Various factors such as brittle columns, stiffness elements, flexible ground floor, short columns, shapes, sizes, number of storeys, type of foundation, location of adjacent buildings, structural layouts etc. affects the degree of damages to buildings during earthquakes.
These factors which influence the degree of damages that a structure experience during earthquake are discussed.
Fig.1: Failure of Buildings Due to Earthquakes
- Factors Affecting Degree of Earthquake Damages to Buildings
- Deviation Between Design and Actual Response Spectrum
- Brittle Columns
- Asymmetric Arrangement of Stiffness Element in Plan
- Flexible Ground Floor
- Short Columns
- Shape of floor plan
- Shape of Building in Elevation
- Slabs Carried by Columns Without Beams
- Damages of Structures due to Previous Earthquakes
- Reinforced Concrete Buildings with Frame Structural System
- Number of Storeys
- Type of Foundation
- Location of Adjacent Buildings in the Block
- Slab Levels of Adjacent Structures
- Poor Structural Layout
Factors Affecting Degree of Earthquake Damages to BuildingsThe factors that affect the extent of earthquake damages to the structures include:
- Deviation between design and actual response spectrum
- Brittle columns
- Asymmetric arrangement of stiffness element in plan
- Flexible ground floor
- Short columns
- Shape of the floor plan
- Shape of the building in elevation
- Slabs supported by columns without beams
- Damages due to previous earthquake
- Reinforced concrete building with a frame structural system
- Number of storeys
- Type of foundation
- Location of adjacent buildings in the block
- Slab levels of adjacent structure
- Poor structural layout
Deviation Between Design and Actual Response SpectrumImproper evaluation of anticipated earthquake characteristics used in the earthquake design of the structure is the most common and critical factors for the damage of buildings. However, this is not the only factor since there are certain features of the structure that could be seismic weak point.
Fig.2: Design Response Spectrum
Brittle ColumnsIt is reported that, the majority of structures failed during earthquake are due to column failure. The column may fail due to deterioration of concrete as a result of cyclic loading and insufficient number of ties embedded in the column at the critical locations.
Fig.3: Brittle Failure of Column
Asymmetric Arrangement of Stiffness Element in PlanCores in structures are the basic stiffness element and its location with regard to the building would influence the behavior of the structure during earthquakes and eventually affect the extent of the damage. However, it is reported that, small percentage of failed buildings was due to eccentricities of the core of staircase and elevators.
Flexible Ground FloorFlexible ground floor is another factor that contributes to the damage that structure may encounter during earthquake. When stiffness is abruptly reduced at specific level of a structure, then stresses on the structural elements of flexible story would increase and subsequently fail. Therefore, the presence of soft story would increase the extent of structural seismic failure Flexible ground floor is made when this floor is used for commercial purposes and broad spaces need to be provided.
Fig.4: Flexible ground floor of multi storey structure which could cause structural failure during earthquake
Fig.5: Soft storey problem during earthquake
Short ColumnsThe failure of short columns due to earthquakes is less common compare ordinary column failure. However, short column may fail in shear in explosive manner and eventually lead to the collapse of the structure.
Fig.6: Short Column in a Building
Shape of floor planIt is demonstrated that, square shape floor plan exhibit the best seismic behavior compare with other shapes such as X, I, and +. Therefore, the extent of building seismic damage is influenced by floor shape plan.
Shape of Building in ElevationIt is proven that, structures with regular upper storeys show superior seismic response compared with buildings which their upper storeys are in form of setbacks.
Slabs Carried by Columns Without BeamsFlat slab system is considerably vulnerable structural system and does not have satisfactory resistance against seismic effects. Such structural system is considerably flexible and has low ductility. That is why EC8 prevents the use of flat slabs unless other seismic resistant structures like shear walls and flexible frames are used as well.
Fig.7: Flat slab system