Clay brick masonry unit(CBMU) walls are widely used in building structures,and its damage and protection under explosion loads have been a matter of concern in the field of engineering protection.In this paper,a serie...Clay brick masonry unit(CBMU) walls are widely used in building structures,and its damage and protection under explosion loads have been a matter of concern in the field of engineering protection.In this paper,a series of full-scale experiments of the response characteristics of 24 cm CMBU walls unreinforced and reinforced with polyurea elastomer subjected to blast loading were carried out.Through setting 5.0 kg TNT charges at different stand-off distances,the damage characteristics of masonry walls at different scaled distances were obtained.The reinforcement effect of different polyurea coating thicknesses and methods on the blast resistance performance of masonry walls under single and repeated loads were also explored.Five failure grades were summarized according to the dynamic response features of masonry walls.Based on the stress wave propagation pattern in multi-media composite structures,the internal stress distribution of masonry walls were analyzed,and the division basis of the masonry walls’ failure grades was then quantified.Combined with Scanning Electron Microscope(SEM)images,the deformation characteristics of soft and hard segments of polyurea and effects of detonation products on microstructures were revealed respectively,which provides an important reference for the design and application of polyurea in the blast resistance of clay brick masonry walls.展开更多
This study investigates a kind of masonry consisting of clay-fired brick(f_(c)=10 MPa;r=1:38 g/cm^(3))and mortar(f_(c)=10 MPa;r=1:8 g/cm^(3)).Clay-fired brick masonry connotes a traditional construction material of ol...This study investigates a kind of masonry consisting of clay-fired brick(f_(c)=10 MPa;r=1:38 g/cm^(3))and mortar(f_(c)=10 MPa;r=1:8 g/cm^(3)).Clay-fired brick masonry connotes a traditional construction material of old architecture and public buildings.We carried out penetration experiments in which four clay-fired brick walls employing two different patterns were subjected to impact from small high-speed projectile,i.e.12.7 mm armor-piercing explosive incendiary projectile and material tests in which the static and dynamic compressive strengths of clay-fired brick and mortar were determined by quasi-static and SHPB(Split Hopkinson Pressure Bar)tests.The experimental data include hit and exit velocities,damage configuration of clay brick masonry and mechanical properties of material at low and high strain rates,though which influence of thickness and bonding patterns of wall on kinetic loss of bullet,the damage patterns of masonry observed experimentally and dynamic increase of material strengths are analyzed.To keep minimum boundary inconsistency with reality,full 3D detailed finite element model consisting of two different material is established.Sharing common nodes and employing automatic tiebreak contact are combined to reduce computational time usage of large-scale model.For description of clay-fired brick and mortar RiedeleHiermaiereThoma(RHT)material model is employed.Material parameter set is derived based on experimental data,available literature and engineering assumptions.The numerical simulations study the mesh resolution dependency of material model,reproduce the crucial phenomena of masonry in experiment acceptably and offer more time-resolved insight into motion of bullet in the process of penetration.The feasibility of means of constructing finite element model and applying RHT model to the masonry herein and analogous constructions is explored through numerical investigation.展开更多
The recent increase in blast/bombing incidents all over the world has pushed the development of effective strengthening approaches to enhance the blast resistance of existing civil infrastructures.Engineered geopolyme...The recent increase in blast/bombing incidents all over the world has pushed the development of effective strengthening approaches to enhance the blast resistance of existing civil infrastructures.Engineered geopolymer composite(EGC)is a promising material featured by eco-friendly,fast-setting and strain-hardening characteristics for emergent strengthening and construction.However,the fiber optimization for preparing EGC and its protective effect on structural elements under blast scenarios are uncertain.In this study,laboratory tests were firstly conducted to evaluate the effects of fiber types on the properties of EGC in terms of workability,dry shrinkage,and mechanical properties in compression,tension and flexure.The experimental results showed that EGC containing PE fiber exhibited suitable workability,acceptable dry shrinkage and superior mechanical properties compared with other types of fibers.After that,a series of field tests were carried out to evaluate the effectiveness of EGC retrofitting layer on the enhancement of blast performance of typical elements.The tests include autoclaved aerated concrete(AAC)masonry walls subjected to vented gas explosion,reinforced AAC panels subjected to TNT explosion and plain concrete slabs subjected to contact explosion.It was found that EGC could effectively enhance the blast resistance of structural elements in different scenarios.For AAC masonry walls and panels,with the existence of EGC,the integrity of specimens could be maintained,and their deflections and damage were significantly reduced.For plain concrete slabs,the EGC overlay could reduce the diameter and depth of the crater and spallation of specimens.展开更多
To improve the effectiveness of control of surrounding rock and the stability of supports on longwall topcoal caving faces in steeply inclined coal seams, the stability of the roof structure and hydraulic supports was...To improve the effectiveness of control of surrounding rock and the stability of supports on longwall topcoal caving faces in steeply inclined coal seams, the stability of the roof structure and hydraulic supports was studied with physical simulation and theoretical analysis. The results show that roof strata in the vicinity of the tail gate subside extensively with small cutting height, while roof subsidence near the main gate is relatively assuasive. With increase of the mining space, the caving angle of the roof strata above the main gate increases. The characteristics of the vertical and horizontal displacement of the roof strata demonstrate that caved blocks rotate around the lower hinged point of the roof structure, which may lead to sliding instability. Large dip angle of the coal seam makes sliding instability of the roof structure easier.A three-hinged arch can be easily formed above both the tail and main gates in steeply inclined coal seams. With the growth in the dip angle, subsidence of the arch foot formed above the main gate decreases significantly, which reduces the probability of the roof structure becoming unstable as a result of large deformation, while the potential of the roof structure's sliding instability above the tail gate increases dramatically.展开更多
基金supported by the National Natural Science Foundation of China nos.51978660。
文摘Clay brick masonry unit(CBMU) walls are widely used in building structures,and its damage and protection under explosion loads have been a matter of concern in the field of engineering protection.In this paper,a series of full-scale experiments of the response characteristics of 24 cm CMBU walls unreinforced and reinforced with polyurea elastomer subjected to blast loading were carried out.Through setting 5.0 kg TNT charges at different stand-off distances,the damage characteristics of masonry walls at different scaled distances were obtained.The reinforcement effect of different polyurea coating thicknesses and methods on the blast resistance performance of masonry walls under single and repeated loads were also explored.Five failure grades were summarized according to the dynamic response features of masonry walls.Based on the stress wave propagation pattern in multi-media composite structures,the internal stress distribution of masonry walls were analyzed,and the division basis of the masonry walls’ failure grades was then quantified.Combined with Scanning Electron Microscope(SEM)images,the deformation characteristics of soft and hard segments of polyurea and effects of detonation products on microstructures were revealed respectively,which provides an important reference for the design and application of polyurea in the blast resistance of clay brick masonry walls.
基金The work presented in this paper is funded by Opening Project of Science and Technology on Transient Impact Laboratory(Grant No.614260601010517).
文摘This study investigates a kind of masonry consisting of clay-fired brick(f_(c)=10 MPa;r=1:38 g/cm^(3))and mortar(f_(c)=10 MPa;r=1:8 g/cm^(3)).Clay-fired brick masonry connotes a traditional construction material of old architecture and public buildings.We carried out penetration experiments in which four clay-fired brick walls employing two different patterns were subjected to impact from small high-speed projectile,i.e.12.7 mm armor-piercing explosive incendiary projectile and material tests in which the static and dynamic compressive strengths of clay-fired brick and mortar were determined by quasi-static and SHPB(Split Hopkinson Pressure Bar)tests.The experimental data include hit and exit velocities,damage configuration of clay brick masonry and mechanical properties of material at low and high strain rates,though which influence of thickness and bonding patterns of wall on kinetic loss of bullet,the damage patterns of masonry observed experimentally and dynamic increase of material strengths are analyzed.To keep minimum boundary inconsistency with reality,full 3D detailed finite element model consisting of two different material is established.Sharing common nodes and employing automatic tiebreak contact are combined to reduce computational time usage of large-scale model.For description of clay-fired brick and mortar RiedeleHiermaiereThoma(RHT)material model is employed.Material parameter set is derived based on experimental data,available literature and engineering assumptions.The numerical simulations study the mesh resolution dependency of material model,reproduce the crucial phenomena of masonry in experiment acceptably and offer more time-resolved insight into motion of bullet in the process of penetration.The feasibility of means of constructing finite element model and applying RHT model to the masonry herein and analogous constructions is explored through numerical investigation.
基金National Natural Science Foundation of China(Grant Nos.51908188 and 51938011).
文摘The recent increase in blast/bombing incidents all over the world has pushed the development of effective strengthening approaches to enhance the blast resistance of existing civil infrastructures.Engineered geopolymer composite(EGC)is a promising material featured by eco-friendly,fast-setting and strain-hardening characteristics for emergent strengthening and construction.However,the fiber optimization for preparing EGC and its protective effect on structural elements under blast scenarios are uncertain.In this study,laboratory tests were firstly conducted to evaluate the effects of fiber types on the properties of EGC in terms of workability,dry shrinkage,and mechanical properties in compression,tension and flexure.The experimental results showed that EGC containing PE fiber exhibited suitable workability,acceptable dry shrinkage and superior mechanical properties compared with other types of fibers.After that,a series of field tests were carried out to evaluate the effectiveness of EGC retrofitting layer on the enhancement of blast performance of typical elements.The tests include autoclaved aerated concrete(AAC)masonry walls subjected to vented gas explosion,reinforced AAC panels subjected to TNT explosion and plain concrete slabs subjected to contact explosion.It was found that EGC could effectively enhance the blast resistance of structural elements in different scenarios.For AAC masonry walls and panels,with the existence of EGC,the integrity of specimens could be maintained,and their deflections and damage were significantly reduced.For plain concrete slabs,the EGC overlay could reduce the diameter and depth of the crater and spallation of specimens.
基金the Joint Funds of the National Natural Science Foundation of China (No. U1361209)the National Basic Research Program of China (No. 2013CB227903)
文摘To improve the effectiveness of control of surrounding rock and the stability of supports on longwall topcoal caving faces in steeply inclined coal seams, the stability of the roof structure and hydraulic supports was studied with physical simulation and theoretical analysis. The results show that roof strata in the vicinity of the tail gate subside extensively with small cutting height, while roof subsidence near the main gate is relatively assuasive. With increase of the mining space, the caving angle of the roof strata above the main gate increases. The characteristics of the vertical and horizontal displacement of the roof strata demonstrate that caved blocks rotate around the lower hinged point of the roof structure, which may lead to sliding instability. Large dip angle of the coal seam makes sliding instability of the roof structure easier.A three-hinged arch can be easily formed above both the tail and main gates in steeply inclined coal seams. With the growth in the dip angle, subsidence of the arch foot formed above the main gate decreases significantly, which reduces the probability of the roof structure becoming unstable as a result of large deformation, while the potential of the roof structure's sliding instability above the tail gate increases dramatically.
