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This study presents numerical investigation of blast overpressures on blast-resistant doors by changing the number of side chambers and the number and shape of expansion chambers for an external detonation. Blast overpressures for four types of door and zero to four chambers were simulated. For the original shape of the underground ammunition magazine with side chamters installed, the peak time delay was approximately 40 ms, showing a clear different, whereas the reduction in the maximum value appeared as small as 3 kPa. Reducing the overpressure and delaying peaks using bottleneck devices and side chambers revealed that, because the size of the tunnel with underground ammunition magazines was partially reduced, the effects of the reduction and time delay of blast overpressures were negligible. When expansion chambers with a size 1.1 times the passage width and side chambers were used, the time delay in the peaks and overpressure reduction were observed. When expansion chambers with a size 1.2 times the passage width and side chambers were used, the delay and reduction effects were significant when two or more chambers were installed, and the effect was almost the same as when the size was 1.1 times the passage width.

The single-degree-of-freedom (SDOF) analysis with elastic-plastic resistance is often used for design of protective structures subjected to blast loads. Several documents such as UFC 3-340-02 present design charts for the maximum responses of the elastic-plastic SDOF system. The SDOF design charts are available for far-field detonations but seldom for near-field detonations of high explosive in free air, noting that the focus of security design is the near-field. Further, the assumption of uniformly distributed load for the SDOF analysis may not be appropriate for the near-field detonations where blast pressure distribution varies significantly with distance and angle of incidence. In this paper, to resolve these issues, updated SDOF design charts including the response to the near-field detonations are suggested based on numerical calculations. These generated charts are verified with comparison to UFC 3-340-02 predictions and finite element analysis results of steel components. The recommendations and limitations for the utility of the SDOF design charts for blast assessment of steel components are provided with an emphasis on the near-field detonations.

When a blast wave impinges on the front face of a structure, rarefaction waves are formed along its free edges and propagate toward the center of the front face, and reduce the reflected ov...

Protective structures subjected to blast loads are often evaluated using the equivalent single-degree-of-freedom (SDOF) analysis. Design charts for the maximum responses in the SDOF system with elastic-perfectly plastic materials are available in many textbooks and manuals such as UFC 3-340-02. These charts provide data for large scaled distances, namely, in the far field. However, few data are available for small scaled distances, namely, in the near field. This paper presents a numerical study to extend the SDOF elastic-plastic design charts to the near field. A sensitivity study for time-step size and positive phase duration is performed to obtain the optimal solutions. The proposed charts are verified using the existing design charts and the finite element methods. Recommendations for the use of the proposed charts are provided.

Nuclear power plants (NPP) should resist local impact loads such as aircraft engine impact as well as internal and external missile impacts based on the international regulations for NPP structures. Although a wide variety of studies on the local responses of conventional reinforced concrete (RC) walls under impact loading have been performed and the design methods for preventing local failure are previously established, no appropriate design methodology is available for steel-plate concrete (SC) walls except for that recently cited in AISC N690 specifications. In this paper, the local resistance and behavior of SC walls subjected to missile impact were investigated experimentally. A total of ten large-scale impact tests for SC and RC walls were performed. The SC wall specimens were designed using various parameters including wall thickness and steel-plate thickness (reinforcement ratio). A set of RC wall specimens were designed for comparison. Initial and residual velocities of projectile, strain and acceleration of the rear plate, local failure mode and deformation, etc. were measured utilizing high speed cameras and various instrumentation devices. From this study, the actual local impact behaviors of SC walls were investigated and the quantitative impact resistance was evaluated. Overall, the current AISC N690 design method was somewhat conservative and needs to be improved for beyond-design-basis events such as aircraft engine impact.

This paper presents an experimental study to investigate the local response of steel plate-concrete (SC) composite walls subjected to impact loads. Seven SC-wall specimens of an intermediate scale with plane dimensions of 2100 × 2100 mm and thicknesses in the range 320–360 mm are tested with target impact projectile velocities in the range 122–159 m/s. Wall thickness, steel-plate thickness, reinforcement ratio, yield strength of the steel plate, and tie bars are considered as the main design parameters for SC walls. For the projectiles, the impact velocity and weight are varied with the wall design parameters. Test results are evaluated using the design equations presented in AISC N690s-1 Appendix N9 based on the three-step method developed using an experimental database comprising the results of 130 prior tests. The impact tests conducted in this study indicate that the three-step method tends to be overly conservative, requiring an improved method to predict accurately the impact behavior of SC walls for beyond design basis impact evaluation. The effects of tie bars and strain rate, which were not addressed in the three-step method, are also examined. The test results and new findings provided in this paper are valuable for more reasonably predicting the impact responses of SC walls and improving the current design methods.

Background: Pure ground glass opacity (GGO) or part-solid GGO with small solid component (≤5 mm) are likely to be non-invasive or minimally invasive lung cancer. However, those lesions sometimes are diagnosed as invasive adenocarcinoma postoperatively. The aim of this study was to determine the predictors of invasive adenocarcinoma in clinical non- or minimally invasive lung cancer. Methods: From January 2010 to December 2017, 203 patients were diagnosed as clinical adenocarcinoma in situ (AIS) or minimally invasive adenocarcinoma (MIA) identified on chest computed tomography (CT) and they underwent surgical resection. A retrospective study was performed to analyze the prediction of invasive adenocarcinoma in clinical non- or minimally invasive lung cancer. Results: Of all clinical AIS or MIA patients, invasive adenocarcinoma was diagnosed in 55 patients (27.1%). In clinical AIS, invasive adenocarcinoma was diagnosed in 19 patients (17.9%) and 36 patients (37.1%) were diagnosed as invasive adenocarcinoma in clinical MIA (P=0.002). Tumor diameter and the presence of solid component were confirmed to be significant predictive factors for invasive adenocarcinoma in a multivariate analysis [hazard ratio (HR) 1.071, P=0.037; HR 2.573, P=0.005; respectively]. Conclusions: Large tumor size and the presence of solid component in clinical AIS or MIA are predictive factors for invasive adenocarcinoma. Therefore, early surgical intervention is recommended for those lesions.

Close-in detonations can damage or destroy components of buildings. The damage to reinforced concrete components is often simulated using finite element codes with considerations of material erosion that are based on either a damage algorithm or a user-specified criterion, and both are explored in the paper. Single element simulations of concrete are performed to establish reliable values of concrete erosion strain as a function of strain rate, compressive strength, element size and loading condition. Numerical analyses of a reinforced concrete column subjected to blast loadings are performed using alternate representations of erosion to characterize the influence of concrete compressive strength, transverse reinforcement, and applied axial load, on predictions of damage.

Equivalency is often used to enable calculations of overpressures and impulses for explosives other than TNT. Equivalent mass factors are available for far-field detonations but none are available for near-field detonations. These reported factors are associated with incident overpressure and impulse and assumed appropriate for reflected overpressure and impulse. Numerical studies of TNT-equivalent mass factors for four high explosives (PETN, Composition B, Pentolite and Tetryl) for incident and normally reflected peak overpressure and scaled impulse are presented for a wide range of scaled distance 0.06 ≤ Z ≤ 40 m/kg1/3. Emphasis is placed on near-field detonations for which no reliable factors are currently available.

Incident and reflected peak overpressures and reflected impulses are often used to compute blast loads on structures, components of structures, and objects. Reflection coefficients are used...

The effects of close-in detonations of high explosives are characterized in terms of incident and reflected overpressures and impulses. Studies are performed using a verified (1D) and validated (2D) CFD code. Calculations are performed to verify the code in 1D, estimate blast effects using 1D models, predict incident overpressures and impulses in the near field, provide guidance on the use of reflecting and transmitting boundaries in 2D and 3D models, provide recommendations on cell size, and predict reflected overpressures on a rigid reflecting surface for close-in detonations. Contact detonations and their effects are not modeled. The complex wave field in the Mach stem region is studied.

Charts in technical manuals and standards of practice can be used to compute incident and reflected peak overpressures and scaled impulses generated by a detonation of a high explosive. Design values are reported for spherical free-air bursts and hemispherical surface bursts as a function of scaled distance and angle of incidence, where the charges are detonated at the center of the sphere. This paper describes a numerical study with a verified and validated computational fluid dynamics code that characterizes the influence of charge shape, charge orientation, and the point of detonation within the charge on free-field incident overpressures and impulses. Analyses are performed with cylindrical charges of different aspect ratios and masses, and results are compared with those of a baseline analysis of a spherical charge. In the near field and midfield, charge shape and point of detonation affect the peak overpressure and impulse, providing values that are significantly different from those associa...

Air-blast parameters, including incident and reflected peak overpressures and impulses, and shock-front arrival times, are typically estimated for protective design using charts developed by Kingery and Bulmash. The charts underpredict incident and normally reflected peak overpressures and incident impulse near the face of the charge. Numerical analyses of detonations of spherical charges of trinitrotoluene in free air are performed using a verified and validated computational fluid dynamics (CFD) code to understand the shortcomings of current approaches for calculating incident and normally reflected overpressures and impulses, and for shock-front arrival time. New equations and design charts are proposed based on CFD calculations.

This paper presents experimental and numerical studies for predicting the seismic responses of welded and bolted steel beam–column connections, namely, welded unreinforced flange and bolted web connection, and welded unreinforced flange and welded web connection. Cyclic tests of these connections composed of members applied widely to steel structures are conducted to examine their seismic performance. Numerical simulations with a focus on the bolted joint are conducted using a nonlinear finite element code. Two different strategies of modeling bolted parts are provided to improve the computational efficiency of numerical analysis: solid contact elements and more simply using shell connector elements. Numerical solutions obtained for full connection models are experimentally validated. The rotational capacity and dissipated energy of the welded and bolted connections are discussed. The local responses for stress and strain in the vicinity of welded and bolted joints are also investigated.