Expansion Joints in Buildings Technical Report No. 65 (1974) / Chapter Skim
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III. Discussion
III. Discussion
Pages 9-32
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From page 9... ...
Experience indicates that appropriate use of expansion joints presents a rather complex design problem and requires a thorough understanding of those factors that dictate their need as well as those that affect their ultimate performance after installation. The design, location, and performance of expansion joints can be influenced by such factors as building form, function, and economics; construction techniques; the varying characteristics of the different materials employed, changes of these characteristics under varying environmental conditions, and the physical relationship of one to the other; and the ability to withstand stresses resulting from dimensional changes.
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From page 10... ...
The configuration of a building is a parameter influencing the severity of the effects of temperature changes on a building and, as such, should be given consideration during the design process. Rectangular buildings and buildings with two axes of symmetry in plan with no internal open courts experience temperature-induced stresses that have relatively simple patterns, while buildings with a more complex configuration, such as U-shaped or L-shaped buildings, experience horizontal dimensional changes that result in complex stress patterns, particularly at re-entrant corners.
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From page 11... ...
Birmingham, Alabama Anchorage, Alaska Jan 1 April 24 Almose, Colorado May 8 Daytona Beach, Florida Jan 1 Dec 31 Oct 8 Sept 28 Dec 31 Construction Season Mean Temperature ___ ~ 50.6 60.4 70.3 Annual Mean Temperature (OF)
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From page 12... ...
Thus, with respect to expansion joint requirements, a differential temperature profile can be replaced by the superposition of a uniform temperature change corresponding to the change at the level of the centroidal axis of the member and a differential temperature change that causes no change in the overall length of the member.
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From page 13... ...
Type of Frame, Type of Connection to the Foundation, and Symmetry of Stiffness against Lateral Displacement Thermal effects on buildings with fixed-column bases are likely to be more severe than on buildings with hinged-column bases. Comparison of the behavior of two identical tall buildings, one with fixed-column bases and one with hinged-column bases, subjected to the same temperature changes indicates that both buildings underwent virtually the same dimensional changes in all levels above the first.
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From page 14... ...
The empirical approach is likely to be the simpler of the two, but is the more conservative. The analytical method requires that the designer fully evaluate and account for in the overall design the effects of all factors influencing the need for expansion joints (discussed in Section III.A)
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From page 15... ...
Curves for heated and unheated buildings (Figure 3) are used to relate the maximum allowable length of a building without expansion joints as a step function to design temperature changes.
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From page 16... ...
investigated expansion joint movement over a period of one year (September 1943 to August 19443 in nine federal buildings to obtain measurements of dimensional changes over a complete cycle of seasons.*
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From page 17... ...
Given the value for this coefficient of 3.3 for brick, 5.5 for concrete, and 6 for steel and the uncertainty of the assumption used to evaluate the temperature change on the basis of which the range from 2 to 5 was derived, the investigation seems to confirm that the upper levels of buildings undergo dimensional changes corresponding to the coefficient of thermal expansion of the principal material of which each is constructed.
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From page 18... ...
bent hinged at ground. In the multistory and multibay frame conditions illustrated in Figure 5, a temperature increase will produce a pattern of stresses and deformations similar to those of the single bent of Figure 4.
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H1 7 , H2 (b) H' 1 FIGURE 5 Analysis of multistory and multibay frame subjected to uniform temperature change (x = points of maximum bending moments and maximum shear forces)
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M-2) All frames were analyzed for a 100 OF uniform temperature increase and for a coefficient of thermal expansion equal to 6 per million degrees Fahrenheit.
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~4 ·rl o o $o o o A]
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From page 22... ...
. Therefore, if both ends of a frame are equally free to displace, the horizontal displacement of the outside joints of upper stories will be equal to one half of the unrestrained elongation of the frame corresponding to a temperature change, At, and a coefficient of thermal expansion, a; that is, A° ~At~l/2L)
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From page 23... ...
2. The Analytical Method The difficulties of categorizing every conceivable building configuration and the complexity of the stress and deformation patterns created by thermal change effects in buildings with other than a rectangular configuration make it impracticable to always determine the need for expansion joints on an empirical basis.
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From page 24... ...
For these reasons, the calculation of the design temperature change for heated and/or air-conditioned buildings should include a minimum empirical coefficient that will reduce the maximum temperature change to which the structure is expected to be exposed but will not give full value to the influence of internal temperature control. In the absence of technically sound data that dictate otherwise, the uniform design temperature change, CAt, can be satisfactorily determined by considering At = (TW-Tm)
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From page 25... ...
Most field experiences indicate that buildings with continuous masonry bearing walls should be provided with expansion joints at intervals not exceeding 200 feet and with additional subjoints in accordance with the recommendations of the Brick Institute of America and the National Concrete Masonry Association.* The portions of walls at and near the intersection of two walls, surfaces likely to be weakened by numerous openings for doors and windows, and the rigid connections between horizontal elements (particularly concrete or other stiff roofs)
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From page 26... ...
(2) Provide for an expansion joint (also called an "isolation" or "separation" joint)
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From page 27... ...
1. The width of the expansion joint should exceed the maximum potential dimensional changes by an amount sufficient to prevent the complete closing of the joint and, simultaneously, provide for construction tolerances and nature of filler material.
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From page 28... ...
b. If, however, either segment has one end substantially stiffer than the other, the dimensional change resulting from temperature fluctuation will be distributed unevenly between the two ends of such a segment with comparatively less deformation 'developing at the stiff end.
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From page 29... ...
The term 50 OF in the factor (50°F+Ate) represents a temperature equivalent to the dimensional changes resulting from potential of swelling of clay masonry under moisture conditions.
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From page 30... ...
Temperature fluctuations also effect dimensional changes in the vertical direction and the performance of the nonstructural building components; while such effects are not considered in this report, they cannot be ignored during design. Execution of the most efficient design with respect to the total effects of temperature changes on building performance requires criteria developed on a data base more technically sound than exists at present.
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From page 31... ...
. Buildings supported on masonry walls require special examination since effects of temperature changes on the performance of such buildings will vary according to the type of masonry material or combinations of material used.
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