Introduction
The bridge needs to be efficiently coordinated to meet with the various codes of practice listed by the government. In the instance of this footbridge, I have studied British Standards and The Design Manual for Roads and Bridges. Within this blog, I hope to list, in brief, the various parts of these standards that meet the environment that we are designing our bridge to.
Our intention as a group is to give each other various headings to talk about during our presentation, it also gives us an idea of how to split our poster.
The standards mainly used to generate this list include:
TD 27/05 – Cross sections and headroom – Available via CIS
BD 74/00 and BS 8004 – Code of Practice for Foundations – Available via CIS
BD 29/04 – Design Criteria for Footbridges – http://www.standardsforhighways.co.uk/ha/standards/dmrb/vol2/section2/bd2904.pdf
Bridge Foundations (BD 74/00 and BS 8004)
- Abutments are defined as substructure
- If the soil is found to be non-cohesive, bridge piers will need an element of reinforcement/safety put in place to avoid further settlement
- Important that in the excavation of these foundations that elements of water control is put in place. Piers built in water logged ground can rise and dimensionally change the bridge design
- Loads to be distributed evenly to all foundations
- Eccentric loading of foundations due to any cause other than wind pressures should be fully investigated
- Excavation near to existing structures can reduce the stability of their foundations
- Foundations need to resist against lateral forces such as wind
General Principles (Section 2 of BD 29/04)
- Design against vandalism
- High scrap value materials not to be used or to be secured efficiently so that no damage is done to the structure
- Consideration into visually impared users as well as mobility impared
- User groups are key to the bridge design, orientate to facilitate the main user
Layout (Section 3 of BD 29/04)
- Maximise topography use before including ramps
- People walking towards the bridge should be facing traffic where is provisional
- Limit access from the road
- Access stairs and ramps are the most environmentally damaging and should be avoided as much as possible
- Suitable guard rails should be installed to encourage people to use the structure
- Use existing foliage to minimise visual impact of the road
- Accumulation of rubbish underneath stairs needs to be considered
- The user should never be concerned for their personal safety at any time
- Aesthetically pleasing
- Visually pleasing from all viewpoints
Bridge Supports (Section 4 of BD 29/04)
- Foundations to be designed as to cause minimum delay to traffic during construction
Design Standards (Section 5 of BD 29/04)
- Minimum thickness of steel components is 6mm
Dimensional Standards (Section 6 of BD 29/04)
- The horizontal clearance from the edge of the carriageway to the bridge supports shall be a minimum of 4.5m
- Ramps and footbridge should not be less than 2m wide
- Ramps can be continuous at 1:20 level
- Gradients of the bridge should be no steeper than that of an access ramp
- Stairs to comply with BS 5395
- No more than 13 stairs in a single flight
- A maximum of 3 successive flights may be used in a line
- Risers and tread of each stair to be uniform
- Risers should not vary in height
- No more than 150mm for a riser
- Tread width no less than 300mm and no more than 350mm
- Landing lengths shall not be less than 2m
- Riser should be sealed or perforated
- No steeper than 1:20 for a ramp unless agreed with local authority, no steeper than 1:15 preferable, definitely no steeper than 1:12
- Cycle paths should not ‘link up’ with the ramp
- Landings for ramps at 1:20 should be a maximum rise of 2.5m
- Ramps steeper than 1:20 should have a max rise of 650mm
- Landings should not be less than 2m
Parapets (Section 7 of BD 29/04)
- Parapets are required on all bridges
- Handrails should be provided for stairs and should be no less than 900mm and no greater than 1000mm
- Handrails to have a diamater of 50mm
- Handrails to have a different colour to the parapet as to help the visually impared
Enclosed Footbridges and Clearance Gauge (Section 8 of BD 29/04)
- Where it is likely that things can be thrown from the bridge, this should be enclosed
- If very windy or unsafe, bridge should be enclosed
- Headroom inside enclosure
- Pedestrian only 2.3m
- Pedestrian and Cyclist 2.4m
- Equestrian 2.7m
- Equestrian (mounted) 3.7m
- Primary structural elemetns should not penetrate the enclosure
Drainage (Section 9 of BD 29/04)
- Drainage is required
- It should not spill onto the users below
Surfaces (Section 10 of BD 29/04)
- Materials on surface need to be slip and corrosive resistant.
- Decks should be waterproofed
- No gaps larger than 12mm in walkway
Lighting (Section 11 of BD 29/04)
- Footbridges should be illuminated
- Should adopt onto existing lighting supply, consider parapet lighting, parapets cannot be used as cable ducts
Requirements for Combined Use by Pedestrians and Cyclists or Equestrians (Section 12 of BD 29/04)
- Paths can be shared or segregated dependent on use
- Segregation widths
- Unsegregated – 2m
- Segregated by railing – 1.95m
- Segregated by line – 1.5m
- Segregated by kerb – 1.75m
- Minimum footbridge width is 3.5m
- Should be able to see through the bridge whereas curved bridges could cause crash incidents
- Suitable signs warning of cycle shared footbridge to be included
Cross sections and headroom (Table 6-1 of TD 27/05)
- Minimum crossing level is 5.7m+Sag