The main reinforcement for twoway slab are designed in two directions which are xdirection and ydirection. Corners of the twoway slab lift up if the slab is not cast monolithically with the supports wallsbeams. Twoway slab action is assumed in a ribbed floor made of the doubletee section precast, in the ribbed floor with integral beams. The design bending moment of twoway restrained slab can be calculated as follows. Slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. Beams, see lecture 3 punching shear requirements e. The domeshaped forms create a matrix of voids surrounded by orthogonal ribbing, producing a twoway configuration very suitable for largespanning slabs. Design of two way ribbed slab 18 x 25 m clear span slideshare. Slab design is comparatively easy when compared with the design of other elements. The best book to refer to is reinforced concrete design to eurocode by bill mosley. The two way waffle slab is provided with a bigger span as compared to the solid slab. The twoway waffle slab is economical when it is used in the modular or prefabricated form. The twoway slab s1 is supported by four beams twoway slab behaviour the behavior of a twoway slab is similar to that of a oneway slab the only difference being that now the slab loads will be carried in both directions. In this example, the latter option will be used to achieve better understanding for the design of two way joist slab often called two way ribbed slab or waffle slab.
The slab has to carry a distributed permanent action of 1. In twoway slabs shorter direction strip carry greater %age of load. The twoway waffle slab is provided with a bigger span as compared to the solid slab. Generally all the cantilever slabs are one way slab. These conditions are set out in last section dealing with oneway ribbed slabs. According to the way loads are transferred to supporting beams and columns, slabs are classified into two types. Comparison of one way and two way slab behavior economic choices flat plate suitable span 20 to 25 ft with ll 60 100 psf advantages low cost formwork exposed flat ceilings fast disadvantages low shear capacity low stiffness notable deflection. Waffle slab analysis and design is similar to the procedure used with flat plates except that special considerations need to be taken into account to reduce the complexity of calculations needed when. Deep ribs, the concrete and steel quantities are relative low expensive formwork expected.
The ratio of the total costs was found to be within the range 1. A waffle slab or twoway joist slab is a concrete slab made of reinforced concrete with concrete ribs running in two directions on its underside. They may be solid of uniform thickness or ribbed with ribs running in one direction or two directions waffles. Determine moments at critical sections in each direction, normally the negative moments at supports and positive moment near midspan. Which slab is better ribbed slab or solid slab one way or two way. Load transfer in a one way slab, b two way slab nilson fig. This paper focuses on analysis of twoway ribbed and waffle slabs with hidden beams. 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. This condition occur when the slab are supported at four side of the beams or walls and the ratio of long span to short span is equal or less than 2. The 2012 edition of the reinforced concrete design manual sp1711 was developed in accordance with the design provisions of aci 31811, and is consistent with the format of sp1709. Analysis and design of twoway slabs page 1 chapter 3. Waffle slabs are preferred for spans greater than 40 feet 12 m, as they are much stronger than flat slabs, flat slabs with drop panels, twoway slabs, oneway.
Ce 433, summer 20 slab design example 1 5 design a one. In reality, sandwich slabs are ribbed slabs with a slab placed both to their upper and lower surface. With accurate to temperature and shrinkage, minimum of. The load on the slab is carried by the short span in one direction. Use thickness of the slab as 150 mm, nominal cover. Ribbed and waffle slabs types, advantages, disadvantages. This form of construction is not very common because of the formwork costs and the low fire rating. However main reinforcement bar and distribution bar in transverse direction.
Reinforced concrete slab slabs are plate elements forming floors, roofs. Ribbed slab design spreadsheets to eurocode engineering books. The two way waffle slab is economical when it is used in the modular or prefabricated form. Two way slab action is assumed in a ribbed floor made of the doubletee section precast, in the ribbed floor with integral beams. It has got detailed worked example of all cocncete elements, including ribbed and waffle slabs. Waffle slabs can be described as the equivalent of 2 way solid slabs especially when the spans are large, and ribbed system is to be adopted. Analysis and design of slabs two way civil engineers pk. Reinforced concrete ribbed slabs with widebeam lajes. 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. Two way slab design by direct design method as per aci 31811. Aci 31811 code provides two methods for two way slab design one of which is direct design method. Bb example 2 design the twoway ribbed slab the covering materials weigh 2.
Nov 30, 2018 the two way ribbed slab and waffled slab system. For the love of physics walter lewin may 16, 2011 duration. Design the concrete floor slab system shown below for an intermediate floor with partition weight of 50 psf, and unfactored live load of 100 psf. Simply supported one way slab a rectangular reinforced concrete slab is simplysupported on two masonry walls 250 mm thick and 3. Twoway joist slab often called twoway ribbed slab or waffle slab is an economical.
Twoway ribbed slab system waffle system the system was designed to decrease the weight of traditional fullconcrete slabs. Assume partitions cannot be damaged by deflections. Introduction in reinforced concrete construction, slabs are used to provide flat, useful surfaces. I am submitting it to you and i want students or professional engineers to download it and use it for their studies or projects. They are either oneway spanning systems known as ribbed slab or a twoway ribbed system known as a waffle slab. Chapter 3 design of rectangular beams and oneway slabs. The twoway slab will deflect in a dish or saucerlike form under the action of loads. Twoway joist concrete slab floor waffle slab system. The name waffle comes from the grid pattern created by the reinforcing ribs. I have developed a microssoft excel software for design of a two way rcc slab. The two way slab will deflect in a dish or saucerlike form under the action of loads. Example design of two way edgesupported solid slab.
They may be supported on two opposite sides only fig. Oneway and twoway slabs university of asia pacific. This is because its length to width ratio is longshort not big enough for loads to travel in the short direction onl. The same is true for a two way slab or any other floor system where. Direct design method, that could have been named the direct analysis method because it determines or prescribes moments for different parts of the slab panel without the need to conduct structural analysis, is explained in the following sections.
Teaching twoway ribbed slab analysis and design using. Design of reinforced concrete structures ii two way slabs 1 1. Design of concrete structures 14th edition, 2009, by arthur h. Waffle slab design example structural engineering general. Oneway and twoway slabs oneway slabs transfer the imposed. Rectangular beams and one way slabs page 2 of 9 two methods. Corners of the two way slab lift up if the slab is not cast monolithically with the supports wallsbeams. In this study, the aci direct design method is used as a manual. Learning outcomes at the end of this lecture, the student should be able to a classify all types of solid slabco1 b identify one way and two way solid slab co1 c use a relevant clauses in code of practice co1 d design oneway slabs co2 e details the slabsco1. Pdf analysis of two way ribbed and waffle slabs with. This paper presents an experimental and computational study on ribbed slabs with widebeam, two oneway slabs and two twoway slabs, with variable. The lateral loads are independently resisted by shear walls.
Accordingly, main reinforcement is required in the two directions. Analysis of two way ribbed and waffle slabs with hidden beams. Reinforced concrete design 1 design of slab examples. Distribute moments transverse at critical sections to column and middlestrip and if. Two way rcc slab designing tool in microsoft excel developed by shankar tayal a 3rd year student of school of infrastructure, indian institute of technology, bhubaneswar. Ribbed floors consisting of equally spaced ribs are usually supported directly by columns. This condition occur when the slabs are connected monolithically with support. Reinforced concrete design 1 design of slab examples and.
Chajjas and verandahs are an practical example of one way slab. Reference 5 focused on analysis of two way ribbed slabs with. Worked example to eurocode 2 eurocodes are one of the most advanced suite of structural codes in the world. Two way slab is a slab supported by beams on all the four sides and the loads are carried by the supports along both directions, it is known as two way slab. Slabs are usually used in floor and roof construction.
Twoway ribbed slabs consist of beams spaced at regular intervals in perpendicular directions, which are monolithic with a slab. The design of waffle slabs is the same as that of ribbed slabs, with the difference being that waffle slabs have ribs spanning in both directions, and the coefficients used for analysing the slab is similar to those used for twoway restrained slab. The twoway slab is designed for both the directions as it bends in both directions. They may be solid of uniform thickness or ribbed with ribs running in. The domeshaped forms create a matrix of voids surrounded by orthogonal ribbing, producing a two way configuration very suitable for largespanning slabs. 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. A monolithic reinforced concrete floor is to be composed of rectangular bays measuring, as shown. Cornell university, david darwin university of kansas, charles dolan university of wyoming 3. Which slab is better ribbed slab or solid slab one way. Ultimate behavior of oneway spanning slab linear elastic analysis methods such as moment distribution are linear elastic methods. Design of reinforced concrete structures ii twoway slabs. This gives you complete waffle slab design with rebar detailing and schedules. Bending will take place in the two directions in a dishlike form. 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.
When a slab is supported on all four sides and the ratio of long span to short span is equal or greater than two, it will be considered as one way slab. First of all, it depends on the use of the structure. There are many methods that are used to analyze twoway slabs and the precision of these methods vary depending on method assumptions. Check the applicable joist dimensional limitations as follows. The first stage of the design is finding the bending moment of the slab panels. Two way slab design static equilibrium of two way slabs total moment in both beams full load was transferred eastwest by the planks and then was transferred northsouth by the beams. Foreword the reinforced concrete design manual sp1711 is intended to provide guidance and assistance to professionals engaged in the design of castinplace reinforced concrete structures. Bb example 2 design the two way ribbed slab the covering materials weigh 2. Moments for design may be taken from table 3 for slabs simply supported on four sides.
Oneway and twoway slabs oneway slabs transfer the imposed loads in one direction only. In oneway ribbed slab, loads are transferred in one direction, and the main reinforcement is distributed in the same direction of the load. Two way slabs have two way bending unlike one way slab. Jul 22, 2015 my graduation project with my mate ghassan faris, a two way ribbed slab of clear span of 18 x 25 m was designed by safe 2014, the building is 3storey concrete. Design of a two way rcc slab structural engineering. Rectangular beams and oneway slabs page 2 of 9 two methods. Twoway joist slab often called twoway ribbed slab or waffle slab is an economical floor system when the spans are long andor loads are high. Nov 20, 2018 a twoway slab tws is simply a slab carrying loads in both directions length and width to its supports beams or columns. One way ribbed slab as a model is analyzed by the two methods traditional and the finite element method. Mpa f c 25 mpa f y 420 b a b a 3 evaluate load distribution in both directions. The implementation of structural systems with ribbed flat slabs is growing. One way slab design how to design one way slab daily civil. My graduation project with my mate ghassan faris, a two way ribbed slab of clear span of 18 x 25 m was designed by safe 2014, the building is 3storey concrete.
Design of slab examples and tutorials by sharifah maszura syed mohsin. Ribbed slab design spreadsheets to eurocode engineering. The design of waffle slabs is the same as that of ribbed slabs, with the difference being that waffle slabs have ribs spanning in both directions, and the coefficients used for analysing the slab is similar to those used for two way restrained slab. This is a part of his project economic design of two way rcc slabs under prof s. Twoway joist waffle slab design approach and methodology. Pdf analysis of two way ribbed and waffle slabs with hidden beams. In this case, it was used the same method employed for the calculation of beams, and. Allowable stress design or working stress design wsd 2. These conditions are set out in last section dealing with one way ribbed slabs. Waffle slabs can be described as the equivalent of 2way solid slabs especially when the spans are large, and ribbed system is to be adopted.
Twoway slabs have two way bending unlike oneway slab. Load transfer in a oneway slab, b twoway slab nilson fig. Which slab is better ribbed slab or solid slab one way or. Two way ribbed slab system waffle system the system was designed to decrease the weight of traditional fullconcrete slabs. The basic design procedure of a two way slab system has five steps. Design of slab examples and tutorials by sharifah maszura syed mohsin example 1. Bending moment and shear force of twoway slab are depend on l y l x ratio and. Slabs are structural members forming floors and roofs in buildings. Two way joist slab often called two way ribbed slab or waffle slab is an economical floor system when the spans are long andor loads are high. A reinforced concrete slab is a broad, flat plate, usually horizontal, with top and bottom surfaces parallel or nearly so.
Twoway restrained slab if the slabs consist more than one panel or corner of the slab are prevent against lifting it is define as twoway restrained slab. The slab was 610m simply supported on four sides and subjected to uniform load 1tm 2 and as shown in fig. Chapter 3 design of rectangular beams and oneway slabs 12. My graduation project with my mate ghassan faris, a two way ribbed slab of clear span of 18 x 25 m was designed by safe 2014, the. Dec 06, 2017 basic of ribbed slab with aci 31802 code requirements. The brazilian code, for example, proposes that ribbed slabs are. The general provisions for construction and design procedure are given in cop 20. Jul 02, 2015 for the love of physics walter lewin may 16, 2011 duration.
Example on structural design of waffle slab structville. The two way slab s1 is supported by four beams two way slab behaviour the behavior of a two way slab is similar to that of a one way slab the only difference being that now the slab loads will be carried in both directions. Comparison of oneway and twoway slab behavior economic choices oneway slab on beams suitable span 3 to 6m with ll 35knm2. A twoway slab tws is simply a slab carrying loads in both directions length and width to its supports beams or columns. In this study, the aci direct design method is used as a manual or hand method of calculation and the solution will be compared with the analysis.
The basic design procedure of a twoway slab system has five steps. Twoway joist concrete slab floor waffle slab system analysis and design. The covering materials weigh is 2knm 2, and the live load is 3knm 2. In this example, the latter option will be used to achieve better understanding for the design of twoway joist slab often called twoway ribbed slab or waffle slab. The first reinforced concrete design manual formerly titled aci design handbook was developed in accordance with the design provisions of 1963 aci 318 building code by aci. To see their result for this slab we will find the load factor. Strength design or ultimatestrength design usd strength design or ultimatestrength design usd with strength design method, the working dead load dl and live load ll are. Slab thickness cm example example i t 70 t h h1 preliminary design slab depth calculation based on the design span and the imposed load it is possible to make a preliminary assessment of the required thickness of a skydome slab, as shown in the chart to the right. Can be used for larger spans with relatively higher cost and higher deflections oneway joist system suitable span 6 to 9m with ll 46knm2. In two way slabs shorter direction strip carry greater %age of load. The two way slab is designed for both the directions as it bends in both directions. Design of reinforced concrete structures ii twoway slabs 1 1. Comparison of oneway and two way slab behavior economic choices flat plate suitable span 20 to 25 ft with ll 60 100 psf advantages low cost formwork exposed flat ceilings fast disadvantages low shear capacity low stiffness notable deflection. Beams of width and depth are provided on all column lines.
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