Eurocode footbridge design

Footbridge as an access for passenger to step in floating dock are need to consider its strength and integrity so can accomodate any potential unsafe situation that would happend for example in peak season when passengger are overloaded has to be considered in design.
Below pict. Are General arrangement for floating dock service with preliminary bridge design. The bridge are flexible mounted so can be follow vertical movement of pontoon as tidal effect, there are other structure that holding pontoon to prevent horizontal movement.

As per project spec, the bridge consist of aluminium framebase structure with steel handrailing also several condition need to be fullfilled.

1. The bridge are assembled from two structure with hinge connection for mobility reason
2. Total bridge weight not more than 1Ton since the availabe winch at site has SWL 1Ton for bridge lifting purpose.
3. Design optimization only allowed at framebase section.

Bridge modeling :
The bridge are modeled in 3D space structure.

Bridge Section 1                                                                                        Bridge Section 2

Bridge Assembly

Update general arrangement by applying new design structure:

Note: There are possibility colliding between bridge frame structure with pontoon handrail.
Structure size and weight:

Bridge portion at quay use wheel support and hinge connected to pontoon walkway
PICT.3
Bridge hinge for this model assume as fix node and the other have release nodes behaviour at splice area.
PICT.4
There are several bridge code that can be use as guidance but eurocode has more conservatife approach for public fasilities related with safety service. The design parameter refer to eurocode are below:
Applied load :
1. Selfweight of bridge structure
2. Trafic load (See EN 1991-2 Part. 5)
- Uniform distributed load 5 kN/m² applied perpendicular to floor surface
3. Wind load (See EN 1991-1-4)
- With site data for wind are:

• Air Density (r) = 1.25 kg/m³
• Wind Velocity (Vb) = 10.3 m/s

- Calculated wind force :

• Peak velocity pressure (q(z)) = 0.16 kN/m²
• Wind force at direction (F_w,i) :
  • Perpendicular to the bridge = 1.14 kN
  • Paralel to the bridge = 0.94 kN
  • Vertical direction = 0.28 kN

Load combination :
Load combination will refer to EN 1990 with using Ultimate Limit State (ULS) and Service Limit State (SLS), since only wind that considered as environmental load so load factor can be simplified as per below:

1. Service Limit State

2. Ultimate Limit state

Acceptance criteria :
1. Stress material
For material propertied for aluminium structure refer to EN 1999

- Material	:	AL 6061 T6
- Density	:	2712.6	kg/m3
- Yield Strength (fy)	:	240	Mpa
- Ultimate Strength (fu)	:	290	Mpa
- Modulus of elasticity (E)	:	68900	Mpa
- Shear Modulus (G)	:	26000	Mpa
- Poisson’s Ratio	:	0.33

Permissible stress for tension, compression and bending members:

s_perm = f_y/y_m = 240 Mpa

Permissible shear stress :

t_perm = f_y/(y_mxÖ3) = 139 Mpa

Where :

f_y= Yield stress of material

y_m= material factor = 1.0

2. Deflection
With refference to EN 1990-Annex A1.4 limits for vertical deflections according to figure A1.1 should be specified for each project and agreed with the client. Due to no specified maximum vertical deflection by client, maximum vertical deflection in SLS cases in the middle of bridge span assumed as L/250 = 9500mm/250 = 38mm

3. Frequency
With assumption:
1. No horizontal force acting on the brige because of pontoon movement
2. Analysis structural in frame-base, the handrail and any other appurtenance only contribute self-weight loading.

Analysis result :
1. Max stress generated at ULS cases are 137.2 Mpa at L.C 1.2 still below permissible

2. Max deflection at SLS cases are 16.7mm at L.C 1.2 still below allowable deflection limit

3. Frequency at mode shape 1 is 2.97 hz still in alowable limit

New foot-bridge structure design comply with Eurocode