PipeClass has recently been updated to an online application negating the need for downloading an executable file. The revised application is PIPECLASS3.
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. Details of the calculations and calculated values can be checked at any time by clicking on the calculation details button. 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 Print function is used to view and print detailed design criteria, results and sample installation specifications.
Print options are detailed below:
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.
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.
The joint type selection options are:
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.
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:
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).”
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:
These installation conditions are shown in the diagram above.
Other special types of installation conditions are:
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.
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.
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).
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:
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 parameter (apparent soil cohesion) with values given in Table 3 of AS/NZS 3725: 2007”
.
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.
The minimum design load (Wg) for jacking pipe is based on the soil parameter © of zero (effectively ignoring soil arching effects), and a value of Ct = 1.5 ensures that the resultant load class for jacking pipe is necessarily conservative.
It should be noted that in addition to the earth loads acting on the pipe there are other significant (jacking) 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 allows the user to input the project specific 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.
The density is the density of the fill material above the pipe which should be obtained from actual measured values. PipeClass provides 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 the required density and appropriate value of Kμ entered.
The height of fill (H) is the height from the top of the pipe to either the natural ground surface (or underside of sleeper) 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.
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. PipeClass3 also adopts this minimum height of fill.
The minimum height of fill requirements for Other Vehicle Loads is the same for Standard Vehicle Loads.
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 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.
Standard vehicle loads are provided for Australian Road Vehicles in accordance with vehicle configurations from AS5100:2017
and New Zealand Road Vehicles in accordance with NZ Transit Authority Bridge Manual:
The 0.85 HN and HN loads include the option of applying the 1.35 SLS load factor
The input of the different live loads has been grouped as:
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. AS 5100 and Waka Kotahi Dynamic Load allowance is applied when determining the average intensity of live load at the top of the pipe. 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 modify the live loads properties.
Other vehicle loads are vehicles selected from the vehicle library. Use the Add, Remove and properties buttons to edit the vehicles in the list
AS/NZS3725 and AS5100.2:2017 vary in the manner with which live loads are treated. AS/NZ3725 methodology was developed with pipe structures in particular which are somewhat smaller in scale than bridges and also installed underground with distribution always through fill.
PipeClass 3 provides the designer with the option of utilising AS/NZS3725 or AS5100 as the basis for treatment of live loads.
The differences in live load calculations between AS/NZS3725 and AS5100 can be summarised as:
A table summarising the differences can be found in the section AS3725 vs AS5100 load and load distribution topic.
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.
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.
The pipe design resulting from the long term loads (in service design loads) can be reviewed on the right hand side of the screen. The controlling loads are the specific combination of selected loads which results in the maximum loading on the pipe. The minimum test load is the actual load resulting from the controlling loads.
The minimum test load for drainage and sewerage pipes (Tc) is defined in section 10.2 of AS/NZS 3725:2007 and is a working load corresponding to a particular value of a factory test load which is carried out by the reinforced concrete pipe manufacturer.
The minimum test load for pressure pipes (Tcp) is defined in section 10.4 of AS/NZS 3725:2007 and is slightly different to the test load for drainage pipes as it is increases by an additional factor to account for the combined loading from external loads and internal water pressure which the pipe will experience.
Also shown is the pipe load class that has been selected as defined in AS/NZS 4058:2007, the proof load corresponding to that load class and the reserve capacity which the calculated working loads on the pipe would result in. PipeClass will automatically select the lowest load class of pipe which will support the design loads.
The standard Australian and New Zealand road vehicle loadings in PipeClass are taken from AS/NZS 3725:2007:
Australian Road Vehicles
The relevant wheel loading arrangements from AS 5100.2 are used in AS/NZS 3725:2007 and adapted to suit buried concrete structures. These include:
New Zealand Road Vehicles
The relevant standard wheel loading arrangements include the vehicles appropriate to the HN-HO-72 traffic loading contained in the Transit New Zealand “Bridge Manual” and specifically includes the following vehicle loadings:
Under Australian loading conditions, the SM1600 model traffic design load is generally utilised for major arterial roads. The SM1600 load case may, in some cases, be in excess of the intended application of the pipe structure. Please check whether or not this selection is applicable to your design before specifying.
Tip – Details of all these vehicles can be viewed by accessing these vehicles in the vehicle library.
Vehicles passing – PipeClass can consider the combined load effects associated with two vehicles placed in adjacent traffic lanes with the appropriate lane width. This option is only relevant to the S1600 stationary traffic load, M1600 moving traffic load and the New Zealand HN (Normal) Loading.
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
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.
(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 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.
In calculating the average intensity of live load acting on the pipe it is necessary to include the appropriate dynamic load allowance. PipeClass generally uses an assigned dynamic load allowance which is allocated to a particular type of equipment or loading – the assigned dynamic load allowance is shown in items 1 to 6 in the table below. This dynamic load allowance is used when the particular type of equipment or loading is selected as either a Standard Vehicle Load, a Railway Load or as an Other Vehicle Load.
When a particular type of equipment or loading, however, is selected as a Construction Load the dynamic load allowance is limited to a maximum of 1.1, as shown as item 7 in the table below.
SUMMARY OF DYNAMIC LOAD ALLOWANCE FIGURES TO DETERMINE THE IMPACT FACTORS USED BY PIPECLASS
| 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 | Waka Kotahi – NZ Transport Agency Bridge Manual SP/M/)022 – Third Edition |
| 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 **** |
* The dynamic load allowance of 0.1 is applied at all heights of fill.
** The dynamic load allowance of 0.0 is applied at all heights of fill.
*** AS 5100.2 does not provide guidance on a suitable dynamic load allowance for railway loads distributed through fill. This has therefore been calculated in accordance with the American Railway Engineering Association (1997), “AREA Manual For Railway Engineering – Part 10.
**** For equipment where the assigned dynamic load allowance is 0.0, this figure is adopted. (It is common practice to include dynamic effects in vibratory compaction equipment in the total static load and as such an allowance of 0.0 is defined for this type of equipment.)
DYNAMIC LOAD ALLOWANCE (ALPHA) TO DETERMINE IMPACT FACTORS FOR AS/NZS 3725:2007 STANDARD LOADS (From AS/NZS 3725 Supp 1:2007)
| 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 |
The following table summarises the different requirements relative to loads and load distribution.
Railway loadings included in PipeClass are:
Sleeper types included represent the common gauge widths occurring in Australasia.
PipeClass can consider the combined load effects of a dual track situation with the user specifying the track spacing.
Other Vehicle Loads are vehicles or equipment which may be permanent design loads which are not included in the Standard Vehicle Loads. Such loads may include a mining truck on a mine haul road, a new design vehicle nominated by a State Road Authority such as the T54 truck load from the TfNSW or a special vehicle which the user wishes to design for. All vehicles are selected from the Vehicle Library. All Other
Vehicle Loads are applied at the final height of fill, H with an impact factor in accordance with the defined impact for that vehicle or item of equipment.
Vehicles that are not in the built in library can be added by users.
Vehicles can be added as a In Service Other Vehicle
or as a construction load.
To add a vehicle select the Add new vehicle button.
Add the vehicle name, description and axle configurations and loads.
Choose an appropriate vehicle category so it is listed if future searches for this type of vehicle.
Choose the method of distribution from the drop down list.
Choose the impact factor method to be applied. The user can define the impact factor specific to the vehicle or project by choosing Other from the drop down list. If Other is chosen, a further input of the value for impact appears and needs to be input.
The vehicle configuration is edited by adding axles and wheels, using the add buttons.
Selecting the three dots button 
on the axle section provides a drop down
Selecting the properties button adds a screen for adding the axle properties where the axle spacing and load is input.
To duplicate an axle, simply use copy from the drop down on the three dots button
The default shows a wheel configuration that can be edited. To add another set of wheels, simply select add.
To edit wheel loads and dimensions, select the three dots button and select Properties to add the wheel width, length and spacing.
To copy a set of wheels, select copy from the three dots dropdown.
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:
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:
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:
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.
The Construction Loads section is for specifying live loads that will only be applied during construction, for example, one or more specific construction vehicles. Construction loads can differ from in service loads win that construction loads are only applied during the construction phase and, importantly, can be applied at fill heights less than the nominated design height of fill. This section allows the user to quickly determine what the minimum amount of fill is required to support a range of construction loads that may be present on a project site.
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.
| 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.
PipeClass assume impact from construction equipment is minimised by speed and appropriate height of fill prior to application of load. The default value for the impact factor for construction loads in PipeClass is 1.1, however the user can edit the impact factor for any vehicle by editing the properties.
In the event that the chosen construction load cannot be used at any fill height or the range of fill heights is unacceptable to proposed construction methods, PipeClass provides the ability to change the base design to cater specifically for the construction load condition.
The design can be adjusted by:
How the adjustment affects the design can be seen immediately by any change in the allowable fill range for the construction loads.
Another option for mitigating high construction loads would be to locally increase the fill above a pipe to satisfy the construction load. i.e locally mound up over the pipe.
IMPORTANT – default impact values used for vehicles of equipment selected as a construction load can differ in PipeClass from impact factors for in service loads. Users should check impact factors attributable to site specific construction vehicle operation.
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 Soil Properties area.
Whilst default values for the bulking factor are included users should input values applicable to the particular materials being used. Use the Bulking Factors button to open and edit the values for soil appropriate to the project.
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 |
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:
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).”
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:
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.
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 M270), 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.
New Zealand Traffic Loads, HN-HO-72 and 0.85HN are defined in Waka Kotahi NZ Transport Agency Bridge manual (SP/M/022) Third edition. HN-HO-72 is intended for highway and main road bridges and other buried structures (including precast concrete pipe culvert).
Appendix D of the Bridge manual defines 0.85HN which is intended to apply to bridges and culverts in other roads with lower traffic volumes and speed limits.
HN (normal) Loading.
The HN Normal loading consists of two parts:
Wheel contact area is 500mm x 200mm with a wheel spacing of 1800mm on each axle.
HO (overload) Loading
The HO loading consists of two parts:
Wheel contact area is 3000mm x 200mm, or 900mm x 600mm. The wheel contact area used in PipeClass 3 is 3000mm x 200mm as this generally generates the highest loads.
0.85 HN loading
The 0.85 HN Loading consists of two parts:
Wheel contact area is 500mm x 200mm with a wheel spacing of 1800mm on each axle.
Serviceability Limit State (SLS) Load Factor
The NZTA Bridge Manual (SP/M/022) Third edition requires a serviceability limit state (SLS) load factor of 1.35 to be applied to HN & 0.85HN for ‘Major Culverts’ (those with a cross section greater than 3.4m2, equivalent to a pipe diameter ≥2 100 mm).
This requirement has also been adopted by NZTA for minor culverts on the State Highway Network.
The 1.35 SLS factor was not included in AS/NZS 3725: 2007 as this was not known at the time of publication.
PIPECLASS3 provides designers with options for 0.85HN & HN vehicles with & without 1.35 SLS factor.
Adopting the 1.0 SLS factor with HN for culverts/structures not on a State Highway (or other major roads) should be based on Council specifications or a site-specific assessment.
Dual Lane
PipeClass 3 allows the consideration of HN (normal) Loads on two adjacent load lanes of equal width where the width of the carriage way exceeds 6 m. To allow for the improbability of concurrent loading a 0.9 reduction factor is applied to the total normal live loading (refer to 3.2.4 in the Bridge Manual).
In practice the dual lane effects only marginally increase the live load pressures acting at the top of pipe once the depth exceeds 0.75 m. This option has been included for Designers to consider if necessary
