Blast Behavior of Columns Built with High-Strength Concrete and Grade 690 MPa High-Strength Reinforcement

As part of this study a series of columns built with high-strength concrete (HSC) and Grade 690 MPa high-strength reinforcement are tested under blast loads using a shock-tube. The performance of the columns is compared to a set of columns specimens built with Grade 400 MPa reinforcement. In addition to the effects of concrete and steel type, the effects of longitudinal steel ratio and seismic detailing are also investigated. The results show that concrete strength has limited effects on blast behavior. Conversely, use of high-strength bars significantly enhances column blast performance by reducing displacements and increasing blast resistance, with an ability to reduce reinforcement. The results further demonstrate that increasing the longitudinal steel ratio and seismic detailing improve the blast behavior of columns built with conventional and high-strength bars. As part of the analytical study the blast response of the columns is predicted using SDOF analysis and finite element modelling.

Analysis Method for Reinforcing Circular Openings in Isotropic Homogeneous Plate-Like Structures Subjected to Blast Loading

An analysis method is formulated to predict the peak bending stress concentrations around a small circular opening in an idealized isotropic homogeneous, linear elastic-perfectly plastic plate-like structure subjected to uniform blast loading. The method allows for the determination of corresponding concentrated bending moments adjacent to the opening for the design of reinforcement that can prevent the formation of localized plasticity around the opening during a blast event. The rapid formation and growth of localized plasticity around the opening can lead to a drastic reduction of the plate-like structure’s local and global stability, which could result in catastrophic failure of the structure and destruction of the entity it is protecting. A set of elemental formulas is derived considering one-way and two-way rectangular plate-like structures containing a single small circular opening located where flexure predominates. The derived formulas are applicable for elastic global response to blast loading. Abaqus was employed to conduct numerical verification of the derived formulas considering various design parameters including material properties, plate dimensions, position of opening, and explosive charge size. The formulas demonstrate a good correlation with FEA albeit with a conservative inclination. The derived formulas are intended to be used in tandem with dynamic SDOF analysis of a blast load-structure system for ease of design. Overall, the proposed method has the potential to be applicable for many typical conditions that may be encountered during design.

Comparison of Predicted and Experimental Behaviour of RC Slabs Subjected to Blast using SDOF Analysis

<p>Explosions emanating from terrorist attacks or military weapons cause damage to civilian and military facilities. Understanding the mechanical behaviour of reinforced concrete structures subjected to blast is of paramount importance for minimizing the possible blast damage. A full-scale experimental program consisting of six reinforced concrete slabs with compressive strengths of 60 MPa, 50 MPa and 40 MPa, measuring 1.0 m × 1.0 m × 0.08 m, and subjected to 2.7 kg of non-confined plastic bonded explosive, was conducted in blast test area of Science and Technology Aerospace Department (Brazilian Air Force). This paper compares experimentally measured peak displacement values with theoretical values. Theoretical analysis was carried out using single degree of freedom (SDOF) models. The comparison showed that SDOF analysis worked very well in predicting the reinforced concrete slab peak displacement against blast effects. Qualitative analysis after the experiments showed that the blast wave shape generated by the cylindrical explosive was not uniformly distributed on the slabs for the standoff distance of 0.927 m∕kg1/3.<br /><br /></p>

Characterization of adobe wall structural systems for dynamic response

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Adobe building construction exists around the world. Most of the adobe structures are located in active seismic zones, and a considerable amount of research has been conducted on the seismic response of adobe structures. Protocols and standards for adobe structural analysis, design, and construction has been established to ensure quality assurance and structural stability. The vulnerabilities to seismic loadings have been established, and research and design of seismic retrofits for existing and new adobe construction have been conducted. The type of retrofit utilized can depend on the availability of materials, impact on the aesthetics of the structure, and region of the world that the structure exists. Very limited research exists on the structural response of these structures when subjected to an external blast load. This dissertation evaluates current adobe wall designs for blast resistance and provides recommendations for their blast retrofits. Although limited research has been conducted on the effect of blast loadings on adobe structures, it is possible that some seismic retrofit designs can be extended to enhance the blast resistance of adobe structures. The result would provide a multi-hazard retrofit that includes resistance to blast and seismic loadings. Research has been conducted to evaluate adobe blocks, adobe block component specimens, and adobe block walls. The adobe block testing provides material properties such as block compressive strength, modulus of rupture, shear strength, and mortar strength. These properties are important when analyzing the component and conducting wall testing research. The static adobe block-mortar bond shear strength and flexural strength of a column of adobe blocks subjected to bending were determined through research on adobe block component specimens. Research efforts also investigated the strength and failure modes of unreinforced and reinforced full-scale adobe block walls. Slender walls, referred to as wallettes, are the same height and approximately one-third the width of the full size adobe walls that were tested. The wallettes were tested in a four-point bending setup to determine the load capacity, deflection, and failure mode. The effect of wall thickness was determined by testing three unretrofitted wallettes of varying wall thicknesses of 10, 20¾, and 31½ in. A retrofit concept, with two variations, was applied to the 20¾-in. wallettes to determine their performance in increasing the load capacity, change the failure mode, and increase the stability of adobe block walls. The unretrofitted 20¾-in. wallette served as the baseline to evaluate the retrofitted wallettes. This research effort was extended to investigate full-scale unretrofitted and retrofitted adobe walls statically tested in a vacuum chamber. The vacuum chamber applies a uniform loading on the adobe block walls. A pretest compressive load was applied to the top of the wall and maintained during the test. The dead load of the roof that adobe walls typically support is represented by this compressive load, which is achieved through five 4×4 timber rafters that are connected to the top of the wall. Two unretrofitted and three retrofitted 10-in.-thick adobe block walls were tested. The loaddeflection curve and failure mode of the each wall were determined. Additionally, three unretrofitted 10-in.-thick adobe block walls were dynamically tested in a blast load simulator (BLS), located at the U.S. Army Engineer Research and Development Center (ERDC) in Vicksburg, MS, to determine the dynamic responses of adobe block walls to blast loadings. The walls were constructed with the same adobe blocks and mortar as in the static testing phase of the research, and a similar compressive load and system was used in the BLS tests. The experimental research will assist in developing blast resistant design methods for adobe walls and retrofits. The wallette tests results were analyzed to determine loaddeflection curves for the wallettes and if the curves could be used to assist in dynamic analyses of adobe walls of other thicknesses. The load-deflection curves gathered from the vacuum chamber provided experimental resistance functions for unretrofitted and retrofitted adobe block walls. Single-degree-of freedom (SDOF) analysis uses the resistance functions and can also be used to predict the responses of adobe walls to dynamic loads. The dynamic adobe block wall tests provide a reference of how well the SDOF analysis predicts the dynamic responses of adobe block walls. Additionally, the retrofit techniques provide guidance for retrofitting adobe block walls to sustain dynamic blast loads.

Energy Harvesting of Piezoelectric Stack Actuator From a Shock Event

The energy harvesting performance of a piezoelectric stack actuator under a shock event is theoretically and experimentally investigated. The first method is derived from the single degree of freedom constitutive equations, and then a correction factor is applied onto the resulting electromechanically coupled equations of motion. The second approach is deriving the coupled equations of motion with Hamilton's principle and the constitutive equations, and then formulating it with the finite element method. Two experimental cases matched well with the model predictions where the percent errors were 3.90% and 3.26% for the SDOF analysis and 1.52% and 1.42% for the FEM.

Feature Variation and Its Impact on Structural Acoustic Response Predictions

This paper presents a screening technique to assess the impact on model fidelity introduced by variations in the properties or positions of features in harmonically forced fluid-loaded structural acoustic models. While fluid-loading is included, it is not a requirement or restriction to the methods presented. The perspective taken is one of knowledge of a reference state, with a desire to determine the impact on the total radiated acoustic power due to perturbations in the reference state. Such perturbations change the predicted resonance frequencies of a structure under consideration, and hence, change the predicted response amplitudes. The method uses a single degree of freedom response model in the local region of each fluid-loaded resonance, coupled with eigenvalue sensitivities or variations, to estimate the perturbation impact. The SDOF model argues for the use of proportional bandwidth analyses. Elements of the analysis method are not necessarily restricted to model perturbations nor acoustic power, rather they may be used to assess the perturbation of any quadratic response quantity of interest due to changes in resonance frequency. The SDOF analysis method is limited by its assumption of constant modal forcing between the reference and perturbed states.