Lecture 9 - ARCH 106 Materials of Construc6on...

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Unformatted text preview: ARCH 106 Materials of Construc6on Sitecast Concrete CEMENT AND CONCRETE Concrete ingredients: •  Fine aggregate (sand) •  Coarse aggregate (gravel) –  Coarse and fine aggregate provide the structural mass of the concrete and cons5tute the majority of the concrete volume. •  Portland cement –  Cement binds the aggregate. •  Water –  Water is necessary for the chemical hydra5on of the cement and the hardening of the concrete. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CEMENT AND CONCRETE Maximum Aggregate Size •  Generally, with larger aggregates, less cement is required in the concrete mix. Reducing the quan5ty of cement reduces cost, since cement is the most expensive ingredient in the mix. •  The largest aggregate must fit comfortably between reinforcing bars and within the overall thickness of the concrete. Largest aggregate size should not exceed: –  1/5 distance between form faces –  3/4 of the space between reinforcing bars –  1/3 the depth of a slab •  Common maximum aggregate size for concrete used in buildings ranges from 3/8 to 1 ­1/2 in. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CEMENT AND CONCRETE Water •  Water is an essen5al ingredient in concrete, that combines chemically with the cement as the concrete hardens. •  Water must be free of contaminants. •  Water that is potable is acceptable for use in making concrete. •  ASTM C 1602 permits the use of other sources such as waste water from washing out concrete trucks or storm water runoff at concrete produc5on facili5es that may contain limited amounts of concrete waste material. •  The quan5ty of water in the concrete mix must be controlled as closely as any other ingredient: Adding unneeded water dilutes the cement paste, weakening the hardened concrete. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CEMENT AND CONCRETE Admixtures •  Other ingredients in the concrete mix used to alter or improve concrete proper5es in various ways: –  –  –  –  –  –  –  –  Air ­entraining Water ­reducing Cure accelera5ng or retarding Workability modifying Shrinkage ­reducing Corrosion inhibi5ng Freeze protec5ng Coloring •  E.g., High ­strength concrete for very tall buildings: –  Supplementary Cemen55ous Materials (SCMs), for greater strength –  Water reducers, to increase concrete strength while maintaining workability –  Admixtures to improve pumpability –  Retarding admixtures, to allow adequate 5me for placing Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. Burj Dubai, world's tallest concrete framed building (800+ meters, 2600+ feet) MAKING AND PLACING CONCRETE Water ­Cement Ra5o •  The water ­cement ra;o (w/c ra;o) is the most important determinant of concrete strength. Lowering the propor5on of water to cement: –  Increases concrete strength and durability –  Decreases workability –  Increases cost •  W/C ra5o is measured by weight, not volume. •  When supplementary cemen55ous materials are added to the mix, the ra5o is measured as the water ­ cemen;;ous materials ra;o. •  Why use higher ­strength concrete: –  Reduce column dimensions in tall buildings. –  Achieve higher earlier strength, allowing construc5on to proceed more quickly. –  Sa5sfy more stringent structural requirements. Copyright © 2009 J. Iano. All rights reserved. (A ­E Concrete: Air ­entrained concrete) Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on MAKING AND PLACING CONCRETE Slump Test •  The slump test provides a rough measure of the workability of concrete while wet. •  Concrete is placed into a conical cylinder; the cylinder is removed, and the loss in height of the concrete mass is measured. –  Concrete with too low slump may be difficult to place. –  Concrete with too high slump may have had too much water added. •  Specified maximum slump is usually in the range of 3 to 5 inches. •  Slump tests are performed on batches of concrete as the arrive on the concrete site. •  Slump that varies excessively from one batch to the next may indicate quality control problems in the concrete mixes. Copyright © 2009 J. Iano. All rights reserved. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on MAKING AND PLACING CONCRETE Placing Concrete •  Avoid delays, during which concrete can s5ffen and become difficult to place. Depending on condi5ons, concrete can placed up to 90 minutes aier mixing commences. •  Concrete that does s5ffen can have water added prior to placing, provided that: –  Maximum w/c ra5o is not exceeded –  Maximum slump is not exceeded –  Agita5on limits are not exceeded •  Concrete may be placed on site directly from the discharge chute of a transit ­mix truck, or by combina5on of wheelbarrows, power buggies, crane ­liied buckets (right), conveyor belts, pumpers, or other devices. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. MAKING AND PLACING CONCRETE Placing Concrete •  Segrega;on, separa5on of large aggregate from the finer por5ons of the mix, must be avoided. •  Place concrete as close to final posi5on as possible. •  Do not push concrete over large horizontal distances. •  Avoid dropping concrete from high heights or discharging against obstacles (use drop chutes if needed). •  Right: Concrete delivered to its final loca5on by pumping. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. MAKING AND PLACING CONCRETE Consolida5ng Concrete •  Consolida;on (compac;on): The elimina5on of voids and air pockets within the concrete pour. –  –  –  –  Hand rodding or tamping Screeding (top) Internal vibra5on (bojom) External vibra5on •  Consolida5on is especially cri5cal with s5ff concrete mixes or when concrete is placed around densely packed reinforcing arrays. •  Over ­consolida5on must be avoided, as it can lead to segrega5on of aggregate as larger par5cles descend and finer components rise to toward the surface. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. MAKING AND PLACING CONCRETE Curing Concrete •  Concrete hardens by hydra;on, the chemical bonding of water and cement. •  If concrete dries out prematurely, the hydra5on process stops and maximum strength is not achieved. •  Hydra5on, along with increasing strength and durability, can con5nue for a very long 5me, even years. Concrete strength is normally specified at 28 days. •  Exposed surfaces of newly poured concrete must be protected from evapora5on and drying. Concrete may be regularly misted, covered with moisture ­retaining materials, or treated with a chemical surface sealer. •  In very hot or cold weather, steps may be taken to moderate the temperature of the concrete, such as pre ­hea5ng of ingredients, adding water as ice, or the use of retarders or accelerators to adjust cure rate. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. REINFORCING Reinforcing a Simple Beam •  Top: In a simply supported beam, the greatest tension forces occur at the bojom middle of the beam. •  Where tension forces cross compression forces closer to the beam ends, shear forces also occur. •  BoGom: The placement of reinforcing in a concrete beam approximates the lines of tension, but is simplified to reduce fabrica5on costs. Theoretical lines of tension and compression in a simple beam. Simple concrete beam reinforcing, including heavy bottom bars, lighter top bars, and U-shaped shear stirrups Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. PRESTRESSING Prestressing •  Prestessing: Applying an ini5al compressive stress to a concrete member, so as to improve its structural efficiency. •  High ­strength steel strands are stretched 5ghtly and then restrained by the concrete, pukng the concrete into ini5al compression. •  When normal service loads are added, the concrete in prestressed members is subject to less tensile force. •  Prestressed members are typically more slender and lighter than comparable conven5onally reinforced members. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. 14 SITECAST CONCRETE FRAMING SYSTEMS CASTING A CONCRETE SLAB ON GRADE Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE SLAB ON GRADE Concrete Slabs •  Slab On Grade: A concrete surface, lying upon, and con5nuously supported by, the ground beneath (upper) •  Suspended or Structural Concrete Slab: A concrete slab that spans between intermediate lines or points of support (lower) Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE SLAB ON GRADE Subgrade Prepara5on •  Site is cleared and grubbed if necessary. •  Organic top soil is removed. •  Subsoil, or subgrade, is excavated to required depth. •  Subgrade is graded level and compacted to the required density. •  If the subsoil is too soi or unstable, it is over ­ excavated and replaced with more competent material. •  Proof rolling: A heavy roller or loaded dump truck makes mul5ple passes over the subgrade (right). Areas that are revealed to be soi or unstable are corrected. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE SLAB ON GRADE Capillary Break or Drainage Layer •  A layer of crushed rock or gravel, usually 4 inches deep, is placed over the subgrade. •  This rock material is well sorted (comprised of par5cles mostly uniform in size), that may range from approximately ¾ ­inch to 1½ ­ inch in diameter. •  This layer drains water easily and prevents moisture in the ground from rising up to the concrete slab through capillary ac5on. •  This layer also provides a structurally sound base for the concrete slab to follow. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE SLAB ON GRADE Slab Edges •  Isola;on or expansion joints: Where slabs abut walls, columns, or other elements, compressible joint material is placed to create an isola5on joint or expansion joint. •  Isola5on joints allow unrestrained expansion and contrac5on of the slab, as well as differen5al sejling between the slab and the abukng elements. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE SLAB ON GRADE Vapor Retarder or Moisture Barrier •  A heavy plas5c sheet or other impervious material may be laid over the drainage layer. •  This layer provides the slab with addi5onal protec5on of the slab against subgrade moisture and protec5on of the drainage layer against concrete filling in. •  Vapor retarders are used only with interior slabs, not with exterior slabs. Tape (blue in this photo) is used to seal laps in the vapor retarder sheets. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE SLAB ON GRADE Vapor Retarder or Moisture Barrier •  Vapor retarder materials must be durable enough to resist being punctured or torn during subsequent construc5on opera5ons, such as laying reinforcing steel or pouring the concrete. •  Penetra5ons and tears in the in the vapor retarder are sealed 5ghtly to maintain a con5nuous barrier. •  In cases of extreme ground water condi5ons, the moisture barrier may be replaced with a heavier, more impervious waterproofing membrane. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE SLAB ON GRADE Pouring the Concrete •  Concrete is placed by any of a number of methods, depending on the size of the pour and ease of access to the slab. –  Above: Concrete delivered by pumper –  Below: Concrete delivered by wheel barrow •  Concrete should be placed as close as possible to its final des5na5on. •  Pushing concrete along the ground can cause segrega5on of large and small par5cles in the concrete mix, leading to a lack of uniform density and uneven finish quali5es in the completed slab. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE SLAB ON GRADE Finishing the Concrete •  Striking off or screeding: A wood plank or metal straightedge is drawn across the surface of the freshly poured concrete, using an end ­to ­end sawing mo5on. •  A bulge of concrete is maintained in front of the screed, to fill low spots as the screed progresses. •  Striking off establishes the eleva5on of the upper slab surface. In this photo, note the use of the edge form to guide the screed. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE SLAB ON GRADE Finishing the Concrete •  Floa;ng: Immediately aier screeding, floa5ng is performed to consolidate and smooth the slab surface. •  Right: A bull float is drawn back and forth over the slab. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE SLAB ON GRADE Finishing the Concrete •  Floa5ng may be performed a second 5me, to further consolidate and densify the surface of the slab. •  Floats are made of wood or metal with a slightly rough surface. The floa5ng opera5on leaves the slab with a lightly textured surface. •  Floa5ng may be done by hand, or with power machinery (right). Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE SLAB ON GRADE Finishing the Concrete •  Broom Finish: A s5ff broom is drawn across the slab surface to create a striated, slip resistant texture (right) •  Restraightening: Aier each floa5ng or troweling opera5on, a long straightedge may be drawn over the slab surface to reduce minor undula5ons •  Shake ­On Hardeners: Dry powders may be floated into the slab surface to create a harder, more durable surface •  Laser Screeds: Laser ­guided power screeds can be used to finish slabs to more precise flatness and levelness requirements. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE SLAB ON GRADE Finishing the Concrete •  Curing: To ensure proper curing of the concrete, freshly poured slabs must be kept damp for at least the first week. •  Slabs are especially vulnerable to premature drying because of their rela5vely large exposed surface area: –  Cover slab with impervious plas5c sheets (right). –  Cover slab with absorbent, dampened straw, sawdust, or burlap. –  Coat slab with a liquid ­ applied curing compound, that dries to form a clear moisture barrier. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE SLAB ON GRADE Controlling Cracking •  Control joint or contrac;on joint: A par5al ­depth joint or groove that creates a natural plane of weakness in the slab. •  Control joints encourage shrinkage cracking to occur in an organized, visually acceptable manner. •  Right: Control joints may be saw ­cut into a slab aier the slab has par5ally hardened. •  Control joints can also be formed during slab finishing opera5ons using hand tools called groovers. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE SLAB ON GRADE Controlling Cracking •  Control joints need to extend at least ¼ the depth the slab to be effec5ve. •  As a rule of thumb, control joints should be spaced from 24 to 30 5mes the depth of the slab. (E.g., for a 4 ­inch slab, joints should be spaced no more than 8 to 10 feet in both direc5ons.) Where the control joint stops, the crack which was hidden in the joint continues to propagate and now becomes visible. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE SLAB ON GRADE Controlling Cracking •  Expansion joint or isola;on joint: Expansion and isola5on joints are full ­depth separa5ons between slab sec5ons, that allow full freedom of movement between sec5ons. •  Reinforcing is also interrupted across expansion joints. (Across control joints, reinforcing is usually uninterrupted.) •  Other means of crack control: –  Concrete mixtures can be adjusted to reducing drying shrinkage. –  Addi5onal reinforcing or posjensioning can be added to a concrete slab to increase its tensile strength. A diamond-shaped section of slab around a column is bordered by an isolation joint separating it from the surrounding slab on grade. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. 14 SITECAST CONCRETE FRAMING SYSTEMS CASTING A CONCRETE WALL Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE WALL Wall Foo5ng •  Concrete walls are most commonly cast over concrete strip foo5ngs. •  The steel reinforcing projec5ng from the foo5ng will overlap with reinforcing in the wall, to structurally 5e the two elements. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE WALL Reinforcing •  The size, spacing, and arrangement of reinforcing bars varies with the structural requirements of the wall. •  Typically, reinforcing is placed in one or two layers of ver5cal and horizontal reinforcing bars. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE WALL Wall Forms •  Slender rods, called form ;es, hold the forms in posi5on and resist the outward pressure of the concrete when it is placed. •  The plas5c cones prevent the formwork for sliding along the 5es, and form a neat, conical hole in the finished surface of the concrete. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE WALL Wall Forms •  Aier the wall is cast and the forms removed, the protruding ends of the metal 5es are broken off and the plas5c cones removed. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE WALL Wall Forms •  Right: On the outside, the form 5es engage with slojed metal wedges. The wedges restrain the horizontal walers. •  The walers (and some5mes ver5cal studs) brace the formwork panels. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE WALL Wall Forms •  Wall forms must be constructed sufficiently s5ff to resist the fluid pressures of the freshly poured concrete. •  Right: A proprietary, modular wall form system, that can be easily raised and reused as wall construc5on proceeds upwards. •  Note the temporary scaffolding integrated into the form system, providing workers with access to the top of the wall. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE WALL Wall Forms •  Self ­climbing formwork relies on hydraulic jacks to climb the concrete core structure as it is constructed. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE WALL Finishing the Concrete •  A residen5al concrete founda5on wall with the formwork stripped. •  Without special efforts, the form panels and 5es leave strong pajerns on the wall surface. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE WALL Finishing the Concrete •  A concrete founda5on wall with blockouts to create openings in the wall for passage of building services. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE WALL Finishing the Concrete •  Rough boards were used to line the inside of the wall forms, crea5ng a board form finish on the cast wall. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE WALL Finishing the Concrete •  Poor quality formwork construc5on leads to defects in the concrete wall that do not become evident un5l the formwork is removed. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE WALL Finishing the Concrete •  Incomplete consolida5on leads to a rock pocket in the concrete wall. •  Note the exposed reinforcing bar. •  Unsound concrete will be removed and the area patched. •  Segrega5on Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE WALL Controlling Cracking •  Like slabs, concrete walls are suscep5ble to cracking due to concrete shrinkage during curing, thermal stresses, and other effects. •  Ver5cal control joints, spaced at 24 to 30 5mes the thickness of the wall, can be formed in the wall to organize and conceal shrinkage cracks. •  Full ­depth expansion joints can also be inserted at larger spacings, if required. Shrinkage cracks in a concrete retaining wall highlighted by moisture migrating through the joints. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE WALL Insula;ng Concrete Forms (ICF) •  Concrete forms made from rigid plas5c foam blocks or other lightweight insula5ng materials are easy to erect. •  The forms become a permanent part of the structure, crea5ng a more energy efficient wall in comparison to conven5onal concrete construc5on. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE WALL Tilt ­Up Construc;on •  Concrete wall panels are poured lying flat, much like a slab on grade. •  Once the panels have gained sufficient strength, they are liied into final posi5on. •  Tilt ­up construc5on significantly reduces formwork costs, which can account for 50 per cent or more of the cost of conven5onal concrete construc5on. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. 14 SITECAST CONCRETE FRAMING SYSTEMS CASTING A CONCRETE COLUMN Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE COLUMN Column Foo5ngs •  Columns may rest on isolated foo5ngs, pile caps, caissons, or enlarged por5ons of strip foo5ngs. •  Right: The lower layer of reinforcing has been placed for an isolated foo5ng. Addi5onal reinforcing, including ver5cal dowels that will project out of the foo5ng and overlap with ver5cal reinforcing bars in the column, will be added next. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE COLUMN Column Reinforcing •  Ver;cal reinforcing bars increase the column's load carrying capacity and give it resistance to bending forces generated by lateral forces on the building structure or by connected beams. •  Ties, lighter in weight, wrap around the ver5cal bars to resist outward buckling of the bars. •  Ties also increase a column's resistance to extreme cyclical seismic loads. Spiral reinforcement, right, is more expensive and produces stronger columns than those reinforced with conven5onal 5es. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE COLUMN Column Reinforcing •  Ver5cal bars are bent inward at the top, so as to nest with the next sec5on of reinforcing as construc5on proceeds upward. •  The length of the overlapping por5ons of reinforcing are sufficient to fully transfer stresses from one set of bars to the next. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE COLUMN Column Reinforcing •  Prefabricated column reinforcing stacked on site, ready to be liied into posi5on. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE COLUMN Column Forms •  Column forms may be square, rectangular, or round. •  Unless the column is unusually wide, no form 5es are required. •  Right: A reusable column form is maneuvered into place around column reinforcing. •  The ver5cal bars in this column are bent horizontally at their top ends, to engage with steel reinforcing in the not ­yet ­constructed concrete slab. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. CASTING A CONCRETE COLUMN Pouring Concrete •  Concrete is deposited into the column form by any number of means. •  The concrete is vibrated or otherwise consolidated as needed as it is placed. •  Right: A concrete bucket liied by a construc5on crane is used to deliver concrete to the column form. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. 14 SITECAST CONCRETE FRAMING SYSTEMS ONE ­WAY FLOOR AND ROOF FRAMING SYSTEMS Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. ONE-WAY FLOOR AND ROOF FRAMING SYSTEMS One ­Way Solid Slab •  A system of beams support a slab. The slab is reinforced to span in one direc5on only. –  Girders (deeper beams) span between columns. –  Beams (shallower) span from girder to girder. –  The slab spans between the beams. •  Depending on beam and column arrangements, this system can be designed for a wide range of load condi5ons. •  Forming for girders and beams makes this system more expensive than many other systems. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. ONE-WAY FLOOR AND ROOF FRAMING SYSTEMS One ­Way Concrete Joist (Rib Slab) •  A system of beams and slender, closely ­space ribs support a one ­way slab. –  Beams span between columns. –  Joists (ribs) span from beam to beam. –  The slab spans between the joists. •  Greater spans are possible than with solid slab. •  Modular, prefabricated form systems help to keep this system economical. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. ONE-WAY FLOOR AND ROOF FRAMING SYSTEMS One ­Way Concrete Joist (Rib Slab) •  In one ­way joist systems, the bojoms of the beams and joists are all on the same plane, simplifying formwork construc5on. •  A simple, level surface is formed on site. Next, prefabricated metal or berglass joist pans are placed on this surface to form the system of beams and ribs. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. ONE-WAY FLOOR AND ROOF FRAMING SYSTEMS Wide ­Module Concrete Joist System •  Like one ­way joist, but ribs are spaced 4 to 6 feet rather than 20 to 30 inches. •  A thicker slab is required to span the greater distance between ribs (useful when greater thickness is required for greater fire resistance). •  Also called "skip ­joist" system. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. 14 SITECAST CONCRETE FRAMING SYSTEMS TWO ­WAY FLOOR AND ROOF FRAMING SYSTEMS Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. TWO-WAY FLOOR AND ROOF FRAMING SYSTEMS Two ­Way Framing Systems •  A two ­way slab is reinforced so that it spans structurally in both direc5ons. •  Two ­way slabs are more structurally efficient than one ­way slabs of the same thickness. •  Two ­way slabs must span roughly the same distance in both direc5ons. As the layout of slab supports becomes increasingly rectangular in propor5on, the efficiency of the two ­way slab decreases. •  In contrast, one ­way slab systems are more suitable for column and beam layouts that create rectangular bays. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. TWO-WAY FLOOR AND ROOF FRAMING SYSTEMS Two ­Way Solid Slab •  A system of beams supports a two ­way slab. •  Suitable for very heavy loads. •  Forming of the beam systems tends to make this system more expensive than other two ­ way slab systems. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. TWO-WAY FLOOR AND ROOF FRAMING SYSTEMS Two ­Way Flat Slab •  A two ­way reinforced slab is supported by columns without beams. •  The flat slab system includes added structure where columns meet slabs: –  Mushroom capitals: Conical widening toward the top of the column –  Drop panels: Thickening of the slab around the column •  This added structure allows the system to carry heavier loads than would otherwise be feasible (see Flat Plate following). Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. TWO-WAY FLOOR AND ROOF FRAMING SYSTEMS Two ­Way Flat Plate •  Like the flat slab, a two ­ way reinforced slab is supported by columns without beams. •  There are no column capitals or drop panels in the flat plate system. •  Addi5onal reinforcing within the depth of the slab at the column/slab junc5on is used to increase strength in that area. •  Flat plate systems are best suited to lighter loads than flat slab systems. The simplified formwork also makes them less expensive to construct. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. TWO-WAY FLOOR AND ROOF FRAMING SYSTEMS Two ­Way Flat Plate •  A cross ­shaped array of shear studs (with orange heads in the photo) provides addi5onal strength at the column/ slab junc5on of a two ­way flat plate system. •  The green cables are posjensioning strands, as discussed in the last lecture/video. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. TWO-WAY FLOOR AND ROOF FRAMING SYSTEMS Two ­Way Flat Plate •  Two ­way flat plate construc5on in a residen5al tower •  Two ­way flat plate is one of the thinnest of floor framing systems available in any structural material, an economy that is compounded in mul5 ­ story construc5on. •  Note the reshoring (yellow clad columns) in use underneath the upper two slabs. When the formwork is removed, reshoring is inserted to provide support for the slabs un5l the concrete gains addi5onal strength. Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. TWO-WAY FLOOR AND ROOF FRAMING SYSTEMS Two ­Way Waffle Slab (Two ­Way Concrete Joist) •  Similar to one ­way joist, but with a two ­way system of ribs •  Constructed with prefabricated domes that simply formwork construc5on. •  Around the columns, domes are filled solid to create heads that strengthen the column/ slab connec5on, like drop panels in flat slab construc5on. •  Example: Cal Poly Library Fundamentals of Building Construc5on, Materials & Methods, 5th Edi5on Copyright © 2009 J. Iano. All rights reserved. Reading Assignment: Chapter 14 Page 554 ­609 Sitecast Concrete •  Slab on Grade •  Cas5ng Wall and Columns •  Roof Framing systems •  Reinforcing •  Building Codes ...
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