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. In one way ribbed slab, loads are transferred in one direction, and the main reinforcement is distributed in the same direction of the load. Jul 02, 20 introduction hollow block and ribbed slabs are formed by placing blocks on the slab and concrete ribs. One way shear in slab structural engineering general. If slab is supported on all four sides and r shorter side longer side waffle slab system. The test system was adopted for twoway ribbed slabs l3 and l4, as mentioned before, in which the load applied in the y direction widebeam was twice the applied load in the x direction ribs. The general provisions for construction and design procedure are given in cop 20. 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. The twoway slab shown in figure below has been assumed to have a thickness of 7 in. The one way shear capacity for the ribbed slab portions shown is permitted to be increased by 10%. Parameters include support conditions nine cases, span ratios lalb 0. Aug 15, 2016 download code ribbed slab design spreadsheet. Oneway and two way slabs one way slabs transfer the imposed loads in one direction only. This form of construction is not very common because of the formwork costs and the low fire rating.
However, the waffle slab is considered as nonprismatic members and the following expressions are. The results of this analysis are compared with the results of the finite element method by sap program. The above analyses reveal imprecisions in the codes prescriptions for oneway and twoway ribbed slabs with widebeam. To enforce oneway action, assign small m11 or m22 stiffness modifiers to the slab. Introducing voids to the soffit of a slab reduces dead weight and increases the efficiency of the concrete section. The load on the slab is carried by the short span in one direction. Once design compressive strength of concrete and yield stress of reinforcement are specified, the next steps are followed. For the love of physics walter lewin may 16, 2011 duration. 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 345 length and l2 is the transverse distance or frame width. 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. Check the adequacy of slab thickness for beam action oneway shear. 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. Reinforced concrete, 2014, 9th edition, aci 31811 code edition, by jack c. One way slabs are those supported continuously on the two opposite sides so that the load sare carried along one direction only.
One way ribbed slabs shall be calculated according to the direction of the ribs, being neglected transverse stiffness and torsional rigidity. Chapter 3 design of rectangular beams and oneway slabs 12. Minimum thickness of two way slab as per aci 31811 for. A slightly deeper section is required but these stiffer floors facilitate longer spans and provision of holes. Reference 5 focused on analysis of two way ribbed slabs with. With accurate to temperature and shrinkage, minimum of 33 bars diameter will be used in both direction and crossing each other over the blocks practically. Reinforced concrete ribbed slabs with widebeam lajes. Accordingly, main reinforcement is required in the two directions. Minimum thickness for two way slab construction designed as per methods provided by aci 31811 code namely, direct design method and equivalent frame method. Nov 27, 20 one way slab oneway slabs are those slabs with an aspect ratio in plan of 2. The slab was 610m simply supported on four sides and subjected to uniform load 1tm 2 and as shown in fig. The main reinforcement for two way slab are designed in two directions which are xdirection and ydirection. The simplest routine structural element for illustration of design provisions in the code is the oneway slab. Jul 02, 2015 for the love of physics walter lewin may 16, 2011 duration.
These slabs are constructed to provide flat surfaces, usually horizontal, in building floors, roofs or other types of structures. Ribbed floors consisting of equally spaced ribs are usually supported directly by columns. Minimum thickness of one way ribbed slabs summary of one way ribbed slab design procedure. 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. See more ideas about waffle ceiling, architecture and ceiling design. Oneway slabs are required to have slab edges that are parallel to the beam edges just like a beam supported floor.
One way shear in slab mrhershey structural 20 nov 17 15. In concrete slab floors, the draw slab edge tool allows you to draw any shaped edge which is very powerful for a 2 way slab but will break the slab edge rules for one way slabs. Section aa in the figure shows the beam cross section. This 300 mm deep ribbed slab is required for an office to support a variable action of 5 kn m2 it is supported on wide beams that are the same depth as the slab, as shown in figure 3.
Minimum thickness of beams and oneway slabs values given in this table shall be used directly on members with normalweight concrete and grade 60 reinforcement. Ribbed slab design spreadsheet civil engineering community. If slab is supported on all four sides and r shorter side longer side one way slab. One way ribbed slab manual mechanical engineering building. In general, the beamslab flexural stiffness ratio is about 0. Design of concrete structures 14th edition, 2009, by arthur h. In two way slabs, load will be carried in both the directions. Types of one way slab one way slab may be solid hollow ribbed 6. One way slab oneway slabs are those slabs with an aspect ratio in plan of 2.
Bending moment and shear force of two way slab are depend on l y l x ratio and. Difference between one way slab and two way slab system the one way and two way slab systems are the most commonly used floor system in the reinforced concrete structure. Application of lb ratio in first figure slab is supported on two opposite sides only. Oneway and twoway slabs oneway slabs transfer the imposed. Civilax is the knowledge base covering all disciplines in civil engineering. They may be supported on two opposite sides only fig.
Design of one way joist ribbed slab according to aci. The thickness of slab and depth of rib of waffle slab can be then computed by equalizing the moment of inertia of equivalent flat slab to that of waffle slab. Our friend mohit sharma has already highlighted the essentials for a one way slab. Two way slabs are normally supported from four sides. Deflection of two way slab could be calculated by using available methods to make sure that the deflection will not. Chapter 3 design of rectangular beams and oneway slabs 12 h a 12 strip in a simply supported one way sl ab. The simplest routine structural element for illustration of design provisions in the code is the one way slab. These modifiers, available through assign area stiffness modifiers, should be applied relative to the local axes and the desired direction of oneway action. The ratio of longer span l to shorter span b is equal or greater than 2, considered as one way slab because this slab will bend in one direction i. Analysis of two way ribbed and waffle slabs with hidden beams. 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. Continuous ribbed slabs concrete structures eurocode. Ribbed and waffle slabs provide a lighter and stiffer slab than an equivalent flat slab, reducing the extent of foundations. One way slabs are required to have slab edges that are parallel to the beam edges just like a beam supported floor.
The saving of materials tends to be offset by some. In two way slab, the ratio of longer span l to shorter span b is less than 2. The main reinforcement for twoway slab are designed in two directions which are xdirection and ydirection. Bending will take place in the two directions in a dishlike form. They are either oneway spanning systems known as ribbed slab or a twoway ribbed system known as a waffle slab. These conditions are set out in last section dealing with oneway ribbed slabs. Difference between one way slab and two way slab system. One way ribbed slab manual free download as word doc. These conditions are set out in last section dealing with one way ribbed slabs. Twoway joist slab often called twoway ribbed slab or waffle slab is an economical floor. One way slab is a slab which is supported by beams on the two opposite sides to carry the load along one direction. Slabs are usually used in floor and roof construction. The ratio lb which is less than 2 is known as two way slab.
Ribbed slabs oneway joists introducing voids to the soffit of a slab reduces dead weight and increases the efficiency of the concrete section. For other conditions, the following modifications should be applied. 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. 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. Introduction hollow block and ribbed slabs are formed by placing blocks on the slab and concrete ribs.
One way ribbed slab as a model is analyzed by the two methods traditional and the finite element method. In the one way ribbed slab where the ribs are in one direction, it is assumed that the. Chapter 3 design of rectangular beams and oneway slabs. Ribbed slab floors are most economical for buildings such as hospitals, schools, hotels, and. The result is a slight strengthening and stiffening in the span direction, but this effect is small and can be disregarded. Load transfer in a one way slab, b two way slab nilson fig. Another point to be underscored is that it is essential to differentiate calculating the strength of ribbed slabs according to the support condition since the use of solid slab criteria for oneway slabs did not give. Design of reinforced concrete structures ii two way slabs 1 1. For example, when parallel walls connect to either side of a continuous slab, oneway action results. Ribbed and waffle slabs types, advantages, disadvantages. The ribs are tapered in crosssection in its lower part. Table 5 showed that none of the slabs failed by punching shear.
Twoway joist waffle slab design approach and methodology. 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. Analysis and design of slabs one way civil engineers pk. One way slab is supported by two parallel beams or walls.
Load transfer in a oneway slab, b twoway slab nilson fig. In case of hollow block slab voided blocks are placed to reduce the total weight of the slab. The ratio of the total costs was found to be within the range 1. 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. Teaching twoway ribbed slab analysis and design using. Ribbed slabs one way joists introducing voids to the soffit of a slab reduces dead weight and increases the efficiency of the concrete section. A one way slab is defined for purposes of this book as a flexural member with depth small relative to other dimensions, supporting gravity loads applied normal to and directly over its surface, spanning in one direction between parallel supports, and reinforced for flexure. Would love to provide these pictures for better clarity of the viewers.
Twoway joist concrete slab floor waffle slab system. Structural ribbed concrete slabs the cupolex floor slab can be fully or partially suspended on piles, stem walls or gradeedge beams. Mathematical structural analysis of one way ribbed slabs was introduced in this paper. However main reinforcement bar and distribution bar in transverse direction. Design of reinforced concrete structures ii twoway slabs 1 1. The thickness of equivalent flat slab is taken from table 9. The blocks are considered as nonstructural element as they do not contribute to strength of. Waffle slab analysis and design is similar to the procedure used with flat plates except that. Check the applicable joist dimensional limitations as follows. If none of the values satisfies, you need to change d.
Oneway and twoway slabs university of asia pacific. The direction in which the load is carried in one way slab is called the span. Moments for design may be taken from table 3 for slabs simply supported on four sides. For joist depth determination, waffle slabs are considered as flat slab aci. The minimum thickness of slab is specified by aci 31811, section 9. Two way shear is critical on a rectangular section located at d2 away from the face of the drop panel. Difference between one way slab and two way slab simple.
Design of reinforced concrete structures ii twoway slabs. Oct 30, 2012 introducing voids to the soffit of a slab reduces dead weight and increases the efficiency of the concrete section. Ribbed slabs are made up of wide band beams running between columns with narrow ribs spanning the. The slab is the flange of the beam and the extended part is the web. They provide a very good form of construction where slab vibration is an issue, such as laboratories and hospitals. 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.
Furthermore, the flexural resistance of all slabs was calculated by the yield line theory and compared with the experimental results. Nbr 6118 2 provides that the ribbed slabs with spacing l0 between ribs axes less than or equal to 650 mm can do without shear reinforcement to resist tensile stresses caused by shear force when the. A oneway slab is defined for purposes of this book as a flexural member with depth small relative to other dimensions, supporting gravity loads applied normal to and directly over its surface, spanning in one direction between parallel supports, and reinforced for flexure. In a one way slab, this lateral expansion is resisted by adjacent slab strips, which tend to expand also. Design of one way joist ribbed slab according to aci code. In general, the beam slab flexural stiffness ratio is about 0. In case of ribbed slab the blocks are not permanent. Shear strength of reinforced concrete oneway ribbed slabs. Effect of solid parts on nonlinear of one way ribbed slabs journal of. Six steps to build a wafflemat foundation duration. In concrete slab floors, the draw slab edge tool allows you to draw any shaped edge which is very powerful for a 2way slab but will break the slab edge rules for oneway slabs.
Slabs having supports on less than four sides can be designed as one way. This paper presents an experimental and computational study on ribbed slabs with widebeam, two oneway slabs and two twoway slabs, with variable. The spacing between the ribs should be in general 2030 inch. Bending moment and shear force of twoway slab are depend on l y l x ratio and.
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