wire rope bridge design free sample

Parallax background suspended bridge hang above steep mountain cliff, green rocky 2d landscape cartoon beautiful nature scenery summer view with separated layers for game animation vector illustration

Ship of pirates with an island on the horizon. illustration of sail boat bridge view. background for games and mobile applications. sea battle or traveling concept.

Longer span Rope Bridges can be anchored across rivers, lakes and even canyons. Perfect for going tree-to-tree in woodlands, for Tree-Top Walkways and for adding that extra air of excitement in gardens, woodlands, resorts and adventure parks.

Short span Rope Bridges are perfect for treehouses and the ideal go-between when adding platforms or play ‘islands’. Adds real adventure and fantasy plus a playful connection to our whole world of play.

Our Log Rope Bridges are a perfect solution where a treehouse adventure starts from the lawn or woodland floor, leading upwards to a treehouse or platform. Our Log Rope Bridges make an awesome treehouse or platform entrance.

Suspended Rope Bridges can offer a perfect solution when looking to cross over large areas, such as rivers, lakes, ponds and even canyons. They also provide an exciting and flexible design option in Adventure Parks.

We work from anchor points established at each end, using either a zero-impact certified and proprietary ground buried anchor system or suitable ground buried concrete ‘pads’ with integrated structural anchor plates, that are designed and fabricated at our workshop. Typically, if suitable trees are available, we can ‘anchor’ to trees at each end of the Rope Bridge using tree-friendly webbing slings or rope soft-shackles.

In every project, the anchor points can always run longer than the actual Rope Bridge span, allowing us to also integrate ground-based deck platforms (with balustrades if necessary) at each end. This not only creates a truly impressive looking ‘start’ and ‘finish’ to the Rope Bridge, it also helps us to negotiate the height of the Rope Bridge above water, should there be any relevant issues with flood forecasts.

The most common lengths of Rope Bridges we have installed has been anywhere from 5m up to 45m. But if you’re thinking of something on a grander scale, that’s not a problem at all.

We have designed and installed 45m long Rope Bridges that span across rivers and canyons, and on one project, even installed a Rope Bridge directly into granite boulders when the availability of ground anchors or nearby trees was not an option. Whatever your wish our teams at Treehouse Life will always look for a way to make it work.

As ever, with Rope Bridge design and build, the key to structural integrity and design success is very much down to the lay of the land at the proposed location. While we can initially work from location photos to advise and consult regarding your Rope Bridge options, we do offer an on-site visit consultancy so that we can to discuss all opportunities.

Structurally, suspended Rope Bridges work from anchor-to-anchor using structural steel cables or ropes with all elements suspended inbound on the structural lines, including the round timber uprights at each end that are required for the rope-work balustrades.

This is what we call a ‘floating Rope Bridge’ solution, which allows us to work with our own Rope Bridge system in many unique and incredible locations both throughout the UK and around the world.

Our fixed-beam Rope Bridges are a perfect design solution to reach a treehouse or link up multiple platforms or decks. The purpose of the integrated fixed-beam is simply to hold the two ends apart; it typically sits at half-height within the rope balustrades, but can also sit lower or even closer to the upper ‘hand-rail‘.

On this particular Rope Bridge design and installation solution, because the ‘stress-and-strain‘ between the two fixed points is taken up by the fixed-beam, we support the timber walkway treads underneath with ropes that are fixed at each end to a round timber beam.

Structurally perfect and beautiful in design, Fixed-Beam Rope Bridges for treehouses, platforms and decks can add a whole other dimension of fantasy and imaginative play.

With the bridge always sitting level end-to-end, it is possible for us to increase (or decrease) the overall height by installing an additional step up and/or down at either end (usually 300mm).

Although this is a fully integrated Rope Bridge design and installation, there is however a limit to the distance the bridge can actually cover. This is determined by the length of the actual fixed- beams we use; a 3m span or less works perfectly, although there are some other excellent options if a span of up to 6m long is required.

Overall, the structural integrity is always going to be heavily dependent upon what is available at each end of the bridge – so our advice (based on years of experience) would always be for a Rope Bridge to be integral to an overall design rather than being an add-on after everything else has been built.

Include some Climbing Walls, Zip Wires and Fireman’s Poles as part of your child’s treehouse world and you will create the ultimate adventure and fantasy land and a playful connection to a whole world of possibilities – the perfect setup for every family back garden or school playground.

Our Log Rope Bridges are a perfect solution for every magical journey, starting each new treehouse adventure right from the middle of the lawn or woodland floor, and leading it all the way upwards to a treehouse or platform.

What better entrance could there be, than feeling those butterflies of excitement and the rush of make-believe from the moment you place your foot on that very first log and then cross the Rope Bridge into a faraway kingdom or land.

When incorporating a change in height into our designs, using flat Rope Bridge ‘slats’ simply wouldn’t do the job; too much of a gradient and the bridge would literally turn into a slide! The answer is in the use of round timber logs set inbound on ropes or steel cables, providing the intrepid climber with suitable ‘steps’ whilst they hold onto the rope balustrades.

Typically, with Rope Bridges up to approximately 4.8m in length (which is ideal for a Rope Bridge entrance), we integrate a fixed-beam into the Rope Bridge to hold the two ends apart.

The route up and into a treehouse needs to be exciting and imaginative and very much a part of the play journey itself and this is where the magic begins. Log Rope Bridges offer that perfect – not to mention most adventurous – entrance to any garden or backyard treehouse play-set or platform decks.

A superb project built within a desert canyon in the heat of Qatar. Designed to look like a wild jungle-style Rope Bridge this creation is made with high-quality ropes and professional-grade metal supports.

Incredible suspended tree canopy platform. The perfect way to view the surrounding woodland from a high vantage point. Use the treetop walkway bridges to reach the wooden deck and look out to see birds and wildlife. Built within an RSPB nature reserve you can spot, bats, rare birds and other woodland creatures.

An amazing project, a Rope Bridge over a woodland river. An exciting way to introduce new and creative pathways through your own garden. Reach new ground with ease in an adventurous way. A brilliant addition to a family home.

A Tree-top Walkway taking an adventure journey through the woodland and the opportunity to Zip Wire across a lake and bring the button seat back for the next go.

Rope Bridges with a ‘fixed-beam’ structure from treehouses leading to decks and platforms. Perfect for bridging level platforms, decks or treehouses – Fixed-Beam Rope Bridges have an end-to-end ‘beam’ through the rope balustrades.

Beautiful garden project on the amazing island of Jersey. In a wonderful family garden setting Treehouse Life created a long Rope Bridge spanning across a pond, also an exciting Zip Wire for young adventurers to enjoy.

Rounded treads to connect from lawn to treehouse – Log Rope Bridges are fantastic wherever you need a change of height. Leading from the garden and into a suspended ‘free-floating’ treehouse, Tree-top Walkway and Zip Wire. Supported by steel cables extending higher into the tree to create a ‘free-floating’ suspended treehouse and garden Log Rope Bridge entrance.

A stunning collection of professional Rope Bridges accompanied with 4-sided rope ladders. An incredible way to walk around the tree canopy in a safe and exciting way. Brilliant for adding new pathways high in the tree canopy close to nature and wildlife. The hanging V-shaped Hammock Bridges are wonderful for relaxing and laying down in as well as a ton of fun.

School project completed with triple Rope Ladders and a Treetop-Trail Rope Bridge, a brilliant way to encourage active play in the great outdoors getting children to interact with nature.

The UK’s longest and highest treetop walkway at Groombridge Place in Kent. Walking in a deep within a 2.1m ‘V’ shaped safety netting and tree-to-tree in a free-flowing, suspended and ‘floating’ soft ‘hammock-style’ experience. Wild deer adventuring in the woods underneath whilst in a beautifully relaxed and quiet place to observe nature.

Amazing aerial adventure park, built in surrounding woodlands and nature. With Treetop Walkway bridges, Rope Ladders, Zip Wires and Tree Swings this play area hosts a wealth of exciting play equipment.

A selection of Treetop Walkway Bridges by Treehouse Life. These stunning bridges act as large hammocks, perfect for woodland relaxation and fun. Immense enjoyment and excitement for adventurers of all ages. Wonderful adventure play equipment by Treehouse Life.

Scottish adventure park equipped with our Treetop Walkway. Walk around the woodland with ease reaching the tree canopy and wildlife, these bridges are immense fun and make an awesome experience.

A seriously impressive Rope Bridge built in an amazing rural setting. Spanning across a small ravine and surrounded by an established woodland this is an incredible way to walk within the trees. Built with top-quality materials these bridges are fun and built to last.

Such an incredible Rope Bridge built for the National Trust. Designed and made to cross over an impressive river this bridge is exciting and fun. Giving access to new land across the river this bridge is a great addition to the property. Superb fun, safe and adventurous these bridges bring Indiana Jones to mind. Amazing stuff by Treehouse Life.

A superb gallery showcasing some stunning rope bridges and treetop walkways for an Oxford treehouse project. Nestled in a wonderful woodland this adventure play treehouse hosts many different play options and encourages hours of fun in the great outdoors.

“Treehouse Life Ltd created a stunning Treehouse and Rope Bridge for our garden project in Lancashire, The Old Vicarage. The structure is a timeless addition to the garden and is loved by the family. As a garden feature, a destination and a source of play it is just perfect. We have had many enquiries and admiring comments regarding the Treehouse, in fact it features in some of our most popular photos on Houzz. The project was a finalist at the Northern Design Awards in 2015. We would highly recommend Paul and his team to any client and hope very much to join forces in the near future.”

"We hired Paul and his team to build a Rope Bridge in the Seychelles on the site of a Spa we are constructing for a 5 star resort. We are very pleased with the efficient quality service and we were provided with and the end result looks fantastic."

“I would highly recommend Treehouse Life. Their design for a play area for my children was well thought out and fitted perfectly into the space we had. They were quick to install and the quality of the materials and the overall build is exceptional. My children love playing there, so in short it was well worth it.”

Cable-stayed bridges are a subcategory of suspended structures. A cable-stayed bridge is similar to a suspension bridge in having towers and a deck-girder supported by cables; however, its diagonal cables transfer the vertical loads from the deck directly to the towers. Thus, the main deck-girder of a cable-stayed bridge works like a continuous beam on cable supports (more flexible than pier supports) with additional compression force throughout the deck. A cable-stayed bridge is also a prestressed system as its cable-stays are additionally tensioned to counterbalance a significant part of the vertical loads on the main deck-girder.

The Strömsund Bridge in Sweden, completed in 1956 with a 182-meter (597-foot) main span, is considered the first modern cable-stayed bridge. For the following 65 years, cable-stayed bridges have seen a dramatic increase in both the number of new structures and in long-span achievements. By 1995, there were only 3 cable-stayed bridges with spans over 500 meters (1,640 feet); 25 years later, there are already 67 cable-stayed bridges with spans over 500 meters (including three over 1,000 meters or 3,280 feet). Another 29 with spans over 500 meters, with some over 800 meters (2,624 feet), are currently under construction.

The efficient range of cable-stayed bridges is moving towards even longer spans. There is no other bridge structural system exhibiting such rapid development. Most cable-stayed bridges are visually beautiful, and some are among the most impressive of engineering achievements.

The idea for the cable-stayed system was perhaps inspired by the drawbridges of medieval castles and the rope-braced masts of tall ships. The very first documented image of a cable-stayed bridge appears in the Machinae Novae, a book by Fausto Veranzio published in 1615.

Predecessors for modern cable-stayed bridges appeared in the 19th century in the form of different hybrid combinations of suspension systems with additional diagonal straight cables, as in the case of the Albert Bridge, UK (1873). The best known of these hybrid structures is the Brooklyn Bridge, New York, 1883, with a 486-meter main span (1,594 feet), for which John Roebling used diagonal cables for stiffening the structure.

In the 1960s and 1970s, the system was developed further to replace many of the bridges destroyed in Germany during World War II. In this period, the system was also used for roof structures requiring long, column-free spaces in buildings. Initially, cable-stayed structures were used for bridge spans of 60 to 250 meters (196 to 820 feet) but today they span much longer distances and are the only system that challenges suspension bridges in super-long spans. Their spans grew to 302 meters (990 feet) in 1959 with the Severin Bridge (Germany), to 404 meters (1,325 feet) in 1974 with the Saint Nazaire Bridge (France), and 856 meters (2,808 feet) in 1995 with Michel Virlogeux’s Normandy Bridge (France). Today, the Russky Island Bridge (Russia) has the longest span of this system, 1,104 meters (3,622 feet) achieved in 2012 (Figure 1).

In the United States, we can mention the second Sunshine Skyway Bridge with a span 366-meter (1,200 feet) in 1987 (Florida), the Dames Point Bridge with a 396-meter span (1,300-foot) in Florida, and the Arthur Ravenel Bridge with a 471-meter span (1,545-foot) in 2005 (South Carolina).

The main elements of a cable-stayed bridge are towers or pylons, deck girder(s), cable-stays, anchorages, and foundations. Tower and pylon are interchangeable terms; lighter, slender towers are often called pylons. The classic cable-stayed bridges are symmetric with one central span, two side spans, and two towers; such are most cable-stayed bridges with spans above 600 meters. The back-up cables may extend over several side spans.

Asymmetric cable-stayed bridges have one main span and one side span, with a single tower. Multiple-span cable-stayed bridges have two or more (usually equal) main spans. Several examples are shown in Figure 2.

Some sub-divisions are used for cable-stayed bridges: extradosed, under-spanned (under-deck), cradle, inverted Fink truss, and tensegrity. The cables at the towers can be arranged in parallel (harp), fan, star, or mixed configuration. Various structural solutions are used for the towers: single pylons, double-leg portals (vertical, slightly angled, free-standing, or interconnected as a portal frame, with “A,” “H,” “Y,” or inverted “Y” shaped arches).

For deck-girders: beams of prestressed concrete or steel, box girders of prestressed concrete or steel, similar to those in modern suspension bridges;

For cables: high-strength steel wires, usually 270 grade (270 ksi, or 1,860 MPa), built from 7-wire, ⅜-inch (9.5 millimeters) strands per ASTM A886, other higher-grade steel wires, carbon fiber-reinforced polymers (CFRP), or composites. Prestressed concrete has been used in the past, but should be avoided as it has been proven unsafe on some failures such as the Morandi Bridge;

For long-span bridges, foundations on soft soils, or for bridges in high seismic areas, it is preferable to use predominantly steel structures to reduce the self-weight and the related earthquake forces.

The most important part of bridge design is the overall concept for the structure and its elements: the selection of the appropriate structural system for the bridge considering its specific function, site location, and required spans. A well-selected concept determines the efficiency and economy of the bridge, saves materials, cost, and construction time. Good design concepts minimize problems and future difficulties both in the design office and on the construction site.

For the design of early cable-stayed bridges, engineers used a relatively small number of cables. After acquiring more experience and with the introduction of structural design software, engineers were able to use a larger number of cable stays, reducing the demand on the deck girder and leading to greater efficiency and longer spans.

The basics of cable-stayed bridge design are as follows: the vertical loads on the deck are supported by diagonal cable stays that transfer these loads to the towers. At the tower, the horizontal components of the cables from the main span are in balance with those from the side/adjacent spans. The towers support and transfer the vertical load to the foundations. Similarly, the cumulative compression horizontal components of the loads from the main span are in balance with the compression load components of the side spans. Therefore, the entire bridge system is in balance with predominant compression forces in the towers and the deck system, and with tension forces in the cable stays. The system is self-balanced, provided that all elements are designed correctly to sustain the maximum demand from the highest possible combination of loads.

The challenge for the design engineer is to select an appropriate combination of the multiple possible variations of towers, cable-stay arrangements, and deck systems. Like all suspended structures, cable-stayed bridges are sensitive to deformations and it is necessary to check the deformed condition of the system for all load combinations, including those during the different phases of construction.

Today’s structural design software greatly assists engineers in the calculation of cable-stayed bridges. After choosing the main parameters of the system, it is essential to establish the start-up dimensions and sections of the deck-girder, cables, and towers. A simple design approach will help in setting up these dimensions.

For a start, the designer can use a substitution simply-supported beam for determining the approximate bending moments for the main span deck-girder. The upward cable-stays pretension can offset most of the moments from permanent loads on the deck. This is achieved with additional tensioning of the cables after erecting the main elements to counteract permanent loads, resulting in minimal vertical bending in the deck-girder. The cables should be additionally tensioned to counteract 50% of the combined temporary downward loads (live loads, wind, snow, ice, and earthquake). This way, the working bending moments of the deck-girder will vary during operation approximately between 50% of the positive moments (from the worst temporary load combination) to 50% of the negative moments from temporary loads. This “first step” determines the design moments for the main span deck-girder. The compression in the deck-girder due to the horizontal components of cable stays forces is the cumulative sum of these components, approximately 55 to 65% of the total vertical loads on the main span depending on the span, the number of cables, and the height of cable connections at the tower. The cumulative compression force (ΣPc) in the deck-girder is equal to the sum of all compression forces Pci at cable connections (Figure 4) at the deck: the tension cable force Pcable = Pv/sin α,

These calculations will allow the designer to establish the initial design dimensions for the cables, deck-girder, and tower to be used in the computer model for further adjustments and refinements of the system. The deck-girder has to be designed for the compression and bending from the cable-stay system and the typical bridge deck design for vertical dead and live loads. The initial approach described above will help to achieve the desired final goal faster.

Cable-stayed bridges are efficient in cost, materials, and construction time. They have better efficiency than other bridge systems, with the only competitor being suspension systems, while allowing for more straightforward construction methods. An additional advantage of cable-stayed bridges is their larger efficient span range from 100-meter spans (328 feet) to over 1,000-meter spans (3,280 feet).

The multitude of possibilities of the system provide engineers and architects with many design options. The “mid-long range” structures allow more creativity, originality, and possibilities for innovative work. A cable-stayed bridge does not need to be extravagant. The most straightforward bridge with a “sincere” structure is often the best and is usually elegant and attractive.

Cable-stayed bridges have a combination of elegance, slenderness, and a feeling of robustness. The national infrastructure’s demand for more bridges requires the priority of efficiency and economy.

Like all other bridge systems, cable-stayed bridges are continuously improved based on the development of high-strength materials and new construction technologies. More valuable for engineers are the modifications of established structural systems and newer sub-systems. In addition to the increased number of cable-stayed bridges with longer spans (above 600 meters or approximately 2,000 feet), there is increasing use of the system for pedestrian bridges. The lower loads and shorter spans allow engineers to explore new approaches, transforming the building of these bridges into a testing lab for innovation. As such, we may consider the extradosed, under-spanned, and inverted Fink truss sub-bridge systems, all oriented to improved efficiency.

One area of further development is the pursuit of combinations/hybrids of cable-stayed and suspension bridge systems for achieving super-long spans. The idea is to reduce the suspension span length by moving the suspension support points inward along the span. This not only reduces the suspension span length but the required tower height as well while allowing a longer clear span. This is obtained with “cable-stay cantilevered alternatives” at the bridge towers, adding “on-deck” cable-stayed pylons (Figure 5). With 500-meter (1,640-foot) cantilevers and cable-stayed “on-deck” pylons used on each side of a total clear span of 3,000 meters (9,842 feet), the suspension part is reduced to 2,000 meters (6,561 feet). Such reduction would allow using main suspension cables of the size and type of those already used in bridges, like the Akashi-Kaikyo at 1991 meters (6,532 feet), for a much longer main span.

Based on current technical progress and fast development, cable-stayed bridges may reach spans 2,400 to 2,600 meters (7,600 to 8,500 feet) in a short while; such design will require towers about 500 to 570 meters tall (1640 feet to 1,870 feet), something achievable, considering already completed skyscraper structures. This will extend the efficiency range for cable-stayed bridges to very long spans above 2,000 meters (6,561 feet). A hybrid cable-stayed-and-suspension system would make possible even longer spans of up to 3,000 to 3,400 meters (9,842 to over 11,000 feet), incorporating a “pure” suspension bridge of “only” 2,200 to 2,400 meters (7,218 to 7,874 feet).

Based on the efficiency and advantages of cable-stayed structures, American engineers and transportation agencies should consider more cable-stayed bridges when planning new projects. Greater use of cable-stayed bridges may upgrade the infrastructure with these efficient, faster built, and elegant structures. Making cable-stayed bridges more popular may also help our bridge engineering profession regain its position of leadership in the design and construction of long-span bridges.■

A suspension bridge is referred to a type bridge supported by cables. This type of bridge has been with mankind since ancient times. Today’s large and magnificent suspension bridges were made possible through the establishment of structural analysis methods, material developments, construction methods, and computer technology developments. Suspension bridges are one of the most beautiful special bridges, and are considered one of the types of bridges many structural engineers dream to design.

The classification according to the girder type is based on the degree of freedom of the suspension bridge girder. The 3 hinged stiffening girder type is interpreted as a statically determinate structure, and the 2 hinged stiffening girder and continuous girder type are interpreted as statically indeterminate structures. Continuous girder types are used when external loads are large, such as in road rail bridges, because they increase the stiffness of suspension bridges and reduce the amount of deflection.

An earth-anchored suspension bridge is a type of bridge in which the main cables are anchored on large concrete blocks, or on the ground, located at the ends of the bridge. External loads applied to suspension bridges are transferred to the suspenders main cables anchorages & pylons and finally to the ground.

A self-anchored suspension bridge is a type of bridge supported by the main cables anchored to the girder. External loads applied to suspension bridges are transferred to the girder through the suspenders main cables pylons and anchorage inside the girder. Therefore, unlike earth-anchored types, girders behave as bending and compression members.

Suspenders/Hangers of suspension bridges are usually used with vertical suspenders, and diagonal suspenders can be used to increase the damping on bridges. However, an evaluation of slacking and early fatigue due to the large tensile forces is required. In order to take advantage of cable-stayed bridges and suspension bridges, a hybrid bridge system, in which a cable-stayed system and suspension system are used together, can be implemented.

Stiffening girders of suspension bridges are longitudinal structures that support or distribute vehicle loads. Furthermore, since the stiffening girders are supported by cables, aerodynamic stability is required. In the past, I-girders were mostly used for stiffening girders, but later they were developed into truss structures due to aerodynamic stability problems, and most recently been developed into box-shape cross-sections.

Truss girders are proposed for stiffening girders because plate I-girders are disadvantageous with regards to aerodynamic stability. One example in which plate I-girders were used is the Tacoma Narrows Bridge, which is famous for its collapse due to aerodynamic instability. Truss girders can increase the torsional stiffness of suspension bridges by raising the vertical height of the girder and installing horizontal lower bracings. Furthermore, the top and bottom layers of the girder can be used by taking advantage of the height. However, truss girders have large drag due to their heavy weight and long span.

As bridges get longer, it is necessary to secure the torsional stiffness of girders in order to resist aerodynamic loads. This means that it is important to optimize the shape of girders in order to increase the limit wind speed that causes the girder to flutter. Multi-box girders are girder types that secure aerodynamic stability in modern long bridges. Multi-box girders are low in height and light in weight, which reduces the size of cables, pylons/towers, and anchorages, leading to a much economical bridge design.

The main cables used in suspension bridges are tension members, such as ropes, wires, chains, etc., that cannot resists bending or compression, and can only support axial tension. In general, tensile strength of 1,600 ~ 1,800MPa is used for the main cables, but recently, cable steel wires for bridges with tensile strength of 2,200MPa have been developed. Since parallel cables have greater strength than structural steel, the cross-sectional area of the cables is reduced, and thus, secondary stresses, manufacturing errors, and the amount of main cables are significantly reduced.

Cable construction method is mainly divided into Air Spinning method (hereinafter referred to as AS method) and Prefabricated Wire Strand (hereinafter referred to as PWS method).

The AS method uses the cable Hauling system to construct cables in wire units. Wires are formed in strand units at the construction site and constructed as main cables. This method has the advantage of reducing the size of the anchorages. However, wires are sensitive to wind loads and the construction period is longer than wires constructed using the PWS method.

Suspenders are cables that connect the main cables to the girders. There are two main types of suspenders: Center Fit Rope Cores (CFRC) and Parallel Wire Strands (PWS). The CFRC hanger (suspender) system is a method of placing high-strength galvanized steel wires twisted in a spiral shape on top of the band of the main cable and fixing the bearing plate at the saddle-type reinforced girder hanger anchorage. The PWS hanger system is a method of pin-anchoring high-strength galvanized steel wires that are tied together parallelly, forming a hanger rope that is covered by Polyethylene, to the cable band sides and the reinforcing girder sides, respectively.

Special types of suspenders are located at the center of any suspension bridge. These are used to restrict the relative displacement between the girders and main cables in order to suppress the deformation in the longitudinal direction of the girders, and alleviate the deflection angle of the suspenders in the lateral direction. There are mainly two types of special suspenders: center stay types and center lock types. Center stays are prestressed cable stays that connect the girder to the main cable. This type of cable stay is suitable for suspension bridges with a main span of 1,000m or less, assuming fracture during earthquakes. Center lock is a structure that connects the girder to the main cable with a steel frame. This structure can resist axial forces, shear forces, and bending. Furthermore, center locks have structures that can withstand earthquakes and are suitable for suspension bridges with long spans.

Cable bands are members that connect the main cable and the hanger cables. The cable bands wrap the main cable and are fastened by using cable band bolts. These bolts can be fastened horizontally or vertically as shown in the figure below. Horizontally fastened cable band bolts have an advantage in terms of maintenance because they prevent water infiltration, while vertically fastened cable band bolts have the advantage of having fewer bolts for fastening the cable bands, leading to a more economical design.

Saddles rest on top of the pylon and anchorage, and directly support the main cable. Its mechanical role is to transfer the loads from the main cable to the pylons and anchorages. Saddles installed on pylons are called pylon saddles, and saddles installed on anchorages are called splay saddles. For pylon saddles, setting the radius of curvature of the saddles is very important. The radius of curvature should be determined in consideration of the bending stresses of the cables and the contact pressures between the cables and the saddles. In the case of splay saddles, the cables can be fixed to the anchorages in a radial shape. Furthermore, when designing the saddles, the horizontal and vertical curvatures of the strand must be properly calculated.

Pylons of suspension bridges transmit the loads from the main cable to the ground through the foundations. Stones were the first materials to be used for pylons, but nowadays, materials such as steel and concrete are mostly being used. The shape of the pylon is limited in cross-sectional shape due to the limitations of the construction method, and most of the shapes follow a pattern. The Yeongjong Bridge in Korea has a diamond-shaped pylon, but due its narrow tower top, a three-dimensional main cable was applied. Furthermore, suspension bridges with one main tower can diversify the shape of the main pylon to emphasize its aesthetic appearance. In the table below, steel pylons and concrete pylons are briefly compared:

Anchorages are important structures that transmit the horizontal and vertical forces of the main cable to the foundations. The types of anchorages are classified into gravity-type anchorages, tunnel-type anchorages, and rock anchorages. Gravity-type anchorage consists of a method of resisting the loads from the cables with the self-weight of the foundation and anchor frame. Many suspension bridges use gravity-type anchorages. Tunnel-type anchorage is a method of resisting the loads of the cables by using the shear forces of the outer circumference of the steel frame and the pressure of the plug body. Rock anchorage is a method of resisting the loads of the cable by using the weight, adhesion, and frictional resistance of rock wedges. This method is used in areas with good rock formations.

Unlike other types of bridges, there are many factors to be considered in advance in the design of suspension bridges. For example, extensive review is needed in the following factors: selection of the shape of suspension bridges, review of girder cross-section in terms of aerodynamics, structural planning considering the construction method, and maintenance plan. Suspension bridges are often used as memorial structures due to their size and appearance, so the entire landscape, including temporary construction sites, must be reviewed in advance. The schematic design process of suspension bridges is as follows:

Structural analysis of suspension bridges is performed by conducting the displacement method using a frame model consisting of axis lines for the pylons, reinforcement girders, and cables. The cables, which are uncompressed members, can be modeled as truss elements. In this case, compression forces may occur when live loads are applied. These compressive forces only reduce the tensile forces of the cables, and the compressive forces must not be applied to the entire structural system. Furthermore, since the tension and elongation of the cables, due to the cables’ sag, are not in a linear relationship, non-linear characteristics must be considered.

The initial linear analysis is an analysis that identifies what kind of behavior the structure shows when all processes are finished and the structure is completed. The final stage of the suspension bridge is in equilibrium with respect to the structure’s own weight. This is referred to as the initial equilibrium state of the suspension bridge, and calculating the coordinates and tension of the main cable at this time is called the initial equilibrium state analysis. The initial linear analysis of suspension bridges is an analysis of the behavior of the structure under additional loads, including the initial equilibrium state analysis. Suspension bridges exhibit considerable nonlinearity in the construction stage due to their behavioral characteristics; however, they exhibit linear behavior for additional loads (vehicle loads, wind loads, etc.) under the final stage in which sufficient tension is introduced for the main cables and suspenders. Therefore, the tension of the main cables and hangers(suspenders) introduced in the initial equilibrium is converted into geometric stiffness, enabling linear interpretation of additional static loads. This method of linearized analysis by converting the member forces generated in the initial equilibrium state into geometric stiffness is called the linearized finite displacement method. The linearized finite displacement method is applied to the final stage analysis since a sufficient degree of solution can be obtained. This initial linear analysis is carried out to calculate the shape at completion, and to calculate the shape of the main components such as cables, hangers, and reinforced girders.

Unlike the initial linear analysis for determining the initial shape of the structure due to its self-weight, the global structural analysis is intended to examine the design of the main components of the structure and the stability during use. Therefore, in addition to dead loads, the analysis is carried out by combining different loads such as live loads, wind loads, temperature loads, earthquake loads, and differential settlements.

The construction stage analysis is carried out to check the cross-sectional forces for safety check of major components such as cables, pylons, reinforcement girders, etc., and to examine the setback amount of saddles. In the construction stage analysis, the displacements at each stage are large, so the large displacement theory (geometric nonlinear theory), which constitutes the equilibrium equation, should be applied to the shape after deformation in the structural analysis. The construction stage analysis of suspension bridges is performed by backward construction stage analysis, which analyzes the construction procedure in reverse order in the initial equilibrium state of the final stage. In other words, using the geometric shape and initial tension in the initial equilibrium state as a reference model, members added to each construction stage are removed, and the self-weight of the removed members is loaded in the opposite direction of gravity.

, we’re looking at the four most popular bridge types, how they work, the locations they’re ideal for, the benefits of each, and amazing examples across the globe.

Everyone loves looking at — and traveling over —suspension bridges. They’re elegant, light, and airy yet strong. Suspension bridges and their variations are able to span longer distances than any other type of bridge.

As the name suggests, this type of bridge suspends the roadway from cables, which extend from one end of the bridge to the other. The cables rest on top of towers and are secured at the ends of the bridge by anchorages.

The towers make it possible for engineers to stretch the main cables across very long distances. The towers and cables also carry most of the weight of the bridges. The weight is transferred to the anchorages, which are typically embedded in solid rock or large blocks of concrete. Within the anchorages, the cables are spread over a relatively large area to better distribute the load. This helps prevent the bridge cables from breaking free, which would cause the structure to fail.

Believe it or not, the earliest cables used to support suspension bridges were made from twisted grass. By the beginning of the 19th century, engineers started using iron chains to suspend the road beds.

Today, the cables of suspension bridges are made from thousands of steel wires twisted and bound tightly together. Steel is an ideal material for these cables because it can withstand tension. Studies show that a single steel wire only 0.1 inch thick is able to support more than one half ton without breaking.

Unfortunately, history has shown that suspension bridges aren’t unbreakable. Because they are so light and flexible, extreme winds and earthquakes have been known to damage and in some cases, destroy them.

The ultimate example: TheTacoma Narrows Bridgewas the third-longest suspension bridge in the world when it opened in 1940 in Washington state. It was soon given the nickname, “Galloping Gertie,” because of how it performed when it was windy. Not only did the deck sway back and forth, it also jumped up and down, even in only moderate wind conditions. It was so bad that drivers reported that vehicles in front of them would disappear and reappear from view as they crossed the bridge.

Several attempts were made to stabilize the structure using cables and hydraulic buffers. However, they were not successful. The bridge collapsed in a 42-mile-per-hour wind on November 7, 1940, just four months after it opened. Engineers had designed the bridge to hold up against winds of up to 120 miles per hour.

After the Tacoma Narrows Bridge collapse, engineers began applying the science of aerodynamics to bridge design. Today, proposed designs must be wind-tunnel tested. This unfortunate incident ushered in an era of stronger, safer, and more elegant suspension bridge design.

The lessons learned were applied to the replacement for the Tacoma Narrows Bridge, which was finished in 1950. It’s wider than the original, has stiffening trusses under the roadway, and includes a narrow gap down the middle, all of which limit the effect of the wind.

The Akashi Kaikyo Bridge is currently the world’s longest suspension bridge. It links the Japanese city of Kobe on the mainland of Honshu to Iwaya on Awaji Island. It crosses the busy Akashi Strait as part of the Honshu-Shikoku Highway. It was completed in 1998 at a cost of $7.6 billion.

Withcable-stayed bridges, the cables are attached directly to the towers, which handle the load. The cables can be connected to the roadway in two ways:

Today’s cable-stayed bridges often look futuristic, and most people think they’re a new innovation. However, the idea for them goes back more than 400 years. The earliest known design for one appears in “Machinae Novae,” a book published in 1595.

It took until the 20th century for engineers to actually begin building them. The reason was necessity. After World War II, steel was scarce in Europe. The design turned out to be perfect for rebuilding bridges that were destroyed, because they used less steel that other alternatives.

In general, cable-stayed structures are best-suited for medium-length bridges, usually between 500 and 2,800 feet. Although longer cable-stayed bridges have been built, suspension bridges are still typically used for bigger spans.

Compared to suspension bridges, cable-stayed ones are generally faster to build and more cost effective. They’re less expensive because they require less cable and can be built from identical precast concrete sections. Despite this efficiency, cable-stayed bridges are beautiful.

One of the earliest examples of a noteworthy cable-stayed bridge in the U.S. is the Sunshine Skyway Bridge in Tampa, Florida. It was awarded the Presidential Design Award from the National Endowment for the Arts in 1988.

The bridge is painted a bright sunshine yellow, which plays against the water around it. It was one of the first bridges of its type to attach cables to the center of the roadway. Most earlier versions placed cables at the outer edges. This innovation gives drivers a clearer view of the surrounding bay.

One of the most famous — and widest — cable-stayed bridges anywhere crosses the Charles River in Boston, Massachusetts. The iconic structure, completed in 2002, has become a landmark in a city filled with them.

Officially named the Leonard P. Zakim Bunker Hill Memorial Bridge, the viaduct was a critical component of The Big Dig Project, which connected the city using a system of under- and above-ground roads and bridges. The Bridge serves as the impressive northern entrance to the city of Boston and is an ideal example of one perfectly suited to its location.

Bridges are such a common part of everyday life, they’re often taken for granted. Whether driving, walking, or traveling by train, they make it possible for us to cross bodies of water, valleys, roads, and other geological and manmade barriers. Equally important, they allow vital utility lines, including cables and pipelines, to span these barriers as well.

Let’s take a look at some common bridge designs, how they evolved over the centuries, and the purpose each design serves. While we’re at it, we’ll step back and admire a few notable examples of each. It could help you and your clients view bridges in a new light.

Beam bridges are generally considered the simplest form of bridge. How simple? When cavemen laid logs over streams to cross them, they were building the earliest beam bridges.

These basic bridges typically span relatively short distances. In order to build a beam bridge (also known as a girder bridge), all you need is a rigid horizontal structure (a beam) and two supports, one at each end, to rest it on. These things support the downward weight of the bridge and any traffic traveling over it.

The simplest beam bridge could be a log, wood plank, or stone slab laid across a narrow creek or stream. More complicated ones are usually constructed of steel or concrete or a combination of the two. The concrete elements may be reinforced, pre-stressed, or post-tensioned.

To understand how this works, think about this simple model or try it out in your garage. Imagine taking a board and laying it on top of two bricks. This is a simple beam bridge. If you were to place a heavy weight in the middle of the board, it would bend. The top side would bend in under the force of compression, and the bottom side would bend out under the force of tension. Add enough weight, and the “bridge” would eventually break. The top side would buckle and the bottom side would snap.

Beam bridges are generally used to cross relatively short distances (usually less than 250 feet) because unlike other types of bridges, they have no built-in supports. The only supports are provided by piers. The farther apart the supports, the weaker a beam bridge gets. This doesn’t mean beam bridges can’t be used to cross longer distances, it simply requires that a series of beam bridges must be joined together, creating what’s known as a continuous span.

Longer, more complex beam bridges are built using many beams lined up side by side with a deck across the top of them. The main beams could be I-beams (also known as H-beams), trusses, or box girders. They could run halfway across the bridge or across its full length.

Beam bridges are used to carry pedestrians, automobiles, trucks, and rail lines across limited-distance spans. They’re frequently used for monorail and raised transit systems. They’re also valuable for carrying utility cables and pipelines over short distances to homes, isolated communities, and subdivisions.

Hint:Many beam bridges are historic structures, and there are limits as to how utilities can be conveyed over them. The state of Connecticut, home to many such historic bridges,offers guidelineson how to handle this.

A truss bridge features a prominent truss, which is a structure of connected elements that form triangular units. A truss is used because it’s a very rigid structure that transfers the load from a single point on a bridge to a much wider area. Truss bridges can cross longer spans than basic beam bridges.

Truss bridges were built mostly of wood in the early 1800s and slowly shifted to iron construction by the middle of that century. Steel became the standard by the 1880s. Some states continued building steel truss bridges through the 1930s, while others abandoned them sooner, choosing to build concrete girder and beam bridges instead.

Examples of these bridges still exist across the United States, but the number is decreasing because they’re being demolished and replaced with more modern types of bridges. Some truss bridges are extremely plain and utilitarian, while others use more elaborate design details.

Throughout history, engineers experimented with different forms of truss bridges, trying to find better ways to solve particular problems. A truss bridge can have a deck or roadbed on top (deck truss), in the middle (through truss), or at the bottom of the truss. If the sides of the truss extend above the roadbed but are not connected, it is called a pony truss or half-through truss.

Truss bridges are crossed by pedestrians, automobiles, trucks, light rail, and heavy rail. They’re usually used to span rivers rather than roads. Truss bridges have historically been used to carry water and sewage through pipes across spans. Over the years, electrical and cable lines were added as well. Much of this utility infrastructure is aging, and even if the bridge isn’t being replaced, utility lines often need to be.

Note: It’s important to use safe equipment designed specifically for under-bridge maintenance when updating aging utility infrastructure under truss bridges. Check out these examples.

These types of bridges are built using cantilevers, which are structures that project horizontally into space, supported on only one end. For small footbridges, the cantilevers may be simple beams. Larger cantilever bridges designed to handle road or rail traffic use trusses built from structural steel or box girders built from pre-stressed concrete.

Steel truss cantilever bridges were a major engineering breakthrough in the 1800s, since they can span distances of over 1,500 feet and are more easily constructed at difficult crossings, such as highways, deep waterways, or populated areas, using little or no ground support.

Cantilever bridges can be built without false-work below and supporting towers and cables above. This level of construction simplicity is one of their great advantages. They’re also of very rigid construction, so they can carry relatively large loads, including rail lines, which is a common use for these bridges.

Many of these bridges carry utilities across their spans in dense urban areas. Check out this example of a major project that coordinated installation of a variety of utilities, including fiber-optic networks, gas, water, extensive stormwater, wastewater, and government-secure communication lines in a single project.

The arch bridge is one of the most common types of bridges. They came into use over 3,000 years ago and remained popular until the industrial revolution. At that time, the invention of steel, concrete, and other advanced materials helped engineers develop other modern bridge designs. However, arch bridges remain in use even today, and with the help of modern materials, they can be built larger than they were in the past.

An arch bridge has abutments at each end and is shaped as a curved or pointed arch. Arch bridge engineering is based on transferring the weight of the bridge and its loads partially into a horizontal thrust pushed back together by the abutments at either side of the bridge. A longer bridge can be made from a series of arch bridges, although more economical options are typically used today.

Believe it or not, stone and wood arch bridges became very popular during the Roman Empire. Roman engineers built over 1,000 stone arch bridges in Europe, Asia, and North Africa. Many of those bridges remain standing even today, demonstrating their strength and durability. Similar bridge-like structures were among the first to serve a utility-related function. They were used to carry water from outside of cities into urban areas, similar to how bridges today carry pipes to transport water from place to place.

As centuries went on, medieval architects improved on earlier designs, creating arch bridges with narrower piers, thinner arch barrels, pointed arches, and increased arch spans. Renaissance architects not only built some of the most structurally sound bridges in history, they also created some of the most beautiful. The Rialto Bridge in Venice is one such example. In the last 150 years, bigger and more ambitious arch bridges have been built out of iron, steel, and concrete.

The strength and durability of arch bridges allow them to be used to carry pedestrians, vehicles, light rail, and heavy rail, and as mentioned, some have been built to exclusively carry water from place to place. When it comes to supporting modern utilities, arch bridges are often not effective. It’s impossible to support the required infrastructure within the arch, and placing it along the side of a bridge can be unsightly and leave them exposed to weather.

In fact, most states offer guidance on how utilities should be suspended from bridges, and it’s hard to find any that offers advice on how to do so on an arch bridge, except for this example from the state of Washington.

This type of bridge has suspension cables between towers and suspender cables hanging from towers, which hold the deck. Suspension cables are anchored at each end of the bridge, and they carry the majority of the load.

Today’s complex suspension bridges evolved from simple versions dating back to the fifteenth century. They had load-bearing cables but no towers. The most basic suspension bridges include rope, net, and other woven bridges.

The first modern-style suspension bridge in the United States was built in Pennsylvania in 1801. Over the years, suspension bridges became popular because they spanned wide gaps that other bridges could not. In addition to this, they’re less expensive to build because they use less material than most other bridges.

Suspension bridges are more earthquake-proof than virtually any other bridge type. In addition, it’s easy to update them to make room for wider vehicles or additional traffic lanes. It’s also relatively easy to suspend utility cables and power lines over long distances on a suspension bridge.

The negatives: the construction tends to be very rigid in order to make them stand up to high winds, and most cannot handle the heavy weight of trains.  It often takes special hangers to support utility infrastructure off complex types of suspension bridges.

A tied-arch bridge (also called bowstring-arch or bowstring-girder bridge) is a type of bridge that has an arch rib on each side of the roadway (deck) and one tie beam on each of the arches that support the deck. Vertical ties connected to the arches support the deck from above.

This type of bridge can be thought of as a cross between an arch and a suspension bridge. The combined construction style allows the bridge to be built with less bulky foundations than arch bridges, which means they’re a great option for difficult locations that require elevated piers or in places where the soil is unstable. The arch construction makes them ideal for situations when a bridge needs to be built offsite, delivered, and slid into place onsite. This is not possible with suspension bridges.

Tied-arch bridges may have many benefits, but they’re not perfect. They require welds at the connection between the arch rib and the tie girders and at the connection between the arch and vertical ties. These welds have to be repaired regularly, which can be costly, time consuming, and inconvenient. Construction and design of this type of bridge is non-redundant, which means that if even one of the two tie girders fail, the whole structure will collapse. Finally, tied arch bridges are more expensive to build compared to the other types of bridges of the same length.

At first glance, a cable-stayed bridge may look like a variation of a suspension bridge, but they are structurally different. Unlike suspension bridges, cable-stayed bridges don’t require anchorages and two towers aren’t necessary. Instead, the cables can run from the roadway up to a tower that holds all the weight.

The basic design of the cable-stayed bridge goes back almost 500 years. Modern versions started being built in Europe after World War II as cost-effective replacements for bridges damaged during the war.

The tower of a cable-stayed bridge absorbs and distributes all the compressional forces of the bridge. The cables can attach to the roadway in different patterns. For example, in a radial pattern, cables extend from several points on the road to a single point at the tower. In a parallel pattern, the cables attach to both the roadway and the tower at several separate points.

Today, cable-stayed bridges are a popular choice as they offer all the advantages of a suspension bridge but at a lesser cost for shorter spans. They require less steel cable, are faster to build, and incorporate more precast concrete sections. Designs for some of these bridges can offer a significant wow-factor.

Each type of bridge serves a different purpose and can be used to span different types of gaps and barriers. However, bridges are more than just utilitarian objects. They’re also engineering marvels and things of beauty. We hope this overview helps you further appreciate the details of the bridges you cross each and every day.

PFEIFER Structures designs, engineers, and installs cables, wire ropes, and other tension members as components of some of the most iconic suspension bridge structures in the world. Suspension bridges are long-span bridges capable of connecting roadways or walkways over large bodies of water such as rivers and bays. Suspension bridges are differentiated from other bridge structures by how the cables connect to the towers or pillars. A cable(s) will connect to the towers or pillars, and then to the ground, bearing the load of the structure. Cables and tension rod systems will then connect from the load-bearing cable(s) to the bridge. A suspension bridge can function as a pedestrian bridge or footbridge, a very efficient lightweight structure that allows pedestrians to cross potentially dangerous areas such as highways, rivers, and ravines.

Built in a fraction of the time and at around half the cost of conventional construction, our precision-engineered lightweight structures give architects, city planners, and developers a great alternative to traditional, heavy, and time-consuming methods of bridge construction. There are shapes, forms, and solutions we can create with lightweight architecture that cannot be replicated with any other method of construction, for example – a curved bridge deck.

In addition, the advanced membrane and cable materials can be used for covered walkway canopies to provide protection from the elements for pedestrians or to bring an architectural flair to any bridge.

Cable bridge structures are low maintenance, very economical, quick to install, provide long service life, and are sustainable. Our tension members are also used as part of a structural system of large suspension bridges offering superior material properties and exceptional performance over a long life span.

Contact us to get more information about our suspension bridge structures or to get a free consultation with the most experienced designers and engineers in the lightweight structure industry. Fill out the contact form on this page or call us toll-free at 1-877-887-4233.

Early tower installations for radio broadcasting offered problems similar to those met in guying stacks, poles, derricks and similar structures. Guys for these moderate-height structures were commonly made of regular wire rope.

Structural strand is now used for guy systems. Where larger diameter wire rope was once used, structural strand, with its higher modulus of elasticity and lower diameter-to-strength ratio, allows for smaller diameter guys. This reduction in diameter reduces ice and wind loads, which may be important in the overall design of the tower. Structural strand’s higher modulus of elasticity (less stretch) also allows for less take-up of the bolts during tensioning.

Suspension systems are ideal where long spans are required, as in highway and pedestrian bridges, supporting conveyors, pipe lines and overhead passageways in industrial plants, and overhead crossovers above railroads.

When appearance, durability, utility and ease of construction are considered, suspension bridges are often the most economical to build. For example, flood damage to exposed piers is eliminated and difficult or dangerous pier foundations can be avoidedwith a suspension-cable construction. Often the entire problem area is spanned; the foundations can be located at economical installation points where they are least likely to be damaged. Great clearance is obtained since the supporting structure is above the floor and has no intermediate supports.

Stiffening trusses may be incorporated into the design of foot bridges and similar bridges, where they also may serve as hand railings. These trusses add relatively little to the cost of the structure, and they ensure a bridge free from disturbing floor movement.

Structural strand and wire rope is used for the main cables, suspenders and wind cables of highway, pedestrian and pipeline suspension bridges. Structural strand is manufactured through 5 1/2” diameter and wire rope up to 7” diameter.

Pre-stretching greatly reduces the constructional stretch ofthe structural strand or wire rope and improves the overall elastic stability. While in the pre-stretcher, overall lengths and intermediate tower and suspender points can be measured to close tolerances under prescribed tensions.

In a tied arch bridge, the bridge deck is suspended by structural strand or wire rope hangers hung from a steel or concrete arch. Tied arch bridges normally cross short to medium spans. Structural strand has been used in tied arch bridges having span lengths of more than 1,000 feet.

The cable stayed bridge is a relatively new type of bridge, in which structural cables radiate diagonally from one or more towers or pylons to a connection point on the bridge girder. This bridge form allows a very efficient use of material, which results in a lighter structure and less massive foundation.

Cable stayed bridges have been built with a main span as long as 2,300 feet between the towers