The HB vehicle consists of four axles with four wheels on each axle and is applied to the grillage as a series of point loads. Clause 6.3.2 and 6.3.3 allow the wheel loads to be applied as patch loads however there is little to be gained in a global analysis by applying this refinement and point loads will be a suitable representation for the wheel loads.

There are five variations of the inner axle spacing for the HB vehicle that can be applied to the deck. A line beam analysis incorporating moving point loads will indicate the positions of the critical HB vehicle to achieve the design moments and shears. An Excel spread sheet using moment distribution to carry out a line beam analysis of standard moving vehicles can be downloaded by clicking here.

All critical load cases are produced from the vehicle with the 6m inner axle spacing.
As the loading is symmetrical and both ends of the single span deck are simply supported then the position of maximum moment can be measured from either end of the deck.

The transverse position of the HB vehicle will depend on which member is being considered, however it is usual to design all internal beams for the critical loading condition for vehicles on the carriageway. The edge beams will require special consideration to support the additional loading from the cantilever.

This would produce the critical loading condition for the bending moment on the internal beam for an orthoganal deck, however other positions need to be considered to take account of the skew effects.
As a check on the data, the total of the reactions should equal the total load of the vehicle = 4 x 450 = 1800kN. Also the line beam analysis gives a total moment of 5692.5kNm; so as there are four longitudinal members supporting the vehicle, then the moment from the grillage should be in the order of (but less than) 5692.5 / 4 ≈ 1400kNm in the longitudinal member.

Clause 6.5.1 states that the pedestrian live load shall be taken as 5.0 kN/m², but reduced to 0.8 x 5.0 = 4.0kN/m² for members supporting both footway and carriageway loading. Consequently the edge beam should be designed for 5.0kN/m² and the next-to-edge beam designed for 4.0kN/m². The UDL's can be applied to these two members in a similar manner to the HA UDL described above, however, as there is no barrier between the carriageway and footway, Clause 6.6 requires that the footway members are designed for Accidental Wheel Load which is generally more onerous than the pedestrian live load.

Accidental Wheel Loading consists of a 200kN axle and a 150kN axle with two wheels on each axle and is applied to the grillage as four point loads. Clause 6.6.2 and 6.6.3 allow the wheel loads to be applied as patch loads however there is little to be gained in a global analysis by applying this refinement and point loads will be a suitable representation for the wheel loads.

Similarly as with the HB vehicle a line beam analysis incorporating moving point loads will indicate the critical positions of the vehicle to achieve the design moments and shears. An Excel spread sheet using moment distribution to carry out a line beam analysis of standard moving vehicles can be downloaded by clicking here. The Abnormal Load facility is used in the line beam proforma to input the accidental wheel vehicle.
 

The vehicle will be positioned over the parapet beam as shown to obtain the critical loading condition for bending in this member. This may also be the critical position for the design moment in the main edge beam, however the 100kN wheel should be positioned at joint B to confirm the critical case.

Other positions on adjacent transverse members need to be considered to take account of the skew effects.

As a check on the data, the total of the reactions should equal the total load of the vehicle = 200 + 150 = 350kN. Also the line beam analysis gives a total moment of 1657.5kNm; so as there are two longitudinal members supporting the vehicle, then the moment from the grillage should be in the order of (but less than) 1657.5 / 2 ≈ 800kNm in the longitudinal member.

Loads due to collision with parapets need only be considered in a grillage analysis if high level containment parapets (H4a) are required. Collision loads on other types of parapet need only be considered for local effects (how the load is transferred to the main members).

Clause 6.7.2.1 describes the three loads that are to be applied to the top of the parapet over a 3.0m length.
The point loads need to be transferred down to the datum level of the grillage, which is at the centroid of the deck slab, and distributed over a 3.0m length.
The high containment parapet is 1.5m high above the back of footpath level. The centroid of the deck slab is about 0.3m below the back of footpath level, consequently the two horizontal loads will induce moments on the grillage with a lever arm of 1.8m.

The 500kN horizontal load will produce a moment of 900kNm at the centre-line of the deck. This moment is distributed along a 3.0m length giving 300kNm/m moment to be applied to the grillage.

 
The horizontal load of 167kN/m will be taken into the deck which, as it is very stiff axially compared to bending, will distribute evenly between all longitudinal members and therefore have negligible effect in the grillage. The load is however considered in determining local effects in accordance with Clause 6.7.1.

The 175kN vertical load can be idealised as a uniformly distributed load 58kN/m along a 3.0m length of the parapet beam.

The 100kN horizontal load acts in the plane of the parapet and there is an argument that the load will be resisted by the framing effect of the parapet rails with the posts and will therefore be transferred to the deck as a series of horizontal and vertical loads at the base of the posts.

As the loads are to be applied over a 3.0m length then the moment of 100kN x (1.5 + 0.3) = 180kNm can be represented by a vertical couple of 60kN x 3.0m.
The horizontal load of 100kN will be taken into the deck which, as it is very stiff axially compared to bending, will distribute evenly between all longitudinal members and therefore have negligible effect in the grillage. The load is however considered in determining local effects in accordance with Clause 6.7.1.

The three loads can be combined in one load case.

The 3.0m length can be positioned anywhere along the parapet beam and positions are generally chosen to coincide with the critical positions for the accidental wheel load.