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1、7.4 Masonry Structural Design,Walls,Wall Distributions Masonry structures gain stability from the support. Lateral support may be in the vertical direction -floor/roof bearing on the wall horizontal direction-cross walls, piers or buttresses. Lateral supports can limit slenderness of a masonry eleme
2、nt so as to prevent or reduce possibility of buckling of the member resist horizontal components of forces,Walls-Wall Distributions,A structure should have adequate stability in the direction of both the principal axes. cross wall construction may not have much lateral resistance in the longitudinal
3、 direction Walls are to be uniformly distributed along each principal axis of the plan minimum thickness of structural walls should be 240mm.,Walls-Wall Distributions,Cross walls acting as stiffening walls continuous from outer wall to outer wall or outer wall to a load bearing inner wall. The maxim
4、um spacing of cross wall in masonry structure with reinforced concrete floor and roof is 18m for seismic fortification intensity of 6 and 7 15m for seismic fortification intensity of 8 11m for seismic fortification intensity of 9,Walls -Height to Thickness Ratio of Walls,Load carrying capacity of a
5、masonry member depends upon its height to thickness ratio A masonry member may fail due to excessive stress - For materials of normal strength with height to thickness ratio less than 30 due to buckling-for members with higher value of height to thickness ratio through shear action - very short memb
6、er having height to thickness ratio of 4 by vertical tensile splitting member with height to thickness ratio of 4,Walls -Height to Thickness Ratio of Walls,The height to thickness ratio for a wall shall not exceed 26 when the grade of mortar is not less than M7.5. Limiting value of height to thickne
7、ss ratio for column is less than that of walls because column can buckle around either of the two horizontal axes while walls can buckle around the weak horizontal axis only. The height to thickness ratio for a load bearing unreinforced column shall not exceed 17 when the grade of mortar is not less
8、 than M7.5.,Double-Leaf Walls,The traditional stone masonry construction with two outer layers of uncoursed irregularly sized rubble stones with an inner infill consisting of smaller pieces of stone bound together with lime mortar is not recommended in earthquake zones. Single-leaf walls should be p
9、referred to double-leaf walls. Double-leaf cavity walls, where the cavity is filled with concrete, should be preferred to normal cavity walls, since they ensure monolithic behavior of the wall under seismic conditions.,Bond Beams,The function of bond beams is to transfer horizontal shear induced by
10、the earthquakes from the floor and roof to the structural walls. Bond Beams connect the structural walls with each other and improve the rigidity of the horizontal diaphragms.,Bond Beams,Details of cast in-situ reinforced concrete slabs with bond beams,Bond Beams,The minimum cross-section of bond be
11、am is recommended to be 240 x 120mm. The bigger dimension being the thickness of the wall. The minimum bond beam reinforcement in clay masonry shall be four 10mm diameter bars with 6mm diameter stirrups at spacing of maximum 250mm for seismic fortification intensity of 6 and 7. Reinforcement should
12、be spliced and anchored at corners and wall intersections.,Tie Columns,At least four 12mm diameter rebars with 6mm diameter stirrups at vertical spacing of maximum 250mm are required. Closely spaced stirrups should be provided at the top and bottom of columns. connecting the masonry and tie columns
13、by two 6mm diameter rebars diameter at maximum 500mm apart. These links should be placed in the bed joints and be anchored at least 1000mm into the mortar joints,Floors and Roofs,During earthquakes, floors and roofs should act as rigid horizontal diaphragms, which distribute the seismic forces among
14、 structural walls in proportion to their stiffness.,Floors and Roofs,Common roof systems constructed in timber for low-rise masonry housing are joist-rafter roof collar beam attached to rafters is required bracing should be constructed both in the plane of the joists and in the plane of the rafters
15、in two orthogonal directions. Vertical cross bracing in the longitudinal ridge planeis required ceiling joists should be anchored to roof bond beam by steel strap truss roof,Lintels,Lintels are load-bearing elements which support the weight of the wall and floor above opening. Lintels can be made from in-situ reinforced concrete, timber and reinforced masonry.,
