A request was made for documents regarding the planning and construction of the Ballasalla Bypass Bridge, specifically concerning weight restrictions, life expectancy, and aesthetic designs. The Department of Infrastructure disclosed all requested information, providing 210 pages of structural calculations and design records.
Key Facts
The bridge was designed as a portal frame using the unit width method of analysis.
The structure was designed for 30 units of HB loading.
The carriageway is 7.3m wide and divided into two notional lanes of 3.65m each.
Accidental wheel loads on footways were assessed and found to be less onerous than HA and HB loads.
Vertical loads due to centrifugal effects were concluded to be negligible.
Data Disclosed
210
3
2022-09-20
2022-10-12
23 July 2020
2333
30 units
7.3m
3.65m
8m
0.6m
July 2017
24/3/20
Original Request
Please provide all documents and records relating to the planning & construction of the Ballasalla Bypass Bridge over the Isle of Man Steam Railway in relation to:
- Any weight restriction over the bridge during construction and once complete
- The life expectancy of the bridge
- The aesthetic designs for the structure at planning and completion.
Data Tables (103)
Section
no.
[pages]
Description
Rev
Pages
Mb
S1
Introduction to structural calculations
-
3
1.4
S2
HA UDL, HA KEL and HB live loads, centrifugal effects
19
4.6
S3
Traction / braking live loads
4
1.3
S4
Accidental live load on footways
10
1.6
S5
Dead loads and superimposed dead loads
3
0.6
S6
Horizontal earth pressures and live load surcharge
3
0.6
S7
Water pressure and buoyancy
2
0.4
S8
Load combination diagrams (longitudinal design)
Diagram
number
Equilibrium checks
1
Sliding check 1 = HA, disturbing earth pressure with Traction
[S→N]
A-6b-1[HA]
2
1
0.5
2
Sliding check 2 = HA, disturbing earth pressure with Traction
[N→S]
9
Load combination 1.1 = Max vertical HA load with max horiz load.
A-1b-1[HA]
-
1
10
Load combination 1.2 = Max vertical HB load with max horiz load.
A-1b-2[HB]
-
1
11
Load combination 1.3 = Min vertical load with max horiz load.
A-2b-1[no live
load]
-
1
12
Load combination 1.4 = Max vertical HA load with min horiz load.
A-3b-1[HA]
-
1
13
Load combination 1.5 = Max vertical HB load with min horiz load.
A-3b-2[HB]
-
1
14
Load combination 4.1 = Traction S→N with max vertical HA load
A-4b-1-1[HA]
-
1
Ballasalla bridge - over railway
ATR 24/3/20 2333 S1-1
Introduction to structural calculations
1. Design has been carried out in accordance with DMRB Volume 2, Section 2, Part 12
BD31/01 - The design of buried concrete box and portal frame structures.
2. The structure has been designed as a portal frame using the unit width method of
analysis in BD31/01 clause 4.1.1(e).
3. The structure has been designed for 30 units of HB loading, as BD31/01 3.2.1 (b) for
roads other than Trunk Roads or Motorways.
4. The location of the structure is shown on drawing "Bypass OS coordinates" dated
July 2017. The general arrangement of the structure prior to detailed design is shown
on drawings 2333/E/01 Rev P0, 02 Rev P0 and 03 Rev P0 dated July 2017.
5. For the purposes of assessing vertical loads, the 7.3m wide carriageway has been
divided into two notional lanes, each 3.65m wide, in accordance with BS5400-2:2006
clause 3.2.9.3.1.
6. Refer to SK HA 01 Rev - in calculation section 2 for a summary of HA live loads and
superimposed dead loads (SDL) loads. Since cover is less than 0.6m, the HA UDL/KEL
combination has been taken with no dispersal, as BD31/01 3.2.1 (a) (i).
7. Refer to SK HB 01 Rev - in calculation section 2, for a summary of HB live loads.
The loaded length of the bridge is short (8m) and consequently when HB load is placed
in a notional lane, no other live loads are present in front of, or to the rear of, the HB
vehicle.
8. Refer to SK HA+HB 01 Rev - to SK HA+HB 03 in calculation section 2 for a summary
of combined HA and HB loads across the width of the bridge.
9. Footway loads have been taken from BD31/01 clause 3.3.2.
10. Accidental wheel loads on the footways have been assessed in accordance with
CS454 Rev 0 (which supersedes the reference in BD31/01 3.2.3 to BD37). CS454
clause 5.27.4 for non-cantilevered members, specifies accidental loading on a footway
as a single vehicle from "ALL model 1". ALL model 1 axle weights and axle spacings for
normal traffic are given in table B.1. These have been assessed and for analysis of the
portal structure using the unit width method, it has been concluded that the accidental
loading from a single vehicle is less onerous than HA and HB loads for which the
carriageway has been designed and therefore longitudinal reinforcement in the
footways is to be the same as that in the carriageway. No other vertical live load is
taken in combination with accidental wheel load, as BD31/01 32.23 (b).
DRAFT IN PROGRESS LAST UPDATED 23/7/20
Ballasalla bridge - over railway
ATR 24/3/20 2333 S1-2
Introduction to structural calculations (cont)
11. Vertical loads due to centrifugal effects have been assessed in accordance with
CS454 Rev 0 clause 5.24 and concluded to be negligible.
12. HA traction/braking load has been taken from CS454 Rev 0 clause 5.35.1. HB
traction/braking load has been assessed in accordance with BS5400-2:2006 clause
6.10.2.
13. The specified concrete grade (in the AIP) is C35/45 for the deck slab and the walls
and C28/35 for the foundations (base of walls). Reinforcement design has been based
on the specified grade of concrete. E value for frame analysis as been taken from
BS5400-4:1990 Table 3. To more closely reflect the probable actual strength of the
concrete, the E value in the analysis of the portal has been taken as that for C40/50.
14. For assessment of deflections and crack widths, 0.75 of the value has been taken,
i.e. mid-way between the Table 3 value (E = 32.5kN/mm2 for C35/45) and half that
value (16.25kN/mm2), as BS5400-4:1990 clause 4.3.2.1 giving an E value =
24.4kN/mm2.
15. Coefficient of thermal expansion has been taken as 12 x 10-6/OC, which caters for all
aggregates except limestone, as BD31/01 clause 3.2.8 (b).
16. TEDDS 2D frame analysis does not have the facility to model a moving load within
a frame. Approximations have therefore been used for the HA KEL and the HB load
train. Refer to Appendix 1 for details.
17. BD31/01 (clause 41.3) gives stages that are to be analysed as follows:
(i) The completed structure backfilled up to the top of the roof.
(ii) The structure backfilled to an intermediate level between roof level and finished
surface level, at which it is proposed to use the structure for construction traffic.
(iii) The structure, fully backfilled, in service.
In this case, the difference between both stages (i) and (ii) and the final stage (iii) is
considered to be insignificant and therefore analysis has only been carried out on stage
(iii).
18. In this case, wind and snow loads are considered to be insignificant and have been
ignored.
19. Separate analyses have been carried out for the foundations using an Excel
spreadsheet. The reactions from TEDDS plane frame analyses have been applied as actions
on the foundations, taking cognisance of the sign convention to check sliding resistance and
ground bearing pressure.
20. The geometry of the bridge as shown on the drawings in item 4 above was amended as
the detailed design evolved to reduce bearing pressures. The revised geometry is shown on
SK-GEOM-02 Rev A in calculation section 6.
21. Separate analyses have been carried out on the superstructure to model differential
settlement of 15mm between the north and south abutments.
Ballasalla bridge - over railway
ATR 24/3/20 2333 S1-3
S2 / 1
S2 / 2
S2 / 4
S2 / 5
S2 / 6
S2 / 7
S2 / 8
S2 / 9
S2 / 11
Job:
Ballasalla bridge
Date:
20/03/2020
Job number:
2333
Sheet no.
CS454 ACCIDENTAL VEHICLE LOADING. ALL model 1. Table 1.
NORMAL TRAFFIC COMBINED AXLE LOADS EXPRESSED AS SIMPLE EQUIV UDL
low flow factor:
0.9
impact factor:
1.62
VEHICLE TYPE
COMBINED
AXLE LOAD
(kN)
AXLE
WIDTH
(m)
OVERALL
LENGTH
(m)
SIMPLE EQUIV
UDL USING
AXLE SPACING
(kN/m2)
ESTIMATED
OVERALL
WIDTH
(m)
SIMPLE
EQUIV
UDL
(kN/m2)
NOTIONAL
LANE WIDTH
from CS454
Table 5.9a
(m)
SIMPLE
EQUIV
UDL
(kN/m2)
VEHICLE
TYPE
A
315
1.8
8.4
20.8
2.1
17.9
3.0
12.5
A
B
370
1.8
11.9
17.3
2.1
14.8
3.0
10.4
B
C
394
1.8
11.9
18.4
2.1
15.8
3.0
11.0
C
D1
392
1.8
11.4
19.1
2.1
16.4
3.0
11.5
D1
D2
392
1.8
12.4
17.6
2.1
15.1
3.0
10.5
D2
E1
392
1.8
12.7
17.1
2.1
14.7
3.0
10.3
E1
E2
392
1.8
12.7
17.1
2.1
14.7
3.0
10.3
E2
F1
402
1.8
12.98
17.2
2.1
14.7
3.0
10.3
F1
F2
402
1.8
12.98
17.2
2.1
14.7
3.0
10.3
F2
G1
433
1.8
13.5
17.8
2.1
15.3
3.0
10.7
G1
G2
433
1.8
13.5
17.8
2.1
15.3
3.0
10.7
G2
H1
432
1.8
15.05
15.9
2.1
13.7
3.0
9.6
H1
H2
432
1.8
15.05
15.9
2.1
13.7
3.0
9.6
H2
15.6
15.6
14.0
14.0
15.4
15.0
15.0
15.1
15.1
SIMPLE EQUIV UDL USING
NOTIONAL LANE WIDTH FROM
CS454 Table 5.9a including
impactor factor and low flow
factor
18.2
15.1
16.1
16.7
19.9
19.9
21.4
21.4
21.5
21.5
22.3
22.3
21.9
SIMPLE EQUIV UDL USING
ESTIMATED OVERALL
WIDTH including impactor
factor and low flow factor
(kN/m2)
26.0
21.6
23.0
23.9
S5 / 1
S5 / 2
S6 / 1
Rev 1: 20/4/20. Height of walls corrected.
Rev 2: 15/7/20. Both walls made equal height.
Job:
Ballasalla bridge
Date:
31/03/2020
Job number:
2333
Sheet no.
S6-3
Horizontal earth pressures
v1
31/03/2020
Rev 1: 20/04/2020
Rev 2: 15/07/2020
South abutment
Height to
top
(m)
Height to
bottom
(m)
Density
(kN/m3)
Ko
(max)
Ko
(min)
Ka
(disturbing)
K
(restoring)
K
(max sliding
resistance)
Max earth
pressure at
top
(kN/m2)
Max earth
pressure at
bottom
(kN/m2)
Min earth
pressure at
top
(kN/m2)
Min earth
pressure at
bottom
(kN/m2)
Disturbing
earth pressure
at top
(kN/m2)
Disturbing
earth pressure
at bottom
(kN/m2)
Restoring
earth
pressure at
top
(kN/m2)
Restoring
earth
pressure at
bottom
(kN/m2)
Max sliding
resistance
at top
(kN/m2)
Max sliding
resistance
at bottom
(kN/m2)
0.3
5.75
21
0.6
0.2
0.33
0.6
1.5
3 8
72.5
1 3
24.2
2.1
39.8
3.8
72.5
9.5
181.1
0.525
5.75
21
0.6
0.2
0.33
0.6
1.5
6.6
72.5
2 2
24.2
3.6
39.8
6.6
72.5
16.5
181.1
North abutment
Height to
top
(m)
Height to
bottom
(m)
Density
(kN/m3)
Ko
(max)
Ko
(min)
Ka
(disturbing)
K
(restoring)
K
(max sliding
resistance)
Max earth
pressure at
top
(kN/m2)
Max earth
pressure at
bottom
(kN/m2)
Min earth
pressure at
top
(kN/m2)
Min earth
pressure at
bottom
(kN/m2)
Disturbing
earth pressure
at top
(kN/m2)
Disturbing
earth pressure
at bottom
(kN/m2)
Restoring
earth
pressure at
top
(kN/m2)
Restoring
earth
pressure at
bottom
(kN/m2)
Max sliding
resistance
at top
(kN/m2)
Max sliding
resistance
at bottom
(kN/m2)
0.3
5.55
21
0.6
0.2
0.33
0.6
1.5
3 8
69.9
1 3
23.3
2.1
38.5
3.8
69.9
9.5
174.8
Horizontal live load surcharge
South and North abutments
LOAD
Vsc
(kN/m2)
K
K
(disturbing)
Psc
(kN/m2)
Psc
(kN/m2)
HA
10
0.6
0.33
6 0
3.3
HB
12
0.6
0.33
7 2
4.0
Rev
Date
Description
1
20/04/2020 Height of walls corrected
2
15/07/2020 Pressure at centre line of deck added for input to TEDDS. Both abutment walls made the same height as the South abutment, so the figures for the horizontal earth pressure for the North abutment become redundant.
S7 / 1
Extract from Dandara
drawing SI-01 Rev P1
Proposed location
of bridge
S7 / 2
S9 / 1
S9 / 2
S9 / 3
S9 / 4
S9 / 5
S9 / 6
S9 / 7
S9 / 8
S9 / 9
S9 / 10
S9 / 11
S9 / 12
S9 / 13
S9 / 14
S9 / 15
S9 / 16
S10 / 9
TRRL LR 765
S10 / 10
TRRL LR 765
S10 / 11
TRRL LR 765
Ballasalla bridge - over railway
ATR 22/7/20 2333 S11
summary
Maximum ground bearing pressure (GBP)
Using the reactions from TEDDS and the Excel spreasheet the maximum GBP was
as follows for the stated load cases:
A-7b-5 [Dead load and soil pressure (no live load)]: 128kN/m2
A-7b-1 a-e [HA] and A-7b-2 a-e [HA]: 165kN/m2
A-7b-3 a-d [HB] and A-7b-4 a-d [HB]: 182kN/m2
The allowable bearing pressure is 165kN/m2 with a 25% increase permitted under HB
loading.
Dandara Ltd
16 Beech Manor
Stoneywood
Aberdeen AB21 9AZ
Project
Ballasalla road bridge
Job no.
2333
Calcs for
A-7b-1 and 2 supp GBP check: fixed bases. walls equ.7960
Start page no./Revision
S11 / 1
Calcs by
ATR
Calcs date
20/07/2020
Checked by
Checked date
Approved by
Approved date
ANALYSIS
Tedds calcula ion version 1.0.23
Geometry
Geometry (m) - Concrete (C40/50) - R 450 x 1000
South abutment
North abutment
Deck
1
5.225
2
5.225
3
7.974
1
2
3
4
X
Z
Materials
Name
Density
Youngs Modulus
Shear Modulus
Thermal Coefficient
(kg/m3)
kN/mm2
kN/mm2
°C-1
Concrete (C40/50)
2400
34
12
0.000001
Sections
Name
Area
Moment of inertia
Shear area
Major
Minor
Ay
Az
(cm2)
(cm4)
(cm4)
(cm2)
(cm2)
R 450 x 1000
4500
3750000
759375
3750
3750
Nodes
Node
Co-ordinates
Freedom
Coordinate system
Spring
X
Z
X
Z
Rot.
Name
Angle
X
Z
Rot.
(m)
(m)
(°)
(kN/m)
(kN/m)
kNm/°
1
0
0
Fixed
Fixed
Fixed
0
0
0
0
2
0
5.225
Free
Free
Free
0
0
0
0
3
7.96
0.47
Fixed
Fixed
Fixed
0
0
0
0
4
7.96
5.695
Free
Free
Free
0
0
0
0
Elements
Element
Length
Nodes
Section
Material
Releases
Rotated
(m)
Start
End
Start
moment
End
moment
Axial
1
5.225
1
2
R 450 x 1000
Concrete (C40/50)
Fixed
Fixed
Fixed
Yes
2
5.225
3
4
R 450 x 1000
Concrete (C40/50)
Fixed
Fixed
Fixed
Yes
3
7.974
2
4
R 450 x 1000
Concrete (C40/50)
Fixed
Fixed
Fixed
Yes
Dandara Ltd
16 Beech Manor
Stoneywood
Aberdeen AB21 9AZ
Project
Ballasalla road bridge
Job no.
2333
Calcs for
A-7b-1 and 2 supp GBP check: fixed bases. walls equ.7960
Start page no./Revision
S11 / 2
Calcs by
ATR
Calcs date
20/07/2020
Checked by
Checked date
Approved by
Approved date
Members
Name
Elements
Start
End
South abutment
1
1
North abutment
2
2
Deck
3
3
Results
Reactions
Load combination: A-7b-1-a kel mid (Strength)
Node
Force
Moment
Fx
Fz
My
(kN)
(kN)
(kNm)
1
-121.2
255.6
-73.7
3
89.9
245.9
13.1
Load combination: A-7b-1-b kel 1/3 (Strength)
Node
Force
Moment
Fx
Fz
My
(kN)
(kN)
(kNm)
1
-122
260.9
-76.7
3
90.6
240.7
12.7
Load combination: A-7b-1-c kel 2/3 (Strength)
Node
Force
Moment
Fx
Fz
My
(kN)
(kN)
(kNm)
1
-122
248.9
-72.8
3
90.6
252.6
16.6
Load combination: A-7b-1-d kel lhs (Strength)
Node
Force
Moment
Fx
Fz
My
(kN)
(kN)
(kNm)
1
-127.3
270.2
-84.6
3
96
231.3
23.1
Load combination: A-7b-1-e kel rhs (Strength)
Node
Force
Moment
Fx
Fz
My
(kN)
(kN)
(kNm)
1
-127.3
239
-83.2
3
96
262.5
24.5
Load combination: A-7b-2-a kel mid (Strength)
Node
Force
Moment
Fx
Fz
My
(kN)
(kN)
(kNm)
1
-89.9
261.1
-13.5
3
121.2
240.4
73.3
Load combination: A-7b-2-b kel 1/3 (Streng
[Response truncated — full text is 48,115 characters]