Reinforced thin plate elements are supported over beams, masonry walls or directly over columns. The actual structural support of a two way slab is found on two. Difference between one way slab and two way slab daily civil. Good morning, there are lots of advantages of one way slab and two way slab. For those who do not know what are the des ign requirements of a slab. Here the ratio of longer span of slab to the shorter span of slab is less or equals to 2. Slab shear strength twoway shear check the adequacy of slab thickness for punching shear twoway shear at an interior column figure 4.
One way slab is the slab having ratio of longer span to shorter span equal to or more than 1. The ratio of the total costs was found to be within the range 1. One way slab is the slab having ratio of longer span to shorter span equal to or more than 2. Aci 31811 code provides two methods for two way slab design one of which is. The program covers wide range of twoway slab systems and can be used for more complex slab layouts. Unless otherwise noted, all referenced table, figure, and equation. Mathematical structural analysis of one way ribbed slabs was introduced in this paper. Design of concrete structures 14th edition, 2009, by arthur h. In a two way slab the bars, rods or wires are placed at right angles to each other to resist bending stresses in two directions. Reference 5 focused on analysis of two way ribbed slabs with. 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. A reinforced concrete slab is a broad, flat plate, usually horizontal, with top and bottom surfaces parallel or nearly so. Accordingly, main reinforcement is required in the two directions.
We call it two way because this slab transfer loads in both directions and because of that reinforcement is needed in both shorter and longer span directions. One way slab reinforcement details, two way slab reinforcement details. Here are the steps for the design procedure for one way slab in steps. The twoway slab will deflect in a dish or saucerlike form under the action of loads. The dimensions of an interior bay are shown in figure 1. One way slabs are such slabs in which the loads are shared only by the shorter direction of the slab. One way slab is the most basic and common type of slab. In terms of economy of material, especially of steel, the two way slab is often best because of the large effective depths of the beams. The one way slab is deflected in one way direction and primary reinforcement is placed in one direction whereas. If a slab is supported on all the four sides but the ratio of longer span l to shorten span b is greater than 2, then the slab will be considered as one way slab. In two way slab, the ratio of longer span l to shorter span b is less than 2. Use our size comparison calculator to compare the dimensional properties of oneway concrete solid slab with other related elements from our database.
One way slab oneway slabs are those slabs with an aspect ratio in plan of 2. Two way slab design by direct design method as per aci 31811. The following example illustrates the example building. 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.
Verandah slab is a type of one way slab, where the slab is spanning in the shorter direction. The twoway slab is designed for both the directions as it bends in both directions. Oneway and twoway slabs oneway slabs transfer the imposed. Slab resting on walls or sufficiently deep and rigid beams on all sides. Slabs are usually used in floor and roof construction. Chapter 3 design of rectangular beams and oneway slabs 12.
This method was provided in the american concrete institute aci in 1963 to design twoway slabs carried by steel beams, deep beam, or walls. Select an item on the right to compare relative dimensions to oneway concrete solid slab. 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. If a slab is supported on all the four sides but the ratio of longer span to shorter span is greater than two, the slab will be considered as a oneway slab. The results of this analysis are compared with the results of the finite element method by sap program. In case of oneway slab, the main reinforcement of the slab, span along the width of the room while the distribution bars, laid at right angles to the main reinforcement, lie parallel to the length of the room. Minimum thickness for two way slab construction designed as per methods provided by aci 31811 code namely, direct design method and equivalent frame method.
Total load is carried in the direction perpendicular to the supporting beam. The oneway slab is deflected in one way direction and primary reinforcement is. A one way reinforced slab may be stronger than a two way nonreinforced slab, depending on the type of load. Difference between one way and two way slab in terms of their. It is always necessary to design a safe and load bearing capable slab. Reinforced concrete, 2014, 9th edition, aci 31811 code edition, by jack c. Analysis of two way ribbed and waffle slabs with hidden beams. Two way slab being supported on four sides the load will be carried in both the directions. Lylx 2 one way slab one way slab longer spanshorter span 2. The most straightforward routine structural element for illustration of design provisions from the code is that the one way slab. A one way slab is defined for functions of the book as a flexural member with thickness small relative to other dimensions, supporting gravity loads applied normal to and directly above its surface, a span in one direction between parallel supports. Nov 27, 20 one way slab oneway slabs are those slabs with an aspect ratio in plan of 2.
To be able to better evaluate the shear resistance of one way slabs, a series of experiments was carried out on continuous one way slabs 5 m x 2. A slab supported on all four edges with an aspect ratio of longer to shorter theoretical span less than. Dec 22, 2016 a slab which is supported on all four sides having larger span to shorter span ratio less than two is known as two way slab. The ratio of longer span l to shorter span b is equal or greater than 2, considered as one way slab because this s. Use the aci 318 direct design method to design an interior bay of a flat plate slab system of multi bay building. 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. And its depend upon the condition of the structure design and longer to shorter span. The bending moments and deflections in such slabs are less than those in oneway slabs. Difference between one way slab and two way slab what is. In two way slabs, load will be carried in both the directions. Introduction in reinforced concrete construction, slabs are used to provide flat, useful surfaces. Bending will take place in the two directions in a dishlike form. Chapter 3 design of rectangular beams and oneway slabs. Jul 08, 2015 slabs are constructed to provide flat surfaces, usually horizontal, in building floors, roofs, bridges, and other types of structures.
The coefficient method may be the simplest, easiest and the quickest approach for the design of twoway slab supported by edge beam on all slab sides. The transfer of the load is on all of the walls, all four become support walls. Two way slabs are such slabs in which the loads are shared by both the shorter and longer direction of the slab. Pdf shear in oneway slabs under concentrated load close to. Oneway concrete solid slab floor system dimensions. Difference between one way slab and two way slab simple. Determine moments at critical sections in each direction, normally the negative moments at supports and positive moment near midspan. Before going to this topic, please read it there are two types of slab classification based on the direction of bending occurs in these slabs. Slab is a common term used to describe the structural elements such as floors and roofs where the thickness of the element is very small compared to the length and.
One way and two way slabs as floor systems are the most conventional forms of structural floor systems. 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 choosing a oneway slab design, there is a default load attribution direction that must be defined in the slab definitions. Distribute moments transverse at critical sections to column and middlestrip and if. Reinforced concrete design 1 design of slab examples. Figure 1 twoway slab with beams spanning between all supports. Design the slab system shown in figure 1 for an intermediate. In one way slab, the ratio of longer span l to shorter span b is equal or greater than 2, i. Types of one way slab one way slab may be solid hollow ribbed 6. Difference between the oneway slab and twoway slabs are as follows. Different between one way slab and two way slabdifferent. Slab may be supported on walls or beams or columns. But slabs which are supported on four sides and lylx ratio is greater than 2 also comes under the category of one way slab.
Guidelines for a oneway concrete flooring system brewer. They may be supported on two opposite sides only fig. One way slabs will not create a plate submeshed floor slab like the two way slab. Flat slab difference between one way slab and two way slab. Sep 06, 2017 concrete finishing techniques how to mag float, edge, and broom a concrete slab duration. The ratio lb which is less than 2 is known as two way slab. Excel sheets are often very useful to determine the slab thickness and reinforcement detailing. See in this picture this is main rod and this is distribution rod. These slabs are constructed to provide flat surfaces, usually horizontal, in building floors, roofs or other types of structures. Difference between one way slab and two way slab system. One way slab is supported on two opposite side only thus structural action is only at one direction. Static analysis of twoway slabs, subjected to uniform load, is performed using tables, which give the fundamental support moments, span moments and shear forces. 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. One way and two way slab design aspect online civilforum.
Analysis and design of slabs one way civil engineers pk. So, the main rods has provided only in one direction of the slab. The minimum thickness of slab is specified by aci 31811, section 9. Case studies and corresponding regression analysis indicate that non dimensional parameters adopted in the model are related linearly with a correlation.
Analysis and design of slabs two way civil engineers pk. Two way slabs are the slabs that are supported on four sides and the ratio of longer span l to shorter span b is less than 2. Oneway vs twoway slabs lessons for civil lessons for. 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. To determine if the slab is two way, figure the ratio between the longer span and the shorter span. The main reinforcement for two way slab are designed in two directions which are xdirection and ydirection.
In two way slabs shorter direction strip carry greater %age of load. But if the slab is supported on four sides then we have to consider the aspect ration lxly. Beam and slab arrangement can be the best example for one way and two way slabs. However, in terms of labor in building the floor, the flat plate is. Twoway concrete floor slab with beams design and detailing csa a23. The most straightforward routine structural element for illustration of design provisions from the code is that the oneway slab. Slab supported on two sides and bending takes place predominantly in one direction only is called one way slab. Slab having two way action one way and two way slab main. Oneway and twoway slabs university of asia pacific. The following example illustrates the design methods presented in the pca book simplified designreinforced concrete buildings of moderate size and height third edition. In one way slab, main steel is provided in one span. The reinforcement diameter use in oneway slabs will not exceed the 18 of the slab total depth. In one way slab main tensile reinforcement is placed parallel to shorter side which will be the main steel.
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. Load transfer in a one way slab, b two way slab nilson fig. Minimum thickness of two way slab as per aci 31811 for. Due to the huge difference in length, load is not transferred along the longer direction. The two classifications are oneway slab and two way slab. The simplest routine structural element for illustration of design provisions in the code is the oneway slab. The basic design procedure of a two way slab system has five steps. When a one way slab is supported on four sides, the load transfer is along the longer direction than shorter direction.
The slab may be supported by walls, by reinforced concrete beams usually cast monolithically with the slab, by s. The minimum required reinforcement in the support areas is provided in two alternative ways. Rectangular beams and oneway slabs page 3 of 9 design of rectangular beams and oneway slabs continued a. Here ratio of longer span of slab to the shorter span of slab is greater than 2. The output of the program for the slab in the example is shown in the following pages. Twoway concrete floor slab with beams design and detailing. If this roof is not supporting nor attached to non structural elements likely to be. 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 slab, main steel is provided in both span. If the ratio of longer span to shorter span is equal to or less than 2, then such slabs are called as two way slab.
In other words loads in a 2way slab is carried along only one direction. Understanding one way slab, structural action of one way slab. Application of lb ratio in first figure slab is supported on two opposite sides only. Jul 09, 2018 a slab that has only two opposite support can also be designated as the one way slab. Oneway and twoway slabs one way slabs transfer the imposed loads in one direction only. 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. The main reinforcement for twoway slab are designed in two directions which are xdirection and ydirection. Simply supported one way slab a rectangular reinforced concrete slab is simplysupported on two masonry walls 250 mm thick and 3. Jan 19, 2018 in this video we learn that what is one way and two way slab and what is difference between of them. A one way slab is designed to bend in one direction only and the steel is placed in that direction. Bending moment and shear force of twoway slab are depend on l y l x ratio and. Reinforcement detailing of reinforced concrete slabs. Deep ribs, the concrete and steel quantities are relative low expensive formwork expected.
However, sometimes its hard to decide whether the slab is oneway or twoway by looking into the supports or edges thats why we also. However main reinforcement bar and distribution bar in transverse direction. 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. What are the advantages of one way slab and two way slab. Experimental study of shear in reinforced concrete oneway. Reinforcement detailing of a slab is done based on its support conditions. But before that i had written a answer of one another question requested by someo. If slab is supported on all four sides and r shorter side longer side one way slab.
Analysis and design of twoway slabs page 1 chapter 3. In reinforced concrete construction, the slab is an extensively used structural element forming floors and roofs. Composite beams can only be designed on one way slab floor. Slabs having supports on less than four sides can be designed as one way. Excel sheet to design slab one way and two way all. Two way slabs have two way bending unlike one way slab. Comparison of oneway and twoway slab behavior economic choices oneway slab on beams suitable span 3 to 6m with ll 35knm2.
Design of reinforced concrete structures ii twoway slabs. Corners of the twoway slab lift up if the slab is not cast monolithically with the supports wallsbeams. 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. Load transfer in a oneway slab, b twoway slab nilson fig. The choice between two way and beamless slabs for more normal situations is complex. Design of reinforced concrete structures ii two way slabs 1 1. Deflection of two way slab could be calculated by using available methods to make sure that the deflection will not. One way slab is supported by two parallel beams or walls. The calculation of one way slab reinforcement details design is extremely tedious and timeconsuming and after give more time is not 100% sure that design is best or not and also if some minor change comes in design if force to calculate. Generally, there are two types of slab which are one way and two way slabs. Define the term slab, one way slab, two way slab, shrinkage and temperature reinforcement, main reinforcement.
Pdf reinforced concrete oneway slabs subjected to concentrated loads are designed for shear by checking beam shear over an effective width and. One way slab being supported on two opposite sides only leads to the structural action in single direction. Load distribution pattern in two way slab is in four sides. What is the difference between one way and two way slab. Design of slab examples and tutorials by sharifah maszura syed mohsin example 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. The other half span rebars are formed with a straight length. Bending moment and shear force of two way slab are depend on l y l x ratio and. Load distribution pattern in one way slab is in one direction for shorter span. One way and two way slab design aspect the slab provides a horizontal surface and is usually supported by columns,beams or walls. Parameters include support conditions nine cases, span ratios lalb. 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.
Slab supported directly by columns are called flat slab. In the design of twoway reinforced concrete slabs, e. If the length to breadth ratio of the room is less than 2, the slab is designed as a twoway reinforced slab. The load on the slab is carried by the short span in one direction.
The slab has to carry a distributed permanent action of 1. Design procedure steps for one way slab slab design steps. If the ratio of longer span to shorter span is equal to or less than 1. Twoway slabs page 6 of 14 the pca computer program pcaslab can be used to expedite the design of different slab systems. Two way slabs are normally supported from four sides. The two classifications are oneway slab and twoway slab. One way slab is a slab which is supported by beams on the two opposite sides to carry the load along one direction. A twoway slab is supported by 4 beams while a one way slab transfer the loads to only 2 beams.