Connection Demand Prediction for the Design of Precast Concrete Wall Panels Subjected to Blast Loads

Abstract

One challenge in design of structures for highly impulsive loading is accurately predicting the peak transient shear and the corresponding connection force demand at supports. Single-degree-of-freedom (SDOF) approaches are commonly used for analyzing the maximum dynamic deflections and flexural moments, and have been extensively demonstrated to be reasonably accurate for those purposes. However, the typical SDOF methodology assumes that the inertia distribution under the dynamic loading is the same as the simple static deflection shape, which may not be accurate for analyzing the transient shear. The difficulty primarily comes from (1) the complex distribution of inertia forces that vary spatially and temporally and are not easily approximated, (2) the peak transient shear forces tend to be high intensity for only a very short duration, and (3) strain rate effects associated with the short duration shear and connection response are not easily quantified or are otherwise unknown. To circumvent these challenges, engineers often use the design flexural capacity (i.e. ultimate resistance) as the basis for the shear and connection design forces. Although this equivalent static reaction force approach is used for many blast design applications, it must be recognized that it is not founded on solving the equation of motion, and therefore cannot predict true demand. The need for an accurate yet simple equation of motion based approach for predicting shear and connection demand is critical for relatively slender precast panels. This thesis presents the methodology developed for predicting the shear and connection forces associated with blast loaded slender precast panels typically used for exterior wall systems and facades. High fidelity finite element modeling is used to understand the intricate dynamic response mechanics involved, and the modeling and derived analytical SDOF approaches are compared to full-scale explosion load test data. It was found through this research that SDOF dynamic reaction force methodology can predict the reaction forces with reasonable accuracy. Also, it was found that for a range of blast loads magnitudes, dynamic reaction forces exceed the equivalent static reaction force based on the flexural resistance that engineers use to design precast wall connections. Additional research is required however to determine if strain rate effects sufficiently compensate for the difference between the peak dynamic force and the equivalent static reaction force in which the connections are designed.