In two way slabs, load will be carried in both the directions. Brendon burley structural option posttensioned twoway slab figure 23 details of the twoway slab. The basic design procedure of a two way slab system has five steps. Oneway spanning slabs should be treated as beams of unit width and chapter 2 should be followed except for minimum shear reinforcement. Twoway joist concrete slab floor waffle slab system. Design procedure steps for one way slab slab design steps. Twoway slabs have two way bending unlike oneway slab. Design of twoway floor slab system comparison of oneway and. The following example illustrates the example building. 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. The basic design procedure of a twoway slab system has five steps. 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. Slabs are usually used in floor and roof construction.
Corners of the twoway slab lift up if the slab is not cast monolithically with the supports wallsbeams. Step 2 design forces draw panel of slab and indicate maximum design moments, shears and in plane loads, if any, per unit width of slab. In twoway slabs, the load will be carried in both directions, thus main reinforcement is provided in both directions for twoway slabs. Deep ribs, the concrete and steel quantities are relative low expensive formwork expected. If the ratio of long span to short span is less than or equal to 2, the slab is to be defined as two way slab or slab spanning in one direction. Member design reinforced concrete two way spanning. Total load is carried in the direction perpendicular to the supporting beam. Accordingly, main reinforcement is required in the two directions. When a reinforced concrete slab is 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. Bending moment and shear force of twoway slab are depend on l y l x ratio and. D mm d 105 mm loads on slab self weight of slab 3. This is because its length to width ratio is longshort not big enough for loads to travel in the short direction onl. 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. Reference 5 focused on analysis of twoway ribbed slabs with.
The pca computer program pcaslab can be used to expedite the design of different slab systems. Design of reinforced concrete structures ii twoway slabs 1 1. The two classifications are oneway slab and twoway slab. How can you design a 2 way spanning slab and be able to know the reinforcement size to be used in your slab as well as the spacing needed when tieing your reinforcements. According to the way loads are transferred to supporting beams and columns, slabs are classified into two types. 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. According to adoss, the interior spans due not meet the code requirements to neglect deflection.
Construction type continuous span simple span roof floor roof floor oneway solid slabs 50 45 45 40 twoway solid slabs 4548 4045 na na beams 35 30 30 26 oneway joists 42 38 38 35. Design the slab, following the provisions of the ack code. The oneway slab is a simple wide shallow rectangular beam as. Load transfer in a oneway slab, b twoway slab nilson fig. Distribute moments transverse at critical sections to column and middlestrip and if. Introduction in reinforced concrete construction, slabs are used to provide flat, useful surfaces. Design of a two way rcc slab structural engineering. 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. Here the ratio of longer span of slab to the shorter span of slab is less or equals to 2. Two way concrete floor slab with beams design and detailing design the slab system shown in figure 1 for an intermediate floor where the story height 12 ft, column crosssectional dimensions 18 in.
Design of reinforced concrete structures ii two way slabs 1 1. Two way slab being supported on four sides the load will be carried in both the directions. In the absence of advanced analysis software, like fem modelling, it was necessary to idealize the slabs, oneway or twoway slabs, to use direct methods for the design. Design for flexure check if the direct design method of aci sect. Simply supported one way slab modification factor for span less than 7 m 1. The same is true for a twoway slab or any other floor system. Twoway beamsupported slab twoway beamsupported slab an. Long span floor systems are also included in the discussion. Member design reinforced concrete two way spanning slab bs8110 v2015. The thickness of oneway slab varies between 100mm to 150mm or even more depending upon the span and based on the deflection considerations. The twoway slab will deflect in a dish or saucerlike form under the action of loads. Pdf design calculation design of one way slab slab s1. Reinforced concrete design 1 design of slab examples. I have developed a microssoft excel software for design of a two way rcc slab.
Slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. Allowable stress design or working stress design wsd 2. Oneway and twoway slabs university of asia pacific. Cornell university, david darwin university of kansas, charles dolan university of wyoming 3. Design of reinforced concrete structures ii twoway slabs. Unless otherwise noted, all referenced table, figure, and equation. Design of slab examples and tutorials by sharifah maszura syed mohsin example 1. In twoway slabs shorter direction strip carry greater %age of load. Load transfer in a one way slab, b two way slab nilson fig. The ratio of the total costs was found to be within the range 1. The design uses the program adapt floor pro release 20092010 featuring the hong kong code.
Guidelines for a twoway concrete flooring system brewer. Interior left, exterior right deflection analysis the final consideration in the design of the twoway slabs is deflection. Twoway reinforced concrete slab design clear longer span of slab please enter the longer span. 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. Chapter 18 concrete slab structures january 2019 188 18. The slab was divided into strips middle and column or edge strip with the diemension as shown in figure below. For those who do not know what are the des ign requirements of a slab. The slab may be supported by walls, by reinforced concrete beams usually cast monolithically with the slab, by s. 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. The oneway slabs are economical up to the span of 3. Span moment % 2 percentage of compression reinforcement % 3 span to effective depth ratio of twoway slab as per is. Two way joist concrete slab floor waffle slab system analysis and design 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. The following table of span todepth ratios is recommended for the initial preliminary sizing of members. The main reinforcement for twoway slab are designed in two directions which are xdirection and ydirection.
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 output of the program for the slab in the example is shown in the following pages. The program covers wide range of twoway slab systems and can be used for more complex slab layouts. Ratio lylx is determine by dividing the longest span of the slab by the shorter span. The load on the slab is carried by the short span in one direction. So on this post, youll be able to have a clue on how to design a 2 way spanning slab. Twoway joist concrete slab floor waffle slab system analysis and design 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. The twoway slab is designed for both the directions as it bends in both directions. Bending will take place in the two directions in a dishlike form.
Here are the steps for the design procedure for one way slab in steps. Chapter 3 design of rectangular beams and oneway slabs. Analysis and design of slabs two way civil engineers pk. Twoway concrete floor slab with beams design and detailing design the slab system shown in figure 1 for an intermediate floor where the story height 12 ft, column crosssectional dimensions 18 in. For these cases, the flat plate is economical for spans between 15 ft. In two way slab, the ratio of longer span l to shorter span b is less than 2. Determine moments at critical sections in each direction, normally the negative moments at supports and positive moment near mid span. The following example illustrates the design methods presented in the pca book simplified designreinforced concrete buildings of moderate size and height third edition. Static equilibrium of twoway slabs total moment in both beams full load was transferred eastwest by the planks and then was transferred northsouth by the beams. Twoway concrete slab with beams spanning between supports. Analysis of two way ribbed and waffle slabs with hidden beams. This method was provided in the american concrete institute aci in 1963 to design twoway slabs carried by steel beams, deep beam, or walls. 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. 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 design example 02 design of simply supported slab two way spanning span of slab 4. Twoway slabs are slabs that are supported on four sides. The service live load is 100 psf, and 4000 psi concrete is specified for use with steel with a yield stress equal to 60,000 psi. Extend horizontally from center line column at least 16 center line span. The slabs are considered as spanning twoway when the longer to shorter span length is less than a ratio of two. One way slab is supported on two opposite side only thus structural action is only at one direction. Comparison of oneway and twoway slab behavior economic choices oneway slab on beams suitable span 3 to 6m with ll 35knm2. Must span a minimum of 16 the clear span on each side of support aci 18. Basic steps in twoway slab design choose layout and type of slab. However main reinforcement bar and distribution bar in transverse direction. A reinforced concrete slab is built integrally with its supports and consists of two equal spans, each with a clear span of 15 ft.
In other words, it can be said that, twoway slabs span in both directions. Two way slab design spreadsheets to eurocode 2 14 march 2018 off by the engineering community twoway spanning slabs for rectangular slabs with standard edge conditions and subject to uniformly distributed loads, normally the bending moments are obtained using tabulated coefficients. Reinforced concrete design 1 design of slab examples and. Rectangular beams and oneway slabs page 2 of 9 two methods. A twoway slab tws is simply a slab carrying loads in both directions length and width to its supports beams or columns. Can be used for larger spans with relatively higher cost and higher deflections oneway joist system suitable span 6 to 9m with ll 46knm2. Slabs are constructed to provide flat surfaces, usually horizontal, in building floors, roofs, bridges, and other types of structures. Design of concrete structures 14th edition, 2009, by arthur h. Analysis and design of twoway slabs page 1 chapter 3.