Two way slab is a slab in which the ratio of longer side to the shorter side is less than or equal to two. Behavior and reinforcement of one way slab the structural frame consists of four columns, two beams and one slab. Figure 1 twoway slab with beams spanning between all supports. 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. Two way reinforced concrete slab design clear longer span of slab please enter the longer span. Reinforced concrete, 2014, 9th edition, aci 31811 code edition, by jack c. Steps 37 need to be done for both principal directions. In one way slab main reinforcement is parallel to shorter direction and the reinforcement parallel to longer direction is called distribution steel. Pdf strengthening of reinforced concrete twoway slabs.
The two way slab will deflect in a dish or saucerlike form under the action of loads. These slabs are constructed to provide flat surfaces, usually horizontal, in building floors, roofs or other types of structures. On the other hand, when slab is supported on all four sides and bending take place in two directions are said to be two way slab. Full learn to read structural drawing course at the cheapest rate. The one way slab is deflected in one way direction and primary reinforcement is placed in one direction whereas the two way slab deflect in two directions and primary reinforcement placement is in two directions. In flatplate floors, slab column connections are subjected to high shear stresses produced by the transfer of axial loads and bending moments between slab and columns. Oneway and twoway slabs university of asia pacific. Main reinforcement is provided on shorter span due to bending. Two way slabs are such slabs in which the loads are shared by both the shorter and longer direction of the slab. Shrinkage and temperature reinforcement in twoway post. Further discussion of the differences between one and two way systems is given in reference aalami, 1993b.
These tests demonstrated that adequate, codeconformant behavior in twoway posttensioned slabs fig. Reinforcement detailing of a slab is done based on its support conditions. A bentup bar called as crank bar is provided to make rcc slab safe from compressive stresses. Pdf on aug 1, 2002, usama a ebead and others published strengthening of reinforced concrete twoway slabs find, read and cite all the research you. This is because its length to width ratio is longshort not big enough for loads to travel in the short direction onl. Slabs are supported by beams on all the four sides. Two way slab design by direct design method as per aci 31811. Bending will take place in the two directions in a dishlike form. 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. The dimensions of an interior bay are shown in figure 1. Use the equivalent frame method efm and compare the results with spslab model results. Slabs cast with an opening are reinforced by steel bars and slabs with a sawn up opening are strengthened with carbon fibre reinforced polymers cfrp. The dominating failure mode for two way slab, flexural, or punching shear is based on the slab steel reinforcement ratio. Oct 27, 2016 in one way slab, the ratio of longer span l to shorter span b is equal or greater than 2, i.
Thickness of the slab is decided based on span to depth ratio. Reinforced concrete design 1 design of slab examples. Twoway concrete slab with beams spanning between supports. How to detail reinforcements of twoway slabs quora. Design of reinforced concrete structures ii two way slabs 2 2.
The two way slab is designed for both the directions as it bends in both directions. For the purposes of analysis and design, the ribbed slab will be replaced with a solid slab of equivalent moment of inertia, weight, punching shear capacity, and oneway shear capacity. Slab may be supported on walls or beams or columns. Structural redesign two way slab drop panels my redesign of fordham place will comprise of a 9 flat slab with 5. Reinforced concrete beams, oneway and twoway slab systems. Design of oneway slabs check if it is oneway slab system if clear span in one direction, l1, is greater than or equal to two times the clear span in other direction, l2, then it is. Design of reinforced concrete structures ii two way slabs 1 1. No redistribution is allowed when method 1 or method 2 of analysis in section 3. Twoway concrete floor slab with beams design and detailing. Twoway concrete slabs with openings the static system and the design of reinforcement. A twoway slab tws is simply a slab carrying loads in both directions length and width to its supports beams or columns. Additional torsion reinforcement is required at corners when it is restrained against uplifting as shown in fig. Unless otherwise noted, all referenced table, figure, and.
Design methods two way slabs slabs without beams flat plates flat slabs slabs. 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. In two way slab the corners may be held down by restraints or may be allowed to lift up. Member design reinforced concrete two way spanning slab. Dec 16, 2014 reinforcement detailing of a slab is done based on its support conditions. Corners of the two way slab lift up if the slab is not cast monolithically with the supports wallsbeams. They may be supported on two opposite sides only fig.
Determine distribution of moments across the width of the slab. In two way slab main reinforcement is provided along both direction. In two way slab, the ratio of longer span l to shorter span b is less than 2. Sandwich slab reinforcement details in reality, sandwich slabs are ribbed slabs with a slab placed both to their upper and lower surface. One way spanning slabs should be treated as beams of unit width and chapter 2 should be followed except for minimum shear reinforcement. Here the ratio of longer span of slab to the shorter span of slab is less or equals to 2. Concrete slabs are commonly divided into the following types. Two way slab being supported on four sides the load will be carried in both the directions.
Design reinforcement for moments from steps 5 and 6. There are some basic differences between one way slabs and two way slabs. 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. Slabs are supported by the beams on the two opposite sides. To clear the concept of one way and two way slabs a table is shown below. Oneway and twoway slabs oneway slabs transfer the imposed. Difference between one way slab and two way slab daily civil. Determine moments at critical sections in each direction, normally the negative moments at supports and positive moment near midspan. The same is true for a two way slab or any other floor system where. One way slab reinforcement details daily civil engineering. 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 cross sectional dimensions 18 in. Oneway slabs transfer the imposed loads in one direction only.
Difference between one way slab and two way slab simple. So, main reinforcement is provided in both direction for two way slabs. Calculate positive and negative moments in the slab. Please select the clear cover for twoway slab reinforcement.
Beamless slabs beamless slabs are supported only on columns and are applied mostly in large industrial and public buildings. The reinforcement ratios were chosen to serve the purpose of demarcating. Twoway slabs structural engineering forum of india, sefi. Check slab reinforcement at exterior column for moment transfer between. Reinforcement detailing of reinforced concrete slabs. Distribute moments transverse at critical sections to column and middlestrip and if. When a slab is supported on the two different sides and the ratio of longer span to shorter span is equal to or greater than 2, it will be considered as one way slab. The ratio lb which is less than 2 is known as two way slab. Twoway slab design panel select boundary condition of slab for upliftment of corners. Accordingly, main reinforcement is required in the two directions. Design of slab examples and tutorials by sharifah maszura syed mohsin. One way slab is supported by two parallel beams or walls. Nonprestressed bonded reinforcement in posttensioned.
Figure 1 two way slab with beams spanning between all supports. In this video deisgn of two way slabs has been covered using is 456. Use the aci 318 direct design method to design an interior bay of a flat plate slab system of multi bay building. Check the applicable joist dimensional limitations as follows. Slabs could be simply supported, continuous or cantilever. Twoway joist concrete slab floor waffle slab system. The basic design procedure of a two way slab system has five steps. Select reinforcing bars for the slab and concentrate bars near the column, if. The following example illustrates the example building. Reinforcement detailing of reinforced concrete slabs with. Please read the lauses mentioned in the video while solving the problem. Member design reinforced concrete two way spanning slab bs8110 v2015.
Two way slabs are normally supported from four sides. Calculate the live load that can be carried by the slab shown below, if it is reinforced longitudinally as shown below. 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. Simplified design of reinforced concrete buildings, fourth edition, 2011. Buildinghow products books volume a the reinforcement. Twoway slabs page 1 of 14 the following example illustrates the design methods presented in the article timesaving design aids for reinforced concrete, part 2.
Aci 31811 code provides two methods for two way slab design one of which is direct design method. In two way slabs, load will be carried in both the directions. Slab supported directly by columns are called flat slab. Load transfer in a one way slab, b two way slab nilson fig. In the design of twoway reinforced concrete slabs, e.
Aug 23, 2017 this video describes how the the reinforcement is placed at the site. Design of reinforced concrete structures ii twoway slabs. The reinforcement rules are also similar in both directions. 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. Design of concrete structures 14th edition, 2009, by arthur h. 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. Before starting one way slab reinforcement let me clear what is one way slab. Difference between one way slab and two way slab system.