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Flood: Concerns mount over effect on structures

By Victor Gbonegun
31 October 2022   |   4:26 am
The last is yet to be heard on the flooding in cities as concerns are mounting over its effects on submerged homes.

Flooded houses in Lokoja, Kogi State

• Experts demand structural tests on buildings above one-floor
The last is yet to be heard on the flooding in cities as concerns are mounting over its effects on submerged homes.

Built-environment professionals monitoring the development have reinforced the need for the Federal and state governments to embark on a post-disaster survey of buildings in affected states.

They’re also recommending structural integrity or non-destructive tests of the buildings, especially the ones above one-floor to determine their continuous fitness for habitation and mitigate building collapse incidents across the country.

The Federal Ministry of Humanitarian Affairs, Disaster Management and Social Development and the National Emergency Management Agency (NEMA) data revealed that as of October 24, 181,600 houses have been partially damaged and 123,807 houses totally damaged and 392,399 hectares of farmlands have been totally damaged.

Also, 3,219, 780 persons have been affected by the 2022 flooding, 1,427,370 persons internally displaced, 2,776 persons injured, while 612 people were killed.

Prior to the ongoing flooding crisis, cities across the country had recorded repeated structural failure with over 461 buildings collapsing between 1974 to July 2021, and more than 1,090 deaths, including billions of naira worth of properties lost to such disasters.

Out of the figures, Lagos as the busiest construction site accounted for the largest chunk. For instance, over 34 cases were recorded between January and September 2022 in the state according to statistics from the Lagos State Emergency Management Agency (LASEMA).

Speaking on the development, a past president of the Nigerian Institute of Building(NIOB), Mr. Kenneth Nduka told The Guardian that the greatest enemy of any building is water.

He said during flooding, water penetrates the structure passing through the capillary elements of the structure whether wood/metal or concrete.

On the severity of damage to buildings, he explained: “If water passes through the wood, it will eventually rot because water dries out slower in building materials. The material composition of the wood structure will decompose and you can have rot, algae growth and strength of the wood structure is compromised.

“If water enters concrete, it absorbs it and compromises the bounding power. The same thing if water goes into the block work, it becomes wet and loses strength. Then, the chemical composition of the block or concrete will be affected. If it is reinforced concrete, water will be retained in it and encourage rust.

“Afterwards, the building can experience concrete cancer as the rot would manifest, start leaking and showing on the reinforcement. Once that occurs, the integrity of the structure is compromised.”

Nduka observed that efforts are always made to ensure that the foundation of buildings is anchored on firm ground but, he said when the water content of soil is overwhelming, the soil will move and stability of the foundation will be compromised, thereby affecting the structural integrity of the building.

He said: “Everything installed in a building, including tiles and paints will be affected because of water. When the flood goes down, there is what is called efflorescent; water coming out of the block concrete will create moles, which have been proven to be carcinogenic, with health implications that reduce the life span of the building.”

On the environmental impact of the flooding, he noted that most reptiles and animals look for where to hide for safety and there may be openings created by the movement of water, reptiles may move into the ceiling of buildings and multiply. He calls for fumigation of affected buildings to ensure that the environmental health of the structuresaid occupants is assured.

The former NIOB’s boss said to avert collapse, buildings that are above one-floor need structural integrity tests to ascertain fitness before accommodation.

He added: “This is where the government and non-governmental organisations could assist. Owners pains can be alleviated by ensuring that appropriate tests are conducted for structural integrity of buildings before they move back.”

Individuals that have the resources should conduct structural integrity tests on their buildings and government could give assistance to remedy the situation, while government agencies could assist with building materials. A responsible government must ensure that the people return to safe buildings.”

General Secretary, Building Collapse Prevention Guild (BCPG), Mr. Mubarak Gbajabiamila, said there should be building surveys for the affected properties.

“The building survey, which is the initial step to be taken, is to check for possible cracks and other defects. The survey should lead to carrying out a ‘non-destructive test’ to determine whether the flood has affect structural elements of the building. If there are defects, efforts should be made to repair the building.”

On the affordability of integrity test by property owners, he explained that the government should take the challenge as a social responsibility.

“Lagos State government, for instance, has an office that has equipment for such tests and there are professional bodies ready to assist. Government can reach out to these professional bodies to bring up volunteers that can work with its agencies to carry out the test,” he said.

Gbajabiamila emphasised that such step will help to step down the wave of collapsed buildings and restore people’s confidence in the government, as well as bring more attention to the capacity of local professionals.

A past president, Nigerian Institution of Structural Engineers (NIStructE), Mr. Kunle Adebajo, said most people are unaware of the possibility of some water impacting the foundation or Damp Proof Course (DPC) level of buildings.

According to him, structurally, a well-built building should be able to recover since the flooding crisis is a short-term experience and not protracted, adding that when the floodwater dries out, there should be restorations.

“But it can also be a problem depending on certain parameters, like soil conditions, where the building is erected. It is advisable that one should call for the advice of a structural engineer because the professional will be able to look at the situation and suggest if there are possibilities of damage.

“Even without a structural engineer, owners of buildings need to be very observant at all times. If you start to notice some settlement or areas that look as if the building is starting to get some cracks, a professional structural engineer must be consulted.”

On how to prevent future recurrence, he said necessary precautions like cleanup of premises and good drains around buildings should be prioritised so that water doesn’t soak up in building foundations or the walls but goes into the drains.

A past president of NIStructE, Dr. Victor Oyenuga, said owners of affected buildings should allow floodwaters to dry out from the buildings by opening the windows and doors, adding that if there may be a need for integrity test on the buildings, it should be done.

He noted that most of the submerged properties are storey buildings and bungalows. For him, implementing integrity tests on some of the buildings may not be too accurate because such tests are better in a frame building with slabs or columns/pillars.

Oyenuga said: “If there are no cracks on the walls, owners can return but if there are cracks, they may have to call engineers to examine the cracks and treat them for about a month. If the cracks continue, it means there is a problem and if it doesn’t continue, that stops the problem.”

Oyenuga advised the public to stop blaming the government for the disaster, as the situation is a natural disaster that happens everywhere, including in developed countries.

However, he cautioned that what Nigeria needs is improved disaster management and for people to yield to early warnings by government agencies and ministries to relocate from flood prone locations.