Structural Engineering for small State Office building

The real story of construction design, talking about big projects all the time is afraid to create a sense of grandeur. Afraid that people will not believe, today I would like to talk about a small project. Called “small” to the design engineer, in terms of value, but when it comes to construction, to the owner, even if it is a pigsty, it is still a large amount of money, an investment that must be weighed and measured. Therefore, the mindset when designing a small project is “fine”, carefully doing every steel bar to save as much as possible.

 

The project is a 7-storey office building, located on Kim Nguu Street, Hanoi.

 

Designed in 2013. Completed and put into use.

Foundation

The geology of the construction area near Kim Nguu River is very weak. With a layer of mud and clay over 20m thick from the ground. Based on the scale of the project’s load, the pile foundation option was chosen. Square concrete piles 250x250mm, designed pile depth 25m, calculated load capacity 30T per pile.

 

In the field, when demolishing and clearing the site, there were many old piles 200x200mm underground. Because they could not be pulled up, it was necessary to calculate to utilize these piles along with driving new piles. The construction conditions were narrow, not comfortable for pile driving machines to operate. That is also the reason why small piles had to be chosen. Although in principle, using large piles in small quantities is more economical than using many small piles.

 

Select 1 existing old pile, 3 new piles as test piles. The static compression test results were consistent with the design forecast of the load capacity of these piles. From there, it is the basis for approving the construction of mass piles with the following conditions for stopping pile driving: Lmin=21m, Pmax=45T, Pmin=75T.

 

(see Conditions for stopping pile jacking)

 

Also due to the narrow terrain when driving some edge piles, pile driving must be performed with the cantilevered load.

Note the calculation diagram of the pile foundation, the eccentric pile caps need to be processed a bit to avoid the internal force results, and therefore, the pile cap reinforcement, the foundation tie is unreasonably large. Based on the fact that the foundation is buried in the ground, it is necessary to lock the horizontal displacement in the calculation diagram and add the horizontal stiffness of the pile.

 

🎁Attached is the structural design explanation of the foundation of the project.