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Keermuur ontwerp controles volgens ACI 318

Keermuurontwerpcontroles volgens ACI 318-19

Tijdens het proces van een betonnen vrijdragende keermuurontwerp, de eerste stap is het defini├źren van de voorlopige afmetingen en controleer de stabiliteit van deze voorlopige geometrie tegen kantelen, glijden, en lager. Het voltooien van deze stabiliteitscontroles omvat de berekening van alle krachten die op de keerstructuur werken. die ladingen, wanneer in rekening gebracht, zijn de input die nodig zijn om ontwerpcontroles uit te voeren op de betonnen keermuur en zorgen voor de afmetingen en de aangebrachte wapening, zal in staat zijn om de ultieme belasting te weerstaan. Using our Retaining Wall Design Software, it is possible to perform the stability checks required during the process of a concrete retaining wall design.

samengevat, ontwerpcontroles op de verschillende componenten van een betonnen keermuur omvatten::

  • Stang
    • Kritieke sectie: Gelegen aan de basis van de stengel, aan de voorkant van de keermuurbasis. For shear strength check, ACI 318 allows using the section at a distance d from the base as the critical one.
    • werkende krachten: Ingehouden actieve bodemdruk en extra druk door toeslagbelastingen.
    • Effecten om te controleren: Flexure and shear at the critical section cantilever retaining wall’s stem.
  • Hiel
    • Kritieke sectie: Gelegen op het raakvlak tussen de stengel en de muurvoet. For shear strength check, ACI 318 allows using the section at a distance d from the interface as the critical one.
    • werkende krachten: Vastgehouden bodemgewicht, heel self-weight, en verticaal werkende toeslag. Soil pressure below the base could be included, but is usually neglected for being conservative.
    • Effecten om te controleren: Shear and flexure at the critical section cantilever retaining wall’s heel.
  • Teen
    • Kritieke sectie: Located at the face of the stem. For shear strength check, ACI 318 allows using the section at a distance d from the face of the stem as the critical one.
    • werkende krachten: Lagerdruk onder de teen. Passief eigengewicht van de grond dat boven de teen werkt, wordt meestal verwaarloosd, omdat het kan eroderen of worden verwijderd.
    • Effecten om te controleren: Shear and flexure at the critical section cantilever retaining wall’s toe.
  • Schuifsleutel (indien inbegrepen)
    • Kritieke sectie: Gelegen op de interface tussen de breeksleutel en de muurvoet.
    • werkende krachten: Passieve bodemdruk.
    • Effecten om te controleren: Shear at the critical section cantilever retaining wall’s key.

retaining wall design checks as per ACI 318

Load Factors as per ACI-318

When performing a design check on a concrete cantilever retaining wall as per the requirements of ACI-318, all the external forces that act on the structure and generate an internal force at the critical section, are factored in according to their nature, as follows:

  • For lateral earth pressures, due to the soil’s weight and additional loads, the factor for calculating ultimate state loads is \(1.6\)
  • For the structure’s self-weight, the factor for calculating ultimate state loads is \(1.2\)

Those factors reflect the probability of exceeding the calculatedexact” waarde, for the case of the structure’s self-weight, the probability of being exceeded is quite low, and therefore the factor is close to 1.0, echter, external forces such as the weight and lateral pressure of the retained soil and the surcharges are more likely to take a higher value, and that’s why the load factor is closer to 2 than to 1.

Resistance reduction factors as per ACI-318

Apart from increasing the forces acting on the structure, its resistance is also reduced by applying some factors, following the LRFD (Ontwerp van belastings- en weerstandsfactoren) approach. Each resistance value is reduced as follows:

  • For flexure resistance, assuming the member is tension controlled, the reduction factor is \(0.9\)
  • For shear resistance, the reduction factor is \(0.75\)

Design requirements as per ACI-318

Comparing the ultimate state internal forces to the reduced member resistance to that internal force, it is possible to determine whether the provided concrete section and embedded reinforcement are strong enough or not. This can be expressed in the following two equations:

  • For nominal moment resistance \(M_n\) and ultimate state moment \(M_u\)

\(\phi \; M_n \geq M_u\)

  • For nominal shear resistance \(V_n\) and ultimate state shear force\(V_u\)

\(\phi \; V_n \geq V_u\)

Additional requirements as per ACI-318

Apart from fulfilling the requirements mentioned above, ACI-318 presents some additional requirements for successfully completing a Concrete Retaining Wall Design:

  • The reinforcement calculated for flexure on any component of the structure is checked against the beam minimum required flexural reinforcement. According to ACI-318, the beam formula is used instead of the one-way slab formula because of the lack of redundancy:

\(EEN_{s, \; min} = frac{3 \sqrt{f'_c}}{f_y} b_w d\)

  • Once the required steel area for flexure is calculated, the section is checked to ensure it is tension controlled, in other words making sure that the reinforcement steel yields before concrete cracks:

\(\varepsilon_t = \frac{\varepsilon_c}{c}(d-c) > 0.005\)

Waar \(c = \frac{een}{\beta_1}\), \(a = 1.31 A_s\), \(\varepsilon_c = 0.003\) (assuming concrete cracks at that strain level), en \(d\) is the distance from the compression edge to the center of the reinforcement in tension.

  • Some minimum transverse reinforcement area is calculated for each component of the Cantilever Concrete Retaining Wall, using the ratios given in Table 11.6.1 of ACI-318
  • Development and splice lengths are also calculated for each component of the Cantilever Concrete Retaining Wall, using the criteria given in 25.4.2 of ACI-318

SkyCiv Retaining Wall Calculator

Met al die individuele belastingen is het nu mogelijk om de wrijvingskracht te berekenen. De betaalde versie toont ook de volledige berekeningen, zodat je stap voor stap kunt zien, hoe de stabiliteit van een keermuur tegen kantelen te berekenen?, glijden en lager! With the paid account, it is also possible to perform design checks as per ACI on the retaining wall.

= gamma_
Oscar Sanchez
Productontwikkelaar
BEng (Civiel)
LinkedIn
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