March 29, 2019
Det finns flera olika komplicerade faktorer vid byggandet av en bro, exempelvis kanske bron ska byggas över en trafikerad järnväg eller över vatten. Då behöver bron byggas i närheten eller vid sidan av den slutgiltiga platsen för konstruktionen och den här metoden kallas för brolansering. Efter att vissa arbetsmoment och delar av bron är färdig dras de ut till sin slutliga position och för brolansering krävs utrustning av hög kvalité som klarar extrema väderförhållanden, från kalla nordiska vintrar till varmt ökenklimat.
Så gjuter man betongen för broar
De traditionella byggteknikerna fungerar tyvärr inte på alla projekt som exempelvis vid brolansering och glidformsgjutning har blivit ett speciellt sätt att gjuta betong. Det börjar med tillverkning av en glidform på bottenplattan och sedan fylls formen på med betong och armeringsjärn. Allteftersom betongen stelnar flyttas glidformen ett steg uppåt och detta sätt är mer ekonomiskt och effektivt än de traditionella metoderna.
Konstruktioner med stöd
Beroende på byggprojekt krävs olika typer av brolansering och utrustning. Kassuner har länge använts för att underlätta arbetet och ordet kassun kommer från franskans caisson som betyder låda. Dessa är en viktig förutsättning när delar av arbetet ska utföras under vattenytan och det ska ske på ett säkert, smidigt och effektivt sätt. Vanligen byggs kassunen på plats och förflyttas sedan till rätt position under vattenytan och dagens stora kassuner väger flera hundratals ton vilket gör förflyttningen komplicerad. Det krävs kompetens och speciell utrustning för att utföra tunga lyft.
Montering och lansering av överbyggnaden
När bron befinner sig på den slutliga positionen ska den vanligtvis förses med en överbyggnad i betong och sedan beläggas med asfalt. Efter det utförs arbeten som montering av räcken och belysning.
Slutliga finslipningar och kontroller
Grunden i brolansering är att delar eller hela bron byggs vid sidan av eller i närheten av dess slutgiltiga position och sedan flytta hela eller delar av bron ut till sin rätta plats. Själva lanseringen sker när det stör trafiken så lite som möjligt, exempelvis under nattetid. Metoder för att horisontell förflyttning ska bli mer effektiv och säkrare utvecklas ständigt och en ny metod som har nått stor framgång är en kombination av tunga lyft med hydrauliska lyftare och skidding-teknik. Metoden minskar på antalet rörliga delar och istället för att använda traditionella lager används en skidding-teknik med låg friktion.
Hitta företag som hanterar brolansering och utrustning i Sverige
Byggandet av en bro brukar vara komplicerade projekt med många regler och komplicerade faktorer att ta hänsyn till. I Sverige finns flera företag som har gedigen erfarenhet och kunskap om brolansering och utför arbetet på ett säkert och effektivt sätt. Kvalité och säkerhet är de viktigaste faktorerna och våra tjänster erbjuder skräddarsydda lösningar efter kundens behov och projektets mål.Continue reading →
February 26, 2019
In the caisson construction process, a caisson is a wasterlight structure that uses an anchor for foundation. It usually carries the building loads at the lower ends which are shaped as a bell. Caissons are generally constructed of concrete, steel, or wood. As with any construction project, the material to be used will depend on the function of the caisson and the type of caisson being constructed.
Caisson construction services include a whole procedure of pre construction, during construction and post construction. On completion of the caisson system there is a provision of engineered drawings to make the process appear wholesome.
Considering all the processes of construction, a caisson is said to be a critical component since it provides stability. Where the ground can, and will, shift under the weight of a new structure, a caisson can be used to distribute its load evenly.
The Caisson Construction Process
Following are the step to be followed to build a caisson:
- After some initial formwork and concrete pours, the cutting edge is floated to the breakwater by towboat and fastened to the caisson guide. Concrete is placed into steel forms built up along the perimeter of the box. With every concrete placement, the box becomes heavier and sinks into the water along the caisson guide.
- Forms are also built inside the box around the air domes and concrete is placed in between. The resulting open tubes above the air domes are called dredge wells.
- When the caisson finally touches the river bottom, the air domes are removed and earth is excavated through the long dredge well tubes, as shown in the animation below. The caisson sinks into the river bottom. Excavation continues until the caisson sinks to its predetermined depth.
- As a final step, concrete is placed into the bottom of the hollow dredge wells and the tops are sealed.
Conditions Requiring Caisson Construction
Below mentioned are some of the common instances for caisson construction:
- When the soil contains large boulders, which obstruct penetration of piles
- A massive substructure is required to extend to or below the rear bed to provide
resistance against destructive forces due to floating objects and score etc
- A massive substructure is required to extend to or below the rear bed to provide
- The foundation is subjected to a large lateral load
- Depth of water level in the river and sea is high
- There are river forces included in the load compositions
- When the load is needed to carry at the end, caissons are preferred
- The present groundwater level is aggressive inflow, caissons are suitable
Essential Requirements for Caisson Construction
There are a number of requirements for caisson construction that exist for the purpose of sinking, filling and sealing. The most crucial factors include the height of the concrete lifts and length of the reinforcement bars that need to be decided upon in consultation with the construction contractors.
To ensure the maximum assistance of operations, the on-site supervisory staff must maintain the highest standards regarding the quality of materials used in the process. More so, they must be specially trained to handle the challenging situations faced by the personnel during the sinking process of the caisson construction. This will not only make the construction process faster but also ensure safety of the workforce at all times. As it is the case with anything in construction, caisson construction needs to be done with great precision and accuracy for successful results.Continue reading →
January 31, 2019
The bridge launching method is also known as the incremental launching method. It is used for bridge decks that are greater than 250 m in length. In the bridge launching method of construction, the bridge deck is made in sections. This is done by pushing the structure of the bridge outwards using abutments towards the pier.
The incremental bridge launching method needs a considerable amount of analysis and design expertise. It also requires specialized bridge launching machine. This method is most suited for constructing bridges that have a constant radius of curvature. It is a very fast method of construction.
Bridge launching for construction
In the beginning of the construction, a highly mechanized prefabrication deck mould is set up behind one abutment. By doing this, there is no need for temporary support. After this, a rigid framework is attached. This enables the production of cast-in-situ segments. The in-situ deck segments can range anywhere from 5m to 30m in length.
After each segment is complete, it is placed on sliding bearings. Then, it is pushed through into the span. Also, a steel nose is placed in front of the first span formwork. This gives way for all necessary deck cantilever length while the span reaches the first pier.
The average rate of construction using the bridge launching method is 30m a week. The bridge launching method of construction becomes worthy of consideration for project sites that face some challenges. The challenges are:
1. Steep slows or deep valleys. This makes the delivery of materials difficult
2.Deep water crossings
3.Limited or prevention of access due to environmental restrictions
4.Limited access to area beneath the bridge construction. This could be because of heavy traffic on roadways or railways
To simplify fabrication and construction, the bridge that is supposed to be constructed using incremental bridge launching, is designed along a tangent alignment in both horizontal and vertical planes. The bridge sites that fit these ideal conditions are rare. This is especially the case when this scenario is combined with the close proximity of any of the site restrictions listed above. This makes it a more challenging process. It is still possible to construct a bridge along a curved alignment though, in either or both the planes.
It is a necessity for the construction surfaces to remain perfectly aligned with the superstructure, especially during the launch of operations. This is done to eliminate the relocation as well as the adjustment of lateral bearings.
Things to consider when using the bridge launching method of construction
1.There should be proper communication channels set between the contractor, monitoring consultant as well as the structural designer to monitor the to-be launched bridges.
2.There should also be a comprehensive monitoring program implemented. This can be used to alert either the contractor, consultant or designer in case something goes wrong.
3.There should be a pre-launch and post-launch survey of the structure.
4. There should be proper methods of monitoring the plumbness of the piers during the bridge launching and after
There are a lot of other things to be monitored during the bridge launching and after. Some of these are as follows:
1.The structural response of the piers
2.Touchdown forces during the bridge launching as well as the passage of the main structure over the pier
3.Girder flexural behaviour during the bridge launching
4.Load transfer mechanism that comes between girders
5. The horizontal force that is necessary for launching different stages of construction
January 29, 2019
January 29, 2019
January 14, 2019
December 10, 2018
December 3, 2018
December 3, 2018
Caisson construction, also known as caisson foundation, is a water retaining structure that is mainly used in construction projects that take place underwater. Caissons are prefabricated cylinders or hollow boxes that are sunk to the desired depths beneath oceans, rivers and other water bodies. They are then filled with concrete to create a solid foundation for the project, serving as an anchor. Structures such as concrete dams and bridge piers generally require a caisson as a base.
While somewhat similar to pile foundations, caissons are installed using a different method. Soil of adequate bearing strength is found below the surface and a deep foundation is sunk to the required level through material excavation. During caisson construction, steel reinforcement is sometimes used for a portion of its length.
A caisson is essential during construction for the purpose of providing stability to the structure. It helps to distribute the weight of structures evenly as the ground shifts under their weight. Depending on the type of caisson being constructed, the material used for building can vary from concrete to wood.
Requirements for Caisson Construction
There are a few key factors to consider during the construction and transfer of caissons. Depending upon the type of caisson construction, structural conditions and methods of installation used, there are some valid concerns held by the designers and engineers involved in the process. These include issues related to the construction, component design and installation of the caissons. Durability, stability, soil nature, scour depth, and the level of the water table are some of them.
Various requirements for caisson construction are involved for the purpose of sinking, filling and sealing. Important factors such as the length of the reinforcement bars and the height of the concrete lifts need to be decided in consultation with the construction contractors. In order to ensure the optimum facilitation of operations, the on-site supervisory staff must maintain the highest standards when it comes to the quality of materials used. Moreover, they must be specially trained to handle the challenging situations faced by the personnel during the sinking process of the caisson construction.
It is essential for contractors and engineers to keep the following requirements for caisson construction in mind. These involve the strength of the concrete mix design, the concrete shaft cover, and most importantly the quality of the formwork and concrete during caisson construction. Depending on the compliance and quality, the friction resistance to the soil can significantly increase or decrease during the sinking process.
Types of Caissons
There are different types of caisson foundations such as open, pneumatic, box, excavated and floating caissons. Open caissons are generally constructed to the depth of 50 metres and are open at both ends. Pneumatic caissons are open at the bottom but closed at the top for caisson construction at depths of over 100 metres. As the name suggests, excavated caissons are used at excavation sites, while floating caissons are prefabricated boxes with cylindrical cavities.
Advantages and Disadvantages of Caissons
There are some major benefits of using caisson construction for underwater projects. They are cost-effective to construct as compared to their alternatives, and also prove effective at deep depths of water bodies. They also have a high load capacity and can easily adapt to different environments and site conditions.
On the other hand, there are also a few disadvantages to caisson construction. They can be sensitive to gruelling construction procedures and are not considered good for use at contaminated sites. Moreover, only a few construction companies possess the requisite expertise and qualified inspectors needed for the supervision of caisson construction.
Caissons are considered to be essential building blocks during construction. Hence, it is necessary to maintain the highest standards during caisson construction, by ensuring that they are built and installed by a competent team of professionals.Continue reading →
October 1, 2018