Category Archives: Ponte Vecchio

Formation and Assembly of Detail Model

During the model making process, I was tasked to complete the detail model. I decided to do something that can show elements that haven’t been presented to the overall model, and in that case, this would be the staircase and bike ramp.

I started by sketching out the dimensions of the staircase as to the design manual for roads and bridges specification.

I decided that the easiest option for producing the detail would be to make it out of foam board. I measured out the stairs and scored the board before folding it into the desired position.

Then using a glue gun, I fixed it into the desired place.

I then undertook a similar process for the sides back and underneath of the stairs with Drew from Hazelwick Sixth Form. This formed the main stairs.

Then using pins and art straws, we fixed the railings to the side of the stairs and glue gunned the banister on. Finally, we added the bike ramp which was made from a model of an I beam. This was also fixed into place with a pin as to represent the concrete anchor which would be the fixing in real life.

The final detail was scaled at 1:10.

I hope to make annotations on the model as to show literally where this complies with DMRB guidance.

Concept Sketch

Our group discussed that due the size of our bridge, from an engineering and feasibility point of view, a beam bridge would be most suitable. However, beam bridges are not ‘fun’ bridges and we wanted to do something that took a step up from that. Jenny showed us some great images of a helical bridge and we decided that it would be good for us to do something similar.

Once we agreed on the bridge, we discussed possible materials we could use. Once we made a list of these materials, I formulated a concept sketch so we could all get a ‘feel’ for how this will work when it comes to the modeling process.

The only amendment since sketching this drawing would be the notable 1:10 gradient which we now agree will be 1:20 or 1:15 with intermediate platforms.

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

Introduction

The important element that needs to be considered in bridge construction is the overall loads that are dissipated by the piles that the spans sit upon. This is important because an uneven or disproportionate load could cause the whole structure to fail. As this is a concept, no detail into structural calculations has been considered however there are some initial methods of predicting how the structure will act under certain loads.

Likely Concerns and Solutions

The above image shows where the likely problems associated with loads, this includes:

• Wind
• Vibrations
• Overweighting and Live loads

In order to dissipate these problems, the following solutions have been proposed:

Wind

Wind is very prominent in Brighton especially being in the path of the trade winds. In order to stop the structure resisting against this, it has been opted that the design of the bridge lets the wind pass through it. This negates the impact wind and diffuses it through the structure as opposed to around.

Vibrations

Vibrations from traffic will be very prominent so in order to reduce the effect that the vibrations have on the structure. Multiple piles have been selected as opposed to the original upright two piles. This means vibrations are spread and dissipated through the structure as opposed to a fixed location. This will stop soil loosening around the foundations and also stop the build-up of structural vibration.

Overweighting and Live Loads

It is important to consider the live loads on the bridge. By having no sort of lane control on the deck, the pattern of vibrations caused by these loads could be vast and quantifiable. Therefore, by splitting the deck into different pathways, we can focus the live loads on a certain location so there can be suitable reinforcement for this.

In summary, the intention of this preliminary examination into the loads of the structure is to inform us of how we can reduce the loads occurring on the structure before a technical design submittal where the calculations and engineering of the bridge take place.

Reason for Revision A

Upon reflection in our group, we have decided that crossing from Preston Barracks to the Mithras House entrance would be too high up off the ground and would pose more problems in relation to who uses it and how it is accessed.

We have decided to go for bridge option 2 as mentioned in the first revision. This involves positioning the bridge to the most northern part of Mithras House car park and then spanning over to the proposed central square at the Preston Barracks development OR Watts car park dependent on Preston Barracks development outcome.

The levels won’t be affected per se however we will be bridging from the 30m above Ordnance datum as opposed to the original 35m, this reduces wind loads but also mean that the ramps and accessibility aspects which were a concern in the first instance are drastically reduced.

Bike Ramps

In a lot of train stations where there are bridges over the railway there is a problem that bikes have when it comes to crossing platforms. Elevators are available for use in many cases but these may be too small to fit in multiple bikes and people. What is often used instead is a ramp fixed to the stairs that allows the cyclist to push their bike up the ramp why they too go up the stairs. This also applies going down the stairs.

This can certainly benefit the end user as the strain of carrying a bike up the stairs or trying to fit into a tight space is reduced and in some cases negated. It’s a very simple and efficient method to help bikes out significantly. However, consideration into the type of ramp needs to be addressed.

Concrete formed bike ramps are safe and secure however cannot be moved at a later date. Metallic ramps are more susceptible to damage and in some cases can be harder than the concrete stairs as the wheels can rub against the side. The benefit of using a metallic ramp is that these can be easily removed, replaced and fixed to any type of stair.

Our project could include a metallic ramp but with a much larger width. Perhaps it would be wise to combine both the concrete and metallic ramp so there is a ramp present but with the option of a channel for your bike to sit in incase the user is struggling to push these up.

The above image also shows how it is fixed to the stairs. This is by fastening the metallic ramp to the highest concrete stair and stair base with concrete anchors.

Reference: http://cycle-works.com/product/wheeling-ramps/

V Bridge

The ‘V Bridge’ is a proposed bridge at Nine Elms, London by architectural firm Studio Egret West. It spans over 150m with two piers sunk into the bed of the river that it passes over. The bridge uses a very simple process of splitting the cycle path and pedestrian path across the breadth of the bridge deck.

A main concern raised in our group was the fact that cycle paths and pedestrian walk ways on a bridge could be hazardous in the instance that they could collide at a point. This proposal handles this very well and I hope to incorporate this into our design. It also has various seating arrangements and foliage on the bridge itself which for the instance of this project may not be required but may be worth considering.

The disadvantage with this bridge design is that it is very different scenario to ours; In the instance that this bridge were to cross an A road, I doubt that it would use this sort of structural system in the intended design.

In brief, the element we wish to source from this cased based precedence is how it deals with the end user. Even if the design does not split, there needs to be a control element put in place.

Reference: http://egretwest.com/projects/v-bridge

Introduction

Site levels are important for a competent bridge design, in particular when it is crossing a busy highway and needs to be made accessible to all parties. On 07.11.2016 the UoB and Haselwick students went on a site visit to the A270 and Mithras House Building on the Mouslecoomb campus. My intention of this visit was to get a better ‘feel’ for the site, especially for such factors like the line and level. In order to document this I took some photographs of the location.

Bridge Option 1

We agreed in our group that a crossing spanning the entrance of Mithras House and the proposed Preston Barracks development would be possible. However the change at levels at this location is significant. Therefore, I went out to find these through study of existing topography. Using Digimaps, I downloaded a site plan and overlaid this onto a topography expressed in 5m contours. By overlaying both these levels and the site plan, I could take some levels from the site.

I struggled to establish levels of the lower stairs going up to Mithras House through the desktop study, and in order to establish these levels I used a reasonable assumption from the photographs we took of the site. I then sketched these levels.

Bridge Option 2

An alternative to this crossing point would be at a lower level more towards the corner of Preston Barracks as with the planning application made for the Preston Barracks development. This would still use the same levels as expressed above but instead of crossing at high level, these would cross at the lower platform.