Investigation of Wind Projectile Resistance of Insulating Concrete Form Homes. by Ernst W. Kiesling, Ph.D., P.E. Russell Carter, BSCE, EIT

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1 Investigation of Wind Projectile Resistance of Insulating Concrete Form Homes by Ernst W. Kiesling, Ph.D., P.E. Russell Carter, BSCE, EIT R E S E A R C H & D E V E L O P M E N T B U L L E T I N RP122

2 Investigation of Wind Projectile Resistance of Insulating Concrete Form Homes By Ernst W. Kiesling, Ph.D., P.E. and Russell Carter, BSCE, EIT Research and Development Bulletin RP122

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4 TABLE OF CONTENTS Page EXECUTIVE SUMMARY...iv OVERVIEW OF PROJECT...1 APPROACH TO DESIGN...1 SHELTER DESIGN CRITERIA...2 TESTS CONDUCTED...2 Target One: 6-inch thick Reinforced Concrete Wall...3 Target Two: 6-inch thick Reinforced Concrete Wall...4 Target Three: 6-inch thick Flat Wall ICF with Vinyl Siding...5 Target Four: 6-inch thick Flat Wall ICF with Brick Veneer...7 Target Five: 4-inch thick Flat Wall ICF with Vinyl Siding...8 Target Six: Variable thickness Waffle Grid ICF with EIFS...9 Target Seven: Wood Stud Construction with Vinyl Siding...11 Target Eight: Wood Stud Construction with Brick Veneer...12 Target Nine: Steel Stud Construction with Vinyl Siding...13 Target Ten: Steel Stud Construction with EIFS...14 APPENDIX: Table of Results...15 Table A-1 Test Results: Concrete and ICF Walls...15 Table A-2 Test Results: Wood and Steel Frame Walls...16 iii

5 EXECUTIVE SUMMARY Debris driven by high winds presents the greatest hazard to homeowners and their homes during tornadoes and hurricanes. Insulating concrete form (ICF) wall systems provide much greater resistance to the impact of tornado debris than conventional frame construction. Recent laboratory testing at the Wind Engineering Research Center, Texas Tech University, compared the impact resistance of residential concrete wall construction versus convention ally framed walls. The frame walls failed to stop wind driven debris from penetrating. The concrete walls successfully demonstrated the strength and mass to resist the impact of wind driven debris. As a result, the disaster resistance of homes built with ICF wall systems is a significant advantage of this construction technology. Ten wall specimens were subjected to the impact of a 15-pound 2 x 4 wood stud traveling at speeds as high as 119 miles per hour. The Research Center has determined this to be equivalent to the weight and velocity of debris generated during a tornado with 250 mile per hour winds. Wind speeds are less in 99 per cent of tornadoes occurring in the United States. Hurricane wind speeds will be less than the equivalent speeds modeled here. Missile testing designed to mitigate property damage losses from hurricanes use a criterion of a 9-pound missile traveling about 34 miles per hour. The wall specimens were representative of the type of construction now used to build frame homes and concrete homes in the U.S. Four of the test walls consisted of conventional wood or steel framing. Gypsum board was the interior finish for all walls. On the exterior, the specimens were clad in vinyl siding or brick veneer over % plywood sheathing, or synthetic stucco over gypsum board sheathing. Six concrete walls were constructed. Two were reinforced concrete walls built with removable forms. They were tested with no finishes applied. The remaining concrete walls were constructed with stay in place insulating concrete forms (ICFs). Steel reinforcing bars were placed at common intervals for ICF construction. A standard ICF concrete mix design was specified for the test: a 3000 psi compressive strength, a maximum aggregate size of %, and a 6 slump. The Wind Engineering Research Center s compressed air cannon was used to propel a 2 x 4 wood stud debris missile at the test walls. At all velocities, the missile penetrated through the frame wall assembly. All of the concrete walls were subjected to at least one impact, with two of the ICF walls tested twice, once on each of the front and rear faces. The velocities of the missiles fired at he concrete walls were all above 96 mph. No cracking, front face scabbing, or back face spalling was observed in any concrete wall tested iv

6 INVESTIGATION OF WIND PROJECTILE RESISTANCE OF ICF HOMES Ernst W. Kiesling, Ph.D., P.E.* Russell Carter, BSCE, EIT** OVERVIEW OF PROJECT The Wind Engineering Research Center (WERC) at Texas Tech University was engaged by the Portland Cement Association to assess the missile shielding ability of walls constructed using Insulating Concrete Form (ICF) units. Several wall sections were constructed, some using materials and technology which are traditionally used in residential or light commercial construction and additional walls utilizing concrete, most of them with Insulating Concrete Forms. These were subjected to impact of missiles representative of those which are generated by severe winds such as tornadoes. The missile criterion chosen these tests was a fifteen pound 2 x 4 board traveling at 100 miles per hour along the board s axis, striking the wall section perpendicular to its face. This missile speed corresponds to a 250 mile per hour wind and is the criterion used in designing for occupant protection. In 99 percent of the tornadoes which have occurred in the U.S., wind speeds are less than 250 miles per hour: in 90 percent, maximum wind speeds are less than 150 miles per hour. Additional factors of safety are inherent in the criterion since there is a very small probability that a missile will be traveling along its axis and will strike a wall perpendicular to its surface. The wall sections representing conventional construction were tested at missile speeds less than 100 miles per hour but well above perforation threshold levels learned by past experience. As expected, missiles perforated conventional walls. All insulating concrete walls tested in this project withstood impacts of missiles traveling at approximately 100 miles per hour. Approach to Design There are two major problems created by severe winds: 1. Threats to life, safety, or to critical functions or contents. 2. Economic losses, both direct and indirect. Damage to buildings and contents comprise a large part of direct losses. Indirect losses include costs associated with such things as evacuation, business interruption, and loss of productivity. The Wind Engineering Research Team at Texas Tech has approached the hazards of life safety separately from those of economic loss. For life safety, or for protecting critical functions or contents, we recommend hardening and stiffening a room sufficiently large to *Professor, Texas Tech Univesity, Department of Civil Engineering **Graduate Student, Texas Tech University, Department of Civil Engineering 1

7 house occupants or critical functions or contents. To reduce economic loss, we focus on the integrity of building envelopes or of engineering systems to mitigate damage. In buildings, emphasis is placed on connection of walls to floor, roof to wall, ridges, roof decks, and securing large doors and windows. The building envelope should also have sufficient hardness to prevent water intrusion through openings which are created by breaking windows or doors or perforations of walls and roofs. A representative missile criterion in standards for building envelopes aimed at reducing economic loss in hurricane regions is a nine pound missile traveling at 50 feet per second, about 34 miles per hour. Shelter Design Criteria To provide protection to occupants or to critical contents, shelters must possess structural integrity and missile shielding ability. For shelters to become widespread, they must in addition be economical, aesthetically pleasing, and constructable with available materials and technology. Tests Conducted The Wind Engineering Research Center (WERC) at Texas Tech University tested various wall systems for the Portland Cement Association (PCA). The wall systems were built to specifications established by PCA and varied in material and construction. Included were metal stud, wood stud, reinforced concrete, and insulated concrete form (ICF) construction. All samples requiring concrete were placed at one time from the same concrete mix: maximum aggregate size of 3/4 inch and a slump of six inches. Three test cylinders were made and tested. The compressive strength at 28 days was above 3000 psi for all cylinders, averaging 3300 psi. All tested samples were approximately 4 ft wide by 4 ft high. Each sample was impacted with a blunt ended 2in. x 4 in. timber missile weighing 15 lb. The samples were impacted perpendicular to the target surface to simulate the worst impact case scenario at a location on the wall section considered most vulnerable to missile perforation. The specifics about each wall configuration and the corresponding test results follow. Results are given below for the wall sections tested in the order in which the wall sections were defined by the sponsor and listed in the project proposal. 2

8 TARGET ONE: 6-INCH THICK REINFORCED CONCRETE SLAB Vertical Reinforcement: #4 rebar at 12 in. on center. Horizontal Reinforcement: #4 rebar one at top and one at bottom of 4 ft wall. Interior Finish: None. Exterior Finish: None. Test Observations: Target was impacted at MPH. No cracking, front face scabbing, or back face spalling was observed. Photographs taken after the test show only a flat unblemished surface. The missile broke and splintered into pieces on impact. Figure 1. Undamaged impact site 3

9 TARGET TWO: 6-INCH THICK REINFORCED CONCRETE SLAB Vertical Reinforcement: #4 rebar at 24 in. on center. Horizontal Reinforcement: #4 rebar one at top and one at bottom of 4-foot section. Interior Finish: None. Exterior Finish: None. Test Observations: Target was impacted at MPH. No cracking, front face scabbing or back face spalling was observed. Photographs taken after the test show only a flat unblemished surface. The missile broke and splintered into pieces on impact. Figure 2. Undamaged impact site 4

10 TARGET THREE: 6-INCH THICK GREENBLOCK ICF Vertical Reinforcement: #4 rebar at 12 in. on center. Horizontal Reinforcement: #4 rebar one at top and one at bottom of a 4-foot section. Interior Finish: None. Exterior Finish: Vinyl siding attached directly to ICF fastening strips. Test Observations: Target was impacted at MPH. No cracking, front face scabbing or back face spalling of the concrete core was observed. The missile penetrated the vinyl siding and the Greenblock form. The missile broke and splintered into pieces on impact. Figure 3a. Impact site with missile Figure 3b. Missile and foam removed to expose udamaged concrete 5

11 TARGET THREE: 6-INCH THICK GREENBLOCK ICF (Continued) The target was turned around and impacted a second time. The target was impacted at MPH. No cracking, front face scabbing or back face spalling of the concrete core was observed. The missile penetrated the Greenblock form. The missile broke and splintered into pieces on impact. Figure 3c. Second impact site 6

12 TARGET FOUR: 6-INCH THICK FALT ICF WALL Vertical Reinforcement: #4 rebar at 24 in. on center. Horizontal Reinforcement: #4 rebar one at top and one at bottom of 4-foot section. Interior Finish: 5/8 in. Gypsum board attached directly to ICF fastening strips. Exterior Finish: 3-in. brick attached directly to ICF fastening strips with brick ties spaced at 1 ft on center each way. There was a 1-in. air space between the brick and the ICF. Test Observations: Target was impacted at 99.0 MPH. No cracking, front face scabbing or back face spalling of the concrete core was observed. The missile penetrated the brick veneer, cracking it from the point of impact to the top of the sample. The foam of the ICF was indented but the missile never made direct contact with the concrete core. The missile broke and splintered into pieces on impact. Figure 4a. Impact site Figure 4b. Impact site with masonry removed to expose foam 7

13 TARGET FIVE: 4-INCH THICK FLAT ICF WALL Vertical Reinforcement: #4 rebar at 24 in. on center. Horizontal Reinforcement: #4 rebar one at top and one at bottom of 4-foot section. Interior Finish: 5/8 in. Gypsum board attached directly to ICF fastening strips. Exterior Finish: Vinyl siding attached directly to ICF fastening strips. Test Observations: Target was impacted at 96.7 MPH. No cracking, front face scabbing or back face spalling of the concrete core was observed. The missile penetrated the vinyl siding and the Lite Form ICF. The missile made contact with the concrete core but there was no observable damage. The missile broke and splintered into pieces on impact. One of the pieces, likely the trailing section of the missile, made a second impact on the target. The second impact penetrated the vinyl and the Lite Form ICF but did not make contact with the concrete core. Figure 5a. Impact site with splintered missile Figure 5b. Impact site with secondary impact 8

14 TARGET SIX 6-INCH THICK WAFFLE GRID ICF WALL Vertical Reinforcement: #4 rebar at 24 in. on center. Horizontal Reinforcement: #4 rebar one at top and one at bottom of 4-foot section. Interior Finish: : None. Exterior Finish: 1/4 in. thick Exterior Insulation Finish System (EIFS) applied directly to ICF. Figure 6a. Waffle grid profile 9

15 TARGET 6, (Continued) Test Observations: Target was impacted at MPH. No cracking, front face scabbing or back face spalling of the concrete core was observed. The missile penetrated the EIFS siding and the foam form. The missile made contact with the concrete core but there was no observable damage. The missile was aimed to hit the target in its most vulnerable area where the concrete was only 2 in. thick. The missile was off a little bit and glanced along the side of the thicker waffle column. Figure 6b. Impact site with shattered missile fragments Figure 6c. Impact site with EIFS and foam rempoved to expose undamaged concrete The waffle grid ICF target was turned around and impacted again at MPH. This was done to impact the target at its most vulnerable place. The missile hit the target exactly in the most vulnerable area and the target with stood the impact with no observable damage to the concrete core. The missile broke and splintered in to pieces that continued making impact with the target. These pieces penetrated the ICF form but did no observable damage to the concrete core. 10

16 TARGET SEVEN: WOOD STUD CONSTRUCTION WITH VINYL SIDING Interior Finish: : 5/8 in. gypsum board attached directly to wood studs spaced at 16 inches on center. 3 1/2 in. fiberglass batt insulation was placed between the studs. Exterior Finish: Vinyl siding over 3/4 in. plywood sheathing attached to the studs. Test Observations: Target was impacted at MPH. The missile perforated completely though the exterior and interior sheathing. There was little or no damage to the missile. Figure 7. Interior penetration, exposed insulation, broken gypsum board 11

17 TARGET EIGHT: BRICK VENEER,W00D STUD CONSTRUCTION Interior Finish: 5/8 in. gypsum board attached directly to wood studs spaced at 16 in. on center. 3 1/2 in. fiberglass batt insulation was placed between the studs. Exterior Finish: 3/4 in. plywood sheathing attached to the studs with a 3 in. brick veneer. The veneer was attached to the sheathing with metal ties spaced 16 in. on center horizontally and 12 in. on center vertically with a 1 in. air space between the brick and the sheathing. Test Observations: Target was impacted at 69.4 MPH. The missile perforated completely though the brick veneer, exterior and interior sheathing. The brick veneer was cracked horizontally and vertically from the point of impact. There was little damage to the missile. Figure 8a. Exterior impact, penetration of masonry veneer Figure 8b. Interior penetration, imbedded missile, exposed insulation, broken gypsum board 12

18 TARGET NINE: STEEL STUD CONSTRUCTION Interior Finish: : 5/8 in. gypsum board attached directly to steel studs spaced at 16 inches on center. 3 1/2 inch fiberglass batt insulation was placed between the studs. Exterior Finish: Vinyl siding over 3/4 in. plywood sheathing attached to the studs. Test Observations: Target was impacted at MPH. The missile perforated completely though the exterior and interior sheathing. There was little or no damage to the missile. Figure 9a. Exterior impact site Figure 9b. Interior penetration, exposed insulation, broken gypsum board 13

19 TARGET TEN STEEL STUD CONSTRUCTION WITH EIFS Interior Finish: : 5/8 in. gypsum board attached directly to steel studs spaced at 16 inches on center. 3 1/2 inch fiberglass bat insulation was placed between the studs. Exterior Finish: 1 in. thick EIFS (1 in. thick polystyrene insulation board attached to the studs at 16 in. on center.) Test Observations: Target was impacted at 50.9 MPH. The missile perforated completely though the exterior and interior sheathing. There was little or no damage to the missile. Figure 10a. Exterior penetration site Figure 10b. Interior penetration, exposed insulation, broken gypsum board 14

20 TABLE A-1 Test Results: Concrete and ICF Walls Target Wall Test Wall Description Speed Results Type of Debris 1 Concrete: 6 thick reinforced concrete wall, No cracking, front face #4 vertical reinforcement bars, 12 o.c. mph scabbing or back face No finishes. spalling of concrete observed. 2 6 thick reinforced concrete wall, No cracking, front face #4 vertical reinforcement bars, 24 o.c. mph scabbing or back face No finishes. spalling of concrete observed. 3 ICF: Block ICF foam forms, 6 thick flat Debris penetrated vinyl concrete wall, mph siding and foam form. No #4 vertical reinforcement bars, 12 o.c. cracking, front face Vinyl siding. scabbing or back face (Tested a second time with similar spalling of concrete wall results.) observed. 4 Block ICF foam forms, 6 thick flat 99.0 Debris penetrated and concrete wall, mph cracked brick veneer. #4 vertical reinforcement bars, 24 o.c. Foam form dented. No 3 brick veneer with ties spaced 1-0 cracking, front face o.c. ea. way scabbing or back face spalling of concrete wall observed. 5 Panel ICF foam forms, 4 thick flat 96.7 Debris penetrated vinyl concrete wall, mph siding and foam form. No #4 vertical reinforcement bars, 24 o.c. cracking, front face Vinyl siding scabbing or back face spalling of concrete wall observed. 6 Block ICF foam forms, variable Debris penetrated thickness waffle concrete wall, 6 mph synthetic stucco finish, maximum thickness, and 2 minimum and foam form. Impact of thickness. #4 vertical reinforcement wall at 2 thick section. bars in each 6 vertical core at 24 o.c. No cracking, front face Synthetic stucco finish scabbing or back face (Tested a second time with similar spalling of concrete wall results.) observed. 15

21 TABLE A-2 Test Results: Wood and Steel Frame Walls Target Wall Test Wall Description Speed Results Type of Debris 7 Wood 2 x 4 wood studs at 16 o.c., The debris missile Frame: 3 1/2 batt insulation, 5/8 gypsum mph perforated completely board interior finish, vinyl siding through the wall over 3/4 plywood sheathing assembly. Little damage exterior finish to the missile. 8 2 x 4 wood studs at 16 o.c., 69.4 The debris missile 3 1/2 batt insulation, 5/8 gypsum mph perforated completely board interior finish, 3 brick veneer through the brick veneer, with 1 air space, over 3/4 plywood and interior finish. Minor sheathing exterior finish damage to the missile. 9 Steel Steel studs at 16 o.c., 3 1/2 batt The debris missile Frame: insulation, 5/8 gypsum board mph perforated completely interior finish, vinyl siding over through the wall assembly. 3/4 plywood sheathing Little damage to the exterior finish missile. 10 Steel studs at 16 o.c., 3 1/2 batt 50.9 The debris missile insulation, 5/8 gypsum board mph perforated completely interior finish, synthetic stucco through the wall assembly. over 1/2 gypsum board sheathing No damage to the exterior finish missile. 16

22 ACKNOWLEDGEMENT The research reported in this paper (PCA R&D Serial No. 2178) was conducted by the Wind Engineering Research Center at Texas Tech University, with the sponsorship of the Portland Cement Association (PCA Project Index No ). The contents of this paper relect the views of the authors, who are responsible for the facts and accuracy of the data presented. The contents do not necessarily reflect the views of the Portland Cement Association. 17

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