The articles listed below explain how we recognize and diagnose signs of cracking, damage, movement in these different concrete slab construction methods. Concrete slabs and coatingsoftentimes, contractors need to fill and reinforce slab cracks because a coating will be applied to the surface such as that found on a pool deck, garage floors as well as commercial floors. Structure magazine composite steel deck slabs with. Introduction coldformed steel deck sections are used in many composite floor slab applications wherein the steel deck serves not only as the form for the. In places shrinkage may cause the concrete to ride up on the corrugations of the deck and add to the nonuniform conditions that contribute to cracking. Lloyd concrete services the contractor should ask the engineer if its ok to run laserguided screeds on the deck. Things you should know about cracks in slab foundation. Relationships of material propertiesproportions and concrete deck cracking concrete deck materialmixture factors effects on concrete deck cracking cement type, content, and proportion thermal shrinkage hydration and dry shrinkage water loss. But what about steel requirements in negativemoment regions.
The results of threedimensional finite element investigation to study the longitudinal cracking phenomena in the slab of composite steelconcrete beams with ribbed metal deck are presented. Discusses the issues of cracks developing in uncovered composite concrete profiled steel sheet slabs used in floors. Steeldeck reinforced concrete slabs or composite slabs consist of. When the installer of my new and cracking concrete patio told me that, all concrete cracks. Can crackfree concrete floors be built on steel decks. Dispelling the myths about structural steel and sound. Saw cutting concrete slab on grade control joints to help prevent the formation of visible shrinkage cracking slab on grade installation placing concrete slab on grade and associated materials such as. Longitudinal cracking of composite beams with ribbed metal deck.
For most structures and finishes, the presence of such cracks will not be detrimental to the slabs performance in terms of durability or serviceability. However, for loadings once the concrete is hardened, the composite slab is designed for the total load, including slab selfweight, with the slab treated as a single span, unless negativemoment reinforcement is provided over supports in accordance with conventional reinforced concrete slab design disregarding the metal deck as compressive. However, visible cracking is one aspect that occasionally causes problems and complaints from building occupiers. The reinforcement will prevent the concrete from bursting sideways and will confine the concrete around the stud. Cutting too early causes raveling, an effect created by the saw blade pulling the aggregate out of position, leaving a messy, weakened edge along the cut. Sep 19, 2019 concrete suppliers sometimes add water to make the concrete easier to work with, but this weakens the concrete. Oct 16, 2008 new slabs on ground crack when tensile stresses from restrained shrinkage exceed the concrete s strength. Jul 31, 2014 first, the polyethylene film acts as a slipsheet between the underside of the concrete and the subbase. Saw cutting concrete slabongrade control joints to help prevent the formation of visible shrinkage cracking. Cracking in composite concrete metal decking floor slabs. How to repair shrinkage cracks on a concrete slab youtube. Designs roof and floor dek fire resistance ratings floor dek.
Composite concrete profiled steel sheet slabs are a popular form of construction for suspended floor slabs as they are simple and economical to design and construct. Other slab finish options include paint the least expensive choice or a stamped or stained surface to imitate stone or virtually any other material, including wood decking for more on coatings and stamped. Concrete cover depth refers to total slab thickness. Placing elevated concrete slab on metal form deck and. Shallow composite floor decks shallow composite floor decks.
Areas that have high ground water levels from time to time will often cause inground pools to float upward. Cut in control joints to create individual sections no larger than 8 x 8 ft. These interior or exterior slab coatings serve many purposes, either decorative or. Introduction coldformed steel deck sections are used in many composite floor slab applications wherein the steel deck serves not only as the form for the concrete during construction, but also as the principal tensile. Relationships of material propertiesproportions and concrete deck cracking concrete deck materialmixture factors effects on concrete deck cracking cement type, content, and proportion thermal shrinkage hydration and dry shrinkage water loss are influenced by the type of cement. With option 10, a concrete floor slab on metal deck 3in. Composite concrete profiled steel sheet slabs are a popular form of construction for suspended floor slabs, as they are simple and economical to design and construct.
Welded wire mesh can also help reduce shrinkage cracking, but only if it is placed in the middle or upper half of the slab, but at least 2 inches below the surface. My specs included fiber but after the pour it started cracking 6 months out my slab is a 33x 44. Any concrete floor cast on a metal frame and deck is severely constricted. Composite steel floor deck has a ribbed profile with embossments designed to interlock with concrete slabs, creating a reinforced concrete slab that serves the dual purpose of a permanent form and positive reinforcement. Concrete suppliers sometimes add water to make the concrete easier to work with, but this weakens the concrete. Joints shall be spaced at 24 to 36 times the slab thickness but this need to be confirmed by a structural engineer. Tolerances for the floors placed on these suspended systems are often misunderstood. We have a client whos elevated slab on metal deck and bar joists is cracking. These interior or exterior slab coatings serve many purposes, either decorative or for safety.
Then i pointed out that the walkways, driveway, rv pad and garage slab also have no. It appears to be shrinkage cracks but i cannot find much information on control joint locations for elevated slabs. Why polishing suspended concrete slabs is more likely to. Composite concrete profiled steel sheet slabs are a popular form of construction for suspended floor. Cracking in composite concrete slabs using metal decking. The cpaa recommends using contraction joints to minimize slab curling and cracking by spacing joints for four, six and eightin. New slabsonground crack when tensile stresses from restrained shrinkage exceed the concretes strength. Once installed, the concrete slab is ready for tilethe most durable and costeffective deck surface, in my opinionwith minimal prep.
Missouri university of science and technology scholars mine. Engineers who design slabs on metal deck arent thinking about the contractor. Modest cracking over beams in composite floor construction is commonplace because of. Second in popularity, at least in north america, comes the composite slab, a type of suspended floor made of concrete over a steel deck. Cracking in concrete fill on metal decks, cracking in flat plate. Compositedeck slabs usually contain very little reinforcement because concrete bonds to the steel deck, which provides tensile capacity for positivemoment areas.
Contraction joints in elevated slabs american society of. Soil movement and slope creep may cause a heavy inground pool to shift and become out of level. It is recommended to start saw cuts on or at the center of column lines. Cracking of concrete in compositedeck slabs is inevitable, but there are measures you can take to control it installing reinforcing bars in both directions, particularly over beams and girders, will help minimize cracking of compositedeck slabs. While the concrete shrinks the steel frame does not, causing high tensile stresses in the concrete which ultimately lead to cracks. The steel deck institute sdi has had standards in place to accommodate steel fibers in composite steel floor deckslabs for. The international building code 2015 ibc2015 has adopted sdi c2011 allowing the use of steel fibers in place of welded wire fabric to control temperature and shrinkage cracking in composite metal deck applications. Sometimes the floor use dictates that the surface of the composite slab is left uncovered, e.
How do you fix concrete slab that was poured with no fiber. The unshored composite slab on metal deck part iii, level deflected slab strategies. Think about it, theres a solid layer of metal reinfg below the concrete slab the deck and typically the mesh will run thru the joinst anyway. Founded in 1904 and headquartered in farmington hills, michigan, usa, the american concrete institute is a leading authority and resource worldwide for the development, dissemination, and adoption of its consensusbased standards, technical resources, educational programs, and proven expertise for individuals and organizations involved in concrete design. Cracking in composite concretemetal decking floor slabs. Whilst local hogging moments in the slab will still strain the reinforcement in tension and contribute to the crack, they will also compress the concrete around.
See concrete slab crack repair see sinking buildings where we include case histories of both building settlement and slab cracking, heaving, settling. The steel deck is to be used on a threespan condition and shoring is not permitted. An analytical study of the longitudinal cracking of composite beams with ribbed concrete slab on metal deck is presented. Metal decking floors slabs which provides valid mesh sizing and detailing for specific crack.
Modest cracking over beams in composite floor construction is commonplace because of shrinkage and hogging bending of the slab over the supporting beams. This type of earlyage cracking occurs during the first few days of the slab s life and is. The cracks observed on the top surface of all slabs illustrated the nature of the. T h e re are many types of floor sys tems loosely re f e r red to as concre t e slab over metal deck. Repairing common concrete slab problems the concrete network. A composite floor is comprised of a reinforced concrete floor slab and structural steel floor beams acting compositely together. Cracking in concrete fill on metal decks, cracking in flat plate concrete slabs, and cracking in concrete walls. Generally they are found to be satisfactory in service.
Analysis and design of reinforced castinplace concrete diaphragms. Before you start saw cutting concrete, is important to select where these cuts will be done. However, for loadings once the concrete is hardened, the composite slab is designed for the total load, including slab selfweight, with the slab treated as a single span, unless negativemoment reinforcement is provided over supports in accordance with conventional reinforcedconcreteslab design disregarding the metal deck as compressive. Joint spacing normally ranges between 10 to 18 feet depending on. The concrete society document advice c racking in composite concretemetal decking floor slabs outlines the causes of the cracking and steps that could be taken. Guide for concrete floor and slab construction aci 302. In addition to the concrete mix and the weather conditions, determining when to saw concrete is based on the concretes hardness as well as the type of cutting equipment used to make the saw cuts.
See sinking buildings where we include case histories of both building settlement and slab cracking, heaving, settling. Floor decking sheets is also known as profiled steel deck,metal deck,roof decking, etc. A layered finite element is used to model the composite beam in the analysis. Curling is the distortion of a slab into a curved shape by upward or downward bending of the edges. Founded in 1904 and headquartered in farmington hills, michigan, usa, the american concrete institute is a leading authority and resource worldwide for the development, dissemination, and adoption of its consensusbased standards, technical resources, educational programs, and proven expertise for individuals and organizations involved in concrete. The floor slab is made from galvanized steel sheet by cold roll forming,and its cross section is vshaped, u.
Concrete deck slab details the following detailing practice is intended to minimize the bridge deck cracking in both transverse and longitudinal directions. Longitudinal cracking of composite beams with ribbed metal. The earliest name of bondek is called corrugated steel deck,and all steel floor decking sheets that are pressed and formed by a platen press and are collectively referred to. Offset cracks cause a difference of height in the concrete on either side of the crack. When the soil under a concrete deck slab moves, usually the concrete slab will crack. Composite concreteprofiled steel sheet slabs are a popular form of construction for suspended floor slabs as they are simple and economical to design and construct. Saw cutting an elevated slab, however, doesnt create the same weakened plane that it does in a slabonground. For use when metal deck is used as a leave in place form 1. Ca cracking in compositecorrugated metal decking floor slabs. The minimum amount of reinforcement in each direction shall be 0. Society publication, cracking in composite concretecorrugated. First, the polyethylene film acts as a slipsheet between the underside of the concrete and the subbase. Saw cutting of composite slabs to control cracking. How to pour a concrete slab successfully the family handyman.
Sci p300 composite slabs and beams using steel decking best. Floor decking sheets is also known as profiled steel deck, metal deck,roof decking, etc. Placing concrete slabongrade and associated materials such as. The most common concrete floor type is the groundsupported slab, also known as slab on ground or slab on grade. Grooving creates a weakened spot in the concrete that allows the inevitable shrinkage cracking to take place at the groove rather than at some random spot. May 19, 2015 once installed, the concrete slab is ready for tilethe most durable and costeffective deck surface, in my opinionwith minimal prep. The occurrence is primarily due to differences in moisture andor temperature between the top and bottom surfaces of a concrete slab. The steel deck institute sdi has had standards in place to accommodate steel fibers in composite steel floor deck slabs for. Repeated point loading on composite slabs scholars mine. This shrinkage causes forces in the concrete which literally pull the slab. Galvanized corrugated steel deck sheets for concrete slab.
In most cases, this is due to an uneven seat for the slab itself, such as poorly compacted subsoil, invasive pressure from tree roots, previous concrete slabs that have not been removed, or repeated expansions and contractions in the rebar. Although the current investigation focused on composite steelconcrete slab on ribbed metal deck, the metal deck was omitted in beams b18 and b19 to study the effect of the existence of the metal deck on the longitudinal cracking behavior of the composite beam. Further, when combined with timely surface curing, a polyethylene vapor barrier under the slab is an asset, retaining moisture in the concrete to improve hydration during setting. Cracking of concrete in composite deck slabs is inevitable, but there are measures you can take to control it installing reinforcing bars in both directions, particularly over beams and girders, will help minimize cracking of composite deck slabs.
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