|CUREE-Caltech Woodframe Project
Element 1 - Testing & Analysis
Task 1.1.3: Shake Table Tests Simplified Model
PI: R.O Foschi, F. Lam, H. Prion, and C. Ventura (University of British Columbia)
Note: This research program is conducted at the University of British Columbia under a project entitled "Reliability and design of innovative wood structures under earthquake and extreme wind conditions" funded by Forest Renewal BC Research Program.
Mechanics Based Structural Model of Woodframe Systems
A non-linear finite element dynamic analysis model (LightFrame3D_Dynamic) has been successfully developed to study the system performance of 3-dimensional timber light-frame buildings under seismic excitations. One of the uniqueness of the model is the implementation of a mechanics-based representation of the load-deformation characteristics of individual panel to frame nail connections. This approach requires as input basic material properties and static load-deformation characteristics of the connections. The model can be used to study light-frame systems with varied material applications and different structural components under combined loading conditions. Good agreement between model predictions and experimental data of single shear walls was achieved.
Shake Table Tests: Full-Scale 3D Models
In cooperation with private consultants and Simpson Strong-Tie, a large shaker facility was developed in UBC Civil Engineering's Structures Laboratory. This shaker is capable of supporting a full-size structure (two-story house), with horizontal input motion replicating the ground motion of an earthquake. Sixteen subsystem tests of "California" construction systems, fourteen subsystem tests of "BC" construction system, and fourteen tests of 2-story house have been conducted.
Each sub-system test comprised of two or more shear walls, one storey in height with a second floor diaphragm connecting all shear walls. Concrete inertia blocks were placed on the second floor diaphragm to emulate the mass of the complete two-storey house. The full-scale tests were conducted on two-storey single-family house (total floor area of 93 m2) with designs based on current construction practice prepared by a local consulting firm. Some of the features considered are: different type of exterior wall sheathing including horizontal boards for first storey and OSB for second storey; interior walls of gypsum wall board; asphaltic shingle roof with underlying OSB sheathing; and influence of exterior stucco.
Shake Table Tests 3D Simplified Models
Box type structures 2.44 m high with a footprint of 2.44 m x 3.05 m were investigated. On the wide side of the structure, a significant opening of 2.44 m wide x 2.03 m high and a pony wall of 0.61 m wide were introduced. Steel inertia plates of 7500 kg were placed on the second floor diaphragm to emulate the mass of a complete two-storey system. Together with the inertia plates, the second floor diaphragm can be considered as a rigid system.
The systems were tested under monotonic loading, and single and bi-directional dynamic loading (Joshua Tree Station 1992 Landers California). During the single directional dynamic test a peak ground acceleration of 0.4 g was recorded on the shake table.
In the bi-directional dynamic table test, peak ground accelerations of 0.26 g were recorded on the shake table for both directions. Significant torsional response in the structure was observed in all tests. The box models suffered significant damage in the dynamic tests with the major failure modes of nail withdrawal and nail pull through. The experimental data will be used to further validate the structural analysis model.