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Two test programs performed by the National Bureau of Standards (NBS) in 1970 and 1971 on wood-framed houses are discussed as cases in point of the use of full-scale testing for establishing and validating structural performance requirements.
In one study, field tests were conducted on an as-built single-family detached house to measure its deflection characteristics under lateral loading. The test data were used to determine whether the drift limitations required in the design of medium- and high-rise buildings are applicable to low-rise buildings. A series of tests was conducted to determine the stiffness of the house when subjected to simulated wind loading. Load was applied alternately at the second floor level and at the eave line of the two-story house. Horizontal and vertical movements of the building were measured at discrete points on the two levels, for the two loading applications and superposition was used to determine the combined effect. As a result of the two test series, it was concluded that: “The measured second-story drift for the house was considerably less than that derived using the drift limits specified for medium- and high-rise buildings in most areas of the United States.”
In the second study, a series of laboratory tests was conducted on a 3.7-m wide by 18.3 m long (12-ft wide by 60-ft long) factory-built housing module. The tests were to determine the strength and stiffness of a typical wood-frame housing unit and to provide baseline data against which the performance of less traditional construction could be compared. Four of the six tests in the series involved the application of lateral load: (1) monotonic racking, (2) repeated racking, (3) reversals of racking, and (4) racking of capacity. Load was applied perpendicular to the long walls at the eave line of the one-story module using a series of hydraulic jacks to simulate the effects of either wind or earthquake loading. Horizontal and vertical displacements were measured at a number of discrete points. The measured response at various design load levels was compared to the limit states specified in design criteria prepared by NBS for the U.S. Department of Housing and Urban Development's (HUD) Operation Breakthrough. Based on an analytical model used to condition the test results, it was concluded that 1.01 kN/m2 (21 psf) was the maximum static wind pressure at which the housing system could satisfy the conventional drift limitation (that is, h/500, where h connotes height above ground level) applied to medium- and high-rise buildings.
cyclic loading, drift, housing, modules, lateral load, lateral resistance, lowrise construction, racking stiffness, wind load, wood-frame construction, structures
Structural research engineer, Structural Engineering Group, Center for Building Technology, National Bureau of Standards, Washington, D.C.