EIT director Suchatvee Suwansawat said an initial probe had pointed to the engineering design as the possible cause of the crumbled U-Place condominium in Khlong Luang district on Monday evening (August 11).
Four pillars at the rims of the building could not bear the weight of the structure, he added.
The engineers from the institute focused on three main areas in their investigation - engineering design, materials and construction process - to establish the cause of the tragedy.
They also looked at video footages, talked to witnesses, studied the building blueprint and inspected the site to identify the cause.
The collapsed building is one of the six condominiums of the project owned by Plook Plang Co. The first two buildings were completed and already occupied by residents. The third building is also under construction. The crumbled building is the fourth.
EIT president Anek Siripanichgorn said the occupied buildings were safe because the pillars had been reinforced.
Institute secretary-general Siriwat Chaichana said the third building could be impacted by the vibration of the collapse and reinforcements were needed to ensure safety.
Thirty-three workers were at the site when the building flattened.
Three people died and 25 were injured in the fatal incident, according to the Public Health Ministry. Twenty workers were released from hospitals and five including a male Cambodian national identified as Chan, 60, are at Pathum Thani or Thammasat University hospitals, the ministry added.
Five people, presumably workers, are still trapped under the debris, it said.
But police believed there were more than 33 people at the site when the structure gave.
The building collapsed near the end of the afternoon work shift, so relatives of the workers might also have been at the site, Pathum Thani police chief Samit Mukdasanit said.
Heavy equipment was brought into the site to find missing workers today.
Meanwhile, the Thanyaburi Court today approved warrants for the arrest of five construction bosses allegedly at fault in the fatal collapse.
The five were identified as sub-contractor Diaw Prabjone, 43, Pensri Kitipaisalnont, 48, who sought construction permission, engineer Saksit Inthong, 43, who designed the building, Jira Khanman, the engineer who supervised the construction, and Chanaichon Kerdthes, the managing director of Plook Plang.
Pol Maj Gen Samit said they were charged with recklessness causing death.
Later it was reported that Mr Diaw had been arrested and the other suspects planned to surrender.