UNIT 1 Construction of Reinforced Masonry Walls, Pillars and Lintels.pdf

Feb. 8, 2023

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UNIT 1 Construction of Reinforced Masonry Walls, Pillars and Lintels.pdf

  1. Construction of Reinforced Masonry Walls, Pillars and Lintels Building Technology and Material II
  2. Introduction Function of Brick wall? Brick masonry is brittle which implies that,  poor shear resistance  poor flexural ability  resist very little horizontal loading.
  3. Types of failures under horizontal loads  Shear - a wall loaded with significant vertical load as well as horizontal forces can fail in shear. (With Aspect Ratio 1:1 or 2:1 or even in higher vertical loads) (lighter vertical load = less resistance to shear failure)  Sliding Shear - a wall with poor shear strength, Lightly loaded with vertical load and loaded predominantly with horizontal forces can exhibit this failure mechanism. (Aspect ratio 1:1)  Bending - this type of failure can occur if walls are with improved shear resistance. Bending failure can occur due to small vertical loads, rather than high shear resistance. (Aspect ratios 2:1 )
  4. Types of failures under horizontal loads  The bending strength is the governing factor.  Depending on the direction of load the wall exhibits following two failures, Vertical orientation of failure plane and corresponding bending strength normal to bed joints Horizontal orientation of failure plane and corresponding bending strength parallel to bed joints
  5. Necessity Thus, Masonry walls with Shear resistance and better flexural property can be achieved by embedding tensile members which integrates with the masonry so as to assist in resisting shear and bending. The location of the tensile members within the wall would be dictated by the type and magnitude of shear force and bending moment the wall is expected to resist before its failure. Mechanism of action of vertical and horizontal reinforcement of a masonry wall failing in shear
  6. Necessity  For shear resistance - the reinforcement can be placed throughout the cross section of the wall in both horizontal and vertical alignment.  For resistance from bending moments - reinforcement is to be placed vertically near or along the outer edge of the cross section of the wall. Schematic masonry wall section challenges - due to method of construction and necessity of staggering perpends etc. • Custom made bricks • variation in construction methodology
  7. Materials  Masonry Units- Masonry units are formed out of clay, cement concrete, autoclave cured aerated concrete, and natural stone.  The units are shaped in various forms and sizes.
  8. Materials  Reinforcement - Mild steel rods and flats is the most commonly available material  susceptible to corrosion (and increase of volume due to corrosion) which is not acceptable.  5mm to 25mm dia M.S. rod can be used after coating it with anticorrosion paints and should be provided a cover of not less than 15mm if placed horizontally and 30mm if placed vertically.  M.S. flats of 20-25mm width and 3mm thick could also used for horizontal placement in mortar joints after anticorrosion paint coat.  M.S. flat with holes at regular intervals can be placed vertically.  The holes are required to insert links/bolts to tie the flats provided on both faces of the wall.  G.I. rods could also be used instead of Mild steel.  Stainless steel bars and flats though costlier, might work best in very corrosive environments like coastal areas etc.
  9. Materials  Joint reinforcements are usually arrangement of reinforcing bars as chords and web. Common configurations are ladder type or truss type arrangement.
  10. Materials  Motor only high strength motor should be used  For Plain Masonry - the minimum recommended compressive strength of mortar is 5MPa.  For Reinforced Masonry - the minimum recommended compressive strength of mortar is 10MPa.
  11. Reinforced masonry construction systems A construction system where steel reinforcement is embedded in the mortar joints of masonry or placed in holes and after filled with concrete or grout is called reinforced masonry. Types, (based on arrangement of reinforcement)  Reinforced solid unit masonry using common or purpose made brick/blocks  Reinforced and grouted hollow unit masonry  Reinforced grouted cavity masonry  Reinforced pocket type walls and Quetta Bond Reinforced Masonry
  12. Reinforced masonry construction systems Reinforced solid unit masonry masonry using Common brick, stone ashlar blocks, cement concrete block, etc….. using….. steel bars, flats or expanded metal mesh….. embedded in the mortar joint of every course or courses at regular interval…. Minimum required cover on the edge.
  13. Reinforced masonry construction systems Reinforced solid unit masonry  Staggering….. placing of vertical reinforcement…..special masonry units….. allows to introduce reinforcement closer to the face of masonry….. enhanced flexural capability.
  14. Reinforced masonry construction systems Reinforced solid unit masonry Horizontal Reinforcement for long half brick thick partition wall  M.S. flat of section 3 X 25 mm, or M.S. round bars of 6 to8 mm dia.  minimum crushing strength of 10 N/mm2 and mortar should not be leaner than 1 cement : 4 sand.  Reinforcement in every 3rd or 4th course  Minimum mortar cover of 15 mm horizontally and 5 mm in the vertically  Lateral resistance of brick walls in exposed situations should, therefore, be increased where necessary by other means such as increase in thickness of wall or by providing piers or buttresses.
  15. Reinforced masonry construction systems Reinforced hollow unit masonry
  16. Reinforced masonry construction systems Reinforced grouted cavity masonry Two parallel single leaf walls spaced at least 50 mm apart, effectively tied together with wall ties.
  17. Reinforced masonry construction systems Pocket type Reinforced masonry  The reinforced pocket type masonry allows for forming reinforced masonry columns
  18. Reinforced masonry construction systems  Reinforced masonry is expected to resist shear and bending stresses.  In order to span the openings like window and door in the wall a concrete lintel can be employed but for small opening a reinforced brick lintel can also be constructed especially architectural requirement of exposed brick walls.
  19. Reinforced Brick Lintels  The brick lintel or soldier arch(flat arch) can be reinforced by 2 nos. 12mm dia. m.s. bars embedded in the horizontal longitudinal joints and extended to 150 mm beyond the jambs.  Alternatively 6mm diameter MS bars embedded in the continuous longitudinal joints, together with 6mm diameter bent steel bars called stirrups, bedded in every third vertical joint.
  20. Reinforced masonry walls for earthquake prone zone III, IV &V Concept of ‘Containment Reinforcement’ (i)It is recommended that containment reinforcement may be provided for low-rise (up to 3 storey load bearing) masonry buildings in earthquake zones III, IV, and V. This is in addition to horizontal bands. (ii) In case of buildings with heavy roofs/floors (mass of the floor more than 200kg/m2), if height of the wall is 3.0m or less and the length of the wall is less than or equal to 3.0m containment reinforcement need not be provided if there are no openings in the wall.
  21. Reinforced masonry walls for earthquake prone zone III, IV &V Concept of ‘Containment Reinforcement’ (iii) Masonry buildings with light roofs (tiled roof, asbestos or zinc sheet roofs) must have containment reinforcement on all walls irrespective of the aspect ratio of the wall. (iv) Walls with height greater than 3.0m must invariably have containment reinforcement. (v) All door and window jambs must have containment reinforcement on either sides of the opening at a distance of 150.0mm to 200.0mm from the jamb. Masonry piers between door and window openings or between two window openings should not be less than 0.75m in width. (vi) The wires/rods of containment reinforcement must be tied to the steel in the horizontal band to form a coarse two-dimensional cage holding the masonry in place. (vii) Normally, the horizontal spacing between two sets of containment reinforcement should be between 0.75m to 1.25m.
  22. Reinforced Brick Masonry Advantages 1.Reinforced brick masonry does not require shuttering and concrete. 2.Large cost saving compared with that of reinforced concrete. 3.Reinforced brick masonry is easy to construct. 4.Cool rooms. 5.Fireproof work. 6.Cheaply supervised. 7.Weather protection. 8.The tools and implements used are simple and low-tech. Disadvantages 1.There is always limitation in Reinforced brick masonry. 2.Load bearing masonry has a high self-weight or Low strength-to-weight ratio. 3.Labour intensive construction 4.Moisture penetration. 5.Thermal expansion 6.A slow and tedious process. 7.Requires skilled masons. 8.Low tensile strength, can fail during earthquakes