Compressive load carrying capacity of AAC masonry prism

5.6 Results and Discussion

5.6.3 Compressive load carrying capacity of AAC masonry prism

The experimental results of load carrying capacity of AAC masonry prism were used to validate the developed simplified models. The compressive load carrying capacity of PB and SGB masonry prisms were used to predict the load carrying capacity of DGB masonry prism. Similar models have been employed for the masonry prism to predict the compressive load carrying capacity as well as its lower and upper estimates as that of developed for the AAC blocks in the previous Sections. The load carrying capacity of PB masonry prism is given by

MPB mb ,

P  lw (5.23) where σmb is the compressive strength of PB masonry prism. Using average P_MPB = 32.52 kN (from experiments) in Eq. 5.23, the average compressive strength of PB block masonry prism (σmb) was found to be 1.23 MPa. Again, using average P_MSGB = 33.79 kN (from experiments) and σmb = 1.23 MPa, the average compressive strength of the mortar (σmm) in the masonry prism is given by



^{( ) mm}



MSGB mb

P 



l d 



d w, (5.24) The average compressive strength of the mortar in the masonry prism is found to be 1.60 MPa. Further, using σmb = 1.23 MPa and σmm = 1.60 MPa, the average compressive load carrying capacity of the DGB masonry prism is given by



^{( 2 ) mm2}



MDGB b

P 



l d 



d w. (5.25) The average compressive load carrying capacity of DGB masonry prism was estimated to be 35.13 kN against the experimental result of 36 kN. The result of average compressive load carrying capacity obtained from the experiments has a good agreement (2.5% error) with the developed analytical model, again verifying that tests on plain and single-groove cases can carryout predictions for double-groove cases.

The masonry prism with DGB has shown the highest average compressive load carrying capacity, while the PB masonry prism has shown the least. The percentage increase in the load carrying capacity of DGB and SGB masonry over PB masonry was found to be 9.6% and 4%, respectively. However, the increase is marginal. A huge difference in the compressive load carrying capacity of the individual blocks and the masonries has been found in the study (refer Tables 5.1 and 5.3). For instance, the compressive load carrying capacity of PB masonry prism is 32.52 kN, while the compressive load carrying capacity of PB block is 62.02 kN.Also, the compressive load carrying capacity of masonry prism was found to increase with increase in the shear load carrying capacity. The results of compressive load carrying capacity of the AAC blocks and the corresponding compressive strengths (in terms of load carrying capacity) are presented in Table 5.3.During the test, the small cracks initiated from the multiple portions of the masonry prism. For all the types of masonry prisms, after reaching its peak load, the load started decreasing suddenly and the small cracks grew to a multiple large vertical splitting cracks.

Table 5.3 The results of compressive strength test for AAC masonry Masonry

type

load carrying capacity (kN)

Compressive strength (MPa)

Failure strain

PB 32.52 [23.30]^a 1.23 [23.30] 0.008 [41.70]

SGB 33.79 [18.50] 1.28 [18.50] 0.017 [26.60]

DGB 36.00 [13.40] 1.36 [13.40] 0.015 [24.40]

aValue in parenthesis represents coefficient of variation in percentage.

The lower and upper estimates of compressive load carrying capacity of the masonries were evaluated by applying the interval arithmetic in the simplified models. Initially, the lower and upper estimates of load carrying capacity of PB masonry prism were achieved from the experiments. All the relevant experimental data are shown in Appendix E. The lower and upper estimates of the compressive strength of the PB masonry prism (from Eq.

5.23) are given by



^_{mb min}



^

^

^{PMPB min ,}_lw

^

(5.26)

 

^_{mb max} ^

^

^{PMPB max}_lw

^

^, (5.27) where (PMPB)min and (PMPB)max are the lower and upper estimates of load carrying capacity of the PB masonry prism, respectively. The (σmb)min and (σmb)max calculated using Eqs. 5.26 and 5.27 were found to be 0.90 MPa and 1.76 MPa, respectively. The experimental results of (PMSGB)max= 43.30 kN, (PMSGB)min = 25.08 kN, (σmb)max = 1.76 MPa and (σmb)min = 0.90 MPa were used to compute the lower and upper estimates of mortar compressive strength in the masonry. The (PMSGB)minand (PMSGB)max are the lower and upper estimates of compressive load carrying capacity of SGB masonry prism. The lower and upper estimates of the mortar compressive strength (from Eq. 5.24) are given by



^{MSGB min}

  

( mm min) mb max 1 ,

P l

dw d

    ^  ^

  (5.28)



^{MSGB max}

  

( mm max) mb min 1 .

P l

dw d

    ^  ^

  (5.29) The (σmm)_min and (σmm)_max calculated using Eqs. 5.28 and 5.29 were found to be 4.50 MPa and 6.33 MPa, respectively. Since the lower estimate of mortar compressive strength cannot be negative, the (σmm)_minhas been assumed to be equal to the lower estimate of compressive strength of the PB masonry prism i.e., (σmm)_min = (σb)_min = 0.9 MPa. Further, (σmb)max = 1.76 MPa, (σmb)min = 0.9 MPa, (σmm)max= 6.33 MPa and (σmm)min= 0.9 MPa were used to compute the lower and upper estimates of compressive load carrying capacity of DGB masonry prism. The lower and upper estimates of compressive load carrying capacity of DGB masonry prism (from Eq. 5.25) are given by



PMDGB



min 

  

mb min⁽l^{2 ) 2}d 

^

^{mm min}

^

d w



^, (5.30)



PMDGB



max 

  

mb max⁽l^{2 ) 2}d 

^

^{mm max}

^

d w



^. (5.31) The (P_MDGB)_min and (P_MDGB)_max using Eqs. 5.30 and 5.31 were found to be 23.76 kN and 79.36 kN, respectively. The lower and upper estimates of compressive load carrying capacity of DGB block from the experiments are 31.15 kN and 44.08 kN, respectively. The typical stress-strain responses of three specimens from each type of blocks are depicted in Figure 5.9.

For all types of masonry prism, similar failure behavior was observed. The failure at the peak load was caused by vertical splitting cracks. The typical failure behavior of different masonry prism is depicted in Figure 5.10.

(a) (b)

(c)

Figure 5.10 Stress-strain relationship of masonry in compression load: (a) PB masonry, (b) SGB masonry and (c) DGB masonry

(a) (b) (c)

Figure 5.11 Masonry prism specimens after the test: (a) PB masonry, (b) SGB masonry and (c) DGB masonry