How to Conduct a Performance Analysis? What Happens Before and After?
Overview of Performance Analysis
In this article, we will discuss the preliminary work of building performance analysis, how it is done, and the strengthening methods that can be applied afterwards. We will try to explain the roadmap that building strengthening companies should follow and the options available to you as property owners. With awareness in these processes, a more solid, faster, and more economical strengthening path can be followed.
Building performance analysis is only one phase of the building strengthening process. Firstly, property owners must reach a good-faith agreement among themselves. Then, they must explain their requests in detail by agreeing with an experienced engineering company. The evaluation to be carried out directly affects your safety, the time and money you spend, so it is very important to choose the right time, the right price and the right people.
The structural problems of each building are unique. As experts also state, if building a new building is like tailoring, then strengthening is like sewing. A building must go through a good performance analysis, identify its deficiencies successfully, and be implemented with a suitable project. After the project is prepared, it must be based on a mathematical calculation that it has sufficient strength.
It is clear that just preparing the project will not be enough, and the implementation must also be flawless. Strengthening carried out with the thought of the contractor with years of experience, the foreman of the years, or just because they offer a reasonable price, without having experience in building strengthening, can be fatal to you and your loved ones.
1. How Can We Determine the Earthquake Resistance of Our Building
To determine the earthquake resistance of our building, a building performance analysis must be conducted. The first stage of this process is observation, but observation alone is never conclusive, it only provides a suggestion.
Individuals who only observe your building and earthquake testing companies that report to you are not telling the truth. Observation is only beneficial in terms of checking the compatibility between the building and the computer model. To conduct a proper building performance analysis, one must have a complete understanding of the following data:
- The soil on which the structure is located
- The foundation of the structure
- The load-bearing system of the superstructure
1.1 The Soil on Which the Structure is Located
Examining the engineering properties of the soil is one of the important aspects of performance analysis and building strengthening. The quality of the soil greatly impacts the performance of the building. A building in an area with good soil will experience much less earthquake ground motion (force) during an earthquake.
The weak ground had a major impact on the collapse and severe damage of many buildings in the 30th October 2020 Samos Earthquake. Characteristics such as the ground’s bearing capacity, water level, soil condition, and bedding coefficient, indicate whether the ground is good or bad. Particularly in loose sandy or silty grounds with high underground water levels, the bearing capacity decreases due to liquefaction during the earthquake, causing buildings to collapse or tilt sideways, as seen in the 17th August 1999 Marmara earthquake. In this case, even if the superstructure is well designed and constructed, the building becomes unusable.
Therefore, building codes require geotechnical investigations to be carried out, with the number of boreholes determined according to the area of the building’s foundation. Additionally, the seismic site classification method (MASW) provides information about the dynamic and mechanical characteristics of the soil in an economical manner.
1.2 The foundation of the structure
Unfortunately, we observe that some of the companies conducting earthquake tests have neglected to examine the foundation during the study. In this case, the adequacy of the building performance analysis conducted should be questioned, as confirming the contents of the foundation system carrying the loads transferred from the superstructure with the project or understanding its behavior if the project is not available is extremely important.
An inadequate foundation analysis leads to the reinforcement of a building on an imaginary foundation. During the reinforcement of a building on an imaginary foundation, significant application disparities are encountered. To avoid such a problem, it is important to excavate the foundation pit to learn the dimensions of the building’s foundation.
1.3 The load-bearing system of the superstructure
Whether your building has a structural project or not, the accurate determination of the dimensions of the building’s load-bearing elements and the quantity of reinforcement inside them (field survey) is very important for the accuracy of the analysis model.
In most cases, the measurement of beams is neglected while the spacing between columns is measured. This neglect can also be seen in the determination of the quantity of reinforcement in the beams. Data obtained from beams is as important as data obtained from columns which are vertical load-bearing elements.
When answering the question of how to conduct an earthquake resistance test, attention should be paid to beam designs. Beams that are designed either too strong or too weak can impact the behavior of the building. For every new building designed to be earthquake-resistant, the principle of columns being stronger than beams is widely accepted. Special attention is given to identifying the points of the building that are vulnerable to damage, especially at the ends of the beams.
During building performance analysis, especially in older buildings, it is unfortunately common to encounter a situation where the beams are strong and the columns are weak. Cases of beams that are designed too strong or weaker than intended are frequently encountered. Especially in beams where transverse reinforcement is not carried out, the shear safety and shape change capacity of the beam during earthquakes is limited. Thus, the beam is exposed to more earthquake load than its capacity and serious damages can occur.
Careful data collection is also necessary in vertical carrying elements like columns. Column dimensions, amount of reinforcement, corrosion rate of reinforcement, and spacing of transverse reinforcement are key parameters that influence the analysis. The analysis can never perfectly model the building, but the model is interpreted in the light of the engineer’s knowledge and experience, and the behavior of the building is revealed. In this way, an ideal study is carried out and realistic, reliable and economical results are obtained.
2. How is Building Performance Analysis Conducted?
After the preliminary work, a proper modeling can be done using reliable and well-established software. The key factor in seismic risk analysis is for the engineer to construct a realistic model by utilizing their education and experience and to properly understand the behavior of the building.
It is crucial to interpret the results of seismic analysis after modeling. We must determine how the building will perform under seismic forces that are determined by regulations and updated based on ground conditions and we must produce appropriate solutions accordingly.
3. How is Building Performance Analysis Conducted?
In the case where the building does not pass the seismic risk analysis, appropriate building strengthening options should be sought for strengthening. One of the most commonly preferred and reliable strengthening methods is adding new elements to the building. Strengthening existing elements is also a good solution, but adding new elements with known behavior in an earthquake and reinforcing existing ones is a better solution. Briefly, building strengthening techniques are as follows:
3.1 Adding Reinforced Concrete Shear Wall
The integration of reinforced concrete wall elements into most buildings provides a more reliable and cost-effective solution. When the wall panel is properly installed into the building, it bears a significant portion of the forces during earthquakes, thereby protecting the building.
3.2 Strengthening Columns
After reinforcing the building with shear walls, it is recommended to consider local scale column strengthening or carbon fiber reinforcement. For column strengthening, reading our article on how to strengthen columns and the cost involved is suggested.
3.3 Strengthening Beams
The strengthening process is usually carried out on columns. Building owners may sometimes see the strengthening of columns as sufficient, while firms carrying out strengthening projects may avoid working on structural elements other than columns in order to keep costs low and secure the project. However, proper transfer of seismic forces between columns and beams during an earthquake is important for the building’s safety.
Additionally, deficiencies in the beam should also be addressed. Preventing sudden beam failures is crucial. Without a proper beam system, adding partitions and strengthening columns alone will not provide adequate protection. Therefore, beam strengthening is also a building strengthening technique that should not be overlooked.
