Posted in Krah - News. This article describes the basic procedure for the dimensioning of profiled pipes using the ATV-DVWK-A Germany worksheet, as this set of rules also enjoys great international recognition. A new chapter is inserted for special features in the design of profiled pipes; a relevant data sheet ATV-M Part 3 is in preparation". German edition translated.
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Posted in Krah - News. This article describes the basic procedure for the dimensioning of profiled pipes using the ATV-DVWK-A Germany worksheet, as this set of rules also enjoys great international recognition. A new chapter is inserted for special features in the design of profiled pipes; a relevant data sheet ATV-M Part 3 is in preparation".
German edition translated. Pipe soil system When laying new pipes, only the radial cross-section of the pipe wall is considered. The longitudinal direction remains disregarded. The pipe always carries the loads together with the surrounding soil. Without the soil, the pipe would not be verifiable, which is why the worksheet assumes a "pipe soil system".
It also contains information on the dimensioning of perforated pipes for drainage and profiled pipes. System stiffness and locations for verifications The concept of the A requires different verifications, which have to be made at the three prominent points crown, springline, and bottom.
The verifications depend on the system stiffness V RB of the pipe soil system. V RB decides whether a pipe soil system is a flexible or b rigid. From a static point of view, each of the three positions on the inside and outside must be considered. It is not possible to predict which stress would be exceeded first; therefore both sides must be verified.
Materials A generalization regarding the material is difficult. In this case, the deformation and stability check is not required. If pipes made of steel or plastic are very thick-walled, they may well behave rigidly. Time dependency Some materials are time-dependent.
This is taken into account in the statics by examining such pipes for two points in time: a short-term, b long-term with a after one minute and b after 50 years. All plastic pipes are time-dependent, and so is polymer concrete and GRP, while e. Soil groups What regularly surprises some subsoil experts is common practice in pipeline construction: The A knows only four soil groups G Group G1 stands for non-cohesive soils, G4 for cohesive soils. G2 is for low cohesive soils, G3 for cohesive mixed soils and silt.
In addition, the degree of compaction D Pr must be observed: The higher the "Proctor density", the more stable the soil will be. Soil zones Section 6. The grown soil on the side of trench E 3 is of special importance. A supporting effect is only given if the natural soil has at least the modulus of elasticity of the backfill.
Figuratively speaking: Grown soil from e. Loads influences The regulations distinguish between short-term and long-term loads. Short-term are usually traffic loads and short-term internal pressure, if any. All other loads are regarded as long-term, i. Under railway tracks the load model UIC 71 has to be considered. Groundwater If groundwater is present, the number of necessary calculations is usually doubled.
On the one hand, groundwater has a favourable effect because it reduces the earth load above the pipe by buoyancy; on the other hand, it is unfavourable because it worsens the bedding properties of the soil under the pipe. Verifications For a flexible pipe soil system in groundwater, the number of required calculations is maximized. Verifications are necessary in each case at crown, springline, and bottom level as well as in each case inside and outside the cross-section:. A stress analysis is always necessary for all pipes.
Rigid pipe soil systems require further considerations depending on the material, such as the verification of the crack width and compliance with the exposure classes and minimum concrete cover for reinforced concrete pipes. The number of required calculations must be multiplied by the number of checks. Silo theory and embankment condition The frequently encountered trench installation assumes that the trench walls remain intact in operational state and over the service life of the pipe.
If suitable soil types are used, a vault can then form above the pipe. The silo theory "hangs" the soil above the pipe by friction in the trench walls and thereby reduces the vertical load on the pipe. This is expressed in the coefficient k. If the trench width b exceeds four times the outer diameter of the pipe d a , the effect of the trench walls too far away from the pipe has subsided. Foundation angle In the bottom area of the pipe, the contractor must ensure an even subgrade of suitable material.
Very coarse-grained material such as boulders as a bedding layer is harmful for any pipeline. Graded sands are better suited. Many pipe manufacturers provide information on this in their installation instructions.
With the same load, a larger angle has a more favourable effect. Bedding reaction pressure Flexible pipe soil systems can withstand smaller deformations relatively well. Under a vertical load, the pipe deforms, i.
It depends largely on the system stiffness V RB and the soil properties. Shuttering Trench walls — also for space reasons in urban areas — are often not inclined but vertical.
Very few soils remain stable, so that shuttering is usually provided. A suitable type of shuttering depends on the soil conditions and any water retention during the construction phase. A4, which should correctly be named A A3 — where A0 is best and A3 is worst.
A sheet pile wall shoring, for example, which is pulled after backfilling, loosens the soil between backfilling and the grown soil. This has a negative effect on load transfer and may lead to subsidence. Backfilling and compaction should be carried out carefully and in layers; ideally, this process is recorded on the construction site. Quality monitoring of the material and foresighted planning, including static calculations, are ineffective in the event of improper execution. Forces and stresses Until now, it was tacitly assumed that solid wall pipes were used where the wall thickness was the decisive parameter.
In the case of steel, concrete and many plastic pipes, it is often the only criterion that can be changed during the planning phase. Its advantage lies in its ease of manufacture and standardization of wall thicknesses. A solid wall pipe can be manufactured as axial extruded pipe e. Polyethylene: DIN Solid wall pipes provide a smooth inner and outer surface.
The cross-section must bear stresses as elegantly as possible. In the design case, a combination of stresses is usually decisive, namely: normal stresses superimposed with bending stresses.
Normal stresses act perpendicular to the surface under consideration. For example, pure internal pressure alone produces a positive normal stress in the entire cross-section, the pipe wall is completely under tension. Material is required for load transfer; the location of the material is almost insignificant. A solid wall pipe is well suited to carry normal stresses. In reality, pure normal forces are rarely encountered: Earth and traffic loads generate additional bending moments.
It can be assumed that normal and bending stresses are always present in an underground pipe. For the distribution of the bending moments it is very important where the material is located. Solid wall pipes If the planner wants to increase the stiffness of the desired pipe — for example, because the deformation check in the software fails — he usually increases the wall thickness of solid wall pipes. A typical rectangular cross section for a wooden beam is:.
This shows that the height or wall thickness of the profile has a decisive influence on the moment of inertia and therefore the stiffness of the pipe. Wall thickness s enters in the third power.
Two examples:. Profiled pipes Mostly profiled pipes will be manufactured as corrugated pipes or spiral wound pipes. Especially the spiral winding allows a tailor-made design of the wall structure for required stiffness, occurring pressure load and all other internal and external loads. Profiled pipes are also national and international standardized e.
For the flow characteristic it is notable that spiral wound pipes provide a fix inner diameter, even if stiffness classes or pressure classes change. Geometries deviating from the rectangular shape are known from structural steel engineering.
Here, the bending moments are absorbed by the flanges, which are connected to each other by a shear-resistant fillet. A clear advantage lies in the weight and material savings compared to an equivalent rectangular cross-section.
But it has to be considered that the profile itself has to provide sufficient stability, a slender fillets must be stiffened or verified against buckling.
The k Q coefficient The coefficient k Q is frequently queried. It is relatively insignificant. Common CAD programs are able to determine this factor from the profile geometry. Alternatively, a qualified engineering office like  can determine k Q exactly. Dimensioning of profiled pipes From a structural point of view, pipes are dimensioned similar to solid wall pipes.
Regularly updated software  reliably maintains the state of the art. It uses formulas, tables and diagrams. In comparison to M55, which handles compressive stresses only, and in one point only, the A checks all the critical sections in a pipe top, springline, bottom.
Structural engineers and consultants around the globe use and accept this standard work of pipe statics. It is established, tested and proven.
ATV DVWK-A 127-E Static calculations of drains and sewers
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ATV-DVWK-A 127E Statical Calculation of Drains and Sewers
New Customer. New Publications. Drain and Sewer Systems. Rules and Standards. Municipal Wastewater Treatment. Further Publications. Hydraulic Engineering and Hydro Power.
The Working Group has the following members: Dipl. Gert Bellinghausen, Sankt Augustin Dipl. Peter Brune, Gelsenkirchen Dipl. Gnther Buchholtz, Berlin to April Prof. Bernhard Falter, Mnster Dr. Christian Falk, Gelsenkirchen Dipl.