COMPARATIVE STUDY OF LOAD BEARING BLOCK MASONRY WORK IN HOUSING

In order to improve the quality of construction and its sustainability without sacrificing strength, stability, performance, life of the structure and environmental friendly properties, usage of different eco-friendly materials are considered in load bearing masonry structure. In this study a suitable plan is selected and structural elements are designed as per Indian standard codes. Cost comparisons are made between building materials and labour required for construction of a ground plus four residential building using clay bricks, fly ash bricks and cellular light weight concrete blocks. The loads transferred to foundation from block masonry are also considered. From this, based on resources, cost optimized solutions are derived. Keyword Load bearing masonry, Clay bricks, Fly Ash bricks, Cellular Lightweight Concrete blocks.


II. LITERATURE REVIEW
Many experiential studies and researches are carried out on load bearing masonry originated from different sources, they are clinical in construction industry mainly reducing the cost of construction and improving quality of structures built with them. Attempts were made early in U.S.S.R and empirical formulae based on brick strength to predict compressive strength of brick work was formulated (Onishchik. L. I, 1937) [15] which helped a lot in further research, Large scale experimental study was also carried on this field in the western countries to improve the standards of house construction by research on usage of load bearing masonry with improved quality and reduced cost (Mathur. D. C and Berry. S, 1981) [14] . The importance of brick masonry walls as a support to structure was realised early and many studies were conducted in such aspects including load bearing walls (Davidson et al. 1952) [3] (Cross and James. C, 1965) [2] .To ensure the stability and strength of multistoreyed brick structures up to 5 storeys, different realistic tests were also designed to check effect of wind loading, lateral strength of panels with pre-compression, floor/wall interaction, accidental removal of members and many other factors (Sinha B. P and Hendry A. W, 1976) [20] . In recent years the success of construction of buildings with load bearing masonry is such that not only medium storeyed buildings but buildings spanning 5-15 storeyes were constructed in Brazil on thin walls (Santos F. A et al., 2009) [18] , many studies were also carried on the potential of structural masonry in construction industry and the causes for the raise and decline of these type of constructions (Braj P. Sinha, 2002) [1] .
In Switzerland a series of laboratory tests on unreinforced masonry were conducted which made possible the construction of buildings up to 18 storeyes high and of 16 storey buildings with bearing walls measuring 5 "(149.2 mm) in thickness (Haller P) [5] . In addition to this many construction companies and private organizations were conducting studies on the load bearing masonry made from various materials to reduce the cost of their construction projects. The effect of earth quake loading was also considered and its effects were also studied systematically in research process (Dina D'Ayala, 2014) [4] . Not only this, economy of load bearing masonry structures over conventional reinforced concrete structures were also studied and it was found that load bearing structures are significantly economical (Shashank B. S and Raghunath S, 2014) [19] , the load bearing masonry are again classified based on their material sources like burnt clay bricks, fly ash bricks, cellular lightweight concrete blocks (Chiranjeevi Rahul. R and Lakshmayya.M.T.S, 2014) [16] or other types such as brick masonry and hollow concrete masonry and evaluation is made on their load bearing capabilities and economy (Rafiq Ahmad and Mohammad Iqbal Malik, 2014) [17] In India also the trend of constructing structures with load bearing masonry is increasing rapidly because of its advantages, IIM Ahmadabad is a profound example for such structures in India, hence, In current study, cost of construction is compared for a multi storeyed load bearing structures using various types of materials like Clay bricks (IS 2212(IS : 1991 [10] , Fly Ash bricks (IS 12894: 2002) [11] , Cellular Lightweight Concrete blocks (IS 2185: 2008 part IV) [12] . There by evaluating their scope in building construction. Design was done based on (SP 20(S&T) : 1991) [13] ,the properties of these materials were evaluated following the Indian standard codes for usage of plain and reinforced concrete (IS 456-2000) [6] , code of practise for design loads, dead loads and live loads (IS 875 Part-I-1987) [7] , (IS 875 Part-II-1987) [8] ,and code for usage of unreinforced masonry as structural members (IS 1905(IS -1987 [9] . Data collection is performed and by analysing the data, suitable plan is selected, then the structural elements are designed following the standard specifications. After the design process the structural elements are introspected again and load calculations are performed. Then in the next stage bricks of required compressive strength are chosen for the structure based on the load calculations. Rate analysis of the items involved in the structure and labour costs are estimated, these costs are compared with the conventional materials used and necessary conclusions are made. This process is depicted in a flow chart above.

IV. DESIGN CONSIDERATIONS
In this study a suitable plan is selected as shown in Fig. 2 and structural elements are designed as per Indian standard codes. This structure is designed as ground plus four residential building with reinforced concrete slab supported on load bearing masonry. The slab thickness is taken as 120mm, masonry thickness as 200mm, floor height as 3.0m c/c. door height is 2.1 m, and window height is 1.5 m. Floor plan is same for all floors.

Slab:
Size of the slab (L y x L x ) = 4.30m x 8.50m Overall thickness of the slab = 120mm Hence the slab is designed as two-way slab Loads on roof slab Self-weight : 3.0kN/m 2

V. DESIGN OF A WALL CARRYING AXIAL LOAD A. Masonry work in superstructure
Maximum load from the roof slab of top floor is 11.35kN/m. whereas for remaining floors including ground floor maximum load from the slab is 15.15kN/m. Since wall 14 is bearing the maximum load. Determination of minimum compressive strength required for a masonry unit and grade of mortar mix is as follows.
Effective Height, h = 0.75H = 0.75 x3.0 = 2.25m Effective length, l =0.9L = 0.9 x 3.6= 3.5 m Since effective height is less than effective length, SR based on height will control the design. (From Table 9 Table 8 Table 10 of the Code) equals to 1.0.
Thus Basic Compressive stress required = 0.74/1.0= 0.74 N/mm 2 Referring to Table 8 of IS : 1905-1987, masonry required is-bricks of strength 7.5N/mm 2 and mortar of M1 grade. (M1 grade is 1:5 ratios of cement and sand respectively) 3) Cellular Light weight Concrete blocks Unit weight of Cellular Light weight Concrete Blocks of 1200 kg/m 3 density = 11.77kN/m 3 Self-weight of block work = unit weight x length x breadth x height = 11.77 x 1.00 x 0.20 x 2.88= 6.78kN/m Total load for single floor is load on slab + self-weight of block work.
i.e., 11.35 + 11.30 = 21.93kN/m (for 5 th floor) 15.15 + 11.30 = 21.93kN/m (for remaining floors including ground floor) Self-weight of block work in plinth = 11.77 x 1.00 x 0.20 x 0.55 = 1.30kN/m Therefore, total load at base of plinth = 107.15kN/m Compressive stress in masonry at base of plinth = 107.15 1000 20 100   = 53.57 kg/cm 2 = 0.53 N/mm 2 With Shape modification factor = 1, Basic Compressive stress of masonry = 0.53/0.84= 0.63 N/mm 2 Since modular bricks are used which have height to width ratio of 1.0, value of Shape modification factor (from Table 10  These rates are taken in to account on the basis of present construction rates in Visakhapatnam and rates are collected by conducting a survey to the construction sites, builders and material suppliers and quantity of work done per a day by a mason and a coolie is considered from the data collected from the experienced builders and masons considering the weight, size and shape of clay bricks, fly ash bricks and Cellular Lightweight Concrete blocks.