Behavior, Analysis and Design of Steel-Plate Composite (SC) Walls for Impactive Loading
thesisposted on 03.01.2019, 16:30 by Joo Min Kim
There is significant interest in the used of Steel-plate composite (SC) walls for protective structures, particularly for impactive and impulsive loading. The behavior of SC walls is fundamentally different from that of reinforced concrete (RC) walls due to the addition of steel plates on the exterior surfaces, which prevent concrete scabbing and enhance local perforation resistance.
Laboratory-scale SC wall specimens were fabricated, cast with concrete, and then tested in an indoor missile impact test-setup specially-built and commissioned for this research. The parameters included in the experimental investigations were the steel plate reinforcement ratio (3.7% - 5.2%), tie bar spacing, size, and reinforcement ratio (0.37% - 1.23%), and the steel plate yield strength (Gr.50 - Gr.65). Additional parameters include the missile diameter (1.0 in., 1.5 in.), weight (1.3 lbs, 2.0, lbs, 3.5 lbs), and velocity (410 - 760 ft/s). A total of sixteen tests were conducted, the results of which are presented in detail including measurements of missile velocity, penetration depth, rear steel plate bulging deformation, and test outcome (stopped or perforated). The test results are further used to illustrate the significant conservatism of a design method developed previously by researchers (Bruhl et al. 2015a), and the sources of this conservatism including differences in the missile penetration mechanism, dimensions of the concrete conical frustum (breaking out), and the penetration depth equations assumed in the design method.
Numerical models were developed to further investigate local damage behavior of SC walls. Three-dimensional finite element models were built using LS-DYNA software and employed to simulate the missile impact tests on the SC wall specimens. The numerical analysis results were benchmarked to the experimental test results for the validation of the models.
Two sets of parametric studies were conducted using the benchmarked numerical models. The first set of the parametric studies was intended to narrow the perforation velocity ranges from the experimental results for use in evaluating the accuracy of a rational design method developed later in this research. The second set of the parametric studies was intended to evaluate the influence of design parameters on the perforation resistance of SC walls. It was found that flexural reinforcement ratio and steel plate strength are significant parameters which affect the penetration depth. However, shear reinforcement ratio has negligible influence.
Results from the experimental investigations and the numerical parametric studies were used to develop a rational design method which modifies the three-step design method. The modified design method incorporates a proposed modification factor applicable to the penetration depth equations and the missile penetration mechanism observed from the experiments. The modified design method was verified using the larger-scale missile impact test data from South Korean tests as well.
Additional research was performed to evaluate the local failure modes when the perforation was prevented from missile impactive loading on SC walls. Through numerical parametric studies, three different local failure modes (punching shear, flexural yielding, and plastic mechanism formation) were investigated. Also, an innovative approach to generating static resistance functions was proposed for use in SDOF or TDOF model analysis.