New Zealand Bridge Loading

Question:

I am using Midas Civil and am hoping you can provide some guidance on the best way to apply the New Zealand Bridge Live Load model (NZ Bridge Manual). I have heard in one of the guidance videos that it was possible but have not managed to find guidance on this.


Answer:

Hi,

First of all, New Zealand bridge loading is not supported in midas Civil. I checked the possibility of using user-defined vehicles. Here is my recommendation but you will decide whether to go with this or not.

1. Select AASHTO Standard.
 

2. Define vehicle loads.

 - HN load

- HO load

In midas Civil, wheel loads are always loaded as a concentrated load. The contact area is not taken into account. The wheel spacing in the transverse direction will be defined when we define Traffic Line Lane.

3. Define dynamic load factor and Traffic Line Lane
- Dynamic load factor
For example, dynamic load factor = 1.2 for moment, 1.3 for reaction and shear. We need to define two separate lanes one for moment and one for reaction & shear because of different dynamic load factors.

-Transverse wheel spacing
HN: 1.8m, Ho: 2.1m. In midas Civil, we cannot define different wheel spacing by vehicle. Instead, we can define it by traffic line lane. You can choose between the following two methods.
1) Apply the same wheel spacing to all the lanes, e.g. 1.8m.
2) Create two pairs of lanes (one for 1.8m, one for 2.1m) at the same place. When you define Moving Load Case, you need to select an appropriate lane for various cases. I will explain it in details later in this reply. For example, the total number of notional lanes on the bridge is two.
For HN, we define two lanes for each notional lane, one for moment and one form reaction & shear.
    

For HO, we do the same process with the wheel spacing of 2.1 m.
     

4. Define Moving Load Case.
- Reduction Factor
You can see Multiple Presence Factor in the moving load case. According to AASHTO Standard, this factor is determined based on the number of loaded lanes. This is the case when only HN load is applied. But, this Multiple Presence Factor cannot cover the case when overload HO is present, So, we enter 1.0 here.

Next, we define two moving load cases.
   - Moment a:
   Lane 1-HO-Moment: HO, Lane 2-HN-Moment: HN
   - Moment b:
   Lane 1-HN-Moment: HN, Lane 2-HO-Moment: HO

Select Combine for the Loading Effect option.
 

In the same way, we define moving load cases for shear.

5. Define Load Combination with the Envelope type for moment and shear as shown below.

6. Check the results.


I have attached the model file here.

Regards,
DK Lee









Creation date: 11/13/2018 1:58 AM (dklee@midasit.com)      Updated: 11/13/2018 12:30 PM (dklee@midasit.com)
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Tut 4 Arch Bridge - New Zealand.mcb