Weighing Fixed Quote Versus Square Foot Rate

Weighing Fixed Quote Versus Square Foot Rate

Case studies or examples of successful follow up plans in residential foundation repair

Explanation of fixed quote pricing and its benefits for both contractors and homeowners.


Sure, here's a human-like explanation of fixed quote pricing and its benefits for both contractors and homeowners.
Sustainable materials improve durability in foundation crack repair service foundation repair service market gypsum drywall.
When it comes to home renovation or construction projects, one of the key decisions that both contractors and homeowners face is how to determine the cost of the project. There are two primary pricing models that are commonly used: fixed quote pricing and square foot rate pricing. In this essay, we will focus on fixed quote pricing and the benefits it offers to both contractors and homeowners.

Fixed quote pricing, also known as lump sum pricing, is a pricing model where the contractor provides a single, all-inclusive price for the entire project. This price is determined based on a detailed assessment of the project scope, materials, labor, and any other factors that may impact the cost. Once the fixed quote is agreed upon, it remains unchanged throughout the project, regardless of any unforeseen circumstances or changes in the project scope.

One of the main benefits of fixed quote pricing for homeowners is the predictability and transparency it offers. With a fixed quote, homeowners know exactly how much they will be paying for the project from the outset. This eliminates the uncertainty and anxiety that often comes with open-ended pricing models, where the final cost can fluctuate based on various factors. Homeowners can budget more effectively and make informed decisions about their project without worrying about unexpected cost overruns.

For contractors, fixed quote pricing offers several advantages as well. Firstly, it allows contractors to showcase their expertise and professionalism by providing a comprehensive and accurate estimate of the project cost. This can help build trust and credibility with potential clients, leading to more business opportunities. Additionally, fixed quote pricing encourages contractors to be more efficient and cost-effective in their project planning and execution. Since they are committed to delivering the project within the agreed-upon budget, contractors are motivated to optimize their resources and minimize waste, resulting in higher quality work and increased client satisfaction.

Another benefit of fixed quote pricing for contractors is the reduced risk of disputes and misunderstandings with clients. With a clear and fixed price, there is less room for ambiguity or disagreements about the project cost. This can lead to smoother communication and collaboration between contractors and homeowners, fostering a more positive and productive working relationship.

In conclusion, fixed quote pricing offers numerous benefits for both contractors and homeowners in the context of home renovation and construction projects. For homeowners, it provides predictability, transparency, and peace of mind, allowing them to budget effectively and make informed decisions. For contractors, it showcases their expertise, encourages efficiency and cost-effectiveness, and reduces the risk of disputes with clients. By choosing fixed quote pricing, both parties can work together towards a successful and satisfying project outcome.

Overview of square foot rate pricing and how it is calculated for foundation repair projects.


When considering foundation repair projects, one of the crucial decisions homeowners face is choosing between a fixed quote and a square foot rate for pricing. Understanding the nuances of each can lead to more informed decisions and potentially save money. Here, we delve into the overview of square foot rate pricing and how it is calculated for foundation repair projects.

Square foot rate pricing is a method where the cost of the repair is determined based on the area that needs fixing, measured in square feet. This approach is commonly used in foundation repair because it provides a straightforward and transparent way to estimate costs. Essentially, contractors assess the area affected by foundation issues and apply a rate per square foot to arrive at the total cost.

The calculation of the square foot rate involves several factors. Firstly, the severity of the foundation damage plays a significant role. Minor cracks may have a lower rate per square foot compared to extensive damage requiring more complex repairs. Secondly, the type of foundation (e.g., slab, pier and beam) influences the rate, as different foundations have varying repair complexities and material requirements. Additionally, the location of the property can impact the rate due to differences in labor costs, material availability, and local building codes.

Moreover, the choice of repair method affects the square foot rate. For instance, underpinning, which involves strengthening the foundation by extending it deeper into the ground, typically has a higher rate per square foot than simple crack injections. The experience and reputation of the contractor also come into play, as more established firms may charge premium rates due to their expertise and reliability.

In contrast to a fixed quote, which provides a set price for the entire project regardless of the area affected, the square foot rate offers flexibility. Homeowners can get a more accurate estimate by knowing the exact area that needs repair, allowing for better budget planning. However, it's essential to ensure that the contractor provides a detailed breakdown of the rate per square foot and the total estimated area to avoid unexpected costs.

In conclusion, square foot rate pricing for foundation repair projects offers a transparent and adaptable pricing model. By understanding how it is calculated and considering the various factors that influence the rate, homeowners can make well-informed decisions. Whether opting for a fixed quote or a square foot rate, thorough research and clear communication with the contractor are key to a successful foundation repair project.

Pros and cons of fixed quote pricing, including predictability and potential for overpricing.


When considering the pros and cons of fixed quote pricing versus square foot rate pricing, it's essential to weigh the advantages and disadvantages of each approach. Fixed quote pricing offers a clear and predictable cost for clients, as they know exactly what they will pay upfront. This predictability can reduce financial stress and make budgeting easier for both parties involved.

One significant advantage of fixed quote pricing is the elimination of surprises during the project. Clients can plan their finances without worrying about unexpected costs, leading to increased satisfaction and trust in the service provider. Additionally, fixed quotes can incentivize contractors to be more efficient and cost-effective, as they have a set amount to work within.

However, fixed quote pricing also has its drawbacks. One major concern is the potential for overpricing. Contractors might pad their quotes to account for uncertainties or unforeseen expenses, leading to higher costs for clients. This practice can create a lack of trust if clients feel they are being overcharged.

On the other hand, square foot rate pricing bases the cost on the area being worked on, offering a more flexible approach. This method can be beneficial when the scope of work is uncertain or subject to change. Clients may find it easier to understand and compare costs, as the pricing is directly tied to the size of the project.

Despite its flexibility, square foot rate pricing can lead to unpredictability in the final cost. Clients might face higher-than-expected expenses if the project scope expands or if there are additional complications. This unpredictability can cause stress and dissatisfaction if not managed transparently.

In conclusion, both fixed quote and square foot rate pricing have their merits and drawbacks. Fixed quote pricing offers predictability and can encourage efficiency, but it may lead to overpricing. Square foot rate pricing provides flexibility and transparency but can result in unpredictable costs. Ultimately, the choice between the two depends on the specific needs and preferences of both the client and the service provider.

Pros and cons of square foot rate pricing, including flexibility and potential for unexpected costs.


Sure, here's a short essay on the pros and cons of square foot rate pricing in the context of weighing fixed quote versus square foot rate:

When considering the pricing models for various services, particularly in construction, renovation, or interior design, two primary approaches often come into play: fixed quote pricing and square foot rate pricing. Each has its own set of advantages and disadvantages, and understanding these can help clients make informed decisions.

Square foot rate pricing is a method where the cost of a project is determined based on the area to be covered, typically in square feet. This approach has several benefits. One of the main advantages is flexibility. With square foot rate pricing, clients have the ability to adjust the scope of the project more easily. If they decide to add or remove certain elements, the cost can be recalculated based on the new square footage, allowing for more adaptability throughout the project. This can be particularly useful in dynamic projects where changes are frequent.

Another pro of square foot rate pricing is that it provides a clear and straightforward way to estimate costs. Clients can often get a quick idea of what their project might cost by simply knowing the square footage and the rate per square foot. This transparency can help in budgeting and planning.

However, there are also significant cons to consider with square foot rate pricing. One major drawback is the potential for unexpected costs. While the initial estimate might seem straightforward, additional factors such as the complexity of the design, the quality of materials, and unforeseen issues (like structural problems) can drive up the cost. These extras are not always accounted for in the initial square foot rate, leading to budget overruns.

Moreover, square foot rate pricing may not always capture the true value of a project. High-end finishes, custom designs, and intricate details might not be adequately reflected in a simple per square foot calculation. This can lead to clients feeling that they are not getting their money's worth, especially if they are comparing square foot rates across different providers without considering the quality differences.

In contrast, fixed quote pricing offers a set price for the entire project, which can provide more certainty and peace of mind. While it may lack the flexibility of square foot rate pricing, it ensures that clients know exactly what they will pay upfront, reducing the risk of unexpected costs.

In conclusion, square foot rate pricing offers flexibility and a straightforward way to estimate costs, but it comes with the risk of unexpected expenses and may not always reflect the true value of the project. Weighing these pros and cons against the certainty and predictability of fixed quote pricing is essential for making an informed decision that aligns with the client's needs and budget.

Factors to consider when choosing between fixed quote and square foot rate pricing for foundation repair.


When deciding between fixed quote and square foot rate pricing for foundation repair, several factors should be taken into consideration to ensure you make an informed decision that best suits your needs and budget.

Firstly, the scope of the repair work is crucial. If the foundation issues are clearly defined and the repair work is straightforward, a fixed quote might be more appropriate. This is because a fixed quote provides a clear, upfront cost, which can be beneficial for budgeting purposes. However, if the foundation problems are complex or extensive, a square foot rate might be more suitable. This pricing model allows for flexibility as the cost is calculated based on the area being repaired, which can be more accurate for larger or more intricate projects.

Secondly, consider the level of transparency and communication with the contractor. A fixed quote often implies that the contractor has a thorough understanding of the work required and is confident in providing a definitive price. This can be reassuring, but it also means that any unforeseen issues could lead to additional costs. On the other hand, a square foot rate can offer more transparency as the cost is directly tied to the amount of work done. This can help avoid unexpected expenses, but it requires clear communication with the contractor to ensure that all potential variables are accounted for.

Thirdly, think about your budget constraints and financial flexibility. A fixed quote can be advantageous if you have a strict budget and need certainty about the total cost. Conversely, if you are more flexible with your budget and prefer to pay for the actual work done, a square foot rate might be preferable. This can also be beneficial if you anticipate that the repair work might evolve during the project, allowing you to adjust the budget as needed.

Lastly, consider the reputation and reliability of the contractor. A reputable contractor will be transparent about their pricing model and provide a detailed breakdown of costs, whether they offer fixed quotes or square foot rates. Reading reviews, asking for references, and ensuring that the contractor is licensed and insured can help you make a more informed decision.

In conclusion, choosing between fixed quote and square foot rate pricing for foundation repair depends on the specific circumstances of your project, your budget, and your preference for transparency and flexibility. By carefully evaluating these factors, you can select the pricing model that best aligns with your needs and ensures a successful repair process.

Tips for homeowners on how to evaluate and compare pricing structures for foundation repair services.


When it comes to foundation repair, homeowners often face the challenge of choosing between two primary pricing structures: fixed quotes and square foot rates. Understanding these options can greatly influence both your budget and the quality of service you receive. Here are some tips to help you evaluate and compare these pricing structures effectively.

First, let's delve into fixed quotes. A fixed quote is a predetermined price for the entire repair project. This can be appealing because it provides clarity and predictability in budgeting. You know exactly how much you'll be paying upfront, which can help avoid unexpected costs. However, fixed quotes are typically offered for straightforward repairs where the extent of the damage is clearly defined and agreed upon by both the contractor and the homeowner. If unforeseen issues arise during the repair process, additional charges may be added, which can complicate the initial budget.

On the other hand, square foot rates are calculated based on the area that needs repair. This method is often used for larger or more complex projects where the extent of the damage may not be fully known at the outset. With square foot rates, you pay for the amount of work done, which can be more flexible but also less predictable. This pricing structure can be beneficial if the repair work is extensive and you want to ensure that you're only paying for what is necessary. However, it's crucial to get a detailed estimate upfront to avoid any surprises.

When comparing these two pricing structures, it's essential to consider the scope of the work. For minor repairs, a fixed quote might be the more straightforward and cost-effective option. For more significant issues, square foot rates might offer more flexibility and accuracy in pricing. Additionally, always ask for a detailed breakdown of costs, regardless of the pricing structure. This will help you understand what is included in the quote and what might incur extra charges.

Another important factor is the reputation and experience of the contractor. A reputable contractor will be transparent about their pricing structure and provide a thorough explanation of the costs involved. Don't hesitate to ask questions and seek clarification on any aspect of the quote. It's also beneficial to get multiple estimates from different contractors to compare not only the prices but also the quality of service offered.

In conclusion, whether you choose a fixed quote or a square foot rate for your foundation repair, the key is to be informed and proactive. Take the time to understand the pricing structure, get detailed estimates, and choose a reputable contractor. By doing so, you can ensure that you make a well-informed decision that best suits your needs and budget.



 

Soil with broken rock fragments overlying bedrock, Sandside Bay, Caithness, Scotland
Soil profile with bedrock labeled R

In geology, bedrock is solid rock that lies under loose material (regolith) within the crust of Earth or another terrestrial planet.

Definition

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Bedrock is the solid rock that underlies looser surface material.[1] An exposed portion of bedrock is often called an outcrop.[2] The various kinds of broken and weathered rock material, such as soil and subsoil, that may overlie the bedrock are known as regolith.[3][4]

Engineering geology

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The surface of the bedrock beneath the soil cover (regolith) is also known as rockhead in engineering geology,[5][6] and its identification by digging, drilling or geophysical methods is an important task in most civil engineering projects. Superficial deposits can be very thick, such that the bedrock lies hundreds of meters below the surface.[7]

Weathering of bedrock

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Exposed bedrock experiences weathering, which may be physical or chemical, and which alters the structure of the rock to leave it susceptible to erosion. Bedrock may also experience subsurface weathering at its upper boundary, forming saprolite.[8]

Geologic map

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A geologic map of an area will usually show the distribution of differing bedrock types, rock that would be exposed at the surface if all soil or other superficial deposits were removed. Where superficial deposits are so thick that the underlying bedrock cannot be reliably mapped, the superficial deposits will be mapped instead (for example, as alluvium).[9]

See also

[edit]
  • icon Geology portal
  • icon Geography portal
  • Maps portal
  • Minerals portal

References

[edit]
  1. ^ Jackson, Julia A., ed. (1997). "Bedrock". Glossary of geology (4th ed.). Alexandria, Virginia: American Geological Institute. ISBN 0922152349.
  2. ^ Jackson 1997, "Outcrop".
  3. ^ Jackson 1997, "Regolith".
  4. ^ Allaby, Michael (2013). "Regolith". A dictionary of geology and earth sciences (4th ed.). Oxford: Oxford University Press. ISBN 9780199653065.
  5. ^ Price, David George (2009). "The Basis of Engineering Geology". In de Freitas, Michael H. (ed.). Engineering Geology: Principles and Practice. Springer. p. 16. ISBN 978-3540292494.
  6. ^ McLean, A.C.; Gribble, C.D. (9 September 1985). Geology for Civil Engineers (Second ed.). CRC Press. p. 113. ISBN 978-0419160007.
  7. ^ Swinford, E. Mac (2004). "What the glaciers left behind  – the drift-thickness map of Ohio" (PDF). Ohio Geology. No. 1. Ohio Department of Natural Resources, Division of Geological Survey. pp. 1, 3–5. Archived (PDF) from the original on 2 October 2012. Retrieved 12 September 2012.
  8. ^ Lidmar-Bergström, Karna; Olsson, Siv; Olvmo, Mats (January 1997). "Palaeosurfaces and associated saprolites in southern Sweden". Geological Society, London, Special Publications. 120 (1): 95–124. Bibcode:1997GSLSP.120...95L. doi:10.1144/GSL.SP.1997.120.01.07. S2CID 129229906. Retrieved 21 April 2010.
  9. ^ "Digital Geology – Bedrock geology theme". British Geological Survey. Archived from the original on 13 December 2009. Retrieved 12 November 2009.

Further reading

[edit]
  • Rafferty, John P. "Bedrock". Encyclopædia Britannica. Archived from the original on 29 July 2019. Retrieved 1 April 2019.
  • Harris, Clay (2013). "Bedrock". In Lerner, K. Lee; Lerner, Brenda Wilmoth (eds.). The Gale Encyclopedia of Science. Vol. 1 (5th ed.). Farmington Hills, MI: Cengage Gale. pp. 515–516.
[edit]
  • Media related to Bedrock at Wikimedia Commons

 

Suspended slab under construction, with the formwork still in place
Suspended slab formwork and rebar in place, ready for concrete pour.

A concrete slab is a common structural element of modern buildings, consisting of a flat, horizontal surface made of cast concrete. Steel-reinforced slabs, typically between 100 and 500 mm thick, are most often used to construct floors and ceilings, while thinner mud slabs may be used for exterior paving ( see below).[1][2]

In many domestic and industrial buildings, a thick concrete slab supported on foundations or directly on the subsoil, is used to construct the ground floor. These slabs are generally classified as ground-bearing or suspended. A slab is ground-bearing if it rests directly on the foundation, otherwise the slab is suspended.[3] For multi-story buildings, there are several common slab designs (

see § Design for more types):

  • Beam and block, also referred to as rib and block, is mostly used in residential and industrial applications. This slab type is made up of pre-stressed beams and hollow blocks and are temporarily propped until set, typically after 21 days.[4]
  • A hollow core slab which is precast and installed on site with a crane
  • In high rise buildings and skyscrapers, thinner, pre-cast concrete slabs are slung between the steel frames to form the floors and ceilings on each level. Cast in-situ slabs are used in high rise buildings and large shopping complexes as well as houses. These in-situ slabs are cast on site using shutters and reinforced steel.

On technical drawings, reinforced concrete slabs are often abbreviated to "r.c.c. slab" or simply "r.c.". Calculations and drawings are often done by structural engineers in CAD software.

Thermal performance

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Energy efficiency has become a primary concern for the construction of new buildings, and the prevalence of concrete slabs calls for careful consideration of its thermal properties in order to minimise wasted energy.[5] Concrete has similar thermal properties to masonry products, in that it has a relatively high thermal mass and is a good conductor of heat.

In some special cases, the thermal properties of concrete have been employed, for example as a heatsink in nuclear power plants or a thermal buffer in industrial freezers.[6]

Thermal conductivity

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Thermal conductivity of a concrete slab indicates the rate of heat transfer through the solid mass by conduction, usually in regard to heat transfer to or from the ground. The coefficient of thermal conductivity, k, is proportional to density of the concrete, among other factors.[5] The primary influences on conductivity are moisture content, type of aggregate, type of cement, constituent proportions, and temperature. These various factors complicate the theoretical evaluation of a k-value, since each component has a different conductivity when isolated, and the position and proportion of each components affects the overall conductivity. To simplify this, particles of aggregate may be considered to be suspended in the homogeneous cement. Campbell-Allen and Thorne (1963) derived a formula for the theoretical thermal conductivity of concrete.[6] In practice this formula is rarely applied, but remains relevant for theoretical use. Subsequently, Valore (1980) developed another formula in terms of overall density.[7] However, this study concerned hollow concrete blocks and its results are unverified for concrete slabs.

The actual value of k varies significantly in practice, and is usually between 0.8 and 2.0 W m−1 K−1.[8] This is relatively high when compared to other materials, for example the conductivity of wood may be as low as 0.04 W m−1 K−1. One way of mitigating the effects of thermal conduction is to introduce insulation (

see § Insulation).

Thermal mass

[edit]

The second consideration is the high thermal mass of concrete slabs, which applies similarly to walls and floors, or wherever concrete is used within the thermal envelope. Concrete has a relatively high thermal mass, meaning that it takes a long time to respond to changes in ambient temperature.[9] This is a disadvantage when rooms are heated intermittently and require a quick response, as it takes longer to warm the entire building, including the slab. However, the high thermal mass is an advantage in climates with large daily temperature swings, where the slab acts as a regulator, keeping the building cool by day and warm by night.

Typically concrete slabs perform better than implied by their R-value.[5] The R-value does not consider thermal mass, since it is tested under constant temperature conditions. Thus, when a concrete slab is subjected to fluctuating temperatures, it will respond more slowly to these changes and in many cases increase the efficiency of a building.[5] In reality, there are many factors which contribute to the effect of thermal mass, including the depth and composition of the slab, as well as other properties of the building such as orientation and windows.

Thermal mass is also related to thermal diffusivity, heat capacity and insulation. Concrete has low thermal diffusivity, high heat capacity, and its thermal mass is negatively affected by insulation (e.g. carpet).[5]

Insulation

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Without insulation, concrete slabs cast directly on the ground can cause a significant amount of extraneous energy transfer by conduction, resulting in either lost heat or unwanted heat. In modern construction, concrete slabs are usually cast above a layer of insulation such as expanded polystyrene, and the slab may contain underfloor heating pipes.[10] However, there are still uses for a slab that is not insulated, for example in outbuildings which are not heated or cooled to room temperature (

see § Mud slabs). In these cases, casting the slab directly onto a substrate of aggregate will maintain the slab near the temperature of the substrate throughout the year, and can prevent both freezing and overheating.

A common type of insulated slab is the beam and block system (mentioned above) which is modified by replacing concrete blocks with expanded polystyrene blocks.[11] This not only allows for better insulation but decreases the weight of slab which has a positive effect on load bearing walls and foundations.

Formwork set for concrete pour.
Concrete poured into formwork. This slab is ground-bearing and reinforced with steel rebar.

Design

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Ground-bearing slabs

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Ground-bearing slabs, also known as "on-ground" or "slab-on-grade", are commonly used for ground floors on domestic and some commercial applications. It is an economical and quick construction method for sites that have non-reactive soil and little slope.[12]

For ground-bearing slabs, it is important to design the slab around the type of soil, since some soils such as clay are too dynamic to support a slab consistently across its entire area. This results in cracking and deformation, potentially leading to structural failure of any members attached to the floor, such as wall studs.[12]

Levelling the site before pouring concrete is an important step, as sloping ground will cause the concrete to cure unevenly and will result in differential expansion. In some cases, a naturally sloping site may be levelled simply by removing soil from the uphill site. If a site has a more significant grade, it may be a candidate for the "cut and fill" method, where soil from the higher ground is removed, and the lower ground is built up with fill.[13]

In addition to filling the downhill side, this area of the slab may be supported on concrete piers which extend into the ground. In this case, the fill material is less important structurally as the dead weight of the slab is supported by the piers. However, the fill material is still necessary to support the curing concrete and its reinforcement.

There are two common methods of filling - controlled fill and rolled fill.[13]

  • Controlled fill: Fill material is compacted in several layers by a vibrating plate or roller. Sand fills areas up to around 800 mm deep, and clay may be used to fill areas up to 400 mm deep. However, clay is much more reactive than sand, so it should be used sparingly and carefully. Clay must be moist during compaction to homogenise it.[13]
  • Rolled fill: Fill is repeatedly compacted by an excavator, but this method of compaction is less effective than a vibrator or roller. Thus, the regulations on maximum depth are typically stricter.

Proper curing of ground-bearing concrete is necessary to obtain adequate strength. Since these slabs are inevitably poured on-site (rather than precast as some suspended slabs are), it can be difficult to control conditions to optimize the curing process. This is usually aided by a membrane, either plastic (temporary) or a liquid compound (permanent).[14]

Ground-bearing slabs are usually supplemented with some form of reinforcement, often steel rebar. However, in some cases such as concrete roads, it is acceptable to use an unreinforced slab if it is adequately engineered (

see below).

Suspended slabs

[edit]

For a suspended slab, there are a number of designs to improve the strength-to-weight ratio. In all cases the top surface remains flat, and the underside is modulated:

  • A corrugated slab is designed when the concrete is poured into a corrugated steel tray, more commonly called decking. This steel tray improves strength of the slab, and prevents the slab from bending under its own weight. The corrugations run in one direction only.
  • A ribbed slab gives considerably more strength in one direction. This is achieved with concrete beams bearing load between piers or columns, and thinner, integral ribs in the perpendicular direction. An analogy in carpentry would be a subfloor of bearers and joists. Ribbed slabs have higher load ratings than corrugated or flat slabs, but are inferior to waffle slabs.[15]
  • A waffle slab gives added strength in both directions using a matrix of recessed segments beneath the slab.[16] This is the same principle used in the ground-bearing version, the waffle slab foundation. Waffle slabs are usually deeper than ribbed slabs of equivalent strength, and are heavier hence require stronger foundations. However, they provide increased mechanical strength in two dimensions, a characteristic important for vibration resistance and soil movement.[17]
The exposed underside of a waffle slab used in a multi-storey building

Unreinforced slabs

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Unreinforced or "plain"[18] slabs are becoming rare and have limited practical applications, with one exception being the mud slab (

see below). They were once common in the US, but the economic value of reinforced ground-bearing slabs has become more appealing for many engineers.[10] Without reinforcement, the entire load on these slabs is supported by the strength of the concrete, which becomes a vital factor. As a result, any stress induced by a load, static or dynamic, must be within the limit of the concrete's flexural strength to prevent cracking.[19] Since unreinforced concrete is relatively very weak in tension, it is important to consider the effects of tensile stress caused by reactive soil, wind uplift, thermal expansion, and cracking.[20] One of the most common applications for unreinforced slabs is in concrete roads.

Mud slabs

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Mud slabs, also known as rat slabs, are thinner than the more common suspended or ground-bearing slabs (usually 50 to 150 mm), and usually contain no reinforcement.[21] This makes them economical and easy to install for temporary or low-usage purposes such as subfloors, crawlspaces, pathways, paving, and levelling surfaces.[22] In general, they may be used for any application which requires a flat, clean surface. This includes use as a base or "sub-slab" for a larger structural slab. On uneven or steep surfaces, this preparatory measure is necessary to provide a flat surface on which to install rebar and waterproofing membranes.[10] In this application, a mud slab also prevents the plastic bar chairs from sinking into soft topsoil which can cause spalling due to incomplete coverage of the steel. Sometimes a mud slab may be a substitute for coarse aggregate. Mud slabs typically have a moderately rough surface, finished with a float.[10]

Substrate and rebar prepared for pouring a mud slab

Axes of support

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One-way slabs

[edit]

A one-way slab has moment-resisting reinforcement only in its short axis, and is used when the moment in the long axis is negligible.[23] Such designs include corrugated slabs and ribbed slabs. Non-reinforced slabs may also be considered one-way if they are supported on only two opposite sides (i.e. they are supported in one axis). A one-way reinforced slab may be stronger than a two-way non-reinforced slab, depending on the type of load.

The calculation of reinforcement requirements for a one-way slab can be extremely tedious and time-consuming, and one can never be completely certain of the best design.[citation needed] Even minor changes to the project can necessitate recalculation of the reinforcement requirements. There are many factors to consider during the structural structure design of one-way slabs, including:

  • Load calculations
  • Bending moment calculation
  • Acceptable depth of flexure and deflection
  • Type and distribution of reinforcing steel

Two-way slabs

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A two-way slab has moment resisting reinforcement in both directions.[24] This may be implemented due to application requirements such as heavy loading, vibration resistance, clearance below the slab, or other factors. However, an important characteristic governing the requirement of a two-way slab is the ratio of the two horizontal lengths. If where is the short dimension and is the long dimension, then moment in both directions should be considered in design.[25] In other words, if the axial ratio is greater than two, a two-way slab is required.

A non-reinforced slab is two-way if it is supported in both horizontal axes.

Construction

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A concrete slab may be prefabricated (precast), or constructed on site.

Prefabricated

[edit]

Prefabricated concrete slabs are built in a factory and transported to the site, ready to be lowered into place between steel or concrete beams. They may be pre-stressed (in the factory), post-stressed (on site), or unstressed.[10] It is vital that the wall supporting structure is built to the correct dimensions, or the slabs may not fit.

On-site

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On-site concrete slabs are built on the building site using formwork, a type of boxing into which the wet concrete is poured. If the slab is to be reinforced, the rebars, or metal bars, are positioned within the formwork before the concrete is poured in.[26] Plastic-tipped metal or plastic bar chairs, are used to hold the rebar away from the bottom and sides of the form-work, so that when the concrete sets it completely envelops the reinforcement. This concept is known as concrete cover. For a ground-bearing slab, the formwork may consist only of side walls pushed into the ground. For a suspended slab, the formwork is shaped like a tray, often supported by a temporary scaffold until the concrete sets.

The formwork is commonly built from wooden planks and boards, plastic, or steel. On commercial building sites, plastic and steel are gaining popularity as they save labour.[27] On low-budget or small-scale jobs, for instance when laying a concrete garden path, wooden planks are very common. After the concrete has set the wood may be removed.

Formwork can also be permanent, and remain in situ post concrete pour. For large slabs or paths that are poured in sections, this permanent formwork can then also act as isolation joints within concrete slabs to reduce the potential for cracking due to concrete expansion or movement.

In some cases formwork is not necessary. For instance, a ground slab surrounded by dense soil, brick or block foundation walls, where the walls act as the sides of the tray and hardcore (rubble) acts as the base.

See also

[edit]
  • Shallow foundation (Commonly used for ground-bearing slabs)
  • Hollow-core slab (Voided slab, one-way spanning)
  • Beam and block (voided slab, one way spanning)
  • Voided biaxial slab (Voided slab, two-way spanning)
  • Formwork
  • Precast concrete
  • Reinforced concrete
  • Rebar
  • Concrete cover

References

[edit]
  1. ^ Garber, G. Design and Construction of Concrete Floors. 2nd ed. Amsterdam: Butterworth-Heinemann, 2006. 47. Print.
  2. ^ Duncan, Chester I. Soils and Foundations for Architects and Engineers. New York: Van Nostrand Reinhold, 1992. 299. Print.
  3. ^ "Ground slabs - Introduction". www.dlsweb.rmit.edu.au. Archived from the original on 2019-11-18. Retrieved 2017-12-07.
  4. ^ "What is a rib and block slab?". www.royalconcreteslabs.co.za. Royal concrete slabs.
  5. ^ a b c d e Cavanaugh, Kevin; et al. (2002). Guide to Thermal Properties of Concrete and Masonry Systems: Reported by ACI Committee 122. American Concrete Institute.
  6. ^ a b Campbell-Allen, D.; Thorne, C.P. (March 1963). "The thermal conductivity of concrete". Magazine of Concrete Research. 15 (43): 39–48. doi:10.1680/macr.1963.15.43.39. UDC 691.32.001:536.21:691.322.
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[edit]
  • Concrete Basics: A Guide to Concrete Practice
  • Super Insulated Slab Foundations
  • Design of Slabs on Ground Archived 2021-05-08 at the Wayback Machine

 

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Reviews for


Jeffery James

(5)

Very happy with my experience. They were prompt and followed through, and very helpful in fixing the crack in my foundation.

Sarah McNeily

(5)

USS was excellent. They are honest, straightforward, trustworthy, and conscientious. They thoughtfully removed the flowers and flower bulbs to dig where they needed in the yard, replanted said flowers and spread the extra dirt to fill in an area of the yard. We've had other services from different companies and our yard was really a mess after. They kept the job site meticulously clean. The crew was on time and friendly. I'd recommend them any day! Thanks to Jessie and crew.

Jim de Leon

(5)

It was a pleasure to work with Rick and his crew. From the beginning, Rick listened to my concerns and what I wished to accomplish. Out of the 6 contractors that quoted the project, Rick seemed the MOST willing to accommodate my wishes. His pricing was definitely more than fair as well. I had 10 push piers installed to stabilize and lift an addition of my house. The project commenced at the date that Rick had disclosed initially and it was completed within the same time period expected (based on Rick's original assessment). The crew was well informed, courteous, and hard working. They were not loud (even while equipment was being utilized) and were well spoken. My neighbors were very impressed on how polite they were when they entered / exited my property (saying hello or good morning each day when they crossed paths). You can tell they care about the customer concerns. They ensured that the property would be put back as clean as possible by placing MANY sheets of plywood down prior to excavating. They compacted the dirt back in the holes extremely well to avoid large stock piles of soils. All the while, the main office was calling me to discuss updates and expectations of completion. They provided waivers of lien, certificates of insurance, properly acquired permits, and JULIE locates. From a construction background, I can tell you that I did not see any flaws in the way they operated and this an extremely professional company. The pictures attached show the push piers added to the foundation (pictures 1, 2 & 3), the amount of excavation (picture 4), and the restoration after dirt was placed back in the pits and compacted (pictures 5, 6 & 7). Please notice that they also sealed two large cracks and steel plated these cracks from expanding further (which you can see under my sliding glass door). I, as well as my wife, are extremely happy that we chose United Structural Systems for our contractor. I would happily tell any of my friends and family to use this contractor should the opportunity arise!

Chris Abplanalp

(5)

USS did an amazing job on my underpinning on my house, they were also very courteous to the proximity of my property line next to my neighbor. They kept things in order with all the dirt/mud they had to excavate. They were done exactly in the timeframe they indicated, and the contract was very details oriented with drawings of what would be done. Only thing that would have been nice, is they left my concrete a little muddy with boot prints but again, all-in-all a great job

Dave Kari

(5)

What a fantastic experience! Owner Rick Thomas is a trustworthy professional. Nick and the crew are hard working, knowledgeable and experienced. I interviewed every company in the area, big and small. A homeowner never wants to hear that they have foundation issues. Out of every company, I trusted USS the most, and it paid off in the end. Highly recommend.

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