I am working on a RC beam–slab bridge model in SOFiSTiK and I am using ELLA with the French bridge code (Fascicule 61 – Titre II).
Context
Structure: RC beam–slab bridge
Spans: 3 spans, 15 m – 20 m – 15 m
Code: BAEL + Fascicule 61 – Titre II
Traffic: French load trains including BC (Fascicule 61), evaluated with ELLA
Software: SOFiSTiK ELLA (French bridge code option enabled)
According to Fascicule 61 (Titre II, §5.5), the dynamic amplification factor δ for the BC load depends on the span length and on the G/S ratio, and it can be different for each span of a continuous bridge.
I am computing δ manually for each span, and I then want to apply a corresponding impact factor PHI in ELLA, with:
PHI = δ – 1
My difficulty / what I want to do
I would like to apply different PHI values for the same BC load train, depending on the span:
δ_15m → PHI_15m for the two 15 m spans
δ_20m → PHI_20m for the 20 m span
In other words, the same BC convoy (same geometry and axle loads) should be:
multiplied by (PHI_15m) when it is on a 15 m span,
multiplied by (PHI_20m) when it is on the 20 m span.
Thank you in advance for your help and clarifications.
At modelling stage (SOFIMSHC), I would create secondary groups depending on the span (e.g. GRP NO ‘SPA1’, ‘SPA2’, ‘SPA3’) containing the relevant structure elements (e.g.SLN).
After computing the internal forces (ASE), I would create a database copy for each span (e.g. span1.cdb, span2.cdb, span3.cdb).
In each database (e.g. span1.cdb), at combination stage (MAXIMA) I would multiply the load cases of the relevant actions with PHI (LC NO -1 FACT #PHI). This #PHI is different in each of your spans. Then I would use the results of these superpositions in the design combinations.
To avoid confusion when working with several databases, you can limit the combinations and the design checks to the relevant elements using your secondary groups:
in MAXIMA: SUPP COMB FROM GRP TO “SPA1”
in AQB: BEAM FROM GRP TO “SPA1”
Would this workflow help? This is how I operate for bridges according to Eurocode, where there is a dynamic factor depending on the member type/member span.
When you work with ELLA, you have minimum three possibilities:
In SOFiLOAD you can define with
LANE LANE.1 SA 0 SE 20 L 20
LANE LANE.1 SA 20 SE 50 L 30
…
the relevant length for each span. If the load has an impact factor (see SOFiLOAD manual about impact factors in load trains) they will be applied onto loads automatically by ELLA in each span.
You define for different elements different values PHI in ELLA-command
CALC… FROM 10001 TO 19999 INC 1 PHI 1.13
CALC… FROM 20001 TO 20500 INC 1 PHI 1.09
You evaluate internal forces in ELLA without an impact factor and define pre- and end-superpositions with maxima for only the desired elements.
PROG MAXiMA $ pre-superposition
HEAD
COMB 1 EXTR STAN… BASE 20000
LC [load cases from ELLA] FACT 1.13 TYPE A1
SUPP… ETYP BEAM FROM 10001 TO 19999 INC 1 OPT S $ only these beams
END
PROG MAXiMA $ pre-superposition
HEAD
COMB 2 EXTR STAN… BASE 21000
LC [load cases from ELLA] FACT 1.09 TYPE A1
SUPP… ETYP BEAM FROM 20001 TO 20500 INC 1 OPT S $ only these beams
END
PROG MAXiMA $ end-superposition
HEAD
COMB 3 EXTR STAN… BASE 31000
LC (20001 20xxx 1) TYPE A1
LC (21001 21xxx 1) TYPE A1
SUPP… ETYP BEAM $ all beams together
END