AR413S_Module-1_Types-of-Slabs-and-Construction-Methods.pdf

College of Architecture and Fine Arts Education 4th Floor, DPT BuildingMatina Campus, Davao City Phone No/...

College of Architecture and Fine Arts Education 4th Floor, DPT BuildingMatina Campus, Davao City Phone No/Telefax: (082) 305-0646 loc 109 COURSE PACK 1ST SEMESTER A.Y. 2024-2025 AR413/S Alternative Building Construction Systems Prepared by: Ar. Noel T. Amor, Jr./Designed for UM-CAFAE Bachelor of Science in Architecture Program | Page | 1 WHY STUDY BUILDING TECHNOLOGY? Definition Knowledge of the technical processes and methods of assembling buildings. It encompasses materials and their applications, physical properties, capacities and vulnerabilities; the functioning of components and systems; the principles, procedures and details of building assembly; operating strategies and so on. Without understanding basic building technology, an architect cannot demonstrate a design's constructability or its compliance with codes. Course Description : This course is designed to present, explain construction methods and techniques or different types of buildings using any appropriate alternative building construction system. 1. CAST-IN-PLACE SYSTEM Also called as “cast-in-situ”, is a construction technique where building components like walls, slabs, beams, columns, roofs, etc., are cast at the site by formwork. Cast-in-place concrete is poured directly on the building site to form the desired structural system or application. The concrete then cures within the environmental conditions of the site. There is no transportation required for the cured concrete. This concrete is commonly called site-cast concrete. Site casting involves pouring concrete directly into a mold on-site to achieve the required shape for specific construction projects. Although no transportation is required, there is an increased requirement for other labor. The curing of the concrete itself takes weeks. Additionally, weather conditions can stall the construction project duration for months. 2. PRE-CAST SYSTEM ` Is a concrete product that is created offsite and then delivered to its project destination for final use. Pre-Cast is sometimes called prefabricated or pre-made concrete that is ready to use right away on the construction site. Prepared by: Ar. Noel T. Amor, Jr./Designed for UM-CAFAE Bachelor of Science in Architecture Program | Page | 2  Involves casting concrete in a reusable mold or form, which is then cured in a controlled factory environment off-site. The curing conditions are not always ideal at a construction site. Therefore, precast concrete provides a higher quality structure, as the curing or hardening process takes place in optimal conditions. Precast units come in different shapes made in controlled precast facilities. The manufacturers use high-end raw materials that can be difficult to source for local builders. The precast panels are shipped to the final job site. WHAT IS SLAB? Slabs are flat, horizontal structural elements made of reinforced concrete that receive the load and transfer it through the beams to the columns and to the footings to the soil below. Slabs are used in both load-bearing structures and framed structures. Figure No.1 Slab Construction Types of Slabs 1. Conventional Slab The slab which is supported by beams and columns, is called conventional slab. In conventional slab the thickness of the slab is small but depth of the beam is large. The load is transmitted from slab to beam and then from beam to column. Prepared by: Ar. Noel T. Amor, Jr./Designed for UM-CAFAE Bachelor of Science in Architecture Program | Page | 3  These types of slabs are provided with reinforcement where the horizontal bar is called main reinforcement and vertical bar is called distribution bar. Conventional slabs are two types. a. One way slab b. Two way slab One Way Slab One way slab is a conventional horizontal slab rectangular in shape and supported by beams on two of its four sides. The slabs are supported on beams opposite to each other. Therefore, the deflected shape is cylindrical. In one way slabs the longer span is more than twice of the shorter span. The ratio of longer span to the shorter span is greater than two. As a result, the shorter span is subjected to bending. The main reinforcements are provided in the shorter directions to resist the bending and the secondary reinforcements are provided in the longer direction. Figure No. 2 – Deflection in One-way Slab Two Way Slab Two-way slabs are also conventional slabs mostly rectangular in shape and supported on all four sides of a beam. In two-way slabs, the longer span is less than twice the shorter span. The ratio of longer span to shorter span is lesser than two. The deflected shape of the slab is like a dish or saucer shape. In this case, both the shorter and longer directions are subjected to bending. Therefore, the main reinforcements would be provided in both directions based on the magnitude of bending. The Prepared by: Ar. Noel T. Amor, Jr./Designed for UM-CAFAE Bachelor of Science in Architecture Program | Page | 4 two-way slabs are economical to a size of 6m x 6m. Also, the quantity of steel used in two-way slab is more than the one-way slab. Figure No. 3 – Deflection in Two-way Slab 2. Flat Plate Unlike conventional slabs, the loads are not transferred from the slabs to the beams in flat plates. Instead, the loads are transferred directly to the columns. Depending on the design plan, the flat plate system may be one-way or two-way. Figure No. 4 – Application of Flat Plate 3. Flat Slab Flat slabs are the modified version of flat plates with a column head and/or a drop panel cast monolithically with the slab. There are no beams present in the flat slabs but the drop panels and column heads will transfer the loads smoothly to the columns. a. Flat Slab with column heads b. Flat Slab with drop panels c. Flat Slab with column heads and drop panels Prepared by: Ar. Noel T. Amor, Jr./Designed for UM-CAFAE Bachelor of Science in Architecture Program | Page | 5 Flat Slab with column heads The column heads are provided below the drop panels, and they are mostly sloping to meet the column dimensions. A flat slab with column head increases the shear strength of the slab and reduces the moment in the slab by reducing the clear or effective span. Figure No. 5 – Flat Slab with column head Flat Slab with drop panels The drop panels are square or rectangular in shape and increase the shear capacity of the slab. The drop panels add deflection to the slab and thus minimize the deflections. A flat slab with drop panels increases the shear strength of the slab and the negative moment capacity of the slab. It also stiffens the slab, hence reduces deflection. Figure No. 6 – Flat Slab with drop panels Prepared by: Ar. Noel T. Amor, Jr./Designed for UM-CAFAE Bachelor of Science in Architecture Program | Page | 6 Flat Slab with drop panels and column head The flat slabs are mostly popular in unconventional structures without column symmetry. The column heads and drop panels act as a special beam confined to that particular space. However, the formworks become complicated due to the need for column heads and drop panels. Figure No. 7 – Flat Slab with drop panel and column head Figure No. 8 – Application of Flat Slab Benefits of using Flat Slab Quickest method available Short construction time since it's the most common method Prepared by: Ar. Noel T. Amor, Jr./Designed for UM-CAFAE Bachelor of Science in Architecture Program | Page | 7  All Construction members and many other concrete frame contractors can undertake this work Are particularly appropriate for areas where tops of partitions need to be sealed to the slab soffit for acoustic or fire reasons Are considered faster and more economic than other forms of construction, as partition heads do not need to be cut around downstand beams or ribs Can be designed with a good surface finish to the soffit, allowing exposed soffits to be used. This allows the exploitation of the building’s thermal mass in the design of heating, ventilation, and cooling requirements increasing energy efficiency. Uniform surface for suspended water sprinkler system Piping and shafting Flexibility in room layout Saving in building height Shorter construction time Pre-fabricated welded mesh Buildable score Allows architect to introduce partition walls anywhere required Allows owner to change the size of room layout Allows choice of omitting false ceiling and finish soffit of slab with skim coating Lower story height will reduce building weight due to lower partitions and Cladding to the façade. Saves 10% in vertical members Reduce foundation load Prefabricated in standard sizes Minimized installation time Better quality control Punching Shear Shear reinforcement in the form of shear heads, shear studs or stirrup cages may be embedded in the slab to enhance shear capacity at the edges of walls and columns. Prepared by: Ar. Noel T. Amor, Jr./Designed for UM-CAFAE Bachelor of Science in Architecture Program | Page | 8  Figure No. 9 – Illustration of Punching Shear 4. Waffle Slab Waffle slabs are lightweight slabs with hollow grid-like systems on their soffit. The hollow grid system reduces the self-weight of the slab without compromising its structural stability. The grids are spaced at equal intervals, and they transfer the load from above to the beams. The space between the ribs is sometimes treated as a beam and reinforced to increase the Figure No. 10 – flexural rigidity of the slab. Waffle Slab Due to their lightweight, they can span long distances with ease. The waffle slabs may have a Prepared by: Ar. Noel T. Amor, Jr./Designed for UM-CAFAE Bachelor of Science in Architecture Program | Page | 9 grid system or a girder system where the bands of beam run throughout the slabs. The grids can be or any shape – square, rectangular, triangular etc. Characteristics of Waffle Slab Waffle slabs are generally suitable for flat areas. The volume of concrete used is much less compared to others. The reinforcement in the waffle slab is provided in the form of mesh or individual bars. Separate excavation for beams is not required in the case of a waffle slab. The bottom surface of the slab looks like a waffle which is obtained by using cardboard panels or pods etc. The recommended thickness of the waffle slab is 85 to 100 mm while the overall depth of the slab is limited to 300 to 600 mm. The width of beams or ribs provided in waffle slab are generally 110 to 200 mm. The spacing of ribs recommended is 600 to 1500 mm. Reinforced waffle slabs can be constructed for a span of up to 16 meters while beyond that length prefabricated waffle slab is preferable. Waffle slab is good against shrinkage and it is lower than stiffened rafts and footing slabs. Waffle slab requires only 70% of concrete and 80 % of steel from the concrete and steel used for the stiffened raft. Advantages of Waffle Slab Waffle slabs are used for larger span slabs or floors and used when there is a limited requirement for a number of columns. The load-carrying capacity of the waffle slab is greater than the other types of slabs. They provide good structural stability along with aesthetic appearance. Hence, it is constructed for airports, hospitals, temples, churches, etc. The waffle slab can be made of concrete or wood or steel among those concrete waffle slab is preferred for commercial buildings and other two are preferred for garages, decorative halls etc. It has good vibration control capacity because of two directional reinforcement. So, it is useful for public buildings to control vibrations created by the movements of the crowd. Waffle slabs are lightweight and require less amount of concrete, hence it is economical. Prepared by: Ar. Noel T. Amor, Jr./Designed for UM-CAFAE Bachelor of Science in Architecture Program | Page | 10  Construction of the waffle slab is easy and quick with good supervision. Concrete and steel volume required is small, hence, the light framework is enough for the waffle slab. Several services like lighting, plumbing pipes, electrical wiring, air conditioning, insulation materials, etc. can be provided within the depth of the waffle slab by providing holes in the waffle bottom surface. This system is called a Holedeck. Disadvantages of Waffle Slab Formwork tools required are very costly because of the large quantity requirement of pods and some special tools. The floor height should be more hence number of floors is reduced. The services provided in the waffle arrangement without proper maintenance may cause damage to the slab. Skilled workers are required during its construction. They are not suitable for sloped areas. If there is a slope area, the area must be leveled with filling or by excavating. For soil filling, good soil should be used. They are not suitable against high winds or cyclonic areas because of their light weight. Figure No. 11 – Laying of pods and reinforcements for Waffle Slab Prepared by: Ar. Noel T. Amor, Jr./Designed for UM-CAFAE Bachelor of Science in Architecture Program | Page | 11  Figure No. 12 – Application of Waffle Slab 5. Ribbed Slab Ribbed slabs are very similar to waffle slabs but often mistaken for being the same. A ribbed slab has wide grids or bands of beams in the soffit of the beam whereas a waffle slab has deeper corresponding parts. The ribbed slabs like waffle slabs are flexible, light in section, economical and can be Figure No. 13 – Ribbed Slab constructed for longer spans. They have the same advantages and disadvantages as the waffle or grid slab. The main advantage of ribbed floors is the reduction in weight achieved by removing part of the concrete below the neutral axis. This makes this type of floor economical for buildings with a long span with light or moderate loads. This includes apartment buildings and hospitals. Prepared by: Ar. Noel T. Amor, Jr./Designed for UM-CAFAE Bachelor of Science in Architecture Program | Page | 12  Figure No. 14 – Application of Ribbed Slab Methods of Slab Construction 1. Slip-form Method The slipform construction technique is an alternative to the conventional formwork system which helps in continuous vertical and horizontal construction. The slip form helps to conduct the continuous pouring of the concrete to the moving formwork. The process stops only when the required length of casting is completed. Applications of Slip-form Construction Method a. Construction of Regular core high-rise structures b. Slipform Technique for Chimney Construction c. Construction of Steel Tanks d. Construction of Water Towers Advantages of Slip-form Construction Method Non-stop Method of Construction Increase the rate of construction Increase the productivity Provide more working space Creates a safe work environment for the workers Employs less accessory equipment Increase flexibility in construction Reduced Labor costs Scaffolding and temporary works in construction is reduced Uniform wall sections and layouts are obtained Disadvantages of Slip-form Construction Method High –cost for initial setup Requires Specialized workers and expertise Prepared by: Ar. Noel T. Amor, Jr./Designed for UM-CAFAE Bachelor of Science in Architecture Program | Page | 13  Need sophisticated Equipment Dimensional Accuracy can go low in certain conditions Figure No. 15 – Application of Slip-form Construction Figure No. 16 – Slip-form Construction Technique Prepared by: Ar. Noel T. Amor, Jr./Designed for UM-CAFAE Bachelor of Science in Architecture Program | Page | 14  2. Lift-Slab Lift slab construction is a precast method of constructing concrete buildings by casting the floor or roof slab on top of the previous slab and then raising the slab up with hydraulic jacks, so being cheaper and faster as it does not need forms & shores as it is needed for cast-in-place slabs. Lift-slab is a type of pre-casting used in building construction involves casting floor and roof slabs at or near ground level and lifting them to their final position, hence the name lift-slab construction. The method was invented and developed in the early 1950’s by a collaboration of Philip N. Youtz and Thomas B. Slick. Resulting in Youtz-Slick Lift-Slab Method of Construction. It offers many of the advantages of pre-casting and eliminates many of the storing, handling, and transporting disadvantages. It normally requires fewer joints than other types of precast building systems. Typically, columns are erected first, but not necessarily for the full height of the building. Near the base of the columns, floor slabs are cast in succession, one atop another, with a parting compound between them to prevent bond. The roof slab is cast last, on top. Usually, the construction is a flat plate, and the slabs have uniform thickness; waffle slabs or other types also can be used. Openings are left around the columns, and a steel collar is slid down each column for embedment in every slab. The collar is used for lifting the slab, connecting it to the column, and reinforcing the slab against shear. To raise the slabs, jacks are set atop the columns and turn threaded rods that pass through the collars and do the lifting. As each slab reaches its final position, it is wedged in place and the collars are welded to the columns. Prepared by: Ar. Noel T. Amor, Jr./Designed for UM-CAFAE Bachelor of Science in Architecture Program | Page | 15  Figure No. 17 – Application of Lift-slab method Factors of lifting the slabs The sequence of lifting the slab is influenced by the following factors: Weight of the slabs Height of the building Lifting capacity of jacks Cross-sectional area of columns during initial lifting Sequence of lifting the slabs 1. The steel or concrete columns are first put position and rigidly connected to the foundation then the ground floor slab is cast. 2. When it has matured it is sprayed with two or three coats of a separating medium consisting or what is called bond breaker. 3. Lifting collars are cast into each slab around each column. 4. The first floor slab is cast inside the edge of the formwork on top of the ground floor slab and when it is mature, it is in turn coated or covered with the separating medium and next floor slab is cast on top of it. 5. The casting of the other slab continues until all the floors and roof have been casted one after the other on the ground. Prepared by: Ar. Noel T. Amor, Jr./Designed for UM-CAFAE Bachelor of Science in Architecture Program | Page | 16  6. The slabs are lifted by hydraulic jacks, operating on top of each column, which is lifted by a pair of steel rods attached to each lifting collar while the slab is being raised. 7. A central control synchronizes the process for a uniform lift from all directions. Figure No. 18 – Sequence of lifting the slab Tools and Materials used in lifting the slab4 Hydraulic Jacks This jack is a hydraulic piece of equipment which has positive safety devices on it. The jack can lift slabs on columns loaded up to 100,000 pounds at a speed of up to 14 feet an hour. Prepared by: Ar. Noel T. Amor, Jr./Designed for UM-CAFAE Bachelor of Science in Architecture Program | Page | 17  Figure No. 19 – Hydraulic Jack use to lift the slab Lifting Collars Lifting collars are cast into each slab around each column providing a means to lift the slab and also providing shear reinforcement, slabs are fixed into the columns by welding shear blocks to the plates or welded column flanges and to the collar after the slab has been raised in its final position. Figure No. 20 – Lifting Collars Shear Blocks Shear blocks is a steel component used to hold the lifted slab in its final elevation. Prepared by: Ar. Noel T. Amor, Jr./Designed for UM-CAFAE Bachelor of Science in Architecture Program | Page | 18  Figure No. 21 – Shear Blocks Bond Breakers The main function of bond breakers is to minimize dynamic loads during lifting or stripping of precast members and permit their complete, clean separation from casting slabs or molds. In lift-slab construction, bond breaking compounds permit the slabs to be separated cleanly and easily from one another. Bond breakers include wax dissolve in a volatile spirit, polythene sheet or building paper may also be used. Advantages of Lift-slab Method Only formwork for edges of the slab and no centering to soffit of slab is required. The slabs are cast monolithically and can be designed to span continuously between the points of support and so employ the least thickness of slab. Lift-slab construction method becomes more advantageous in buildings with similar floor plans throughout the height of the building and where flush slab may be desired. Lift-slab method may be employed with ribbed slabs not only flat slabs with some compromise of the ease of casting. Prepared by: Ar. Noel T. Amor, Jr./Designed for UM-CAFAE Bachelor of Science in Architecture Program | Page | 19 Disadvantages of Lift-slab Method If not properly handled, the precast units may be damaged. It becomes difficult to produce satisfactory connections between the precast members. It is necessary to arrange for special equipment for lifting and moving of the precast units. The economy achieved in precast construction is partially balanced by the amount to be spent in transport and handling of precast member. It becomes therefore necessary to locate the precast factory at such a place that transport and handling charges are brought down to the minimum possible extent. Prepared by: Ar. Noel T. Amor, Jr./Designed for UM-CAFAE Bachelor of Science in Architecture Program | Page | 20