PipeClass has recently been updated to an online application negating the need for downloading an executable file.
The software is available on line for use on desktops, iPads and iPhones.
Design results are visible to the right of the screen, enabling quick checks of require load class for any given set of parameters. Sensitivity of design can be easily checked as the pipe load class required updates as parameters are changed.
The design application now includes the option of AS5100:2017 Bridge Design loads, load distribution and dynamic load factors. The option to design to AS/NZS 3725:2007 distribution has been maintained as a great proportion of installed pipe is not under major roads.
In order to align with the current version of the Waka Kotahi – New Zealand Transit Authority Bridge Manual SP/M/022 Third edition, amendments to New Zealand standard vehicles, SLS and DLA values have been incorporated.
Additional vehicles have been added to the built in vehicle library whilst maintaining the ability for users to add details of vehicles as they need.
PipeClass 3.0 has been developed as an intuitive application to enable ease of use.
If you have difficulty using PipeClass your first port of call for technical support is this help file. The answers to most questions can probably be found here. The next step is to try the CPAA web site or contact the CPAA or one of its member companies for assistance.
CONTACT DETAILS
PipeClass 3.0 approaches pipeline design in a logical manner, moving through a sequence of steps as data is gathered from the user about the pipe and how it is to be installed. As this data builds up a design emerges on the right hand of the screen for handling the required long term and short term loads. Finally, PDF outputs can be generated to keep on file, aid specification documentation and sharing.
There are five discrete sections that are the basis of the application:
The Pipe section is where the specific dimensions of the pipe are given along with the intended application and joint type. Information can also be given for multiple barrel installations and the orientation of the pipeline under a road or railway.
Pipe Inputs
The pipe application refers to the intended use for the completed pipeline and will have some effect on the input parameters and final calculations. Selection of the appropriate application affects the joint type selection options and the option of consideration of internal water pressure effects for pressure pipes. Options are:
Drainage – This includes all pipes used for conveyance of stormwater or as a pipe culvert under a road or railway which are subject to hydrostatic working pressures of less than 60-70 kPa. All joint types are possible with this selection.
- Sewerage – This includes all pipes used for gravity sewer applications. Rubber ring joint (RRJ) joint type is the default joint type and the most common. It is also possible to select the jacking pipe joint option but as jacking pipes for sewerage applications are non-standard it is recommended that users contact their local CPAA member company for advice. Note for pumped sewer mains (rising mains) it is necessary it is necessary to select the pressure pipe option.
- Pressure – This includes all pipes used for the conveyance of water subject to a hydrostatic test pressure of greater than 90 kPa. This could be either a gravity or a pumped pipeline. When this option is selected the option of inputting the working and test pressures on the Long Term Loads page becomes available. Rubber ring joint (RRJ) joint type is the default joint type and the most common. It is possible to select the jacking pipe joint option but as jacking pipes for pressure applications are non-standard it is recommended that users contact their local CPAA member company for advice.
Joint Type
The joint type selection options are:
- Flush Joint (FJ) pipes are generally used for road or railway culverts and some stormwater applications. FJ pipes provide an interlocking joint but have limited capacity to prevent exfiltration of water being carried or infiltration of groundwater. (Flush joints are normally provided with a sandband or similar.)
- Rubber ring joint (RRJ) pipes are used for all applications and are always used for sewerage and pressure applications. The RRJ pipe is supplied with an elastomeric (rubber) ring which is used when joining the pipes and generally provides one or more of the following benefits :
- Provision of a watertight seal to suit various test pressures;
- Prevents soil and root ingress into the pipeline;
- Allows greater flexibility of joint deflections:
- Maintains integrity of the pipeline if ground settlement is expected.
- Jacking pipe joint (JPJ) pipes are used for the specific installation methods of pipe jacking and/or micro-tunnelling – PipeClass only uses the term pipe jacking or jacking pipes and for more information refer to the Concrete Pipe Association of Australasia’s publications Concrete Pipe Jacking and Pipe Jacking Design Guidelines for additional information. The publication is available on the CPAA web site or consult your local CPAA member company.
Pipe Diameter
The nominal pipe diameter is nominal internal diameter which is a convenient rounded number loosely related to manufacturing dimensions of the pipe. The actual external diameter, D, is the external diameter of the pipe barrel used in the calculation of working loads on the pipe. PipeClass contains a library of default external diameters which are generally commercially available in Australia and New Zealand, but if known, the actual external diameter can be input. This is generally not significant or required except in special applications. If in doubt consult your local CPAA member company.
For rubber ring joint pipes the pipe socket external diameter is shown and is a function of the external diameter. This variable is used in the calculation of minimum allowable trench widths and/or multiple pipe spacing.
BARRELS
The number of barrels, sometimes called cells, is the number of individual pipes laid side by side for a particular application. It is important that the correct selection is made here as it will affect both the calculation of the earth loads acting on the pipe and the quantities. Particular attention should be paid to the barrel spacing.
Barrel spacing is the clear distance the outside of the barrel of the pipeline – note that the spacing between the outside of adjacent sockets (socket spacing) will be less.
For multiple barrels it is necessary to include a value of the barrel spacing (Ic). The default values for the barrel spacing are taken from Figure 4 of AS/NZS 3725:2007. For compacted fill, it is:
The minimum spacing between adjacent pipe sockets, for socketed pipes, is 50mm. If a value of spacing less than the default value is input a warning will be displayed.
To achieve compaction between such pipes normal mechanical compaction methods may not be suitable and as such the use of alternative methods of compaction may be required such as:
- Flooding of a sand backfill (note provision for water to escape is required)
- Placement of a single sized aggregate such as a concrete aggregate with suitable tamping (note in some native soil conditions the use of a geotextile will be required)
- Placement of a self compacting slurry or cement stabilised fill.
- Or some other suitable means which does not require mechanical compaction techniques.
Note that the minimum required spacing between adjacent pipe sockets may, for some socketed pipe diameters, result in a larger default value for the barrel spacing (Ic) than recommended by AS/NZS 3725:2007.
AS/NZS 3725:2007 Clause 6.3.3.3 Multiple Pipe Conditions states, “Where two or more pipes are laid side by side in a single trench or embankment the working load per pipe due to fill (Wg) is calculated as for the embankment condition using equation 2 (formula for positive projection condition).”
PIPE ORIENTATION
The pipe orientation refers to the location of the pipeline relative to the direction of the traffic flow as shown below. The significance of this input governs how traffic loads are applied to the buried concrete pipe.
If Perpendicular is selected the vehicle loads (road or rail) are applied in one orientation only with the width of the live load applied along the length of the pipe only (for road vehicle width would refer to the distributed width of the tyre contact area at the top of the pipe)
If Longitudinal is selected the vehicle loads (road or rail) are applied in one orientation only with the length of the live load in the direction of travel applied along the length of the pipe only (for road vehicle width would refer to the distributed length of the tyre contact area at the top of the pipe.
If the pipe is skewed to the direction of traffic flow or the direction is unknown then the both or skew option must be selected.
For skewed orientations, this program calculates the worst case of transverse and longitudinal orientations. In isolated cases skews (usually between 40 – 60 °) will induce a moderate increase, above this, in the working live load. It is recommended that this influence be confirmed independently for these skews when reserve capacity is low.
The Earth Loads page contains a number of inputs which are used to calculate the earth loads acting on the buried concrete pipe. Like AS/NZS 3725:2007, the software is based on the work of Anson Marston and, later, Marvin G. Spangler and others at the Iowa Engineering Experiment Station. Users of this software seeking further information are encouraged to use the references below.
Click here for more information of the different sections of the Earth Loads page.
References:
AS/NZS 3725:2007 Design for installation of buried concrete pipes, Standards Australia/Standards New Zealand.
AS/NZS 3725 Supp 1:2007 Design for installation of buried concrete pipes – Commentary (Supplement to AS/NZS 3725:2007), Standards Australia/Standards New Zealand.
SPANGLER M.G., and HARDY R.L. Soil engineering. McGraw Hill, 1982.
The installation condition relates to how the pipe is installed in the ground, usually relative to the surface level of the natural ground. The installation condition significantly effects the loads acting on the concrete pipe and it is extremely important for designers to understand in what installation condition the concrete pipe will be installed and then communicate that condition to the installation contractor. The installation conditions included in PipeClass are based on those contained in AS/NZS 3725:2007 Design for installation of buried concrete pipes.
The types of installation conditions are generally based on two major types of installation conditions:
- Trench condition – in this condition the pipe is placed in a narrow trench which has been dug into natural undisturbed ground.
- Embankment condition – in this condition the pipe is installed into the natural ground or partly constructed embankment and then the balance of embankment fill is constructed above the pipe. In a positive projection embankment condition the concrete pipe is placed such that the top of the pipe is at or above the natural ground and in a negative projection condition the top of the pipe is placed below the natural ground surface.
These installation conditions are shown in the diagram above.
Other special types of installation conditions are:
- Induced trench condition – this type of condition is achieved by placing compressible material over an otherwise positive projection embankment condition which may replicate similar effects to a trench condition – hence the name “induced” trench. This type of installation condition is not commonly used and as such is not included in AS/NZS 3725:2007 or PipeClass v3.0.
- Jacking pipe condition – this condition occurs when pipes are placed by either pipe jacking or micro-tunnelling and pipes are pushed through a tunnel of just slightly greater diameter than the pipe.
Trench Condition
In a trench condition the pipe is placed in a narrow trench which has been dug into natural undisturbed ground. In this condition the load acting on the pipe is considered to be a function of the weight of the fill material in the trench above the pipe. The fill in the trench has a tendency to settle relative to the walls of the trench. This settlement results in frictional forces between the fill and the walls of the trench being generated which tend to decrease the resultant weight of earth acting on the pipe.
The resultant earth load acting on the pipe in this condition, which includes the effects of friction developed at the walls of the trench, is calculated in accordance with the equation (1) of AS/NZS 3725:2007 which is shown in the equation below:
in which:
Wg is the working load due to fill in kN/m; w is the unit weight of fill material in kN/m3; B is the trench width.
Ct is the load coefficient proposed by Spangler for the trench condition (generally referred to as the Spangler coefficient for the trench condition) which is calculated from the equation:
in which:
K and µ’ are soil properties;
H is the height of fill above the top of the pipe; D is the external diameter of the pipe.
PipeClass includes options for selection of different trench installation conditions. For all three options the load calculation is exactly the same except the trench width B is taken to be the trench width at the top of the pipe.
As the trench width increases, the load on the pipe in accordance with equation (1) increases and the significance of the frictional forces decreases. As the trench width increases further the installation condition will approach that of a positive projection embankment condition. As such the load acting on the pipe is also checked for this installation condition, with the actual load acting on the pipe taken to be the lesser value of the trench or positive projection embankment condition.
In a positive projection embankment condition the pipe is installed, with the top of the pipe extending above the natural ground surface level, and then the embankment fill is constructed above the top of the pipe.
The natural ground surface can either be the existing undisturbed ground or an equivalent built up compacted fill – refer to AS/NZS 3725 Supp 1:2007 for a detailed definition of “equivalent”.
The earth load acting on the pipe in this type of condition is a function of the weight of fill above the outside diameter of the pipe which is often referred to as the prism load (the prism load = wDH kN/m length of pipe, where w is the unit weight of fill above the pipe).
With this type of installation the fill material either side of the column of earth above the outside diameter of the pipe tends to settle more than the fill above the pipe due to the concrete pipe having a much greater stiffness than the compacted fill adjacent to it. The combination of this differential settlement and the settlement of the pipe into the foundation induces frictional forces between the column of earth above the pipe and the adjacent earth resulting in an increase in the load on the pipe above that of the prism load. The extent of this differential settlement will vary with fill height and, in some installations, there will be a height above the pipe at which there will be no net differential settlement – this height is known as the height of the plane of equal settlement (He).
The resultant earth load acting on the pipe in this condition, which includes the effects of friction developed, is calculated in accordance with the equation (2) of AS/NZS 3725:2007 which is shown in the equation below:
in which:
Wg is the working load due to fill in kN/m;
w is the unit weight of fill material in kN/m3;
D is the outside diameter of the pipe in mm
C’e is the load coefficient for the positive projection embankment condition. This is a variation of the coefficient used by Spangler and is generally referred to as the modified Spangler coefficient for the positive projection embankment condition.
AS/NZS 3725:2007 Clause 6.3.3.3 Multiple Pipe Conditions states, “Where two or more pipes are laid side by side in a single trench or embankment the working load per pipe due to fill (Wg) is calculated as for the embankment condition using equation 2 (formula for positive projection condition).”
The calculation of C’e is quite complex and depends on the location of the height of plane of equal settlement, He. If He >= H, then C’e is calculated from the following equation,
or if He < H, then
To apply either of the above equations, He must be known which is obtained from a solution of the following equation:
Note: In the case where He > H then the plane of equal settlement is indeed imaginary and the actual value obtained in solving the above equation is meaningless. As such, if He > H, then PipeClass will return a value of He = H.
In a negative projection embankment condition the pipe is installed in a trench (with the top of the pipe below the existing or equivalent natural ground surface level).
In this installation condition the fill above the trench will tend to settle more relative to the fill adjacent to it resulting in shearing forces which tend to reduce the net weight of the column of earth above the pipe.
The resultant earth load acting on the pipe in this condition, which includes the effects of friction developed, is calculated in accordance with the equation (3) of AS/NZS 3725:2007 which is shown in the equation below:
in which:
Wg is the working load due to fill in kN/m;
w is the unit weight of fill material in kN/m3;
B is the trench width.
C’n is the load coefficient for the negative projection embankment condition. This is a variation of the coefficient used by Spangler and is generally referred to as the modified Spangler coefficient for the negative projection embankment condition.
C’n is calculated (from Spangler) in accordance with the following equations for various values of the negative projection ratio p’ and settlement ratio rs:
PipeClass limits the values of the projection ratio’s to between 0.5 and 2.0. For p’ < 0.5, it is recommended that users adopt a positive projection embankment condition with the positive projection ratio p of 0.0. For intermediate values of p’ within the range listed above, PipeClass will adopt the C’n value for the nearest lowest value of p’. For example for p’ = 0.9, PipeClass will return a value of C’n for p’ = 0.5.
In an induced trench condition the concrete pipe is installed in a positive projection embankment condition and fill is then placed over and above the top of the pipe. After the fill is placed to a certain height a trench is dug above the pipe, usually with a trench width equal to the outside diameter of the pipe (D), and compressible material such as straw bales is placed in the trench. Following this the remainder of the embankment fill is placed. Due to the nature of the compressible material, the fill in the column of earth above the pipe will tend to settle more than the soil either side of the pipe inducing frictional forces much as would exist in a trench installation – hence the name “induced trench”.
The loads acting on the pipe are calculated using exactly the same formula as for the negative projection installation.
Limitation to the use of this installation type are recommended:
- It can only be selected for single barrel installations.
- The minimum height of fill is 6 m. The choice of this limit is somewhat arbitrary; however the fill height must be sufficiently large such that there is sufficient force to compress the compressible material.
AS/NZS 3725:2007 has removed reference to the induced trench as it has not been used to any great extent in Australia or New Zealand. For this reason PipeClass v3.0 does not include this option. For more details, refer to AS/NZS 3725 Supp 1:2007.
Jacking pipe installation is one in which a pipe is placed in a tunnel generally circular in nature and of a diameter slightly greater than the outside diameter of the pipe which has been excavated through undisturbed ground. The earth load acting on the concrete pipe in such an installation is calculated in accordance with equation (4) of AS/NZS 3725:2007 which is shown in the equation below:
in which:
Wg is the working load due to fill in kN/m and shall not be less than 1.5wB2;
w is the unit weight of fill material in kN/m3;
B is the excavated width of tunnel;
Ct is the load coefficient for the trench condition;
c is the soil cohesion.
It should be noted that this equation is basically the equation for a pipe installed in a trench condition less an expression related to the soil cohesion above the pipe.
It should be noted that in addition to the earth loads acting on the pipe there are other significant loads acting on the pipe during installation as a result of the pipe jacking. PipeClass does not calculate these loads and users should refer to the Concrete Pipe Association of Australasia’s publications Concrete Pipe Jacking and Pipe Jacking Design Guidelines for additional information.
Due to the nature of the jacking forces the final strength requirements of the jacking pipe may be determined by a combination of external loads and jacking forces.
For all installation conditions other than for jacking pipes, PipeClass gives three options for the selection of soil type with default properties shown in the table below.
If these defaults are not suitable then “other” can be selected which requires the user to input the soil parameter values.
Density
The density is the density of the fill material above the pipe which should be obtained from actual measured values. PipeClass does give default values of density which the user should verify as being suitable prior to accepting. If the default density value is not suitable then “other” should be selected and then the density required can be input and then a suitable value of Kμ. will also need to be input.
Soil Parameter Kμ
The soil parameter Kμ has been adapted from Spangler and is the product of two soil parameters:
K = (1 – sinϕ)/(1 + sinϕ) and is the Rankine earth pressure coefficient;
μ = tanϕ, and is the coefficient of internal friction of fill material;
where ϕ is the angle of internal friction of the soil under consideration.
Spangler also used the term Kμ‘ where μ’ = tanϕ’ and is the coefficient of friction between the fill material and the sides of the trench. As such the term Kμ‘ should be used for trench installation conditions and Kμ for embankment type installations. Spangler stated that μ’ may be equal to or less than μ but could not be greater. PipeClass adopts Kμ = Kμ‘ and only displays a value of Kμ.
PipeClass includes a more comprehensive list of soil types if the jacking pipe installation condition is selected. The list of soil types corresponds to what is presented in AS/NZS 3725:2007 Table 3. Default values of the different soil parameters are shown in the table below however actual measured values should always be used especially the soil parameter c. To input a different value of density and K<sub>μ</sub> it is necessary to select “other” in the list of soil types.
The soil parameter c is the soil cohesion and actual measured values should always be used in the design. PipeClass recommends a maximum value of the soil cohesion of 5 kPa if actual design values have not been determined by testing.
The height of fill (H) is the height from the top of the pipe to either the natural ground surface or the top of the embankment. This value may be input directly or the user may prefer to input the depth to invert and PipeClass will then calculate the height of fill or vice versa.
Users should note that the depth of invert or the height of fill calculated is based on nominal wall thicknesses which are typical of pipes which are commercially available.
The position of the top of the pipe relative to the natural ground surface is an important parameter which significantly influences the earth loads acting on a pipe installed in either an embankment or induced trench condition.
POSITIVE PROJECTION EMBANKMENT CONDITION
For a positive projection embankment condition the projection height (h) is the height the top of the pipe extends above the natural ground surface level and the positive projection ratio (p = h/D) is the ratio of this height (h) divided by the pipe diameter (D). The maximum projection height allowed by PipeClass is limited by the support type selected. To allow compaction of the material in the support a trench must be dug into the natural ground equal to the total depth of the support selected. For example for an HS support type the support extends up to a height of 0.5D from the bottom of the pipe, as such for this support type the maximum allowed projection height (h) is 0.3D.
The minimum projection height is zero which is a special case which is on the generally referred to a zero positive projection and is the transition between the positive and negative projection embankment conditions. In this case the load acting on the pipe is equal to the weight of the column of earth above the pipe (prism load).
PipeClass will accept an input of either the projection height (h) or projection ratio (p) and will automatically calculate the other value.
NEGATIVE PROJECTION EMBANKMENT CONDITION
For a negative projection embankment condition the projection depth (h’) is the depth the top of the pipe extends below the natural ground surface level and the negative projection ratio (p’ = h’/B) is the ratio of this height (h’) divided by the trench width (B). PipeClass, like AS/NZS 3725:2007, only allows four values of the negative projection ratio p’ – allowable values are p’ = 0.5, 1.0, 1.5 and 2.0. If an intermediate value is input PipeClass will calculate the load based on the nearest lower value, eg. if p’=0.9 is input then the load will be calculated based on p’=0.5.
PipeClass will accept an input of either the projection depth (h’) or projection ratio (p’) and will automatically calculate the other value.
The support provided to the buried concrete pipe acts as both the foundation but also can significantly increase the load carrying capacity of the pipeline. The support types allowed by PipeClass, for all installation conditions other than jacking pipes, are those contained in AS/NZS 3725:2007. The usually granular support limits load effects (bending moments and shear forces) acting in the wall of the concrete pipe for a given application of external load. Associated with each support type is a numerical measure of this reduction or increase in load carrying capacity of a given pipe installation which is known as the bedding factor.
The bedding factor is in fact a ratio of the bending moment in the wall of the pipe which will be developed in factory three edge bearing test and the bending moment which will result in the field installation for a given value of external load applied. A schematic diagram of the two different loadings is shown below.
For more information on the factory test load refer to AS/NZS 4058:2007.
The bedding factors included in PipeClass for each support type are shown in the following table.
The reduced bedding factors can be selected when the grading limits required for the material in the haunch zones cannot be met.
A detailed description of each support type is contained in AS/NZS 3725:2007 Design for installation of buried concrete pipes. A brief description of each support type is given below.
Type U Support – Uncontrolled. In this type of support pipes are basically placed directly on the excavated foundation and then backfilled with no specific control of compaction. If there is a rock foundation then there is a minimum requirement for compacted material to be placed in the bed zone. This type of support is only recommended for minor pipelines where there are light loads and little or no live loads.
Type H1 & H2 Supports – Haunch Support. In these types of supports compacted granular material is placed in the bed and haunch zones to varying heights and compaction standards. The H2 support is recommended for most drainage pipe installations not under roadways.
Type HS1, HS2 & HS3 Supports – Haunch and Side Support. In these types of supports compacted granular fill is placed in the side zone in addition to the material placed in the haunch and side zones of the type H supports. The extent and compaction requirements of the different support types varies. The HS2 support type is recommended for most installations under a roadway and the HS3 support is recommended for high embankment fill situations.
Controlled Low Strength Material (CLSM) – Can be used as an alternative to mechanically compacted granular fill used in the haunch and side zones. Materials such as slurry fill, flowable fill, mortar, soil-cement slurry and non-shrink fill may all be suitable provided they are of suitable stiffness and stability. Refer to AS/NZS 3725:2007 for detailed information on CLSM’s.
The In Service Design Loads section is for specifying live loads that will be applied over the life of the pipeline such as those from regular vehicle traffic. These in service design loads are distinct from construction loads, which are those that are only applied during construction, for example, one or more specific construction vehicles.
PipeClass contains a number of options for including the effects of different in service design loads which may act on the buried concrete pipe.
The input of the different live loads has been grouped as:
- Road vehicle loads – these are basically standard road vehicle loads which are applicable to Australian and New Zealand conditions.
- Railway loads which are in use in Australia and New Zealand.
- Other vehicle loads which are from the Vehicle Library.
- Other loads which can include a uniform surcharge load, a point load, weight of internal water and an internal pressure load.
A particular live load will be included in the analysis if a tick appears in the column to the left of the live loads description. Click in this column to toggle the live load on and off.
Some live loads in each group have various properties that can be modified. When a live load with properties is selected the Properties button to the right of the group will be enabled.
Click the Properties button to view and modified the live loads properties.
Other vehicle loads are vehicles selected from the vehicle library. Use the Add and Remove buttons to edit the vehicles in the list.
AS/NZS 3725:2007 requires a minimum height of fill over the top of a pipe of 0.150 m and contains other requirements regarding the minimum height of fill when different live loads are applied. When considering applying live loads to a buried concrete pipe, PipeClass has certain limits on the minimum heights of fill over the top of the pipe at which the live loads are applied. These differ for different types of live loads:
For Standard Vehicle Loads the minimum height of fill PipeClass will allow is 0.15 m (in addition there are special requirements for the distribution of these loads below a height of fill of 0.4 m). A lower height of fill, however, down to 0.1 m can be selected as it is recognised that on occasions designers may wish to check loadings at these fill heights, although it is not recommended. If a height of fill (H) of less than 0.15 m is input the following message will appear.
The user has the option of selecting the AS/NZS 3725:2007 recommend minimum of 0.15 m or selecting the lower height of fill which in the example shown above is 0.1 m. In this case the designer must accept responsibility for the selection of this height of fill.
For Railway Loads, AS/NZS 3725:2007 requires a minimum height of fill over the top of the pipe of 1.0 m. PipeClass also adopts this minimum height of fill.
The minimum height of fill requirements for Other Vehicle Loads is the same for Standard Vehicle Loads.
- Vehicle footprint size
- Angle of load distribution
- Dynamic Load allowance
The basic concept of calculating live load effects in PipeClass follows the procedure as detailed in section 6.5 of AS/NZS 3725:2007. Once the loads are known the first step is to calculate the average intensity of live load (q) acting at the top of the pipe in accordance with equation (6) of AS/NZS 3725:2007 which is:
in which:
α = the dynamic load allowance;
ΣP = the sum of the wheel loads which act over the combined area, in kN;
A = the area of the overlapping footprints at the top of the pipe, L1 x L2, in m2.
For Australian and New Zealand road vehicle loadings (including W80, A160, M1600, HLP400, SM1600, HO, HN and 0.85HN vehicles) the value of q can be obtained from Tables B2 and B3 in Appendix B of AS/NZS 3725:2007 for depths of fill between 0.4m and 1.0m.
For the 300LA railway loading the value of q is obtained from Table B4 in Appendix B of AS/NZS 3725:2007.
Once the pressure at the top of the pipe has been calculated, this pressure is converted to a line load acting along the pipe, such that the working load due to live load (Wq) is calculated in accordance with equation (7) of AS/NZS 3725:2007 which is:
in which:
q is taken from AS/NZS 3725:2007;
L1 = length of the distributed load(s) acting along the length of the pipe, in m;
S = lesser of L2 and D (for 300LA railway load S is always = D);
Le = the effective length of pipe supporting the load, refer diagram below.
| Item | Live load classification | Dynamic Load Allowance (Alpha) | Reference |
| 1 | W80, A160 standard loads | Refer to table below | AS/NZS 3725 Supp 1:2007 |
| 2 | M1600 standard load | Refer to table below | AS/NZS 3725 Supp 1:2007 |
| 3 | HLP320, HLP400 | Alpha = 0.1 * | AS/NZS 3725 Supp 1:2007 |
| 4 | S1600 | Alpha = 0 ** | AS 5100.2 |
| 5 | 0.85HN, HN, HO standard loads | Alpha = 0.3 – 0.3H but not < 0 | Transit NZ Bridge Manual |
| 6 | Railway loading 300 LA | Alpha = (1.4 – 0.4(Max(H, 0.5))) / 3 but not < 0 | AREA Manual *** |
| 7 | Construction loads | As per items 1 to 5, but not > 1.1 **** |
| Standard Load | Height of fill (H) m | Alpha |
| W80, A160 | H = 0 | 0.4 |
| 0 < H < 2 | 0.4 – 0.15H | |
| H ≥ 2 | 0.1 | |
| M1600 | H = 0 | 0.3 |
| 0 < H < 2 | 0.3 – 0.1H | |
| H ≥ 2 | 0.1 |
Road vehicles are distributed at a ratio or “angle” of 0.725 : 1 as shown above.
Wheel loads applied over an area “a x b” at the surface are then applied over an area “(a + 1.45H) x (b + 1.45H)” at a depth H to determine the pressure acting at the top of the pipe. Where adjacent wheel loads, separated by a distance “G”, distributed areas as shown above overlap the sum of the two loads is applied over an area L1 x L2. Where the distributed areas of loads of any wheels or wheel group overlap the sum of all the loads are then applied over the combined overlapping areas. The sum of these loads x impact divided by this area is known as the live load pressure at the top of the pipe (q).
Railway loads are distributed at a ratio or “angle” of 0.5:1 as shown above. Rail axle loads are distributed from the underside of the sleeper from the ends of the sleeper in the direction perpendicular to the rail.
For M250 loading (and M220 and M250), AS/NZS 3725:2007 does not give any details of the distribution of rail loads in the direction of travel. As such for these loads PipeClass calculates the length L1 only for these loads and then calculates the load effect by taking the live load pressure at the top of the pipe (q) as that given in Table B4 of AS/NZS 3725:2007 and applies that pressure over an area L1 x the pipe outside diameter, D.
For the 300LA loading PipeClass distributes the rail axle load in the direction of travel from a length of 1m from the underside of the sleeper
(shown as dimension “a” above) to the top of the pipe in accordance with the 0.5:1 distribution. The axle load is then applied over an area L1 x L2 to calculate the live load pressure at the top of the pipe (q). Where these areas at the top of the pipe from adjacent axles intersect q is calculated as the sum of these axle loads x impact divided by the area of the combined overlapping areas
(Footprint shape at the top of pipe)
The shape of the distributed area or footprint at the top of the pipe is, for most vehicle loads, rectangular in shape with sides of length L1 and L2. For overlapping axle loads where axle widths are not constant the combined area of the overlapping rectangles will result in a non-rectangular combined area. In such instances PipeClass approximates this combined area into a single rectangular area with sides L1 x L2 with the same area (in m2) as the actual footprint.
AS/NZS 3725:2007 requires that to distribute road vehicle loads over an increasing area below the surface of the road a minimum height for heights of fill greater than 0.4 m is required. For heights of fill in the range 0.200 to 0.399 m, PipeClass allows the designer a choice of whether to distribute loads through the fill above the pipe or, as AS/NZS 3725:2007 requires, to apply live loads directly with no distribution, as is shown below.
However, please note that AS/NZS 3725 Supp 1:2007, Clause 6.5.3.2 states that – “Where authority referenced specifications are not mandatory, such as within private property, experience has generally shown that for earth covers between 0.2m and 0.4m, satisfactory performance can be achieved by a design using the same distribution assumptions as illustrated in figure 9 (“Distribution of wheel loads” in AS/NZS 3725:2007). In these circumstances the user is responsible for the design method adopted.”
If the “Do Not Distribute” option is selected the effective length of pipe supporting the load (Le) is still calculated as for the case with distribution as shown below.
This option applies to all Standard Vehicle Loads and Other Vehicle Loads
With an absolute minimum height of fill of 1.0 m for railway loads the selection of either “do not distribute” or “distribute” will have no effect on the final load effect calculation for railway loads as this option is only effective for heights of fill less than 0.4 m.
- W80 load – 80 kN load distributed over the tyre contact area (0.5 x 0.2 m)
- A160 load – an individual heavy axle load
- M1600 load – moving traffic load
- HLP400 load – heavy load platform vehicle
- 0.85 HN (Lightly Trafficked Rural) Loading · HN (Normal) Loading
- HO (Overweight) Loading
- All these loads also contain a lane loading of 3.5 kPa.
Railway loadings included in PipeClass are:
- M220 railway loading – this is the M250 railway loading with axle loads divided by 220/250.
- M250 railway loading – this is the railway loading which was originally contained in the Australia and New Zealand Railway Conference (ANZRC) Railway Bridge Design Manual (1974)
- M270 railway loading – this is the M250 railway loading with axle loads divided by 270/250.
- 300LA – this is the railway loading which is detailed in AS/NZS 3725:2007, with details being shown below.
Sleeper types included represent the common gauge widths occurring in Australasia.
PipeClass contains a number of options for including the effects of what has been termed “Other Loads” which may act on the buried concrete pipe.
There are four possible other loadings:
- Flexible Pavement – For flexible pavement in road construction. PipeClass will determine the equivalent height of fill for design purposes.
- Uniform Surcharge Loading – This type of uniformly distributed load may be result from loading from an earth stockpile, a large structure or floodwaters covering the area where a pipe is buried.
- Point Loading – This type of point load may result from loading from a foundation of a building or bridge abutment above where a pipe is buried.
- Internal Water Loading – this includes the loads applied to the buried concrete pipe due to the static weight of water flowing inside the pipeline.
The selection of a flexible pavement load is generally required during road construction.
PipeClass allows the user to select from the following typical pavement types: asphalt, concrete, granular or pavers. For each of these pavement types a default density figure is adopted and the user is expected to include the thickness of the pavement into the program (in metres).
The program will then include this load as extra height of fill. PipeClass will calculate the working load on the pipe due to the flexible pavement in accordance with clause 6.4 of AS/NZS 3725:2007 by applying it as an extra height of fill. The extra height of fill = (surcharge pressure kPa) / (soil density kN/m3) is added to the previously selected height of fill (H) on the Earth Loads input screen. AS/NZS 3725:2007 then states that the new total height of fill is to be substituted for H in the formulae for calculating the earth loads according to the installation condition that has been selected – i.e. trench condition, positive projection embankment condition etc. It should be noted that the displayed height of fill (H) does not change to include the flexible pavement. The working load due to the application of the flexible pavement as an equivalent height of fill is included as a dead load and is included in the calculation of the earth load (Wg).
Rigid pavement design requires a more detailed calculation and is not considered in AS/NZS 3725:2007 or this program.
This type of uniformly distributed load may occur for a variety of reasons including, but not limited to, loading from an earth stockpile, a large structure or floodwaters covering the area where a pipe is buried.
PipeClass allows the user to include the load effects from a uniformly distributed load which may be applied to the ground above the buried concrete pipe. This is input as a surcharge pressure in kPa. PipeClass allows the user to decide as to how this load should be applied. The surcharge could be applied as:
Extra height of fill – if this option is selected PipeClass will calculate the working load on the pipe due to the surcharge loading in accordance with clause 6.4 of AS/NZS 3725:2007 by applying it as an extra height of fill. The extra height of fill = (surcharge pressure kPa) / (soil density kN/m3) is added to the previously selected height of fill (H) on the Earth Loads input screen. AS/NZS 3725:2007 then states that the new total height of fill is to be substituted for H in the formulae for calculating the earth loads according to the installation condition that has been selected – i.e. trench condition, positive projection embankment condition etc. It should be noted that the displayed height of fill (H) does not change to include the surcharge loading. The working load due to the application of the surcharge loading as an equivalent height of fill is included as a dead load and is included in the calculation of the earth load (Wg). This option should be selected when the settlement effects and internal frictional forces described in for each of the different installation conditions are also applicable to the surcharge loading. If this is not the case then it is probably more appropriate to apply the surcharge loading directly.
Direct Load – if this option is selected PipeClass will apply the surcharge pressure directly to the top of the pipe. The working load due to this surcharge is calculated as a dead load in addition to the earth load (Wg), with Wg then being calculated in accordance with the expression:
Wg = Earth Load + (Surcharge pressure x D) in which:
D = pipe external diameter (m);
Wg is the working load due to surcharge pressure in kN/m.
This type of point load may result from loading from a foundation of a building or bridge abutment above where a pipe is buried. PipeClass allows the user to include the load effects from a user defined point load which may be applied to the ground above the buried concrete pipe. This is input as a point load applied over a rectangular area with dimensions A x B. This load is distributed in the same manner as a vehicle load as shown below.
A user defined point load would usually be applied as a dead load, however, PipeClass does allow the user to apply such a load as a live load (e.g. a footprint of a support foot of a crane may be considered as a live load) and as such the user then has the option of including an appropriate impact factor. As with the calculation of live loads the load effects are first calculated by determining the pressure at the top of the pipe (q) in kPa in accordance with the equation:
in which:
α= the impact factor (for a dead load impact = 1.0);
P = the value of the user defined point load, in kN;
A = the area of the overlapping footprints at the top of the pipe, L1 x L2, in m2.
Then PipeClass will then calculate the load effects of this point load either as an additional component of the earth load (Wg) or as a live load (Wq) in accordance with either :
for a live load, or
if the point load is applied as a dead load.
AS/NZS 3725:2007 states that the “vertical water load on pipes due to the mass of water carried by the pipe may be disregarded for pipes less than 1800 mm in diameter but should be considered for larger diameter pipes.”
PipeClass will include or exclude the weight of internal water loading by default as follows:
- For pipe diameters 1800 mm and less the weight of internal water load is NOT selected by default,
- For pipe diameters > 1800 mm the weight of internal water load is selected by default, and if users do not wish to include this load in the calculation it can be deselected in this input screen.
The weight of internal water load (Ww) is calculated in accordance with the following equation:
in which:
ID = the internal diameter of the pipeline.
The value of the internal diameter is not displayed by the program and is selected from values of typical internal diameters of commercially available pipes contained in the program.
AS/NZS 3725:2007 requires that for pipes where the internal test pressure is greater than or equal to 50 kPa that the value of the test load for reinforced concrete pipes shall be calculated from the equation:
which is equation (10) in AS/NZS 3725:2007 in which:
Pt = the hydrostatic test pressure (which concrete pipes are tested to in the factory);
Pw = the internal working pressure of the pipeline including allowance for hammer and other dynamic effects; and 1.2 Pw ≤ Pt ≤ 2.4 Pw.
Internal pressure loading is only available when the pressure pipe application has been selected. To allow PipeClass to assist users in the selection of appropriate design values of Pt and Pw the user is required to select the appropriate type of pipeline – select either Gravity or Pumped pipeline as appropriate.
As it is necessary for Pw to include all dynamic effects then PipeClass gives the user two options:
- Pw Excludes Dynamic Effects – in other words no detailed water hammer study has been carried out and as such the user probably only knows the maximum working pressure under constant or steady state operating conditions. To assist users in making a suitable allowance for dynamic effects the CPAA recommends the following “rule of thumb” design rules for minor pipelines:
- for gravity pipelines select Pt = 1.25 x Pw or Pw + 150 kPa, whichever is greater.
- for pumped pipelines select Pt = 1.5 x Pw or Pw + 150 kPa, whichever is greater. PipeClass uses these rules to calculate and appropriate value of Pt.
- Pw Includes Dynamic Effects – in other words a detailed water hammer has been carried out and the design value of Pw already includes an allowance for dynamic effects. In this case for all values of Pw entered PipeClass will display a default value of Pt equal to the minimum allowed value of 1.2 x Pw for both gravity and pressure pipelines.
Legal values of Pt – PipeClass allows the user to alter the value of the test pressure Pt to any value allowed by AS/NZS 3725:2007 (i.e. 1.2 Pw ≤ Pt ≤ 2.4 Pw), however, various warnings may be displayed if the user selects a value which exceeds a recommend maximum value or selects a value which exceeds the maximum allowable test pressure of greater than 2.4 Pw.
PipeClass will check to see if the selected value of the test pressure (Pt) may exceed certain recommended values. The recommended maximum test pressures are intended to represent a minimum value of test pressure which are generally commercially available from member companies of the CPAA who supply reinforced concrete pressure pipes. These recommended maximum test pressures vary with pipe diameter and are shown in the table below:
If a value of test pressure exceeding these values is selected then the following warning message will appear.
This gives the user the options of using the higher value in the design after the local CPAA member company has confirmed that reinforced concrete pressure pipes with this test pressure are commercially available. The other option available to the designer is to simply select the maximum recommended value of the test pressure. If this is selected then PipeClass will then include an appropriate adjusted value of the working pressure Pw.
Needs amendment
The Construction Loads section is for specifying live loads that will only be applied during construction, for example, one or more specific construction vehicles. These construction loads are distinct from in service design loads, which are those applied over the life of the pipeline such as those from regular vehicle traffic.
The selection of construction loads are intended to allow the designer to include loading from compaction equipment and other construction equipment such as dump trucks, scrapers, rollers, etc, which may be applied to the pipe during installation of the pipeline. Such loads can and are intended to be applied at fill heights lower than the height of fill or height to top of rail, H, and are not intended to be permanent design loads. Construction loads are vehicles selected from the vehicle library. Use the Add and edit the vehicles in the list.
A particular construction load will be included in the analysis if a tick appears in the column to the left of the construction loads description. Click in this column to toggle the live load on and off.
A unique feature of PipeClass is the graphical representation of the effect of construction loads. This feature provides the designer with the direct means of seeing at what point the construction load exceeds the design proof load. To access this feature select a construction load and then click on the Graph button to the left of the list of loads.
Interpreting the Construction Load Graph
| Green line | The earth load as it varies with fill depth. |
Blue line | The construction load as it varies with fill depth. |
| Purple line | The combined earth and construction loads as they vary with fill depth. |
| Red line | The proof load for the pipe load class. |
| Black line | The design fill height. |
| Green shaded area | The fill depth range where the construction load can be applied using the current pipe design. Lack of a green shaded area means there is no fill height at which the chosen construction load can be |
| safely applied. | |
| Yellow shaded area | The fill depth range where problems may occur during construction as it is very close to the proof load for the pipe load class. Use extreme caution when applying construction loads at this depth of fill. |
| Red shaded area | The fill depth at which the construction load cannot be used. |
The x-axis range input field to the bottom of the graph allows variation of the right hand x-axis limit between 1 to 50 metres in various steps.
As with in service design loads, construction loads in at heights less than 0.4m can be distributed or not distributed. For more information on this option see the discussion for in service design loads.
The design can be adjusted by:
- Increasing the bedding factor by increasing the support type; · Increasing the pipe load class; · Both of the above.
The right hand screen segment provides a concise summation of the pipe design and includes material quantities for the installation. Also shown is a diagram of the installation quantities.
Clicking on the Details button at the bottom of the page will open the Load Calculation Details window.
Clicking on the Print button at the bottom of the page will allow the user the option to print the Pipe Load Summary, the Pipe Installation and Quantities, a Detailed Load Report, the Installation Specification and the Construction Load Graphs.
Clicking on the Export button at the top of the left hand screen segment will allow the user to print the details of the design.
The installation quantities show the height of each zone and the volume of each zone. The bulking factor used to convert the solid or compacted volume to a loose volume is input on the Other tab of the “Project Details and Global Settings” window. Whilst default values for the bulking factor are included users should input values applicable to the particular materials being used.
Material specification details are shown on the “Pipe Installation and Quantities Sheet” printed report and refer to grading details contained in AS/NZS 3725:2007.
The trench width (B) is an important design parameter with the definition varying slightly for different installation conditions which are detailed below.
The trench width calculated by PipeClass is the minimum recommended by AS/NZS 3725:2007. However, in many instances a wider trench is required to ensure that installation can be carried out appropriately. This is particularly the case for HS bedding requirements. A wider trench can be designed for by overriding the default minimum calculated by the program. Note that the minimum required clearance between the trench wall and the socket (50mm) may, for some socketed pipe diameters, result in a larger value for the minimum trench width than recommended by AS/NZS 3725:2007. The default trench width (B) is based on the pipe OD (D) and minimum horizontal distance at the spring line of the pipe and the trench wall (lc as given in Figure 4 of AS/NZS 3725: 2007. The designer should verify whether this trench width is appropriate for the installation type being considered and the likely excavation equipment being used. Note: Increased trench width results in higher working loads (Wg) acting on the pipe |
BARRELS
The number of barrels, sometimes called cells, is the number of individual pipes laid side by side for a particular application. It is important that the correct selection is made here as it will affect both the calculation of the earth loads acting on the pipe and the quantities. Particular attention should be paid to the barrel spacing.
Barrel spacing is the clear distance the outside of the barrel of the pipeline – note that the spacing between the outside of adjacent sockets (socket spacing) will be less.
For multiple barrels it is necessary to include a value of the barrel spacing (Ic). The default values for the barrel spacing are taken from Figure 4 of AS/NZS 3725:2007. For compacted fill, it is:
The minimum spacing between adjacent pipe sockets, for socketed pipes, is 50mm. If a value of spacing less than the default value is input a warning will be displayed.
To achieve compaction between such pipes normal mechanical compaction methods may not be suitable and as such the use of alternative methods of compaction may be required such as:
- Flooding of a sand backfill (note provision for water to escape is required)
- Placement of a single sized aggregate such as a concrete aggregate with suitable tamping (note in some native soil conditions the use of a geotextile will be required)
- Placement of a self compacting slurry or cement stabilised fill.
- Or some other suitable means which does not require mechanical compaction techniques.
Note that the minimum required spacing between adjacent pipe sockets may, for some socketed pipe diameters, result in a larger default value for the barrel spacing (Ic) than recommended by AS/NZS 3725:2007.
AS/NZS 3725:2007 Clause 6.3.3.3 Multiple Pipe Conditions states, “Where two or more pipes are laid side by side in a single trench or embankment the working load per pipe due to fill (Wg) is calculated as for the embankment condition using equation 2 (formula for positive projection condition).”
PIPE ORIENTATION
The pipe orientation refers to the location of the pipeline relative to the direction of the traffic flow as shown below. The significance of this input governs how traffic loads are applied to the buried concrete pipe.
If Perpendicular is selected the vehicle loads (road or rail) are applied in one orientation only with the width of the live load applied along the length of the pipe only (for road vehicle width would refer to the distributed width of the tyre contact area at the top of the pipe)
If Longitudinal is selected the vehicle loads (road or rail) are applied in one orientation only with the length of the live load in the direction of travel applied along the length of the pipe only (for road vehicle width would refer to the distributed length of the tyre contact area at the top of the pipe.
If the pipe is skewed to the direction of traffic flow or the direction is unknown then the both or skew option must be selected.
For skewed orientations, this program calculates the worst case of transverse and longitudinal orientations. In isolated cases skews (usually between 40 – 60 °) will induce a moderate increase, above this, in the working live load. It is recommended that this influence be confirmed independently for these skews when reserve capacity is low.
A new feature introduced in PipeClass 3 is the visibility of the design outputs on the right hand screen segment.
The detailed design is accessed in two ways:
- clicking on the Calculation Details button on the right screen segment. This will open a pop up where design parameters and results details are visible.
- clicking on the Print Options button, choosing Detailed Load Report, and printing the report.
The Calculations Details pop up has tabs for each design component of earth and live loads included in the design.
Designing for pressure pipe is catered for in PipeClass3.
If the application is a pressure pipe, the value of Tcp (the maximum permissible proof load for a pressure pipe) is determined in accordance with AS/NZS 3725.
The pipe application is chosen as “pressure” with the joint type defaulting to rubber ring joint.
The type of pressure pipe, either gravity of pumped is chosen in the Other Loads section.
Clicking on the check box to the right of the load description allows the user to edit the properties of the working pressure and the test pressure.
The settlement ratio is a ratio of the various settlements which occur with buried concrete pipes installed in either positive projection condition or negative projection condition installations – a detailed definition can be found in AS/NZS 3725 Supp 1:2007.
As in AS/NZS 3725:2007 the ratio is not calculated but is an input which varies with the foundation the concrete pipe is installed on. A yielding (earth) foundation will result in different relative settlements than an unyielding (rock) foundation which in turn will influence the load acting on the concrete pipe.
PipeClass allows values of the settlement ratio which are contained in AS/NZS 3725:2007 which is a limited range of values suggested by Spangler.
The settlement ratios allowed by PipeClass are shown below
which occur with buried concrete pipes installed in either positive projection condition or negative projection condition installations – a detailed definition can be found in AS/NZS 3725 Supp 1:2007. As in AS/NZS 3725:2007 the ratio is not calculated but is an input which varies with the foundation the concrete pipe is installed on. A yielding (earth) foundation will result in different relative settlements than an unyielding (rock) foundation which in turn will influence the load acting on the concrete pipe.
