A well-known problem with the old structure is that it becomes less serviceable over time. A recent example is the collapse of the Genoa bridge in Italy. Deterioration and neglecting maintenance requirements cause the disaster in 2019. Prolonged exposure to harsh environmental conditions can result in poor structural performance. Using them without further repair or improvement can lead to dire situations. Structural audits are a common answer for investigating the overall health and performance of a structure and its capacity.
Why it’s important
Many reasons can weaken the structures over time. The most common of them are,
- Structural deficiency: There can be various construction defects in the structures. Not following proper standards, neglecting consultant’s recommendations, covering up construction mistakes without proper repairs might cause structural defects over time.
- Material deterioration: Even with a very slow rate, construction materials deteriorate. Harsh environmental conditions and chemical exposure accelerate the deterioration.
- Unexpected overloads: Some times people will use the structure beyond its design capacities. Stacking heavy storages, vehicle loads can cause slight failures in the members. These will improve over time and the performance of the members reduces.
- Physical damage due to accidents: This is one of the common causes of structural failure. Impacts of accidents will develop cracks, cause deformations, and even crush the concrete in some cases.
Structural audits are an effective way of identifying defects and asses the current condition of the structure. This makes it easy to implement the required maintenance and repairs well before failure. You can ask an experienced structural consultant to analyze the structure and make suggestions for improvements. The general advice is to conduct structural audits every 5 years for buildings older than 15 years and every 3 years for buildings older than 30 years.
Advantages of doing structural audits,
- Uplift safety standards of the building and the users
- Improve the serviceability of the building
- Identify critical repairs early and save money
- Enhance the life span of the building
Steps in structural auditing
There are a few possible ways to investigate your structure during the audit. 5 important steps of the audits are as follows,
1) Visual inspection
First and the easiest thing to do is the visual inspection. A complete inspection of each element will reveal you followings,
- Maintenance history
- Leakages & spalling
- Unwanted vibrations
- Emptiness inside
- Color variations
- Chemical reactions
- Identify critical members (floating columns, transfer beams, and slender members)
- Identify modifications (partitions & additions)
2) Calculate structural capacity using drawings
Use structural drawings to calculate member capacities. It is mandatory to calculate the design capacity of members in evaluation. Having an idea about the initial state will be easy to understand the performance drop over time.
3) Non-destructive tests & Computer analysis
There are a few possible tests that will help to understand the actual situation of the structure. These tests are called non-destructive tests because minor or no damage has been done due to this. Common non-destructive tests are,
- Rebound hammer test: Measure surface hardness
- Ultrasonic pulse velocity test: Identify internal cracks or voids, determine structural integrity and material homogeneity
- Core strength test: Measure compressive and tensile strengths
- Carbonation test: Determine carbonation depth and pH inside the concrete
- Chloride test: Determine acidic chloride iron solubility in concrete
- Sulfate test: Determine sulfate content in concrete
- Cover meter test: Determine actual depth of cover to rebar and spacing
- Half cell method: Determine corrosion content in embedded reinforcement
- Permeability test: Determine water permeability through concrete
Several computer applications are available to asses the structural stability and performance. SAP 2000 and Etabs are the most popular applications you can use to model the structure and analyze.
4) Report & suggestions
With the results of the test and observations after visual inspections, the engineer can submit the audit report and suggestions. The report should mention demand/capacity ratios for every member and critical repairs to attend immediately.
Strengthening and retrofitting repairs are common after a structural audit. This will help to regain its capacity, improve serviceability conditions, and add better aesthetic appearance. Some of the repairing methods are as follows,
- Epoxy crack treatment
- Anticorrosive treatments
- Termite treatments
- Shotcrete & other ground stabilization methods
- Use of high strength mortar
- Steel reinforcement addition & steel jacketing
- Fiber reinforcing
- Cement grouting
- Recasting/adding members