The method of construction on the cable stayed bridge will consider the «Composite Prefabricated System» which is consisted of prefabricated beams that are connected in situ with reinforced concrete infusion. The transverse distance is 3.75m and therefore a reinforced fiber panel permanent formwork can be used. As the distance of the prefabricated beams does not exceed the distance of 20 m (max is 17.26m) we will follow the «mixed system», where the beams are placed in a distance between them and afterwards using the reinforced fiber panel permanent formwork the concreting of the concrete slab is taken place. In parallel we have the tower’s construction that necessitates very special prefabrication (notably the tower’s partition and the last part of it comprises 5 beams on the edge of the tower). Therefore, the construction and erections of prefabricated units in general is being made and achieved only with special machinery (cranes with appropriate capacity) and equipment. For the edge beams, torsion is avoided with the connection of the cross girders during the cantilever falsework. As mentioned previously, deck will be divided into 10 different parts, the tower in 4 pieces and the connection beams will arrive in the site without police supervision. The transverse beams will be transported as a continuous member.
CONSTRUCTION WORKS’ SEQUENCE
Environmental and Construction Feasibility Studies are endorsed by Relevant Authorities
Key Leaders Engagement and Liaison with relevant Authorities to resolve possible problems
Request for approval by relevant local authorities of using landfills/dumps in the area
Warning Traffic signs are established.
Road Traffic regulations concerning possible deviations/detours is approved by Local Authorities.
Appropriate technical teams’ integration and establishment.
Identification of the appropriate subcontractors.
Assignment specific works to the respective subcontractors
Controlled Dismantle of the existing Bridge
Waste wrecks of the dismantled bridge disposal at identified landfills.
Indication of appropriate areas to be used for settlement for the personnel and appropriate construction sites-Approval from the Authorities
Site Clearance in general including site compound establishment using several kind of jack leg hutments, traffic regulations in support of transportation major parts of the project, construction units, Fire Brigade
Training of the relevant personnel and subcontractors regarding the model of the proposal and the safety measures to be followed
Trimester review of the works done to correct the shortfalls identified to reach specific milestones we should have set
Construction of the necessary works followed according to the roadmap and milestones defined.
With reference to beams, girders, tower and deck erection of major parts connecting together the several smaller partitions at the construction sites.
In situ reinforced concrete infusion.
Employment addition subcontractors’ teams to accelerate the necessary works in case of force majeure.
Special refinement works to improve the utility of the bridge such as painting of the steel elements, drainage system and power of electricity installations.
Environmental restoration to the extent to return to the previous condition before the initial works.
Pollution Decontamination Unit
Joint Final Acceptance Inspection between the Construction Company and the Client representatives to accept the performance and the final outcome of the project works.
Further analysis of the appropriate works can be shown at the Appendix 4: Constructions Works’ detailed programme
RESEARCH COMPONENT – Dynamic response of composite cable stayed bridge under moving loads
The research component below investigates the behaviour of the composite cable stayed bridges under a moving load for both an eccentric load case and a concentric and the modal frequencies of the bridge were defined. For the dynamic analysis the software OASYS GSA 8.7 (Oasys, ) was used and a modal analysis and a time history response was completed.
To provide a slender and elegant appearance on the bridge, the prestressing procedure was followed to the cables. Because of their aesthetical appearance and durability, they increase the efficiency of the structure and reduce the cost and the need for maintenance By prestressing the cables, the flexural stiffness increases but the bending moments οn the deckare reduced, therefore a slender deck can be provide to reduce the total mass and therefore the total costs for the structure.
The current study is completed using the commercial software OASYS GSA 8.7 (DES) for a five-span composite cable- span bridge. The total span of the bridge is 150m and the spacing between the longitudinal beams is equal to the bridge’s width, 17.26m. All section characteristics are preliminary and in detail designed as mentioned in the section 188.8.131.52 and fulfill the conditions for ULS and SLS checks. For the design of the composite ladder deck, to determine the effects of the moving loads a 3D model analysis is considered to provide comprehensive results. Longitudinal beams are designed with the total steel area of the longitudinal beam considering the effective width of the equivalent steel slab using the modular ratio for short term analysis, but the total second moment of area of the section is modified to comply with the second moment of area of the composite section. (REFERENCE STA CALCS). The concrete slab is modelled as 2D shell element with full bending and in-plane stiffness.
Table 2: Composite section properties.
Area of steel section m^2 0.13585
Iyy of composite section m^4 0.1188021
Izz m^4 1.1037E-3
Short term modular ratio n 5.96
Effective concrete width m 1.25
Effective steel width m 0.21
The loads applied in the structure remain the same and the prestressing is used in order to counterbalance the vertical deflections of the beck. Because nonlinear analysis requires a more detailed design at a first stage only linear analysis was considered because nonlinearities can be neglected in the case of conventional bridges with high stiffness deck and service loads. (ANAFORA 3, 23, 24). It is mentioned earlier that an appropriate meshing for the bridge should be square elements with dimensions equal to the distributed area of the wheel on the concrete slab. Nevertheless, because of numerical difficulties in the analysis a mesh of 0.54×1.25m is chosen. The total length of the bridge was splitted into ten equal segments (Surface 1 to Surface 10) with a length of 15m to define the position of the moving load in different time. The modal superposition method is employed to examine the response of the bridge under the moving vehicle as it can be seen below in the Figure 15 for a concentric load and Figure 16 for an eccentricity of 3.78m.
For each span a load curve was defined with a Δt of 2 sec and a maximum total point load of 400kN that is divided into two loads of 200kN per axis with a distance of 2m transversely according to different codes (25-38). The selected vehicle velocity is 54km/h and the choice of the vehicle is dependent to the time step as OASYS GSA didn’t allow for the use of non-integer time. The point loads of 200kN per axis are distributed to equivalent constant surface loads after they are divided with the elements’ surface of 0.54mx3.75m and finally the total used pressure is 98.7kN/m^2. The final applied load comes from the superposition of each load multiplied with the time dependent factor δ_i (t). A structural damping ratio of 1% is adopted as OASYS GSA doesn’t allow for values less than 1% but a more recommended value for a structure like the one presented would be 0.5%. With the use of the time dependent amplitudes, the constant distributed load moves along the deck.
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