Dynamic Characteristics of Woodframe Structures

The main objective of Task 1.3.3 of the CUREE-Caltech Woodframe Project is to determine the dynamic characteristics of woodframe buildings and to develop a period formula specific for wood structures by regressing on appropriate structural characteristics. Much research has been done on the dynamic and cyclic characteristics of wood subsystems and connection panels, but a literature review shows that full-scale testing of wood shearwall buildings has been sparse. This scarcity emphasizes the importance of Task 1.3.3 because the dynamic characteristics of woodframe buildings as a whole must be better understood in order to establish code requirements for their safe and cost-effective design, and to improve current building practices.

Through analysis of recorded earthquake response and by forced and ambient vibration testing, Task 1.3.3 has developed a database of periods and damping ratios of woodframe buildings. The focus is on the fundamental mode behavior of low-rise shearwall buildings, the predominant type of woodframe construction in North America, as the fundamental mode tends to dominate the dynamic characteristics. A regression analysis was performed on the period database using building height to produce a simple but reasonably accurate period formula for design of woodframe buildings. This formula gives shorter periods than the 1997 UBC period formula, but it should be noted that all test results, including the seismic data, are at small drifts (in the order of 0.0004 or less). Despite these low amplitudes, the equivalent viscous dampings for the fundamental modes were usually more than 10% of critical during earthquake shaking.