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Bridge loading analysis specification

As discussed in the References entry on bridge loading, there are three different ways of using the tools available for bridge loading. This specification dialogue is used to distinguish between these methods and set up the parameters for the first method.

Note: As the number of analysis cases in the bridge analysis task depends on the bridge specification, the editing of bridge analysis specification will be disabled if there is a bridge analysis task. The bridge analysis task must be deleted to allow the specification to be edited.

Bridge design loading code​

Unless working on constant width carriageways, with one of the codes listed below, the code must be set to Undefined”, and individual lane paths defined. Otherwise, the user can select the appropriate code from the options below:

  • UK_BD37 (old) – For HA and HB loading to the United Kingdom Design Manual for Roads and Bridges.
  • EC1 UK – Eurocode loading as implemented by UK National Annex (NA) covering LM1 and LM3
  • EC1 LM1 – Generic Eurocode loading covering LM1 only
  • HK_SDM (old) – For HA and HB loading to the Hong Kong Structures Design Manual.
  • AUS_AS5100-2 – Australian loading to AS5100-2
  • US AASHTO 17 – USA loading to AASHTO 17th edition
  • UK_BD21_HB – For HA to BD21 and HB to BD37
  • US-LRFD-3 – USA loading to LRFD 3rd edition
  • UK_BD86_SV-TT – For HA to BD21 and SV-TT to BD86
  • UK_BD86_SV-Train – For HA to BD21 and SV-Train to BD86
  • UK_BD86_SV-150 – For HA to BD21 and SV-150 to BD86
  • UK_BD86_SV-100 – For HA to BD21 and SV-100 to BD86
  • UK_BD86_SV-80 – For HA to BD21 and SV-80 to BD86
  • UK_CS454_HB – For HA to CS454 and HB to BD37

Using these options where possible makes the most efficient use of the tools available for bridge loading in GSA. Where a newer version of the loading code than the one listed above has been adopted, the user will need to compare the standards to decide if the changes will make analysis using this option invalid.

UK BD37 /BD21 /BD86 /CS454 and HK SDM loading (old)​

To allow for different load factors in different combinations, the user can specify one or more of the following:

  • ULS Comb1: for ULS load combination 1 (dead and live load only)
  • ULS Comb3: for other ULS load combinations (dead, live and temperature or dead, live and wind)
  • SLS Comb1: for SLS load combination 1

The number of HB units to be used for ULS (typically 45 units) and SLS (typically 0 units) should be specified.

The SV loading types are an approximate implementation of the requirements of BD86 requirements. Intensity of SV vehicle loading is adjusted to compensate for the different load factors (1.1 for vehicles, 1.3 for associated lane loading). SV loading is applied in a similar way to HB loading to BD37.  HA loading applied over the full width of lanes, not on 2.5m widths within lanes as required by BD86/BD21/CS454; note that this is unconservative if there is little or no transverse distribution in the bridge. All HA loading is factored by 0.91 (equivalent to heavy traffic / poor surface to BD21/CS454).

In addition, for CS454:

  • Single axle consideration (CS454, clause 5.17(2)) is not included.
  • A pedestrian live load factor of 0.8 from CS454 Table 5.32b is be adopted. Elements supporting footways only, will need to be run with path loading to allow a factor of 1.0
  • A pedestrian width factor of 1*width (the value of 1 from Table 5.32b is adopted)

ECI-UK loading​

To allow for different load factors in different combinations, the user can specify one or more of the following:

  • Characteristic (LC1) gr1/gr5 (traffic load leading action)
  • Combination (LC3) gr 1 (other load leading action)
  • Frequent (LC4) gr 1 (to combine with accidental action / reversible SLS)

Note: Both LC3 and LC4 give identical results in the UK implementation of EC1. Specify the heaviest gr 5 vehicle (SV or SOV) to be considered in the analysis.

EC1-LM1 loading​

This option allows users in Europe to define appropriate Nationally Defined Parameters (NDP) from the local National Annex (NA) to take advantage of the full carriageway optimisation in GSA for LM1 loading. Because different countries use different abnormal vehicles and different rules for combining these with LM1 loading which cannot be covered by simple NDPs, it is not recommended to use GSA full carriageway optimisation for LM3 loading.

To allow for different load factors in different combinations, the user can specify one or more of the following:

  • Characteristic (LC1) gr1/gr5 (traffic load leading action)
  • Combination (LC3) gr 1 (other load leading action)
  • Frequent (LC4) gr 1 (to combine with accidental action / reversible SLS)

The user must then define the NDP from the appropriate NA.

Alpha q values – see EN 1991-2 Clause 4.3.2 (3) adjust the intensity of vehicle (tandem axle system TS) and UDL loading on different lanes.

Psi factors – see EN 1990 Table A2.1 define factors to apply for combination (psi 0) and frequent (psi 1) loading for the tandem axle system (TS), the UDL, full pedestrian loading (PED) and reduced pedestrian loading see EN1991-2 Table 4.4a (PEDRD) and abnormal vehicles (LM3).

Australian loading​

Specify walkway loading, heavy loading and load factors, and lateral position of heavy vehicles.

US AASHTO loading​

Specify highway loading class.

US LRFD loading​

No additional requirements to specify.