50SiMnVB钢圆筒在爆炸载荷作用下断裂行为研究

研究了在爆炸载荷作用下,50 SiMnVB钢圆筒自然破碎和高能束改性破碎后,破片拉伸和剪切断口在整个断面上的比例所发生的变化规律,表明采用高能束局部改性技术可以实现脆性材料圆筒断裂方式的转化。试验中还观察到在拉伸断口应力方向的断面上出现了熔化现象,这说明在拉伸断裂区局部存在着剪切现象,同时证明采用高能束改性后圆筒在爆炸载荷作用下可产生全壁厚剪切断裂。

柱状装药爆破的岩石压碎圈与裂隙圈计算

利用Ｍｉｓｅｓ强度准则，并考虑岩石三向受力及其强度的应变率效应，导出柱状药包爆炸在岩石中引起的压碎圈与裂隙圈半径的计算式，进而对周边控制爆破的单孔装药量进行探讨。对于常见的岩石种类，计算式能取得与爆破实际相符的结果。

Pressure-impulse diagram with multiple failure modes of one-way reinforced concrete slab under blast loading using SDOF method

Two loosely coupled single degree of freedom (SDOF) systems were used to model the flexural and direct shear responses of one-way reinforced concrete slabs subjected to explosive loading. Blast test results show that the SDOF systems are accurate in predicting the failure mode of the slab under blast loads by incorporating the effects of the strain rate effect caused by rapid load application. Based on different damage criteria, pressure-impulse (P-I) diagrams of the two failure modes were analyzed with the SDOF systems. The effects of span length, concrete strength, and reinforcement ratio of the slab on the P-I diagram were also investigated. Results indicate that a slab tends to fail in direct shear mode when it is of a smaller span length and tends to fail in flexure mode when it is of a larger span length. With the increase of the concrete strength or reinforced ratio, both the flexure and shear capacity increase. Based on numerical results, a simplified method and a semi analytical equation for deriving the P-I diagram are proposed for different failure modes and damage levels.

Mitigation of blast loadings on structures by an anti-blast plastic water wall

Seven in-situ tests were carried out in far field to study the blast mitigation effect of a kind of water filled plastic wall. Test results show that the mitigation effect of water filled plastic wall is remarkable. The maximum reduction of peak reflected overpressure reaches up to 94.53%, as well as 36.3% of the minimum peak reflected overpressure reduction in the scaled distance ranging from 1.71 m/kg1/3 to 3.42 m/kg1/3. Parametric studies were also carried out. The effects of the scaled gauge height, water/charge scaled distance(the distance between the explosive charge and the water wall), water wall scaled height and water/structure scaled distance(the distance between the water wall and the structure) were systematically investigated and compared with the usual rigid anti-blast wall. It is concluded that these parameters affect the mitigation effects of plastic water wall on blast loadings significantly, which is basically consistent to the trend of usual rigid anti-blast wall. Some formulae are also derived based on the numerical and test results, providing a simple but reliable prediction model to evaluate the peak overpressure of mitigated blast loadings on the structures.

A simplified model to predict blast response of CFST columns

In order to study the dynamic response of concrete-filled steel tube(CFST) columns against blast loads,a simplified model is established utilizing the equivalent single-degree-of-freedom(SDOF) method,which considers the non-uniform distribution of blast loads on real column and the axial load-bending moment(P-M) interaction of CFST columns.Results of the SDOF analysis compare well with the experimental data reported in open literature and the values from finite element modeling(FEM) using the program LS-DYNA.Further comparisons between the results of SDOF and FEM analysis show that the proposed model is effective to predict the dynamic response of CFST columns with different blast conditions and column details.Also,it is found that the maximum responses of the columns are overestimated when ignoring the non-uniformity of blast loads,and that neglecting the effect of P-M interaction underestimates the maximum response of the columns with large axial load ratio against close range blast.The proposed SDOF model can be used in the design of the blast-loaded CFST columns.

Strengthening of Concrete Box Girder Bridges under Close-in Detonations

The response of a bridge superstructure under blast loading might depend largely on the extent of the local damage experienced due to close-in explosion threats. This paper investigates the local and structural response of box girder bridge decks strengthened using CFRP （carbon fiber reinforced polymers） under close-in detonations. Due to the lack of experimental research on this topic, the study is conducted using the explicit finite element computer program LS-DY-NA. The numerical study will be verified using the results of strengthened reinforced concrete slabs under field detonations. The blast load was assumed to be detonated above the bridge deck. The key parameters investigated are the charge size, and the strengthening location on the deck. This paper will present the results of this investigation and provides recommendations for predicting the local damage level based on the CFRP strengthening design under blast threat.

Simplified Damage Assessment of Slab Against External Blast Load

Recently, the mode approximation method(MAM) has been adopted to analyze beam elements against blast load. However, in real cases, the main structural element of an underground structure is slab and side wall since they not only support the structure itself but also may sustain external loads from blast, earthquake, and other kinds of impact. In the present study, the MAM is extended from beam to plate elements and the soil-structure interaction is considered and simplified when calculating structural response under blast load. Pressure-impulse diagrams are generated accordingly for further quick damage assessment.

Behavior of Cantilever Slabs in a Blast Environment

Behavior of structural elements under blast loading is different from that under usual loading conditions that are considered in conventional structural deigns. Cantilever slabs are more vulnerable than most other elements under blast loads because of their shape. Understanding the blast behavior of cantilever slabs is useful in strengthening them against blast loads. In this paper, blast loading design envelopes for cantilever slabs are proposed using which, the blast behavior of conventional cantilever slabs can be identified. The paper describes the theories behind these envelopes and the way they can be applied to improve conventional designs. These envelopes have been prepared using numerical techniques. The theories used are accepted, verified and validated theories. The paper shows the possibility of converting a conventional cantilever slab design into impulsive regime design with minor adjustments to the structural design. It points out the importance of increasing slab thickness and controlling steel/concrete ratio for strengthening conventional cantilever slab designs and the requirement of reinforcement at top and bottom fibers.

Dynamic Response of Structure under Blast Load

The paper follows from the theory of explosion and interaction of an impact wave formed by the explosion and a structure. Firstly, the paper determines the parameters of the blast wave excited by a small charge explosion. The empirical formulas on the basis of our own experimental results are shown and used for the structure analysis. Evaluations of structures loaded by an explosion based on dynamic response in rotations round the central line of plate or beam systems during the dynamic load of this type is discussed in the paper and comparison of own limit values and published ones is presented. Blast loads typically produce very high strain rates in the range of 102 to 10-4 s-1. The effect of strain rate for concrete material is discussed. The formulas for increased compressive strength of concrete and steel reinforcement are presented. The ductility of structural members is influenced by the corresponding values under high strain rate of reinforcement, Damage to the structure is assessed accordingly firstly by the angle of rotation of the middle axis/surface, and secondly by the limit internal forces of the selected structure. The extreme nature of blast resistance makes it necessary to accept that structural members have some degree of inelastic response in most cases. This enables the application of structure dissipation using the ductility factor and increased of concrete strength. The limits are correlated with qualitative damage expectations. The methodology of dynamic response assessment and its application to the simple bridge structure is discussed.

A Two-step Approach to Progressive Collapse Analysis of Building Structures under Blast Loading

Structural collapse under blast loads is a very complex process. For several decades, the engineering profession has considered some approaches to analyze the essential physics of collapse phenomena. Recently, the interest in this topic has risen to an apex since the collapse of the World Trade Center towers. A two-step analysis approach to capture the characteristics of structural collapse during explosions is proposed. A numerical example is presented to illustrate the performance of the presented approach.