Testing at the University of California, Berkeley
Although wood faced, expanded polystyrene SIPs make up the majority of the SIP market, there are emerging alternative facing materials and insulations available to manufacturers. Likewise, although simple plywood splines make up the majority of the most common SIP to SIP connections, other connections are available. However, as an industry, SIPs have not been comprehensively tested as a composite system and optimized as a composite assembly. FAS has worked with Professor Khalid Mosalam of University of California, Berkeley and the Structural Insulated Panel Association (SIPA) to address this shortcoming, developing a test matrix of SIP specimens with varying facing materials, laminated to a combination of insulating cores with alternative connection details.
While previous studies have been limited to the comparison of SIPs to stick frame construction alternatives, FAS will work to determine which insulation maximizes the energy saving of the assembly verses the panel’s structural performance to resist lateral loads and shear forces. As the performance specifications for SIPs are developed both in terms of the thermal and seismic requirement, a design strategy can be developed to engineering new composite systems, facing materials, connections, and insulation materials to optimize SIPs for thermal performance and structural loading.
Pseudo-dynamic testing strategies will be used in place of conventional seismic test. The traditional approach to conducting simulated cyclic seismic test is to run monotonic tests to attain the load-deformation curve and from that curve to obtain a reference deflection, Δr=0.6Δm. From the maximum load, Pmax, the deformation at 0.8Pmax on the descending branch (deformation capacity, Δm) is obtained (deformation at Pmax, i.e. Δpmax, can also be determined). Both factors (0.6 and 0.8 above) are completely arbitrary, being largely based on seismic testing of other materials, e.g. reinforced concrete or steel. This justifies resorting to the more realistic pseudo-dynamic experimentation of the component tests.
The SIP specimens will be tested to collect data about the performance under cyclic (push and pull loading pattern following common test practices such as the Curee test protocol developed for wood components and systems) loading conditions, which are useful for assessment of the capacity (e.g. ductility, energy dissipation, etc.) of the test structure.
Attention will be given to the connections between panels forming a single shear wall capable of resisting seismic loading. In addition, we will conduct initial baseline testing of monolithically cast shear wall to evaluate the effect of introduced connections and improve the connection details. It may be useful to consider areas of local density variations near connections to determine the density contribution and/or voids to panel behavior and their effect on sound connections between panels in a shear wall system. Preliminary testing designed to calibrate testing equipment has already highlighted the difference between conventional methods and SIPs with respect to seismic performance. Initial results show SIPs can withstand up to 50 percent more seismic force before failure, as well as a more brittle failure (compared to a more gradual decrease observed in conventional building methods).
A paper detailing results of some of this testing can be found here.
Upon the project’s completion, FAS will use the results and analysis to maximize SIP building systems in hopes of the construction industry adopting SIPs on a larger scale.