Static Resistance Functions for Unbonded Retrofit Unreinforced Concrete Masonry Walls with Plate Connection for Blast Design Applications
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Over the past two decades the use of explosives to attack both commercial and government buildings has increased. A substantial amount of research has been conducted to be able to protect not only the occupants but the structure also. New construction practices have been developed to mitigate the damages, but retrofit of existing buildings does not have a single answer. The resistance functions of all the components of the wall including a retrofit system are needed to be able to model an accurate simulation to ensure safe design of the retrofit. For design purposes the amount of energy dissipation is important; however, the design codes, such as UFC 3-340-02, do not use energy dissipation as a criterion for safe design. Rather deflection and rotation limits are set for different levels of protection. In order to determine if a wall meets these limits, a dynamic analysis is performed to determine the maximum deflection a wall will exhibit during a loading. Typically a single-degree-of-freedom (SDOF) model is used to solve for the midspan deflection. This simplified method requires a definition of the relationship between resistance and deflection. Unreinforced, ungrouted masonry (URM) walls are commonly found throughout the world. Masonry buildings have been around for thousands of years and comprise over 70% of buildings worldwide. Because of their popularity and susceptibility to fragmentation, it is imperative to ensure masonry walls are capable of withstanding a blast load. The two main categories of URM walls examined are non-arching walls and arching walls. Several methods have been developed to simulate how these walls will resist a lateral load and an in depth comparison is presented. Many methods have also been developed for the resistance definition of an unbonded retrofit system. These methods have also been heavily examined. An analytical method was developed to incorporate the effects of the retrofit connection on the resistance function. This method was validated using finite element modeling. Many different geometric models were used to assess the validity of the algorithm. Lastly, all of the components of the walls resistance definitions were combined to form the total resistance of the wall. This resistance was used in a single-degree-of-freedom model to generate a retrofit system for a specific design example.