Shear reinforcement in two way slabs without beams. In two way slabs, load will be carried in both the directions. One way shear in slab structural engineering general. 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. The oneway slab is a slab, which is supported by parallel walls or beams, and whose length to breadth ratio is equal to or greater than two and it bends in only one direction spanning direction while it is transferring the loads to the two supporting walls or beams, because of its geometry. Brendon burley structural option posttensioned twoway slab figure 23 details of the twoway slab. Pdf analysis of two way ribbed and waffle slabs with hidden beams. According to the way loads are transferred to supporting beams and columns, slabs are classified into two types. These conditions are set out in last section dealing with oneway ribbed slabs. In one way slab, the ratio of longer span l to shorter span b is equal or greater than 2, i. 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 this case four options can be considered 1 increase the slab thickness further 2 use headed shear. Ca vent pipe between beams pilebeam foundation prepared subbase vent riser pipe to roof beton stop cupolex form pontex internal rib beam form cupolex concrete slab applications there may be many reasons for suspending a floor slab that may include. The one way slab is a slab, which is supported by parallel walls or beams, and whose length to breadth ratio is equal to or greater than two and it bends in only one direction spanning direction while it is transferring the loads to the two supporting walls or beams, because of its geometry. Twoway joist concrete slab floor waffle slab system. Bending moment and shear force of twoway slab are depend on l y l x ratio and. They are either one way spanning systems known as a ribbed slab or a two way ribbed system known as a waffle slab. Pdf analysis of two way ribbed and waffle slabs with. In two way slab, the ratio of longer span l to shorter span b is less than 2. The one way waffle slab system contains a hollow slab with a height more than.
Distribute moments transverse at critical sections to column and middlestrip and if. All about structural analysis and design 4,029 views 55. Difference between one way slab and two way slab simple. The two way slab is designed for both the directions as it bends in both directions. In sap program, the model has been divided to frame elements to represent ribs and beams and shell elements to represent the slab and solid part. 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. However main reinforcement bar and distribution bar in transverse direction. 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. Check the applicable joist dimensional limitations as follows. Slabs are constructed to provide flat surfaces, usually horizontal, in building floors, roofs, bridges, and other types of structures. The structural action of a oneway slab may be visualized in terms of the deformed shape of the loaded surface. Minimum thickness for two way slab construction designed as per methods provided by. Buildinghow products books volume b slabs twoway slabs.
May 15, 2020 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. Minimum thickness of two way slab as per aci 31811 for deflection. They are either oneway spanning systems known as a ribbed slab or a twoway ribbed system known as a waffle slab. 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. Determine moments at critical sections in each direction, normally the negative moments at supports and positive moment near midspan. Difference between one way slab and two way slab daily civil. The basic design procedure of a two way slab system has five steps. These conditions are set out in last section dealing with one way ribbed slabs. In reality, sandwich slabs are ribbed slabs with a slab placed both to their upper and lower surface. Lb2 is one way slab lb slab, 3 apply drop panels at columns, or 4 use two way joist slab system. A reinforced concrete slab is a broad, flat plate, usually horizontal, with top and bottom surfaces parallel or nearly so.
Reference 5 focused on analysis of twoway ribbed slabs with. 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. Cost optimization of a composite floor system, oneway waffle slab. A slab supported on all four edges with an aspect ratio of longer to shorter theoretical span less than. Concrete slab types construction, cost, and applications. The twoway waffle slab is provided with a bigger span as compared to the solid slab.
The basic design procedure of a twoway slab system has five steps. Waffle slabs are preferred for spans greater than 40 feet 12 m, as they are much stronger than flat slabs, flat slabs. 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 concrete slab with beams spanning between supports. According to adoss, the interior spans due not meet the code requirements to neglect deflection. Analysis and design of twoway slabs page 1 chapter 3. Pdf ribbed slabs have been widely used in buildings due to their many advantages, especially the decrease of concrete below the neutral.
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. Verandah slab is a type of one way slab, where the slab is spanning in the shorter direction. The main reinforcement for twoway slab are designed in two directions which are xdirection and ydirection. How to design two way slab simply supported corners free to lift limit state method is 4562000 duration. Two way slab design by direct design method as per aci 31811. Waffle slabs have a thin topping slab and narrow ribs spanning in both directions between column heads or band beams. This is a part of his project economic design of two way rcc slabs under prof s. Ribbed slab design spreadsheet free download description. Slab resting on walls or sufficiently deep and rigid beams on all sides.
Static analysis of twoway slabs, subjected to uniform load, is performed using tables, which give the fundamental support moments, span moments and shear forces. The structural action of a one way slab may be visualized in terms of the deformed shape of the loaded surface. Twoway slab systems offer several possible arrangements for the tendon layout 10. Design of reinforced concrete structures ii two way slabs 1 1.
In addition, the scope of this study is to design oneway ribbed slab and twoway. Bb example 2 design the twoway ribbed slab the covering materials weigh 2. Minimum free edge distance for punching shear 4 times slab thickness. One way slab is a slab which is supported by beams on the two opposite sides to carry the load along one direction. Two way slab action is assumed in a ribbed floor made of the doubletee section precast, in the ribbed floor with integral beams. Twoway slab analysis and design using equivalent frame method efm aci 318 states that a slab system shall be designed by any procedure satisfying equilibrium and geometric compatibility, provided that strength and serviceability criteria are satisfied. Pdf comparison between ribbed slab structure using. The results of this analysis are compared with the results of the finite element method by sap program.
The ratio of the total costs was found to be within the range 1. Analysis and design of slabs two way civil engineers pk. Introduction in reinforced concrete construction, slabs are used to provide flat, useful surfaces. 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. The one way slab is deflected in one way direction and primary reinforcement is placed in one direction whereas. Interior left, exterior right deflection analysis the final consideration in the design of the twoway slabs is deflection. Mathematical structural analysis of one way ribbed slabs was introduced in this paper. The oneway slab is deflected in one way direction and primary reinforcement is placed in one direction whereas. 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. Reinforced concrete, 2014, 9th edition, aci 31811 code edition, by jack c. Oneway and twoway slabs oneway slabs transfer the imposed.
The two way waffle slab is provided with a bigger span as compared to the solid slab. The results of the parametric analysis indicate that the deflection of posttensioned twoway slab is more affected by the span length than by the other variables. Chapter 3 design of rectangular beams and oneway slabs 12. Teaching twoway ribbed slab analysis and design using the. Accordingly, main reinforcement is required in the two directions. Design of reinforced concrete structures ii twoway slabs 1 1. Two way slabs supported on beams the critical location is found at d distance from the column, where the supporting beams are stiff and are capable of transmitting floor loads to the columns. 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. 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.
Corners of the twoway slab lift up if the slab is not cast monolithically with the supports wallsbeams. Reference 5 focused on analysis of two way ribbed slabs with. Two way slabs beam structure column free 30day trial. Ribbed floors consisting of equally spaced ribs are usually supported directly by columns. The result of this study shows that one way ribbed slab with beam used in residential building is more preferable from the economical point of view since it is less expensive than the two way. Slabs are usually used in floor and roof construction. In two way slabs shorter direction strip carry greater %age of load. One way slab design how to design one way slab daily civil. Aug 02, 2017 build house with concrete hollow blocks laying cement brick constriction engineer build house duration. Twoway slabs supported on beams the critical location is found at d distance from the column, where the supporting beams are stiff and are capable of transmitting floor loads to the columns.
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 form of construction is not very common because of the formwork costs and the low fire rating. 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. 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. Twoway slab article about twoway slab by the free dictionary. The name waffle comes from the grid pattern created by the reinforcing ribs. The twoway waffle slab is economical when it is used in the modular or prefabricated form. Twoway slab action is assumed in a ribbed floor made of the doubletee section precast, in the ribbed floor with integral beams. The two way slab will deflect in a dish or saucerlike form under the action of loads. The slab may be supported by walls, by reinforced concrete beams usually cast monolithically with the slab, by s. The result of this study shows that oneway ribbed slab with beam used in residential building is more preferable from the economical point of view since it is less expensive than the twoway. Slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. Corners of the two way slab lift up if the slab is not cast monolithically with the supports wallsbeams. 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.
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 main reinforcement for two way slab are designed in two directions which are xdirection and ydirection. Rectangular beams and oneway slabs page 5 of 9 maximum permissible steel ratio, max an overreinforced beam will fail in a brittle manner while an underreinforced beam will. Load transfer in a one way slab, b two way slab nilson fig. Skydome is a system of modular formwork in plastic used to build twoway ribbed slabs in residential and commercial buildings. 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. The load on the slab is carried by the short span in one direction. Mpa f c 25 mpa f y 420 b a b a 3 evaluate load distribution in both directions. Two way slab design bibloteka free online learning. Two way slabs are normally supported from four sides. Two way slabs have two way bending unlike one way slab. They are either oneway spanning systems known as ribbed slab or a twoway ribbed system known as a waffle slab.
Aug 22, 2018 how to design two way slab simply supported corners free to lift limit state method is 4562000 duration. Twoway slabs have two way bending unlike oneway slab. Chapter 3 design of rectangular beams and oneway slabs. Load transfer in a oneway slab, b twoway slab nilson fig. Design of concrete structures 14th edition, 2009, by arthur h. 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 ratio lb which is less than 2 is known as two way slab. A twoway slab tws is simply a slab carrying loads in both directions length and width to its supports beams or columns. Bending will take place in the two directions in a dishlike form. Analysis of two way ribbed and waffle slabs with hidden beams. Design of reinforced concrete structures ii twoway slabs.
One way shear in slab mrhershey structural 20 nov 17 15. The twoway slab is designed for both the directions as it bends in both directions. The twoway slab will deflect in a dish or saucerlike form under the action of loads. The covering materials weigh is 2knm 2, and the live load is 3knm 2. Bending moment and shear force of two way slab are depend on l y l x ratio and. Two way slab design by direct design method as per aci 31811, step by step procedure and limitations of direct design method for two way slab is presented. 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. Two way joist concrete slab floor waffle slab system pdf. This is because its length to width ratio is longshort not big enough for loads to travel in the short direction onl.
489 739 295 494 306 727 786 768 693 879 1512 776 731 1330 295 1506 26 1373 826 1509 620 1014 482 1558 724 445 26 47 1091 888 292 198 1471 99 1512 1424 192 502 1388 340 627 866 666 906 869 314 947 1197 138