Abstract
Masonry infilled walls have been widely used in civil structures,due to its poor blast resistance,especially the masonry fragments generated under the close-in range vehicle or suicide bomb explosions will lead to the secondary damage,which seriously threaten the safety of people and equipment inside the buildings.Under the close-in range explosion,the wall is mainly suffered from local damage and disintegrated into more debris,which is greatly different from the global failure of walls in the farrange explosion scenarios,and the related studies are still insuf ficient.
The explosion load is mainly controlled by the scaled distance Z,where Z=R/W 1/3,R is the standoff distance,W is the equivalent TNT weight.Orton et al.[1]pointed out that when scaled distance Z≤0.4 m/kg1/3,the explosion belonged to the near-field explosion.Henrych and Major[2]used Rw＜R＜10Rw as the standard of nearfield explosion,where Rw was the radius of charge.
Varma et al.[3]reported a series of blast test data,including reflected pressure,reflected impulse,damage level and maximum deflection of twenty-seven brick panels with dif ferent thickness.Based on Varma's tests,Wei and Stewart[4]carried out numerical simulations to estimate the response and damage of unreinforced brick masonry walls subjected to explosive blast loading.Michaloudi and Gebbeken[5]conducted the experimental and numerical study of masonry walls under far-field and contact detonations.In addition,the Air Force Laboratory[6-9]carried out systematic experiments and numerical simulations on the anti-explosion performance of hollow CMU walls and spray polyurea reinforced CMU walls.Wang et al.[10,11]carried out the explosion test and numerical simulation of the spray polyurea reinforced clay brick walls.However,the researches on the blast resistance of masonry wall mainly focused on the far-field explosion,further study on damage and dynamic responses of masonry wall under close-in range explosion is needed.
Based on the close-in range explosion test on clay brick infilled wall by Shi et al.[12],the Load Blast method,ALE(Arbitrary Lagrangian Euler)method and impulse method are adopted to simulate the blast loadings and predict the damage and dynamic response of masonry infilled wall.Figure 1 and Figure 2 respectively illustrate the finite element model of ALE method and how to apply the impulse produced by explosion to the wall.By comparing with the test data,the applicability of the impulse method is verified.As what Table 1 shows,under close-in range explosion,the peak overpressures predicted by ALE method can agree well with the data from experiment and more accurate than the data predicted by Load Blast method.Figure 3 also shows that ALE method and impulse method accomplish the better simulations of wall's damage and dynamic response under close-in range explosion.
Figure 1 Finite element model of ALE method
Figure 2 Diagrams of calculation for impulse method
Table 1 Peak overpressure of each measuringpoint under 1kg TNT explosion(MPa)
Figure 3 Terminal deformation and displacement of wall under 6 kg TNT explosion predicted by three methods
Then,the influences of the standoff distance,bonding strength between mortar and bricks,as well as the material constitutive models of bricks are discussed.Figure 4 and Figure 5 respectively show the damage of wall under different standoff distance and identical scaled standoff distance and the terminal damage of wall predicted by different material models.It indicates that,under the closein range explosion,the damage level of wall gets much serious with the increase of the standoff distance under the identical scaled standoff distance,the corresponding failure mode is transferred from local damage to the global collapse failure;the blast resistance of the wall is generally strengthened with enhancing the bonding strength between brick and mortar,and mainly influenced by the shear failure stress;both the MAT_BRITTLE_DAMAGE and MAT_WINFRI-TH_CONCRETE models can give better predictions than MAT_SOIL_AND_FOAM model.
Figure 4 Damage of wall under different standoff distance and identical scaled standoff distance of 0.22 m/kg1/3
Figure 5 Terminal damage of wall predicted by two material models under 6 kg TNT explosion