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OCR for page 3
II
RECOMMENDATIONS
A. GENERAL
1. The structural analysis of a building should include a determination of
the need for thermal expansion joints in view of the potential impact
of temperature-produced dimensional changes on structural integrity and
building serviceability.*
2.
As a minimum, each of the following factors should be examined and taken
into account during expansion joint location and design:
a. Dimensions and configuration of the building.
b. Design temperature change, which should be computed in accordance
with the formula:
At = (TW-Tm) or (Tm-Tc),
whichever is greater, where,
(1)
Tm = the mean temperature during the normal construction season in
the locality of the building. For the purpose of this report,
the normal construction season for a locality is defined as
that contiguous period in a year during which the minimum daily
temperature equals or exceeds 32 OF. [For example, the normal
construction season for Anchorage, Alaska, is 5-1/2 months
(April 24-October 8) and for Birmingham, Alabama, is year-round
(January-December).]
T = the temperature exceeded, on the average, only 1 percent of the
w time during the summer months of June through September in the
locality of the building. (In a normal summer there would be
approximately 30 hours at or above this design value.)
T = the temperature equaled or exceeded, on the average, 99 percent
c of the time during the winter months of December, January, and
February in the locality of the building. (In a normal winter
there would be approximately 22 hours at or below this design
value.)
*Dimensional changes in the vertical direction and methods of fastening non
structural elements to the structural frame of the building do not fall
within the scope of this report.
3
OCR for page 4
Values for Tw, Tm, and Tc for different localities in the United
States are included in Appendix B. The Tw and Tc values were
extracted from the ASHRAM Handbook of Fundamentals (1972) published
.
by the American Society of Heating' Refrigerating and Air-Conditioning
Engineers.
Provision for temperature control.
d. Type of frame, type of connection to the foundation, and symmetry of
stiffness against lateral displacement.
e. Materials of construction.
B. CRITERIA FOR DETERMINING THE NEED FOR EXPANSION JOINTS
The need for thermal expansion joints in buildings may be determined
initially on an empirical basis. If results are deemed by the designer to
be too conservative or if the empirical approach is not sufficiently compre-
hensive to be applicable to the type of structure being investigated, a more
precise analysis should be undertaken. In either case, the following cri-
teria should be utilized in the absence of more rational approaches.
1. Empirical Approach
a. For buildings having a beam-and-column or slab-and-column structural
frame,* the maximum length of the building** without expansion joints
should be determined in accordance with Figure 1 on the basis of the
design temperature change (At) in the locality of construction.
For buildings supported by continuous exterior unreinforced masonry,
expansion joints should be placed at intervals not exceeding 200 feet.
In addition, intermediate subjoints should be positioned and spaced
in accordance with the recommendations of the Brick Institute of
America (BIA) and the National Concrete Masonry Association (NCMA).***
*A building should be considered to have a beam-and-column or slab-and-
column structural frame even if intermittent interior shear walls or other
stiffening elements are incorporated in the frame and even if the frame is
supported on an above-grade reinforced concrete continuous perimeter base
wall. The provisions of this recommendation do not apply to buildings
with fully exposed exterior frames placed outside the cladding elements.
**The maximum diameter or diagonal of a round, elliptical, or closed poly-
gonic building should be considered its maximum dimension.
***At the time of this writing such recommendations are provided in the BIA
publications, Differential Movement, Cause and Effect (No. 18, April 1963),
Differential Movement, Expansion Joint (No. 18A, May 1963), and Differ-
ential Movement, Flexible Anchorage (No. 18B, June 1963) and the NCMA pub
-
lication, Control of Wall Movement with Concrete Masonry (TEE 3, 1972).
4
OCR for page 5
a, 500
to
of
J
400
z
-
m
m 200 _
o
J
30C
a: 10C
Rectangular Multiframed
Configuration with
Symmetrical Stiffness
.Nonrectangular Configuration
(L,T,U Type)
\
-
, , 1 1 1 1
10 20 30 40 50 60
DESIGN TEMPERATURE CHANGE (°F)
Stee
Anv Material
1 1 1
70 80 90
FIGURE 1 Maximum allowable building length without use of expansion joints
for various design temperature changes. These curves are directly applicable
to buildings of beam-and-column construction, hinged at the base, and with
heated interiors. When other conditions prevail, the following rules are
applicable:
(a) If the building will be heated only and will have hinged-column bases,
use the allowable length as specified;
(b) If the building will be air conditioned as well as heated, increase the
allowable length by 15 percent (provided the environmental control
system will run continuously);
(c) If the building will be unheated, decrease the allowable length by 33
percent;
(~) If the building will have fixed-column bases, decrease the allowable
length by 15 percent;
(e) If the building will have substantially greater stiffness against
lateral displacement at one end of the plan dimension, decrease the
allowable length by 25 percent.
When more than one of these design conditions prevail in a building, the
percentile factor to be applied should be the algebraic sum of the adjustment
factors of all the various applicable conditions.
s
OCR for page 6
2. Analytical Method
For those situations in which the need for thermal expansion joints
cannot be determined on an empirical basis or in which the empirical
approach provides a solution that professional judgment indicates is
too conservative, a detailed analysis like that discussed in Section
III.B.2 should be performed. The analysis should include identification
and evaluation of the effects of the factors listed in III.A.2, as well
as a stress-strain analysis of the effects on the structural frame of a
uniform temperature change, C At, where At is computed as described
under III.A.2.b and the coefficient C is:
a. Equal to unity for unheated buildings,
b. Equal to 0.70* for buildings heated but not air conditioned, and
c. Equal to 0.55* for buildings heated and air conditioned.
C. SUGGESTED PROCEDURES FOR DESIGN OF EXPANSION JOINTS
2.
The following guidelines are recommended as bases for expansion joint design
and location:
Expansion joints should extend over the entire height of the building
from the top of the foundation footing (or perimeter basewall) through
the roof. The resulting two separate but adjacent structural frames
may share the same footing.
The upper bound (UB) of horizontal joint closing in buildings with a
beam-and-column frame should be calculated from the expression:
UB = 6 10 6 At .L
where Ate = (TW-Tm) in degrees Farenheit and L = effective length.**
(2)
*The C values of less than unity are based on the assumption that the
environmental control system in the building would operate continuously.
Hence, the lower C value cannot be applied if it is anticipated that the
environmental control system will be regularly shut down for extended
periods of time (i.e., 2 days or longer). Any deviation from these values
should be quantitatively justified.
**The effective length should be considered the average length of the
building segments abutting the joint. If either building segment has one
end substantially stiffer to lateral displacement than the other, the
length of the building segment used for computing the effective length L
should be considered 50 percent greater if the stiff end is farther from
the joint and 33 percent smaller if the stiff end is the one abutting the
J olnt e
6
OCR for page 7
3. To allow for construction tolerances and compressibility and expandability
of the joint sealants, the expansion joint width (W), in inches, should
be computed as follows:
W = Cl-UB,
(3)
where UB is as computed in Eq. (2), and C1* = 2.0 for unheated buildings,
1.7 for buildings heated but not air conditioned, or 1.4 for buildings
for both heated and air conditioned.
For buildings with continuous exterior bearing walls of clay masonry, the
maximum spacing of the expansion joints should be limited to 200 feet,
and the minimum required joint width (W), in inches, should be calculated
from the following expression:
~ = Cl L(50°F Ate)~4 10 ),
where Ate, C1, and ~ are as defined for Eq. (2) and (33.
5.
(4)
The minimum width of an expansion joint should in no case be less than
1 inch. If the computed expansion joint width exceeds 2 inches, special
consideration should be given to the materials and methods of joint con-
struction to ensure that the joint itself will be able to withstand the
distress caused by substantial movement at the joint. (Additional con-
sideration should be given to architectural and structural details to
ensure that the building will tolerate the inherent deformations without
loss of serviceability.)
6. Expansion joint design should permit uninterrupted relative motion of
the abutting building segments, prevent the entrance of water or debris,
and allow for easy inspection and maintenance.
D. AREAS OF FUTURE RESEARCH
Research directed toward the establishment of a valid data base for the
development of technically sound criteria for the design and location of
expansion joints should be initiated immediately. Special attention should
be given to the following:
1. The collection, classification, and interpretation of data on building
damage attributable to temperature fluctuation.
*Coefficient C1 differs from coefficient C in that C1 takes into considera-
tion construction tolerances and the compressibility/expandability of the
joint filler, as well as temperature.
7
OCR for page 8
The development of data necessary for the correlation of ambient
temperature with temperatures of building components (structural and
nonstructural) at the periphery and within buildings for different
building types and materials.
3. The development of data for the correlation of ambient temperature
fluctuations with temperature gradients existing within building com-
ponents under different conditions of exposure and types and methods
of insulation.
4. Analytic and experimental investigation that will lead to the correlation
of stresses in the various building components to the different patterns
of temperature fluctuations and gradients and to the different types of
assembly component (connectors).
The effects of temperature change on the performance of buildings supported
on masonry walls should be examined for each type of masonry material or com-
bination of materials likely to be used, and each type or combination of
materials should be investigated with respect to construction details, con-
nections of walls to horizontal and vertical components (roofs, floors,walls,
and partitions at right angles), optimal spacing of joints, and extent of
joints.
8
Representative terms from entire chapter:
expansion joint
