Building Technology 3: Reinforced Concrete Construction PDF

# Building Technology 3: Reinforced Concrete Construction ## Reinforced Concrete - Concrete in which steel reinforcement is embedded in such a manner that the two materials act together in resisting forces. - Also called *Beton arme* or *Ferroconcrete*. ## Plain Concrete - Concrete having no rei...

# Building Technology 3: Reinforced Concrete Construction ## Reinforced Concrete - Concrete in which steel reinforcement is embedded in such a manner that the two materials act together in resisting forces. - Also called *Beton arme* or *Ferroconcrete*. ## Plain Concrete - Concrete having no reinforcement or reinforced only for drying, shrinkage, or thermal stresses. ## Ferrocement - Constructed of cement-sand mortar over wire mesh that has been preshaped over a mold. ## Cast-in-Place Concrete, Cast In-situ, In-situ Concrete - Concrete which is deposited in the place where it is required to harden as part of the structure, as opposed to precast concrete. ## Reinforcement - A system of steel bars, strands, or wires for absorbing tensile, shearing, and sometimes, compressive stresses in a concrete member or structure. ## Deformed Bar - A reinforcing bar hot-rolled with surface deformations to develop a greater bond with concrete. ## Tension Reinforcement - Reinforcement designed to absorb tensile stresses. ## Compression Reinforcement - Reinforcement designed to absorb compressive stresses. ## Balanced Section - A **balanced section** is one where: - The tension reinforcement theoretically reaches its specified yield strength as the concrete in compression reaches its assumed ultimate strain. - The design is proportional such that the maximum stresses in the concrete and steel are reached simultaneously so that they fail together. ## Overreinforced Section - A concrete section where: - The concrete in compression reaches its assumed ultimate strain before the tension reinforcement reaches its specified yield strength. - This is a dangerous condition because failure of the section could occur instantaneously without warning. - This type of design is not advisable because concrete fails abruptly in compression. ## Underreinforced Section - A concrete section where: - The tension reinforcement reaches its specified yield strength before the concrete in compression reaches its assumed ultimate strain. - This is a desirable condition because failure of the section would be preceded by large deformations, giving prior warning of impending collapse. - In this particular type of design, the steel fails first while the concrete has not yet reached its allowable values but the failure is gradual with steel yielding. ## Assumptions in Elastic Theory in Concrete 1. **Plane section remains plane before and after bending occurs.** 2. **Concrete is elastic;** that is, the stress of concrete varies from zero at the neutral axis to a maximum at the extreme fibers. 3. **Concrete is not good in carrying tension**, and only the steel bars are carrying all the stresses due to bending which is tension. 4. **There must be no slippage between concrete and steel bars.** ## Historical Note - In 1867, Joseph Monier (France) used the concept of iron reinforcing bars (rebars) when he reinforced William Ward's (US) flower pots using wire. ## Beam - A rigid structural member designed to carry and transfer transverse loads across space to supporting elements. - **Simple Beam:** Refers to a beam having a single span supported at its end without a restraint at the support. - **Semi-continuous Beam:** Refers to a beam with two spans with or without restraint at the two extreme ends - **Cantilever Beam:** A beam supported on one end and the other end projecting beyond the support, beam or wall. - **Continuous Beam:** A term applied to a beam that rests on more than two supports. - **T beam:** Part of the floor and beam unit when poured simultaneously thereby producing a **monolithic structure** where the portion of the slab at both sides of the beam serves as flanges of such beam. ## Reinforced Concrete Beam - A concrete beam designed to act together with longitudinal and web reinforcement in resisting applied forces, formed and placed along with the slab it supports. ## Beam Nomenclature | Term | Description | |---|---| | **Effective Depth of Section** | The depth of a concrete section measured from the compression face to the centroid of the tension reinforcement. | | **Bar Spacing** | The center-to-center spacing of parallel bars; the resulting clear distance between the bars being regulated by bar diameter, maximum size of coarse aggregate, and thickness of the concrete section. | | **Span of Supports** | Refers to the distances between posts, columns or supporting walls. | | **Concrete Cover** | The amount of concrete required to protect steel reinforcement from fire and corrosion, measured from the surface of the reinforcement to the outer surface of the concrete section. | | **Bond** | The adhesion between two substances, as concrete and reinforcing bar. | | **Bond Stress** | The adhesive force per unit area of contact between a reinforcing bar and the surrounding concrete developed at any section of a flexural member. | | **Development Length** | The length of embedded reinforcement required to develop the design strength of reinforcement at a critical section. | | **Embedment Length** | Length of embedded reinforcement provide beyond a critical section | | **End Anchorage** | Length of reinforcement or mechanical anchor or hook or combination thereof beyond point of zero stress in reinforcement. | | **Hook** | A bend or curve given to the end of a tension bar to develop an equivalent embedment length, used where there is insufficient room to develop an embedment length. | | **Longitudinal Reinforcement** | Reinforcement essentially parallel to the horizontal surface of a slab or to the long axis of a concrete beam or column. | | **Percentage Reinforcement** | The ratio of the effective area of reinforcement to the effective area of concrete at any section of a reinforced concrete member, expressed as a percentage. | | **Top Bar** | Any Longitudinal bar serving as tension reinforcement in the section of a concrete beam or slab subject to a negative moment. | | **Bottom Bar** | Any longitudinal bar serving as tension reinforcement in the section of a concrete beam or slab subject to a positive moment. | | **Web Reinforcement** | Reinforcement consisting of bent bars or stirrups, placed in a concrete beam or slab to resist diagonal tension. | | **Bent Bar** | A longitudinal bar bent to an angle of 30º or more with the axis of the concrete beam, perpendicular to and intersecting the cracking that could occur from diagonal tension. | | **Bend Reinforcing Bars** | Reinforcing bars that are bent up on or near the inflection point and are extended at the top of the beam across the support towards the adjacent span. | | **No Bent Bars** | Bars that are not bent, an additional straight reinforcing bars placed on the top of the beam across the supports to the required length and other straight additional bars are also placed at the bottom center of the beam span where positive moment develops. | | **Truss Bar** | A longitudinal bar bent up or down at points of moment reversal in a reinforced concrete beam. | | **Stirrup** | Any of the U-shaped or closed-loop bars placed perpendicular to the longitudinal reinforcement of a concrete beam to resist the vertical component of diagonal tension. | ## Standards for Tests and Materials ### Cement - Cement shall conform to one of the following specifications for Portland Cement: - Specifications for Portland Cement (ASTM C 150) - Specifications for Blended Hydraulic Cements (ASTM C 595), excluding Types S and SA which are not intended as principal constituents of structural concrete. ### Admixtures 1. Admixtures to be used in concrete shall be subject to prior approval by the Engineer. 2. An admixture shall be shown capable of maintaining essentially the same composition and performance throughout the work as the product used in establishing concrete proportions. 3. Admixtures containing chloride ions shall not be used in prestressed concrete containing aluminum embedments if their use will produce deleterious concentration of chloride in the mixing water. ### Aggregates - Concrete aggregates shall conform to one of the following specifications: - Specifications for Concrete Aggregates (ASTM C 33) - Specifications for Lightweight Aggregates for Structural Concrete (ASTM C 330) - Nominal maximum size of aggregates shall not be larger than: - 1/5 the narrowest dimension between sides of forms, nor - 1/3 the depth of slabs, nor - 3/4 the maximum clear spacing between individual reinforcing bars, or prestressing tendons or ducts. ## Water 1. Water used in mixing concrete shall be clean and free from injurious amounts of oils, acids, alkalis, salts, organic materials or other substances that may be deleterious to concrete or reinforcement. 2. Mixing water for prestressed concrete or concrete that will contain aluminum embedments, including that portion of mixing water contributed in the form of free moisture on aggregates shall not contain deleterious amounts of chloride ions. ## Metal Reinforcement 1. Reinforcement shall be deformed reinforcement, except that plain reinforcement may be used for spirals or tendons; and reinforcement consisting of structural steel, steel pipe, steel tubing may be used. 2. Reinforcement to be welded shall be indicated in the drawings and welding procedure to be used shall be specified. ## Standard Hook - A 90º, 135º or 180º bend made at the end of a reinforcing bar according to industry standards with radius based on the bar diameter. ## Standard Hooks (NSCP, 4th ed. 1992) 1. 180º bend plus 4db extension, but not less than 65 mm at free end of bar. 2. 90º bend plus 12db extension, at free end of bar. ## For Stirrups and Tie Hooks 1. 16 mm bar and smaller, 90º bend plus 6d, extension at free end of bar. 2. 20 mm bar and 25 mm, 90º plus 12d, extension at free end of bar. 3. 25 mm bar and smaller, 135º bend plus 6d, extension at free end of bar. ## Minimum Bend Diameters 1. Diameter of bend measured on the inside of the bar other than for stirrups and ties in sizes 10 mm through 15 mm diameter, shall be no less than indicated on the table below. | Bar Size | Minimum Diameter | |---|---| | 10 mm to 25 mm | 6d | | 28 mm and 32 mm | 8d | | 36 mm | 10d | 2. Inside diameter of bend for stirrups and ties shall not be less than 4d, for 16 mm and smaller. 3. Inside diameter of bend in welded wire fabric (plain or deformed) for stirrups and ties shall not be less than 4d, for deformed wire larger than D6 and 2d, for all other wires. Bends with inside diameter of less than 8d, shall not be less than 4d, from nearest welded intersection. ## Bending 1. All reinforcement shall be bent cold, unless otherwise permitted by the Engineer. 2. Reinforcement partially embedded in concrete shall not be field bent, except as shown on the drawings or permitted by the Engineer. ## Surface Conditions of Reinforcement 1. At the time concrete is placed, metal reinforcement shall be free from mud, oil, or other nonmetallic coatings that adversely affect bonding capacity. 2. Metal reinforcement, except prestressing tendons, with rust, mill scale or a combination of both shall be considered satisfactory, provided minimum dimensions and weight of a hand-wire-brushed test specimen are not less than applicable ASTM specifications requirements. ## Placing Reinforcement 1. Reinforcement, prestressing tendons and ducts shall be accurately placed and adequately supported before concrete is placed, and shall be secured against displacement within tolerable limits. 2. Welding of cross bars shall not be permitted for assembly of reinforcement unless otherwise authorized by the Engineer. ## Spacing Limits for Reinforcement 1. The minimum clear spacing between parallel bars in a layer shall be d, but not less than 25 mm. 2. Where parallel reinforcement is placed in two or more layers, bars in the upper layer shall be placed directly above bars in the bottom layer with clear distance between layers not less than 25 mm. 3. In spirally reinforced or tied reinforced compression members, clear distance between longitudinal bars shall not be less than 1.5d, nor more than 40 mm. 4. Clear distance limitation between bars shall apply also to the clear distance between a contact tap splice and adjacent splices or bars. 5. In walls and slabs other than concrete joist construction, primary flexural reinforcement shall be spaced not farther apart than three times the wall or slab thickness nor more than 450 mm. 6. Bundled bars shall be done in the following manner: - Groups of parallel reinforcing bars bundled in contact to act as a unit shall be limited to four in any one bundle. - Bundled bars shall be enclosed within stirrups or ties. - Bar larger than 32 mm shall not be bundled in beams. - Individual bars within a bundle terminated within the span of flexural members shall terminate at different points with at least 40d stagger. - Where spacing limitations and minimum concrete cover are based on bar diameter d, a unit of bundled bars shall be treated as a single bar of diameter derived from the equivalent total area. ## Concrete Protection for Reinforcement ### Concrete Cover - The amount of concrete required to protect steel reinforcement from fire and corrosion, measured from the surface of the reinforcement to the outer surface of the concrete section. ### Schedule of Minimum Concrete Cover | Cast in place Concrete | Minimum Cover (mm) | |---|---| | Concrete cast against and permanently exposed to earth | 75 | | Concrete exposed to earth or weather: | | | 20 mm through 36 mm bars | 50 | | 16 mm bar, W31 or D31 wire and smaller | 50 | | Concrete not exposed to weather or in contact with ground: | | | Slabs, Walls, Joists, 32 mm bar and smaller | 20 | | Beams, Columns: Primary reinforcement, ties, stirrups, spirals | 40 | | Shell, Folded Plate members: | | | 20 mm bar and larger | 20 | | 16 mm bar, W31 or D31 Wire and smaller | 15 | | Precast Concrete (Manufactured Under Plant Control Conditions) | | | Concrete exposed to earth or weather: | | | Wall panels: | | | 32 mm bar and smaller | 20 | | Other Members: | | | 20 mm bar through 32 mm bar | 40 | | 16 mm bar, W31 or D31 Wire and smaller | 30 | | Concrete not exposed to weather or in contact with ground: | | | 16 mm bar, W31 or D31 Wire, and smaller | 15 | | Other Reinforcement | | | Slabs, Walls, Joists: | | | 32 mm bar and smaller | 15 | | Beams, Columns: | | | Primary Reinforcement | d, but not less than 15 and need not exceed 40 | | Ties, Stirrups, Spirals | 10 | | Shells, Folded Plate members: | | | 20 mm bar and larger | 15 | | 16 mm bar, W31 or D31 Wire, and smaller | 10 | ### Prestressed Concrete | Concrete cast against and permanently exposed to earth | Minimum Cover (mm) | |---|---| | Concrete exposed to earth or weather: | | | Wall Panels, Slabs, Joists | 25 | | Other Members | 25 | | Concrete not exposed to weather or in contact with ground: | | | Slabs, Walls, Joists | 20 | | Beams, Columns: | | | Primary Reinforcement | 40 | | Ties, Stirrups, Spirals | 25 | | Shells, Folded Plate Member: | | | 20 mm bar and larger | 15 | | 16 mm bar, W31 or D31 Wire, and smaller | 10 | | Other Reinforcement | d, but not less than 20 | ## Reinforced Concrete Column - A concrete designed to act together with vertical and lateral reinforcement in resisting applied forces. - Reinforced concrete columns constituting the principal supports for a floor or roof should have a minimum diameter of 10 in (254 mm) or if rectangular in section, a minimum thickness of 8 in (203 mm) and a minimum gross area of 96 sq. in (61935 sq. mm). ### Short Column - A column having an unsupported height not greater than 10 times the shortest lateral dimension of the cross section. ### Long Column - When the unsupported height is more than 10 times the shortest lateral dimension of the cross section. ### Tied Column - A concrete column reinforced with vertical bars and individual lateral ties. - Lateral ties should have a diameter of at least 10 mm (3/8 in.) spaced apart not more than 48 tie diameters, 16 bar diameters or the least dimension of the column section. ### Vertical Reinforcement - Longitudinal reinforcement placed in a concrete column to absorb compressive stresses, resist bending stresses, and reduce the effects of creep and shrinkage in the column. ### Lateral Reinforcement - Spiral reinforcement or lateral ties placed in a concrete column to laterally restrain the vertical reinforcement and prevent buckling. ### Spiral Reinforcement - Lateral reinforcement consisting of an evenly spaced continuous spiral held firmly in place by vertical spacers. ### Bundled Reinforcement - Reinforcement employed consisting of two to four bars tied in direct contact with each other to serve or act as one unit, reinforcement placed at the corner of lateral ties. ### Lateral Reinforcement for Compression Members #### Lateral Ties 1. All nonprestressed bars shall be enclosed by lateral ties, at least 10 mm in size for longitudinal bars 32 mm or smaller, and at least 12 mm in size for 36 mm and bundled longitudinal bars. Deformed wire or welded wire fabric of equivalent area is allowed. 2. Vertical spacing of ties shall not exceed 16 longitudinal bar diameter, 48 tie diameters, or least dimension of the compression member. 3. Ties shall be arranged such that every comer and alternate longitudinal bar have lateral support provided by the corner of a tie with an included angle of not more than 135 degrees and no bar shall be farther than 150 mm clear on each side along the tie from such a laterally supported bar. Where longitudinal bars are located around the perimeter of a circle, a complete circular tie is allowed. 4. Ties shall be located vertically not more than 1/2 a tie spacing above the top of footing or slab in any story, and shall be spaced as provided herein to not more than 1/2 a tie spacing below the lowest horizontal reinforcement in slab or drop panel above. 5. Where beams or brackets frame from four directions into a column, ties may be terminated not more than 75 mm below lowest reinforcement in shallowest of such beams or brackets. ## ACI Specification for Axially Loaded Tied Columns | Particulars | Remarks | |---|---| | Min. Cross sectional area of column Ag | 60,000 mm² | | Minimum thickness of column | 200 mm | | Minimum covering of ties | 1. Not less than 40 mm<br>2. Not less than 1.5 times the max. size of coarse aggregate | | Minimum diameter of lateral ties | 10 mm diameter | | Lateral ties spacing | 1. Not more than 16 bar diameter<br>2. Not more than 48 tie diameter<br>3. Not more than the least dimension of column | | Clear distance between horizontal bars | Not less than 1.5 times the bar diameter nor less than 1.5 times the max. size of coarse aggregate | | Minimum number of bars | 4-16 mm diameter | | Pg (ratio of gross reinf. area to gross cross sectional area) | 0.01 -0.04 | ## Spiral Column - A concrete column with spiral reinforcement enclosing a circular core reinforced with vertical bars. ## ACI Specification for Axially Loaded Spiral Column | Particulars | Remarks | |---|---| | Minimum diameter | 250 mm | | Minimum diameter of spiral ties | 10 mm diameter | | Spacing of spiral ties | 1. Not more than 75 mm<br>2. Not less than 25 mm<br>3. Not less than 1.5 times the size of coarse aggregate | | Minimum number of bars | 6-16 mm diameter | | Clear distance between longitudinal bars | 1. Not less than 1.5 times bar diameter<br>2. Not less than 1.5 times max. size of coarse aggregate | | Pg (ratio of gross reinf. area to gross cross sectional area of column) | 0.01-0.08 | ## Lateral Reinforcement for Compression Members ### Spiral Reinforcement 1. Spirals shall consist of evenly spaced continuous bar or wire of such size and so assembled to permit handling and placing without distortion from designed dimensions. 2. For cast-in-place construction, size of spirals shall not be less than 10 mm diameter. 3. Clear spacing between spirals shall not exceed 75 mm nor less than 25 mm. 4. Anchorage of spiral reinforcement shall be provided by 1 1/2 extra turns of spiral bar or wire at each end of a spiral unit. 5. Splices in spiral reinforcement shall be lap splices of 48db but not less than 300 mm or welded. 6. Spirals shall extend from top of footing or slab in any story to level of lowest horizontal reinforcement in members supported above. 7. Where beams or brackets do not frame into all sides of a column, ties shall extend above termination of spiral to bottom of slab or drop panel. 8. In columns with capitals, spirals shall extend to a level at which the diameter or width of capital is two times that of the column. 9. Spirals shall be held firmly in place and true to line. ## Composite Column - A type of column where structural steel is embedded into the concrete core of a spiral column. ## Combined Column - A column with a structural steel encased in a concrete of at least 7 cm thick reinforced with wire mesh surrounding the column at a distance of 3 cm inside the outer surface of the concrete covering. ## Lally Column - A fabricated post made of steel provided with a plain flat steel bar or plate which holds girder, girt or beam. The steel pipe is sometimes filled with concrete for additional strength and protection from rust or corrosion. ## Special Reinforcement Details for Columns ### Offset Bars 1. The slope of an inclined portion of an offset bar with axis of column shall not exceed 1 in 6. 2. Portions of bar above and below an offset shall be parallel to axis of column. 3. Horizontal support at offset bends shall be provided by lateral ties, spirals, or parts of floor construction. Horizontal support provided shall be designed to resist 1 1/2 times the horizontal component of the computed force in the inclined portion of an offset bar. Lateral ties or spirals, if used, shall be placed not more than 150 mm from points of bend. 4. Offset bars shall be bent before placement of forms. 5. Where a column is offset 75 mm or greater, longitudinal bars shall not be offset bent. Separate dowels, lap splices with the longitudinal bars adjacent to the offset column faces shall be provided. ## Notes on Concrete Columns 1. Columns shall be of the sizes indicated in the schedule or as detailed in drawings and reinforced as shown, with deformed bars only. Vertical bars of columns shall have a 90º bend and anchored at the supporting footing or other supporting member. 2. Concrete protective covering from the face to the reinforcing steel shall be 40 mm. Splices of vertical bars shall be staggered as much as possible, located preferably at the middle half of the column height. Not more than alternate bars shall be spliced at any one level. Bar splices may be lapped splices, or electrically butt welded that can develop the full capacity of the bar. 3. The spacing of lateral ties shown in the schedule are maximum spacing which shall be used only outside the heights and away from joints, where a reduced spacing of not more than 0.10 meter on center is required. The distance which is measured upward from top of footing or floor lines, and downward from bottom and deepest beam or girder, shall be the largest of the following: (1) maximum column; (2) one-sixth (1/6) of the clear height of the column; and (3) 457 mm (18 inches). 4. If the column is reduced in size at an upper floor, the vertical bars of the column from the lower floor may be crimped or offset to the new position at the upper column if the horizontal distance between the two positions is not more than 75 mm (3 inches). In crimping or offsetting the bars, the angle of bend shall not be more than one horizontal to six vertical (1:6). Extra lateral ties shall be provided at the lower end of the bend to care of at least 1.25 of the outside thrust caused by the inclined position of the bar, and this may be satisfied by providing at least two extra hoops to hold the bent bars at the beginning of the bend, these hoops spaced close together. 5. Lateral ties and spirals shall be provided for the vertical bars of the column within the depth of the beams and/or girders at the intersection with the column and spaced not more than 0.10 meter on centers. ## Minimum Thickness of Non-prestressed Beams ### Notes on Concrete Beams 1. The clear distance from the bar to the farther face of the wall shall not be less than 4 bar diameters (4d) if reinforcing bars end in a wall. 2. Bars may be bundled in twos, threes, fours, as indicated on drawings, such bundled bars shall be securely wired together to prevent them from separating. 3. Use 25 mm separator at 1 m apart for two or more layers of reinforcing bars, with the bars not bundled. 4. Beam reinforcing bars supporting slab reinforcement shall be 25 mm clear from the bottom of the finish. The clear concrete covering between the face of the beam at the bottom of the sides shall be 350 mm. 5. When the beam crosses a girder, rest beam bars on top of girder bars. 6. Beam reinforcing bars shall be symmetrical about the vertical axis whenever possible, and about the center line at midspan except for end spans and where otherwise shown. 7. Stirrups for rectangular beams without flanges shall be closed stirrups. Stirrups for tee beams with flanges on one side only shall likewise be closed stirrups. Stirrups for tee beams with flanges on both sides may be U stirrups. U stirrups may be placed in alternating inverted and upright position. ## Floor System - The horizontal planes that supports both live loads and dead loads and transfer their loads horizontally across to a beam, column, or to load- bearing walls. ### Live Load - Refers to those movable loads imposed on the floor such as people, furniture and the like. ### Dead Load - Refers to the static load such as the weight of the construction materials which generally carry the live load. ### Environmental Load - Consist of wind pressure and suction, earthquake load, rainwater on flat roof and forces caused by temperature changes or differentials. ## Reinforced Concrete Slab - A rigid planar structure of concrete designed to act together with principal and secondary reinforcements in resisting applied forces. ## Slab Nomenclature ### Principal Reinforcement - Reinforcement designed to absorb the stresses from applied loads and moments. ### Shrinkage Reinforcement - Reinforcement placed perpendicular to the principal reinforcement in a one-way slab to absorb the stresses resulting from shrinkage or changes in temperature. Also called *Temperature Reinforcement*. ## Concrete Topping - A thin layer of high-quality concrete placed over a concrete to form a floor surface. ### Bonding Layer - A thin layer of mortar spread on a moistened and prepared existing concrete surface prior to laying a new concrete slab. ### Expansion Joint - A joint or gap between adjacent parts of a building or structure or concrete work which permits their relative movement due to temperature changes (or other conditions) without rupture or damage. Also called *Contraction Joint*. ### Construction Joint - A joint where two successive placements of concrete meet. ### Isolation Joint - Often called *Expansion Joint*, it allows movement between concrete slab and adjoining columns and walls of a building. ### Control Joint - Joint that creates lines of weakness so that cracking that may result from tensile stress occurs along predetermined lines. ## One-way Slab - A concrete slab of uniform thickness reinforced in one direction and cast integrally with parallel supporting beams. One-way slabs are suitable only for relatively short spans. This type of slab is supported by two parallel beams, the beam framing into girders in turn framing into columns. The reinforcement in the slab runs in one direction only, from beam to beam, hence the slab is known as *One Way Slab*. - Maximum spacing of main reinforcing bars should not exceed 3 times the thickness of slab nor 450 mm while the maximum spacing of temperature bars is five times the slab thickness nor more than 450 mm. - Min. main reinforcing bars = 12 mm Φ - Min. Temperature bars = 10 mm Φ - Max. spacing of main bars not than 3 times thickness of slab or 450 mm - Max. spacing of temperature bars not 5 times thickness of slab or 450 mm - Steel Covering = 20 mm - Clear distance from center of reinforcing bars to the bottom of slab = 25 mm - Temperature bars: - As = 0.002 bt for Grade 300 (fy = 300 Mpa) - As = 0.0018 bt for Grade 400 (fy = 400 Mpa) - Minimum Thickness of One way Slab - Simply Supported = L/20 - One end continuous = L/24 - Both ends continuous = L/28 - Cantilevered L/10 - When S/L = 0.5, it is one way slab. - where: S - shorter span ## Two-way Slab - A concrete slab of uniform thickness reinforced in two directions and cast integrally with supporting edge beams or bearing walls on four sides. Two-way slabs are economical for medium spans with intermediate to heavy loads. - S/L = 0.5, it is two-way slab - Min. thickness t = Perimeter/180 - Max. spacing of main bars = 3t not 450 mm - Spacing of bars within the column strip is 3/2 times the spacing at the center ## Beam-and-Girder Slab - A one-way slab supported by secondary beams which in turn are supported by primary beams or girders. ## Continuous Slab - A reinforced concrete slab extending as structural unit over three or more supports in a given direction. A continuous slab is subject to lower bending moments than a series of discrete, simply supported slabs. ## Flat Plate - A concrete slab of uniform thickness reinforced in two or more directions and supported directly by columns without beams or girders. Flat plates are suitable for short to medium spans with relatively light live loads. Since there no column capitals or dorp panels, shear governs the thickness of a flat plate. ## Flat Slab - A flat plate thickened at its column supports with column capitals and drop panels to increase its shear strength and moment-resisting capacity. Flat slabs are suitable for heavy loaded spans. ## Waffle Slab - A two-way concrete slab reinforced by ribs in two directions. Waffle slabs are able to carry heavier loads and spans longer distances than flat slabs. Supporting beams and drop panels can be formed by omitting in selected areas. ## Precast Concrete Slabs - A concrete slab member or product that is cast and cured in a place other than where it is to be installed in a structure. ### Solid Flat Slab - A precast, prestressed concrete plank suitable for short spans and uniformly distributed floor and roof loads. ### Hollow-core Slab - A precast, prestressed concrete plank internally cored to reduce dead weight. Hollow-core slabs are suitable for medium to long spans and uniformly distributed floor and roof loads. ### Single Tee - A precast, prestressed concrete slab having a broad, T-shaped section. ### Double Tee - A precast, prestressed concrete slab having two stems and a broad cross section resembling the capital letters TT. ### Inverted Tee - A precast, prestressed ledger beam having a cross section resembling an inverted capital T. ### L-beam - A precast, prestressed ledger beam having a cross section resembling the capital letter L. ### Ledger Beam - A reinforced concrete beam having projecting ledges for receiving the ends of joists or slabs. ## Notes on Concrete Slabs 1. All slab reinforcement shall be 0.02 m, clear from the bottom and 0.015 clear from the top of slab, unless otherwise indicated or stated in code. 2. In two-way slabs, the bars along the short span shall be at the lower layer for bottom bars, and at upper layer for top bars so that the bars along the shorter span shall have the bigger effective depth, unless otherwise detailed or noted due to the continuity of bars from adjoining spans. 3. In two-slabs, if the top reinforcement over a common support of two adjacent spans are different, the smaller spacing shall be followed at that common support. 4. Slab reinforcement shall rest on the reinforcement of the supporting beams. 5. Bars shall be spliced only where indicated on details. Straight continuous bars in slabs may be spliced (lapped or welded) at supports for bottom bars and at midspan for top bars. ## Notes on Concrete Walls 1. All walls to be reinforced according to the schedule provided in the working drawing shall be observed unless otherwise specified or indicated on drawings. 2. Reinforcing bars shall be 0.03 m. clear from the face of the wall except in 0.10 m wall where they shall be at the center, unless otherwise detailed. ## Schedule of Wall Reinforcement | Wall Thickness | Vertical | Horizontal | Remarks | |---|---|---|---| | 0.10 m | 10 mm at 0.30 m | 10 mm at 0.30 m | At center, hor. Staggered | | 0.15 m | 10 mm at 0.30 m | 10 mm at 0.30 m | Both faces, vert. Outside | | 0.20 m | 10 mm at 0.30 m | 10 mm at 0.25 m | Both faces, vert. Outside | | 0.25 m | 12 mm at 0.30 m | 10 mm at 0.25 m | Both faces, hor. Outside | | 0.30 m | 12 mm at 0.30 m | 12 mm at 0.30 m | Both faces, hor. Outside | | 0.35 m | 12 mm at 0.30 m | 12 mm at 0.30 m | Both faces, hor. Outside | | 0.40 m | 12 mm at 0.30 m | 12 mm at 0.25 m | Both faces, hor. Outside | | 0.45 m | 16 mm at 0.30 m | 12 mm at 0.25 m | Both faces, hor. Outside | | 0.50 m | 16 mm at 0.30 m | 16 mm at 0.30 m | Both faces, hor. Outside | ## Foundation Engineering ### Foundation - The lowest division of a building, its substructure, or other construction, constructed partly or wholly below the surface of the ground, designed to support and anchor the superstructure above and transmit its load directly to the earth; that part of the structure that supports the weight of the structure and transmits the load to underlying soil or rock. - Foundation Engineering applies the knowledge of soil mechanics, rock mechanics, geology and structural engineering to the design and construction of foundation for buildings and other structures. ### Shallow Foundation - A foundation system type which is employed when stable soil of adequate bearing capacity occurs relatively near to the ground surface, they are placed directly below the lowest part of the sub-structure and transfer building loads directly to the supporting soil by vertical pressure. ### Deep Foundation - A foundation system type employed when the soil underlying a foundation is unstable to transfer building loads to a more appropriate bearing stratum of rock or dense sand and gravel well below the superstructure. ### Footing - That part of the foundation bearing directly upon the supporting soil, set below the natural grade line and enlarged to distribute its load over a greater area. ### Tie Beam/ Footing Tie Beam/ Grade Beam - A reinforced concrete beam distributing the horizontal forces from an eccentrically loaded pile cap or spread footing to other pile caps or footings; a reinforced concrete beam supporting a superstructure at or near a ground level and transferring the load to isolated footings, piers, or piles. ### Superstructure - That part of a building or structure which is above the level of the adjoining ground or the level of the foundation. ### Substructure - The underlying structure