Safe structures

Jagvir Goyal

The collapse of a four-storeyed building at Peer Muchalla site in Zirakpur last week has sent shock waves in the region. In the present times, when much advancement has been made in the fields of building design and quality of materials, such an incident is highly unfortunate and redraws our attention towards some basic requirements that must be fulfilled during the construction of a building for its structural safety. In a two-part series we will have a look at some of the key points that have to be adhered to have structurally strong buildings:

Safe design

The design of structural components of a building such as its columns, beams, slabs and foundations must be made by a competent structural engineer. The structural engineer should consider all the loads, including dead load, live load, wind load, seismic load and temperature stresses while designing each and every component.

The design shouldn’t be based on thumb rules but on the prescribed structural design methods elaborated in the BIS codes and National Building Code. The seismic zone of the area should be kept in view and future expansion if any like adding another storey to the building at a later stage should be accounted for. Adequate ‘factor of safety’ should be adopted in the design of buildings.

Load-bearing capacity

To rest a building on the soil without violating its safe load-bearing capacity is the foremost requirement for the safety of a building. Whenever the builders plan multi-storeyed apartment buildings, they must get the safe load-bearing capacity of the soil strata on which they are going to rest the building checked.

The bearing capacity of the soil is checked by plate load test method.

Otherwise it can be assessed by a standard penetration test, but the plate load test method is more reliable.

Agencies and engineering colleges can carry out these tests and determine safe bearing capacity of the soil.

Once this value is received, the designer can go ahead with the design of the foundations of the building.

In case the area is waterlogged, safe load-bearing capacity is determined by keeping this condition in view as waterlogging significantly reduces the bearing capacity of soil.

Plugging a water source near foundations

The load-bearing capacity of the soil beneath the building foundations gets drastically reduced if the area is waterlogged. In such cases, the building design is carried out on the basis of this reduced load-bearing capacity. Sometimes, it so happens that the area is not waterlogged, and the building is designed on the basis of normal load-bearing capacity of soil, but a water source occurs near the foundations from which water keeps leaking and undermines the soil strata below the foundations. Some old water supply or sewer line buried in the soil and having leakage in it may be passing nearby.

In such a case, the water will keep on entering the foundation trenches and weaken the foundations without anybody realizing that something damaging is happening underneath.

The damage will be evident when the foundations will settle and cracks shall begin to appear in the building.

A builder should, therefore, ensure that no such water source that may affect the foundations adversely exists near them. If it is there, then he should get it plugged firmly.

(To be continued)

— The writer is former HoD and engineer-in-chief, Civil Engineering Department in a Punjab PSU