Author Archives: Alex Judd

On Friday, we were tasked to present to our peers and lecturers, Jenny kindly compiled the materials for the poster while myself and Connor worked on the final parts of the model with the Haselwick students. Once complete we sat down in a group and went through what we had to say.

Since having the presentation, it was apparent that we ran out of time, perhaps we needed to time ourselves to make sure we included the most in our presentation without having to go into too much detail.

The lecturers made some good points of which I have discussed below:

Solar Glass

Our coloured glass panels which will be fitted to the helical structure may be able to serve as photovoltaic cells too. In recent times, there have been new developments that involve clear panes of glass acting as photovoltaics. This would be perfect to charge the lighting system and use overnight.

However, despite this, there would still need to be a required service connection onto the local grid. In winter for example, overcast skies and limited daylight could dim the bridge lights significantly. There was also no consideration for animals such as birds that may lay faeces over the panels and stop them from working as efficiently. How is this accessed for cleaning?

Maintenance

Following on from access for cleaning, the mesh like structure will also be a perfect ‘trap’ for leaves and other windswept objects that could get stuck in the mesh. This is only a problem if this can’t be maintained and as this is a busy road, access for maintenance could in fact be a problem.

The best solution we had was to remove the mesh structure and instead provide a much larger helix gap with parapets on the main deck to stop pedestrians falling off the structure.

Reusable Water

Given the loads can be altered to take this weight, the bridge could also act as a massive water storage tank for local use water. Perhaps instead of draining into the local network, it would be wiser to store such water for use in the development. This will obviously have to be treated and cleaned before use within residential and commercial units.

Connection into Student Accommodation

What was also not considered was perhaps another ramp connecting directly into student halls. Perhaps the layout of these buildings could create positive space that could direct occupants into using the bridge more frequently.

Materials

Stainless steel/ stainless steel alloys are quite expensive, perhaps using recycled materials and materials that are more commercially available would be a more sustainable way to construct the bridge.

Different Surfaces

Instead of dropping the deck to include cyclists, perhaps using different materials on each path would be more suitable. For example, using a cobbled/rougher material for pedestrians and a smoother one for cyclists. This would create the split without the need for change in levels.

Channel Drains

Instead of using channel drains, perhaps a material that is porous and light would be better for surface water drainage. This would also make it far easier to suspend but also require a lesser need for a gradient across the width of the bridge deck.

Conclusion

In conclusion, if we then had another week to use these improvements and create another model, we would be able to include a more overall comfortable and sustainable design that could not only stand over time but also provide to the needs of the end user in a more suitable way.

Introduction

Applying the research we have undertaken into a comprehensive model at a 1:75 scale can be tricky, especially with the limited time and resources we had available. In this post I hope to clearly show where we have applied our research and knowledge into the model and how, given we had more time, would we improve on presentation.

Topography

The topography was made of black and white card which we supported with cardboard and foam board. This not only provided a sturdy base but also helps ‘dull’ the background to really bring out the bridge itself. The contrast of the white tipex on the black card also really helped for defining lines on the road.

Given we had more time, despite the intention to ‘dull’ the background, we could apply modelling materials such as grass and concrete to really bring out the aesthetics of the surroundings. We would also do a more thorough analysis into topography so that we could really define the levels clearly, such as kerb drops, road gradient and hoarding.

Foundation

The research we undertook into the foundations showed us clearly that we needed to show a pad foundation with 2x supports going into each foundation. For the pad itself Jenny proposed we should use wooden blocks. We all agreed as this would clearly show where these would be located and would also provide a suitable base for our model. We also decided to glue the white card onto the blocks to match in with the background.

Similarly with the topography, using modelling material to represent concrete would also be good here as it would help people understand the kind of material we are using in this case.

Supports

The bolts for the support I felt were a good representation of what we were proposing and even with better materials, it wouldn’t feel as ‘structural’ as the bolts made it out to be.

The difficulty came with drilling holes into the drain pipe that formed the base of the deck. These were hard to drill close together without connecting and so we decided to produce our ‘v’ shape not across the width of the bridge but down the length of it instead.

Drainage and Ramp

We did not produce a ramp in the end as we felt there were too many options for this given the uncertainty of both developments. Therefore showing the drainage as described in the ‘drainage strategy’ blog would be hard without a staircase. I believe using art straws was the best approach here but perhaps with a ramp we could show how this will be hidden and connect into the ramp structure to drain into the local network.

Bridge

The bridge was the hardest part to model. The mesh and the helical structure I felt weren’t represented as well aesthetically however I do believe the materials and size were presented perfectly. As an improvement, given we had more time, we could look into producing a helical structure ourselves using steel rods and wire. I believe with the time frame this was achieved well.

Associated Problems

Bridge drainage is important for structural loads, end user satisfaction and stain control. An accumulation of water in a certain area of the bridge can add to the dead loads and could put the foundations and supports under a great amount of pressure.

Pools of water can accumulate and may make it difficult for the end user to cross. Stains and water damage to materials can also be a problem here. Therefore it is essential both by regulation and by good design that the drainage strategy for the bridge is

Solution

The idea for an ‘in-built’ drainage strategy came from the use of a drain pipe as part of the formwork for our model. The idea that the ‘undercarriage’ of the bridge could hold and channel water as part of its structure rather than a disapproving piped structure fixed underneath.

At the Mithras House side, the topography is such that a water spout could be used to drain down the existing road and into the gulley. However, the Preston Barracks side is far higher up off the ground to the point where a spout could cause water to fall rapidly and splash around lifting dirt and mud and producing a poor aesthetic.

In turn, this system will need to be piped and this can easily be achieved using a branch over to the supports for the ramp. This will then drain into either an existing system or otherwise the new drainage system within the Preston Barracks development.

Image Reference: http://www.secpinc.com/products/fiberglass-frp-drainage-systems

On Site Constraints

The onsite constraints involve the active Lewes Road which is present to large amounts of traffic and pedestrian activity; it is also a major bus route. Section 4.0 of The Design Manual for Roads and Bridges, requests that all construction activities near to an existing highway must not cause disruption to the traffic. However, in any case, this road is going to require closing in order to complete the connections to the underside of the bridge.

Proposed Solution

Many highways projects involving bridge construction make use of night time/holidays where traffic will be significantly reduced; a road closure would not affect the local residents as much as if it were to proceed within the day time.

The foundations and supports however have been designed as to be constructed far away from the road so that a closure may not be required. However the highways act 1980 requires suitable hoarding around any construction site near to an existing carriageway. Therefore, when the piers are constructed, suitable hoarding and provision for protection against the public realm must be enforced.

Foundations

The foundations will be cast pad foundations that protrude from the existing ground level. These will be cast in situ with suitable falsework and left to cure subject to engineer’s requirements (usually 48hrs). These will be cast in 3 locations as displayed. If possible, the ground should be graded as to incorporate the pad foundations to allow a flush presentation. Excavators and concrete trucks can access these areas through the existing Lewes road.

Supports

The supports will be made of stainless steel or a steel alloy as with the helical design of the bridge. These will use a very similar methodology to that of the M8 bridge whereas they will connect on a pivot to make up loss of tolerance. These will be prefabricated and fixed to the pad foundation using concrete anchors once the concrete has set.

Bridge Sections

The sections will be delivered in quarters, the first half will be fitted within the Mithras house end and the second will be suspended and attached underneath via platform on the Lewes road. It is at this point of the construction process that we will require a road closure. The sections will be delivered by flatbed wagon.

Ramps and Stairs 

The ramps and stairs towards the Mithras house end will not require a great amount of engineering to install as the design intention was to use the majority of the topography before installing ramps ( as specified in the DMRB). Both stairs and ramp at this end will be prefabricated and fixed to the ground.

Towards the other end however there will be a greater height of which to comply which can lead to a requirement in great lengths of ramp. These will also be prefabricated but most likely bought in sections, again with a similar design process to the other side of the bridge, by fixing to relative foundations. The railings and buttresses will be made of similar bridge materials. And the ramp possibly of cast reinforced concrete with waterproofing membrane.

M8 Harthill Pedestrian Bridge

The project involves building a footpath over the Lewes Road which, despite its speed limitations, can get quite busy throughout the day. Building this bridge over a road as important as this one can be quite a challenge and therefore I have decided to study this in detail.

The M8 Harthill Pedestrian Bridge, designed by Burohappold, had a very similar problem in the instance that it had to help the local residents cross the busy road safely and simply. It also uses a lightweight helical structure as per our design.

The bridge uses materials that maximise durability and minimise maintenance, something that would be also very apparent in our design. The construction of this bridge was completed in prefabricated sections which were then raised onto the piers from the road and fixed onto these supports.

If we take this piece of evidence and apply this to our design, we can see that this will be similar to how we can procure the construction of the footbridge. This will entail forming the supports before attaching the pier via a crane. This may entail a partial close of lewes road and deliver prefabricated sections to site.

Reference: http://www.burohappold.com/projects/m8-harthill-pedestrian-bridge/

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.