Can a precast concrete insulated wall panel provide the same level of protection as a solid precast wall panel when exposed to blast generated pressure loads?
With the increased scrutiny in energy savings as directed by new ASHRAE codes, architects are utilizing the inherent benefits of insulated precast concrete wall panels to provide true continuous insulation, moisture vapor control and an unmatched design aesthetic. Until recently however, when faced with a project with a blast load requirement, architects and structural engineers had bypassed insulated precast concrete wall panels because little research had been done as to their capability to provide a level of protection after a blast event. The data received from recent full scale testing of non-load bearing, prestressed, insulated concrete panels at the Air Force Research Lab, Tyndall AFB, proves that an insulated precast concrete panel is a viable solution for buildings exposed to blast pressures at moderate standoff distances.
Insulated precast concrete wall panels are typically constructed using an interior and exterior wythe of concrete, of equal thickness, separated by a layer of rigid insulation. Thickness of the concrete wythe is determined by analyzing the loads on the panel which could be governed by stripping the panel from the forms or through wind exposure and/or seismic loading. The result of this analysis yields a panel cross section that is relatively deeper than an equivalent solid panel with nearly the same mass, which is ideal to resist the dynamic pressures experienced during an explosion.
For the testing program conducted at the Air Force Research Lab, two insulated precast wall panels were constructed; a panel with solid zones connecting the wythes of concrete and a panel that used a carbon fiber reinforced polymer wythe connector. A solid panel was also constructed and was used as a control sample. All panels were of equal length and width and supported in the test apparatus at the top and bottom of the panel and were assumed to be simply supported. The panels were exposed to five progressively higher explosive blasts.
The results of this testing program make it clear that the use of insulated precast concrete wall panels as a cladding system for buildings exposed to blast loads provide a level of protection equal to that of solid concrete panels of equal mass. All panels experienced significant flexural cracking and permanent deflections through all blast intensities, though it’s important to note that no panel experienced catastrophic failure.
Although more testing and analysis should be considered, Architects and owners who want a thermally efficient wall cladding but have to consider a blast design metric should feel comfortable in specifying insulated precast concrete wall panels.
PCI Conducts Blast Research on Insulated Precast Concrete Wall Panels -
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Blog By: Marshall Bassett, PE
Gate Precast Company
mbassett@gateprecast.com
