كتاب Flat Slab

تأليف : الدكتور ياسر الليثى To utilize the slab thickness to optimum level, the essential aspects that should be kept in mind are: Procedure related to design Presence or absence of holes Significance of deflections Previous layout application experience Types of Flat Slab Construction Following are the types of flab slab construction: Simple flat slab Flat slab with drop panels Flat slab with column heads Flat slab with both drop panels and column heads Uses of Column Heads It increase shear strength of slab It reduce the moment in the slab by reducing the clear or effective span Uses of Drop Panels It increase shear strength of slab It increase negative moment capacity of slab It stiffen the slab and hence reduce deflection Advantages of Flat Slabs It is recognized that Flat Slabs without drop panels can be built at a very fast pace as the framework of structure is simplified and diminished. Also, speedy turn-around can be achieved using an arrangement using early striking and flying systems. Flat slab construction can deeply reduce floor-to –floor height especially in the absence of false ceiling as flat slab construction does act as limiting factor on the placement of horizontal services and partitions. This can prove gainful in case of lower building height, decreased cladding expense and pre-fabricated services. In case the client plans changes in the interior and wants to use the accommodation to suit the need, flat slab construction is the perfect choice as it offers that flexibility to the owner. This flexibility is possible due to the use of square lattice and absence of beam that makes channelling of services and allocation of partitions difficult. Thickness of flat slab Thickness of flat slab is another very attractive benefit because thin slab provides the advantage of increased floor to ceiling height and lower cladding cost for the owner. However, there is profound lower limit to thickness of slab because extra reinforcements are needed to tackle design issues. Besides this, added margin must be provided to facilitate architectural alterations at later stages. Types of Flat Slab Design Multitudes of process and methods are involved in designing flat slabs and evaluating these slabs in flexures. Some of these methods are as following: The empirical method The sub-frame method The yield line method Finite –element analysis For smaller frames, empirical methods are used but sub-frame method is used in case of more irregular frames. The designs are conceptualized by employing appropriate software but the fact is using sub-frame methods for very complicated design can be very expensive. The most cost effective and homogenous installation of reinforcements can be achieved by applying the yield line method. A thorough visualization in terms of complete examination of separate cracking and deflection is required since this procedure utilises only collapse mechanism. Structures having floors with irregular supports, large openings or bears heavy loads, application of finite- element analysis is supposed to be very advantageous. Great thought is put into choosing material properties or installing loads on the structures. Deflections and cracked width can also be calculated using Finite- element analysis. Areas That Require Attention in Design of Flat Slab 1. Deflections-Usually at the center of each panel deflections are maximum. Foreseeing deflections can be very tricky and will engage some form of elastic appraisal. While designing structure layout and during implementation using sub frame method, one way to evaluate mid-panel deflection is to use at least two parallel column strips. 2. Proprietary punching sheer reinforcement systems- In case of thin flat slab construction punching sheer reinforcements are indispensable. 3. Optimization of Main reinforcement- In certain design procedures, especially in yield line output is better optimized than in other design methods. Benefits of Using Flat Slab Construction Method Flexibility in room layout Saving in building height Shorter construction time Ease of installation of M&E services Use of prefabricated welded mesh Buildable score
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من الهندسة المدنية - مكتبة كتب الهندسة والتكنولوجيا.