The world today is changing fast and this has an impact on the state and usage of buildings. Building owners are often seeking to repurpose their property ,and this could mean changing an office block to an apartment block or even adding more floors to a building. The challenge with such changes is that they may affect the safety and structural integrity of the existing structure. This is why structural appraisal necessary. Structural appraisal as a process is concerned with the checking and ascertainment of the structural adequacy and safety of a building for a given purpose. The typical output from a structural appraisal is a report which informs the building owner or developer about the state of the building regard to the intended use.
Why appraise structures?
The main purpose of the a structural appraisal is to assess the structural adequacy of a building for a given use case, however, the need for a structural appraisal can arise due to any of the following reasons:
- For purchase, insurance or legal reasons
- Change of use (loading)
- Defects coming from design and construction
- Fire accidents
- Safety assurance
- Structural alterations
- Change in environmental conditions
Principles of Structural Appraisal
At the core of any form of engineering is always a set principles, and this is no different for structural appraisals. When conducting structural appraisals, an engineer needs to consider several principles which include; overall stability, strength, robustness, long term behavior (creep), stiffness, dynamic response and resistance to fire or accidental loading.
Components of a structural appraisal
Before one can conduct a structural appraisal on a building, there are some important aspects as well as stages to consider.
1. The brief
A successful structural appraisal is achieved through a proper understanding of the client’s expectations. By understanding the client’s expectation, one can gain a good idea of the scope and nature of the work to be done which can be very helpful when preparing to appraisal large and complex structures especially a joint venture may be needed.
In terms of the legal aspects, one needs to consider the duty of reasonable skill and care required for the structural appraisal work as well as the liability to the client and possibly to third parties. During the structural appraisal, one may also be liable to tort claims, and hence it is imperative to utilize the information from the client’s brief to assess the possibility of such claims and how they will be handled in the contract. Structural appraisal work also represents the engineer involved with a duty of care for public. Therefore, engineers involved in structural appraisals need to consider public safety during their work.
Since structural appraisal is often a service provided by a business, one needs to consider some commercial aspects involved in conducting this kind of work. First of all, one needs to gain the client’s trust which will help when agreeing on a fee for the work. During the structural appraisal, it is important to limit liabilities , and a professional indemnity (PI) insurance is always advisable.
The success of any structural appraisal also comes from good preparation. In the case of a structural appraisal, good preparation may not only save time but also money. It important that an engineer carries out a desk study before the structural appraisal exercise. The desk study can help provide documented information about the building’s design and condition. This information may be in form of existing drawings and laboratory reports.
A reconnaissance visit to the building’s site is also necessary. During the reconnaissance visit, an engineer can get clear idea about the requirements for the appraisal work as well as the potential risks to public health and safety. The reconnaissance visit can also enable the engineer to identify the possible access to the test sites and the level of exposure required.
During the preparation for the structural appraisal, one also needs to consider a number of factors that influence the nature of the structural appraisal, and some of these factors include:
- Dimensions of the structure
- Structural arrangements e.g. position of columns.
- Actions and loadings
- General conditions (defects)
- Lateral Stability
- Soil pressure and ground movement
- Aggressive ground conditions
- Thermal effects
- Moisture ingress
- Deleterious materials
- Fungal and insect attack
- Atmospheric conditions
3. Appraisal process
A structural appraisal relies on the assessment of the building’s condition through the exercise of judgement on all information obtained pertaining the structural adequacy of the building. The process itself can be done through three stages:
- Initial stage
In the first stage of the appraisal process, the objective is to determine whether a full assessment is required or minimal assessment is sufficient. The engineer can look at different aspects ,such as visible defects, age and size of the building, in order to decide on the extent of the assessment.
- Second stage
The second stage of the appraisal process requires the engineer to utilize the information from the assessments, and make conventional design assumptions so as to model the structure.
- Third stage
In the third stage, the engineer carries out an assessment of the mathematical models of the structure and concludes on the structural adequacy, however, the engineer may need to be make special considerations for; buckling, connections, fatigue and welded joints.
4. Structural testing & monitoring
Testing of the building is important because it helps to confirm assumptions about the building’s design and state as well as the defect distribution & frequency, future deterioration and structural adequacy.
In a structural appraisal, a number of tests can be done depending to the extent and nature of the building or structure. These tests include simple on-site tests like the dampness check and crack measurement, and material tests like the rebound hammer and chemical analysis. Loading tests can also done sometimes, but these may come as a last resort.
A structural appraisal may also involve monitoring a structure in reference to its predicated behavior from the structural analysis. Special techniques such as acoustic emission, do exist ,and help monitoring buildings and structures.
6. Understanding the structural materials
In order to perform a successful structural appraisal, an engineer needs to understand the usage and behaviour of structural materials (such as concrete and steel). The keys aspects that the engineer needs to review and get familiar with include the nature of the material, agents of deterioration and nature of construction.
7. Health and safety
Health & safety is also very important during a structural appraisal. During the structural appraisal, there are number of hazards such as fire, collapse of fragile parts of the structure and asbestos toxins. Therefore, when conducting a structural appraisal, one needs to ensure that there is risk management ,and this can be achieved through use of personal protective equipment (PPE), specialist training and usage of special safety checklists.
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