Upon discussing the projected long-term deflection and the likelihood of serious shrinkage cracking from the ~18" slab, the decision was made to use concrete joists. L = (0.00047hr (fsS) ^2) ^ (1/3) Where, L = Slab Length, hr = Thickness of reinforced slab, fs = Yield strength of steel reinforcement, S = Steel reinforcing ratio Concrete slab maximum length calculation is made easier here. Determine the maximum bending moment for a one meter wide strip of the slab. To save on beam disruption, PT slabs are widely used instead of regular bed and columns because more load carrying capacity with lesser concrete. Design a solid slab bridge superstructure having a clear span of 9.0 metres and carriageway of 7.5 metres with 1.5 metres wide footway on either side for a National Highway. There are some other requirements to ensure perimeter beam stiffness. dik, I assume that you mean 300 + structural topping. Multiply them by about 6 to get realistic long term deflections. 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VIP members get additional benefits. Where, w = total load intensity per square meter of the slab. The precast concrete slab has tubular voids extending the full length of the slab, typically with a diameter equal to the 2/3-3/4 the thickness of the slab. The diameter of main bars may be from 8 mm to 14 mm. Rapt, would you mind posting your creep coefficient, shrinkage strain, sustained load, tension reinforcement and compression reinforcement assumptions. The span requirement for the slabs is given by ACI Code 8.7.1. Get some help. View RCC31 ONEWAY SLABS (A_D).xls from SPAN 1 at University of Nairobi. I don't think there is a maximum span, but there are certainly practical maximums for all systems, including flat slabs. I ultimately decided to break apart the spans and do a frame due to the large thickness of concrete required. And you can sometimes stretch that a bit. rapt (Structural) 19 Nov 17 04:05. dik, But the perimeter is 25 + 25 + 12 + 12 = 74m / 140 = 528mm! If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it. Slabs are generally designed on the assumption that they consists of a number of beams of breadth ‘one meter’. (b) Minimum tension steel. Reinforcement patterns will vary, dependent on the spans/ loads specified. The following sections from the PCI Design Handbook include interaction curves, load tables, and section properties for various precast concrete components. Not to encourage him, but with stiff beams all around, the thickness of the slab between can be the clear span perimeter of the slab divided by 140. I am placing columns along 25 m span. Rib/solid intersection at beam span/7 from centreline of internal support, and at span/9 from end support. Ceiling Joist Span Use this table to determine the maximum lengths of ceiling joists based on species of lumber, joist spacing, and joist size. New electrical systems and wiring harness engineering solutions implement automation, facilitate collaboration and accelerate verification. Building codes for residential decks only require 40 psf. Increasing automotive design complexity demands a shift away from legacy automotive design flows. Also, you said the whole thing is supported on columns? Moulds of bespoke depth. Recently had a 4-column concrete structure and contemplated a flat slab. Please enter your email address. That would increase your deflection to about 4 or 5 times that elastic deflection... Just saying. Solid Slabs can be designed and produced with mild reinforcing or by adding prestressing strands. Please let us know here why this post is inappropriate. All Rights Reserved. VIP members get additional benefits. For example: a floor joist appropriately selected to span 10 feet with an L/360 limit will deflect no more than 120"/360 = 1/3 inches under maximum design loads. The maximum deflection is at mid-span, equal to wl⁴/ 8EI Continuous slab The precise determination of the theoretical bending moments involve mathematical labor. I like to debate structural engineering theory -- a lot. Which type of reinforcement are used in pre-stressing? I'll take a gander at the code... haven't done a 2-way plate in a couple of decades... don't know what the changes are. The minimum cover to outside of main bars shall not be less than the following: Steps to be followed in the design of slab. Joint to Bearing 220 mm 3. What factors were considered in your deflection calculations? Beam span maximums are based on a maximum anticipated live load. The one-way slab is a simple wide shallow rectangular beam as far as its structural analysis is concerned. The industry demands generative design. The shear stress are usually low in a slab except when there are heavy concentrated loads and Compression reinforcement is seldom required The sections can be a simply supported slab and a continuous one-way slab Simply supported slab If the slab is poured separately from the supporting walls then the slab can be considered a simple span. DIMENSIONS Square panels, minimum of three slab spans. DESIGN OF SOLID SLAB S.No Description Dimensions 1. I just hope he will get some help, or he will build a hammock. Simplified maximum span tables for selected visual and mechanical grades of Southern Pine lumber in sizes 2×4 thru 2×12. REINFORCEMENT Maximum bar sizes in ribs: 2T25B, 2T20T (in top of web) and R8 links. 3. You would only get 340 if you have a beam across the middle of the slab as well as the … The allowed recommended span lengths for continuous slabs are equal to 13.6m for two-way slabs and to 12.5m for unidirectional slabs. The longer the joist, the more area of deck the joist supports, and thus the beam supports. The main moment steel spans between supports and over the interior supports of a continuous slab. I would suggest the same here. Registration on or use of this site constitutes acceptance of our Privacy Policy. Span C/C of Expansion Joint 11000 mm 2. Slope of Carriageway 2.50 % 9. These can be an architectural feature and can be cost effective, although not common, they are not archaic. In two way slab, the ratio of longer span (l) to shorter span (b) is less than 2. Hence, one way slabs have ratio between longer to shorter span greater than 2. = intensity of live load per square metre. Sorry, but if you think a 250 slab will span 12 metres with acceptable deflections, you (or your computer program) don't know what you are doing. The overall depth of the floor typically varies from 300 to 600 mm with overall spans of up to 15 m if reinforced, longer if post-tensioned. Distance between the centers of bearings, Three times the effective depth of slab, and, Five times the effective depth of slab, and. Im commercial buildings to save on carpet space the span is kept is 12-15m. In two way slabs, the load will be carried in both the directions. I am also placing column along 12 m span in the middle. Traditional slab spans in small residential buildings vary from 3–3.5m in practice. Distance B/w Exp. What you are doing is not OK, do you even imagine what 12 m x 25 m looks like in real life? Are you talking a two-way slab with edge beams? Close this window and log in. One-way solid slabs are designed as a number of independent 1 m wide strips which span in the short direction and supported on crossing beams. I didn't remember what the factor was, but, if the slab were continuous in all directions the thickness could be clear perimeter / 16o, or 300mm. How thick is your slab? I recently had a similar project come across my desk that was spanning 40' in one direction and 34' in the other so a 2-way slab was requested from the client. Ratio of Longer span to shorter span should not be more than 2.2. Waffle slab is good against shrinkage and it is lower than stiffened rafts and footing slabs. Bending moment due to dead load and live load may be taken as follows (IS: 456 – 2000). Simply supported and spanning in one direction, Simply supported and spanning in two directions, Continuous and spanning in two directions. The reduced weight also lowers material and transportation costs. I used Etabs too it gave around 38 mm where allowable deflecttion is 48mm , so the results are not acceptable. Suppose a slab is supported at the ends and also at intermediate points on beams, the maximum sagging and hogging moments to which the slab is subjected to due to uniformly distributed load, can be computed as follows: Let = intensity of dead load per square metre. 10560 mm 4. Over the years, many flat plates and flat slabs have suffered from excess deflection, partly because that sort of rule of thumb was used. Country What is piping technology for termite treatment in building? Loading: Single lane of IRC Class 70-R (both wheeled and tracked) or two lanes of IRC Class A whichever produces maximum effect: The slab has positive moment across the complete span with maximum moment occurring at mid-span … Have you checked slab shear/breakthrough? Find the effective span which is lesser of (i) distance between centres of bearings, and (ii) clear span and effective depth. Waffle slab requires only 70% of concrete and 80 % of steel from the concrete and steel used for stiffened raft. Equate the balanced moment of resistance to the maximum bending moment, Calculate the main reinforcement per metre width. Due to many concerns with such large spans we alternatively proposed concrete joists, intermediate column lines, and a post-tensioned slab. Assuming suitable bearings (not less than 10cm), find the span of the slab between the centers of bearings. Find the effective depth ‘d’ from the above equation. Design the slab following the provisions of the ACI code. By joining you are opting in to receive e-mail. Something is wrong with your model. So flat slab area is 6m x 5m .. and slab thickness 0.2 to 0.25 m. That is not what you described in your original post. 25 mm allowed for A142 mesh (@ 12m is quite a long span for a flat slab and it will be heavily reinforced, will it not be cheaper to look at. My God Man, stop. I wouldn't do it, but, it's allowable. The service live load is 100 psf and 4000 psi concrete is specified for use with steel with a yield stress equal to 60000 psi. Hokie: there are even tables for greatly reduced +ve and -ve moments using two way action... it's likely a carry over from several decades back... and, I haven't used it for a couple of decades. Tables do not consider reduced capacities for potential service hole requirements or additional loads to those stated above. Rib spacing of 600 to 1500 mm can be used. Reinforced Concrete Slab Design Guidelines, Basics of Reinforced Concrete Slab Design, Chloride Attack on Concrete Structures – Cause and Prevention, How to Design Reinforced Concrete Beam for Shear? Join your peers on the Internet's largest technical engineering professional community.It's easy to join and it's free. Why do you want to use so few columns? Promoting, selling, recruiting, coursework and thesis posting is forbidden. Thank you for helping keep Eng-Tips Forums free from inappropriate posts.The Eng-Tips staff will check this out and take appropriate action. Width of Slab 12900 mm 5. Fig.No.3: Loading Arrangement of Solid Flat Slab Span Deflect Slab Type (mm) ∆ u max (mm) ion due to L.L Permiss ible Deflecti on due to L.L (mm) Long-term Deflecti on Permissib le Long-term Deflection 15 ft x 15 ft Solid flat slab 0.85 0.28 12.62 1.28 25.23 20 ft x 20 ft Solid flat slab 3.40 1.01 16.82 5.50 33.64 25 ft x 25 ft Solid flat slab A reinforced concrete slab is built integrally with its supports and consists of equal span of 15 ft. Therefore under normal circumstances, a concrete cover of 25 mm is usually adequate for floor slabs. Become VIP Member, Do you need to remove the ads? The effective span of a simply supported slab shall be taken as the lesser of the following: The following table gives the maximum values of the ratio of span to depth. Those are much more reasonable spans and it is likely you could get something to work however you are still running at L/30 which you will still want to keep a close eye on long term deflections. Advisable span to depth for light loads is about 45. Solution for A one-way solid concrete slab is to be used for a simple span of 18 ft. For pressure-preservative-treated southern pine no. bh: a 6" slab may have worked with those proportions... with design moments from Tables B1 nand B2. For additional explanations on using these tables, refer to the respective handbook editions. 5. Click Here to join Eng-Tips and talk with other members! Listed are 46 tables based on common loading conditions for floor joists, ceiling joists and rafters. Main reinforcement which is based on the maximum bending moment shall not be less than 0.15 per cent of the gross sectional area. Rafter spans can be extended slightly beyond what the rafter tables suggest, when there is a cantelever extending beyond the supporting wall. That's a L/d=24 right around where it would be expected. Examples of slab thickness and indication of maximum span for solid slabs with ordinary () and prestressed () reinforcement according to. This makes the slab much lighter than a massive solid concrete floor slab of equal thickness or strength. A slab or panel is said to be two way slab if the ratio of longer span to the shorter span is not greater than 2 (two). this is the maximum span what is the minimum to determine if this slab one way or two way and what is the condition of this slab if it sample support or continuous and determine if we can use solid or flat or hollow core slab as per the architectural we should see and study the geometry and determine what is the suitable system. The one-way slabs are economical up to the span of 3.6m. Reinforced waffle slabs can be constructed for the span up to 16 meters while beyond that length prefabricated waffle slab is preferable. Already a Member? for distribution bars, steel 6 mm or 8 mm are generally used. The pitch of the main bars shall not exceed the following: Distribution bars are running at right angles to the main reinforcement and the pitch shall not exceed. We know a lot more about the serviceability problems of flat plates now. Beam and Slab, or concrete or steel joists with a slab over would be far more economical... Can you use steel? View Joist & Rafter Tables. Headers & Beams. That doesn't seem too unreasonable Leo. If I recall, it used to be the clear span perimeter divided by 180 and 200 respectively... just too far back and too many things have nudged it out of my memory. How can we use magnetic levitation method in civil engineering? Citing prime advantages of speed of erection without weather constraints, PCI's manual is titled "Precast Prestressed Short Span Bridges: Spans to 100 Feet." *Eng-Tips's functionality depends on members receiving e-mail. Sign Up to The Constructor to ask questions, answer questions, write articles, and connect with other people. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework. Got precast hollow core where you're at? Thanks for all your suggestions, Allowable deflection for flat slabs is Span/250 right? An integrated E/E solution solves tomorrow’s challenges and supports companies as they strive to overcome complexity and reduce time to market. The OP never mentioned any beams, so I assumed he didn't know they were needed. The maximum bending moment per meter width of slab. Login. This report explains how TotalCAE makes it easy for organizations to utilize cloud computing on AWS to accelerate product innovation, solve complex engineering problems, and reduce the time waiting for CAE simulation results. Traditionally column spacings and floor spans in these buildings have been in the range of 6 to 9 metres, to both contain costs and simplify construction. Become VIP Member. Thanks in advance. Width of Carriage way 10500 mm 6. Two way slab is a slab supported by beams on all the four sides and the loads are carried by the supports along with both directions, it is known as two way slab. 4 Types of Cracks in Concrete Columns and their Causes: Video Included. Already a member? Login to The Constructor to ask questions, answer people’s questions, write articles & connect with other people. You can access tables from previous editions of the handbook as well as the current edition. Copyright © 1998-2021 engineering.com, Inc. All rights reserved.Unauthorized reproduction or linking forbidden without expressed written permission. With edge beams, you could run it as a 2-way flat plate... that would likely give you the minimum slab thickness; two 12m x 12.5m panels and you may get by with 250 or 300 slabs. Maximum deflection limits are set by building codes. Data M25 concrete, Fe500, slab thickness 250 mm , DL - 2.3 KN/m2 + self weight and LL - 3 KN/m2.. this is for 2 storey building. Never heard of that perimeter criteria, but span/depth ratio is a poor substitute for deflection calculations done with consideration of all the factors listed by rapt above. Ribs 150 mm wide @ 750 mm cc.Topping 100 mm. See annex b of CSA A23.3-14. We would like to show you a description here but the site won’t allow us. They are expressed as a fraction; clear span in inches (L) over a given number. Effective Span of Slab. It works well for predominately one way systems. composite steel? The thickness of one-way slab varies between 100mm to 150mm or even more depending upon the span and based on the deflection considerations. I'm trying to match results. When using maximum spans, consideration to the effect of camber/ deflection on finishes/ internal partitions is advised. Solid Slabs are fully customizable concrete slabs of varying width, length and thickness. Time to enter the 21st century, I think. They can be used in a variety of applications such as bridges, piers, building floors, roof systems, detention vault lids and boat launches. treating it as a 2-way slab with stiffened edges. What are the purposes for building dams in semi-arid regions? How to Install Reinforced Concrete Pipe (RCP)? In addition to its own weight, the slab carries a superimposed deadload of… The effective span of a simply supported slab shall be … Example Included, 2 Important Failure Case Studies of Long-Span Steel Structures, Types of Foundation for Buildings and their Uses [PDF], Methods of Rainwater Harvesting [PDF]: Components, Transport, and Storage, Compressive Strength of Concrete -Cube Test [PDF], Procedure, Results, Standard Size of Rooms in Residential Building and their Locations, 16 Types of Heavy Equipment Used in Construction, Sardar Patel Stadium: Construction Features of the Largest Cricket Stadium in the World, Tower Bridge: Construction Features of the World-Famous Symbol of London. Less a little for the beam width reduction in span lengths. Slab depths typically vary from 75 to 125 mm and rib widths from 125 to 200 mm.
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