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.<div><br></div><div>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.<br></div><div><br></div><div>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.<br></div><div><br></div><div>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.<br></div><div><br></div><div>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.<br></div><div><br></div><div>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.<br></div>

<p>  </p> <p>The design of blast-resistant structures is critical for defense related facilities and industries. An emerging option for these applications is Steel-plate composite (SC) systems. SC systems include a steel module and concrete infill. Steel modules can include but are not limited to steel faceplates, tie bars, tie plates, diaphragm plates, and steel headed stud anchors. SC technologies have been adopted as a structural system in the design of nuclear powerplant containment vessels and high-rise buildings. These applications have benefitted from the inherent ductility and modular construction that SC systems provide.</p> <p>When designing structures to resist blast and impact, the desired behavior is for the structure to demonstrate ductility. Previous research has explored the behavior of a variety of SC elements; however, limited research on the behavior of L-joint connections exists. For L-joint connections to demonstrate ductile behavior, it is suggested that the joint that connects SC components- SC beams, columns, or slabs- be stronger than the connected elements. L-joint connections with joints stronger than the connected SC elements are considered full strength connections. As such, the connected elements reach their maximum bending moments and demonstrate ductile behavior. This study proposes a design philosophy for achieving full-strength L-joint connections using a diagonal steel reinforcing plate in the joint. This study evaluated the behavior of L-joint connections with joint reinforcement through large-scale experimental testing and subsequent benchmarked finite element analyses. The inclusion of a diagonal plate contributes to the L-joint connections ability to resist joint failure and develop a greater moment capacity in the SC members. This finding was also validated through finite element analyses comparing the specimen behavior with and without the joint reinforcement. The specimen without joint reinforcement experienced joint shear failure in the concrete while the experimental specimens were able to demonstrate ductile behavior prior to failure. </p>

<p dir="ltr">SC walls have emerged as an advantageous alternative to reinforced concrete (RC) construction for blast resistant structures. SC walls typically consist of shop fabricated steel modules which can be erected on site and filled with concrete, without additional formwork setup or removal. The steel modules typically consist of steel faceplates, tie bars between faceplates, and optional shear studs. SC members offer advantages in strength, ductility, constructability, and construction schedule when compared with RC. The behavior of SC structures have been previously demonstrated and adopted into many building design codes, but there is a knowledge gap on the post-elastic behavior of SC members in two-way bending. The desire to use SC walls for blast resistant design motivates the need to study this behavior for SC walls and slabs. In this study, the behavior of SC panels in two-way bending was evaluated by using analytical, experimental, and numerical methods.</p><p dir="ltr">Structural mechanics was used to develop simple predictions for the static behavior of rectangular, two-way SC panels under a uniform pressure loading. These predictions include the inelastic cross-section flexural capacity, the member static resistance function, the load-mass transformation factor for SDOF analysis, out-of-plane shear demands, and rotation demands. A quick-running SDOF computer algorithm was created to conduct blast load analysis incorporating the nonlinear member behavior predicted by mechanics.</p><p dir="ltr">The two-way bending behavior of a SC panel was experimentally investigated. A SC panel was fabricated and experimentally loaded in two-way bending until flexural failure of the panel was reached. A series of concentrated loads applied to the panel was designed to simulate the yield line pattern of a panel under a uniform applied pressure. The experimental test demonstrated the deformed shape, inelastic capacity, and progression of yield lines throughout a SC panel in two-way bending. A 2D, layered composite shell finite element analysis was benchmarked to the experimental results. The finite element modeled the inelastic flexural behavior of the SC panel, closely matching the capacity, deformed shape, and development of yield lines throughout the panel.</p><p dir="ltr">The finite element modeling approach was used to validate the SDOF predictions of two-way SC panel behavior under static and blast pressure loadings through a parametric study. Detailed comparisons of the two modeling results were made. Iso-damage pressure-impulse diagrams for multiple SC panel geometries were developed.</p>

<p dir="ltr">Steel-concrete composite (SC) walls are increasingly gaining interest as an alternative to reinforced concrete (RC) walls for safety-related nuclear facilities. The major loading for the SC design is seismic loading. Seismic loading results in combined in-plane shear with axial or out-of-plane moment loading on SC structures. The primary resistance against the lateral loading in these structures is provided by in-plane shear resistance. While the AISC N690 design code includes equations for determining in-plane shear capacity and combined loading, its guidance is limited to pure in-plane shear capacity, in-plane shear combined with out-of-plane moments and combined out-of-plane shear forces. It lacks comprehensive design equations for combined loadings, such as in-plane shear with axial or out-of-plane moment loading. Additionally, the N690 design equation for in-plane shear capacity is somewhat conservative. Understanding the behavior of SC walls under these combined loadings is crucial for their optimal design.</p><p dir="ltr">This research addresses this gap by performing numerical investigation based on the finite element modelling (FEM) and mechanics-based approaches to analyze the behavior of SC walls under these loadings. The models were verified and validated using data from previous experimental studies. A parametric study was conducted to evaluate the impact of various design and material parameters on the in-plane shear capacity under combined loadings. Based on the parametric data and linear regression analysis, design equations were formulated to predict the in-plane shear capacity. Interaction envelopes were developed to compare the results from these models with those from previous numerical studies. Finally, practical design guidance and design equations were provided to design these structures.</p>

<p>In safety-related nuclear structures, steel-plate composite (SC) walls are often used in combination with reinforced concrete (RC) walls or foundations. The design demands need to be transferred between the two different structural systems through appropriate connections without connection failure, which is often associated with brittle failure mode. This study presents a design procedure developed for mechanical connections between SC and RC walls. This procedure implements the full-strength connection design approach as per Specifications for Safety-Related Steel Structures for Nuclear Facilities, AISC N690-18, which requires connections to be stronger than the weaker of the connected walls. The study also presents the results from experimental and numerical investigations conducted to verify the structural performance of the full-strength SC wall-to-RC wall mechanical connection.</p> <p>The experimental program involved testing six mechanical connections comprising four full-scale and two scaled specimens. The four specimens subjected to out-of-plane moment (OOPM) and out-of-plane shear (OOPV) represented a unit cell of a typical wall in a nuclear facility. The remaining two specimens subjected to in-plane shear (IPV) were scaled (1:3) to facilitate testing using the existing loading setup. Two specimens were tested for each loading scenario. The two specimens per loading case were differentiated by longitudinal rebar-to-baseplate connection plans: coupler (C) and double nut (DN). The performance, strength, ductility, and failure mode of the proposed mechanical connection were evaluated based on the experimental observations.</p> <p>The observed governing failure mode of all test specimens was either RC wall flexural yielding or RC wall shear failure. The connection region steel plates (tie plates, wing plates, and baseplates) remained within their elastic range until failure ensuring energy dissipation away from the connection region. Additionally, the wing plates and baseplates strains remained comparatively lower than the tie plate strain values. This was attributed to the contribution of concrete during the force transfer between the two structural elements indicating that the proposed connection design procedure is suitable and conservative for SC wall-to-RC wall mechanical connections.</p> <p>Three-dimensional (3D) finite element models (FEM) were developed and benchmarked against the experimental data to gain an additional insight into the connection behavior. Parametric studies were conducted to compensate for the limited experimental database and evaluate the influence of design parameters such as wall thickness and RC wall longitudinal reinforcement layers on the performance of the designed mechanical connection. Numerically predicted results compared favorably with experimental observations. The recommended design procedure is intended to help designers consider mechanically connecting SC-RC walls where non-contact lap splicing is not feasible and in an attempt to utilize the potential for accelerated construction time and enhanced structural performance of SC walls.</p> <p><br></p>