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Experiments and results from recent earthquakes have shown that properly designed and implemented facilities can withstand severe earthquakes without collapsing. However, most of these facilities, especially the old ones, are likely to suffer serious damage or collapse, resulting in losses [1] Structure Performance Survey The occurrence of earthquakes requires that the structure has sufficient resistance to lateral forces and at the same time has sufficient flexibility, i.e. the capacity To keep safe when stress increases, so as to protect the crowd.
Studies of the performance of structures during these earthquakes have also confirmed that structural elements with sufficient resistance to lateral forces must also have sufficient compliance, or the ability to maintain their integrity under increased stress, in order to protect citizens.
The effects of earthquakes on any concrete structure can be summarized, depending on the location of the structure and its distance or distance from the coastal area or from the main epicenter, as they affect the field of this structure with different values of horizontal forces. These horizontal forces contradict the concept of balance in the origin of vertical forces used by design engineers based only on influences that ignore the origin of horizontal forces and design based on these forces.
horizontal forces
Horizontal design of a building
Is to achieve the study of its internal and external balance under the influence of seismic forces.
The internal equilibrium of origin
It is the source of internal forces such as bending moment, shear force and vertical force, so that the concrete part has sufficient internal strength.
The external equilibrium of an origin
It is to stabilize the building under the action of torsional moment and overturning moment, as well as change the soil deformation stress.
Vertical design of the facility
The structure is designed to bear dead loads from the weight of concrete slabs, columns, floors, walls... and live loads from the weight of furniture and furnishings and the weight of the building's occupants.
earthquake-resistant building design requirements
The shape of the building had to be chosen to be symmetrical in the horizontal plane, and to avoid angular shapes. For irregular buildings, buildings should be separated by seismic joints to prevent buildings after frequent earthquakes, and use triangular pieces or parallelograms because they form part of the chance of seismic stress concentrations Weak and strong torsional stress due to earthquakes.
Structural design suitable for earthquake resistance
Concrete buildings are divided into two types:
1- Structural buildings
It consists of concrete columns and beams that bear the weight of the concrete roof. This type has good shock resistance if properly designed and implemented. This type of building is divided into the following parts:
Low-rise buildings: no more than six or seven floors.
Medium-rise buildings: the number of floors does not exceed 14 to 15 floors.
High-rise buildings: not more than 30 floors.
earthquake resistance of structural buildings
First, choose the appropriate structural system for medium and normal height buildings.
Choose the right structural system for the right building design.
Computes the translational response to an earthquake.
Design of critical parts for structural elements.
Consider: a system of concrete columns and beams that, depending on the seismic zone, support buildings up to 14 stories high.
Causes of building collapse
Earthquakes cause buildings to collapse due to lack of iron or poor cement, which undoubtedly contribute to the collapse in some way, but are often not the real cause.
The real reason for the collapse of buildings We must explain the safety factor adopted in the design of ordinary residential buildings:
The first thing the design engineer does is estimate the floor loads accurately, and since the deadweight loads and the weights of the tile cutter and blocks (dead loads) are accurately calculated, it is not a problem.
As for the live loads, they vary according to the nature of the construction investment.
After completing the load analysis (dead and live loads), the design will be calculated based on the strength of the concrete.
Thus, the safety factor of the building is ensured in terms of estimating ideal high value loads and reducing the strength value of concrete and steel.
buildings collapse
There is no doubt that the building as it was designed is safer than the implementation of a building that has exhausted its security options, so adjusting the diameter of the steel and reducing the percentage of cement in the concrete weakens the overall value of the building's resistance. But this is rarely the cause of a sudden crash.
The sudden collapse occurred due to the lack of adequate study of the soil and the designer's ignorance of the subsoil.
The calculation of any facility depends on the calculation of the forces acting on it. Have the facility successfully withstand the elements and maintain stability throughout its expected service life.
Engineers must understand the different aspects of the area… Soil types and topography… Climate… Earthquakes and their average occurrence and frequency…etc.
Strengthening earthquake-resistant buildings
processing and repair
To ensure the required basic resistance of damaged non-structural structural members, well-repaired structural members retain approximately the same strength as before failure.
reinforcement or reinforcement
It is the modification and correction of the strength and stiffness of a single structural element or the entire structure in order to improve the performance of the structure against subsequent earthquakes. Reinforcement usually involves increasing the resistance or compliance of individual elements or adding new structural elements for better performance - Significantly increases a structure's resistance to lateral forces, while sometimes reinforcement may forego making elements Structural elements with lower strength and ductility are chosen to improve the interoperability of structural elements and prevent premature breakdown of weaker neighboring elements.
Earthquake damage
Immediately after a devastating earthquake, it is important to have an initial assessment of each structure by a specialized research team in order to quickly determine the general extent of damage to the structure. When such natural disasters occur, everyone is requested to follow safety measures. The initial research process that follows the initial evaluation process is an independent and more comprehensive evaluation. It is prepared by the design engineers, starting with a detailed determination of the nature and extent of the damage and whether emergency measures or reinforcement are required. As for the second stage, the damage must be studied in detail in order to understand the damage in detail. After the initial investigation, repair and reinforcement procedures can be designed and formulated, and emergency procedures for temporary reinforcement and protection can be initiated. Buildings that had severe damage but did not collapse at the time of the earthquake were immediately carried out.
Temporary protection is intended to ensure temporary resistance or reinforcement of damaged elements and connections on which the integrity of the entire structure depends. Temporary protective measures must ensure the safety of those close to you.
I must decide to fortify in case of danger, but I must order the demolition of structures that threaten danger.
The first operation in the temporary protection operation is to support the vertical members of columns and load-bearing walls that have collapsed or have suffered significant damage, and when the vertical members are evident, the vertical support shall be carried out in the floor. has been damaged.
The designers had to estimate losses in a modeled way, using recorded survey data, and then implement repair and reinforcement procedures that improved the structure's response in subsequent earthquakes by avoiding deviations in horizontal planes and sudden changes in stiffness between tiles.
It is recommended that the results of strengthening members added to the structure be carefully evaluated to ensure that they do not lead to increased damage in subsequent earthquakes.
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