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Expansion Joints in Buildings: Technical Report No. 65 (1974)

Chapter: II. Recommendations

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Suggested Citation:"II. Recommendations." National Research Council. 1974. Expansion Joints in Buildings: Technical Report No. 65. Washington, DC: The National Academies Press. doi: 10.17226/9801.
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Suggested Citation:"II. Recommendations." National Research Council. 1974. Expansion Joints in Buildings: Technical Report No. 65. Washington, DC: The National Academies Press. doi: 10.17226/9801.
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Suggested Citation:"II. Recommendations." National Research Council. 1974. Expansion Joints in Buildings: Technical Report No. 65. Washington, DC: The National Academies Press. doi: 10.17226/9801.
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Page 5
Suggested Citation:"II. Recommendations." National Research Council. 1974. Expansion Joints in Buildings: Technical Report No. 65. Washington, DC: The National Academies Press. doi: 10.17226/9801.
×
Page 6
Suggested Citation:"II. Recommendations." National Research Council. 1974. Expansion Joints in Buildings: Technical Report No. 65. Washington, DC: The National Academies Press. doi: 10.17226/9801.
×
Page 7
Suggested Citation:"II. Recommendations." National Research Council. 1974. Expansion Joints in Buildings: Technical Report No. 65. Washington, DC: The National Academies Press. doi: 10.17226/9801.
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Page 8

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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

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

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

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

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

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

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Many factors affect the amount of temperature-induced movement that occurs in a building and the extent to which this movement can occur before serious damage develops or extensive maintenance is required. In some cases joints are being omitted where they are needed, creating a risk of structural failures or causing unnecessary operations and maintenance costs. In other cases, expansion joints are being used where they are not required, increasing the initial cost of construction and creating space utilization problems.

As of 1974, there were no nationally acceptable procedures for precise determination of the size and the location of expansion joints in buildings. Most designers and federal construction agencies individually adopted and developed guidelines based on experience and rough calculations leading to significant differences in the various guidelines used for locating and sizing expansion joints. In response to this complex problem, Expansion Joints in Buildings: Technical Report No. 65 provides federal agencies with practical procedures for evaluating the need for through-building expansion joints in structural framing systems. The report offers guidelines and criteria to standardize the practice of expansion joints in buildings and decrease problems associated with the misuse of expansions joints. Expansions Joints in Buildings: Technical Report No. 65 also makes notable recommendations concerning expansion, isolation, joints, and the manner in which they permit separate segments of the structural frame to expand and to contract in response to temperature fluctuations without adversely affecting the buildings structural integrity or serviceability.

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