Tutorial-Seismic Loads - Analysis and Design

<div id="editor2" class="ed" contenteditable="true"><div style="background-color:lightgray; border-width:1px 0; border:1px solid #868484; color:#525252; margin-bottom:10px; padding:7px 7px 0 7px">At the beginning, This article assumes a fully aware of CSI Etabs software, in terms of how to build your structure inside, and how to run the analysis and print the output data.</div>The method we are going to discuss here assumes that the building's height is between 15 to 100 meters height, if the height of building is below 15 m, there will be no need to take the Seismic loads into consideration on the other hand if the building height is between 100 to 120 m, the Response Spectrum method should be used instead, whereas if the building height exceeds 120 m, the Time history method should be used by subjecting the structure we built inside the Etabs software to a virtual earthquake.The Earthquake lateral force Equation: V = ZICSWK V: the Lateral Force caused by the Earthquake Z: The seismic zone coefficient In Egypt for example, there are 3 areas A, B and C respectively 0.1,0.2,0.3 Where Zone C is for coastal areas where the soil is very weak C: Seismic frequency which depends on T and H where T is the seismic frequency and H is the height of the building measured from the lowest point of the building(Just at the footings or Raft top) up to the last story, and this part is calculated by the software. I: Importance Factor Meaning that if the building is for Residential Usage, I = 1 whereas if the building was hospital, I = 1.25 according to the code S: Soil Coefficient, we will assume S=1 W: The ٍStructure Total Weight without the Live Load if the LL is less than 500, but if more than 500 will take half of the L.L, because L.L increases the installation of the building and therefore safer in the earthquake and since L.L is not guaranteed to be There when earthquake occurs, therefore not taken into consideration. K: The Rigidity Factor depends on the type of structural system. If the structural system is only columns, the value of K is 0.67, whereas if the structural system is comprised of Columns, Shear Walls, and Cores, then K=1.Type of Centers 1) Center of Shear, in other words, the center of volume for the building, by which we can imagine a virtual box encapsulates the building and find its center, this center is to be respected only when we take the wind load case into consideration while design.  2) Center of Mass 3) Center of Rigidity Based on the distribution of columns, cores, and shear walls, the optimum case will be to have a center of rigidity at the same place as the center of mass ICore = 0.7 IBuilding In the sense that the sum of columns inertia of the building  = 0.3 of the total building Inertia. Therefore, since the earthquake affects the center of mass of the Building, when an earthquake strikes, the relationship between the center of mass and the center of rigidity can be likened by a cantilever beam, where the Center of Mass is the free end where the earthquake force strikes, and Center of Rigidity is the fixed end, therefore the building will be subjected to a torque in addition to a shear force if both centers were not at the same location, this distance between Center of Mass and Rigidity is called the eccentricity (e).</div>