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Failure Mechanisms in Unreinforced Concrete Masonry Walls Retrofitted with Polymer Coatings
When blast waves interact with building walls composed of brittle materials like unreinforced masonry, fragments of wall can be violently thrown into the building. This threat is so severe that the Department of Defense has banned unreinforced masonry, one of the most common construction types in the U.S., for most new construction. But what do we do about existing buildings. One strategy for protecting occupants is to insure that exterior walls can survive the blast by adding strength and mass to the wall, usually with concrete and steel. The Air Force Research Laboratory is pioneering a simpler and much lighter retrofit solution to introduce ductility and resilience into walls using elastomeric polymer coatings. The polymer bonds to the wall forming a tough elastic skin. Although fracture of the masonry may occur (restricting this technology to non-load bearing walls), the polymer material remains intact and contains the debris. The polymer retrofit technique can reduce the standoffs required to limit damage and casualties by as much as 80%. Analysis of unreinforced concrete masonry unit walls for out-of-plane loads is a complex engineering problem. Traditional beam theory and yield line solutions give conservative results for walls subjected to pressures below the threshold at which the mortar joints fracture. The assumptions inherent in these methods are violated as the components of the wall fail and the overall geometry of the wall system breaks down under blast loading. Large variability in mortar joint flexural bond strength or shear strength as well as inconsistencies in polymer thickness compound the difficulties in performing exact analyses. Failure modes can be idealized as purely flexural, purely membrane, or a combination flexural and membrane with local shear failures thrown into the mix. Each of these idealized response modes is discussed and analyzed in this paper. The influence of the failure mode on limit states and blast performance is discussed.
Failure Mechanisms in Unreinforced Concrete Masonry Walls Retrofitted with Polymer Coatings
When blast waves interact with building walls composed of brittle materials like unreinforced masonry, fragments of wall can be violently thrown into the building. This threat is so severe that the Department of Defense has banned unreinforced masonry, one of the most common construction types in the U.S., for most new construction. But what do we do about existing buildings. One strategy for protecting occupants is to insure that exterior walls can survive the blast by adding strength and mass to the wall, usually with concrete and steel. The Air Force Research Laboratory is pioneering a simpler and much lighter retrofit solution to introduce ductility and resilience into walls using elastomeric polymer coatings. The polymer bonds to the wall forming a tough elastic skin. Although fracture of the masonry may occur (restricting this technology to non-load bearing walls), the polymer material remains intact and contains the debris. The polymer retrofit technique can reduce the standoffs required to limit damage and casualties by as much as 80%. Analysis of unreinforced concrete masonry unit walls for out-of-plane loads is a complex engineering problem. Traditional beam theory and yield line solutions give conservative results for walls subjected to pressures below the threshold at which the mortar joints fracture. The assumptions inherent in these methods are violated as the components of the wall fail and the overall geometry of the wall system breaks down under blast loading. Large variability in mortar joint flexural bond strength or shear strength as well as inconsistencies in polymer thickness compound the difficulties in performing exact analyses. Failure modes can be idealized as purely flexural, purely membrane, or a combination flexural and membrane with local shear failures thrown into the mix. Each of these idealized response modes is discussed and analyzed in this paper. The influence of the failure mode on limit states and blast performance is discussed.
Failure Mechanisms in Unreinforced Concrete Masonry Walls Retrofitted with Polymer Coatings
R. Dinan (author) / J. Fisher (author) / M. I. Hammons (author) / J. R. Porter (author)
2003
16 pages
Report
No indication
English
Coatings, Colorants, & Finishes , Materials Sciences , Elastomers , Construction Equipment, Materials, & Supplies , Environmental & Occupational Factors , Structural Analyses , Coatings , Reinforcement(Structures) , Walls , Blast , Blast loads , Blast waves , Concrete , Ductility , Failure(Mechanics) , Flexural strength , Fracture(Mechanics) , Fragmentation , Masonry , Resilience , Retrofitting , Shear strength , Strength(Mechanics) , Bomb blasts , Mortar joints , Polymer coatings
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