This form of construction is not very common because of the formwork costs and the low fire rating. Moments for design may be taken from table 3 for slabs simply supported on four sides. For the love of physics walter lewin may 16, 2011 duration. They are either oneway spanning systems known as ribbed slab or a twoway ribbed system known as a waffle slab. 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. The two way slab is designed for both the directions as it bends in both directions. The twoway waffle slab is economical when it is used in the modular or prefabricated form. The slab has to carry a distributed permanent action of 1. In two way slab, the ratio of longer span l to shorter span b is less than 2. Two way ribbed slab system waffle system the system was designed to decrease the weight of traditional fullconcrete slabs. Reinforced concrete design 1 design of slab examples and. Load transfer in a one way slab, b two way slab nilson fig. 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. I am submitting it to you and i want students or professional engineers to download it and use it for their studies or projects.
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. Rectangular beams and one way slabs page 2 of 9 two methods. 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 system was designed to decrease the weight of traditional fullconcrete slabs. Ribbed slab design spreadsheets to eurocode engineering. Determine moments at critical sections in each direction, normally the negative moments at supports and positive moment near midspan. 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. Design of slab examples and tutorials by sharifah maszura syed mohsin example 1.
Minimum thickness of two way slab as per aci 31811 for. Pdf analysis of two way ribbed and waffle slabs with hidden beams. The name waffle comes from the grid pattern created by the reinforcing ribs. Accordingly, main reinforcement is required in the two directions. In oneway ribbed slab, loads are transferred in one direction, and the main reinforcement is distributed in the same direction of the load. According to the way loads are transferred to supporting beams and columns, slabs are classified into two types. 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. Two way slab action is assumed in a ribbed floor made of the doubletee section precast, in the ribbed floor with integral beams. The twoway slab will deflect in a dish or saucerlike form under the action of loads. The same is true for a two way slab or any other floor system where. Analysis of two way ribbed and waffle slabs with hidden beams ibrahim mohammad arman international journal of civil and structural engineering volume 4 issue 3 2014 343 four slabs are taken in this study to show the moments distribution in two way ribbed slab. Corners of the two way slab lift up if the slab is not cast monolithically with the supports wallsbeams. Two way restrained slab if the slabs consist more than one panel or corner of the slab are prevent against lifting it is define as two way restrained slab.
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. A twoway slab tws is simply a slab carrying loads in both directions length and width to its supports beams or columns. The ratio of the total costs was found to be within the range 1. Two way slabs have two way bending unlike one way slab.
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. Difference between one way slab and two way slab daily civil. Sap2000, slab, twoway, ribbed, waffle, direct design method, beams. The design bending moment of two way restrained slab can be calculated as follows. Rectangular beams and oneway slabs page 2 of 9 two methods. 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. May 02, 2017 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. Deep ribs, the concrete and steel quantities are relative low expensive formwork expected. Design of reinforced concrete structures ii twoway slabs 1 1.
Slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. The minimum thickness of slab is specified by aci 31811, section 9. These conditions are set out in last section dealing with oneway ribbed slabs. Introduction in reinforced concrete construction, slabs are used to provide flat, useful surfaces. The implementation of structural systems with ribbed flat slabs is growing. Twoway slab action is assumed in a ribbed floor made of the doubletee section precast, in the ribbed floor with integral beams. The domeshaped forms create a matrix of voids surrounded by orthogonal ribbing, producing a two way configuration very suitable for. The design process described in analysis of an ultrahigh performance concrete twoway ribbed bridge deck slab is a step toward the development of design specifications for uhpc. 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. Load transfer in a oneway slab, b twoway slab nilson fig.
The slab was 610m simply supported on four sides and subjected to uniform load 1tm 2 and as shown in fig. Analysis of an ultrahigh performance concrete twoway. Cornell university, david darwin university of kansas, charles dolan university of wyoming 3. This condition occur when the slabs are connected monolithically with support. Ribbed slabs types and its advantages in construction.
In one way slab, the ratio of longer span l to shorter span b is equal or greater than 2, i. Corners of the twoway slab lift up if the slab is not cast monolithically with the supports wallsbeams. A waffle slab or two way joist slab is a concrete slab made of reinforced concrete with concrete ribs running in two directions on its underside. 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. The twoway waffle slab is provided with a bigger span as compared to the solid slab. Reference 5 focused on analysis of twoway ribbed slabs with. The load on the slab is carried by the short span in one direction.
One way slab is a slab which is supported by beams on the two opposite sides to carry the load along one direction. 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. Twoway joist concrete slab floor waffle slab system. Allowable stress design or working stress design wsd 2. The twoway slab is designed for both the directions as it bends in both directions. Twoway joist waffle slab design approach and methodology. Ribbed slab grid slab, solid slab, filler slab, folded plate 6 basis of spanning directions. The domeshaped forms create a matrix of voids surrounded by orthogonal ribbing, producing a twoway configuration very suitable for largespanning slabs. The first stage of the design is finding the bending moment of the slab panels. Check the applicable joist dimensional limitations as follows. Pdf analysis of two way ribbed and waffle slabs with. Analysis and design of twoway slabs page 1 chapter 3.
In two way slabs shorter direction strip carry greater %age of load. In two way slabs, load will be carried in both the directions. Verandah slab is a type of one way slab, where the slab is spanning in the shorter direction. Slabs are usually used in floor and roof construction. The slab is the flange of the beam and the extended part is the web. The two way waffle slab is provided with a bigger span as compared to the solid slab. Design of a two way rcc slab structural engineering. 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. The basic design procedure of a twoway slab system has five steps. Nov 30, 2018 the two way ribbed slab and waffled slab system. Design of a two way rcc slab structural engineering forum. The minimum slab thickness allowed for joist slabs is onetwelfth the clear rib spacing or 1. Waffle slabs are preferred for spans greater than 40 feet 12 m, as they are much stronger than flat slabs, flat slabs.
Design of reinforced concrete structures ii twoway slabs. In reality, sandwich slabs are ribbed slabs with a slab placed both to their upper and lower surface. This is because its length to width ratio is longshort not big enough for loads to travel in the short direction onl. A reinforced concrete slab is a broad, flat plate, usually horizontal, with top and bottom surfaces parallel or nearly so.
Reinforced concrete, 2014, 9th edition, aci 31811 code edition, by jack c. The spacing between the ribs should be in general 2030 inch. Analysis of two way ribbed and waffle slabs with hidden 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. The basic design procedure of a two way slab system has five steps. Chapter 3 design of rectangular beams and oneway slabs. 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 committee 340, design.
Chapter 3 design of rectangular beams and oneway slabs 12. 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. With accurate to temperature and shrinkage, minimum of. 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. Distribute moments transverse at critical sections to column and middlestrip and if. Under the general provisions of the 1995 code, chapter, the twoway joist portion may be combined with a solid column head or with solid wide beam sections on the column centerlines for uniform depth construction. One way and twoway slabs one way slabs transfer the imposed loads in one direction only. Reference 5 focused on analysis of two way ribbed slabs with. 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 slabs, and. 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. Twoway ribbed slab system waffle system the system was designed to decrease the weight of traditional fullconcrete slabs. The two way slab will deflect in a dish or saucerlike form under the action of loads. Reinforced concrete ribbed slabs with widebeam lajes. 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.
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. 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. 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. In twoway slabs shorter direction strip carry greater %age of load. The two way waffle slab is economical when it is used in the modular or prefabricated form. Design of reinforced concrete structures ii two way slabs 1 1.
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. Pdf optimum design of reinforced concrete waffle slabs. Oneway and twoway slabs university of asia pacific. Deflection of two way slab could be calculated by using available methods to make sure that the deflection will not. Twoway ribbed slabs consist of beams spaced at regular intervals in perpendicular directions, which are monolithic with a slab. This paper deals with the problem of optimum design of reinforced concrete twoway ribbed waffle slabs using genetic algorithms. Slab design is comparatively easy when compared with the design of other elements. Ribbed slab system which consists of a series of parallel reinforced concrete t beams framing into reinforced concrete girders. 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. The design process described in analysis of an ultrahigh performance concrete two way ribbed bridge deck slab is a step toward the development of design specifications for uhpc. Analysis and design of slabs two way civil engineers pk. Ribbed floors consisting of equally spaced ribs are usually supported directly by columns.
I have developed a microssoft excel software for design of a two way rcc slab. The domeshaped forms create a matrix of voids surrounded by orthogonal ribbing, producing a two way configuration very suitable for largespanning slabs. Jul 02, 2015 for the love of physics walter lewin may 16, 2011 duration. The general provisions for construction and design procedure are given in cop 20. Teaching twoway ribbed slab analysis and design using. When one says ribbed slab it is actually a one way spanning system with ribs where as in waffle slab the joists form a two way system. Twoway slabs have two way bending unlike oneway slab. Skydome is a system of modular formwork in plastic used to build two way ribbed slabs in residential and commercial buildings.
The waffle slab is also sometimes termed as ribbed slab system but you would find it interesting to know that ribbed and waffle slab are somehow two different things. Bending will take place in the two directions in a dishlike form. Design of concrete structures 14th edition, 2009, by arthur h. These conditions are set out in last section dealing with one way ribbed slabs. Design of two way ribbed slab 18 x 25 m clear span slideshare. However main reinforcement bar and distribution bar in transverse direction. Comparison of oneway and twoway slab behavior economic choices oneway slab on beams suitable span 3 to 6m with ll 35knm2.
Analysis of two way ribbed and waffle slabs with hidden beams ibrahim mohammad arman international journal of civil and structural engineering volume 4 issue 3 2014 343 four slabs are taken in this study to show the moments distribution in two way ribbed slab with hidden beams systems. Can be used for larger spans with relatively higher cost and higher deflections oneway joist system suitable span 6 to 9m with ll 46knm2. Analysis of an ultrahigh performance concrete twoway ribbed. Ribbed and waffle slabs types, advantages, disadvantages. 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. One way ribbed slab as a model is analyzed by the two methods traditional and the finite element method. They may be supported on two opposite sides only fig. They are either oneway spanning systems known as a ribbed slab or a twoway ribbed system known as a waffle slab. One way slab design how to design one way slab daily civil. Reinforced concrete design 1 design of slab examples. 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. The design bending moment of twoway restrained slab can be calculated as follows.
Ribbed slab design spreadsheet free download description. Oct 27, 2016 one way slab is a slab which is supported by beams on the two opposite sides to carry the load along one direction. Simply supported one way slab a rectangular reinforced concrete slab is simplysupported on two masonry walls 250 mm thick and 3. Minimum thickness for two way slab construction designed as per methods provided by aci 31811 code namely, direct design method and equivalent frame method.