Oneway and twoway slabs university of asia pacific. This section will explain how the direct design method is used. Two way restrained slab if the slabs consist more than one panel or corner of the slab are prevent against lifting it is define as two way restrained slab. I have developed a microssoft excel software for design of a two way rcc slab. The design bending moment of two way restrained slab can be calculated as follows.
Two way slabs have two way bending unlike one way slab. Chapter 3 design of rectangular beams and oneway slabs. Reinforced concrete design to bs8110 structural design 1. 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. Bridge approach slab analysis and design incorporating elastic soil support presented by. Pdf analysis of slabs spanning in two directions under. Slab shear strength twoway shear check the adequacy of slab thickness for punching shear twoway shear at an interior column figure 4. According to the way loads are transferred to supporting beams and columns, slabs are classified into two types. Dissatisfaction with results of previously required procedures of analysis and design for two way slab beam systems was the original reason for the massive research upon two way slab systems begun about 1955. Analysis and design of slabs two way civil engineers pk. Plan view of floor system assume partitions will not be damaged by deflections. Twoway flat plate concrete floor system analysis and design.
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 ratio of the total costs was found to be within the range 1. They may be supported on two opposite sides only fig. Slab moments calculated by various slab analysis methods are compared with each other for idealized flatplate and twoway slabonbeam structures. One way slab oneway slabs are those slabs with an aspect ratio in plan of 2. One way and twoway slabs one way slabs transfer the imposed loads in one direction only. Reinforced concrete design 1 design of slab examples and.
Direct design method of flat plates per aci 31802 two way slabs are inherently difficult to analyze by conventional methods of statics because of the two way bending occurring. In twoway slabs shorter direction strip carry greater %age of load. In the first part of this series, we explain the concept of one way load transfer in concrete slabs and how to determine the minimum slab thickness based on deflection criteria. Simply supported slab upliftment of corners continuous slab no upliftment. 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.
Reference 5 focused on analysis of two way ribbed slabs with. Oneway concrete slab design part 1 concept explained and. Rectangular beams and oneway slabs page 2 of 9 two methods. One way slab one way slabs are such slabs in which the loads are shared only by the shorter direction of the slab. Slabs are usually used in floor and roof construction. The basic design procedure of a twoway slab system has five steps.
Analysis and design of slabs one way civil engineers pk. Oneway and twoway slabs oneway slabs transfer the imposed. Load transfer in a one way slab, b two way slab nilson fig. Load transfer in a oneway slab, b twoway slab nilson fig. Design of reinforced concrete structures ii two way slabs 1 1. Accordingly, main reinforcement is required in the two directions. If slab is supported on all four sides and r shorter side longer side 2 is one way slab lb london job ref. Structural redesign two way slab drop panels my redesign of fordham place will comprise of a 9 flat slab with 5. The two classifications are one way slab and two way slab. Types of one way slab one way slab may be solid hollow ribbed 6. Department of mechanics, materials and structures english.
Twoway slabs belong to the types of construction forms made with reinforced concrete. For those who do not know what are the des ign requirements of a slab. Allowable stress design or working stress design wsd 2. Whatever may be the width of the slabs it should always be designed for a width of equal to one metre and the same design should be adopted for the rest of the slab. A simplified method for designing rc slabs under concentrated. Aci 31811 code provides two methods for two way slab design one of which is direct design method. The program covers wide range of two way slab systems and can be used for more complex slab layouts.
Accurately determining the moments on a two way slab is typically accomplished by finite element computer analysis. 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. Generally, there are two types of slab which are one way and two way slabs. Designing a composite slab, we encounter semiempirical formulas at this step. Therefore, primary reinforcement is presented in both directions for resisting the loads. Twoway restrained slab if the slabs consist more than one panel or corner of the slab are prevent against lifting it is define as twoway restrained slab. The program covers wide range of twoway slab systems and can be used for more complex slab layouts.
The horizontal shear design according to ec4 offers two approaches which both necessitate serious laboratory work. Twoway slabs have two way bending unlike oneway slab. Design of reinforced concrete structures ii twoway slabs 1 1. Application of lb ratio in first figure slab is supported on two opposite sides only. Oneway spanning slabs should be treated as beams of unit width and chapter 2 should be followed except for minimum shear reinforcement. Two way slab design design of two way slab rc design. It is recommended to create the design of slab with the use of excel sheet as the process will be very simple and lots of time will be saved. Twoway concrete floor slab with beams design and detailing. Two way slab analysis and design 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. Direct design method, that could have been named the direct analysis method because it determines or prescribes moments for different parts of the slab panel without the need to conduct structural analysis, is explained in the following sections. All available load test results indicated that the flat plate or flat slab was a most efficient design with an adequate safety factor. These are the direct design method presented in chap.
Dissatisfaction with results of previously required procedures of analysis and design for twoway slabbeam systems was the original reason for the massive research upon twoway slab systems begun about 1955. The effect of fixing the corners of the slab against lifting 5. The explicit transverse torsional member method is found to give good results for drifts and slabbeam actions, and is recommended for analysis and design of twoway slab systems under combined. Aug 03, 2016 the design steps have been presented in the following question how do i degisn two way slab. Difference between one way slab and two way slab system. Twoway concrete slab on beams floor analysis and design.
However, plastic method can be the best method for designing such cases of twoway slabs. 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. Distinction of two systems from one way systems is given by aci 31814 r8. Design of slab examples and tutorials by sharifah maszura syed mohsin. Pdf influence of longitudinal reinforcement strength on oneway. Twoway concrete floor slab with beams design and detailing csa a23.
Design of concrete structures 14th edition, 2009, by arthur h. Slab shear strength two way shear check the adequacy of slab thickness for punching shear two way shear at an interior column figure 4. Bending will take place in the two directions in a dishlike form. Reference 5 focused on analysis of twoway ribbed slabs with. When the ratio of long span to short span is less than 2, then the slab is known as a slab spanning in two directions or two way slab. The design steps have been presented in the following question how do i degisn two way slab. Application of the yield line theory for more complex situations 8. One way slab is supported by two parallel beams or walls. When the ratio of long span to short span is less than 2, then the slab is known as a slab spanning in two directions or twoway slab. How accurate are the aisc design guide 11 predictions for. The following example illustrates the design methods presented in the pca book simplified design reinforced concrete buildings of moderate size and height third edition. The orientation of the principle axes of bending modifies all through the slab. One way slab being supported on two opposite sides. I am submitting it to you and i want students or professional engineers to download it and use it for their studies or projects.
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. Two way slab design by direct design method as per aci 31811. Here two examples for design of two way slab using the direct design method. Nov 27, 20 one way slab oneway slabs are those slabs with an aspect ratio in plan of 2. Design the slab system shown in figure 1 for an intermediate floor where the. Ce 433, fall 2006 slab design example 1 6 design a oneway slab for an exterior bay of a multistory office building using the information specified below. Reduced cross section of a reinforced concrete beam. What is the design of a one way slab and a two way slab. Please enter the practically physible spacing for main steel of two way slab based on summary. Unless otherwise noted, all referenced table, figure, and equation.
Direct design method of flat plates per aci 31802 twoway slabs are inherently difficult to analyze by conventional methods of statics because of the twoway bending occurring. In case of one ways slabs, the aci approximate analysis is applicable to one way slab system where a one way slab is continuous with a one way slab. Design of slab examples and tutorials by sharifah maszura syed mohsin example 1. Oneway concrete slab design part 1 concept explained. One way spanning slabs should be treated as beams of unit width and chapter 2 should be followed except for minimum shear reinforcement.
The basic design procedure of a two way slab system has five steps. Here are the steps for the design procedure for one way slab in steps. The design bending moment of twoway restrained slab can be calculated as follows. If slab is supported on all four sides and r shorter side longer side way slab. The one way slab is deflected in one way direction and primary reinforcement is placed in one direction whereas.
Design the slab system shown in figure 1 for an intermediate. Here ratio of longer span of slab to the shorter span of slab is greater than 2. The total load of twoway slab loaded with uniformly distributed load and supported on all the four edges is assumed to be transmitted to the supporting walls or edge beams in the manner as shown in fig. The total load of two way slab loaded with uniformly distributed load and supported on all the four edges is assumed to be transmitted to the supporting walls or edge beams in the manner as shown in fig.
The ratio lb which is less than 2 is known as two way slab. Min and max reinforcement as a percentage of the gross csa. In two way slab, load is delivered in both the directions. Design according to ec4 the reassuring check of composite action between profiled steel sheeting and concrete has a crucial importance. Reinforced concrete design 1 design of slab examples.
This condition occur when the slabs are connected monolithically with support. In two way slabs shorter direction strip carry greater %age of load. 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. Twoway slab design panel select boundary condition of slab for upliftment of corners. Reinforced concrete design to bs8110 structural design 1 lesson 5 6 4. Determine moments at critical sections in each direction, normally the negative moments at. The pca computer program pcaslab can be used to expedite the design of different slab systems. The slab has to carry a distributed permanent action of 1. Rectangular beams and one way slabs page 2 of 9 two methods. 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. Download the design of reinforced concrete slabs in pdf.
Aci 318 provides two alternative methods for designing twoway slabs for concrete, the equivalent frame method. The slab is assumed to be divided into two triangles and two trapeziums by lines, ap. Distribute moments transverse at critical sections to column and middlestrip and if. Design procedure steps for one way slab slab design steps. Master of science and hereby certify that, in their opinion, it is worthy of acceptance. Design of slabs direct design method civil engineering. 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. Chapter 3 design of rectangular beams and oneway slabs 12. Difference between one way slab and two way slab simple. The output of the program for the slab in the example is shown in the following pages. The following example illustrates the example building. Define the term slab, one way slab, two way slab, shrinkage and temperature reinforcement, main reinforcement. Nov 04, 2017 in the first part of this series, we explain the concept of one way load transfer in concrete slabs and how to determine the minimum slab thickness based on deflection criteria.
Cornell university, david darwin university of kansas, charles dolan university of wyoming 3. Design of twoway slabs for oneway shear and for twoway shear. No certain method can be found in the design codes or references for designing twoway slabs subjected to concentrated loads. In two way slabs, load will be carried in both the directions. Design of reinforced concrete structures ii twoway slabs. Materials used for this redesign is normal weight concrete with compressive strength of 4ksi and steel rebar with a yield stress of 60 ksi. Design of a two way rcc slab structural engineering. Analysis of two way ribbed and waffle slabs with hidden beams. Accurately determining the moments on a twoway slab is typically accomplished by finite element computer analysis. Design of a two way rcc slab structural engineering forum.
Slabs having supports on less than four sides can be designed as one way. The behavior and analysis of twoway simply supported. Abstractdesigning twoway slabs under transverse concentrated loads is one of the challenges in designing such structures. The design procedure for a uniformly loaded oneway reinforced slab can be divided in the following steps. 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 midspan. These slabs are constructed to provide flat surfaces, usually horizontal, in building floors, roofs or other types of structures. Two way slabs are normally supported from four sides. It is an effective, inexpensive, and extensively recognized structural system.