Construction is perhaps the most critical stage in the life cycle of structures, mainly because of the danger of failure and the high chances of underestimating construction loads.
A report developed by the American Society of Civil Engineers, based on their study of around 600 failed structures, found that around 40% of the structures failed during the construction stage, 36% of the structures failed during the pre-construction stage due to flawed designs, and 24% failed during their operational stage.
The failure of a structure is described as the propagation of local collapse from one segment to another segment, eventually resulting in the failure of an entire building or its lopsided part. It could be a product of natural disasters, for example, seismic tremors, floods, or coincidental acts such as an explosion in the service system or terrorist bombings.
Analyzing the reasons for explicit structural failures and proposing measures to relieve their effects is a successful measure to lessen risks and improve the safety of structures. Therefore, this article discusses the failure of some major structures, their root causes, and the lessons learned.
1. The Skyline Plaza Apartment Building, Virginia, US
The design plan of the Skyline Plaza complex included six office buildings, eight apartment buildings, shops, and one hotel. The project was a $200 million residential-commercial complex and was situated in Fairfax County, Virginia. During the construction of the skyline plaza complex, one of the apartment buildings under construction collapsed. A total of 15 labors were killed, and 40 were injured.
Design drawings of the collapsed building included the construction of 26 stories, a penthouse, and a four-story storm basement for parking. The building design was of a reinforced concrete flat plate with a 200 mm thick concrete slab. The height between each story was 2.7 m.
1.1 Investigation Findings
On 2nd March 1973, some portion of the apartment building collapsed during construction. The collapse began on the 23rd floor when the slab of the 24th floor was being cast. On the 23rd floor, the slab started showing cracks and the failure of the building occurred vertically along the full height of the building, including the basement levels. Also, the adjacent post-tensioned reinforced concrete car parking structure collapsed.
Specialists concurred that the concrete had not acquired sufficient strength to carry the construction loads applied during the construction process. Investigators confirmed that the original design plan had no deficiencies. The most probable reason for the collapse of the building was the punching shear failure on the 23rd floor of the building.
After the collapse, a team from the Occupational Safety and Health Administration (OSHA) came to the site and started an investigation. Further, a detailed investigation was conducted by the National Bureau of Standards (NBS).
NBS and OSHA mentioned in their reports that the collapse of the building was directly related to poorly managed construction processes. The court found that the contractor and the site engineer were guilty of negligence as the contractor didn't follow the building code requirement and the site engineer didn't inspect the work properly.
1.2 Lessons Learned
After the collapse of the Skyline Plaza apartment building, a series of changes were made in the building code related to the progressive collapse failure. Special inspection procedures were added in the inspection section of the building codes. Design criteria were also changed for effective planning to reduce the possibility of failure due to progressive collapse. The following points describe the violations of specified construction requirements and standard practices:
- Violation of prerequisites to completely shore the two stories underneath the floor being cast.
- Failure to permit legitimate curing time before removing shoring.
- Failure to conduct curing test on the concrete specimen in the field.
- Use of out-of-plumb shoring.
- Improper inspection during casting and formwork removal to check the strength of concrete.
- Improper installation of the climbing crane.
2. Ronan Point Tower, Canning Town, London
The need to give substitution lodging to homes destroyed in World War-II encouraged European engineers to develop innovative pre-assembled construction strategies. One such plan included the construction of high-rise buildings using pre-stressed concrete components made in factories.
The structural framework included the construction of load-bearing walls and each floor was directly stacked onto the walls. Grouted bearing surfaces were used to construct the joint between the wall and the floor. This process of construction was termed as system building. A skyscraper at Ronan Point, Canning Town, UK, was built using this system building technique.
On 16th May 1968, a blast occurred due to gas leakage in the kitchen of a house on the 18th floor. Just after the blast, the kitchen walls collapsed, and in-turn, the walls above the 18th floor caved in. This impacted the floors beneath and obliterated the entire corner of the structure. A total of 14 people were injured and three were killed.
2.1 Investigation Findings
The investigation team revealed that the building collapsed due to the non-availability of an alternative load path when one portion of the external wall collapsed. After the demolition of the building, it was also revealed that the quality of the grouted bearing surface for the joints between floors and the walls was poor.
Because of the unprecedented collapse, the government examined the safety of other buildings constructed using the same concept as the Ronan Point Tower. Many buildings were demolished well ahead of their life span.
The concept of progressive collapse of structures was not much known to the engineers before the failure of the Ronan Point Tower. In such collapses, a local failure is followed by widespread collapse through a chain reaction. What was irregular on account of the failure of the Ronan Point Tower was that a minor gas blast set off the collapse of a huge portion of a finished structure.
2.2 Lessons Learned
The experience due to the failure of Ronan Point Tower re-emphasized the following points:
- Progressive failure can also occur in fully constructed structures.
- A structure should have redundancies to reduce the possibility of progressive failure.
- Quality control should strictly be followed in the construction processes.
3. 2000 Commonwealth Avenue, Boston, US
On 25th January 1971, a two-third portion of a 16-story residential building known as 2000-Commonwealth Avenue in Boston collapsed during construction, leading to the death of four workers. The building was under construction for more than six years. The collapse of the building generated approximately 8000 tons of debris. Luckily, the failure of the building was gradual, giving the workers some time to escape from the building site.
The building was designed as a reinforced concrete structure and flat slabs were used for the roofing system with an elevator shaft provided in the center. This type of structural design is mainly famous for multi-story construction as it reduces the thickness of the slab and overall height between the floors. The thickness of flat slabs was between 160-190 mm for all the building areas except near the elevator core where it was 230 mm thick. The arrangement of the structural component constituted a height of 2.7 m for all the floors.
The building, situated at 2000 Commonwealth Avenue, was intended to be 16 stories high with a mechanical room of height 1.5 m for the working of the lift at the rooftop. The plan area of the structure was 56 x 21 m2. The building additionally had underground parking of two levels. A pool, auxiliary spaces, and one flat were situated on the first floor, and a total of 132 flats were on the second through sixteen floors. At first, these flats were to be leased. However, the proprietors later chose to advertise them as apartment suites.
At the hour of the collapse of the building, construction work was almost completed. The brickwork was finished up to the sixteenth floor, and the structure was generally encased from the second to the fifteenth floor. Heating, plumbing, and ventilation frameworks were introduced all through different floors of the structure. The interior work had also started on the lower floors. A temporary lift was constructed to help in moving equipment to various floors. It was assessed that 100 individuals were working in or around the structure at the hour of the collapse.
The collapse of the building occurred in three stages. These stages were, failure due to punching shear in the rooftop at section E5, the failure of the slab, and in the end, the progressive failure of the structure.
3.1 Investigation Findings
The civic chairman of Boston appointed a commission to inquire about the collapse of the building. The commission discovered the following critical observations:
- There was no signature of an architect or engineer found on a single drawing of the building.
- The design engineer didn't give the computations supporting his structural drawings to the commission. No head or representative of the team of contractors held a building construction license of Boston city.
- Ownership of the venture changed a few times, with changes in planners and architects. This scenario added to the general disarray and contributed to the abnormalities referred above.
- The general contractual worker just had a solitary representative on location. Most subcontracts were given directly by the owner to the subcontractors and bypassed the general contractor. A total of seven subcontractors were involved in the construction.
- The subcontractor, who was assigned to conduct the cold weather protection work on the structural concrete didn't carry out the assigned work. However, the structural engineer had indicated these measures.
- There was no proof of any inspection of the work by a specialist despite the fact that the project particulars needed this.
- The quality of construction material and quality inspections were poor.
- The collapse of the building occurred due to the development of punching shear mechanism around column E5. Punching shear developed the flexural cracks around the roof slab located near the elevator core. Thus, the slab collapsed due to flexural yielding.
- The design manual indicated a 28-day strength of 25 MPa. However, at the failure time, 47 days after casting work, the concrete couldn't seem to attain the necessary 28-day strength.
- The most critical inadequacies were an absence of shoring under the slab at the roof and the quality of the concrete.
3.2 Lessons Learned
The following key factors describe the collapse of the multi-story building situated at 2000 Commonwealth Avenue:
- Authorized design engineers should be chosen for the development of working drawings for construction.
- Engineers and architects should be responsible for all the design-related calculations and their design work must be examined by the experts in that field from a government organization.
- Ownership of a project should not change multiple times to reduce the confusion between the previous engineer and the newly appointed engineer.
- Inspection at the construction site should be conducted regularly by government organizations, especially for cold weather work.
- The quality of concrete work should be monitored throughout the project.
- The construction work should conform to design documents and construction procedures.
The collapse of a building is characterized as the propagation of an initial local collapse from component to component, ultimately resulting in the collapse of a whole structure or a disproportionately large portion of it.
Construction is one of the most critical phases in the life cycle of buildings due to the risk of failure and the possibility of underestimating construction loads.
The structural framework included the construction of load-bearing walls and each floor was directly stacked on the walls. Grouted bearing surfaces were used to construct the joint between the wall and the floor. This process of construction was termed system building.