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Bridge Top slab

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Once the curing of bottom slab and web completed. The construction of the top slab will begin. Top slab usually has a small width, therefore using cup-lock as a supportive system (falsework) will be enough. Top slab construction is simple and can be done in a shorter time compared to web and bottoms slab. The reinforcement for the top slab usually consists of four layers of reinforcement — two layers in each direction. The reinforcement in short direction will be more. As we know, the loads will be transferred in a short direction.




After the erection of falsework system. Primary beams will be installed at intervals in the short direction. Intervals between the primary beam shall be matching the calculation by the designer.
Above the primary beam and in the longitudinal direction, the secondary beam will be fixed to support the formwork for top slab.


Figure 2

Marine plywood will be nailed to secondary beams. The final shape, level, and dimension should be identical to the approved drawing. The surveyor should check all levels and dimension. The used plywood should be in good condition, so the resulted concrete surface met the minimum requirements. The location of joining bottom slab to web and top slab to the web should be hunched. The hunched shape will provide a better distribution of stresses compared to the sharp joint.


Figure 3

Before placing reinforcement. Existing concrete should be cleaned, roughened and all unsound concrete should be removed. This very important, and it should be done correctly to ensure strong bonding with the next pour of concrete. The scrabbling machine will be used to roughen the concrete surface. 



Top slab reinforcement:

  • Fix top slab reinforcement as per drawing. 
  • Use enough cover block to maintain minimum cover requirement.
  • Use enough chairs to keep your reinforcement stiff and to prevent movement during casting.
  • Bind reinforcement bars properly. Bind should be provided at each bar, or at least half of bar intersection should be tied. If the reinforcement bar is rusted, remove the rust before placing the reinforcement.

After completion of reinforcement fix the rails for screed vibrator. The surveyor shall check rails level. Usually, steel pipes are used as rails for screed vibrator. The figure no:5 showing screed vibrator rails. Those rails should be adequately tied to top reinforcement mesh. The rails should be rigid and should not move during the casting. The profile of the bridge will be affected adversely if the rails are not rigid. Increasing or decreasing the level of the concrete top surface will affect the bridge surfacing. Difficulties will be faced during the laying of wearing course. Also, the minimum thickness cant maintained if the concrete surface is high.


Figure 5

Concrete should be finished to the required level and cross-section. Concrete surface will be textured with a broom after consolidating concrete with screed vibrator. The broom finishing will allow better bonding between concrete and wearing course.






Comments

  1. Suzhou Omax Building Materials Co., LtdJanuary 12, 2021 at 4:29 AM

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  3. prestigesteelbuildingsJune 24, 2021 at 9:55 PM

    This was huge information for all ,those who needed these type article. This was really good and of course knowledgeable. Thank you for sharing this much information with us.Steel buildings Canada

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  4. JanApril 2, 2022 at 2:35 PM

    Stepwise details, thanks

    ReplyDelete
  5. Stan WilsonSeptember 24, 2024 at 12:35 AM

    I really appreciate the detailed breakdown of the bridge top slab construction process. Your explanation about the importance of load distribution and how the slab transfers forces to the supporting structures was particularly insightful. I found the illustrations to be very helpful in visualizing the concept, especially for someone without a civil engineering background.

    I also found it interesting how you highlighted the role of reinforcement in managing tension. It's clear that proper reinforcement placement can make a huge difference in the overall durability of the structure. I'm curious—when it comes to different environmental conditions, like high moisture or extreme temperatures, are there any specific adjustments in the materials or reinforcement strategies that need to be considered for top slab construction?

    ReplyDelete

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Mohammad
My name is Mohammad Hamdan, and I am a Civil/bridge Engineer with extensive professional background and experience in the field of construction. I have 10+ years of experience in the construction field. During my professional career, my emphasis has been placed on structural projects, mainly bridges, infrastructure and roads. Reading and practicing the design of structures is my passion.i was lucky to be a part of a big team that executed major highway interchanges. I believe in spreading the knowledge, thus, i compose these courses to share my experience and knowledge. My course focuses on the practical side of construction field. On other word, i am sharing some of what new engineers need to know about construction field. Beside working on construction field, i love writing some articles on my website ( curious civil engineer) Moreover, i wrote some engineering papers, you can check them  by searching my name on Google (Mohammad mamon Hamdan)