Friday Nov 08, 2024
FT
Friday Nov 08, 2024
Thursday, 5 November 2020 00:00 - - {{hitsCtrl.values.hits}}
A guiding document in the form of a ‘Building Owner’s Guide’ should be published and made mandatory to be issued with the building applications for building approvals in risk prone areas
A young couple and their infant child died when the adjoining five-storey building collapsed on the two-storey building in which they were sleeping during the early hours of 21 September.
Who is responsible for this tragedy? The building owner of the collapsed building may say that he obtained necessary council approvals, the Municipal Council may say that they had the structural engineer’s signature in the approval drawings and the structural engineer may say that the collapse had occurred due to unforeseen reasons of subsequent events which he had no idea at the time of design.
Media reports said that the collapsed building was built in a valley blocking natural storm water path and was built in 2006. That is before the stringent regulations for building approvals had come in force in the year 2011 of the Kandy Municipality Area. The building was recently renovated and the neighbours observed formation of cracks in the external walls. Has the recent renovation of the building imposed additional loads or disturbed the stability of foundations? Has the building owner done anything detrimental in the process of recent renovations?
A similar tragedy happened on 18 May 2017, in which one worker was killed and 27 workers were seriously injured when a building under construction near Savoy Theatre in Wellawatte, collapsed. The owner was constructing additional floors on the existing structure of a Reception Hall, presumably without proper council approvals and necessary consultation of a structural engineer.
What is important now is to avoid another incident of this nature again
The purpose of this article is to discuss the responsibilities of various stakeholders (partners) who are involved in the construction and usage of buildings built in risk prone locations and make recommendations to mitigate the risks that may lead to similar building collapses in the future.
(Please note the meaning of words: “he” means “he/she” and “his” means “his/her”. “Building owner” means the person who employs other persons to design and/or to construct his residential or commercial building for his own occupation or for renting.)
Current practice
Plan approval process of different Local Authorities namely Municipal Councils, Urban Councils and Pradeshiya Sabhas may vary specific to their own rules and regulations but should be governed by the statutes enacted in Parliament by the Ministry of Provincial Councils and Local Government. However, the controls implemented by these institutions are not adequate to avert major collapses due to the reason that after initial approvals, the involvement of Local Authorities in the monitoring and control of construction activities of approved buildings will be only limited to the major construction works which are under the purview of UDA.
Currently only such major construction works necessitate obtaining the Certificate of Conformity (COC) before the building is occupied. Although Local Authorities can play a major role in this respect, it will be the collective responsibility of several stakeholders who should understand their individual roles and responsibilities, and act unitedly to ensure safety of the buildings during construction and while in service.
Need for guiding document for building owners of domestic houses and commercial buildings in risk prone areas
In order to avoid further recurrence of such disasters in the future, the Government needs to review Local Authority approval procedures of buildings in risk prone areas. The writer proposes that the government appoints a committee comprising of relevant professionals from the Construction Industry Development Authority (CIDA), Ministry of Provincial Councils and Local Government (MPCLG) and Urban Development Authority (UDA) to propose necessary measures to avert similar disasters in the future.
A guiding document in the form of a ‘Building Owner’s Guide’ should be published and made mandatory to be issued with the building applications for building approvals in risk prone areas. This guiding document should explain vulnerable areas of building construction specific to different districts and should explain precautions which the building owners should take before venturing into constructing their own buildings in such areas.
Proposed structure for the Building Owner’s Guide (BOG)
1.0 Selecting an architect
2.0Risk factors specific to risk prone constructions and precautions that should be taken
3.0 Considerations for environment, health and safety during construction
4.0 Considerations in quality control of concrete structures
5.0 Considerations and monitoring of risk indicators of a building constructed in a high risk area during its service life
Constructing buildings in filled marshy lands
There are many real life situations that buildings which are constructed in filled marshy lands have settled and tilted to the extent that such buildings have become not anymore habitable. Although such examples are not directly related to building collapses, money invested in such buildings will go waste without having viable options for rehabilitation.
Some examples can be seen in the filled lands of Wattala area where the building owners had rushed to construct those structures before the fills had adequately settled and constructed without getting professional services of a competent structural engineer.
Precautions that should be taken in filled marshy lands
1.0 Structural design to be done by a competent structural engineer with sufficient experience in designing buildings in poor ground conditions with a successful track record of such previous constructions.
2.0 Allow sufficient number of years for the fill to settle before constructing buildings.
3.0 There should be adequate granular fill above the compressible peat layers. (min 3.0m above the peat layer for a two-storey building)
4.0 Raft foundations should be avoided and strip foundations designed with inverted ‘T’ deep beams.
5.0 Construct the ground floor as a suspended slab with a void created between the existing ground and the soffit of the suspended slab.
6.0 Avoid selecting the option of driving piles using manual and improvised methods by individuals who do not have proper quality control procedures.
Constructing buildings in the hill country
Before the building owner embarks on constructing his domestic or commercial building in the hill country, he should first get himself appraised of the condition and suitability of his land to construct the proposed building. He should study the details of:
1.0 NBRO reports and recommendations of the stability of slopes in the area planned for the building.
2.0 Existing storm water discharge canals, if any across the land.
3.0 Visible signs of soil erosion due to storm water runoff.
4.0 Incidents of previous slope instability inherent in the area.
The following precautions are advisable and shall be observed during and after construction of a building on the hilly slopes:
1.0 Once the foundations are excavated, it is essential to protect the foundation pits from getting disturbed before the laying of the concrete or masonry foundations. In the hill country where the rain fall intensity is high and frequent, if the foundations pits are left unprotected, the clay soils of the underneath load bearing strata can get disturbed. Hence all endeavours should be made to protect the foundation pit bottoms by laying a screed concrete immediately after excavation and re-compaction. Also the time between laying of the screed, completing the foundations and back filing should be kept to a minimum.
2.0 Construction of retaining walls if required within the building, have to be designed and constructed considering all possible risk factors. Excessive building up of lateral pressures on the retaining wall due to hydraulic pressure or/and from earth slips can fail the retaining wall which can in turn push the building structure leading to a major collapse. Drainage pipes which are laid behind the retaining wall to drain out seepage water should be regularly inspected for their functionality.
3.0 Buildings constructed in the cut and fill of the slopes should be properly landscaped and surface drains should be constructed surrounding the building to avoid seepage of storm water into the surrounding ground which can weaken the bearing strength of the soil underneath the foundations. Slopes should turfed to avoid any soil erosion.
4.0 Once the building is functioning, building owner should make periodic inspections to identify any early warnings such as cracks in the walls, tiling of floors, erosion of soil surrounding the building and other common sense observations to identify any possible causes which can change the stability of the structure of the building. Building owner should act promptly upon observing any possible early signs which can lead to a failure, get prompt engineering advice and do early rectifications or strengthening works to avoid a disaster.
5.0 If a building above three storeys is planned to be constructed on a hilly slope, the engineering assessment should be thorough and in case of any doubt, a second opinion may be sought from another competent engineer to ensure that the structural design engineer’s judgment in his design has not missed any vital and critical failure risk factors.
Constructing basements and deep foundations adjoining existing neighbouring buildings
WHEN THE Neighbouring buildings have been built up to the boundary line of the proposed construction or within the close proximity to the boundary line, the building owner should be aware of the risks entailed in the deep excavations for foundations and basements, especially in situations that the neighbouring building foundations are at a higher level than the bottom of the planned excavation.
Situation can be worse in case of high ground water table and the foundation construction of the proposed building will require continuous dewatering. The risks associated with such construction works are:
1.0 Erosion of soil under the foundations of the existing neighbouring buildings during the dewatering process.
2.0 Reduction of soil bearing capacity of the existing building foundations due to the lowering of the ground water table.
3.0 Poorly constructed temporary shoring systems which can move towards the excavation, resulting the soil underneath the existing buildings to move laterally.
Above risk factors may lead to the settlement of the foundations of the existing buildings and in turn the walls and floors of the existing buildings can form cracks. In worse situations, such causes may lead to a building collapse. If these risk factors are not planned in advance and precautionary engineering solutions are not provided, the building owner may face litigation and court injunctions while the construction work is progressing.
Building owner’s responsibility: Selection of an architect/ structural engineer
The building owner having understood the risks entailed in constructing buildings in high risk areas, should take higher precautions in the selection of an architect/structural engineer, if the proposed building exceeds three storeys (ground + two floors) and is constructed in a risk prone area.
He should first acquaint himself with the architect/structural engineer to find out his perspective of designing buildings in such high risk terrains and ground conditions. The building owner should get more details about his prior experience in designing such buildings and the factors he had considered in such designs. The building owner may seek recommendations of his past clientele and talk to them in respect of architect/structural engineer’s responsible behaviour and attitude towards evaluating the risks that are associated with the risk-bearing construction works of this nature.
He can also ask the architect/structural engineer to prepare a brief report detailing the risks identified in the proposed construction works and how he will tackle such risks in his design. What actions he will take to mitigate the risks and specific guidance that should be followed during the construction of the building.
If the building owner having hired a selected architect/structural engineer for the design and supervision of his proposed construction, at a later stage, feels certain doubts about the designs proposed by the architect/structural engineer, he may get second opinion from another competent architect/structural engineer or from a friend in the same field to verify the safety in the concerned areas.
Building owner’s responsibility: Selection of a contractor
Selection of a contractor to construct the proposed building should be done with prior recommendations and considering their experience in constructing buildings of similar scale and size in similar terrain conditions. The contractor and his lead workers need to understand the risk factors involved in such construction work in order to mitigate such risks.
Similar to how the building owner selects the architect/structural engineer, he should have a discussion with the prospective contractor and his lead workers to check on their knowledge and past experience in similar construction works. If the team selected for the construction works do not have adequate experience in the specific works but they are generally competent to perform the task, then the building owner should hire the services of a competent technical person to supervise the work.
Conclusion
All the stakeholders (partners) who are involved in the chain of activities leading to the completion and occupation of a building constructed in risk prone area should understand and demonstrate the responsible behaviour expected from each partner of this chain. It will be the responsibility of any of the partners to notify the building owner, if he has the slightest doubt about the performance of another partner, to give the chance for the building owner to go into details of such concerns and take necessary advice and measures to rectify any such shortcomings to avert a major disaster in the future.
(The writer is a Structural Engineer who is presently working for a leading construction company. He can be contacted on [email protected])
