That is, the load factor at which the uls moment equals the moment capacity. Reinforced concrete design 1 design of slab examples. This paper presents an experimental and computational study on ribbed slabs with widebeam, two one way slabs and two two way slabs, with variable. In oneway ribbed slabs ribs may be arranged in any of the two. Comparison of one way and two way slab behavior economic choices one way slab on beams suitable span 3 to 6m with ll 35knm2.
A slab supported on four sides with length to width ratio greater than two, should be designed as one way slab. In one way slab main reinforcement is parallel to shorter direction and the reinforcement parallel to longer direction is called distribution steel. Introduction concrete slabs on grade are a very common type of concrete construction. Nonreinforced slabs may also be considered one way if they are supported on only two opposite sides i. Ultimate behavior of one way spanning slab linear elastic analysis methods such as moment distribution are linear elastic methods.
The slab is the flange of the beam and the extended part is the web. Comparison of one way and two way slab behavior w s load taken by short direction w l load taken by long direction d a d b rule of thumb. Quick guide to design of one way slab with is code 456. A one way slab has momentresisting reinforcement only in its short axis, and is used when the moment in the long axis is negligible. This paper deals with the problem of optimum design of reinforced concrete two way ribbed waffle slabs using genetic algorithms. Draw a plan of the slab and representative cross sections showing the dimensions and the selected reinforcement, as shown in figure 8.
Pdf optimum design of a reinforced concrete ribbed slab. M before discussion of this method, we have to study some concepts. In two way slab main reinforcement is provided along both. Member design reinforced concrete one way spanning slab. Can be used for larger spans with relatively higher cost and higher deflections one way joist system suitable span 6 to 9m with ll 46knm2. Ribbed slabs one way joists introducing voids to the soffit of a slab reduces dead weight and increases the efficiency of the concrete section. Ribbed slabs types and its advantages in construction purpose. In second figure there are beams on all four sides with a intermediate beam. Ribbed slabs types and its advantages in construction. To see their result for this slab we will find the load factor. Ribbed slab grid slab, solid slab, filler slab, folded plate 6 basis of spanning directions.
Twoway joist waffle slab design approach and methodology. The ribbed slab consists of the following key components. The slabs having ratio of longer length to its shorter length l y l x greater than 2 is called one way slab otherwise as two way slab. One way slabs are such slabs in which the loads are shared only by the shorter direction of the slab. The joists which are spaced at 400mm are supported by girders.
Design of reinforced concrete structures ii twoway slabs. Now let us have a numerical on it to get a full concept on the procedure to design of one way slab. One way slabs carrying predominantly uniform load are designed on the assumption that they consist of a series of rectangular beams 1 m wide spanning between supporting beams or walls. Design moments and shears in one way slabs can be found either by elastic analysis or through the use of the same coefficients as used for beams aci 8. Maximum reinforcement ratiooneway solid slabs are designed as rectangular. The topping can be treated as a two way slab where 1. Q design a floor slab for an interior room, with clear dimensions of 3. In reality, sandwich slabs are ribbed slabs with a slab placed both to their upper and lower surface. Moments for design may be taken from table 3 for slabs simply supported on four sides. The equivalent thickness based on moment of inertia is used to find slab stiffness considering the ribs in the direction of the analysis only. In this case the structural action of the slab is essentially one way.
In the analysis and design of one way slab systems, the cover requirement. One way slabsin this section, two types will be discussed, one way solid slabs and one way ribbed slabs. Reinforced concrete structures ii ribbed slab example 2 1 example 2. Depending on the boundary condition and the properties of the slabs, methods of finding bending moment is expressed in the bs 8110 part 01 as follows. This paper presents an experimental and computational study on ribbed slabs with widebeam, two one way slabs and two two way slabs, with variable depths were tested to evaluate their resistance. One way slab being supported on two opposite sides only leads to the structural action in single direction. Such designs include corrugated slabs and ribbed slabs. For design of oneway joistslab sys tems, see chapter 4. Job title xx multispan slab singlespan beam floor plate beam span 6. Ribbed slabs have been widely used in buildings due to their many advantages, especially the decrease of concrete below the neutral line. The overall depth of the slab without finishing materials is 300mm. When the space between beams is filled with lightweight material, they are called lightweight hollow block slabs.
Design and cost comparison of the solid slabs and hollow. Figure 1 shows a rectangular slab, simply supported along its two opposite long edges and free of any support along the two opposite short edges. One way slab design procedure with example design of one. In this section, two types will be discussed, oneway solid slabs and oneway ribbed slabs. The ribs are usually tapered and uniformly spaced and supported on girders that rest on columns. The four slabs are modeled using sap2000 software as three dimensional structures. The construction and design of concrete slabs on grade. The construction and design of concrete slabs on grade d. Memberlocation all beams beam sag beam hog ebeam sag ebeam hog. One way ribbed slab as a model is analyzed by the two methods traditional and the finite element method. In addition, the scope of this study is to design one way ribbed slab and twoway solid slab by using esteem software. This type of slab, also called ribbed slab, is supported by reinforced. The spacing between the ribs should be in general 2030 inch. Here ratio of longer span of slab to the shorter span of slab is greater than 2.
Egyptian code for design and construction of reinforcement concrete structures. For the purposes of analysis and design, the ribbed slab will be replaced with a solid slab of equivalent moment of inertia, weight, punching shear capacity, and one way shear capacity. This guide covers the analysis and design of slabs to eurocode 21. Design of slab examples and tutorials by sharifah maszura syed mohsin example 1.
The basic data that is used for analysis of these slabs are. The ribs in a one way spanning ribbed slab can be treated as beams and reference can be made to how to design concrete structures using eurocode 2. Minimum thickness of nonprestressed one way slab normal weight concrete and grade 60 grade 420 reinforcement. Member minimum thickness, h simply supported one end continuous both end continuous cantilever solid one way slab. A reinforced concrete slab is a broad, flat plate, usually horizontal, with top and bottom surfaces parallel or nearly so. The ribs are tapered in crosssection in its lower part. Reinforced concrete design 1 design of slab examples and. Standard fire minimum dimensions mm resistance one way a,b two way a,b,c,d ribs in two way spanning ribbed slabs e l y l x. A reinforced concrete slab is built integrally with its supports and consists of equal span of 15 ft. A reinforced concrete slab is built integrally with its supports and consists of two equal spans, each with a clear span of 15 ft. The saving of materials tends to be offset by some. In addition, the scope of this study is to design oneway ribbed slab and twoway solid slab by using esteem software. Additional reinforced internal ribs are then used in the slab by introducing pontex, the structural cupolex accessory to provide a structure capable of spanning between foundations or piles. Tension property of concrete and its role in serviceability issues.
Sandwich slabs may have the disadvantage of a larger weight compared to the ribbed ones but on the other hand, they have the advantage that their spans and supports behave in the same proper way. A ribbed slab also called as waffle slab is a twoway joist. Structural ribbed concrete slabs the cupolex floor slab can be fully or partially suspended on piles, stem walls or gradeedge beams. Analysis of two way ribbed and waffle slabs with hidden beams. The slab in fig 2 can be modeled according to the mathematical model as shown in. If the slab rests freely on its supports, the span length may be taken equal to the clear span plus the depth of the slab but need. Asce, secb course content slab on grades construction. The general provisions for construction and design procedure are given in cop 20. The slab was 610m simply supported on four sides and subjected to uniform load 1tm 2 and as shown in fig.
Two bays one way ribbed slab is analyzed by both traditional and finite element methods to determine the induced moments of the rib. A ribbed slab also called as waffle slab is a two way joist. One way solid slabs are designed as rectangular sections subjected to shear and. For the one way ribbed slabs, the total dead load to be used in the analysis and design is. The service live load is 100 psf and 4000 psi concrete is specified for use with steel with a yield stress equal to 60000 psi. The service live load is 100 psf, and 4000 psi concrete is specified for use with steel with a yield stress equal to 60,000 psi. The first stage of the design is finding the bending moment of the slab panels. Frame strip cross section at distance d from the face of the supporting column the one way shear capacity for the ribbed slab portions shown is permitted to be increased by 10%. The slab has to carry a distributed permanent action of 1. The sections through a simply supported slab and a continuous slab are shown in figure below.
Simply supported one way slab a rectangular reinforced concrete slab is simplysupported on two masonry walls 250 mm thick and 3. Introduction in reinforced concrete construction, slabs are used to provide flat, useful surfaces. Deep ribs, the concrete and steel quantities are relative low expensive formwork expected. These conditions are set out in last section dealing with one way ribbed slabs. One way slab and twofigure 1 way slab in figure 2a slab is supported on two opposite sides only. Ribbed and waffle slabs types, advantages, disadvantages. Oneway solid slabs are designed as rectangular sections subjected to shea.
Feb 04, 2018 5 basis of cross section or sectional configuration. Load transfer in a one way slab, b two way slab nilson fig. A slightly deeper section is required but these stiffer floors facilitate longer spans and provision of holes. Analysis and design of two way slabs page 1 chapter 3. Ribbed slabs larger than the minimum limits are designed as slabs and beams section 8. The slab is two way ribbed slab of 450mm thickness.
For uniformly distributed loads of w per square foot of the slab, each strip acts approximately like a simple beam uniformly loaded by its share of w. Member design rc one way spanning slab made by date chd. Member design rc one way spanning slab 030915 member design reinforced concrete one way spanning slab bs8110 v2015. The mathematical method in this work is not exact solution for analysis of one way ribbed slabs but it is more accurate than the traditional method as will be shown in the results. Twoway joist concrete slab floor waffle slab system. Comparison between ribbed slab structure using lightweight. Types of one way slab one way slab may be solid hollow ribbed 6. If the ribs are provided in one direction only, the slab is classified as being one way, regardless of the ratio of longer to shorter panel dimensions. Reinforced concrete ribbed slabs with widebeam lajes. Floor slabs can range from a simple residential basement slab to a heavyduty industrial floor.
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