Response of masonry systems against blast loading

Eid Bdshh ,Amjd Nseer ,Mohmmd Ashrf ,Tuseef Ahmd

a Department of Civil Engineering,UET Peshawar,Pakistan

b Electrical Engineering Department,CECOS University of IT&Emerging Sciences Peshawar,Pakistan

Keywords: Peak over pressure Pressure sensor Composition-B TNT Scaled distance Stand-off distance Charge shape Confined Unreinforced Ferrocemented

ABSTRACT In this paper eight successive experimental blast tests with an increasing TNT equivalent charge weights ranging from 0.56 kg to 17.78 kg were conducted on unreinforced,ferrocemented overlay masonry and con fined masonry walls.The pressure-time history caused by the blast was recorded by pressure sensors installed on the test specimen.The resulting damage pattern was observed during each test.Weak zones in the three systems of masonry were identi fied.Scaled distances for different damage levels in the three masonry systems were experimentally obtained.The results provide a basis for determining the response of each masonry system against blast loading.Consequently,ef ficiency of ferrocemented overlay masonry and con fined masonry was found established in mitigation against blast loads.

1.Introduction

The use of explosive material by terrorists against public and civil infrastructure for the last several decades continues unabated(Badshah et al.[1]).When a structure,especially masonry building is exposed to blast loading;it results in damages to life and property due to shock waves,flying debris and complete collapse.Human injuries and deaths due to striking of high velocity projectiles ejected from the structural and non structural elements of building in terrorist bombing or accidental explosion is always more than the shock waves itself.Brick masonry is used as the main structural and non-structural component in fabrication of buildings in several regions of the world.Brick masonry is weak against out-of-plane loading such as seismic loading,impact of falling debris from rocks,and blast loading(Ahmad et al.[2],Gurreiro et al.[3],Li et al.[4]and Parisi et al.[5]).

The simple techniques required for synthesis of explosive materials and limited access to the research data on blast loading has made the proper response to blast loading a challenging issue for the structural engineers,architects and people involved in construction industry(Badshah et al.,[1]).

However,several researchers have carried out numerical and experimental studies for evaluating the response of masonry against blast loading.According to Badshah et al.[1],structural response is a function of wave parameters of blast load,geometry,boundary conditions,material properties and natural time period of target structure.Knox et al.[6]and El-Domiaty et al.[7]enumerated various techniques for improving performance against blast loading of unreinforced brick masonry(URM)such as changing boundary conditions,increasing masonry wall thickness,and incorporating steel reinforcement.

Keys and Clubley[8]reported structural failure in masonry walls when exposed to positive overpressure with positive phase duration exceeding 100 ms.Failure mode,initial fragmentation and distribution of debris were found dependent on overpressure and impulse of blast,and wall geometry.Pandey and Bisht[9],Pereira et al.[10],Wei and Stewart[11]and Parisi et al.[5]reported enhanced dynamic performance with increasing thickness of brick masonry wall against blast loading.

The response of structure is also dependent on material properties of brick masonry.Wei and Stewart[11],in numerical study found a decrease in maximum de flection in masonry and rotation at support by increasing the strength of brick masonry unit and mortar under small blast loading scenario.

Pereira et al.[10]after experimental study on in fill masonry wall against blast loading found decreased maximum de flection in masonry with increasing compressive and tensile strengths up to certain level of in fill masonry for small scaled distances.Similarly,increasing Mode-I fracture energyGf,reduces the maximum displacement in the region of small scaled distances.While,increasing Young’s Modulus of ElasticityE,decreased maximum de flection of in fill masonry for all scaled distances.According to Pandey and Bisht[9],max de flection at the centre as well as at the interface of masonry and frame is decreased when mortar of richer quality and higher friction coef ficient is used in masonry.Parisi et al.[5]found considerable in fluence of material strength of tough tile masonry(TSM)in resistance to impulsive and dynamic loading.

Structural response and damage level of structural or nonstructural elements against blast loading is also dependent on boundary conditions.Wei and Stewart[11],in numerical study using LS-DYNA,found decreasing trend in maximum de flection of masonry walls as the number of fixed ended supports was increased.Similarly,El-Domiaty et al.[7]reported an appreciable change in response of brick masonry as the boundary conditions of masonry were changed.According to Hao and Wu[12]and Wu and Hao[13],when the material model of in fill masonry is kept constant but material models of RC frames are changed,then for the same damage level(non excessive)the required scaled distances are different.Ahmad et al.[2]reported no damage at scaled distance of 2.28 m/kg1/3for cantilever brick masonry wall in experimental study.Wu and Hao[13]in numerical study reported collapse at a scaled distance of 2.37 m/kg1/3of in fill CMU masonry in RC frame.

Pre compression in masonry wall improves its performance against blast loading.According to Parisi et al.[14],increasing pre compression ratio of tough tile masonry(TSM)improves its response against blast loading.

Performance of brick masonry against blast loading is also enhanced by using retro fitting techniques such as FRP,polyurea,polyurethane,aluminum foam,engineered cementitious composites,and ferrocement(Badshah et al.[1]).

Urgessa and Maji[15],studied the response of FRP applied eight masonry walls arranged in circular fashion around point of detonation and reported enhanced performance of masonry applied with different arrangements of FRP.El-Domiaty et al.[7]after experimental and numerical studies coupled the charge weight and stand-off distance with damage levels in masonry walls.FRP retro fitted masonry walls showed enhanced performance against more severe threat levels.Furthermore,FRP reinforced masonry walls failed in safer manner avoiding fatal shrapnels.Sielicki[16],in Ph.D.studies,reported highest safety threshold by applying composite fabric reinforcement to concrete masonry unit(CMU)wall.Similarly,Badshah et al.[1]reported the work of Tan and Patoary[17],Baylot et al.[18],Stanley et al.[19],Stratford et al.[20],Alsayed et al.[21],Bui and Limam[22],Chen et al.[23],Hamed and Rabinovitch[24],Hamed and Rabinovitch[25],and Haderi et al.[26].These researchers have found improved response of FRP reinforced masonry against blast loading.

Similarly,Badshah et al.[1]reported enhanced response of polyurea treated masonry subjected to blast loading.

Su et al.[27]and Aghdamy et al.[28]numerically studied the performance of aluminum foam applied to masonry and reported its potential as retro fitting material for brick masonry against blast loading.

Maalej et al.[29],recommended the use of engineered Cementitious Composites for increasing resistance of masonry against blast loading.

All the above retro fitting techniques are expensive and require special expertise and tools for field applications.Therefore,there is an urgent need for exploring alternative techniques,which are low cost and simple yet ef ficient against blast loading in terrorist prone regions.Two of such techniques are con fined masonry and ferrocemented overlay masonry systems.

Ferrocemented overlay masonry has been widely used for mitigation against seismic loading and Badshah et al.[1],reported its potential against blast loading.Similarly,con fined masonry has an enhanced effect on the performance against seismic loading as reported by Naseer.A[30].Furthermore,these techniques are relatively simple,indigenous,low cost,and require no special expertise for application to brick masonry in the field.Therefore,in the current research study,the response of unreinforced masonry,ferrocemented overlay masonry and con fined masonry against blast loading is studied experimentally.The damage level of each masonry system after each successive event was compared to pre defined threat and damage levels.Consequently,the response of each masonry system against blast loading has been quanti fied.

2.Test set-up

2.1.Test specimens geometrical models and material properties

The unreinforced,ferrocement overlay and con fined masonry walls each 23 cm thick were placed on the perimeter of 3.66 m radius circle as shown in Fig.1(a).The height of walls was kept 1.83 m above ground level in each case.U-shaped masonry walls were used to simulate portion of walls used in actual practice of masonry buildings(Bui and Limam.[22]).

Brick units with nominal size 23 cm×11.40 cm×7.60 cm and compressive strength 13.4 MPa in 20 mm thick cement-sand(1:6)mortar were used in fabrication of test specimens.Compressive strength of masonry was 3.13 MPa obtained in laboratory as per ACI-530 criteria.as shown in Fig.2.

In ferrocement overlay masonry,wire mesh with speci fications shown in Fig.1(c)was fixed to the URMwall by 38 mm long screw and rawal plug as shown in Fig.3(a).Subsequently,the wall surface was plastered with cement sand(1:4)mortar.

The confining element in con fined masonry as shown in Fig.1(d)was fabricated using Grade 40 steel.The concrete used in RC confining elements listed 28 days cylinder compressive strength as 10.3 MPa.Reinforcement in RC confining elements was provided in accordance with Building Code of Pakistan-Seismic Provision(2007).

Concrete in these RC elements was poured after the walls are constructed.The concrete filled all gaps and covered vertical bars protruding out from the foundation.On hardening of concrete,the RC elements held the masonry wall segments tightly without any space between them as shown in Fig.3(b).

2.2.Explosive material

The walls were subjected to successive blast events.Different weights of Composition-B with TNT equivalent weight factor1.11(Badshah et al.[1])were used in each event.The explosives charges were cylindrical in shapes with different length to diameter ratio(L/D)given in Table 1.

Composition-B samples in each event were placed at the center of circle as shown in Fig.1(a).Consequently,all the three walls were subjected to uniform shock waves simultaneously in each blast event.Average height of explosive material laden by suicide bomber in standing position or in car and pick up used in terrorist activities is 0.91 m from the ground surface.To simulate the stated scenario,the explosive charges were detonated at height of 0.91 m from the ground by use of wooden tripod as shown in Fig.4(c).Primary explosive PE3 was used as booster.Safety fuse No11 as shown in Fig.4(a and b)was used to ensure safe evacuation of personnel and logistics before explosion.It was calibrated at site with burning speed of 27±3 s/30.5 cm.Each charge was detonated from the top.

Fig.1.(a)Instrumentation and placement of walls with reference to charge position(b)Detail of URM wall(c)Details of ferrocement overlay masonry wall(d)Detail of con fined masonry wall(Badshah.E[31]).

Fig.2.Experimental set up for compressive strength of brick masonry prism.

2.3.Pressure transducers

Kistler series(211B1.B5)pressure sensors with max pressure recording capacity as 3.45 MPa were used in the field as shown in Fig.5(a).The sensor was inserted into the hollow plug which was fixed in elbow of galvanized steel pipe as shown in Fig.5(b).The steel pipe carrying pressure sensor was fixed with steel hooks on the test specimen at required height and orientation as shown in Fig.5(c).The sensor was connected to data acquisition system through a cable passing through steel pipe.The cables were buried 5 cm deep in ground up to 12 m distance from the centre of explosion to avoid blowing of and damage due to stronger shock waves in the vicinity.Data acquisition system was placed in a 1.22 m deep and safe concrete bunker at distance of 57 m from the centre of explosion as shown in Fig.5(d).

3.Experimental results of pressure data

The explosive charges were detonated as shown in Fig.6.The TNT equivalent charge weight was increased from 0.55 kg to 17.88 kg shown in Table No.1 but stand-off distance remained constant for the respective sensor in the eight successive events.The TNT weight and stand-off distance in each event were coupled in scaled distances(Z=R/W1/3)as shown in Table 2.

Peak over pressure measured by PS2and PS3sensors are given in Table 2.

Table 1 Weight of Composition-B with different L/D ratio.

Table 2Measured peak overpressure for different events.

Pressure sensor PS2was installed on ferrocemented wall at a height of 0.91 m from the ground surface.It was oriented so as to face the centre of explosive sample in the same horizontal plane.Consequently,the peak re flected pressure recorded was maximum due to zero angle of incidence and minimum stand-off distance between the specimen and centre of explosive.Similarly,Pressure sensor PS3was installed on con fined brick masonry at a height of 1.12 m(0.203 m above the centre of explosive in each event)from the ground surface to ascertain the variation of peak re flected overpressure with variation in stand-off distance and angle of incidence.The peak re flected overpressure recorded by PS3was found less than PS2in each event.The data acquired by these two pressure sensors will be the same for all three systems of brick masonry on the respective points,as all the walls were symmetrically placed around the point of detonation in each event.

The pressure pro file developed from the data acquired from the sensor PS2at the scaled distance 4.353 m/kg1/3is shown in Fig.7.

4.Scaled distance versus damages

The damages pattern and intensity were recorded after each successive blasts.

Fig.3.Fabrication of test specimens(a)Ferrocement overlay masonry wall(b)Confined masonry wall.

4.1.Event No,1(Scaled distance 4.353 m/kg1/3)

Confined and ferrocemented overlay masonry walls showed no cracks anywhere.Unreinforced masonry wall,suffered minor vertical cracks appearing at the centre shown in Fig.8 because of flexural effect and at the orthogonal walls joint due to rotation.The confining element in con fined masonry and ferrocemented overlay restrained the masonry against damages.

4.2.Event No.2(Scaled distance of 3.020 m/kg1/3)

Confined masonry showed vertical hairline cracks following mortar joints at the centre as shown in Fig.9(a).Ferrocemented overlay masonry listed no damages as shown Fig.9(b).The cracks in unreinforced masonry appearing in the preceding event were found widened and extended due to absence of any confining mechanism.Horizontal minor shear cracks appeared near the ground because of outward movement of wall at the center.Shear cracks developed in the right corner of out-of-plane wall starting from top layer extending to 5th layer in downward direction shown in Fig.9(c).

4.3.Event No.3(Scaled distance of 2.744 m/kg1/3)

Fig.4.(a)Cylindrical shaped explosive with booster and safety fuse(b)Preparation of sample in the field(c)Tripod for ensuring 0.91 m height above ground surface(Badshah.E et al.,2017).

In con fined masonry,vertical crack at the centre appearing in event No.2,widened and further propagated.Horizontal hairline cracks appeared in the top layer.Cracks in vertical direction,following mortar joints appeared near the two columns.Separation of column and out-of-plane wall was initiated at mid height as shown in Fig.10(a).High velocity flying debris ejecting from ground surface during explosion impacted the ferrocemented layer and damaged it in small patches at several locations throughout the surface of out-of-plane masonry wall as shown in Fig.10(b).In unreinforced masonry,the three vertical cracks in the out-of-plane wall in the preceding event widened and extended throughout the depth of the wall.Horizontal crack in the previous event appeared near ground surface in the out-of-plane wall,widened.Additional horizontal and diagonal cracks produced.Bricks in the top layer loosened and displaced out-of-plane wall as shown in Fig.8(c).Cracks in the preceding event were widened and propagated and additional cracks were observed in the in-plane portion of unreinforced masonry as shown in Fig.8(d).

Fig.5.(a)Kistler series pressure transducer(b)Pressure sensor fixed in steel pipe(c)Pressure transducer mounted on masonry(d)Data acquisition system.

Fig.6.Blast event using 7.49 kg TNT equivalent charge weight.

Fig.7.Pressure-time history.

4.4.Event No.4(Scaled distance 2.195 m/kg1/3)

Similarly,after blast event No.4 with scaled distance of 2.195 m/kg1/3,minor diagonal cracks appeared in the in-plane wall of con fined masonry.Vertical central crack appeared in event No.3,widened and diagonal crack appeared in the upper region of out-ofplane wall.Separation between column and out-of-plane wall widened and propagated as shown in Fig.11(a).In ferrocement overlay wall,wire mesh was exposed and de-bonded in patches just above ground level as shown in Fig.11(b).Unreinforced masonry out-of-plane wall damaged so much so that it concaved in outside direction and walls separation increased as shown in Fig.11(c)and(d).Diagonal crack produced in the in-plane wall in the previous event widened and extended to the ground at the middle width.

4.5.Event No.5(Scaled distance 1.830 m/kg1/3)

In con fined masonry,separation between column and out-ofplane wall was further increased.Out-of-plane wall concaved outside near the ground level shown in Fig.12(a).In ferrocement overlay masonry,steel mesh was exposed and debonded in larger areas near the ground and in small patches near the top.The two walls separated but remained intact due to steel mesh as shown in Fig.12(b).Bricks in alternate layers near the ground were loosened and fell down as shown in Fig.12(c).Unreinforced masonry out-ofplane wall and in-plane walls collapsed completely as shown in Fig.12(d).The in-plane walls collapsed outside due to peak negative(suction)pressure following positive pressure and pushing of falling of out-of-plane wall.

Fig.8.Masonry response after No.1(a)Confined masonry(b)Ferrocemented overlay masonry(c)Unreinforced masonry.

Fig.9.Masonry response after event No.2(a)Confined masonry(b)Ferrocemented overlay masonry(c)Unreinforced masonry.

4.6.Event No 6(Scaled distance 1.662 m/kg1/3)

Confined masonry remained intact.Out-of-plane wall concaved outside further near ground surface and separation b/w columns and walls increased.Number of cracks increased in the in-plane walls.Cracks in the beam column joints appeared as shown in Fig.13(a)-(b).The out-of-plane wall of ferrocement overlay masonry was fully damaged and one in-plane wall completely separated and inclined in outward direction as shown in Fig.13(c).

4.7.Event No 7(Scaled distance 1.470 m/kg1/3)

Confined masonry out-of-plane wall was partially collapsed.Cracks in wall-column joints widened.Diagonal cracks in the inplane walls extended as shown in Fig.14(a)-(b).Ferrocemented overlay masonry out-of-plane wall collapsed and since the bricks were already loosened in the previous events,therefore,these were scattered up to a distance of 6.1 m in the direction of shock waves.One of the in-plane walls fell down outside in integral form and other remained inclined in outside direction as shown in Fig.14(c).

4.8.Event No 8(Scaled distance 1.371 m/kg1/3)

Similarly,after event No.8 with scaled distance of 1.371(m/kg1/3),remaining portion of out-of-plane wall of con fined masonry collapsed leaving the confining frame intact.Masonry scattered at a distance of 3.66 m outside from the out-of-plane wall.The inplane walls remained intact but with more open cracks as shown in Fig.15.

Failure patterns:The out-of-plane wall of unreinforced masonry accrued vertical cracks near the centre and in the upper part which is unsupported(Figs.8(c),9(c)and 11(d))due to bending loading.The cracks at the joint(intersection of out-plane wall and in-plane wall)were produced due to the loading of out-of-plane wall which produced rotation at the corner posts as shown in Figs.8(c),9(c)and 10(c)-10(d)and Fig.11(c).The in-plane walls were subjected to in-plane shear.Consequently,diagonal cracks were produced.

In ferrocement overlay masonry wall the cracks were less severe.The mechanism of the cracks at the centre as well as at joints is the same as in unreinforced masonry wall.

In con fined masonry wall,the central cracks are due to bending load.These central cracks are located in middle part of wall(in contrast to the upper part of the wall as is the case in unreinforced masonry wall)due to confining element at the top and support at ground.

5.Response of walls

The response of three(03)different masonry systems was evaluated experimentally against same blast scenario.The damage level in each preceding blast event was correlated to scaled distance‘Z’(m/kg1/3).In experimental program,four damage levels were selected as hazards level,and four design parameters at different threat levels as used by El-Domiaty et al.[7]shown in Tablse 3 and 4 respectively.

The three wall systems were subjected to same blast load events successively.

5.1.Unreinforced masonry wall

The unreinforced wall could sustain the first four events(scaled distance 4.353-2.195 m/kg1/3)and collapsed completely after event No.5(scaled distance 1.830 m/kg1/3).The scaled distance,damage level and threat levels for unreinforced masonry wall are correlated as shown in Table 5.

5.2.Ferrocemented overlay masonry wall

The ferrocemented overlay masonry wall could sustain the first six events(scaled distance 4.353-1.662 m/kg1/3)and collapsed completely after event No.7(scaled distance 1.470 m/kg1/3).The scaled distance,damage level and threat levels for ferrocemented overlay masonry wall are correlated as shown in Table 6.

Fig.11.Response of masonry after event No.4(a)Appearance of diagonal crack and widening of beam column joint in con fined masonry(b)Debonding of wire mesh in ferrocement overlay masonry wall(c)Out-of-plane wall of unreinforced masonry wall(d)In-plane wall of unreinforced masonry wall.

5.3.Con fined masonry wall

The con fined masonry wall could also sustain the first six events(scaled distance 4.353-1.662 m/kg1/3)and out-of-plan wall collapsed partially and in-plane walls remained in light damage mode even after event No.7(scaled distance 1.470 m/kg1/3).The scaled distance,damage level and threat levels for con fined masonry wall are correlated as shown in Table 7.

All the above indicate increasing response order against blast loading is unreinforced masonry;ferrocemented overlay masonry and con fined masonry.No damage response was demonstrated by all the three against minimum threat level(Z=4.353 m/kg1/3).For low threat level(Z=3.020 m/kg1/3),unreinforced suffered light damage while ferrocemented overlay masonry and con fined masonry revealed no damage again.For medium threat level(Z=2.744 m/kg1/3),unreinforced masonry and ferrocemented overlay cement showed light damage but con fined masonry showed no damage again.For high threat level,(Z=2.195 m/kg1/3),unreinforced masonry showed heavy damage,while,ferrocemented overlay masonry and con fined masonry displayed light damages.For second high threat level,(Z=1.830 m/kg1/3)with scaled distance smaller than the previous event,unreinforced masonry collapsed completely,while ferrocemented overlay masonry and con fined masonry exhibited light damages again.For third high threat level,(Z=1.662 m/kg1/3),ferrocemented overlay masonry showed heavy damages but damages in con fined masonry were again contained in the light damage mode.For forth high threat level(Z=1.470 m/kg1/3),ferrocemented overlay masonry failed completely but con fined masonry partially collapsed.The out-of-plane wall of con fined masonry was fallen out of the confining element and in-plane walls remained intact even after the fifth and last high threat level(Z=1.371 m/kg1/3).

Fig.12.Masonry response after event No.5(a)Confined masonry wall(b)Debonding of ferrocement overlay from masonry wall(c)Loosening and falling of bricks from ferrocement overlay masonry wall(d)Collapse of unreinforced masonry wall[Badshah et al.(2017)].

Fig.13.Response of con fined masonry after event No.6(a)Separation of walls and column and(b)Failure of beam-column joint(c)Ferrocement overlay masonry wall.

The experimental results(scaled distance vs damage)were compared to the of Ahmad et al.[4]study of cantilever URM brick masonry wall(2 m×2 m×0.37 m)as shown in Table 8.

The table shows better performance of simple cantilever wall as compared to U-shaped URM wall in this experimental study.Furthermore,the table shows comparable response of cantilever and ferrocement overlay masonry wall.This better performance is attributed to greater thickness of wall(0.37 m)of the former in comparison to the later(0.23 m).This validates Pandey and Bisht[8],Pereira et al.[9],Wei and Stewart[10]and Parisi et al.[5]findings that increasing thickness of brick masonry,the performance is enhanced against blast loading.

Stand-off distance and damage level:The charge weight in terrorist activities is generally estimated by considering stipulated attack scenario.The explosive charge varies from 10 kg(suitcase bomb)to 10,000 kg(explosives laden on large truck)depending on resources and access to the target structure.Explosives charges along with means of transportation are given in Table 9.

Table 3 Levels of damage to tested walls.

Table 4 Antiterrorism/Force Design Parameters along with scaled distance.

Table 5 Blast Events and scaled distances versus damage and threat level for unreinforced masonry wall.

Explosive nature and quantity are uncertain in terrorist activity.Therefore,an increase of 20%is applied to the explosive weight invariably(Karlos and Solomos 2013).

Fig.14.Response of con fined masonry after event No.7(a)Partial collapse of out-plane-wall(b)Widening of wall-column joint and(c)Collapse of ferrocement overlay masonry.

Fig.15.Response of con fined masonry after event No.8(a)Complete collapse of outplan-wall(b)Widening of wall-column joint.

Using scaled distances for speci fic damage level from Tables 5-7 and perceived terrorist attack scenario from Table 8,the minimum safe stand-off distance before collapse for masonry systems is evaluated by re-arranging Hocpkinson-Cranz law(Z=R/W1/3)as shown in Table 10.

Table 6 Blast Events and scaled distances versus damage and threat level for ferrocemented overlay masonry wall.

Table 7 Blast Events and scaled distances versus damage and threat level for con fined masonry wall.

Table 8 Comparison of experimental study with Ahmad et al.

Table 9 Maximum limit of charge weight and means of transportation[Karlos and Solomos(2013)].

Table 10 Minimum Stand-off distance before collapse in speci fic attack scenario after 20%increase in charge weight.

The table shows an increasing order of minimum stand-off distance requirements for unreinforced,ferrocement overlay and con fined masonry walls.Therefore,in an expensive urban environment,ferrocement overlay and con fined masonry may be used as substitute for unreinforced masonry in buildings susceptible to accidental or terrorist blast loadings.

6.Conclusions

1 For minimum threat level(Z=4.353 m/kg1/3),the response of all the three systems is nearly the same but the response amongst the walls change appreciably as the severity of threat level is accentuated.Unreinforced,ferrocement overlay masonry and con fined masonry walls collapsed completely,at scaled distances 1.83 m/kg1/3,1.47 m/kg1/3and 1.371 m/kg1/3respectively.

2 The damages in con fined masonry are not only small in magnitude but also limited to lesser area.Failure in con fined masonry was found governed by masonry component only.Therefore,the material models of both confining element and masonry components shall be properly adjusted for optimization against speci fied threat level.

3 Ferrocemented overlay masonry falls in bulk and the danger of flying debris is minimized.

4 Ferrocement also fails in de bonding like FRP retro fitted masonry walls.

5 Joints of walls in unreinforced masonry as well as ferrocemented overlay masonry are succeptitable to more damages against blast loadings.Therefore,joints of wall shall be strengthened for mitigation against blast loads.

6 Bricks in the upper layers of free standing masonry wall in unreinforced as well as ferrocemented overlay masonry,pose greater potential dangers for human casualties as well as material loss.Therefore,proper strengthening techniques such as pre compression shall be applied for the top layers of bricks in unreinforced boundary masonry wall.

7 The in-plane wall in each category listed lesser damages as compared to out-of-plane wall after each successive event as the input pressure(side on/incident pressure)was always less than re flected pressure.Therefore,in brick masonry,the reinforcing techniques shall be mainly focused on the out-of-plane wall against the stipulated threat level.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to in fluence the work reported in this paper.