PUSHOVER ANALYSIS

Pushover Analysis DEFINITION: • Pushover is a static-nonlinear analysis method where a structure is subjected to gravity loading and a monotonic displacement-controlled lateral load pattern which continuously increases through elastic and inelastic behavior until an ultimate condition is reached Lateral load may represent the range of base shear induced by earthquake loading, and its configuration may be proportional to the distribution of mass along building height, mode shapes, or another practical means DIFFERENCE BETWEEN PUSHOVER ANALYSIS AND RESPONSE SPECTRUM METHOD PUSHOVER ANALYSIS RESPONSE SPECTRUM ANALYSIS Simplified nonlinear static analysis Suitable for assessing the seismic vulnerability of existing structures Can be used also in new structural design to see the nonlinear Static effect Dynamic linear analysis Suitable for problems involving the structural design of new structures types: • Presently, there are two non-linear static analysis procedures available, one termed as the Displacement Coefficient Method (DCM), documented FEMA-356 and other the Capacity Spectrum Method (CSM) documented in ATC-40(Applied Technology Council) Both methods depend on lateral load-deformation variation obtained by non-linear static analysis under the gravity loading and idealized lateral loading due to the seismic action Capacity Spectrum Method is a non-linear static analysis procedure which provides a graphical representation of the expected seismic performance of the structure by intersecting the structure’s capacity spectrum with the response spectrum (demand spectrum) of the earthquake The intersection point is called as the performance point, and the displacement coordinate dp of the performance point is the estimated displacement demand on the structure for the specified level of seismic hazard Displacement Coefficient Method is a non-linear static analysis procedure which provides a numerical process for estimating the displacement demand on the structure, by using a bilinear representation of the capacity curve and a series of modification factors or coefficients to calculate a target displacement The point on the capacity curve at the target displacement is the equivalent of the performance point in the capacity spectrum method BUILDING PERFORMANCE LEVEL: • Operational level (OL): As per this performance level building are expected to sustain no permanent damages Structure retains original strength and stiffness Major cracking is seen in partition walls and ceilings as well as in the structural elements • Immediate occupancy level (IO): Buildings meeting this performance level are expected to sustain no drift and structure retains original strength and stiffness Minor cracking in partition walls and structural elements is observed Elevators can be restarted Fire protection is operable • Life Safety Level (LS): This level is indicated when some residual strength and stiffness is left available in the structure Gravity load bearing elements function, no out of plane failure of walls and tripping of parapet is seen Some drift can be observed with some failure to the partition walls and the building is beyond economical repair Among the non-structural elements failing hazard mitigates but many architectural and mechanical and mechanical systems get damaged • Collapse Prevention Level (CP): Buildings meeting this performance level are expected to have little residual strength and stiffness, but the load bearing structural elements function such as load bearing walls and columns Building is expected to sustain large permanent drifts, failure of partitions infill and parapets and extensive damage to non-structural elements At this level the building remains in collapse level BUILDING PERFORMANCE LEVEL: Force - Displacement curve of a Hinge  Point A is the original state(OL) of Structure  Point B represents yielding No deformation occurs in the hinge up to point B  Point C represents the ultimate capacity/Limit for pushover analysis  Point D represents a residual strength limit in the structure After this limit Structure initialize collapsing  Point E represent total failure of the structure After this point hinges break down hinge: • Point of Inelastic action of the structural member is called as Plastic hinge In this state structural member starts loosing strength to come back in previous position(As we know elasticity helps members to come back in it’s identical/safe/previous position, Plasticity starts after crossing elastic limit) We assign hinges to Model for observing the structural behavior of sequential lose of strength in different performance level of the structure due to seismic effect • A hinge property is a set of non linear properties that can be assigned to points along the length of one or more Frame elements Assigning Hinge starts from 0(Starting point) of Member to 1(End Point) of that member Relative distance of Hinge ‘0.1’ means if the member length meter, then the location of the hinge at 0.1meter (10% of the length) from starting point of the member ANALYSIS STEPS IN ETABS Finalize/Design the Structural Members Then we will decide to push displacement value upto which we want to observe the behavior of structure For example we will use here 300mm as our push Displacement Consider the corner joint label of top floor for that displacement Define Load Case: Convert Dead load to Nonlinear Static Load Case so that program can use this case as the starting point for the Pushover Define>LoadCase>Add New>Name-PAx>Type-NS>MassSource-MsSrc1 (as we defined before)>Initial Condition-Continue from State-Dead>Loads Applied-Add-Ltype-Acceleration Ux-Factor1>Load Application>Displacement Control>Use Monitored Displacement>300mm at Joint 1>DOF>U1> ResultsSaved>Modify>Multiple Stage> Same way Define PAy using Acceleration Uy direction Assign Hinge Properties- Select All Beams>Assign>Frame>Hinges>AutoM3>Distance to 0.9 >Table Concrete Beam, V Value from PAx ANALYSIS STEPS IN ETABS Similar way Assign Hinge for Columns & Walls Then select all beams & columns Assign Hinge OverWrights> This will discretize the members & can give better result Then Set the Load Cases to Run analysis Linear Analysis is used to design the section sizes of the members & Nonlinear Analysis used to observe the Designed Structure’s behavior So, Here we will run only Nonlinear Static analysis to observe proper structural behavior for defined Push Displacement 10 After running analysis see deformed shape for Push along X direction & Y Direction and observe what hinges are forming>OL>IO>LS>CP>C>D>E 11 Display Pushover Curve- 1st Base Shear vs Displacement,(See how the base shear drops as the hinges forms & reach different stage) ANALYSIS STEPS IN ETABS The demand curve is plotted here for Seismic Co-efficient 0.28 & 0.4, We can modify the co-efficients to see how the demand curve changes without doing another analysis The point where the Capacity & Demand curve intersects, that is Performance point Upto CP level the structure will not collapse locally for this level of Earthquake ANALYSIS STEPS IN ETABS 12 Display Hinge Result>Select Hinge> At the end the program has soften the drop in order to get convergence 13 Lastly we can display h Member force Diagram(SFD/BMD) for Pushover Analysis Thanks for watching downloading the video will take your disk space, will make us disappointed, So Watch it on youtube, subscribe the channel, Share & like the tutorial to inspire us for more tutorials ... practical means DIFFERENCE BETWEEN PUSHOVER ANALYSIS AND RESPONSE SPECTRUM METHOD PUSHOVER ANALYSIS RESPONSE SPECTRUM ANALYSIS Simplified nonlinear static analysis Suitable for assessing the... analysis Linear Analysis is used to design the section sizes of the members & Nonlinear Analysis used to observe the Designed Structure’s behavior So, Here we will run only Nonlinear Static analysis. .. Static effect Dynamic linear analysis Suitable for problems involving the structural design of new structures types: • Presently, there are two non-linear static analysis procedures available,