Seismic Vulnerability: what it is
When catastrophic natural events such as an earthquake occur, in addition to the loss of people’s lives, there must also be extensive damage to homes and all buildings and infrastructure, adding to the suffering of the victims.
Teknoprogetti is involved in analyzing and intervening both in situations of buildings that have suffered seismic damage, and in proposing and implementing preventive works that avoid major damage.
It is precisely prevention that is the correct approach we try to apply to our work methodologies, starting with the correct assessment on the resilience of a structure to limit the consequences of natural disasters.
There are several factors that contribute to what we call seismic risk, which basically tries to calculate the probability of an earthquake event occurring in a certain area, taking into account seismic hazard, exposure and vulnerability of buildings.
So let’s begin to delve into terms that help us understand how to deal from a technical perspective, with seismic hazard situations.
Seismic risk and seismic vulnerability
Seismic risk is a value calculated from the probability that an earthquake event will occur in a certain area, with what intensity, and over a certain period of time. These are statistical calculations that, using the vast amount of data we now possess, try to give a possibility value by estimating how likely it is that certain seismic activities will be reproduced.
Exposure is an index that detects the more or less significant presence of people, houses, structures, and infrastructure that may be damaged by the possible event. Naturally, an earthquake that strikes an urban or densely populated area causes different damage than one that strikes an agricultural or mountainous area.
This value is a probability calculation and cannot be influenced by external factors because it is derived from a large amount of historical data, which cannot be modified.
On the other hand, when we talk about seismic vulnerability, we refer to elements on which it is possible to carry out interventions that change their characteristics. This is particularly true on buildings on which reinforcement work can be carried out that changes their vulnerability.
It is also true that certain data set a boundary from which it is not possible to escape, such as the age of the building, the use of certain construction materials rather than others. Another factor affecting the calculation of a building’s vulnerability is also the construction technique used, which in turn is related to the era in which the structure was built.
Also not to be forgotten, of course, is the state of maintenance of a property. A proper seismic vulnerability calculation must take into account that a building, although constructed with excellent materials and the best construction techniques but on which no maintenance has been carried out for many years, may be more at risk of damage than others with inferior characteristics but which is maintained in good condition.
All this tells us that a building’s seismic vulnerability index is a figure that can be modified and that significantly increases safety in the event of adverse events.
Anti-seismic regulations establish clear criteria, the application of which would result in a low vulnerability index. The criteria are different for new buildings than for existing ones, but all are designed to ensure that buildings are able to dissipate at least a certain amount of the energy generated by an earthquake.
Of course, the seismic vulnerability index is determined by many factors that also depend on the characteristics of the building being analyzed and therefore indicate specifically the interventions to be carried out for each specific situation. Being able to have these analyses performed on the largest number of buildings in a certain area at greatest seismic risk would greatly decrease the extent of damage that a seismic event would cause to the entire community.
Ideally, the most effective approach would be to analyze the totality of all these data as a single complex system that takes into account all risk, vulnerability, and exposure factors so that effective intervention strategies can be devised to prevent the worst situations. At the same time, a culture of earthquake risk prevention should be promoted, involving both local governments and the citizens themselves who must take care of a certain area to make it safer. Industry professionals themselves, such as engineers, architects and contractors, can contribute their expertise to spread best practices to prevent the spread of building abuse situations that endanger community safety.
Through the use of advanced technologies, strict enforcement of earthquake-resistant regulations and careful land-use planning, it is possible to mitigate the impact of earthquakes and protect people’s lives and property.
How to assess the vulnerability of a building
As we have seen, calculating the seismic vulnerability of a building allows us to establish a value that determines a structure’s ability to withstand the effects of an earthquake. In particular, several energies are unleashed during an earthquake that threaten the strength of the structure and its ability to absorb ground displacements. The vulnerability index indicates the amount of energy that the building is able to withstand.
The main data to start with are the physical and construction characteristics of the building. Starting from the processing of data such as physical surveys of the structure itself, of the characteristics of the materials used and on their state of preservation, models are developed that can create simulations to verify the tightness of the structure subjected to stresses of different levels of intensity, processed with advanced computational methodologies.
Documentation relating to the analysis of the materials used, obtained from in-depth analyses carried out on samples taken on site using highly specialized equipment, is also very useful. These will take into account both the chemical analysis of the preservation of the material and its resistance to external stresses, which differs for different types of construction and materials used in different eras.
A final phase includes the actual structural analysis to determine the actual seismic vulnerability of the building and, if necessary, propose improvements. These interventions are also evaluated in terms of cost and benefit to ensure optimal management of the resources available for seismic retrofitting.
The greater the level of data that can be processed, the better the outcome that processing these data will propose for improving the structural safety coefficient of the building subjected to seismic events.
Seismic vulnerability index
At the end of all these calculations, the ability of a structure to withstand the devastating effects of an earthquake is expressed in a number. This represents the indicator that expresses the ratio between the stress caused by the earthquake and the resistance of the structure.
The technical anti-seismic standard establishes that if this number is greater than or equal to 1, the test result is positive. On the other hand, if the number is less than 1, the building is more or less structurally deficient.
As we have seen, the calculation of this index involves the processing of numerous data regarding the structure, its conformation and history. However, it remains a valuable though not entirely comprehensive indicator of the building’s situation. Not all critical issues affecting a structure can be included in this calculation because the conformation of a building also includes other aspects that may be less structural but equally important for safety.
For example, the deterioration of non-structural elements of a building is not taken into account in these calculations, but can become a safety issue since they may become detached, with consequent problems.
In addition, the seismic vulnerability index cannot determine up to what degree of magnitude the structure can withstand. Compliance with earthquake regulations certifies a certain level of strength of the structure but can quantify the force that can compromise its stability. However, it would be very difficult to stable this value because the forces released by an earthquake are more complex. The damage that an earthquake can cause to homes depends on the intensity but also on the duration of the tremors, the depth of the epicenter, the surface area, and the distance of the inhabited center from the epicenter.
It is therefore understandable that regulations cannot address all types of risk, but at the very least they can establish minimum safety levels that buildings must comply with in order to guarantee an adequate level of safety for those who live in or frequent them. Most importantly, the earthquake regulations indicate the retrofits that must be carried out in the circumstances of greatest risk, to protect human lives and property in that specific area.
Are old buildings less safe?
Contrary to what you might think, it is not a given that a new building is safer than one built centuries ago. The ancient wisdom of past generations, who often used materials available in their area with characteristics suited to their specific situation, often combined with construction techniques refined over generations, offered results that are still appreciated today, both from a technical and safety point of view.
On the other hand, innovation and research have made great strides, and the contribution of new technologies to the discovery and use of materials capable of guaranteeing the highest level of performance is undeniable.
For buildings of all ages, however, the rule remains that good maintenance preserves structural integrity and prevents premature deterioration. This rule applies in general, but it is necessary to point out that maintenance must also be done judiciously, because renovations have not always raised the safety level of a structure. Replacing lightweight structural elements, such as wooden floors and roofing, with heavier materials such as latero-concrete has not always proven to be the right choice.
It is for this reason that in calculating the vulnerability index of a building, it is not enough to take note of the year of construction, but the construction techniques, the materials used and certainly the maintenance work carried out in its history must be investigated in depth.
Teknoprogetti is a company that, through its specialists, can analyze a building and prepare all the necessary measures to achieve the desired level of seismic adaptation.
In most cases, action is taken because obvious stability issues arise due to the appearance of cracks, but the maintenance of a structure can also include all those interventions that contribute to improving its seismic vulnerability index.
When considered as a whole in an organic manner, all of the above contributes to improving the safety level of a building and, when applied to an entire territory, to improving the quality of life even in areas with a high seismic risk.
How is a seismic vulnerability analysis performed?
In order to objectively determine the ability of a structure to withstand the effects and stresses of a seismic event, it is necessary to conduct analyses of the seismic event that, through the assignment of a unique number, can give a measure of this ability.
