-existing chimneys it did little to meet the horizontal reinforcement and anchorage required by newer codes. Also the use of cement as a filler added extra weight to a chimney such that foundations were unable to support it.
The 1991 Uniform Building Code for new home and new chimney construction in earthquake prone zones, such as seismic zone
4
, require a chimney to be affixed to a house's frame in order that a chimney does not fall away from the house during an earthquake.
FIG. 2A
illustrates the use of a mason's anchor strap
220
that is attached to a wooden beam
221
by nut/bolt assemblies
222
and
223
that satisfies the 1991 Uniform Building Code seismic anchorage requirement for new chimney construction. The mason's anchor strap
220
is inserted into the chimney while it is being constructed. The wooden beam
221
is attached to the homes joists and the mason's anchor strap
220
is attached to the wooden beam
221
during the homes construction. Horizontal reinforcement in newly constructed chimneys is provided by horizontal reinforcing ties
208
A-N at eighteen inch intervals using a minimum of one quarter inch diameter steel such as a number two pencil rod that horizontally ties the vertical steel rebars
100
together.
FIG. 2B
illustrates a new mason's anchor strap
220
with the nut/bolt assemblies
222
and
223
. The mason's anchor strap
220
has a flat tongue
234
with two holes
232
and
233
for bolting the strap to either wooden beam
221
or wooden beam
219
. Having two holes
232
and
233
in the mason's anchor strap
220
reduces the strength of the strap and is disadvantageous. The flat steel tongue of the anchor strap
220
is twisted ninety degrees at
235
such that a hooked blade
236
is created. The hooked blade
236
is twisted around the steel rebar
100
such as illustrated in FIG.
2
C and then the tongue
234
is bolted to the wooden beam
221
or
219
.
FIG. 2C
illustrates how two mason's anchor straps
219
and
220
a
Alford William E.
Chilcot Richard
LandOfFree
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