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Previous Missile Impact Tests for Wood Sheathing

The information below discusses previous missile impact tests for wood sheathing.

Reinforced concrete and reinforced masonry have been the most common wall and roof materials used with success in community safe rooms. The use of wood panels for exterior wall sheathing in community safe room applications had been limited. The following provides limited information on wood panel testing that has been performed for both hurricane and tornado safe room applications.

Data from the missile impact tests on walls with plywood and oriented strand board (OSB) sheathing conducted at Texas Tech University1 and at Clemson University2 have been combined to determine the variation of missile perforation resistance with thickness of the sheathing. In order to put all the data on a consistent basis, missile weights and lowest impact velocities for perforation of the sheathing have been extracted from previous test results. The weight and impact velocity information were used to calculate the impact momentum {weight (lb) x velocity (ft/sec)/acceleration of gravity (32.2 ft/sec2) = momentum (lb/ sec)} and the impact energy {weight (lb) x velocity squared (ft/sec)2/acceleration of gravity (32.2 ft/sec2) = energy (ft/lb)}. The resulting impact momentum and impact energy for perforation of the sheathing are plotted as a function of sheathing thickness (in 1/32 inch) in Figures 1 and 2.

The momentum required for a wood 2x4 missile to cause perforation varies essentially linearly with thickness of the sheathing material for both plywood and OSB. This suggests, at least for this type of missile and common sheathing materials, that a desired target penetration resistance (ability to resist a certain impact momentum) can be achieved by simply adding up the contributions of the various layers of sheathing. For example, in Figure 1, sheathing with a 30/32-inch thickness represents two layers of 15/32-inch material.

Figure 3 provides information on the relative resistance of various common sheathing materials, in terms of impact momentum absorption, for a compact impact area such as that associated with a wood 2x4 missile impacting perpendicular to the sheathing material. Summing the momentum resistance of the various layers of common sheathing materials is permissible when developing initial design criteria for walls that provide adequate protection. However, this process may not work for other types of missiles or for wall materials that absorb impact energy by undergoing large deformations (i.e., corrugated metal panels).

For the large test missile specified in FEMA P-361 (2015) or ICC 500 (2014) (a 15-lb wood 2x4 missile), the maximum horizontal impact speed designated in the criteria is 100 mph, and the corresponding momentum is approximately 68 lb/sec. For vertical impacts, the maximum impact velocity designated is reduced to 67 mph; the corresponding momentum to the maximum vertical impact speed is approximately 46 lb/sec.

Graph showing the variation of impact momentum required for missile penetration vs. wall sheathing thickness.
Figure 1. Variation of impact momentum required for missile penetration vs. wall sheathing thickness

 

 

 

 

 

 

 

 

Figure 2 is a graph showing the variation of impact energy required for missile penetration vs. wall sheathing thickness.
Figure 2. Variation of impact energy required for missile penetration vs. wall sheathing thickness

 

 

 

 

 

 

 

Figure 3 is a graph showing the impact momentum required for a 2x4 wood missile to penetrate various common sheathing materials including various thicknesses of plywood, OSB, fiberboard, and sheet rock.
Figure 3. Impact momentum required for a 2x4 wood missile to penetrate various common wood sheathing materials (impact perpendicular to sheathing surface)

 

 

 

 

 

 

 

 


1 Carter, R. R. 1998. Wind-Generated Missile Impact on Composite Wall Systems. MS Thesis. Department of Civil Engineering, Texas Tech University, Lubbock, TX. May.

2 Clemson University Department of Civil Engineering. 2000. Enhanced Protection from Severe Wind Storms. Clemson University, Clemson, SC. January.

Publication resources for safe rooms:

  • FEMA P-320. Fourth Edition, 2014. Taking Shelter from the Storm, Building a Safe Room for Your Home or Small Business. [Free]
  • FEMA P-361. Third Edition, 2015. Safe Rooms for Tornadoes and Hurricanes: Guidance for Community and Residential Safe Rooms. [Free]
  • ICC 500. 2014. ICC/NSSA Standard for the Design and Construction of Storm Shelters. [For purchase and download]
  • Highlights of ICC 500-2014 [Free]

Webpage links for safe room information:

Return to FEMA P-361 - Safe Rooms for Tornados and Hurricanes: Guidance for Community and Residential Safe Rooms.

Questions? Click on the "Frequently Asked Questions" link to view FAQs about design and construction of safe rooms. If you need additional information about the design and construction of safe rooms, contact the Safe Room Helpline by emailing Saferoom@fema.dhs.gov or calling (866) 927-2104.

Last Updated: 
11/15/2017 - 07:56