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How many levels of Falsework for Transfer beams? | Structural Engineering skill

Everyone knows how to prop up 2 and a half levels of falsework in building construction. Why not 1 level? Will the falsework collapse? How many levels of falsework are needed to pour large concrete blocks of transfer beams? Here is a simple way to practice construction design with specific numbers for this construction problem.
 

Problem statement

 
🏐Constructions with beams or transfer floors are popular in high-rise buildings today. Experienced contractors only need to prepare the formwork to arrange scaffolding to withstand the large concrete volume of the transfer floor beam: keep 4-5 floors of scaffolding below, even prop it all the way down to the foundation for safety. The problem is how many floors of scaffolding are needed to prop up the minimum so that when constructing the transfer floor structure, for economic and progress reasons, the formwork can be rotated. Therefore, it is necessary for design engineers to calculate convincingly instead of prescribing based on empiricism.
Design advice on anti -beams

The project is located in Thanh Xuan district, Hanoi, 44 floors high, 3 basements, typical structural design is prestressed concrete floor, 5th floor uses conventional reinforced concrete transfer beam structure, height 1.8m and width >2m, very large volume of concrete.

 

Design advice on anti -floors of transfer

Falsework for Transfer floor

How to determine the construction load transfer to the scaffolding system and the poured concrete structure of the lower floors? Vietnamese standards up to now only have TCVN 4453:1995 “Construction of monolithic reinforced concrete structures”, there are very few provisions related to the design of scaffolding structures, especially the simultaneous operation of the scaffolding system with the load-bearing structure of the constructed house. How much percent of the load of newly poured concrete is transferred to the poured structure compared to the scaffolding system, right at the concrete pouring location but also below several floors.

 

Anti-structure design of ACI table

Foreign construction design standards such as ACI 347.2R “Guide for Shoring/ Reshoring of Concrete Multistory Building” have their own handbook-like regulations on this issue. In which, the common case is the scaffolding of 2 and a half floors of a normal civil house as experienced for many generations. However, looking up the table does not help determine the detailed internal force in the floor structure at the floor where the scaffolding has been removed due to the load of concrete pouring.

 

Design anti-album structure

Using structural design software such as ETABS, the quick model of the scaffolding column system in the main structure calculation diagram is available. This is a popular and productive way for engineers. In the calculation diagram, ignore the operation of the horizontal scaffolding bar system, considering them as only having the effect of bracing the vertical support system to ensure stability. Note that the stiffness of the scaffolding column is very small compared to the stiffness of the concrete wall column of the main structure, it needs to be handled otherwise the result will be incorrect: tensile load appears in the scaffolding column.

 

Software-based anti-frigific structure design
The model of the supporting column only works under compression by using the nonlinear analysis feature (Nonlinear): The tensile force limit in the supporting column model is 0. The nonlinear calculation diagram will eliminate the tensile struts and redistribute the internal forces in the scaffolding system.
 
Now it is time to find an economic answer to the design consulting problem, by gradually testing:
 
First, test at least according to the experience of 2 full scaffolding floors under the transfer floor (floor 3 and floor 4) according to the experience of normal civil houses. The result is that the 3rd floor floor cannot withstand: the construction load on the scaffolding system.
 
Try again by increasing the scaffolding point support within the projection range of the transfer beam under the 2nd floor floor.

 

Design of anti-structural structure-checking main structure

The results of the test of the concrete structure of the 3rd and 2nd floors (post tensioned) ensure the requirements for bearing the construction load according to the first and second Limit State.


🎁Conclusion:


The calculation diagram shows that the large construction load of the beam is transferred quite quickly to the 2 scaffolding floors and 1 support floor below (3 and a half floors including the scaffolding floor supporting the transfer floor). This problem can be expanded to design scaffolding systems for all types of constructions, ensuring the fastest economic falsework circulation while ensuring safety, avoiding the collapse of the floor due to scaffolding as has occurred in many projects.

Tuannm
Tuannm

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