On the morning of the 20th, at Songdo Lux Ocean SK View apartment complex in Songdo International City, Yeonsu-gu, Incheon.

Entering the complex, the accident site where an exterior terrace had completely collapsed just 1 year and 6 months after completion immediately caught the eye.

Beyond the safety control line, a temporary screening barrier was set up in the empty space on the second-floor exterior wall of the apartment where the terrace should have been.

To prevent additional accidents, steel pillar-type supports (jack supports) were noticeably installed on other terraces along the exterior wall of the building concerned.

Workers deployed across various spots continued safety reinforcement work while riding aerial work platforms.

A resident who requested anonymity said, "It is a relief that there was no occupant in that unit," adding, "Now that an unexpected accident has happened once, I am scared that another accident might occur."

Administrative authorities have launched a full-scale investigation into the recent terrace collapse accident at this apartment complex.

However, as it is expected to take a long time for the investigation results to come out, residents' anxiety persists.

The accident occurred on the 2nd floor of one building at the Lux Ocean SK View apartment in Songdo-dong, Yeonsu-gu, Incheon, at 6:2 a.m. on the 7th.

At that time, the terrace structure and stone finishing materials on the exterior wall of the second-floor unit fell to the ground together.

Although the unit had been sold, move-in procedures had not taken place, and no residents were passing by at the time, so fortunately there were no casualties.

SK ecoplant, the main contractor, pointed to "insufficient performance of the post-installed terrace joint" as the likely cause of the accident during a resident briefing held on the 10th.

The collapsed terrace is a so-called cantilever structure, where only one end of the structure is fixed to the building slab (reinforced concrete floor plate) while the other end protrudes and floats.

This means a defect occurred during the post-installation process of connecting the protruding terrace structure afterward, once the building was fully constructed.

If the joint construction is shoddy, such cantilever structures carry the risk of collapsing under the weight without being able to withstand the load.

SK ecoplant estimated that the rebar "anchorage length" (the embedded length of rebar inside the concrete to support the structure) in the terrace entrance section was insufficient.

The joint rebar design called for 190 mm, but it explained that the actual construction was about 50 mm shorter at 140 mm.

It added that an insufficient injection amount of chemical anchor adhesive at the accident site was also a construction problem.

This is a method of fixing by drilling a hole in the concrete, inserting rebar, and hardening it with a chemical adhesive.

Experts pointed out that while this construction method requires a high degree of caution during the process, supervision and oversight may not have been properly carried out.

Jung Kwang-ryang, former president of the Korea Concrete Institute (※ Note: translated per original reference context), diagnosed, "The method of drilling holes in the concrete, injecting epoxy, and inserting rebar is the method that requires the most thorough caution even among post-installation methods, and I suspect that the supervision and oversight for this were poor."

He continued, "In our country, when building apartments, formworks are used, so walls are built first and protruding structures are constructed later," explaining, "The part where the balcony is joined to the existing structure is the most critical point, and the vulnerability there was missed."

Seo Kyu-seok, former president of the Korea Structural Engineers Association, said, "When constructing protruding parts like balconies with chemical anchors, there are risk factors unless they are designed so that the adhesive strength is accurately exerted," adding, "Thorough review of details is required, but this part does not seem to have been done properly."

He further pointed out, "For such protruding parts, there are also methods such as constructing them integrally when pouring the main body slab," and noted, "It is somewhat regrettable that a part subject to high shear force (force acting on a structure) and high risk was handled through a post-installation method using chemical anchors."

The terrace unit where the accident occurred heavily marketed a specialized design boasting a "West Sea ocean view" prospect at the time of sale.

There are a total of 24 households within the complex to which this type of protruding terrace is applied.

However, as a collapse accident instead occurred in a space moved into after paying expensive subscription prices, complaints are growing among residents worried about additional accidents.

At the briefing session held by the contractor, placards created directly by residents appeared, bearing messages such as "Is my home a bomb?" and "My classmates say they won't come over because the house might collapse," giving voice to anger over this accident.

An official from the residents' emergency committee emphasized, "Since many terraces are designed, it could easily have led to a major disaster," and added, "Following the accident, due to the fear that it might collapse at any moment, jeonse and wolse tenants are demanding contract cancellations, causing massive turmoil."

In this apartment complex, 57,296 defect complaints have been filed from the start of move-ins in March of last year until recently, raising ongoing concerns about construction overall.

The residents' emergency committee is urging SK ecoplant to refund the purchase price for households wishing to relocate and to fully reconstruct the exterior walls and terraces for residents who wish to stay.

Regarding the detailed structural safety diagnosis to be promoted in the future, an agreement has been reached whereby the emergency committee will directly select the firm, with SK ecoplant covering the costs.

The management is also reportedly reviewing plans to file a criminal complaint against the supervision company.

Amidst this situation, administrative authorities have also embarked on full-scale aftermath handling and fact-finding.

Incheon City, together with the Ministry of Land, Infrastructure and Transport, has formed a Facility Accident Investigation Committee (Investigation Committee) to conduct a rigorous investigation into the cause.

The committee plans to intensively examine the entire construction process, including design, construction, supervision, and licensing, for three months until November 20th.

An Incheon City official said, "Safety measures are currently underway at the terrace units on-site," adding, "Through future on-site investigations and other steps, we will uncover the cause of the accident and prepare safety measures for similar protruding structures as well."

(Photo: Yonhap News)